HIGH DATA RATE TRANSMISSIONS FOR HIGH … · public transport use and multimodal behavior by optimizing door-to-door mobility. Today, with the ... (par exemple, une traduction, etc.),

Today the key challenge for sustainable mobility and sustainable development is to reduce the

impact of transport on the physical, social and human environment. Promoting a set of solutions that aims to optimize the use of existing infrastruc-tures for road and rail domains, to enhance safety and security, to reduce exploitation and mainte-nance costs and to offer new services to customers and staff developing inter modal behavior, may constitute an important contribution. This set of solutions is based on political decisions, best prac-tice challenges and technological solutions deve-loped within several Intelligent Transport Systems programs all over Europe.In this context, new information and communi-cation technologies represent great opportunities to develop Intelligent Public Transport Systems. This sector has always been very open for new technologies innovations but their development and deployment require integration with existing public transport environments. New information and communication technologies are the keys to optimize exploitation and maintenance costs, to enhance the friendliness, comfort and security fee-ling of public transport by offering new services to passengers while traveling with the aim to promote public transport use and multimodal behavior by optimizing door-to-door mobility. Today, with the development of “always on” behavior, customers on board a train ask to receive while traveling the same information they use to receive at home or at their office. The Train-IPSAT project aims at developing such services. This report constitutes the final report of the work performed regarding “user requi-rements analysis” and a technical state of the art on the technologies suitable to answer the problem.

Synthèse n° 51Février 2007

Prix : 15,24 €

ISSN 0769-0274ISBN 978-2-85782-643-5

HIG

H D

ATA

RAT

E TR

AN

SMIS

SIO

NS

FOR

HIG

H S

PEED

TR

AIN

S D

REA

M O

R R

EALI

TY?

Syn

thès

e IN

RE

TS

n°

51

L E S C O L L E C T I O N S D E L ’ I N R E T S

HIGH DATA RATE TRANSMISSIONS FOR HIGH SPEED TRAINS DREAM OR REALITY? TECHNICAL STATE OF THE ART AND USER REQUIREMENTS

M. BERBINEAUM. CHENNAOUICh. GRANSARTH. AFIFIJ.M. BONNIND. SANZR. COUTUREAUD. DUCHANGE

SY

NT

HÈ

SE N ° 5 1

Train-IPSAT Project – WP1PREDIT 3 - CALFRANCE

M. BERBINEAU is senior researcher and head of the Research Unit LEOST/INRETSM. CHENNAOUI, Ch. GRANSART are resear-chers at LEOST/INRETSD. SANZ is researcher at SNCFJ.M. BONNIN is researcher at INTR. COUTUREAU is researcher at Cysco SystemD.DUCHANGE is researcher at FT R&D

Conformément à la note du 04/07/2014 de la direction générale de l'Ifsttar précisant la politique dediffusion des ouvrages parus dans les collections éditées par l'Institut, la reproduction de cet ouvrage estautorisée selon les termes de la licence CC BY-NC-ND. Cette licence autorise la redistribution noncommerciale de copies identiques à l’original. Dans ce cadre, cet ouvrage peut être copié, distribué etcommuniqué par tous moyens et sous tous formats.

(CC BY-NC-ND 4.0)

Attribution — Vous devez créditer l'Oeuvre et intégrer un lien vers la licence. Vous devez indiquer cesinformations par tous les moyens possibles mais vous ne pouvez pas suggérer que l'Ifsttar voussoutient ou soutient la façon dont vous avez utilisé son Oeuvre.

Pas d’Utilisation Commerciale — Vous n'êtes pas autoriser à faire un usage commercial de cetteOeuvre, tout ou partie du matériel la composant.

Pas de modifications — Dans le cas où vous effectuez une adaptation, que vous transformez, oucréez à partir du matériel composant l'Oeuvre originale (par exemple, une traduction, etc.), vousn'êtes pas autorisé à distribuer ou mettre à disposition l'Oeuvre modifiée.

Le patrimoine scientifique de l'Ifsttar

Le libre accès à l'information scientifique est aujourd'hui devenu essentiel pour favoriser la circulation dusavoir et pour contribuer à l'innovation et au développement socio-économique. Pour que les résultats desrecherches soient plus largement diffusés, lus et utilisés pour de nouveaux travaux, l’Ifsttar a entrepris lanumérisation et la mise en ligne de son fonds documentaire. Ainsi, en complément des ouvragesdisponibles à la vente, certaines références des collections de l'INRETS et du LCPC sont dès à présentmises à disposition en téléchargement gratuit selon les termes de la licence Creative Commons CCBY-NC-ND.

Le service Politique éditoriale scientifique et technique de l'Ifsttar diffuse différentes collections qui sontle reflet des recherches menées par l'institut :

• Les collections de l'INRETS, Actes• Les collections de l'INRETS, Outils et Méthodes• Les collections de l'INRETS, Recherches• Les collections de l'INRETS, Synthèses• Les collections du LCPC, Actes• Les collections du LCPC, Etudes et recherches des laboratoires des ponts et chaussées• Les collections du LCPC, Rapport de recherche des laboratoires des ponts et chaussées• Les collections du LCPC, Techniques et méthodes des laboratoires des ponts et chaussées, Guide

technique• Les collections du LCPC, Techniques et méthodes des laboratoires des ponts et chaussées, Méthode

d'essai

www.ifsttar.fr

Institut Français des Sciences et Techniques des Réseaux,de l'Aménagement et des Transports14-20 Boulevard Newton, Cité Descartes, Champs sur MarneF-77447 Marne la Vallée Cedex 2

Contact : [email protected]

http://creativecommons.org/licenses/by-nc-nd/4.0/deed.fr



M. BERBINEAU,M. CHENNAOUI, Ch. GRANSART,H. AFIFI, J.M. BONNIND. SANZR. COUTUREAUD. DUCHANGE

High data rate transmissions for high speed trains

dream or reality?Technical State of the Art and

User requirements

Train-IPSAT Project – WP1PREDIT 3 - CALFRANCE

Synthesis INRETS N°51June 2006

The authors

Marion Berbineau (INRETS)

M. Chennaoui

Ch. Gransart (INRETS)

D. Sanz (SNCF)

H. Afifi (INT)

J.M. Bonnin (ENSTB)

R. Coutureau (Cysco System)

D. Duchange (FT R&D)

The research Unit:

Laboratoire Electronique Ondes et Signaux pour les Transports20 Rue Elisée Reclus – BP 366

F-59650 Villeneuve d’Ascq

Tél.: 03 20 43 83 28 – Fax: 03 20 43 83 97

Referes:

Didier Van Den Abeele – ALSTOM - Transport Information Solution

Pr Jean-Michel Rouvaen – IEMN-DOAE – Université de Valenciennes et du Hainaut Cambresis

High data rate communications for HST - State of the Art and User requirements

Institut National de Recherche sur les Transports et leur Sécurité INRETSService des publications 2, avenue du Général Malleret-Joinville

94114 ARCUEIL CEDEX - www.inrets.fr

© Les collections de l’INRETSN° ISBN 278-2-85782-643-5 N° ISSN 0769-0274

En application du code de la propriété intellectuelle, l’INRETS interdit toute reproduction intégrale ou partielle du présent ouvrage par quelque procédé que ce soit, sous réserve des exceptions légales

Synthèse INRETS n° 51 3

Fiche bibliographiqueUR (1er auteur)

Marion Berbineau

Projet N° 51 Synthèse INRETS N° 51

Titre

Communications haut débit pour les trains à grande vitesse rêve ou réalité ? – Etat de l’art technique et besoins utilisateurs

Sous-titre

Train-IPSAT Project – WP1 - PREDIT 3- CALFRANCE

Langue

Anglais

Auteur(s)

M. Berbineau, M. Chennaoui, Ch. Gransart, D. Sanz, H. Afifi, J.M. Bonnin, R. Coutureau, D. Duchange

Rattachement ext.

INRETSSNCFINT, ENSTB, CISCOFT R&D

Nom adresse financeur, co-éditeur N° contrat, conv.

Ministère de l’environnement, du logement, du Tourisme, de la Mer et des Transports, DGMT

Date de publication

Juin 2006

Remarques

Résumé

Les évolutions prodigieuses des techniques de communications et d’information associées à leur démocratisation créent de nouveaux besoins. Aujourd’hui les passagers à bords d’un train demandent à disposer des mêmes services et des mêmes informations que ceux dont ils dispo-sent en fixe. Dans le même tems, les opérateurs ferroviaires s’appuient de plus en plus sur ces nouvelles technologies de l’information et de la communication afin d’accroître les performances du transport ferroviaire en général mais aussi d’augmenter le confort, la convivialité et le senti-ment de sécurité des passagers en offrant de nouveaux services à la place.

Le projet Train-IPSat vise à démontrer la faisabilité d’offrir des services à bord via un réseau WIFI et une liaison bidirectionnelle entre le train et le sol qui s’appuie soit sur un lien satellite, soit sur un lien terrestre en fonction de la disponibilité des systèmes ou du débit demandé.

Dans un premier temps, ce document liste les besoins tels qu’ils sont perçus. Dans un deuxième temps, les systèmes de communications sans fil existants et futurs (cellulaires, WLAN, WMAN Satellite) susceptibles de répondre aux besoins sont décrits. La conclusion propose une comparaison rapide des technologies présentées au regard de leur capacité à répondre aux problématiques du projet Train-IPSAT.

Mots clés

Télécommunications sans fil, haut debit, ferroviaire, GSM, WIFI, UMTS, Satellites, IPV6, NEMO

Nb de pages

116

Prix

15,24 €

Bibliographie

oui

4 Synthèse INRETS n° 51

Publication data formUR (1st author)

Marion BERBINEAU

Projet N° 51 INRETS synthesis N° 51

Title

High data rate transmissions for high speed trains dream or reality - Technical State of the Art And User requirements

Subtitle

Train-IPSAT Project – WP1 - PREDIT 3- CALFRANCE

Language

English

Author(s)

M. Berbineau, M. Chennaoui, Ch. Gransart, D. Sanz, H. Afifi, J.M. Bonnin, R. Coutureau, D. Duchange

Affiliation

INRETSSNCFINT, ENSTB,CISCOFT R&D

Sponsor, co-editor, name and address Contract, conv. N°

Ministère de l’environnement, du logement, du Tourisme, de la Mer et des Transports, DGMT

Publication date

Juin 2006

Notes

Summary

The prodigious evolutions of information and telecommunication techniques as well as the democratization of their usage have set up new needs. Today, customers on board a train ask to receive while traveling the same information they use to receive at home or at their office. In the same time, railways operators rely more and more on the new information and communication technologies to enhance railway performances from a general point of view but also to increase the friendliness, comfort and security feeling by offering new services to passengers.

The Train-IPSat project intends to demonstrate a transparent connection to the inside of the train with a WIFI network and a bi-directionnal satellite and terrestrial links and. The terrestrial link will substitute the satellite link when the satellite is not available or will alternatively provide other ranges of data rates.

In a first part, this document gives briefly the user needs. In a second part existing and future wireless technologies (cellular, WLAN, WMAN, Satellite) able to answer the needs are described. The conclusion gives a short comparison among the wireless technologies presented in the report regarding their capacity to answer the Train-IPSAT project needs.

Key words

Wireless Telecommunications, high data rate, railways, GSM, WIFI, UMTS, Satellites, IPV6, NEMO

Nb of pages

116

Price

15,24 €

Bibliography

yes


Table of content

Acknowledgments 11

Synthesis 13

Glossary 15

Introduction 19

Chapter 1 - User requirements 21

1. What are the requirements for Train-to-Track communications? 21

2. High data rate transmission for high speed train dream or reality? 23

3. Existing projects 25

4. Conclusion 26

Chapter 2 - System architecture 27

1. Introduction 27

2. General system architecture 28

3. The terrestrial link 29

4. The satellite link 29

5. The mobile router 30

Chapter 3 - Wireless terrestrial Train to Tracks transmission systems 31

1. Introduction 31

2. Cellular systems and evolutions 322.1. Cellular concept 322.2. GSM, GSM data, HSCSD, GSM-GPRS 332.3. GSM-R 332.4. EDGE Enhanced Data rates for GSM 352.5. IS 95 – IS 136 372.6. Universal Mobile Telecommunication System (UMTS) 38

3. WLAN, WMAN and BRAN1 systems 423.1. The IEEE 802.11x (Wi-Fi) standard 42

3.1.1. Introduction 423.1.2. Subgroup and variant of the Wi-Fi standard 423.1.3. Wi-Fi layers 443.1.4. Wifi architecture 46


3.1.5. Wi-Fi base services 473.1.6. Security 473.1.7. Power management 48

3.2. The HIPERLAN standards 483.3. IEEE 802.15.3 (HR-UWB) 49

3.3.1. Introduction 493.3.2. The UWB waveform 503.3.3. Properties of UWB technique 50

3.4. IEEE 802.15.4 (ZigBee and LR-UWB) 523.4.1. Spectrum 523.4.2. Access method 53

3.5. The WIMAX standard – IEEE 802.16 and IEEE 802.20 families 533.6. Wireless Meshed Networks 58

4. Conclusion 58

Chapter 4 - Existing satellite systems 61

1. Satellites for communications in general 611.1. Introduction 611.2. Satellite communication network structure 62

2. The different existing systems 642.1. WorldSpace 642.2. INMARSAT 642.3. EUTELTRACS/OMNITRACS 652.4. MSAT 662.5. OPTUS (AUSSAT) 662.6. ITALSAT (EMS) 662.7. IRRIDIUM (S-PCS) 662.8. GLOBALSTAR (S-PCS) 662.9. ICO (S-PCS) 672.10. ODYSSEY (S-PCS) 672.11. Thuraya 672.12. Satellite-based mobile system supporting broadband interactive servi-

ces on fast trains or on planes 67

3. On test or existing deployed solutions 683.1. PointShot Wireless 683.2. IComera 713.3. 21Net 743.4. The MOWGLY solution 76

4. Conclusion 77

Chapter 5 - Mobile router 79

1. Introduction 79

2. Multi models architecture 79



3. Overview of Mobile IPv4 803.1. Locating Mobility Agents and Movement Detection 813.2. Registration Procedures 823.3. Datagrams Delivery and Tunneling 833.4. Improvement of Mobile IP: Micro Mobility Solutions compared to last

section 833.4.1 Foreign Agents Based Mobility Management Proposals 833.4.2 Hierarchical Mobile IP 84

4. Virtual Interface Architecture 88

5. IPV6 – NEMO platform 945.1. Overview of Mobile IPv6 945.2. IPv6 Mobile Networks: NEMO 96

6. CISCO Mobile IP Overview 986.1. What Is It and why do we care? 986.2. How CISCO Mobile IP Works? 99

7. Conclusion 100

Chapter 6 - Propagation and EMC constraints in the Railway domain 101

1. Introduction 101

2. Geometric characteristics of high speed lines 101

3. Propagation channel characteristics in the case of the terrestrial link 103

4. Propagation channel characteristics in the case of satellite systems. 104

5. Frequency allocation 106

6. EMC considerations 107

Conclusion 109

Bibliography 113

Table of content


Table of figures

Figure 2.1: Telecommunication System Architecture .................................. 29Figure 3.1: GSM-R frequency band repartition in Europe compared to

GSM bands ............................................................................... 34Figure 3.2: GSM-R Applications [source INTEGRAIL Deliverable D3D4.1] .. 35Figure 3.3: Technologies evolution towards UMTS [Fromann, 2001] ......... 38Figure 3.4: Increasing bandwidth demand and on going technological

evolution as key drivers [Drzisga, 05] ....................................... 41Figure 3.5: Wireless market evolution [Krenik, 05] ..................................... 41Figure 3.6: Wifi Frame format ..................................................................... 45Figure 3.7: Infrastructure mode ................................................................... 46Figure 3.8: adhoc mode .............................................................................. 47Figure 3.9: extended mode ......................................................................... 47Figure 3.10: Power save mode in infrastructure ........................................... 48Figure 3.11: Time representation of the Gaussian (a) and monocycle (b)

pulses ........................................................................................ 50Figure 3.12: Spectrum allocation in the ISM band ........................................ 52Figure 3.13: Typical Wimax deployment ....................................................... 53Figure 3.14: Mobilis network architecture ..................................................... 57Figure 4.1: BroadBand Internet for trains by PointShotWireless

[source internet] ........................................................................ 68Figure 4.2: Icomera Internet access service architecture ........................... 71Figure 4.3: antenna system and embedded IComera System ................... 72Figure 4.4.: embedded wireless network ..................................................... 72Figure 4.5: Configuration of equipments in the train ................................... 73Figure 4.6: performance of forward et return links of the Icomera system ... 73Figure 4.7: shows an example of a web application that provides train

positioning and status information. ........................................... 74Figure 4.8: 21Net system Architecture ........................................................ 75Figure 4.9: 21Net antenna .......................................................................... 76Figure 5.1: The Virtual Interface architecture .............................................. 88Figure 5.2: Handover scenario .................................................................... 89Figure 5.3: test bed topology ...................................................................... 91Figure 5.4: VIP Handover delay .................................................................. 91Figure 5.5: VIP Jitter for an eth-eth handover (control-intervall= 60ms) ..... 92Figure 5.6: VIP throughput overhead (UDP traffic) ..................................... 92Figure 5.7: VIP throughput overhead (TCP traffic) ..................................... 93


Figure 5.8: UDP packet number received at the CN .................................. 93Figure 5.9: VIP TCP packet number (handover WIFI->eth) ........................ 94Figure 5.10: How Cisco Mobile IP works? .................................................... 99Figure 6.1: Pilone in the railway domain ..................................................... 103Figure 6.2: Pilone outside the railway domain ............................................ 103Figure 6.3: angular distribution of power due to multipath .......................... 104Figure 6.4: Long fadings due to a bridge .................................................... 105Figure 6.5: Fast and periodic fadings due to the catenary metallic

supports. ................................................................................... 105Photography 6.6: Example of metallic supports along the tracks ................... 105



Acknowledgments

The authors would like to express their gratitude to the people who have sup-ported the project, those who have contributed to the writing of this report and those who have finally accepted to review it.

People of the French Ministry of Transport who have funded this project and more specifi cally to Caroline Bigot of the Terrestrial Transport Division whose constant support has been appreciated by the whole team and than to J.F Janin and Marie Vilette.

Didier Van Den Abeele from ALSTOM –TIS and Pr Jean-Michel Rouvaen from IEMN-DOAE at University of Valenciennes who accepted to review this work.

Colleagues from other past and on going Europeans projects, in particu-lar the ESCORT and INTEGRAIL projects, who have kindly provided docu-ments and information.

All the members of the Train-IPsat project who provided the necessary infor-mation to this analysis.

Contributors to the WP1 report: listed as co-authors from INRETS, INT, ENSTB, Cisco Systems, FT R&D and SNCF

–

–

–

–

–


Synthesis

The prodigious evolutions of information and telecommunication techniques as well as the democratization of their usage have set up new needs. Today, customers on board a train ask to receive while traveling the same information they use to receive at home or at their office. In the same time, railways opera-tors rely more and more on the new information and communication technolo-gies to enhance railway performances from a general point of view but also to increase the friendliness, comfort and security feeling by offering new services to passengers.

Wireless transmission systems able to answer the needs of passengers should offer availability, robustness and high QoS. Such requirements lead to the question of the matching of radio coverage characteristics and the availa-ble throughput per passenger. The problem of high data rate transmission for railways applications is not a new subject but even yet there is no effective solution able to cope with the specific constraints of high speed trains. First of all, most of the railways applications required high data rate in both direc-tions. Furthermore, existing and future telecommunication standards (DVB-T, IEEE802.11x, WiMax, UMTS, WCDMA…) concerned mainly high data rate broa-dcasting services (downlink) or internet services. They do not take into account technical constraints due to fast mobility, robustness and response time specific to high speed railways.

The cornerstone of the “Train Connected” Project is to define, specify and experiment innovative services offered both to passengers and train operators of a running train through a wireless and seamless communication system over different networks such as WiFi in the train, and WirelessMAN (802.16, 802.20), cellular or satellite for the link outside the train. The communication system will secure the connection of the passenger terminals to Internet providing them with all the existing services and in addition with new specific services defined within the project. The passenger terminals (Laptop, PDA or 2.5/3G mobile phones) will be linked via a wireless LAN (WiFi or other) deployed across the train to an access point which could be considered as a “Super Mobile Device” from the outdoors of the train. This “Super Mobile Device” will be connected to the outside transparently through bi-directional satellite and terrestrial links. The terrestrial link will substitute the satellite link when the satellite is not available for the train (masking effect) or will alternatively provide other ranges of data rates. This transparent switch between the satellite and the terrestrial link will be managed by a “vertical handover” that will be specified, implemented and evaluated in the framework of the project. The combination of these two techni-ques should enhance the global system availability and the QoS offered to the end users.



As a first step in the project, this document first lists first the user needs regar-ding communications and then describes existing and future wireless technolo-gies able to answer the requirements of the applications not related to control-command and particularly high data rate connections on the move in order to support several applications such as passenger and operator ones. Regarding the propose system architecture combining a satellite and a terrestrial link, the main interesting terrestrial wireless systems as well as satellites ones are descri-bed in specific chapters. Technical solutions for mobile routers are presented. The last chapter of the report highlights the specific propagation context of railways and the possible electromagnetic problems able to impact availability, QoS and throughputs.


Glossary

ATP Automatic Train Protection

ATO Automatic Train Operation

ATC Automatic Train Control

ATCS Automatic Train Control System

AVI Automatic Vehicle Identification

AM Amplitude Modulation

AP Access Point

BPSK Binary Phase Shift Keying

BSS Base station Sub-System

BTS Base Transceiver Station

BRAN Broadband Radio Access Network

CCR Central Control Room

CDMA Coded Division Multiple Access

CEN Comité Européen de Normalisation

CEPT Conférence Européenne des Postes et Télécommunications

CSMA/CA Carrier Sence Muiltiple Access / Collision Advoidance

CSMA/CD Carrier Multiple Access with Collision Detection

DAB Digital Audio Broadcasting

DBPSK Differential Binary Phase Shift Keying

DQPSK Differential Quadrature Phase Shift Keying

DVB Digital Video Broadcasting

DECT Digital European Cordless Telephone system

DL Data Link Layer

DSRC Dedicated Short Range Communications

DSSS Direct Spread Spectrum Sequence

EDGE Enhanced Data rates for GSM

EIRENE European Integrated Railway Radio Enhanced Network

ERTMS European Rail Traffic Management Systems

ETSI European Telecommunications Standards Institute

ETCS European Train Control System



ETSI European Technical Scientific Institute

FDMA Frequency Division Multiple Access

FHS Frequency Hopping Sequence

FHSS Frequency Hopping Spread Spectrum

FM Frequency Modulation

FSK Frequency Shift Keying

GMSK Gaussian Minimum Shift Keying

GSM Groupe Spécial Mobiles / Global System for Mobile communication

GSM-R Global System for Mobile communication – for Railways

GPRS General Packet Radio Service

HIPERLAN High Performance Radio LAN

HLR Home Location Register

HSCSD High Speed Circuit Switch Data

IS 95 Interim Standard 95

IS 136 Interim Standard 136

MAC Media Access Control

MIMO Multiple-Input – Multiple-Output systems

M-PSK M-Phase Shift keying

M-QAM M-Quadrature Amplitude Modulation

MS Mobile Station

NSS Network Sub-System

MSC Mobile Switching Centre

OFDM Orthogonal Frequency Division Multiplexing

PDA Personal Digital Assistant

PLMN Public Land Mobile Network

PSK Phase Shift Keying

PHY PHYsical layer

QoS Quality of Service

QPSK Quadrature Phase Shift Keying

RER Réseau Express Régional

SACEM Système d’Aide à la Conduite, à l’Exploitation, à la Maintenance

SISO Single-Input – Single-Output systems

TDD Time Division Duplex


TDMA Time Division Multiple Access

TGV Train à Grande Vitesse (high speed train)

TA Timing Advance

TS Time Slot

TETRA Trans European Trunked RAdio

TVM Transmission Voie Machine

UMTS Universal Mobile Telecommunication System

UWB Ultra Wide Band

VHF Very High Frequency

UHF Ultra High Frequency

VLR Visitor Location Register

VOD Video On Demand

WiFi Wireless Fidelity

WLAN Wireless Local Area Network

Glossary


Introduction

The prodigious evolutions of information and telecommunication techniques as well as the democratization of their usage set up new needs. Today, customers on board a public or private vehicle ask to receive while traveling the same infor-mation they use to receive at home or at their office. In the same time, pushed by international trends to develop Intelligent Transport Systems in order to promote sustainable mobility, railways operators rely more and more on the new informa-tion and communication technology to optimize exploitation and maintenance costs but also to enhance the friendliness, comfort and security feeling of public transport by offering new services to passengers while traveling.

The problem of high data rate transmission for railways applications is not a new subject but even yet there is no effective solution in the case of high speed trains. Existing and emerging telecommunication standards (DVB-T, IEEE802.11x, WiMax, UMTS, WCDMA…) concerned mainly high data rate broa-dcasting or internet services. They do not take into account technical constraints due to fast mobility, robustness and response time specific to high speed railways. Furthermore, available systems today can provide high data rate mainly in the downlink direction. The maximum throughout for fast moving UMTS (Universal Mobile Telecommunications System) vehicles is 384 kbits/s that is still very low to transmit good quality video for which, generally a minimum of 450 kbits/s is required. On the contrary, most railways applications required high data rate in both directions. These topics are not widely studied in the literature.

