Ece Viii Wireless Communication [10ec81] Notes

5/22/2018 Ece Viii Wireless Communication [10ec81] Notes

1/108

Wireless Communication 10EC81

Department of ECE,SJBIT Page 1

Subject Code : 10EC81 IA Marks : 25

No. of Lecture Hrs/Week : 04 Exam Hours : 03

Total no. of Lecture Hrs. : 52 Exam Marks : 100

PART - A

UNIT1

Introduction to wireless telecommunication systems and Networks, History and evolution

Different generations of wireless cellular networks 1G, 2g,3G and 4G

etworks.

6 Hours

UNIT - 2

Common Cellular System components, Common cellular network components, Hardwareand software, views of cellular networks, 3G cellular systems components, Cellular

component identification Call establishment.

6 Hours

UNIT - 3

Wireless network architecture and operation, Cellular concept Cell fundamentals, Capacityexpansion techniques, Cellular backbone networks, Mobility management, Radio resources

andpowermanagementWirelessnetwork

6 Hours

UNIT - 4

GSM and TDMA techniques, GSM system overview, GSM Network and system

Architecture,GSMchannelconcepts,GSM

6 Hours

PART - B

UNIT - 5

GSM system operation, Traffic cases, Cal handoff, Roaming, GSM protocol architecture.

TDMA systems

6 Hours


2/108



UNIT - 6

CDMA technology, CDMA overview, CDMA channel concept CDMA operations.

8 hours

UNIT - 7

Wireless Modulation techniques and Hardware, Characteristics of air interface, Path loss

models, wireless coding techniques, Digital modulation techniques, OFDM, UWB radio

techniques, Diversity techniques, Typical GSM Hardware.

6 Hours

UNIT - 8

Introduction to wireless LAN 802.11X technologies, Evolution of Wireless LAN

Introduction to 802.15X technologies in PAN Application and architecture Bluetooth

Introduction to Broadband wireless MAN, 802.16X technologies.

8 Hours

TEXT BOOK:

1. Wireless Telecom Systems and networks, Mullet: Thomson Learning 2006.

REFERENCE BOOKS:

1. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002.

2. Wireless communication- D P Agrawal: 2nd

Edition Thomson learning 2007.

3. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath,

Cambridge 2005.


3/108



INDEX SHEET

Sl.No Unit & Topic of Discussion Page no.

UNIT --- 1

1 Introduction to wireless telecommunication systems

5 to 19

2 Introduction to wireless telecommunication Networks

3 History of different generations of wireless cellular

networks

4 Evolution of different generations of wireless cellularnetworks

5 1G,2G networks

6 3G and 4G networks

UNIT2

7 Common Cellular System components

20 to 30

8 Common cellular network components9 Hardware and software10 Views of cellular networks11 3G cellular systems components12 Cellular component identification Call establishment13 Call release

UNIT3

14 Wireless network architecture and operation

31 to 42

15 Cellular concept , Cell fundamentals16 Capacity expansion techniques, Cellular backbone

networks17 Mobility management18 Radio resources and power management19 Wireless network security

UNIT --4

43 to 54

20 GSM and TDMA techniques

21 GSM system overview22 GSM Network

23 system Architecture


4/108



24 GSM channel concepts25 GSM identifiers

UNIT5

26 GSM system operation

55 to 67

27 Traffic cases28 Call handoff29 Roaming30 GSM protocol architecture31 TDMA systems32 NA TDMA

UNIT--6

33 CDMA technology

68 to 81

34 CDMA overview35 CDMA channel concept CDMA operations36 CDMA channel concept CDMA operations37 CDMA channel concept38 CDMA channel assignement

UNIT-740 Wireless Modulation techniques and Hardware

82 to 94

41 Characteristics of air interface , Path loss models42 Wireless coding techniques43 Digital modulation techniques, OFDM, UWB radio

techniques44 Diversity techniques45 Typical GSM Hardware

UNIT-7

46 Introduction to wireless LAN 802.11X technologies

95 to 108

47 Evolution of Wireless LAN48 Introduction to 802.15X technologies in PAN

architecture

49 802.16X technologies


5/108



UNIT - 1

Introduction to wireless telecommunication systems and Networks, History and Evolution

Different generations of wireless cellular networks 1G, 2g,3G and 4G networks.