To support high data rates in the case of high speed trains a transmission architecture combining a satellite and a terrestrial links is proposed in the Train-IPSat project. The project intends to demonstrate the bi-directionnal satellite and terrestrial links and a transparent connection to the inside of the train. The terrestrial link will substitute the satellite link when the satellite is not in the line-of-sight of trains or will alternatively provide other ranges of data rates. The users inside the train, are not connected directly to the external wireless links. Several WLAN are deployed inside the train and connected to specific mobile routers able to support handovers betweens the satellite and terrestrial links according to availability and QoS.

Previous work already performed [Berbineau, 01], [Cromatica, 96], [ESCORT, 00] have identified the main existing transmission systems used for control-com-mand, management or passenger applications in the railway or urban guided transport field.

In the Train-IPsat project we focus on the applications not related to control-command and particularly on the Internet access on the move and we aim to provide a high data rate link from the train to the ground able to support several



applications: passenger ones but also operator or staff oriented ones. Other on going or past European projects such as Euromain, Traincom, Modtrain, Integrail deal with communications systems on-board, for train to ground and for train to train applications. In this document, existing solutions applied to railways are mentioned. Information on related projects are available for interested reader in [Services and usage report].

This book is organized as follows. Chapter one is dedicated to “user require-ments” short description. This chapter tries to give an exhaustive view of the user needs and takes into account already published works on the subject. Chapter two presents briefly the architecture of the system able to answer the needs and studied within the Train-IPSAT project. Chapter three focuses on the state of the art and future wireless telecommunication standards: existing terrestrial systems such as classical cellular systems and also local wireless networks such as WIFI like systems. Chapter four is devoted to the main satellite wireless systems able to serve moving users. Chapter five presents possible solution for mobile routers technologies. Chapter six set up some questions regarding radio propagation characteristics in railways environment, frequencies availability and EMC pro-blems. The conclusion gives a short comparison among the wireless technologies presented in the report regarding their capacity to answer the Train-IPSAT project questions.


Chapter 1

User requirements

1. What are the requirements for Train-to-Track communications?

Following the traditional UIC classifi cation, it is possible to classify the funda-mental user needs in the following application fi elds:

1. Voice and data communications between CCC (Command Control Centre) and drivers.

This application consists in providing voice and data communications in order to control, guaranty and increase the safe movement of trains on an underground network.

2. Voice and data communications from and towards a train for staff, customer’s services, diagnosis and maintenance message.

These messages aim to increase operation effi ciency.

train status

ticketing information, about the number of passengers that come into a station, etc..

train identifi cation

fi les transfer in garage areas

3. Voice and data communications for Automatic Train Control (ATC)

4. Data communications for remote control applications

Remote control of engine for shunting

Remote control of trains at line opening and closure

Remote control of customers information systems

Remote control of interlocking s

Remote control of electrical substations

Remote control of lighting, electrical stairs, lifts, emergency ventilation ins-tallations, etc…

5. Voice communications for broadcast emergency calls

6. Voice communications for shunting in garage areas

7. Voice communications for workers during tracks maintenance

8. Voice and data communications in garage, maintenance and yard areas

–

–

–

–

–

–

–

–

–

–



9. Voice and data transmission for crew members

Train conductors are often equipped with mobile terminals like handheld ter-minals (PDA’s, PocketPCs) or bigger terminals like laptops or tablet-PCs. Some of those equipments are already equipped with mobile communications technolo-gies, the other can be easily 'connected’ by:

adding a cellular communications card (GSM/GPRS/EDGE/UMTS) in order to be able to synchronize with central servers in zones covered by the concerned cellular technology, send receive messages from control centers,…

adding a WiFi card in order to do the same in WiFi covered areas as for instance station hotspots.

Today, those technologies don’t allow the implementation of a broadband con-nectivity service for the crew everywhere, since cellular systems coverage of the railway lines is quite poor, and WiFi coverage of the 31000 km of French railway lines cannot be foreseen. The transmission system proposed in the Train-IpSat project can answer this need.

10. Voice and data communications for passenger services

Passengers on public transport (underground, train or plane) or private transport (car) expect the information they usually receive in day-to-day life, whether pro-fessional or private, to be available to them during their journeys. These demands will increase signifi cantly with the growing market of mobile telecommunications.

Today, the fi rst passengers demand is the use of the basic telephone service. GSM radio coverage of high speed lines is often required as well as the possibility of radio coverage inside of the trains. Underground operators also have allowed GSM operators to retransmit their signals in tunnels and particularly in stations.

Needs such as sending and receiving faxes, access to electronic mail, con-necting personal computers to external databases and computer networks, Internet and Intranet connections (to their fi rm’s network) are also increasing with the opening of new data transmission services in existing cellular systems offering higher data rates and packet transmissions.

Furthermore, other demands are emerging, such as the reception of radio stations and television broadcasted into the trains, communication with informa-tion and reservation centers and communication with tourist information centers. Generally, this type of information contains images or sound and requires high data transfer rates.

Passengers’expectation concerning multimedia services on-board is going to grow very rapidly, along with the deployment and development of high speed access technologies as: ADSL and CABLE for high speed connections at home, GPRS/EDGE/UMTS for medium rate data connections “on the move”, and WiFi wireless LAN for high speed connections in public places (HotSpots) as airports, congress centers, hotels and, of course, railway stations. Passengers will very soon be used to stay “connected” anywhere and anytime, and they will not under-stand that this kind of services stop when they get on the train.

–

–


The main needs identifi ed in general are listed here after.

public phone

fax

passenger call service

connexion to external networks and computers

entertainment videos

live radio channels

live TV channels

video-on-demand

tourist, multimodal and traffi c information

information panels at the platforms and inside the units

Data base enquires for passengers or staff

E-mail

Internet browsing

Other Internet services:

ftp, telnet, ssh, …

VPN secure connection to company’s Intranet

Audio and video streaming

Visio-conference,

P2P applications such as Skype, Kazaa,…

11. Voice and data transmission for security applications

the supervision with discreet voice listening inside trains or buses from a central control room to the surface; (Centralized Control room, Security Control room). Discreet listening can be triggered when an alarm is set up by a passenger or staff or on request of the Central Control room.

the supervision of trains with discreet digital video record for trains or buses from a central control centre on the surface. The Discreet listening must be triggered by a user, or upon request of the central control.

digital video broadcast in the drivers’cabin of the platform supervision at stations

2. High data rate transmission for high speed train dream or reality?

Track-to-train or in-train transmissions are generally divided in three main applications that answered very different functional specifi cations and then pres-ent very different characteristics and performances. These three applications are the following:

speech and data transmissions for train control-command equipment and safety,

–

–

–

–

–

–

–

–

–

–

–

–

–

–

•

•

•

•

•

–

–

–

–

User requirements



speech and data transmission for exploitation purposes or train manage-ment systems (freight and passengers) such as remote diagnosis, pre-dictive maintenance, connectivity for crew members (conductors) mobile terminals, etc…

Speech and data transmissions for passengers, fret customers, etc…

The fi rst track-to-train transmission systems were designed for safety pur-poses and repeated the messages from the line side signaling (particularly the most important of them) to the cab in order to bring them to the driver’s attention. At the beginning of the sixties, radiotelephone links between dispatching centers and engines have appeared to answer the needs for regulation inside dangerous areas such as mountain areas. This type of link became very widespread and was extended to cover most of the network in many countries.

More recently, transmission requirements have increased as a result of the growing complexity of train or underground control-command equipment and because of the need to augment the capacity of existing lines and optimize their management. Additional requirements have also appeared with the provision of new services to passengers or operators, which aim to improve the quality of the service provided to customers by public transport and to enhance effi ciency of the systems.

Ten years ago, Internet accesses were mainly devoted to professional uses and personal accesses were rare and connections were made thanks to low data rate phone connectors at 56 kbps. Since this period, technological jumps allow the generalization and democratization of internet access.

First of all, the mobile phone boom allowed data connections when moving fi rst with circuit-switch mode at low rate (GSM-data at 9,6 kbps), then with packet-mode at higher rate (GPRS: 54 kbps), and now EDGE and then UMTS will allow to reach data rate greater than 300 kbps in downlink direction.

At the same time, ADSL multiplied by ten the throughputs available for per-sonal fi xed accesses to Internet at home. 20 Mbps are now possible at reasonable costs for users due to hard competition between providers.

The set up of Wifi standard, also called Wireless Internet, changed dras-tically the way to access to Internet and generally to informatics networks fi rst at work and quickly everywhere in public areas due to the deployment of so called Hot-Spots. Today high data rate wireless connections in hotels, station, airport, restaurants become widely develop. In 2005, the sale per-centage for PC with wireless technology is greater than 60%.

Internet accesses are everywhere. People are connected at work, at home and while traveling. Internet connections are so widely spread that the demand to have internet connections on board the trains are increasing drastically. The railway operators have to avoid that the train remains a “non-connected” trans-port mean. Internet connectivity is also developed for cars and aircrafts. The train must be capable to guaranty “information continuity” for travelers in order to avoid gaps with the services available outside the trains. Railway operators need to fi nd

–

–

–

–

–


solutions to allow high data rate communication links between train and ground. The fi rst customer needs identifi ed are the following:

business passengers (email, secure Intranet accesses using VPN connec-tions,…), but also usual connections (Internet browsing, audio/video strea-ming, TV on demand, P2P, chat, games,…).

operation: railway operator or partner companies crew on board the train (control, WagonLits, CinéTrain,…), connection between trains for real time transmissions towards control centers (remote diagnosis et remote control of equipments, image streams for embedded video monitoring,…).

The solutions have to fi t the train operator needs, to be integrated, reliable, robust, opened and economically viable. Existing and future solution must cope with railway specifi c environment such as tunnels, satellite visibility, Electromagnetic constraints…

3. Existing projectsSeveral national or European projects deal with the topic of communication and

information systems in the railway domain to answer exploitation or maintenance needs. The following table 1.1 summarizes the main ones at a European level. Most of them are based on existing technologies. The last one, INTEGRAIL, is try-ing to introduce global and fl exible communication architecture in order to provide the integration of the different applications mentioned in the previous paragraphs and to allows data excenges between processes today completely separated.

Other projects focus on how to provide internet services on board trains. Several terrestrial or satellite solutions have been experimented. Sixteen main projects have been identifi ed and are presented in [service and usage] co-published in the frame-work of Train-IPSAT project and available in the same collection than this book. Some of the projects using satellite link are also described in chapter four of this book.

In most of the projects (Click TGV en France, 21Net en Espagne, SJ Scandinavia, Linx en Suède et au Danmark, Via rail au Canada, Train Connected et Alamount Commuter Express aux USA, Eurostar), Internet on board is deliv-ered thanks to a Wifi access point installed in each coach. The outside link from is provided by a satellite for the downlink and using GSM/GPRS or EDGE connec-tions for the downlink. In the case of non symmetric services such as INTERNET connections, trials showed the feasibility of the solution but some delays, discon-nections problems and low throughput have been experienced and show that the solutions must be enhance for commercial deployments. These limits are often highlited in rural areas where GSM/GPRS traffi c is limited.

Two projects in Japan and India are based on several WiFi access points deployed along the tracks. In Japan, research projects study also the use of DSCR technology as access point in the range of 5.8 GHz or very high data rate millimetric beacons in the range of 60 GHz. The Le DSB project in Danemark is based only on cellular links with existing deployed cellular systems in the vicinity of the tracks. There is no WiFi systems deployed in the train.

–

–

User requirements



The FIFTH project leads on a bi-directionnal GEO satellite link only (Hot Bird Signal) and on a Wifi network deployed on board. Experimentation conducted at high speed in Italy were show the feasibility and the interest of the solution but big masking effects have been experienced.

Table 1.1: Railway projects dealing with the topic of communications for exploitation, maintenance and control-command applications [IGR04].

INTEGRAIL(2005-2008)

Integration of railway systems by means of intelligent interfaces and processes

MODURBAN(2005-2008)

To design, develop and test an innovative and open common core system architecture and its key interfaces (this covers Command Control, energy saving and access subsystems), paving the way for the next generations of urban-guided public transport systems.

MODTRAIN(2004-2007)

Specifi cation of subsystems and interfaces for a modular train architecture

EUROMAIN(2002-2005)

Specifi cation of a complete railway maintenance system at European level taking advantage of open Internet-based technologies.

TRAINCOM(2000-2004)

Integration of railway and ICT to link train and ground systems, allowing to develop new interoperable applications

ROSIN(1996-1999)

Specifi cation and validation of a complete train network platform, open to other systems and to any kind of suitable applications

4. ConclusionIn the fi rst part of this chapter, we presented the different and general user

needs for communication in the railway domain.

The main needs to be satisfi ed are those related to control-command of train movement. Nevertheless, the necessity to increase effi ciency, reliability and gen-erally speaking the global performances of railway transport has conducted to a multiplication of communication, localization and surveillance needs between several entities: train, infrastructure, command centre. It is today mandatory to satisfy communication needs for exploitation and maintenance applications with integrated, innovative and interoperable solutions.

Today, it is vital for railway transport to gain market parts against individual cars and air planes. Such strategy requires the development and deployment of new added value services for trains customers and among these, the possibility to access while moving to all the services and information the customers use to receive at home, at offi ce (mobile phone, Internet browsing, interactive multime-dia services, mail, intranet connections). The different type of services related to these needs have been described and explained.

Some existing projects dealing with communications in the railway domain have been presented briefl y.

The following chapter details the transmission architecture chosen for the Train-IPSAT project. The system relies on the complementarity between a satel-lite and a terrestrial links connected through a mobile router to a WiFi network deployed onboard the train.


Chapter 2

System architecture

1. IntroductionFollowing the train operator needs expressed by SNCF, the main objective of

the Train-IPSAT project is to set up a whole solution for high data rate communi-cations between train and ground using both satellite and terrestrial technologies with transparent handover between the technologies. This solution will enhance simultaneously:

service delivers to passengers: offering un best access to information while traveling and improving comfort feeling, productivity and reducing subjective

service for railway operation: real time rolling stock tracking and tracing, maintenance applications, crew demand …

These improvements represent competitive advantages for railway trans-port system as well as an answer to the increasing demand for such services by passengers.

Nevertheless, several studies [TESS, 05], [Click TGV] showed that no already deployed technology is able to answer all the needs and constraints set up on one hand by the applications themselves (throughput, QoS, service availability,…) and on the other the very specifi c railway environment in which the system will be integrated (high speed, space available for antennas on the roof regarding UIC rules, installation constraints, EMC, train dynamic, vibrations, aerodynamics, safety standards, heat generated, unstable electrical feeding…).

The advantages of satellite solutions, particularly with geostationary satellites, are mainly the wide geographical coverage and the immediate availability of com-munication infrastructures for deployment of services. Main drawbacks are the bandwidth price (~1 to 3 M€ per year for a 36 MHz transponder) and the exis-tence of areas where the satellite signal is not received on the train (stations, tunnels, cuttings, urban canyons, mountain areas…). Furthermore, the satellite tracking performed by the antenna sets up technical requirements that increase system complexity and cost also in the context of railway applications (vicinity of catenary, EMC potential problems, space available…).

It is now obvious that in a near future, terrestrial solutions will be able to propose in the up-link more capacity than satellite ones for mobile applications at reason-

–

–



able costs. Nevertheless, two main drawbacks exist for these solutions: stations and antennas deployment along the railway lines and sensitivity to Doppler effects particularly in the case of TGV. Today, SNCF operates on more than 31000 km of lines (property of Réseau Ferré de France). A national deployment of a ter-restrial system represents very high costs (masts every 1 or 5 km, fi ber optic backbone…) and very important delays before service availability along the lines. Consequently, for short and medium term strategies, but also with long term eco-nomic vision, the solution obviously relies in the technology complementarities: satellite wherever it is available and WiFi or WiMAX like technologies elsewhere to guaranty service accesses.

This is the objective of the Train-IPSAT project. Such a solution allows also due to its fl exibility to envisage a progressive deployment: quick opening of the services using satellite accesses and then terrestrial accesses fi rst in the areas where the satellite is not available and then along the main axes if it is economi-cally viable.

The SNCF interest for this kind of system is not obviously limited to the TGV case. The system developed in the project will be available for any type of train if there is enough space available on the roof for antenna but also for other transport modes (buses, ships..). The project focuses on the TGV case because it is the most constraining for the communication system (capacity available for each pas-senger at the same moment) and the one that represent the highest economical interest for SNCF.

2. General system architectureA bi-directional link offering high data rate (at least 20 Mbits/s) is necessary

between the train and the ground to deliver to a great number of passengers access to multimedia services using IPv6 platform while supporting video monitor-ing, remote diagnostic and predictive maintenance.

In order to guarantee communication without interruption and breakdown along the whole travel even at speed up to 350 km/h, a specifi c architecture was already proposed in several projects by some of the Train-IPSat partners [Mostrain, 98], [Winters, 03], [Train-Connected, 03] and is now generally commonly agreed, in order to provide a service for any kind of device on board (phones, PDA, PC, intel-ligent sensors…). This architecture combines a terrestrial link and a satellite link as depicted in fi gure 2.1.

The mobile stations inside the train as well as the embedded sensors (cam-eras or microphones) are not directly connected to the external links. They are connected to a specifi c access point called “super mobile” through a wireless net-work WLAN such as IEEE802.11g (Wi-Fi) deployed along the train. The access point is connected to the ground either to the bidirectional terrestrial link or to the satellite ones depending of the availability and the QoS of the link.


Figure 2.1. Telecommunication System Architecture

3. The terrestrial linkThe terrestrial link will be based on the emerging standards IEEE802.16a,

IEE802.16e or IEEE802.20. A specifi c applications was developed within the national TESS project [TESS, 05] and allows message saving in case of break-down of the wireless communication link [Gransart, 03]. The data transfer restarts as soon as the connection is established again. This application permits to guar-anty the handover process between the satellite system and the terrestrial one. The Cisco Mobile Router 32xx will be tested as well as IPv4 and IPv6 platforms and particularly the NEMO (Network in Motion) concept [Ernts, 04]. These tech-nologies will be presented in chapter 5.

4. The satellite linkThe satellite communication system is probably today the most promising solu-

tion for fast inter city trains. Thanks to the absence of specifi c infrastructure to be placed along the track, the service is potentially available everywhere including the far out areas with no deployment costs and delays. The main drawbacks to guarantee connectivity and QoS are due to the satellite visibility related to the occurrence of mask effects encountered in the specifi c railways environments (tunnels, cutting, lattice mast supporting catenaries, stations, etc). To cope with these problems, specifi c signal processing such as coding and interleaving must be developed. Furthermore, specifi c antenna system have to be build to follow the satellite signals. In the terrestrial link the multipath fading effect and high speed of the train and consequently the fast Doppler variations degrade the transmissions between the ground and the train. In these cases also, specifi c coding and modu-lation schemes will have to be used to cope with these phenomena.

System architecture



The satellite link available for the project duration is the EUROBIRD geosta-tionary satellite operated by Eutelsat situated at 28,5° E in Ku band. Future defi l-ing satellite constellations in Ku or Ka band are also considered in the project.

5. The mobile routerDue to the various environments of the high speed trains along the different

existing lines all over Europe, it is impossible to identify at short term a unique technology able to answer all the connectivity needs on the whole trip. As an example, satellite technology is not available in stations, dense urban areas, tun-nels or cuttings. It is also unrealistic to cover all the existing lines with a unique terrestrial technology such as Wifi or Wimax. The solution will consist in using several technologies with a real time roaming also called “vertical handover” to switch from a system to another depending on the best availability and perhaps on the services prices. A Wifi link can replace a satellite link when entering a tun-nel, a WiMax link will be used near the cities sometimes along the lines to offer more data rate for example after departure or before arrival to satisfy upload and download requirements as well as for private or professional uses.

This “roaming” or “vertical router” will be performed thanks to a specifi c device that will act as a “multi access router”. Its main role will be to allow permanent links while the train is traveling using alternatively several access technologies transparently for the customer. Recently, a number of micro-mobility protocols have been proposed to manage transparent mobility to application layers. These include Mobile IP [Perkins, 96] and its multiple variants [Sun, 01], message ori-ented middleware (MOM) technologies [Kaddour, 03] at higher levels. These solu-tions solve some of the inherent IP mobility problems, but as they are working at higher layers (3 and above), important delays are introduced [Montavont,03].

The communication devices on-board the train could be PDA, PC, smart-phone, but also “intelligent IP sensors”. To cope with this diversity, a multi models software infrastructure has to be used to access continuously to the different ser-vices while traveling.

The Train-Ipsat project will analyze these different solutions: CISCO router, Ipv6–NEMO solution [Ernst, 04] and multimodel software infrastructure such as MOM technology that will be presented in chapter 5 of this report.


Chapter 3

Wireless terrestrial Train to Tracks transmission systems

1. IntroductionCurrently wireless track-to-train transmission systems listed in chapter 1 mainly

employ the following three types of communication media:

spot communications or beacon-based systems for short range communications,

continuous wired induction systems,

radio-based systems for medium and long range communications.

Beacon-based systems and continuous wired inductive systems are mainly dedicated to command-control, train operation applications (speed limit, track cir-cuits, wagon identifi cation…). The main technologies are describe in [Berbineau, 01] and are not suitable for the Train-IPSat project.

Radio is the more appropriate medium to support medium and long range track to train communications. The systems can be classifi ed into several categories: cellular radio network and specifi c radio systems developed for high data rate point to point links or for point to multi-point communications or for the new local wire radio applications, WLAN and BRAN. Today, the systems’technical evolu-tions answer the following requirements:

to complete and/or replace fi xed communication networks offering the same services,

to optimize Internet access,

to optimize the quality of video image reception,

to increase the offered traffi c

to increase the offered rates,

to secure the transmissions,

to decrease the error rates.

Currently, the most employed frequency bands over the world for railway appli-cations are the VHF in the 70-88 MHz or 155-220 MHz band and the UHF in the 420-470 MHz band. These waves propagate in line of sight and are well adapted

–

–

–

–

–

–

–

–

–

–



for communications with mobiles. The VHF-UHF spectrum is full and the trend today is to allocate higher frequency bands in order to increase the number of available RF channels and the transmission rate.

Important works were performed at a European level to develop the new con-trol and command system ERTMS (European Rail Traffi c Management System). The functionalities at level 2 and 3 involve a digital radio system derived from the public GSM phase 2+ standard, known as EIRENE (European Integrated Railway Radio Enhanced Network) operating in the 900 MHz band. This new railway stan-dard is called GSM-R. The “R” is given as the specifi c frequency band allocated by CEPT to the European railway networks (876-880 MHz and 921-925 MHz). One of the advantages of the choice of the GSM technology is the fl exibility of its system interfaces with fi xed communication networks. This new system will be easily introduced in existing networks. Furthermore, the GSM-R standard can benefi t of all the GSM standard evolutions such as HSCSD, GPRS and EDGE. GSM-R deployments are on going all over Europe. India and China have also decided to adopt this technology.

An overview of existing radio systems suitable for railways applications were published in [Berbineau, 01] and [Escort, 01]. This chapter focuses on the sys-tems suitable for high data rate applications mainly passenger oriented.

2. Cellular systems and evolutions

2.1. Cellular concept

A radiotelephone system allows the access to a fi xed telephone network using a moving terminal. To guarantee such a service, it is necessary to deploy a radio electrical link between the mobile terminal and the network. The cellular concept relies on a fundamental property of radio waves: the attenuation versus the dis-tance. Thank to this property, a frequency band used by a transmitter can be reused on an other transmitter if this transmitter is suffi ciently far away the fi rst one.

In a cellular system, the radio coverage is not performed by a unique high power transmitter but by several transmitters each with different output power and called “base stations”. These transmitters are deployed on the area to be covered. The surface where a mobile terminal can establish a radio electrical link with the base station while traveling, is called a “cell”. In a cellular system, the area to be covered is divided in several size cells. The boundary between cells must be transparent from a communication point of view. This cutting out allows frequency reuse on the area if interference rules are respected. These rules represent gen-erally some of the systems’characteristics.

Within a cellular system, the cellular network ensures the communication con-tinuity when the mobile is traveling using a procedure called “handover” which consists in the communication transfer from a cell to another in a transparent way from the user point of view. Due to traffi c load or co-channel interferences in one cell, the handover process can be set up inside this cell to allocate new radio


resources. Communication continuity between several cellular network operated by several operators is called “roaming”.

2.2. GSM, GSM data, HSCSD, GSM-GPRS

The GSM or Global System for Mobile communications is a digital cellu-lar system allowing circuit mode voice and data communications at four rates (2400, 4800 and 9600 bits/s) everywhere the system is deployed [Lagrange, 96]. Information protection is performed using convolutional channel coding. The pro-tection levels are fi xed and related to different services with different billings. In the case of circuit-switched transmission, time slots (TS) are allocated for the whole call duration.

The High Speed Circuit Switch Data service (HSCSD) is supported by the GSM standard protocol. The throughput is increased with the allocation of several Time Slots (TS) to a single customer. Up to six TS can be allocated to transmit with a 57.6 kbits/s rate (ie 6*9.6 kbits/s). This service exists theoretically and is seldom offered due to high costs.

The Global Packet Radio Service (GPRS) is an addition to the existing GSM network allowing optimization to Internet access thanks to Packet transmission. GPRS allows allocating non permanent corresponding to the duration of one or several IP packets. GPRS allows the dynamic allocation of several time slot for a single user.

GPRS relies on different protocols than the GSM’s ones. Nevertheless, GPRS is generally implemented in an existing GSM network with the addition of two new functional entities needed for packet mode transmissions. GSM and GPRS share the same physical channels. Four coding schemes based on convolutional codes are possible in the GPRS system. The information protection level is related to the coding schemes. The data are fi rst transmitted with no protection. At reception side, if the decoding process is unsuccessful, redundancy is increased until when the information is correctly decoded. The initial coding scheme used is chosen after periodic measurements of the radio link performed within the GSM standard. In order to optimize the radio resources management, several QoS are defi ned in the GPRS standard and allows also different billings.

171.2 kbits/s corresponds to the maximal data rate with no mobility on the downlink direction. When the mobile station is moving, the throughput falls down to 40 kbits/s. On the reverse direction, the data rate equals 20 kbits/s per chan-nel and can reach 40 kbits/s if two TS are used. These performances are really too low to answer the transmission needs for the video, audio and multimodal information.

2.3. GSM-R

GSM-R (Global System for Mobile Communication for Railways) is a digital cellular system standardized in order to harmonize the train to ground radio sys-




tems for control-command of trans-European trains with the aim to allow seam-less trains travels. A specifi c frequency allocation has been attributed by CEPT to railway community: 876-880 MHz and 921-925 MHz as depicted in fi gure 3.1. GSM-R relies on GSM phase 2+ standard and is interoperable with GSM public network.

Figure 3.1: GSM-R frequency band repartition in Europe compared to GSM bands

GSM-R is the result of over ten years of collaboration between the various European railway companies, the railway communication industry and the dif-ferent standardization bodies. In order to achieve interoperability across Europe using a single communication platform, the GSM-R standard combines all key functions and past experiences from the 35 analogue systems used previously across Europe. GSM-R provides a secure platform for voice and data communi-cation between the operational staff of the railway companies including drivers, dispatchers, shunting team members, train engineers, and station controllers. It delivers advanced features such as group calls, voice broadcast, location based connections, and call pre-emption in case of an emergency, which signifi cantly improves communication, collaboration, and security management across opera-tional staff members.

GSM-R is part of the ERTMS/ETCS standard associated with Eurobalise. In ETCS level 2 lines, GSM-R medium carries part of the signaling information directly to the train on board signaling unit, enabling higher train speeds and traffi c density with a high level of safety.

GSM-R will be easily introduced in existing networks. Furthermore, the GSM-R standard can benefi t of all the GSM standard evolutions such as HSCSD (High Speed Circuit Switch Data), GPRS (Global Packet Radio System) and EDGE. GSM-R deployments are ongoing all over Europe and beyond: India and China have also decided to adopt this technology.

It provides a rich set of features addressing the specifi c needs of railway oper-ators. The following diagram is the architectural framework of the services that can be offered by the GSM-R network:


Standard GSM phase 2+ features such as point-to-point voice and Short Messaging Service (SMS) between in-cab radios, handheld radios inside trains, signalers, controllers, shunting crew, and track-side workers. In addi-tion, the platform can also support supplementary services such as call wai-ting, call forwarding, etc.

Advanced Call Speech Items (ASCI): Call Pre-emption, Voice Group Calling Service, Voice Broadcast Service

Railway Specifi c Features: Functional Addressing, Access Matrix, and Location Based Addressing.

Figure 3.2: GSM-R Applications [source INTEGRAIL Deliverable D3D4.1]

GSM-R is a proven technology, currently being implemented in 15 countries worldwide. While GSM-R specifi cations were fi nalized in 2000, it has already been selected by 35 countries across the world, including all member states of European Union, and a growing number of countries in Asia, Eurasia and northern Africa. This number is increasing every month, making GSM-R one of the fastest growing wireless markets.

GSM-R is an enhancement of GSM compliment with the so called GSM 2+ in the ETSI references. About 85% of the GSM-R system is GSM. Frequency alloca-tion is different but the main changes concern the MSC (Mobile switching centre) part of the GSM network. Specifi c requirements for radio coverage and network tuning are related to ETCS constraints to guaranty a given QoS for Euroradio pro-tocols and handover process at high speed as well as at very low speed.

2.4. EDGE Enhanced Data rates for GSM

GSM offers rates up to 14.4 kbits/s with circuit-switched mode transmission and 22.8 kbits/s with packet mode transmission with GPRS. Higher data rates can be reached while using several time slots but the GMSK modulation used in the GSM standard, sets a lower limit.

–

–

–




It is possible to increase transmission rate by increasing the number of states m of the modulation. Thus, the EDGE protocol uses an 8-PSK modulation with 8 phase states. The modulation speed remains 271 kbits/s, thus the speed per time slot is 22,8 kbits/s with GMSK modulation and 69,2 kbits/s with the 8-PSK modu-lation. The 8-PSK burst shape is linearised to respect the spectral occupancy of the GMSK modulation. The EDGE protocol allows transmission schemes either with the GMSK modulation, either with the 8-PSK modulation. RF channel spac-ing remains 200 kHz. EDGE includes a packet mode, EGPRS –Enhanced GPRS, and a circuit mode, ECSD-Enhanced Circuit Switched Data.

The EDGE packet mode: EGPRS:

The EGPRS protocol allows the adaptation of the channel coding schemes with the radio link quality. A specifi c Radio Link Control protocol is used. The data are fi rst coded with low level of redundancy. If the receiver is not successful in decoding the information, the level of redundancy is progressively increased until the transmitted data are correctly decoded. The higher the code redundancy is, the lower the data rates are and the greater the transmission delays are. The initial choice for coding and modulation is based on regular measurements of the link quality. The maximum possible rate with EGPRS service will be, for example 384 kbits/s, for terminals traveling at speed lower than 100 km/h and 144 kbits/s for speed up to 250 km/h.

The EDGE circuit mode: ESCD

The aim of the ESCD protocol is to keep the GSM transmission protocols in circuit mode. Three new coding schemes based on the 8-PSK modulation have been introduced. The rate vary from 3.6 to 38.8 kbits/s per time slot. For non-transparent data transmission, the standard GSM protocol is maintained. With the set up of EDGE, the GSM standard will offer height transparent and non-transpar-ent data transmission services.

8 transparent services with constant data rate from 9.6 kbits/s to 64 kbits/s.

8 non-transparent services with data rate varying from 4,8 to 57.6 kbits/s.

The user rate can vary regarding the channel quality and the transmission rate. The non-transparent services use a Radio Link Protocol which guarantees the data transmission without error.

The EDGE protocols will not change the service defi nition but the way of coding and transmitting data. As an example, the 57.6 kbits/s non-transparent service rate can be obtained with the ECSD TCS-1 coding scheme using two time slots. The same rate can be obtained with GSM-HSCSD using height time slots and the TCH/F14.4 coding scheme. Thus, EDGE allows higher user rates using less time slots. This is very interesting from the terminals and the system capacity point of view. Nevertheless, it is necessary to fi nd a compromise between the new possibilities offered with EDGE and the low cost, low size and long battery life requirements.

Compared with a GPRS architecture, the BSC, Abis and Um interfaces will be the main network parts affected by the introduction of EDGE. EDGE can be intro-duced in an existing GSM network. Simulations show that EDGE is able to cope with data rate peaks and to multiply by three the spectral effi ciency.

–

–


The trends today show that GPRS and EDGE introduction in GSM networks will be probably replaced by the set up of UMTS. It is important to mention at this point that the EDGE concept has been designed both for GSM and for the IS-136 allowing a convergence between these two systems.

2.5. IS 95 – IS 136

The IS 95 system is a 2nd generation system deployed in the USA and a direct competitor of GSM, which has been developed under the auspices of the European Commission. The IS95 system was deployed since 1995 in the US. IS 95 uses the CDMA technique. The architecture is similar to the GSM one. The base stations broadcast a “pilot channel” to be identifi ed by the mobiles. In the CDMA context, a pilot channel is composed with a unique PN (Pseudo Noise) sequence that defers between them with the delay and the phase. This technique requires an accu-rate synchronization of the base stations. The allocation of the resources in IS 95 consists in the allocation of a Walsh code different for each mobile. There are 64 different Walsh codes orthogonal between them. To reduce interferences between mobiles using the same code in different cells, the signal is scrambled with a very long PN sequence. This process is called “scrambling”. From a theoretical point of view, in order to respect orthogonality between the codes (important to distinguish a subscriber from another in the same cell), it is mandatory for all the mobiles to be received with the same power level. This condition is very important because the propagation channel distortions introduce delays and fadings that will degrade seriously the orthogonality properties of the Walsh sequences. This effect is well known in CDMA systems as the “near-far effect”. The performances of the systems using the CDMA techniques are dependant of the quality of the power control. In IS 95, it must be set up every 1.25 ms. Convolutional codes and interleaving are used for channel coding and different code rates and interleaving depths are used depending on the services. The modulation format is QPSK modulation.

One of the advantages of CDMA systems is their ability to set up asymmet-ric links between uplink and downlink thanks to different coding schemes. This is particularly interesting for Internet applications that require higher data rate in the downlink direction than in the uplink which corresponds only to the user requests.

The IS 95 follows similar enhancements than those explained for GSM. Some technical characteristics are modifi ed to decrease interferences, to increase the number of users with higher QoS, to set up packet transmissions and the opening of high data rate transmissions for multimedia applications.

Another TDMA system exists in the US and is called IS136. This is a TDMA successful second-generation system. The evolutions of IS-136 concern the intro-duction of GPRS services and the global convergence of GSM and IS-136 via EDGE. The data rate available is 14.4 kbits/s in average. Direct evolution of IS 95 and IS 136 is the CDMA 2000 system based on Multi carrier CDMA technologies (MC-CDMA). The following fi gure 3.4 shows the system evolutions planned from an industry point of view from GSM to UMTS.




Figure 3.3Technologies evolution towards UMTS [Fromann, 2001]

2.6. Universal Mobile Telecommunication System (UMTS)

The progression observed in the number of mobile telephone subscribers and the traffi c explosion of Internet networks confi rm the necessary convergence of these evolutions towards a market of mobile multimedia services. These trends, concerning subscribers and data transmission rates increase, create new spec-trum demands and have pushed telecommunication actors to develop a new gen-eration of mobile systems called UMTS. An important constraint on the UMTS air interface is the mandatory interoperability with 2nd generation systems and particularly with GSM.

The radio interface chosen by ETSI in January 98 is UTRA (UMTS Terrestrial Radio Access) and comprises two access modes:

W-CDMA used with FDD (Frequency Domain Duplex) for duplex UMTS bands,

TDD (Time Division Duplex)/CDMA for non-duplex UMTS bands.

The FDD-W-CDMA mode:

The W-CDMA mode uses a DSSS technique. The spreading factor is variable (4 to 256) offering several possible rates. The maximal allowable rate is 384 kbits/s. Several codes are allocated simultaneously to one user to reach the highest rates, as an example, fi ve codes for the 2 Mbits/s rate. To ensure orthogonality, a fast power control is mandatory. The power control is set up at least every 0.5 ms. With the W-CDMA mode, it is not necessary to synchronize the base stations because the cells use different spreading codes (512 Gold codes). The automatic transfer between cell is a fast process called “soft handover” for which the mobile must be connected with two base stations. The FDD mode is not well adapted to asymmetric traffi c as TDD is.

The TDD – CDMA mode:

–

–


The TDD-CDMA mode is a multiple access technique based on a GSM frame and on spread spectrum techniques within the time slot. A traffi c channel will be defi ned as an RF channel, a time slot and a code. A joint-detection process enables the systems to detect the codes being used in the same time slot. This process requires high computing power but the power control needed in W-CDMA is no longer necessary.

The TDD principle requires base station synchronization at the frame level in order to avoid mobile-to-mobile interferences. This synchronization is on the range of 5 µs and can be easily obtained using GPS facilities in outdoor and fi xed network indoor. The handover procedures are identical than those used in GSM but the network synchronization avoids “user capacity stealing” as done in GSM. The TDD/CDMA concept offers a large panel of services and rates with the allo-cation of several time slots and several codes per user. The maximum data rate, 2 Mbits/s, is obtained with the 16-QAM modulation, in very small cells (pico-cells) and without channel codes.

Both FDD/W-CDMA and TDD/CDMA modes will have to collaborate into the same terminal and inside the same network in order to cover all the services and all the environments foreseen for UMTS and particularly new low cost dual-mobiles have to be designed and guarantee interoperability with other systems like GSM.

Other modes

Next UMTS evolutions are HSDPA (High Speed Downlink Packet Access), HSUPA (High Speed Uplink Packet Access), HSOPA (High Speed OFDM Packet Access), Flash-OFDM and EV-DO. Among these techniques the use of several antennas and associated algorithms called MIMO techniques (Multiple Input - Multiple Output) both at transmitting and receiving sides help to increase either data rates either robustness.

HSDPA will allow increasing the downlink data rates from 384kbps (theoreti-cally 2Mbps) to 10Mbps (theoretically 14Mbps). HSDPA delivers higher capacity through improved spectral effi ciency, hence providing higher data rates, shorter response times and better QoS.

HSUPA specifi cations are not yet fi nished but theoretically HSUPA should boost the uplink speed to 3.5Mbps.

Finally, introducing HSOPA will allow increasing the download capacity to 40Mbps.

FLASH-OFDM (FLASH (Fast Low-latency Access with Seamless Handoff)), also called fast-hopped OFDM which uses multiple tones and fast hopping to spread signals over a given spectrum band. Flash-OFDM is an innovative air interface technology designed for the delivery of advanced Internet services in the mobile environment. As its name suggests, the technology is based on the OFDM airlink, a wireless access method that combines the attributes of its two predeces-sors — TDMA and CDMA — to address the unique demands posed by mobile




users of broadband data and packetized voice applications. FLASH-OFDM is developed by QUALCOMM Flarion (Lucent/Bell Labs spinoff) Technologies

EV-DO (Evolution-Data Optimized) is a wireless radio broadband data stan-dard adopted by many CDMA mobile phone service providers. It is standardized by 3GPP2, as part of the CDMA family of standards. The initial design of 1xEV-DO was developed by Qualcomm in 1999 to meet IMT-2000 requirements for a greater-than 2-Mbit/s downlink for stationary communications. Initially, the stan-dard was called HDR (High Data Rate), and was renamed to 1xEV-DO after it was ratifi ed by the International Telecommunications Union (ITU); it was given the numerical designation IS-856. Compared to the 1x (1xRTT) networks still being used by operators, or the GPRS and EDGE networks employed by their GSM competitors. 1xEV-DO is signifi cantly faster, providing access terminals with air interface speeds of up to 3.1 Mb/s. Only terminals with 1xEV-DO chipsets can take advantage of the higher speeds. HSDPA is a competing technology for UMTS (W-CDMA) networks standardized in 3GPP. HSDPA has the advantage of maintaining voice and data channels simultaneously. While possible in a CDMA deployment, no operator or phone manufacturer has introduced a phone with the required chipsets to demodulate both the cdma2000 voice and 1xEV-DO channel. When deployed with a voice network, 1xEV-DO requires a separate radio channel of 1.25 MHz and offers fast packet establishment on both the forward and reverse links along with air interface enhancements that reduce latency and improve data rates. EV-DO supports low latency services including VoIP and Video Telephony on the same carrier with traditional Internet packet data services.

MIMO (Multiple Input, Multiple Output) techniques were introduced recently. They are derived from smart antennas principles and take advantage of different diversity properties (space, polarization, time and frequency) in the propagation channels thanks to the use of several antennas both at transmission and recep-tion sides. MIMO techniques aims at increasing data rates or robustness of the transmission links with simple processing implemented on the lower layers of the system. This technique was fi rst introduced by the Bell Labs in the 90’s [Foschini, 96] and is now widely studied in the telecommunication community. MIMO con-cept has been introduced in the fi rst drafts of IEEE802.11n and IEEE 802.16 a (WiMAX) standards but they are not completed yet. They are also used in broad-cast radio-relay systems. First experiments with MIMO in the guided transport fi eld were performed on the basis of a GSM-R transmission in tunnels in 2003 for metro application in the ESCORT (Enhanced diversity and Space Coding for under-ground metrO and Railway Transmission) project within the IST European program [ESCORT, 02]. Researches are in progress based on WIMAX for urban buses at national level in France in the framework of the EVAS (Etude de système de Vidéo et Audio Surveillance Sans fi l) project from the PREDIT (Programme de Recherche et D’Innovation dans les Transports) program [EVAS, 06]. This concept will be applied also for regional trains in the BOSS (On Board Wireless Secured Video Surveillance) project that will be launched in the CELTIC cluster from EUREKA program. MIMO principles can be also used at network level with collaborative or cooperative approaches (Virtual MIMO) in which each terminal is considered as a


single antenna. Such approaches can help the optimization of radio resources in a system and are considered today as main issues in the telecommunication world and as a fi rst step towards software defi ned radios and cognitive radios.

As already mention, it is important to understand that all these new techniques are not considered as specifi c systems but correspond to signal processing enhancements on the physical and MAC layer of existing systems allowing higher data rates and higher QoS but also cross-layers cooperation. The following fi g-ures 3.4 and 3.5 show some technological trends.

Figure 3.4: Increasing bandwidth demand and on going technological evolution as key drivers [Drzisga, 05]

Figure 3.5: Wireless market evolution [Krenik, 05]




3. WLAN, WMAN and BRAN1 systems

3.1. The IEEE 802.11x (Wi-Fi) standard

3.1.1. Introduction

A great interest for data transmission began since 1990. Because the cellular network concept has given mobility to phones, it became necessary to give the same freedom to laptops and to allow wireless connections to a fi xed local net-work. To answer this need of wireless data transmissions Wireless local area net-works (WLAN) and particularly the IEEE 802.11x standards were set up with other proprietary solutions to ensure a location independent connection. In Europe, the organization around the HIPERLAN (HIgh PErformance Radio LAN) standards in development have supported the allocation of the necessary spectrum to allow the set up of high rate wireless data transmissions for high performance wireless local area networks. These high rate transmissions are mandatory to allow the emerging of wireless multimedia communications between laptops or PDA.

3.1.2. Subgroup and variant of the Wi-Fi standard

Wireless local area network (WLAN) is a data transmission system designed to ensure a location independent connection. The standards generally called “Wi-Fi” for Wireless Fidelity have been developed within the IEEE international organization. WiFi is often deployed under the name of “HotSpot”. It consists in installing a group of connected access points for free usage or after paying a fee and dedicated to public use. The WLANs develop in the university campuses and enterprises, allowing any person provided with a portable computer or a PDA to reach public services for information or to connect himself to the Internet through the local area network.

The IEEE 802xx standard family focus on the two lower layers of the ISO model: the physical one (PHY) and the data link layer (DL). In the informatics networks world, the most known standard is the IEEE 802.3 standard, also called Ethernet. The works dealing wireless systems are grouped under the IEEE 802.11x refer-ences. A fi rst version of the standard appeared in 1997. The resources alloca-tion protocol is the well known CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). This fi rst version allows theoretical data rate from 1 to 2 Mbit/s. Evolutions defi ned in 1999 allow increases of data rate.

This standard, in its original version, provided bandwidth between 1 and 2 Mbit/s. Now, the IEEE802.11n is targeting 190 Mbits/s theoretical bandwidth and 100 Mbits/s effective. IEEE802.11x is divided in sub-groups identifi ed by a letter.

IEEE802.11b: operates between 2.401 GHz and 2.483 GHz. The maxi-mal raw data rate is 11 Mbit/s. This throughput automatically falls down to 5.5 Mbit/s, 2 Mbit/s or 1 Mbit/s as a consequence of the radio channel degradation. The physical layer uses the DSSS technique. The carriers are DBPSK or DQPSK modulated. The main existing equipments on the market are compatible with this standard.

–


IEEE 802.11a: operates within two bands: 5.15-5.35 GHz and 5.470-5.825 GHz and enables throughput of 54 Mbit/s. The availability of these frequen-cies depends on national regulations in each country. This version relies on the OFDM (Othogonal Frequency Division Multiplexing) modulation using 48 orthogonal sub-carriers. Each sub-carrier can be BPSK, QPSK, 16--QAM modulated. The standard specifi es 11 independent channels to be compared to the 3 channels defi ned in the fi rst version of the standard;

IEEE 802.11g uses OFDM in the 2.4 GHz range and was published in 2002. It’s an extension of 802.11b using OFDM modulation schemes in order to allow throughputs up to 54 Mbps and to cope with multipath channels fre-quent in indoor environments. 802.11g works also in the 2.4 GHz frequency band and is retro-compatible with 802.11b equipments. In the 455 MHz band allocated for a and g standards, 200 MHz are dedicated to indoor and 255 for outdoor.

IEEE 802.11e supports quality of service (QoS)

IEEE 802.11i corrects some of the security threats discovered in WEP.

IEEE 802.11n: current standard to attain (190 Mbit/s) in the 2.4 GHz range with MIMO techniques.

IEEE 802.11p improves on the range and speed of transmission on the dedicated 5.9 GHz licensed band, promising around 1,000 feet and 6 Mbit/s in average use. The vehicular communications protocol is aimed at vehicles, such as toll collection, vehicle safety ser-vices, and commerce transactions via cars. The IEEE 802.11p Task Group was established for Wireless Access in Vehicular Environments (WAVE). The Dedicated Short Range Communications (DSRC) is a general purpose communications link between the vehicle and the roadside (or between vehicles). A specifi c fre-quency band was allocated at European level for this kind of application, especially for road pricing applications. The IEEE 802.11p is foreseen to answer this need on the American continent. ITS America stressed the need to support the adoption of a single nationwide standard in the FCC rules. The US government is pushing forward to cover the highways with access points that support this new type of extra-secure hotspots, that ride over 5.9 GHz [dailywireless.org].

IEEE 802.11r is designed to speed handovers between access points or cells in a wireless LAN. The working group is drafting the fi nal protocol, which should be approved toward the end of 2006. 802.11r refi nes the tran-sition process of a mobile client as it moves between access points. The pro-tocol allows a wireless client to establish a security and QoS state at a new access point before making a transition, which leads to minimal connectivity loss and application disruption. The overall changes to the protocol do not introduce any new security vulnerabilities. This preserves the behavior of current stations and access points [www.networkworld.com];

IEEE 802.11s: Mesh architectures for wireless bridging, and ad hoc networks.

–

–

–

–

–

–

–

–




3.1.3. Wi-Fi layers

The physical layer, which is in charge of the transmission of the MAC frames on the wireless medium, uses several techniques of modulation and binary coding.

Infra Red

a spreading code technique using frequency hopping (FHSS Frequency Hopping Spread Spectrum) in the band 2.4 GHz;

the spreading of spectrum in direct sequence (Direct Sequence Spread Spectrum) in the band 2.4 GHz;

the OFDM, orthogonal multiplexing in the frequency space.

The IR physical layer relies on an infrared transmission that can cover 900 m. As far as we know, no equipment using this specifi cation exists.

The second version of the physical layer relies on the slow frequency hopping technique. The carriers are GFSK (Gaussian Frequency Shift Keying) modulated. The expected data rates are also 1 to 2 Mbit/s. Interferences with Bluetooth equip-ments that relies on the same technique are possible.

In the DSSS mode, the bandwidth of each channel is 22 MHz, thus there will be overlapping between the channels. It is needed to avoid adjacent channel use. Generally the Wifi modems operate tacking into account this constraint.

OFDM is based on a frequency division. The band is divided into several car-riers the data are multiplexed. A channel consists of 52 carriers of 300 kHz width. 48 carriers are dedicated to transport of useful information and 4 for the pilot car-rier error correction. OFDM supports a series of modulations and code schemes making it possible to offer the whole range of data fl ows. Eight 20 MHz width channels are defi ned in the low band (from 5.15 to 5.35 GHz). A Co-localization of eight networks within at the same place is possible. The frame structure is close to the Ethernet one). Three types exist: control, management and data. Different MAC headers allow the identifi cation.

The MAC layer defi nes two different access methods, Distributed Coordination Function (DCF) which is used for an random access like that of 802.3 with several other algorithms specifi c to the WLAN and another method which is the Hybrid Coordination Function (HCF) for a controlled access. DCF is conceived to deal with the transport of the asynchronous traffi c. All the users who want to transmit have an equal chance to reach the medium. The HCF technique is based on the interrogation in round robin of the terminals (polling). It requires the existence of a control point. HCF is conceived for the data transmission which has constraints such as the traffi c of real time voice and video. DCF is thus the basic access method whereas PCF is an optional method of access. CFP (Contention Free Period) is the period of the mode PCF and CP (Contention Period) is the duration of the time to ask for a service. Information relative to the two access modes with and without contention is disseminated in the BSS through the control beacons called beacon frames or beacons. One speaks about a super frame made up by a part of CFP following which data passes in DCF. The beginning of a super frame is delimited by a control mark.

–

–

–

–


Figure 3.6: Wifi Frame format

The access mode to the medium is random and is called the CSMA/CA. The basic access mechanism, called Distributed Coordination Function is typically close to Carrier Multiple Access with Collision Detection (CSMA/CD). Contrary to CSMA/CD which is based on the collision detection, CSMA/CA allows an access to the medium by avoiding the collision. If collision detection is adapted for a cabled local area network, it cannot be used in a Wifi environment, for two main reasons:

a collision detection mechanism required the implementation of a radio connection in full duplex. This approach which would increase the price signifi cantly;

in a Wifi environment, one cannot be sure that all the stations see each other (it is the basic assumption of the principle of collision detection). Moreover, the fact that a station wanting to transmit tests if the support is free, does not mean inevitably to say that the support is free in the vicinity of the receiver (multipath channels, fading...);

the listening to carrier takes a relatively long time in comparison with the wired networks (typically 30-50 microseconds into wired). Indeed, the transmission involved unknown new problems such as: hidden stations or exposed stations,

SIFS (Short Inter Frame Space) is used to separate the transmissions belong-ing to the same dialogue (data and control frames). It is the smallest difference between two frames and there is always, at most, only one station authorized to transmit after the duration of this short period, taking thus precedence over all the other stations. This value is fi xed by the physical layer and is calculated in such way that the transmitting station will be able to commutate in reception mode to be able to decode the entering packet. SIFS of high priority is thus used to transmit ACK, CTS, response to a polling...

PIFS (point coordination IFS) is used by the access point to gain the access to the medium before any other station. It refl ects an average priority to transmit the traffi c with time constraints;

DIFS (Distributed IFS) is the IFS of priority weaker than the two precedents; used in the case of the normal transmission of the asynchronous traffi c;

EIFS (Extended IFS) is the longest period. It is used by a station receiving a packet which was corrupted by collisions to wait more time than the usual DIFS in order to avoid future collisions. These timers make it possible to defi ne degrees of priority. When several stations wish to emit simultaneously, the station wishing to emit the priority frame will be able to send them in fi rst.

–

–

–

–

–

–




Lastly, the least important information which relates to the asynchronous traffi c will be emitted after a longer latency.

Performance analyses of this PCF protocol showed that it was not adapted to the transmissions of a traffi c with strong time constraints and thus of this fact no product on the market implemented it. Indeed, if a station takes the channel to send a long frame slowly, it can monopolize it during a long time and the beacons can be delayed. A successor of this mode, HCF (Hybrid Function Coordination) proposed by the working group 802.11e, will be integrated in the future products. It allows an explicit reservation of a bandwidth by signaling and the differen-tiation of service is possible by modifying the values of the intervals explained previously.

3.1.4. Wifi architecture

Today 3 architectures are possible for Wi-Fi deployment: infrastructure, ad hoc and point to point topologies.

a) Infrastructure

In this mode, there is an access point connected to the internet infrastructure of IP network and a group of wireless equipment connected together through a classical Ethernet backbone. Before any communication within a cell can happen, the wireless stations must carry out a procedure for association with their access points. The cell is identifi ed by a name called SSID.

Figure 3.7: Infrastructure mode

b) Adhoc

The ad hoc mode (or point-to-point) represents simply a group of wireless stations which communicate directly between them without having access to an access point or a connection to a fi xed network. One chooses the same transmis-sion channel and as in the infrastructure mode, an ad hoc network is also identi-fi ed by an identifi er IBSSID.

This mode allows better bandwidth that the infrastructure mode because one passes only one time on the wireless medium whereas in the infrastructure mode one can pass twice on the medium. Moreover, it is simple to set up. The result is a simple confi guration in which the network is completely meshed.


c) Extended mode

It is fi nally possible to combine several infrastructures to obtain an extend mode. In this case, the mobiles change an access point to the other more quickly and it is possible to maintain the continuity of the service. Today we call it a re-association. It is however happening with delays that may reach the second so this technique is not comparable to a classical cellular network with 50 ms delay for a complete handover.

Figure 3.8: adhoc mode Figure 3.9: extended mode

3.1.5. Wi-Fi base services

The following principles can be implemented in a Wi-Fi device.

authentication /de-authentication,

association/de-association/re-association,

multicast,

SSID beacon,

Confi dentiality.

Clearly, these mechanisms do not exist in traditional Ethernet networks but are necessary in the case of wireless to improve management of the air interface. Association makes it possible to know for an access point the list of the terminals are attached to it. Re-association makes it possible to change access point in a wider area. The beacon which makes it possible to announce the SSID is also very useful to choose between the various networks available. Finally the confi -dentiality which remains rather complex makes it possible to obtain ciphering of good level on the link.

3.1.6. Security

The security problem and confi dentiality complicate the installation of a local area wireless network. By nature, it is easy to listen to the network passively. In the same way, one can interfere between a user and his network mimiquating this layer, which bears the name of a man in the middle attack. But most banal attacks remain simple by jamming on the frequency of the Wifi protocol. Even if certain security devices are integrated into the local area networks in their fi rst

–

–

–

–

–




version (WEP), their security can be easily violated if the relevant precautions are not taken into account. A special Committee in 802.11 indeed brought a solution to the problem of security by working out all a fi rst version called WEP (Wired Equivalent Privacy) but serious failures were quickly detected in the mechanisms proposed. Today the new standard bears the name of 802.11i and makes the fol-lowing modifi cations:

Dissociation of the authentication which is done by procedures using other protocols such as EAP and TLS.

Very robust coding using AES block cipher with dynamic rekeying

Dynamic keys which change with the liking of the user to the network

Integrity and protection against replay by signature of the frames. Moreover, if we consider this system too heavy, one can use the currently standardized 802.11r for lightweight and fast mobility.

3.1.7. Power management

Although MAC layer is very roughly designed on the level of power management criterion, there is a mode for energy saving in the standard under the name of Power Save Mode. In infrastructure mode, time composed of the intervals by beacons. When the station informs the access point, the access point stores the packets tem-porarily. In the adhoc mode we can also implement the power save mode. All sta-tions have a wakeup interval and they can communicate only during this interval.

Figure 3.10: Power save mode in infrastructure

3.2. The HIPERLAN standards

The HIPERLAN1 standard has been designed by ETSI to offer wireless exten-sions to an Ethernet like fi xed local network up to 10 Mbits/s. The idea was to be able to connect a portable computer wherever it is with the less diffi culty as pos-sible. This idea can be generalized to non-portable or family use computers for which it represents a very interesting alternative because the accesses to the fi xed network are not necessarily well situated. For the HIPERLAN1 standard a fre-quency band has been allocated between 5.15 and 5.30 GHz so that 5 carriers can be used that is to say 5 independent parallel channels. The HIPERLAN1 standard permits a maximum transmission rate of 23.5 Mbits/s and is designed for direct terminal-to-terminal communications without connection to the fi xed network.

–

–

–

–


When a mobile terminal moves from an AP to another AP, it will decide to per-form a “handover”. This “handover” requires signaling exchanges between the two Access Points through the fi xed network. This possibility is not very well detailed in the standard and has to be set up by the supplier when he deploys the system. The medium access protocol is a modifi ed CSMA/CA protocol called EY-NPMA (Elimination Yield None Pre-emptive Priority Multiple Access).

The HIPERLAN1 standard coverage is 50 m for indoors with a maximal terminals’speed of 5 km/h. The standard foresees a terminal speed up to 10 km/h but with important quality degradation. There is no constraint on the maximal number of terminals. The interoperability between equipments is guaranteed to the user.

The HIPERLAN 2 standard is a new generation standard for WLAN applica-tions and designed for very high transmission rate of 54 Mbits/s using OFDM. The main technical characteristics are recapitulated in the table 3.1.

Table 3.1: Main technical characteristics of HIPERLAN2

HIPERLAN2

Frequency 5,15 – 5,35 GHz or 5,47 – 5,725 GHz19 channels - 20 MHz between channels

Maximum rate 6, 9, 12, 18, 27, 36 et 54 Mbits/s

Modulation OFDM

Sub-carriers 48 (data channels) - 4 (pilot channels)12 (empty)

Modulation BPSK, QPSK, 16-QAM, 64-QAM

Channel Coding Convolutional codes 1/2 or 3/4 or 9/16

Interleaving yes

Handover yesSome of the signaling messages are defi ned. The messages between AP have to be defi ned in the fi xed network.

Fixed network Ethernet, IP, ATM, IEEE 1394, PPP

Multiple access TDMA/TDD

At the moment, the equipments supporting HiperLAN1 and/or HiperLAN2 stan-dards are rare. We could even say inexistent… IEEE standards have taken the entire market...

3.3. IEEE 802.15.3 (HR-UWB)

3.3.1. Introduction

In the last few years there has been a rapidly growing interest in Ultra Wide Band (UWB) systems. These systems operate by running, as signalling wave-forms, base band pulses of very short duration, typically of the order of one nanosecond or less, rather than the traditional method using a sinusoidal carrier. The large bandwidth of an UWB system is dominated by its pulse shape and duration.




Originally, UWB signals are defi ned as signals having a fractional bandwidth of at least 0.25 or occupying at least 1.5GHz spectrum. In recent literature [3], these two factors are modifi ed to 0.20 and 0.5 GHz respectively. The fractional bandwidth η is defi ned as:

η =+

2 10 10

10 10

. f ff fH dB L dB

H dB L dB

Where fH db−10 and fL db−10 represent the highest and lowest -10dB bandwidth frequencies of the signal spectrum respectively.

3.3.2. The UWB waveform

Major concerns in the UWB radio technology are the choice of the pulse waveform and the modulation types. This waveform can be generated using Gaussian pulses, Manchester pulses or monocycle pulses. The expression of the monocycle pulse and the Gaussian pulse, respectively, are given by the fol-lowing equations:

v tt t

( ) exp( )= −τ τ

2

w tt

( ) exp( )= −τ

2

with τ the pulse duration.

Figure 3.11: Time representation of the Gaussian and monocycle pulses

3.3.3. Properties of UWB technique

Several properties are in favour of the use of UWB technique. Depending on what type of applications considered, different objectives can be identifi ed.

Large bandwidth - high resolution: High resolution is of great impor-tance in radar and geolocalisation applications. From signal theory it is

–


know that a narrow pulse in time-domain results in a wide spectrum in fre-quency domain. The inverse of bandwidth 1/ Λf is proportional to achieved resolution.

Large bandwidth – high multipath resistance: Large bandwidth implies that multipath may be resolved to a greater extent and because of the very short pulse used, UWB would have a good multipath resistance. It is then well suited to operate in indoor environment.

Low frequency –Good penetration properties: Electromagnetic theory yields that lower frequencies have better penetrating properties. The pos-sibility to use a large spectrum in combination with low frequencies results in desirable properties. UWB have thus been studied and is being used for very applications type like GPR (Ground penetrating radar), foliage penetra-ting radar and short range radar to detect hidden objects behind walls. This penetration property is also of great importance for indoor geolocalisation systems.

Covert radio LPI/LPD: UWB technique spreads the energy over a large spectrum. This results in a low probability of detection (LPD), and a low probability of interception (LPI). This means that it is highly interesting for military applications like covert communication in hostile environment. Also, it is relatively insensitive to intentional jamming.

Fairly stuffed spectrum: the low energy density implies possible use on an unlicensed basis. The normalisation organisations (FCC, ITS), who deci-des upon regulatory issues in the USA market, is now considering this. The transmitted signal is noise-like and overlay schemes could be used without interfering with existing radio systems.

Implementation cost: since the technique can be carrier free, it implies that transceivers can be inexpensively produced with CMOS (complementary Metal Oxide Semiconductor) technology, instead of expensive GaAs MIMIC (Monolithic Microwave Integrated Circuit). Thus UWB seems to be promi-sing solution to a vast array of low cost applications. Automotive collision avoidance systems, sensors for airbags and liquid level sensors are only some examples of proposed implementations.

The Ultra Wide Band technology allows wireless communications up to 480 Mbits/s over very short distances (few meters) while using a very large frequency band (528 MHz or 2736 MHz). Typical throughputs are 110 Mbps at 10 meters, 200 Mbps at 4 meters and 480 Mbps at 1 meter.

3.1-10.6 GHz is the frequency band allocated for UWB systems with TDD mode. Two main solutions exist. One is using OFDM access technique and sup-ported by the MBOA (Multi-Band OFDM Alliance) consortium. The other one is supported by Motorola and exploits DS-CDMA technique. They are the basis of IEEE 802.15.3a and IEEE 802.15.4a standards.

–

–

–

–

–




3.4. IEEE 802.15.4 (ZigBee and LR-UWB)

This standard was proposed in 2003 and is based on IP like protocols such as TinyTCP, TinyAODV, TinySec. The aim of this standard, also called Zigbee is to provide a standard for wireless network management.

3.4.1. Spectrum

The spectrum allocated is situated in the ISM band (cf fi gure 3.12 and table 3.2). In Europe only the 868 MHz is permitted. This frequency limitation reduced the possible throughputs. Table 3.3 shows the performances versus the number of channels used.

Figure 3.12: Spectrum allocation in the ISM band

Table 3.2: IEEE 802.15.4 (Zigbee) in the world

Frequency Modulation Band Data rate

Europe 868,3 MHz BPSK 5 MHz 20 kbit/s

United States 902-928 MHz BPSK 10 MHz 40 kbit/s

Others 2,4 – 2,4835 GHz OQPSK 16 MHz 250 kbit/s

Table 3.3: Performances versus frequency allocation

PHY(MHz)

Frequencyband(MHz)

Spreading parameters Data parameters

Chip rate(kchip/s)

ModulationBig rate(kb/s)

Symbol rate(ksymbol/s)

Symbols

868/915 868-868.6 300 BPSK 20 20 Binary

902-928 600 BPSK 40 40 Binary

2450 2400-2483.5 2000 O-QPSK 250 62.5 16-aryOrthogonal


3.4.2. Access method

This standard supports two access methods With synchronous networks time multiplexing is possible. With no time constraints the CSMA/CA is considered. The operation mode can be centralized or distributed (adhoc).

3.5. The WIMAX standard – IEEE 802.16 and IEEE 802.20 families

The Wimax constitutes the range of the metropolitan protocols of the IEEE. It is standardized in the group 802.16 which was divided historically in three sub-groups: 802.16, A and the E. The following fi gure shows a typical use of WiMax. For railway applications, the size of the cells can reach several kilometers. It could be possible with the E version for the standard. A system derived from the Wimax standard appears as the best solution for a wireless connection with a TGV but the capacity to cope with high speed and high Doppler shifts is not yet demonstrated.

Figure 3.13: Typical Wimax deployment

There is however a problem with the MAC layer. The MAC layer allows only reservation of fl ows and no random access as in Wifi . The mechanism uses a traditional window in contention mode which makes it possible for stations on the radio operator link to require in turn their requirements in bandwidth. Wimax 2000 corresponds to the standard 802.16a. The addresses used remain MAC ones and it is generally obligatory to be confi gured in IP protocol as network protocol. Several mechanisms are possible in the standard. Four classes of services allow different reservations. We have the class constant bit rate (UGS) for the applica-tions in real time to assured fl ow such as voice, the class called RTPS which offers the service for real time but with variable bit rate such as the MPEG AVC, the class NRTPS which uses bursts such as the ftp and the best effort (BE).




WIMAX uses a signaling protocol for control and admission. It is close to an ATM network in the sense that each communication is associated to a virtual channel called CID. A contention happens when two stations wish to transmit data at the same time. That generally causes a collision. The base station is able to detect this kind of problem because it manages the tasks on the channel uplink and determines which mini slot is prone to collisions. The collisions can occur only during the initial negotiation at the time of the requests for intervals for connec-tions. The potential occurrence of the collisions in these intervals generates a con-tention period in the base station. The method used is a method with exponential back off where we double our waiting time after each collision. In this situation, the base station draws a random number inside the window values and it decides to treat the requests below this random value. For example, for a window of 16, the station draws 9 as random number; it decides to treat nine requests and to leave 7 in standby. The stations wait and will have to retransmit their requests later.

The physical layer in the uplink direction (PHY) is based on a multiple com-bination of time division multiple access (TDMA) and (DAMA). All that on a cod-ing technique based on OFDM and various modulations. In particular, the uplink channel is divided into a certain number of periods assigned according to the vari-ous uses (recording of a new terminal, contention, or traffi c of traditional users). These partitions are ordered by the MAC layer in the base station and can vary for an optimal bandwidth management. The channel going down to users is in TDM, with the information dedicated to each station of subscriber sent on a data fl ow on a CID negotiated in advance, received by all the stations of subscribers in the same zone. The downlink also supports the FDD mode. In this case one can emit and receive at the same time on different frequencies. Each burst can have a fl ow identity different and characteristics with different FECs. This results in return to a standard with formidable fl exibility but also a very large complexity.

WiBro: As of 2004, WiBro began to align itself with the WiMAX Forum’s imple-mentation of IEEE with Mobile WiMAX, but the 802.16-2005 using a two-phased approach.

Phase I of WiBro is now based in part on the two technologies will remain IEEE standard; however, the WiBro community has selected a different set of options which incompatible with each other results in WiBro Phase I equipment being dif-ferent from, and non-compatible with, Mobile for the next few years.

Over the next few years, the WiBro community will move to Phase II of WiBro, which will help harmonize WiBro and Mobile WiMAX. However, the migration to Phase II will likely require meaningful hardware and software changes to Phase I WiBro equipment which will make it an overly complex and expensive upgrade to complete.

Operators who are evaluating a mobile broadband wireless strategy need to carefully weigh the time-to-market advantage of WiBro with the long-term implica-tions of deploying infrastructure and client devices that are not aligned with the WiMAX Forum’s requirements. In the end, these operators should fi nd that select-ing WiMAX will result in a far greater choice of vendors, lower total cost of owner-


ship, and a smooth migration to future Mobile WiMAX enhancements without the risk of technology obsolescence.

IEEE 802.16-2005: The mobile variant of the IEEE 802.16 standard is IEEE 802.16-2005, which, as of February 28, 2006, is a published standard. It is now referred to as IEEE 802.16-2005 and defi nes the Physical and MAC requirements for a mobile broadband wireless technology that operates in licensed spectrum below 5 GHz at speed lower than 120 km/h. The availability of a wide spectrum band gives the standard a high degree of fl exibility with respect to the spectrum in which the technology can be deployed. For example, 3.5 GHz is widely avail-able across the globe so the standard defi nes the requirements for that particular frequency band.

However, in the United States 3.5 GHz is not currently available so other fre-quencies, such as 2.5 GHz have to be used instead. As discussed later in this paper, 2.3 GHz spectrum is another viable band, although outside of South Korea, and a few other countries, such as Australia and New Zealand, it is already been used for other services or, as is the case in North America, only a few channels are available in the spectrum.

The IEEE 802.16-2005 standard is designed with fl exibility in mind, but this fl exibility can also result in incompatibility if vendors do not agree and work toward a common set of features.

WiMax product: the WiLAN: The WiLAN Company is based in Calgary, Canada and has developed Wi-Max solutions, based on W-OFDM. It provided a broad-band wireless solution adapted to a mobile environment. This company actively participates to the Wi-Max Forum. Moreover, some of the Mobilis solution (the one developed by WiLAN) is currently evaluated in order to include them into the coming soon standard WiMax.

While participation to the WiMax forum, WiLAN insists on the fact that W-OFDM has a strong potential for embedded environments, and tries to promote Mobilis as a solution for Broadband mobility. This solution has been designed for trains operators, and more specifi cally for suburbs trains, in order to quickly deploy security and survey applications onboard trains, as well as added value services for passengers, such as Internet access and real time information ser-vices, like information or e-ticketing.

Built on its LIBRA platform, the Mobilis solution supports speeds up to 110 km/h. This solution provides seamless mobility between different cells. The Mobilis solution includes the following elements:

A W-OFDM technology Wi-LAN

Sequential handover

Bandwidth up to 32 Mb/s

Use of validated NLOS Taking multiple path into account

Frequency ISM 5.8 GHz without license

Multi-layer security

–

–

–

–

–

–




Mobilis network architecture: The Mobilis solution needs the installation of transceivers (Access Unit, or Base Stations) along the track. Another set of transceivers (Mobile Unit, or Subscriber Station) should be installed onboard the train. When the train roams from one Access Unit zone to another, the fi rst AU transfers the connection to the next AU. The system uses a software handover solution in order to provide continuity of service when roaming. The connection with the fi rst AU stays alive while the second connection is made. When this is done, the system switches to the second one and closes the fi rst connection. The following table 3.4 gives a sum-up of the technical specifi cations of the solution.

Table 3.4: technical specifi cations of the AU/MU equipments.

Output Power +17 to 0 dBm - 10 channels

Frequency band 5.725-5.850GHz

Technology W-OFDM

Coverage domain Up to 2 km (mod 16QAM)Up to 5 km (mod BPSK)

Bandwidth Up to 32 Mb/s

Receiver sensibility -84 dBm (mod BPSK)-81 dBm (mod QPSK)-75 dBm (mod 16QAM)

Channel interval 10MHz/12.5MHz

Access mode Time Division Duplexing TDD

Speed Up to 110 km/h

Handoff capacity Fast sequentialHandoff

Mobility support Level 2 mobility / transparent mobility level 3

The solution has been built based on a platform that uses W-OFDM techno-logy. W-OFDM is supposed to improve the radio channel whenever working in a NLOS environment. The 5.725-5.85 GHz frequency band that is used is not much used. Thus the technology allows transfers up to 32 Mbauds/s, and effective 20 Mbit/s. Main characteristics of the architecture are sum-up in table 3.5.

Validation tests, done at high speed

W-OFDM technology, developed by the WiLAN compagny, has been proven for several applications at high speed. Technical trials have been performed early 2004, and have proven the handoff capacity of the solution. WiLAN planned some tests in order to prove this technology at speeds of 350 km/h, but without provi-ding the target bandwidth.


Table 3.5: Network architecture characteristics

Modulation 16QAM, QPSK, BPSK The operator can choose between several modulations depending on the service offered or the environment.

Auto attachment Allows the MU to automatically determinate with wich AU to communicate when initializing connection.

Dynamic modulation scheme Allows the system to operate under optimal conditions, by automatically adjusting the modulation uplink and downlink according to the quality of the channel

Channel commutation Allows to change frequency and to choose the best channel for the communicationAllows the operator to optimize its system

Layer 2 mobility Fast detection of mobility on the layer 2 and handoff according to the diagram of handoff

Layer 3 mobility transparency Mobile IP users can transparently use this solution

Mobility up to 110 km/h Provides a broadband mobile solution

Software maintenance done remotely

Reduces maintenance costs

Proprietary solution Data transfer is secured by wireless mobilis solution

Bandwidth up to 32Mb/s per AU Supports broadband applications

Sequential software handover Allows a services without interruption

Telnet and SNMP v2c Reduces maintenance costs

Wi-LAN W-OFDM Technology Allows NLOS communications

Figure 3.14: Mobilis network architecture

Services offered by the Mobilis solution are:

On-board Internet access

Information and entertainment services for passengers

Real-time information services (news, weather, sports, …)

VoIP

On-board messages

E-ticketing

Video on demand

–

–

–

–

–

–




3.6. Wireless Meshed Networks

Basically the wireless meshed networks are built upon the Wireless LAN net-works described before. They correspond to the IEEE 802.11s standard that will be notifi ed in 2007. Every access point has two WLAN interfaces: one Interface is intended for the access of potential users of the accesspoint, whereas the second interface is used for the interconnection to other Access Points or Access Points which are somehow connected to a router. The meshing between the Access Points is automatically done, the only resource that Wireless Meshed Network Access Points need is a power supply.

In France a fi rst solution for a WiFi-Mesh network is evaluated in rural or urban area (htpp:/www.serialless.net/breve.php3?idbreve=518). Several interfaces are used: optical fi bre, PLC, WiMAX, WiFi, GPRS or other 3G systems. This technol-ogy will be probably deployed where there is a high density of potential users.

4. ConclusionThe fi rst part of this chapter is devoted to the main cellular systems description.

Starting from the GSM system, we have described the GSM-R system and then the various evolutions such as GPRS, EDGE and fi nally UMTS. The main charac-teristics of the American systems IS-95 and IS-136 are also presented. All these cellular systems are able to serve large cell size depending on the Transmitted Power at the base station (BTS), the antenna gain and the resistance to interfer-ence levels defi ned for the cell planning and frequency reuse rules of the cel-lular system. It is important to notice for railway applications, that these systems are designed for mobile applications and specifi c procedures such as “handover” are included in the standard. Ability to resist to high speed up to 350 km/h were proven for GSM-R technology with specifi c radio coverage constraints and net-work tuning.

Another key point for cellular systems is the number of traffi c channels avail-able for a single cell. This number is directly proportional to the number of carriers (TRX) on the BTS, to the radio resources allocation process of the system and also to the traffi c load at one instant. In this context a comparison between sys-tems in term of capacity should take into account the relationship between traffi c channels availability versus cell size, TRX number and traffi c load particularly in dense areas in which a large number of trains will need to transmit big amount of information at the same time.

It is also important to notice that the maximum possible throughput in existing cellular systems is feasible only in small cell size, generally using several traffi c channels and at low speed (fi xed or pedestrian).

One common characteristic for all the existing wireless systems launched after GSM with the introduction of GPRS technology, is that they are generally designed for Internet like applications. Thus they offer non symmetrical links in term of data rate. Low rate in uplink corresponds to requests or acknowledgements from the users, high data rate in the downlink corresponds generally to downloading (appli-


cations, software, video, music…). This point must be highlighted from a railway point of view because the multiplexing of several applications sending information from the train to the ground on a unique medium will lead to the need of high data rate on the up-link direction. In this context, we can assess that today there is no existing public cellular system able to provide data rate around 500 kbits/s in the uplink in the context of mobility (greater than 100 km/h).

The second part of this chapter is devoted to the description of WLAN and WMAN systems. All the IEEE.802.11x variations have been presented. The main characteristics of the very promising IEEE.802.16x family also called WIMAX are detailed. WLAN and WMAN standards are today widely deployed but they provide high data rate only in a small coverage area. They are submitted to the same electromagnetic laws than cellular systems, thus covered area sizes are directly related to transmitted power limitations, antenna gain and sensitivity to interfer-ences. The maximum throughput available is directly related to the bandwidth available per user at the same time and to the distance to the access point.

The use of WiFi or WiMax like technologies for railways applications that required periodic or continuous transmissions will certainly require the develop-ment of handover and roaming protocols adapted to these systems. Even if the cost of one single WiFi or Wimax access point is very low, what will be the cost of developing handover and roaming protocols and network signalling able to cope with railway requirements?

The fi rst versions of the WiFi standard were not design for mobility. Very basic handover procedures have been implemented in the last versions mainly for car to car communication applications. Resistance to high speed in the context of railway is not proven yet. The last evolution of the WIMAX standard will take into account fast mobility. Consequently, this technology is a good candidate for high data rate communication in the context of high speed trains and will be tested in the second phase of the Train-IPSAT project.

The new standards related to the UWB wave form are also described. Their main drawback at the moment is the very short range coverage characteristics due to the drastic power limitation in Europe. Nevertheless, WPAN systems rep-resent very promising emerging systems able to provide high data rate for very short range communication needs thus they can be foreseen only for specifi c local applications.



Chapter 4

Existing satellite systems

1. Satellites for communications in general

1.1. Introduction

Satellite systems for communication with terrestrial civil mobiles were under development only during the last years in contrast to their use for communica-tion with maritime and aeronautical mobiles particularly in the military domain. This trend was mainly the consequence of low cost and low size requirements for the on board transmitting-receiving equipments for terrestrial mobiles. This reality changes with the launching of constellations such as GLOBALSTAR, IRIDIUM and ICO as complement of terrestrial cellular networks. These sys-tems are also in expansion with the development of digital TV broadcasting and “TV on demand”, service for which the user receives only what he has paid for. Applications of data transmission using the European VSAT system are also in development.

Today, the satellite-based solutions are intensively studied in public transport applications to suppress a ground infrastructure that will decrease track mainte-nance costs and vandalism on the ground based equipment.

One of the advantages of satellite-based solutions is that the only terrestrial infrastructures needed are the on board equipment. They are generally able to provide communication facilities in areas where there is a lack of telecommunica-tion infrastructures. The drawbacks are mainly in the availability of the systems particularly in dense urban areas or in cuttings and tunnels where the satellite sig-nals are masked or blocked. Terminal and bandwidth costs could also represent additional drawbacks.

Today, the satellite-based solutions are intensively studied in public transport applications in order to suppress ground infrastructure with the aim to decrease track maintenance costs and vandalism on the ground based equipment. Nevertheless the research is mainly focused on the localization and navigation applications. This is the case for example for all research projects dealing with the use of GPS and the future GALILEO for control and command applications (LOCOPROL, LOCOLOC, GADEROS, INTEGRAIL) [Raymond, 04].



1.2. Satellite communication network structure

A satellite communication network is composed by one satellite and a set of terrestrial transmitting and receiving stations. The satellite consists of a platform and a load. The load includes telecommunication equipments and antennas. The platform welcomes equipment for energy feeding, heating control, altitude control, remote control equipment and remote measurement equipment.

Telecommunication equipments also called repeaters, play the same role than a broadcast radio-relay system. They received transmissions coming from the ground and retransmit the signals after amplifi cation and frequency transposition. A “demodulation-remodulation” of the received signal or jamming rejection tech-niques are sometimes implemented on board the satellite. Telecommunication systems using satellites are generally able to provide communication facilities in areas where there is a lack of telecommunication infrastructures. Satellites are placed in the space on dedicated orbits. Tableau 4.1 gives the different orbits characteristics, the altitude regarding ground surface and an average satellite life duration.

Table 4.1: satellites main used orbits

Orbit LEO MEO HEO GEO

Altitude (km) 400-800 1200-2000 8000-15000 35786

Life duration 3-5 years 5-8 years 8 years 15 years

LEO: Low Earth Orbit,

MEO: Medium Earth Orbit,

HEO: Highly Elliptical Orbit,

GEO: Geosynchronuous Earth Orbit.

In order to share the satellite spectral and temporal resources between seve-ral transmitters and receivers, multiple access techniques are used. Among the most popular in the satellite domain one can fi nd: PAMA (Pre-Assignation Multiple Access): one way for transmission is assigned for whole communication dura-tion; DAMA (Demand Assignation Multiple Access); FDMA (Frequency Division Multiple Access); TDMA (Time Division Multiple Access); CDMA (Coded Division Multiple Access).

Three telecommunication services are possible: fi xed, braodcasting and mobile. We focus in this report on mobile service. This service allows a link between the satellite and maritime, aeronautical and terrestrial moving transmitters/receivers. The main categories of systems are: Satellite Mobile System, Satellite-Personnal Communication System and Large band multimedia satellite system.

Satellite Mobile Systems (SMS) are mainly operated by INMARSAT (satellite GEO) serving more than 30000 users in the world (among them 18000 boats). Offered services are duplex voice, fax, data transmission at low data rate. User terminal are very different (size and height) according to demand.

–


Satellite Personal Communication Systems (S-PCS) offer a global or regio-nal coverage. Spacial segment is composed with geostationary constella-tions (GEO), medium orbit ones (MEO) or low orbit ones (LEO). Interface with terrestrial public fi xed or mobile networks is organized in a manner that S-PCS systems are used to complement terrestrial infrastructures someti-mes non available or non existing. Terminals are portable systems or fi xed phones directly linked to the satellite networks. They are multi mode sys-tems (ex: satellite/GSM). Available services are: voice, fax, low data rate transmission, messaging and localization.

Multimedia satellites offer bidirectional high throughput services for cus-tomers and for professional uses such as videophone, visio-conference, informatics networks, digital libraries, tele-teaching, fast internet. To allow this kind of services the technology is mainly based on geostationary high power satellites in Ka and Ku bands with advanced digital modulation and coding techniques.

The areas covered by satellite systems are separated in three main areas or region distributed as follows: Region I: Europe, Afrique, Middle Orient, CEI - Région II: American Continent - Region III: Asia (except Middle Orient, CEI et Oceania). Tableau 4.2 summarized the frequency bands allocated to satellite systems in the world.

Table 4.2: Frequency bands allocated to satellites and usage

Name Band Main Service

VHF 30 - 300 MHz messaging

UHF 300 - 1000 MHz military, navigation, mobile

L 1 - 2 GHz mobile, audio broadcasting, radio localization

S 2 - 4 GHz mobile, navigation

C 4 - 8 GHz fi xed

X 8 - 12 GHz military

Ku 12 - 18 GHz fi xed, video broadcasting.

K 18 - 27 GHz fi xed

Ka 27 - 40 GHz fi xed, video broadcasting.Inter satellite

Millimetric waves > 40 GHz Inter satellite

Satellite based communication systems are generally non symetrical. They allow information transfer at high data rate in the downlink direction (satellite towards the ground) and only a few data rate in the reverse direction (uplink). Nevertheless, some satellite systems offer bi-directional symmetrical links. The architecture of a satellite based communication network is different from the ter-restrial system one. The satellite is considered as a central node and received several communications coming from several transmitters on the ground. For fi xed users, the information is sent through terrestrial stations. Such an architec-ture with big distances betweens the different nodes leads to signifi cant transmis-sion delays that can reach 500 ms.

–

–




Satellite based communication systems throughput are generally non sym-metrical. They allow information transfer at high data rate in the downlink direction (satellite towards the ground) and only a few data rate in the reverse direction (uplink). Only some satellite systems offer bi-directional symmetrical links.

Multiple access techniques such as TDMA (Time Division Multiple Access), le FDMA (Frequency Division Multiple Access) or CDMA (Code Division Multiple Access) are used to allow several simultaneous communications on the same RF link. The architecture of a satellite based communication network is different from the terrestrial system one. The satellite is considered as a central node and received several communications coming from several transmitters on the ground.

For fi xed users, the information is sent through terrestrial stations. Such archi-tecture with big distances betweens the different nodes leads to signifi cant trans-mission delays that can reach 500 ms. Communication protocols at the application level vary from a system to an other. Several systems use the IP (Internet Protocol) one, other the ATM (Asynchronous Transfer Mode) one.

2. The different existing systemsThe following paragraphs summarize the main technical characteristics of the

existing satellite systems that can answer the transmission needs studied in the Train-IPSat project.

2.1. WorldSpace

WorldSpace is composed of 3 GEO satellites AfriStar, AsiaStar and AmeriStar. The broadcasting is operated in the L band between 1.453 GHz and 1.492 GHz, with a maximal user data rate of 128 kbits/s. The WorldSpace data transmission mainly concerned organizations that want to transmit a big amount of data to users disseminated all over the world generally where communication infrastruc-tures area rare and very expensive. A WorldSpace satellite uses 576 channels. The digital transmission fl ow is MPEG-3. Channels are TDM multiplexed. The carrier frequency is QPSK modulated.

2.2. INMARSAT

The coverage offered by INMARSAT is global. The constellation is composed of 9 GEO satellites and 4 of them are effectively used. Frequency bands are C and L. For INMARSAT A, the Uplink frequencies are situated between 1636.5 – 1645 MHz. The downlink frequencies are situated between 1535 – 1543.5 MHz. Terrestrial segment is composed of terrestrial stations which correspond to central communication nodes linked to public networks. The whole network is managed by the NCS (Network Coordination Stations). The satellites are controlled from a centre based in London. The satellites do not communicate each other. The


traffi c generated by the users is transmitted to the satellites and then goes down to terrestrial stations. 40 terrestrial stations are situated over 30 countries. The data fl ow is managed by the control centre. INMARSAT sells only the satellite access and does not deal with interconnexion with terres-trial networks. Inmarsat provides several services:

Inmarsat B, is the digital version of Inmarsat A. The terminal is smaller but still heavy (100 kg). The data rate 64 kbits/s. Uplink frequencies are situa-ted between 1626.5 – 1646.5 MHz. The downlink frequencies are situated between 1525 – 1545 MHz.

Inmarsat C does not provide telephony. It carries data at 600 bits/sec with time com-pensation. The weigh of the terminal is 10 kg. Uplink frequencies are situated between 1626.5 – 1645.5 MHz. The downlink frequencies are situated between 1530 – 1545 MHz.

Standard E is an emergency beacon.

Inmarsat AERO I, provides a service to passengers in planes. It allows tele-phony, fax and data transmission from 600 bits/s to 4.8 kbits/s. AERO-L provides low speed data communications at 600 kbits/s for air traffi c control, operational and administration procedures.

Inmarsat M allows digital telephony, fax and data transmission at 2.4 kbits. It is smaller than the other Inmarsat hand set (less than 3 kg). The transmis-sion power is 24 dBm (0.25W) for the “Mini M” terminal. For INMARSAT-M maritime, the uplink frequencies are situated between 1626.5 – 1646.5 MHz. The downlink frequencies are situated between 1525 – 1545 MHz. The land mobile version operates between 1626.5-1660.5 MHz (UL) and 1525-1559 MHz (DL).

Swift64 is Inmarsat’s latest service offering for airlines, business aviation and government users, enough data bandwidth for applications such as high-quality voice, e-mail, Internet and Intranet access, and videoconfer-encing. Swift64 terminals can offer up to four 64 kbit/s channels that can be bonded to produce a 256 kbit/s data rate. Application of compression and acceleration techniques can boost the effective rate to beyond 0,5 Mbps.

2.3. EUTELTRACS/OMNITRACS

EUTELTRACS (also called OMNITRACS) is worldwide communication net-work with mobiles that offers bilateral radiomessaging services in Ku band asso-ciated with a localization service. EUTELTRACS is composed of 7 satellites above Europe. Main users are trucks which are about 4 millions all over Europe. Eutelsat has launched 2 broadband internet access services, IP-access and IP-connect, based on DVB-RCS standard, and allowing bidirectionnal (symmetrical and asymmetrical) communications from a few kbps up to 40 Mbps, with guar-anteed QoS.

–

–

–

–

–

–




2.4. MSAT

MSAT is a communication system developped by AMSC (American Mobile Satellite Consortium) and TMI (Telesat Mobile Inc). It comprises 2 geostation-ary satellites one is American, the other is canadian and they cover only North-American continent. Services offered to terrestrial, maritimes et aeronautical mobiles are: telephony and data transmission in L band.

2.5. OPTUS (AUSSAT)

AUSSAT is an Australian system offering national, broadcasting and also mobile services. The system is composed of three satellites OPTUS working at Ku and L bands. Telephony and data transmissions services are available for ter-restrial, maritime and aeronautical mobiles.

2.6. ITALSAT (EMS)

ITALSAT system (national Italian system) allows mobile services in L band in addition with fi xed services in Ka Band.

2.7. IRRIDIUM (S-PCS)

The IRRIDIUM system is a network for personal satellite wireless communica-tions in Ka band design for any type of transmission (voice, data, fax), everywhere in the world. 66 satellites of the IRIDIUM constellation (plus 6 satellites for fall back solutions) area placed in low orbit (LEO) at 780 km above the ground. This allows portable phones smaller than the ones used with geostationary systems (INMARSAT like). IRIDIUM system is able to establish a mobile link without any transfer via a terrestrial station. Each satellite is more than a simple repeater (as it is the case for geostationary systems) but acts as a terrestrial base station man-aging all received communications. A terrestrial segment composed of two control centers called SCC (Satellite Control Center) and connexion stations, allows links establishment with the RTC and to manage customers mobility. Uplink and down-link frequencies are between 1616-1626.5 MHz

2.8. GLOBALSTAR (S-PCS)

Like IRRIDIUM, the GLOBALSTAR system is dedicated to mobile communi-cations (voice, data, fax). The GLOBALSTAR architecture is design in order that each call end through the RTC and existing terrestrial mobile networks. The global system can be seen as a complementary system to existing cellular terrestrial systems. It is compatible with existing cellular systems such as GSM and IS95 and offers the same services. The GLOBALSTAR spacial segment is composed of 48 LEO satellites (1414 km), 8 emergency satellites and 2 control centers called SOCC (Satellite Operation Control Center). The terrestrial segment is composed of connexion stations (Gateway) that allow the establishment of links with pub-


lics networks but also to manage customers mobility and services attribute. The L, S and C bands are used. Uplink frequencies are between 1610-1626.5 MHz. Downlink frequencies are between 2483.5-2500 MHz.

2.9. ICO (S-PCS)

The ICO (Intermediate Circular Orbit) system offers communication services (voice, data 2400 bits/s, fax) to its customers everywhere in the world. The spatial segment is composed of 10 MEO (10355 km) satellites, plus 2 emergency satel-lites and control centre. Terrestrial segment is composed of a network that links the 12 connexion nodes between satellites, terrestrial networks and management network centers. This network is called OCINET.

2.10. ODYSSEY (S-PCS)

ODYSSEY offers communication services with portable terminals as a comple-ment of terrestrial cellular systems thanks to multi modes terminals. Services are the following: digital voice (4800 bits/s), data, fax, radio messages, radio localiza-tion with 15 m accuracy. The spatial segment is composed of 12 MEO satellites (10354 km). The terrestrial segment is composed of a network, an operational centre and 7 terrestrial stations.

2.11. Thuraya

The Thuraya system is composed of 2 geostationary satellites located above th African continent. Geographical areas covered are: Middle-Orient, North Africa, Central Africa and Europe. Thuraya terminal is a combination of a satellite and GSM system. Roaming agreements exist with the operators of the countries cov-ered. Thuraya operates in L band. Thuraya DSL is a satellite GPRS data transmis-sion service for vehicles up to 144 kbits/s.

2.12. Satellite-based mobile system supporting broadband interactive services on fast trains or on planes

Today there is no existing satellite systems able to cope with fast mobility related to high speed trains supporting broadband interactive services.

A solution has been designed for aircrafts: the Connexion By Bœing able to offer broadband connectivity that enables internet services and live TV reception for individual passengers onboard aircrafts in the Ku Band (14-14.5 GHz for air-craft to satellite, 11.2-12.75 GHz for satellite to aircraft link. The initial system is designed to provide up to 20 Mbps from satellite to aircraft and up to 1 Mbps in the reverse direction.

Several research projects are on going for public or military applications in order to enhance the satellite physical layer for example in order to provide high throughput with fast mobility, masking effects, electromagnetic perturbations,




vibrations…. The Train-IPSAT project will propose and test solutions based on a modifi ed DVB-RCS standard using an existing antenna from the 21Net project describe later. The project will study particularly the infl uence of fast mobility on an optimised DVB-RCS link, the effect of masking effects in the context of railway environment, the optimisation of the satellite link tracking.

3. On test or existing deployed solutionsCurrent deployed industrial solutions or pre-tested solutions are provided by

PointsShot Wireless (Canada) and IComera (Sweden). These solutions are mainly deployed in California and Canada for the fi rst one and in Europe for the second. These solutions are built on a multi-segment architecture, composed of a satellite network, a cellular network, and a terrestrial broadband network. The network inside the train is based on a Wi-Fi technology. Alenia is working on a solution developed during the FIFTH project, and 21Net is currently testing a bidirectional satellite solution with Thalys. Another solution is in development in the MOWGLY (www.mowgly.org) that aims at developing a solution for high speed trains and planes. These solutions and experimentations are described in the following paragraphs.

3.1. PointShot Wireless

PointShot Wireless is a Canadian company, built in 2002, which provides full wireless solutions for sites with no wired broadband possibility. This company is based at Ottawa Canada. It provides a full set of solutions from which RailPoint is specifi cally developed for broadband Internet on trains. The general architecture of the system provided by PointShot is described in the following fi gure 4.1.

Figure 4.1. BroadBand Internet for trains by PointShotWireless [source internet]


This solution allows the train operator and customers to connect to ser-vices such as local applications and contents, or Internet. Local connection is made by WiFi, and connection with ground is made by Satellite, cellular (GSM, GPRS, UMTS), and terrestrial links (Wi-Fi, Wi-Max). This solution is theoretically able to optimize bandwidth between several links, and to switch from one to another when the environment changes. Little technical informa-tion is available for the RailPoint solution, but the following component list can be set up:

The RailPoint server supports access points, traffi c control, communication with external WANs, security, and embedded contents and applications

The package of antennas, satellite, cellular and WiFi WAN, on few informa-tion is available

Internal 802.11 Access Points

The RailPoint gateway to be installed with the NOC (Network Operating Center)

The software which manages the routing of the traffi c between the train and connections WAN, and the traffi c monitoring.

The integration of a Radius server for AAA functionalities

The RailPoint solution includes the SolutionPoint platform which allows the inter-connection of cellular networks, satellite and WiFi, in order to provide an Internet access. This solution integrates the following components:

Access points which provide access to satellite channels or 3G, and can provide proxy functionalities for caching of mails and web contents. These AP are installed aboard trains. When the train is at a railway station, the SolutionPoint has the capacity to integrate AP of another operator present in the station

applications: the software provides access to Internet, connectivity network, VPN capacity, instant messenger, entertainment, safety, ticketing, billing, and applications provided by the railway company. The key point of this application is that it allows a vertical between networks satellite, Wifi and cellular handover without disconnection of the service.

The gateway; it makes tunneling in order to integrate packets to be sent to the Internet provides an intelligent control of the link, and compression.

The technical characteristics of the solution, which answer to specifi cs needs, are detailed in the following paragraphs:

Metropolitan zones - To answer to signal loss issue while moving into met-ropolitan zones, PointShot uses a WAN integration technology. The RailPoint embedded server constantly maintains a data link during the journey, by using a combination of all existing links (satellite, cellular, and terrestrial). The server allows to commute between links, and to select the best link in order to keep con-nection up and functional.

–

–

–

–

–

–

–

–

–




Tunnels - When entering into tunnels, the network becomes unavailable. Then the Railpoint system is able to provide web caching, and email store-and-forward. Users then can continue to browse Internet and to send emails without interruption.

Rural zones - Lack of coverage in rural areas due to hills and trees, which obstruct the Line Of Sight. The RailPoint solution constantly performs link quality measures, without mailing any link break, in order to commute between terrestrial or satellite links.

Inside coverage - Several RailPoint servers can be installed in the train. A pri-mary RailPoint server should be installed to provide connection with the ground, and secondary RailPoint servers should be installed in the train in order to provide connectivity to users along the train, and to route packets to the main server.

In the train, users can use several kinds of applications. The traffi c controller is able to analyze traffi c in order to prioritize traffi c according to application types, and to optimize bandwidth allocation in the train. The open RailPoint architecture is able to support several application types.

The fi rst set of tests was performed in July 2003, with the ViaRail company (Canada), and Bell Canada. The service was deployed by Bell Canada on 1st class of ViaRail trains, between Montreal and Toronto. The service was free till September 2003. The offered downlink bit rate was 400kbit/s. The return path was provided by the Bell CDMA cellular network. When train was in railway stations, the service was provided by local HotSpots. Other tests have been performed on ACE (Altamont Commuter Express) trains, and Amtrak train from Capitol Corridor in California in September 2003, for a 3 months period.

FTR&D San Francisco performed some tests in 2003. These tests have been performed with CDMA technology, on the ACE trains, with the PointShot solution. The following table 4.1. gives a sum up of the test results.

Table 4.1: synthesis of comparative tests with CDMA/PointShot

Web-mail(Hotmail)

Corporate Mail

Corporate Mail w/Attachment

(834KB)

Websites Speed Test

CDMA-1RxTT Aircard

Two minutes delay. Sent at 1:44pm

Two minutes delay. Sent at 1:50pm.


55 seconds to load the entire web page.

59.1kbps

CDMA-1RxTT Aircard w/VPN


One-minute delay. Sent at 2:13pm

Failed Twice. 45 seconds to load the entire web page.

55.9kbps

PointShot Wireless

Two minutes delay. Sent at 5:16pm.

One-minute delay. Sent at 5:57pm.

12 minutes delay. Sent at 5:58pm.


63.4kbps

PointShot Wireless w/VPN



Eight minutes delay. Sent at 5:26pm.


69.2kbps to37.8kbps


These results show that performances were poor. Moreover, it was performed with only 5 simultaneous users, while the system should be able to support up to 20. More over, the following observations have been made:

The PointShot service is not optimized for PDAs and laptops.

Delay is manly due to upload of fi les from the laptop to the network.

Connection has been broken in the tunnels.

3.2. IComera

Icomera is a Swedish company which develops an embedded Internet access solution in a train coupling a satellite access to a cellular access in zones where satellite is not available. Aboard train, a WiFi network makes it possible to distrib-ute the traffi c in the cars. The architecture of the service developed by Icomera is represented on the following fi gure 4.2.

Figure 4.2: Icomera Internet access service architecture

This wireless communication solution for high-speed trains is called “Wireless Onboard Internet ”. This service allows passengers of a train to obtain last-minute news on the way, to browse the Internet, to check their emails, to read the news and to reach information of their Intranet. For the train operators, online reservation infor-mation is accessible aboard train. To provide its Internet access, Icomera associates communication links based on satellite, GPRS/UMTS, CDMA, and Wireless LAN for the distribution of the network in the cars. The alignment of the Tx/Rx antenna is assisted by GPS. The system supports AAA functionalities to be integrated into the management of a mobile network for example. A remote management system allows Icomera or the railway operator to monitor each part of the system. The solution developed by Icomera includes industrial parts that constitute a modular system. The main components of the embedded system are the following:

–

–

–




The antenna unit which includes antennas GSM, GPS, WLAN, CDMA and the satellite antenna. A protection “radome” against high voltages is also provided.

The Icomera embedded system rack. This one contains a calculator equip-ped with communications cards, switches, the management software and optimization of the system

The embedded wireless network. A wireless network with the standard 802.11b/g providing network access to users.

These equipments are presented on the following fi gures 4.3 and 4.4.

Figure 4.3: antenna system and embedded IComera System

Figure 4.4.: embedded wireless network

The Internet access services provided by Icomera are intended to the passen-gers and to the railway operator. Most signifi cant are as follows:

Services to passengers:

Web browsing

Sending and receiving of emails

Intranet secured access

Access to the operator web-site, on order to perform reservation, and to get information on traffi c

On-line Reservation for customers: taxi, train, …

Services to the train operator:

Information for train operator are available onboard.

sending of maintenance information while traveling

reserved but non occupied seats can be listed and sent back for sell for last minute passengers.

onboard credit card transactions.

–

–

–

–

–

–

–

–

–

–

–

–


broadcast of information to on board staff.

real-time geographic information, including cards and time statistics.

The IComera system relies on a satellite/cellular network, where cellular net-work is used for the return path. This system uses a 4 to 6 links aggregation, in order to maintain internet connection in tunnels. The IComera solution can use data channels from GSM, satellite, DVB-T, and is able to select automatically the best available channels, and to maintain internet connection between them. The mobility software solution is based on a protocol which is able to maintain several connections at the same time.

The Gateway is packaged in a rack including Windows XP. The antenna sys-tem is composed of active elements, and does not use a mechanic antenna. The antenna subsystem on the roof of the train is composed of: GSM, GPS, WLAN, CDMA, and satellite. The satellite network capacity is brought by the SIRIUS satellite. DHCP and DNS forwarding functionalities are integrated to the W-LAN network.

The following fi gure 4.5 presents Icomera equipment installation onboard the train. Figure 4.6 shows downlink and uplink bit rates announced by Icomera.

Figure 4.5: Confi guration of equipments in the train

Figure 4.6: performance of forward et return links of the Icomera system

–

–




Figure 4.7 shows an example of a web application that provides train positioning and status information.

3.3. 21Net

The 21Net solution has been developed with the help of the ESA “BroadBand to Trains” theme, which consists of developing a system that is able to provide broadband multimedia Internet access onboard trains. The target market is high speed lines for Western Europe, for which travel time is long enough to use this kind of solution. In addition to Internet and VPN/Intranet access services, 21Net offers entertainment services to passengers.

The 21Net system architecture (fi gure 4.9) is based on a bidirectional satellite link between the Internet Backbone connection and an embedded server. Users connect to this local server via a local Wi-Fi HotSpot.Television is also available in the 21Net solution. The architecture is composed of the following elements:

The HUB (earth station), which provides connectivity to the Internet, via a satellite link with the embedded satellite antenna.

Local access to GPRS and Wi-Fi available networks (in tunnels or railway stations)

Local Wi-Fi Hotspots, that provides wireless connectivity to end-users

The project started in mars 2004. A fi rst test campaign has been performed in Spain in june and july 2004. A test campaign were performed with the Thaly company in summer 2005.

–

–

–


Project key points:

Availability of a pursuit Ku-band antenna, low profi le, at reasonable cost. Photos are given on fi gure 4.10.

Necessity to respect railway operator requirements in terms of security, in the high speed context.

Project goals:

The 21Net solution aims at providing seamless broadband Internet access to fi rst class passengers, at a reasonable cost.

The access service should provide a better bandwidth and QoS than cellu-lar networks (GPRS)

Use of Ku-band satellite links, in order to provide a 2Mb/s downlink and a 512kb/s uplink, without contention, to be shared by 50 users

High Speed trials

Preliminary tests have been performed at 300km/h in June and July 2004 with the spanish RENFE company, in order to validate the system concept. For those tests, the system was the following:

Bidirectional satellite roof antenna

Antenna controller

Satellite modem

On-board Wi-Fi distribution system

Figure 4.8: 21Net system Architecture

The system was managed from a Northern Europe back offi ce. Hardware equipments were installed in a lab control wagon. The satellite link was main-tained at 4 Mbit/s downlink and 2Mbit/s uplink. 10 WiFi users were downloading fi les and using streaming video simultaneously in order to saturate the link. 4 lap-tops established a 700kbit/s downloads during a 5 hours trip.

–

–

–

–

–

–

–

–

–




Figure 4.9: 21Net antenna

First user feelings was that the affair class service was good enough, even if some issues were still to be solved: it was necessary to re-establish manually the connection after tunnels (several seconds), even if users were able to switch to local content whenever passing through tunnels.

3.4. The MOWGLY solution

The aims of the MOWGLY (a Broadband Access Satellite Architecture for Mobile Collective User’s) project are to solve the most signifi cant and critical tech-nical issues prerequisite to development, deployment and evolution of broadband access satellite architecture for collective mobile users. The project concerns three transport means: aircrafts, trains and vessels.

MOWGLY will be based on DVB-S2, DVB-RCS broadband access standards. MOWGLY will produce technical analysis and demonstrations for the extension of these standards to mobile applications.

For the space segment MOWGLY uses existing satellite capacity and cover-age at Ku band to achieve early roll-out but with synergy to future system evolu-tions operating in Ka band to provide additional capacity and more cost effective systems. MOWGLY will develop versatile Ku/Ka collective mobile onboard antenna. This project aims at developing both Passengers Services and Crew Services.

Passengers Services

Access Services (High Speed Internet (HSI), web browsing for individual users, e-mail access).

Interconnection Services (Professional/Corporate services with bi-directio-nal connection such as for VPN’s, Intranets):

Entertainment Services (Audio, video, games, news, etc…)

Crew Services

Maintenance Services

Security Services

Medical Services

Management Services

–

–

–

–

–

–

–


4. Conclusion

The satellite communication system is probably today the most promising solu-tion for fast inter city trains. Thanks to the absence of specifi c infrastructure to be placed along the track, the service is potentially available everywhere including the far out areas. The main drawbacks to guarantee connectivity and QoS are due to the satellite visibility related to the occurrence of mask effects encountered in the specifi c railways environments (tunnels, cutting, lattice mast supporting cat-enaries, etc).

This chapter presented the main satellite systems design for mobile appli-cations. The systems presented offer commercial services able to complement GSM/GPRS/EDGE or IS-95/IS-136 services in the areas where there is no GSM deployment. None of them is able to support high data rate and fast mobility. Some research projects are trying to set up satellite-based mobile system sup-porting broadband interactive services on fast trains or on planes.

The Train-IPSAT project will propose and test solutions based on a modifi ed Physical layer of the DVB-RCS standard using an existing antenna from the 21Net project described in this chapter.



Chapter 5

Mobile router

1. IntroductionDue to the various environments of the high speed trains along the different

existing lines all over Europe, it is impossible to identify at short term a unique tech-nology able to answer all the connectivity needs on the whole trip. The solution is to use several technologies with a real time transparent roaming also called “vertical handover” to switch from a system to another depending on the best availability.

This “roaming” or “vertical router” will be performed thanks to a specifi c device that will act as a “multi access router”. Its main role will be to allow permanent links while the train is traveling using alternatively several access technologies transparently for the customer. Recently, a number of micro-mobility protocols have been proposed to manage transparent mobility to application layers. These include Mobile IP [Perkins, 96] and its multiple variants [Sun, 01], message ori-ented middleware (MOM) technologies [Kaddour, 03]. These standards solve some of the inherent IP mobility problems, but as they are working at higher lay-ers (3 and above), important delays are introduced [Montavont, 03].

The communication devices on-board the train could be PDA, PC, smartphone, but also “intelligent IP sensors”. To cope with this diversity, a multi models soft-ware infrastructure has to be used to access continuously to the different services while traveling.

The Train-Ipsat project will analyze these different solutions: CISCO router, Ipv6 –NEMO solution [Ernst, 04] and multimodels software infrastructure such as MOM technology. We present briefl y these concepts and technologies in the next paragraphs.

2. Multi models architectureA lot of software distributed architecture models have been defi ned in the last

years (distant invocation mechanism, synchronous mail, share tuple space…) and are today used in industrial systems. These models are well known for fi xed appli-cations on local area network or internet, their use in a mobile environment is not easy. The LEOST’s experience (TESS and RouVéCom projects) in this domain shows that the different models can be used for specifi c applications but none of them is able to answer all the cases as well as to answer generally the problem of mobility (deconnexion, technology or network changes, location dependant …).



The works conducted at ENST by L. Pautet & al. on PolyORB (schizophrenic middleware) [Pautet, 01] contributed to allow interoperability between middleware that implement different distribution models. Nevertheless, the chosen approach is static: the different models used by one application have to be defi ned at the application opening and cannot be modifi ed during execution.

In the train IP-Sat project the aim of the research work on multi model architec-ture, will be to defi ne new mechanisms that allow to change distributed application model dynamically on a transparent way. This will allow to use the more appropri-ate model (and the associated technology) in the user context at a given instant.

The envisaged approach is the use of Aspect Oriented Programming (AOP) techniques that allow to generate the application code during execution and thus to change the application behavior instantaneously. First of all, the work consists in the identifi cation of the different design models for distributed applications. Then a common basis has to be identifi ed as well as the rules to switch from a model to another (naming, invocation …). Finally, an implementation will be realized to demonstrate the feasibility of the approach. The research has to take in mind that the system must be open in order to integrate easily new applications models that can be set up in a next years. Applications using this system will be realized in the framework of the project.

3. Overview of Mobile IPv4In Mobile IPv4 the mobile node resolves the problem of being reachable in

a foreign subnet by acquiring a new IP address, called a care-of address, each time it moves into a new foreign subnet. The Mobile IPv4 uses the well-known UDP port 434 for communications between protocol parties. The protocol also uses ICMP Router Advertisement and ICMP Router Solicitation messages’format extensions for mobility agent advertisements. The Mobile IPv4 protocol specifi ca-tion is described in RFC 2002.

Mobile IPv4 involves two kinds of mobility agents that are used in order to achieve the mobility. These agents are the home agent and the foreign agent. At least one home agent is required to be present in the home subnet of the mobile node. Instead, foreign agents are not necessary but usually one or more foreign agents are present in the foreign subnets.

A home agent keeps a list of registered mobile nodes. The registrations are called bindings and are defi ned as triplet (home address, care-of address and life-time). A binding holds an association between the permanent local home address and a temporary foreign address and it is valid only for a given period of time. The home agent intercepts the packets destined for home addresses that it has a bind-ing for and tunnels them to their corresponding care-of addresses. A mobile node may at any time update its associated binding and thus cause the packets to be tunneled into another foreign subnet.

To make the packet interception possible, the home agent performs proxy address resolution protocol (ARP) for each of the home addresses that it has a


binding. The proxy ARP is not always necessary because home agents also act as routers and can hence receive, as a part of the normal routing function, the packets to be intercepted. In the special case where correspondent node and mobile node are in the same foreign subnet, the home agent is not required to forward datagram to mobile node. The correspondent node can instead send the datagram directly to mobile node because no routing is involved.

A foreign agent acts as a router for the mobile node while it is visiting a foreign subnet. The foreign agent holds one or more care-of addresses that are used for all of its mobile nodes. The foreign agent desencapsulates the tunneled packets sent to the care-of address and forwards them to the mobile node in the foreign network. The foreign agent is generally expected to have a common link with the mobile node, hence the foreign agent simply sends the desencapsulated datagram to the mobile node although it contains a topologically incorrect source address. This is possible because no routing is involved. The foreign agent also acts as a proxy between the mobile node and the home agent in the registration process.

Alternatively, instead of using foreign agent care-of address, the mobile node may use a co-located care-of address that is usually obtained via some dynamic assignment protocol such as DHCP. When a mobile node is using a co-located care-of address, no foreign agents are involved. The mobile node performs the desencapsulation and communication between the home agent and itself. The use of co-located care-of addresses improves the performance of the protocol but poses some problems concerning address allocation within the foreign network.

A mobile node uses the received agent advertisements to determine whether it is on the home subnet or in a foreign subnet and to fi nd out whether it has moved to a new subnet. Each time the mobile node detects that it has moved to another subnet, it acquires a new care-of address and sends a message called registra-tion request to its home agent. The home agent then changes the binding it has for this mobile node and starts tunneling the packets to the new care-of address.

A special case is when the mobile node returns to its home subnet from a for-eign network. The mobile node then sends a message to the home agent, asking to destroy its binding. The home agent then removes the binding, stops tunnel-ing the packets destined to mobile node and stops performing proxy ARP for the mobile node.

3.1. Locating Mobility Agents and Movement Detection

In Mobile IPv4, the mobility agents periodically broadcast ICMP router adver-tisement messages which contain an agent advertisement extension. Each advertisement has a unique sequence number that identifi es the advertisement sent. The bit-fi eld within agent advertisement contains information of whether the advertising mobility agent is a home or a foreign agent or both, as well as infor-mation about the supported encapsulation mechanisms. The registration lifetime fi eld tells the maximum time in seconds that the mobility agent is willing to grant registrations. If the advertising agent is a foreign agent, the advertisement exten-

Mobile router



sion contains one or more care-of addresses. These are the foreign agent care-of addresses that the mobile nodes within that foreign network can use to register bindings to their home agents.

The Mobile IPv4 protocol specifi es two algorithms that a node may use to detect movement. Both of the algorithms are based on continuously listening for agent advertisements.

In the fi rst algorithm the mobile nodes record the lifetimes for each source that they get agent advertisements from. The lifetimes are updated each time when new advertisements arrive. If the mobile node notices that lifetime for its current mobility agent has expired, it must assume that it has lost contact with it. In that case, the mobile node is free to try registering with any other agent that it has a valid lifetime for.

The second algorithm detects the movement from network prefi xes carried in received agent advertisement messages. The agent advertisements must con-tain prefi x-length extension for the necessary prefi x information to be available. Prefi x-lengths extension describes the prefi x length in bits for each of the care-of addresses contained in the agent advertisement. When receiving agent advertise-ments, the mobile node compares whether it is getting the same network prefi x as in the previous advertisements. If it notices that the network prefi xes received in the advertisements have changed, it may assume that it has moved.

The mobile node may assume that it has returned home when it receives an agent advertisement from its own home agent. The mobile node should then update its routing tables for the home network and deregister with its home agent.

3.2. Registration Procedures

Once a mobile node has detected that it has moved, it must inform its home agent about its new location. Otherwise, the home agent is unable to tunnel the packets to the mobile node. The registration process can be carried out in two ways depending on whether a foreign agent is used or not.

When the mobile decides to register its new binding, it sends a registration request message to its home agent. Furthermore, if the mobile node is using a co-located care-of address and none of the received agent advertisements contained 'R'-bit (registration required), it can send the registration directly to the home agent.

Otherwise, if the mobile node is using a foreign agent care-of address it must instead send the registration to its foreign agent which shall process it and forward it to the home agent. If the 'R'-bit in agent advertisement was set and the mobile node is using a co-located care-of address, it is recommended but not mandatory that the registration is sent via foreign agent

The registration request message contains fi elds for the home address, the care-of address, and the preferred lifetime of the binding; all these fi elds contain the necessary values to form a valid binding triplet. The lifetime has two special values: 0x0000 value indicates a deregistration request, and 0xffff value indicates infi nite lifetime.


Additionally, the registration request message contains the address of the home agent, various fl ags and the identifi cation fi eld. Identifi cation fi eld is used to distinguish different registration requests and to provide help in authentication. The registration request can contain extensions after the actual message, the most common of them being the authentication extension.

When a registration request is received, the home agent processes the request and sends back a registration reply. The home agent can either accept or deny the registration. If the registration request was sent via a foreign agent, the home agent sends the registration reply also via the foreign agent which, upon receipt, processes the reply and forwards it to the mobile node. Otherwise, the registration reply is sent directly back to the mobile node.

3.3. Datagrams Delivery and Tunneling

In Mobile IPv4, all packets destined to a mobile node pass through the mobile node’s home agent unless the mobile node is at home. The datagrams are routed from correspondent nodes to the mobile node’s home network by the standard IPv4 routing mechanisms. If the mobile node is at a foreign network, the mobile node’s home agent intercepts the datagrams and tunnels them into the care-of address indicated by the mobile node’s binding.

The care-of address can be a foreign agent care-of address or a co-located care-of address. In the former case, the tunnel ends at the foreign agent which performs the decapsulation of the datagrams. As the mobile node is present in the same subnet as the foreign agent, the foreign agent just sends the decapsu-lated packet normally to the mobile node. In case of a co-located care-of address, the mobile node itself does the decapsulation and loops back the decapsulated packet to itself.

The Mobile IPv4 assumes that source address of IPv4 header does not affect routing. If the mobile node sends a datagram, it does it exactly as if it were in its home subnet. If the assumption is valid (i.e., ingress fi ltering is not used), the data-gram gets routed to the destination address in the IPv4 header.

Thus, the datagrams delivery in Mobile IPv4 follows a “triangle routing”. Triangle routing generally introduces increased delay for the packets sent by the correspon-dent node and also places a heavy load on the home agent which has to forward all packets sent by a correspondent node to the corresponding mobile node.

3.4. Improvement of Mobile IP: Micro Mobility Solutions compared to last section

3.4.1 Foreign Agents Based Mobility Management Proposals

Several of the micro-mobility proposals manage user mobility on the basis of interactions between Foreign Agents (FAs). Hierarchical Mobile IP (HMIP) is an extension to Mobile IP that supports a hierarchy of FAs between the mobile node

Mobile router



(MN) and the home agent (HA). Fast Handoff and Proactive Handoff are two very close proposals that are based on Hierarchical Mobile IP but include improved handoff mechanisms.

In these proposals, we have a set of wireless IP Points Of Attachments (IPPOAs), each of them being associated with a dedicated FA. The FAs are then connected to a so-called Gateway Foreign Agent (GFA). There can also be a more complex architecture with a multi-level hierarchy of FAs between the GFA and the leaf FAs.

3.4.2 Hierarchical Mobile IP

In Hierarchical Mobile IP, after the fi rst connection of a MN to a domain and its home registration with the address of the GFA as care-of address (COA), the MN will perform Regional Registrations only. The mobile node sends the registration message to the GFA each time it changes the FA (i.e., IPPOA).

The registration contains the new “local” COA of the MN, i.e., the address that can be used by the GFA to reach the MN while it remains connected to the same FA (this COA can be either a co-located address or the FA address). Thus, a packet destined to the MN is fi rst intercepted by the HA and tunnelled to the GFA. Then, the GFA decapsulates and re-tunnels it towards the current “local” COA of the MN.

Hierarchical Mobile IP also supports a multi-levels hierarchy of FAs between the leaf IPPOA and the GFA. Each FA in the hierarchy must maintain a binding in its vis-itor’s list for each MN connected to an IPPOA lower in the hierarchy. These bindings are established and refreshed by the regular registration requests and replies that the mobiles exchange in the network. In this case, the regional registrations sent by a MN are only forwarded to the fi rst FA that already has a binding for this MN.

The upper levels of the hierarchy are not aware of the details of the mobile nodes movements since they do not have to change their binding. In this way, the handoff management is limited to a very small number of nodes.

Fast Handoff

Fast Handoff re-uses the architecture and principles of Hierarchical Mobile IP and addresses a set of remaining problems of this proposal. These are mainly the need for a fast handoff management for real-time applications and the presence of triangular routing inside the domain.

The Hierarchical Mobile IP does not improve the Mobile IP movement detec-tion and it only relies on the ICMP messages used by Mobile IP. Fast Handoff assumes the possibility of an interaction with the radio layer to anticipate the handoff and allows the MN to perform its registration with a “new FA” through the “old FA” before the handoff actually occurs.

The basic principle is that the IP layer receives the handoff events as “triggers” from the radio layer; these triggers are designed to inform the IP layer of the immi-nence of a handoff by providing the next IPPOA of the MN (i.e., the IP address of the new FA). This interaction with the radio interface is called Strong Handoff Radio Trigger (SHRT), as it contains the new IPPOA of the MN.


Moreover, the triangular routing inside the domain is limited by the use of the information found in the visitor’s list. When a FA receives a non-encapsulated packet (i.e., coming from another MN), it consults its visitor’s list to see whether it contains an entry for the destination address. If it contains one, the FA can directly send the packet to this address. Otherwise, it forwards the packet as nor-mal Mobile IP packet.

Proactive Handoff

Proactive Handoff assumes the same architecture as Hierarchical Mobile IP (except the multi-levels hierarchy) and aims at providing a fast handoff mech-anism by using a Strong Handoff Radio Trigger. The main difference from the Fast Handoff is that the IP handoff is not performed by the MN with a registration request but by the two concerned FA.

After a short negotiation exchange, the new FA sends a Regional Registration Request to the GFA on behalf of the MN. At this time, it is possible to bicast the traffi c destined to this mobile to the two FAs. The new FA will then send an agent advertisement to the MN so that it can perform a normal registration.

Cellular IP

In Cellular IP access networks, the base station serves as a wireless access point and as a router of IP packets, thus, performing all mobility-related functions. Cellular IP access networks are connected to the Internet via gateway routers. Mobile hosts attached to an access network use the IP address of the gateway as their Mobile IP care-of address. Inside a Cellular IP network, mobile hosts are identifi ed by their home address, and data packets are routed without tunneling or address conversion.

In this approach, location management and handoff support are integrated with routing. To minimize control messaging, regular data packets transmitted by mobile hosts are used to refresh host location information. Uplink packets are routed from a mobile host to the gateway on a hop-by-hop basis. All intermediate base stations cache the path taken by these packets. To route downlink packets addressed to a mobile host, the path used by recently transmitted packets from the mobile host is reversed. When the mobile host has no data to transmit, it sends special route-update ICMP packets toward the gateway to maintain its downlink routing state. The mobile hosts that have not received packets for some period of time allow their downlink routes to be cleared from the cache.

Cellular IP supports two types of handoff scheme:

Hard Handoff: it is based on signal strength measurements. To perform this kind of handoff a mobile host tunes its radio to a new base station and sends a route-update packet which creates routing cache mappings in its route toward the gateway. The crossover point is defi ned as the common branch node between the old and new base stations (in the worst case the crossover point is the gateway). Handoff latency is the time elapses between handoff initiation and the arrival of the fi rst packet along the new route, and in this case is equal to the round-trip time between the mobile host and the crossover point (during this time, downlink

–

Mobile router



packets may be lost). Routing cache mappings between the crossover point and the old base station are not cleared when handoff is initiated; yet, a timer is started and when it times out the mappings are removed.

Semi-soft Handoff: in this case a mobile host sends a “semi-soft” packet to the new base station and immediately returns to listening to the old base sta-tion. The semi-soft packet establishes new routing cache mappings between the crossover point and new base station; during this route establishment phase the mobile host is still connected to the old base station. After a “semi-soft” delay (i.e., an arbitrary value that is proportional to the mobile-to-gateway round-trip delay), the mobile host performs the handoff to the new base station. This delay ensures that by the time the mobile host fi nally tunes its radio to the new base station, its downlink packets are being delivered through both the old and new base stations. Indeed, the downlink packets consume twice the amount of resour-ces during “semi-soft” delay period; however, this period should represent a short duration in the complete semi-soft handoff process. Furthermore, as the time to transmit packets from the crossover point to the old and new base stations may differ, a constant delay along the new path between the crossover point and the new base station is introduced. If this delay is not introduced and the new base station is ahead of the old one, packets will be missing from the stream received at the mobile host.

In order to remain reachable, a mobile host transmits paging-update ICMP packets at regular intervals defi ned by a paging-update-time. As in the case of data and route-update packets, paging-update packets are routed toward the gateway on a hop-by-hop basis. Base stations may optionally maintain paging cache with the same format and operation as routing cache. However, paging cache map-pings have a longer timeout period and any packet sent by mobile hosts, including route-update packets, can update paging cache (but paging-update packets can-not update routing cache).

Handoff-Aware Wireless Access Internet Infrastructure (HAWAII)

The HAWAII access network is segregated into a hierarchy of domains, the gateway into each domain is called domain root router, and each host is assumed to have an IP address and a home domain. In this approach, the mobile host maintains the assigned IP address when operating in a domain, regardless of its location inside that particular domain.

In order to maintain IP routing between the domain root router and the mobile host, HAWAII establishes special paths as the mobile host moves. At power-up, the mobile host fi rst sends a Mobile IP registration message to its current base station. The base station identifi es that the mobile host is powering up in its home domain based on parameters in the registration message. It then adds a forward-ing entry for the mobile host and initiates a HAWAII power-up message upward to the next router.

This router similarly adds a forwarding entry to forward packets for the mobile host toward base station and also sends the power-up message upward to the

–


next router. Eventually, the message arrives at the domain root router which sends an acknowledgement back to the base station, and the base station sends now a Mobile IP registration reply to the mobile host.

When packets destined for the mobile host arrive from the Internet to domain root router, they get delivered till base station through routers involved in the power-up path setup procedure; fi nally the base station delivers the packets to the mobile host. There is no tunneling involved in this case, and packets traverse the optimal route to the mobile host.

When the mobile host is handed off from one base station to other base sta-tion within the same HAWAII domain (micro-mobility domain), the mobile host maintains its IP address. As before, the mobile host sends a Mobile IP registration message to its new base station informing it about the identity of the old base station. The new base station initiates a HAWAII handoff message toward old base station. The old base station adds an entry for the mobile host, so that future packets are forwarded toward new base station. The old base station then sends a HAWAII message upward to the next router.

This router changes its forwarding entry, so that packets destined for the mobile host now travel to the new base station. This particular way of updating routers and base stations is called the forwarding path setup scheme. In the case of networks where the mobile host could listen to multiple base stations simultane-ously (i.e., CDMA), it is possible to directly divert traffi c from router (if this router is common to the old and new base stations). This leads to a different algorithm for updating the routers and is called a non-forwarding path setup scheme.

In HAWAII architecture an IP multicast group address is used to identify the set of base stations belonging to the same paging area. If the mobile host is in the standby mode and packets destined to the mobile host arrive at the domain root router, this router will forward the packets downstream. Eventually, the packets will arrive at a router that is part of the multicast tree for that paging area. The router then buffers the data packets and initiates a HAWAII page request mes-sage to the multicast group address.

The base stations which belong to the multicast group, receive the page mes-sage and broadcast a low-level page message on their respective wireless inter-faces utilizing the underlying link-layer technology. The mobile host receives the link-layer page message (for example, by periodically scanning the broadcast paging channel in CDMA) and sends a Mobile IP registration message to a base station. This triggers a HAWAII path setup message from the base station to the paging initiator; the buffered data packets are then forwarded to the mobile host through the base station.

When the mobile host moves between base stations connected to different HAWAII domains, the mobile host acquires a care-of address in the new domain and sends a Mobile IP registration message to the new base station. Based on the parameters in the message, the base station detects that this is an inter-domain handoff.

Mobile router



The base station fi rst initiates the HAWAII power-up procedure in the new domain. It then sends a Mobile IP registration message to the home agent of the mobile host (the home agent can be physically collocated with the domain root router). Thus, the home agent establishes a tunnel entry, which will tunnel packets destined to the mobile host IP home address to its new care-of address. Subsequent handoffs by the mobile host in this new domain will be handled locally by HAWAII as described previously.

4. Virtual Interface ArchitectureTo avoid additional delays during handover procedure generally due to layers

crossings, we propose to manage the data fl ow at the link layer level of the proto-col stack. We propose a specifi c adaptation interface that will interact with the IP and link layer and makes it possible to have transparent IP service over different wireless technologies.

The layer 2 architecture that we describe hereafter works when we stay on the same subnet or when we use a NAT and doesn’t require any modifi cation at the IP stack of the remote end-point if it is a fi xed one.

Conceptually, by assigning to all the physical devices on the host the same IP and MAC addresses (as they are in the same subnet), the mode of communica-tion during vertical handover will be transparent to higher-layer transport proto-cols. But, since it is not possible with today implementations, we add a new virtual MAC layer between the hardware level and IP level.

For upper layers, the virtual interface acts as a classical interface. For exam-ple, it is declared as an Internet device to the IP layer. We assign a unique unicast IP address to this virtual MAC address, consequently, application might think of any fl ow as dealing with traffi c corresponding to a single interface only. The mobile station will be always identifi ed in the network by this IP address.

Figure 5.1: The Virtual Interface architecture

The proposed interface hides the presence of the different network devices to the applications layer by providing the illusion of a unique MAC address (virtual one) (fi gure 8). This architecture allows a complete compatibility with IP. All appli-cation’s fl ows are sent to this virtual MAC interface that tries to spread and redirect


them on the available interfaces. The generation of the virtual MAC address can be done using a well known hash function H.

Examples of use

The Virtual interface allows a complete support for IPv4 and IPv6, including auto-confi guration mechanisms. It also provides a complete connectivity with the Internet, in regards to routing but also multicast and other services mechanisms.

To explain how our solution addresses the vertical handover problem, let’s take the example of a videoconference between two stations A and B (fi gure 5.2). When the mobile station A leaves the coverage of the Bluetooth AP, the Bluetooth connection is no more valid, the virtual interface detects it and automatically switches the communication from the Bluetooth to the 802.11 interface. However the station A has changed its network interface, it has not change from IP address and is always known as 159.159.50.100 to higher layer and to the remote station B. The TCP/IP connection is always valid and the handover doesn’t cause the application interruption.

Figure 5.2: Handover scenario

VIP implementation

We have implemented a Linux prototype driver for the Virtual interface as a loadable kernel module. As a result, VIP can be easily installed and used without modifying or recompiling the operating system kernel. The module can be loaded at any time and will then commence virtualizing and translating connections as needed.

The virtual interface may or may not handle all network devices of a host. The set of handled devices is variable and may be modifi ed during run-time. It may be confi gured automatically according to a particular policy. For example the virtual interface may by default handle all wireless interfaces. It may also be confi gured directly by the user which chooses to add or to remove physical devices from the virtual interface.

In Linux operating system, most network interfaces, such as eth0 and ppp0, are associated to a physical device that is in charge or transmitting and receiv-ing data packets. However, there are exceptions to this rule, and some logical network interface doesn’t feature any physical packet transmission; the most known example is shaper [Shaper, 98] interface. Our prototype was inspired from

Mobile router



this example. All network devices that are part of VIP should have SLAVE and MASTER defi nitions. In fact, after the virtual interface is created, all the network interfaces that have to be attached must be confi gured as VIP slaves by adding the “MASTER=VIP” and “SLAVE=YES” directives to their confi guration fi les.

The MAC address of the virtual interface is taken from its fi rst slave device. This MAC address is then passed to all following slaves and remains persistent (even if the fi rst slave is removed) until the VIP interface is brought down or reconfi gured.

The virtual interface can regularly check all its slaves’links by checking the “control_response” status registers. The check interval is specifi ed by the module argument “control_interval”. It takes an integer that represents the checking time in milliseconds. Transmissions are received and sent out via the fi rst available attached slave interface. Another slave interface is only used if the active slave interface fails. The way VIP is implemented violates this unique MAC address per device standard, by deliberately making several NICs have the same MAC address.

From the kernel’s point of view, a network interface is a software object that can process packets, while the actual transmission mechanism is hidden inside the interface driver. A network-interface object, like most kernel objects, exports a list of methods so the rest of the kernel can use it. These methods are function point-ers located in fi elds of the object data structure, here structnet_device [Stevens, 94]. When a user program confi gures the behavior of the interface, it invokes the ioctl() system call. For example for packet transmission, the most important entry point for a network interface driver is hard_start_xmit, where hard is a shorthand for hardware. The device method gets called whenever a network packet gets routed through the interface. When the virtual interface is concerned, no actual hardware transmission takes place in the interface itself. The VIP interface will instead resort to another network interface to perform transmission. Packet pass-ing is implemented in two steps: fi rst (within ioctl), VIP connect to another inter-face (slave), the one that can transmit packets; then, its own hard_start_xmit take proper action to pass the packet.

A. Experimental Results

With the deployment of several delay sensitive applications, such as voice over IP and the increasing popularity of wireless internet, delivery of delay related quality of service guarantees in wireless networks becomes a necessity. The International Telecommunication Union recommends that the one-way delay should be kept lower than 150 ms and the jitter not to exceed 50ms for VoIP acceptable conversation quality [ITU-TG.114].

We present hereafter some experimental data measuring the performance of VIP in terms of throughput, handover latency, jitter and overhead. Figure 10 depicts the network topology which formed the backbone of our test-bed. For the measurements, we used one laptop as mobile client and one desktop as a server. The laptop was a 1.2 GHz DELL with 512 MB of RAM running Fedora Linux 9.0 and equipped with one Ethernet and one 802.11b cards. The desktop machine was a 1.5 GHz DELL Pentium 4 with 512 MB RAM. To collect statistics


from the network, we used iperf [Iperf], a simple network benchmarking program. We conducted data transfers from the server on the fi xed host to the client on the mobile host. The client initiates the connection from one interface, and switches to another one at some later point.

Figure 5.3: test bed topology

As it can be seen from the fi gures 5.4 and 5.5, the use of a standardized inter-face to convey helpful information (hints) from L2 to L3 helps the network layer so that handoffs perform well. In fact, VIP performs with very low handoff delay (less then 55ms when the control interval =50ms). Compared to previous solu-tions such as Mobile IP (where the handoff delay is about 1s [Campbell, 01]), VIP reduces the handoff latency considerably. The use of such virtual interface will be needed to support seamless and fast handoff in much architecture such as to assist handoff in Mobile IP (both MIPv4 and MIPv6).

Figure 5.4: VIP Handover delay

0

50

100

150

200

250

300

0 20 40 60 80 100 120

control_interval (ms)

eth_eth eth_wifi wifi_eth

Hand

off

dela

y (m

s)

Mobile router



Figure 5.5: VIP Jitter for an eth-eth handover (control-intervall= 60ms)

0

0 ,1

0 ,2

0 ,3

0 ,4

1 8 2 0 2 2 2 4

Time (s)

Jitt

er (s

)

Using VIP has a cost since packets have to go through an additional layer before being sent on the physical medium. Anyway, this overhead is not sig-nifi cant compared to standard Linux implementation (fi gures 5.6 and 5.7). First, because we operate at the link layer which does not reduce the volume of data a packet may include. Second, because all the physical interfaces share the same MAC address (as the virtual interface), no MAC address translation or swapping is needed; which means no additional packet encapsulation. VIP overhead is only due to the time needed by the virtual interface to consult its local commutation table to decide on which physical interface it could send data.

Figure 5.6: VIP throughput overhead (UDP traffi c)

0

2

4

6

8

1 0

1 0 0 3 0 0 5 0 0 7 0 0 1 0 0 0 1 5 0 0 2 0 0 0

Packet size (B ytes)

Thro

ughp

ut (M

b/s)

W IFI+V IP W IFI E th+V IP E th

To evaluate the proposed solution, we also measured connection restoration time using a simple client and server program representing typical UDP and TCP connections created by real world applications. In each experiment, we assume that one mobile node (MN) handoff occurs during the 20 second packet transmis-sion from the CN to the MN.


Figure 5.7: VIP throughput overhead (TCP traffi c)

0

2

4

6

8

1 0 0 3 0 0 5 0 0 7 0 0 1 0 0 0 1 5 0 0 2 0 0 0

Packet size (Bytes)

W IFI+ VIP W IFI ET H + VIP E T H

Thro

ug

hp

ut (

Mb

/s)

Figure 5.8 shows the effects of handoffs on UDP traffi c between CN and MN. For UDP traffi c the VIP handoff interval simply means a service disruption equiva-lent in length to the handoff interval. At time = 19.7s the mobile host lost the wire-less connection, as depicted by the dotted line. The virtual interface detects this and begins using the Ethernet interface. All packets received during the switching process are lost. At time 19.75s the MN receives again packets from the CN using the Ethernet interface, which indicate the end of the switching process at the vir-tual interface, and by consequence the end of the handoff.

Figure 5.8: UDP packet number received at the CN

0

1000

2000

3000

4000

5000

6000

7000

Handoff

19,2 19,4 19,6 19,8 20 20,2 20,4

Time (s)

UDP

pack

et n

umbe

r

It is on TCP traffi c that the handoff interval has the greatest impact due to the Exponential backoff of the TCP retransmission mechanism [Sethom, 04]. Figure 0 shows the TCP sequence trace of the MN. At time = 8.4s the mobile host starts the handoff. The switching between interfaces completes at time 8.45s. The MN is able to receive packets again from the CN using the Ethernet interface.

Mobile router



However, the CN is still waiting for ACKs for the lost segments, thus it will con-tinue sending packets to the MN until it reaches the advertised receive window of the MN (at time 8.6s). When the retransmission timer expires (approximately at 9.4s), the CN retransmits the lost segments using the slow-start algorithm [Snoeren, 00] and wait for ACKs.

The retransmission timeout value stored in t_rxtcur, is calculated according to the current RTT in the network. Further, the upper and lower bounds of the retransmission timer are given by:

TCPTV-MIN< t_rxtcur <TCPTV_REXMTMAX

In typical TCP implementation, TCPTV-MIN and TCPTV_REXMTMAX are set to 1 second and 64 seconds respectively [9]. Since in our experiments the RTT was suffi ciently small, the retransmission timer was approximately about 1sec (8.4s + 1s = 9.4s).

When received by the MN, the retransmitted packets are immediately acknowl-edged, and the TCP resumes transmission in slow-start after the timeout.

Because TCP implementation uses congestion control mechanisms and retransmissions, the handoff delay is more important than in the case of UDP.

Figure 5.9: VIP TCP packet number (handover WIFI->eth)

0

500

1000

1500

2000

2500

3000

3500

4000

2,5 4,5 6,5 8,5 10,5 12,5 14,5 16,5

Time (s)

TCP

pack

et n

umbe

r

5. IPV6 – NEMO platform

5.1. Overview of Mobile IPv6

IPv6 introduces new features and improvements over IPv4, the most obvious one of them being the larger address space as IPv6 addresses are 128 bits long. The large address space makes it possible to allocate large blocks of addresses for specifi c purposes. This has also positive implications on mobility since care-of addresses can be more easily obtained. IPv6 recognizes the following address types: unicast, anycast, and multicast. Unicast as a destination address specifi es


a single host in a given subnet to which the datagram is to be routed. Anycast identifi es a group of machines that reside in the same subnet but in such sense that only one of the members of the group gets the datagram. The last address type is multicast address and it works the same way as in IPv4.

Mobile IPv6 [RFC 3775] retains most of the concepts presented in Mobile IPv4. In IPv6 the three fundamental functional units within the protocol are the corre-spondent node, the home agent, and the mobile node. Therefore, the Mobile IPv6 does not involve foreign agents as Mobile IPv4.

In IPv6 the header is of fi xed length but it contains a fi eld called “next header” telling which extension header follows the IPv6 header. The extension headers also have a similar fi eld to indicate what extension header comes after them. Examples of extension headers are: fragmentation header, hop-by-hop options header, destination options header, routing header, authentication header (AH), and encapsulated security payload header (ESP).

The Mobile IPv6 adds four new destination options to the list of IPv6 destina-tion options. These options are:

Binding Update: it is used by a mobile node to announce that it has chan-ged its point of attachment to the Internet, or to renew an existing binding which is about to expire. The Binding Update is a Mobile IPv6 equivalent to the registration request message in Mobile IPv4. A Binding Update can be sent to the home agent of the mobile node or to a correspondent node of the mobile node. The Binding Update option requires that also the Home Address option is present in the same datagram;

Binding Acknowledgement: it is sent as a reply to a Binding Update if the “acknowledgement required”-fl ag in the Binding Update was set. The Binding Acknowledgement contains status code, which enables it to also function as a negative acknowledgement if necessary. In addition, the Binding Acknowledgement holds a verifi cation lifetime fi eld which is usually the same as supplied with Binding Update but can be lower if the recipient does not want to guarantee such long lifetime;

Binding Request: offers the correspondent nodes a way to improve the per-formance of the protocol. If the correspondent node’s binding to a mobile node is about to expire, the correspondent node may ask the mobile node to renew that binding. In case the mobile node agrees, it responds to Binding Request by sending a Binding Update, otherwise it does not respond at all;

Home address: is used to fake the actual source address of the packet to the protocols above network layer. The Home Address destination option includes an alternative source address that will overwrite the source address in the IPv6 header when the packet is passed to higher protocol layers. In Mobile IPv6, the mobile node attaches the home address option to all packets that it sends while it is at a foreign network and to all packets containing a Binding Update. The Home Address option holds the home address of the mobile node. When a node receives a datagram equipped

–

–

–

–

Mobile router



with home address option, the datagram seems to have originated from the mobile node’s home address although the IPv6 header contained the mobile node’s current care-of address in its source address fi eld.

In Mobile IPv6 route optimization is a mandatory part of the protocol. Correspondent nodes may have binding caches that contain the currently valid bindings that the node is aware of. Each time when a correspondent node is about to send a datagram, it fi rst checks if it has a binding for the destination. If the bind-ing exists, the correspondent node attaches a routing header to the datagram, sets the IPv6 destination address to the care-of address indicated by the binding and sets the original destination address to the route segment within the routing header. When the datagram arrives at the receiving mobile node, the mobile node detects the routing header and sends the packet onward to the address indicated in the routing header. Because the address is local to the mobile node, the packet is not actually sent but looped back to the mobile node, the destination address being the mobile node’s home address. Unfortunately, since each Correspondent Node may choose to not allow route optimization and which is likely due to some security concerns MobileIPv6 will probably use bidirectional tunneling via the HA instead of the route optimization. This is also the mode of operation used for NEMO as we will see later.

5.2. IPv6 Mobile Networks: NEMO

Since MobileIP is a single device mobility management protocol, additional features have to be added in order to manage entire network mobility. This is exactly the aim on the NEMO IETF Working Group. NEMO is a NEtwork MObility over MobileIPv6 support protocol that has been proposed for the purpose of man-aging the mobility of a network as a unit.

As mobile terminals are becoming more common the need to provide connec-tivity to a set of IPv6 hosts moving together has appeared. Such a set of nodes is collectively known as a “mobile network” or a “network mobility (NEMO)” (for instance on cars, trains or airplanes, etc.).

This usage has triggered the extension of the Mobile IPv6 protocol from han-dling a single mobile node to supporting a complete mobile network. This is neces-sary in order to avoid the change of addresses inside mobile networks, especially for nodes with no mobility support capabilities (i.e., LFN), or to minimize signaling overhead during handovers. If the internal addressing within a mobile network changes, each node inside the network has to inform its Home Agent (HA) and its correspondent nodes (CN) each time the mobile network moves; this could lead to a large amount of signaling traffi c on the radio link which is a scarce resource by excellence. Therefore, the IETF NEMO working group has designed a mecha-nism that maintains the connections between the Mobile Network Nodes (MNN) and their Correspondent Nodes regardless of the end-nodes’movements. The effort to provide NEMO support was divided into two parts, namely NEMO Basic Support [RFC 3963] and NEMO Extended Support.


NEMO Basic Support is a simple extension of the Mobile IPv6 protocol. A mobile network preserves its connectivity by dynamically constructing bi-direc-tional tunnels between the Home Agents and the Mobile Routers (MR) acting as gateways between the mobile network and the rest of the Internet. Then, the HA is responsible for forwarding all the traffi c destined to the mobile network pre-fi xes (MNP) toward the current position of the mobile network, i.e., the Care-of Address (CoA) of the Mobile Router. Thus, the HA manages a list of MNP (the prefi x table) which is associated to the Home Address (HoA) of the Mobile Router. The MR interfaces connected to the visited link are called egress interfaces (E-faces), whereas the ones connecting the mobile subnet to the MR are designated as ingress interfaces (I-faces). A NEMO may have several MRs connected to the Internet or it may use several E-faces simultaneously in order to gain access to the Internet.

A NEMO is composed of one or more mobile routers (MR) along with nodes called mobile network nodes (MNN) attached behind the MR. There are three kinds of MNNs: local fi xed nodes (LFN), local mobile nodes (LMN) and visiting mobile nodes (VMN). LFN never change their point of attachment with respect to the MR, while LMN and VMN do. LFN and LMN belong to the mobile network, while VMN do not. All MNN are connected to the Internet via the MR.

The MR and the access router (AR) connect to each other over a wire-less link (WiFi, WiMAX or 3G). Then the MR get a Care-of Address related to the access network and update it’s binding in his Home Agent binding cache. Indeed, the NEMO protocol is based on Mobile IPv6 and use Mobile IPv6 messages with some minor modifi cations. The home agent (HA) and the MR always communicate by means of bidirectional tunneling in the NEMO basic support [RFC 3963]. When the mobile network moves, the MR sends a binding update (BU) to its HA with the care-of-address (CoA) is has just acquired. In this way, the HA can forward packets destined one of the prefi xes announced by the MR to the home address (HoA) of the MR and therefore to his CoA. The MR is also in charge to encapsulate all the traffi c coming from node hosted in the mobile network to the HA. This one will strip the outer header and for-ward the paquet to its fi nal destination. This way all correspondant nodes over the Internet are able to communicate transparently with nodes embarked in the mobile network as if they have been stayed at home. This is particularly important for LFNs since this kind of node do not have mobility management capability (sensors).

A typical Mobile Network will be connected to the Internet through various wireless access technologies that are using different and/or complementary radio technologies. Therefore, to overcome the well-known drawbacks of these tech-nologies, the main idea is to equip the Mobile Routers with several egress inter-faces using different technologies. Even if some extensions to the NEMO protocol are required [Ernst, 04], the benefi ts of the multi-interface approach are obvious. These benefi ts have been presented, for example, in [Ernst, 02] and [SHISA]; we just give a brief description of them in the following paragraphs.

Mobile router



First, it will be easier for the Mobile Routers to offer a ubiquitous access because several access technologies may be available within a location at any given time. Moreover, the redundancy can be guaranteed in a more effortless man-ner if several egress interfaces are employed for communication. Then, diverse load-sharing and load-balancing schemes can be applied for spreading the traffi c on several interfaces. Finally, various policy/preferences routing mechanisms can be imagined in order to let the mobile end-users and/or the applications to choose amongst the MR’s egress interfaces based on their requirements in terms of QoS, cost or security.

Since a Mobile Router may have several communication interfaces. It will probably have to act as a policy decision and enforcement point when several E-faces (interfaces connected to the Internet) are present. Thus, the MR may simul-taneously use several E-faces in order to perform load balancing and map the communication fl ows on E-faces depending on the administrator and the network operators’preferences, or to improve the handover management.

To have these functionalities implemented and take advantage of them, a num-ber of improvements are currently under discussions within the IETF. Unfortunately, even if their importance is recognized (e.g., see [Ernst, 02]), the decision mecha-nisms for selecting “best” egress interface (also known as path selection) are not within the scope of the IETF work. Nevertheless, the optimum interface selection problem within the multi-interface mobile nodes communicating in heterogeneous radio environments has already been in the researchers’view for a while (e.g., see [Droma, 03], [Suciu, 04]).

6. CISCO Mobile IP Overview

6.1. What Is It and why do we care?

Mobile IP is an Internet Engineering Task Force (IETF) standard and network architecture that allows a host device to be identifi ed and attached to the network continuously and seamlessly via a single IP address, even though the device may move its physical point of attachment from one network to another. Roaming from a wired network to a wireless or wide-area network is possible, so ubiquitous connectivity is achieved from within a private enterprise network or far away from home. Part of both IPv4 and IPv6 standards, Mobile IP have been available since Cisco IOS Software Releases 12.0T.

Cisco IOS Software and its support for Mobile IP provide the technology that gives an IP node the ability to retain the same IP address and maintain exist-ing communications while traveling from one network to another. In our e-vehicle environment and especially the Train environment, Mobile IP enables us to create a Wireless WAN connectivity through different access technologies and access networks, between the on board infrastructure, the Cisco Mobile Routeur 32xx and the ground datacenter. The use of Mobile IP and the Cisco Mobile Router 32xx will position IP as the glue to solve this issue seamlessly as well as it will guarantee an easy integration of any upcoming Wireless IP technology.


After a quick overview of Mobile IP principles, we will address the key details describing the Cisco Mobile Router 32xx. In a third part we will address the business environment that should match the technical architecture for deployment.

6.2. How CISCO Mobile IP Works?

Although Mobile IP can work with wired connections in which a computer is unplugged from one physical attachment point and plugged into another, it is particularly suited to wireless connections. The Mobile IP architecture includes a router called a Home Agent that tunnels datagrams for delivery to a Mobile Node that can be a laptop, a computer on a satellite, a wireless PDA, a router, or other client device that maintains the same IP address wherever it goes. The third ele-ment is a router on a remote network called a Foreign Agent that provides routing services to a registered Mobile Node.

Figure 5.10: How Cisco Mobile IP works?

In our Case the Mobile Node is the Mobile router embarked on the train.. The Home Agent is a router on the home network serving as the anchor point for communication with the Mobile Node; it tunnels packets from a device on the Internet, called a Correspondent Node, to the roaming Mobile Node. (A tunnel is established between the Home Agent and a reachable point for the Mobile Node in the foreign network.) The Foreign Agent is a router that can function as the point of attachment for the Mobile Node when it roams to a foreign network, delivering packets from the Home Agent to the Mobile Node.

The Mobile IP process has three main phases: agent discovery, registration, and tunneling.

Agent Discovery - During the agent discovery phase, the Home Agent and Foreign Agent advertise their services on the network by using the ICMP Router Discovery Protocol (IRDP). The client then takes appropriate action depending on whether it is at home or at large.

•

Mobile router



Registration - When a Mobile Node recognizes that it is on a foreign network and has acquired a care-of address, it needs to alert a Home Agent on its home network and request that the Home Agent forward its IP traffi c.

Tunneling - When a Mobile Node is registered with a Home Agent, the Home Agent must be able to intercept IP datagrams sent to the Mobile Node home address so that these datagrams can be forwarded via tunneling. The stan-dard does not mandate a specifi c technique for this purpose but references Address Resolution Protocol (ARP) as a possible mechanism.

Mobile IP uses a strong authentication scheme for security purposes. All regis-tration messages between a Mobile Node and Home Agent are required to contain the Mobile-Home Authentication Extension (MHAE). Cisco IOS Software allows the mobility keys to be stored on an authentication, authorization, and accounting (AAA) server that can be accessed using TACACS+ or RADIUS protocols. Mobile IP in Cisco IOS Software also contains registration fi lters, enabling companies to restrict who is allowed to register.

The different technical characteristics of the CISCO mobile router are pre-sented in Annex 1.

7. ConclusionThis chapter presented the different possible solutions able to provide mobile

routing. We have fi rst described the multi models architecture. Then we have given an overview of Mobile IPv4. The concept of Virtual Interface Architecture is presented. Then the IPV6 technology and the NEMO platform is detailed. The last paragraphs give a CISCO Mobile IP overview.

All this solutions will be evaluated from a theoretical point of view in the second phase of the Train-IPSAT project. The NEMO platform and the CISCO mobile router will be implemented for the trials on the TGV.

•

•


Chapter 6

Propagation and EMC constraints in the Railway domain

1. IntroductionIncreasing needs for high data rate in the case of transport applications have

to face to the specifi c nature of the propagation channel and robustness con-straints. The propagation channel for terrestrial wireless systems is most of the time affected by multipath and varies rapidly versus the time. For satellite sys-tems, the channel impairments are also related to the state of reception of the satellite (Line Of Sight, Non Line Of Sight and obstructed). In proportion with the train speed, a Doppler shift is introduced in the signal. These phenomena create perturbations that increase with data rate. The defi nition of high data rate wireless links (particularly in the uplink direction ie train to ground) is a challenge today for railway applications because most of the existing systems presented in this document allow high data rate mainly in the downlink direction (ground to train).

2. Geometric characteristics of high speed linesThe railway environment and besides, the environment of high-speed trains is

a very particular environment by comparison with the environments traditionally met in the mobile communications world. Indeed, high speed lines present spe-cifi c profi les in order to minimize curves and slopes so to authorize high speeds. Generally, the more permitted commercial speed is high, the bigger will be the curving rays, the weaker will be the maximum slopes and the bigger will be the sections of tunnels or covered areas.

As an example for the “North TGV line” in France where commercial speed reaches 320 km/h, the curving ray varies between 4000 m and 600 m, the maxi-mum slope is 2.5% (25 mm/m). The transition areas for the various slopes have rays equal to 25000 m on average, tracks occupy 13 - 14 m and the distance between the axes of both ways is equal to 4.5 m. Furthermore, to protect the local residents of the noise pollutions, tracks are surrounded with sound-proof walls [MOST,97].

Consequently, these high-speed lines are mainly made of deep trenches, long tunnels, bridges and viaducts in particular in hilly or mountainous areas. Along the



line an important number of metallic pylons, which support catenaries are present. This metallic environment is a potential source of masking in particular in the case of a satellite link and generates additional multipaths [Knör05].

Photography 6.1 Photography6.2

Photography 6.3 Photography 6.4

The environments of TGV tunnel are well known and were the object several measurements campaigns [Most97], [Mora97]. The signal can be broadcast by antennae or by radiating cables when the frequency remains lower than 2 GHz. With this frequency, the spreading of the delays is of the order of 20-25 ns in a 11.60 m by 6.20 m tunnel. A three slope models is generally considered to char-acterize propagation paths in the tunnel. Important attenuation (32 dB/100m) of the signal is observed the fi rst 150 meters, then the attenuation decreases around 13 dB/100 m until it reaches 2 dB/100m beyond 1000 m after the emission point. When the signal is broadcast by antennae, the Doppler shift in front of antennae can be very important.

In trenches or cutting areas, the very important curving rays of the line autho-rize to consider that from a propagation point of view, in most of the situations, the signal is received by direct way in particular when antennae are close to the track. In this confi guration the Doppler shift can also be maximal.


3. Propagation channel characteristics in the case of the terrestrial link

Cutting slopes are generally of the order of 20-30 degrees. These slopes can reach 90 ° in the urban or in the mountainous areas. In the case of walls at 90 °, a waveguide effect provoked by walls is observed. According to the position of the transmission/ reception stations related to tracks, two cases can be considered and are illustrated by Figure 6.1 and Figure 6.2.

Figure 6.1: Pilone in the railway domain

Figure 6.2: Pilone outside the railway domain

If the transmission/reception station is located far from the cutting Figure 6.2: Pilone outside railway domain, the confi guration of the propagation channel is more or less similar to the usual case of the mobile telecommunications. The signal is generally received with NLOS (Non Line of sight) and the Doppler shift is moderated. Antennae are generally omnidirectionnal ones both at fi xed station and mobile side, the distribution of the angles of arrivals of the signals is uniform between [0,2π] both at fi xed station and the mobile sides.

If the transmission / reception station is directly located at the level of the tracks, the spreading of the delays is weak, the propagation can be compared with a clas-sic two rays model. It is advisable to note that in this situation, the transmission / reception stations along tracks are very close to the train (2 or 3 m), the propagation channel then varies very quickly and especially if directive antennae are used.

The angular distribution of the angles of arival depends on the geometrical distribution of the scatters inthe vivinity of the antenna but also on the angle of aperture of the considered antenna. Durgin and Rappaport gave the spreading angular expression for various propagation models [Durg00] [Rapp02]. In the case of a directive antenna at reception, the angular distribution of the power by multipath illustrated fi gure below is given by the relation (6.1):

pPT

θ αθ θ θ α( ) =

≤ ≤ +

,

,

0 0

0 elsewhere

(6.1)

α represents the distribution of the angle of arrival, θ0 is the angular shift and PT is the scarred average local power.




Figure 6.3: angular distribution of power due to multipath

The angular spreading varies between 0, the extreme case of a single compo-nent coming from a single direction and 1 which corresponds to the case in which the angular distribution of the received power is 360 degrees.

3D ray tracing modeling tools allow to model the input delay spread response of the channel, the angular distribution of power and the spreading Doppler in a given environment. Recent works [Knör05] allowed to model the railway environ-ment by this method as well as the train in motion on a 800 m distance and a speed of 400 km/h with a 5 GHz frequency. The results confi rm on one hand how the metal masts generate supplementary multipath and on the other hand the fast variations of the Doppler shift between its maximum values.

In the context of railway high speed, the mobile receivers are submitted to a Doppler shift and important Doppler spreading that considerably corrupts for example the OFDM signals by generating interferences between carriers (IEP). Besides, the multipaths context may provoke interferences between symbols (ISE). So, the modeling of parameters which express the temporal and frequency variation of the channel is fundamental and the choice of the adapted channel model is necessary. This work is part of the second phase of the Train-IPSAT project.

4. Propagation channel characteristics in the case of satellite systems.

In the case of a satellite link, the signal experiences fadings due to multipath but also fadings varying in duration and depth as a function of the satellite eleva-tion regarding the masks in the vicinity of the antenna (tunnels, bridges, cuttings, buildings when entering a station, vegetation as illustrated on photography 6.1 to 6.4. Other fadings are caused while the signal is traveling through the atmo-sphere, particularly in Ku and Ka band, attenuations are due to rain.

The duration of fadings due to the atmosphere is long but their occurrence is low. These effects can be compensated with an optimization of the link budgets and by techniques increasing the robustness of the link [Evan91].

The fadings due to masking effects are deep and long. The occurrence is directly related to the train environment characteristics and to the position of the satellite as illustrated on fi gure 6.3.


Figure 6.4: Masking effects on the satellites as a function of the environment

Fadings due to multipath and partial masking of the satellite are very simi-lar than those observed on terrestrial links. They can be model with a Rice or Rayleigh process depending on the existence or not of a direct path [Saun99]. Even in a rural environment, the mandatory directivity of antennas in Ku or Ka band increases the masking effect.

Other fadings should be considered. They are deep and very short as illus-trated on fi gure 6.4 and 6.5. They are frequent, quasi periodic and due to the pres-ence of the catenary metallic support (photography 6.5). The frequency is related to the pylon position and train movement. The existence of such fadings is related to the track orientation regarding the satellite position.

Several statistical satellite channel models exist in the literature with different com-plexity levels. Most of them consider the state of reception of the signals (bad or good – in LOS or not) in order to take into account the masking effect while moving (mobile or satellite). This work is part of the second phase of the train-IPSAT project.

Figure 6.5: Long fadings due to a bridge

Figure 6.6: Fast and periodic fadings due to the catenary

metallic supports.

0 0.5 1 1.5 2 2.5-80

-70

-60

-50

-40

-30

-20

-10

0

10

Temps (s)0 0.5 1 1.5 2 2.5

-80

-70

-60

-50

-40

-30

-20

-10

0

10

Temps (s)0 0.5 1 1.5 2 2.5

-80

-70

-60

-50

-40

-30

-20

-10

0

10

Temps (s)0 0.5 1 1.5 2 2.5

-80

-70

-60

-50

-40

-30

-20

-10

0

10

Temps (s)0 0.5 1 1.5 2 2.5

-80

-70

-60

-50

-40

-30

-20

-10

10

Temps (s)0 0.5 1 1.5 2 2.5

-80

-70

-60

-50

-40

-30

-20

-10

10

Temps (s)

La

puis

sanc

e du

sig

nal

(db)

La

puis

sanc

e du

sig

nal

(db)




Photography 6.5: Example of metallic supports along the tracks.

5. Frequency allocationSince a long time, railways in Europe use radio communication devices. Some

specifi c frequency bands have been allocated to railways at national level and national railway organizations have been licensed as private users groups in sev-eral different frequency bands.

In a recent past, the trains did not cross the borders, thus it was possible to allocate frequencies at national level. This is why the frequency band used for very similar systems are very different all over Europe. The main frequency bands are:

Low VHF band 70 - 88 MHz

High VHF band 155 - 220 MHz

UHF band 420 - 470 MHz

Today trains cross borders and it is mandatory to obtain frequency allocation at European level and to harmonize existing allocations. The fi rst example was the CEPT allocation in the 457-468 MHz band. The second success is related to GSM-R. Two 4 MHz bands have been obtained by the UIC organization in the 876-880 MHz and 921-925 MHz and are now dedicated to the GSM-R sys-tem for the ERTMS. Other allocations were obtained for the EUROBALISE and EUROLOOP systems, radio communication component of the ERTMS.

Today with the development of numerous wireless telecommunication sys-tems, the radio spectrum is saturated particularly in dense urban areas. This situ-ation conducts national and international radio spectrum regulation authorities to reinforce their role. Today and for the future, it will be impossible for railways operators to obtained specifi c frequency allocations if safety is not concerned. In this context it is urgent to promote new radio technologies able to optimize radio resources consumption, able to operate in various frequency bands and also with various radio access techniques and able to reconfi gure themselves as a function of the electromagnetic environment. These devices are known as Software Defi ned Radio or Cognitive Radio and will be the next generation of wireless mobile radios.

–

–

–


6. EMC considerationsElectromagnetic perturbations are important problems in the railway domain.

The main causes of theses perturbation phenomena are:

low tension level of electronic circuits,

existence of multiple radio systems everywhere,

necessity for cohabitation in a same system between high power (traction) and low power systems (electronic and command),

necessity to integrate all the systems in a same box,

introduction of new composite and plastic materials that cancel blindage effect.

Electromagnetic perturbations will decrease availability and safety levels but also can provoke degradation of the QoS of a radio link by increasing consider-ably the errors rate but also by affecting the available throughput.

The problem of electromagnetic compatibility should be taken into account at the beginning of the system development. The need to reduce the problems related to electromagnetic sensitivity of the equipments and the prediction of sys-tem performances with interferences in real conditions are mandatory steps of a telecommunication system development. Some past and existing projects deal with this important topics at national and European levels (EMCARTS [xx] was dealing specifi cally with the Eurobalise EMC aspects, RAILCOM [xx] extend the approach to GSM-R and WiFi systems, CEMRAIL [XX] deals with the cohabitation between high and low power in a same environment)

•

•

•

•

•



Conclusion

Today the key challenge for sustainable mobility and sustainable development is to reduce the impact of transport on the physical, social and human environ-ment. Promoting a set of solutions that aims to optimize the use of existing infra-structures for road and rail domains, to enhance safety and security, to reduce exploitation and maintenance costs and to offer new services to customers and staff developing inter modal behavior, may constitute an important contribution. This set of solutions is based on political decisions, best practice challenges and technological solutions developed within several Intelligent Transport Systems programs all over Europe.

In this context, new information and communication technologies represent great opportunities to develop Intelligent Public Transport Systems. This sector has always been very open for new technologies innovations but their development and deployment require integration with existing public transport environments. New information and communication technologies are the keys to optimize exploitation and maintenance costs, to enhance the friendliness, comfort and security feeling of public transport by offering new services to passengers while traveling with the aim to promote public transport use and multimodal behavior by optimizing door-to-door mobility. Today, with the development of “always on” behavior, customers on board a train ask to receive while traveling the same information they use to receive at home or at their offi ce. The Train-IPSAT project aims at developing such services. This report constitutes the fi nal report of the work performed regarding “user requirements analysis” and a “technical state of the art on the technologies suitable to answer these requirements” in the context of Train-IPSAT project.

The fi rst chapter is devoted to the user needs presentation in term of informa-tion and communication. The main needs to be satisfi ed are fi rst those related to control-command of train movement. Nevertheless, the necessity to increase effi ciency, reliability and generally speaking the global performances of railway transport has conducted to a multiplication of the needs related to communication, localization and surveillance applications between several entities such as train, infrastructure, command centre. The train-IPSAT project focus on this second cat-egory of requirements.

Today, it is vital for railway transport to win market parts against individual cars and air planes domains. Such strategy requires the design of integrated, inno-vative and interoperable telecommunication solutions. Among these solutions, it is needed to develop and deploy new added value services for train customers while moving. Some existing projects dealing with communications in the railway domain have been presented briefl y. The Train-IPSAT project aims at providing an innovative solution to satisfy this demand but also operators needs regarding seamless high data rate communication while travelling.



One important characteristics of the passengers communication needs is that generally speaking, no application requires specifi cally very high data rate if video streaming is excluded, but the multiplexing of several applications on a same RF medium will lead to high throughput requirements. Furthermore, some of the applications require high QoS and time constraints, which implies also as a direct consequence high data rate and time constraints needs on the global transmis-sion system.

The second chapter presents the transmission system architecture chosen in the Train-IPSAT project in order to demonstrate the feasibility and the interest of a solution able to support high data rate applications for passengers. The solution combines transparently a satellite and a terrestrial links connected to a mobile router and a WiFi network deployed in the coach on which passengers are con-nected. The innovation relies on the transparent complementarity between the satellite and the terrestrial links achieved thanks to the development and evalua-tion of a “vertical handover” procedure.

Chapter 3 gives the main physical characteristics of the existing and emerg-ing terrestrial wireless systems starting from the most deployed cellular ones and describing the existing and emerging WLAN, WMAN and also WPAN technolo-gies. Only cellular systems are design to offer large radio coverage and to support mobility. Nevertheless, high throughputs are possible only in micro cells and with no or pedestrian mobility. WLAN, WMAN and WPAN standards are able to offer high data rate but were not design to cope with mobility. We have seen that some evolutions of the fi rst standards (IEEE 802.11 r and IEEE 802.16e) will take into account mobile users. The descriptions of the systems have shown that maximum possible throughput is reachable only in small cell size, generally using several traffi c channels and at low speed (fi xed or pedestrian).

One common and very important characteristics to notice regarding all the existing wireless systems launched after GSM, is that they are generally designed for Internet like applications thus they offer non symmetrical links in term of data rate: low rate in uplink corresponding to requests or acknowledgements from the user, high data rate in the downlink corresponding generally to downloading (appli-cations, software, video, music…). This point must be highlighted from a railway point of view because the multiplexing of several applications sending information from the train to the ground on a unique medium will lead to the need of high data rate on the up-link direction. In this context, we can assess that today there is no public existing system able to provide data rate around 500 kbits/s in the up-link in the context of mobility (greater than 100 km/h).

One other important characteristic of wireless systems described in this chap-ter, is that the cell size to obtain a suffi cient radio coverage level to serve the mobile devices is directly related to the transmitted power, the antenna gain and the resistance to interference levels defi ned for the cell planning and frequency reuse rules. Furthermore, the number of traffi c channels available in an area that is directly proportional to the number of carriers (TRX) on the BTS and to the traf-fi c load at one instant. In this context a comparison between systems in term of


capacity should take into account the relationship between traffi c channels avail-ability versus cell size, TRX number and traffi c load particularly in dense areas in which a large number of trains will need to transmit big amount of information at the same time. In other words, it is clear that the throughput available per user is directly related to the radio coverage levels and the interference levels.

When it is planned to use a public cellular systems to answer some railway communication needs, it is important to remember that when the base station is far from the tracks, the Doppler spread is greater than when the base station is located near the railway line. Using directive antennas will permit to cover only the railway tracks, to optimize the cell shape regarding the applications and to reduce Doppler effect. Such a solution means specifi c frequency allocation or at least specifi c deployments along the lines which means suffi cient returns on investments for telecommunication operator and also real and perennial offers for suitable services (GPRS or data transmission for example).

One possible advantage of cellular systems compared to WLAN regarding mobility is the existence of standardized handover and roaming protocols already implemented in all the system devices. But it is important to notice that speed and high speed has infl uence on handover process and thus on QoS. As an example, data lost of about 400 ms have been observed during long handover times gen-erally due to bad coverage in the case of GSM-R. Generally speaking, to cope with high speed, slow speed and high QoS at the same time, a specifi c coverage design and network tuning are needed like for GSM-R applications.

WLAN and WMAN standards are today widely deployed but they provide high data rate only in a small coverage area. They are submitted to the same electro-magnetic laws than cellular systems, thus covered area sizes are directly related to transmitted power limitations, antenna gain, interferences sensitivity. The maxi-mum throughput available is directly related to the bandwidth available per user at the same time and to the distance to the access point. WPAN systems represent very promising emerging systems able to provide high data rate for very short range communication needs thus they can be foreseen only for specifi c, local and fi xed applications. The use of WiFi, WiMax or WPAN like technologies for rail-ways applications that required periodic or continuous transmissions will certainly require the development of handover and roaming protocols adapted to these systems. Even if the cost of one single access point is very low, what will be the cost of developing handover and roaming protocols and network signalling able to cope with railway requirements?

Chapter four presents an overview of satellite systems for mobile applications. They are designed to minimize the ground infrastructure and to provide very wide radio coverage. Nevertheless, the availability of these systems is not as good as one can imagine in a railway environment due to masking effect and tunnels and delays up to 500 ms are often experienced due to the specifi c system archi-tecture where the signals are travelling through the terrestrial station. Systems offering direct connexion between the mobile and the satellite offers today the same technical characteristics than GSM, EDGE and UMTS in term of data rate

Conclusion



when the satellite is correctly received. Satellite-based mobile system supporting broadband interactive services are still under development and one solution will be evaluated in the Train-IPSAT project.

Due to the various environments of the high speed trains along the different existing lines all over Europe, it is impossible to identify at short term a unique technology able to answer all the connectivity needs on the whole trip. The solu-tion chosen in the Train-IPSAT project is to use several technologies with a real time transparent roaming also called “vertical handover” to switch from a system to another depending on the best availability. This “roaming” will be performed thanks to a specifi c device that will act as a “multi access router”. Its main role will be to allow permanent links while the train is travelling using alternatively several access technologies transparently for the customer. Recently, a number of micro-mobility protocols have been proposed to manage transparent mobility to applica-tion layers. These include Mobile IP and its multiple variants, message oriented middleware (MOM) technologies. These standards solve some of the inherent IP mobility problems, but as they are working at higher layers (3 and above), impor-tant delays are introduced.

The communication devices on-board the train could be PDA, PC, smart phones, but also “intelligent IP sensors”. To cope with this diversity, a multi mod-els software infrastructure has to be used to access continuously to the different services while travelling.

Chapter 5 presents the technologies and solution available to solve the prob-lem of mobile routing: CISCO router, Ipv6 –NEMO solution and multi models soft-ware infrastructure such as MOM technology.

Chapter 6 focus the reader’s attention on the specifi c phenomena occurring when dealing with radio propagation in railway environment such as tunnels, cuttings that increasing masking effects, high speed and base station position that create high Doppler shifts. EMC problems and their consequences are also mentioned.

The technical analysis presented in this document highlighted clearly for all the described systems, drawbacks and advantages versus the user needs and the railways requirements. The solution studied, developed and tested within the Train-IPSat project is promising to satisfy the passenger needs such as Internet or intranet browsing on the move for a given number of passengers. The system dimensioning will be an important step in the project regarding the technology capabilities and will be performed during the phase 2 of the project. Nevertheless, it’s appear clearly that none of the described systems is able to answer at the same time all the existing and future telecommunication needs and suppose to be integrated or multiplexed on a same medium. This validates the Train-IPSAT project choice to use several technologies with a real time transparent “vertical handover” to switch from a system to another depending on the best availability and QoS offered to users.


Bibliography

[BERBINEAU, 01] M. BERBINEAU, ‘‘Les systèmes de télécommunication existants ou émergents et leur utilisation dans le domaine des transports guidés’’- Synthèse INRETS N°40 – ISSN 0769-0274- ISBN 2-85782-562-5- Novembre 2001

[Campbell, 01] A.T.Campbell and J.Gomez. “IP Micro-Mobility Protocols”. IEEE Wireless Communications, October 2001

[Chennaoui, 04], CHENNAOUI M, “Communications haut débit depuis les trains à grande vitesse” – Communiquer, naviguer, Surveiller dans les transports – rencontre des doctorants du LEOST- 12 Février 04.

[Click TGV] Projet SNCF

[dailywireless.org]

[Droma, 03] M. O’Droma et al., “‘Always Best Connected’Enabled 4G Wireless World”, IST Mobile and Wireless Communications Summit 2003, June 2003

[Drzisga, 05] Torsten Drzisga, Siemens Communications Mobile Networks – WWC’05]

[Ernst, 02] Ernst T., Uehara K. “Connecting cars to the Internet”, ITST workshop, Seoul, November 2002.

[Ernst, 04] Ernst T and Charbon J, “Multi-homing with NEMO Basic Support”, ICMU, January 2004

[ESCORT, 02] ESCORT - Enhanced diversity and Space Coding for underground metrO and Railway Transmission - IST 1999-20006 - D 6021 – Final Report – 12/02

[EVAS, 06]. Rapport de projet intermediaire – Janvier 2006

[Foschini, 96] Foschini (G.J.), “Layered Space-Time Architecture for Wireless Communication in a Fading Environment When Using Multi-Element Antennas”, Bell Labs Technical Journal, Vol. 1, n° 2, Autumn 1996, pp. 41-59

[Fromann, 2001] Isabelle Frommann, Dennis Yuan, S. Vanessa Winter – Mobile communications – PPT presentation – Institute of Ecommerce

[Gransart, 03] C. Gransart, J. Rioult, Guillaume Uster, ‘‘Mobile objects and ground transportation innovative services’’, Int. Conf. on Parallel and Distributed Processing Techniques and Applications PDPTA’2003, Las-Vegas, USA, June 2003.

[IEEE 802.11] The IEEE 802.11 standard, Imad Aad, INRIA, Planete team



[IEEE 802.11-1999] IEEE standard 802.11, 1999 edition: WLAN MAC and PHY layers specifi cations

[IEEE 802.11b, 1999] IEEE standard 802.11b, 1999 edition (supplement to 802.11-1999), Higher-Speed Physical Layer Extension in the 2.4 GHz Band

[Supplement to 802.11-1999] IEEE standard 802.11a, 1999 edition (supplement to 802.11-1999): High-Speed Physical Layer in the 5GHz Band

[Iperf] Iperf, http://dast.nlanr.net/Projects/Iperf/

[Kaddour, 03] M. Kaddour, L. Pautet “Towards an Adaptable message oriented Middleware for Mobile environment”, ASWN 2003.

[Krenik, 05] Dr. Bill Krenik - Advanced Architectures Manager –Wireless Terminals Business Unit - texas Instruments – WWC’05

[Lagrange, 96] LAGRANGE X., GODLEWSKI P., TABBANE S., les réseaux GSM-DCS, édition HERMES

[Montavont, 03] N. Montavont, T. Noel, “Anticipation des handovers dans les réseaux sans fi l”, DNAC 2003

[Most97] Projet Mostrain- rapport D301- WP3- Programme ACTS

[Most98] Projet MOSTRAIN – 4e PCRD – Rapport Final – 98-Programme ACTS

[MOWG, 05] www.mowgly.org

[O’Droma, 03] M. O’Droma et al., “‘Always Best Connected’Enabled 4G Wireless World”, IST Mobile and Wireless Communications Summit 2003, June 2003

[Pautet, 01] L. Pautet, Intergiciels schizophrènes: une solution à l’interopérabilité entre modèles de répartition, Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, France, 2001.

[Perkins, 96] C. Perkins, “IP Mobility Support”, RFC 2002, October 1996.

[Raymond, 04] G. Raymond, J. Marais, M. Berbineau – Innovation brings Satekllite-based train control within reach, RAILWAY GAZETTE INTERNATIONAL, DECEMBRE 2004.

[RFC 3775], “Mobility Support in IPv6”, June 2004

[RFC 3963], “Network Mobility (NEMO) Basic Support Protocol”, January 2005

[Sethom, 04] K.sethom, H.afi fi , Guy pujoelle “Wireless MPLS: A New Layer 2.5 Micro-mobility Scheme”, ACM Mobiwac 2004

[Shaper, 98] Shaper, www.lwn.net/1998/1119/shaper.html

[SHISA] SHISA stack at www.mobileip.jp

[Snoeren] A.C.Snoeren and H.Balakrishnan, “An End-to-End Approach to Host Mobility”, MobiCom’00, August 2000.

[source INTEGRAIL Deliverable D3D4.1]


[Stevens, 94] R. Stevens, TCP/IP illustrated, 1994, Addison-Wesley.

[Suciu, 04] L. Suciu et al., “Achieving Always Best Connected through Extensive Profi le Management”, in Proc. of 9th International PWC Conference, Sept. 2004

[Sun, 01] J.Sun, D.Howie, J.Sauvola, “Mobility management techniques for the next generation wireless Networks”, Wireless and Mobile Communications, 2001.

[Tess03] C. Tatkeu, M. Berbineau, Evaluation théorique et expérimentale de la couverture GSM-GPRS et Globalstar dans l’agglomération Lilloise, présentation comité de pilotage TESS – 2003

[TESS, 05] AMBELLOUIS, S & AL. – Projet Transport Espace et Société (TESS) – Rapport fi nal – Autobus communicant - INRETS, 2005.

[Winters, 03] Annexe technique proposition IST- 5e PCRD – 2003.

bookmarks

www.etsi.org

www.dect.ch

www.bluetooth.com

www.homerf.org

www.hiperlan.com

www.art-telecom.fr

www.itu.int

www.galileosworld.com

www.wapforum.org

www.mobilewap.com

www.nokia.com

www.phone.com

www.francetelecom.fr

www.tcm.hut.fi /Opinnot/Tik-111.550/1999/Esitelmat/Wap/wap/WAP.html

www.gsmworld.com

www.inmarsat.com

www.eutelsat.com

www.networkworld.com

dailywireless.org

Bibliography

Imprimé en France – JOUVE, 11 bd de Sébastopol – 75001 PARIS427679C – Dépôt légal : Juillet 2007

Documents

HIGH DATA RATE TRANSMISSIONS FOR HIGH … · public transport use and multimodal behavior by optimizing door-to-door mobility. Today, with the ... (par exemple, une traduction, etc.),