6 Hours

TEXT BOOK:


REFERENCE BOOKS:

1. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002.2. Wireless communication- D P Agrawal: 2

ndEdition Thomson learning 2007.


Cambridge 2005.


6/108



UNIT-1

Introduction to wireless telecommunication systems and networks

1.1 Introduction to wireless telecommunication systems and networksCommunication is the transfer of information form one point to another. Invention

of telephone by Bell in 1876 was the first manually switched wireline network.

Radio or wireless was invented during 20th

century which had the convenience of

mobile operation to electronic communication. Advances in IC technology gave thecordless telephones during late 1970s , and in 1983 the public had the opportunity

to subscribe for cellular telephone systems. These wireless systems gave access to

public switched telephone network which had mobile access.

The wireless and mobile communications was found useful in commerce,

education, defense etc., according to the nature of particular application they can be

used in home based, industrial, commercial, military environment. For example, incommercial wireless communications can be employed for purchase or selling of

goods, services , playing audio and video, payment of telephone bills , airline , bus

reservations etc.,

1.2 History and Evolution of Wireless Radio Systems

In 1887 , Heinrich Hertz performed laboratory experiments which proved the

existence of EM waves .

From 1895 to 1901 Marconi experimented with a wireless telegraph system who

built several radio telegraph stations in England and started commercial servicebetween England and France in 1899.

Early AM wireless systems

The early wireless transmitter consists of inductance and capacitance which is used

to tune the output frequency of the spark gap. Max power is generated at lower freq

and longer wavelength. The transmitter emits the signal either long or short

duration depending on length of time telegraph key is closed. The transmitter

signal is the EM noise produced by the spark gap discharge.


7/108



Fig 1. Typical early wireless transmitter

The transmitter signal propagates through the air to a receiver which is located at some

distance . At the receiver the detected signal is interpreted by the operator as either a dot ordash depending upon its duration by use of Morse code.

Modern AM :

Amplitude modulation is used for low frequency radio broadcasting the AM include

quadrature amplitude modulation which is used for high speed data transmission at RFfrequencies.

1.2 The Development of Modern Telecommunications Infrastructure

The early days of telecommunications

The public switched telephone network

The local exchange Intraoffice calls


8/108



Fig: 1.2 A PSTN intraoffice call through a local exchange

Circuit-switched calls Interoffice calls T-carrier transport

Fig: 1.3 A PSTN intraoffice call over an inter-exchange trunk line


9/108



Signaling System #7

Signal transfer points Service switching points Service control points Operations support systems

Signalling System No. 7(SS7) is a set of telephony signaling protocols which are used to

set up most of the world's public switched telephone network telephone calls. The main

purpose is to set up and tear down telephone calls. Other uses include number translation,local number portability, prepaid billing mechanisms, short message service (SMS), and a

variety of other mass market services.

It is usually referenced as Signalling System No. 7 or Signalling System #7, or simplyabbreviated to SS7. In North America it is often referred to as CCSS7, an abbreviation for

Common Channel Signalling System 7. In some European countries, specifically the

United Kingdom, it is sometimes called C7 (CCITT number 7) and is also known as

number 7 and CCIS7 (Common Channel Interoffice Signaling 7). In Germany it is oftencalled as N7 (Signalisierungssystem Nummer 7).

There is only one international SS7 protocol defined by ITU-T in its Q.700-series

recommendations.[1]

There are however, many national variants of the SS7 protocols. Most

national variants are based on two widely deployed national variants as standardized byANSI and ETSI, which are in turn based on the international protocol defined by ITU-T.

Each national variant has its own unique characteristics. Some national variants with rather

striking characteristics are the China (PRC) and Japan (TTC) national variants.

The Internet Engineering Task Force (IETF) has also defined level 2, 3, and 4 protocols

that are compatible with SS7:

Message Transfer Part (MTP) level 2 (M2UA and M2PA)

Message Transfer Part (MTP) level 3 (M3UA)

Signalling Connection Control Part (SCCP) (SUA)

The public data network Connectionless systems Private data networks Virtual private data networks Tunneling protocols


10/108



Fig: 1.4 Network elements of the SS7 system

1.3 Different Generations of wireless cellular networks:

1G Cellular Systems

AMPS system components and layout Radio base stations Communications links Mobile switching office

First-generation cellular systems have been around for a few decades now, and we expect

them to remain in place for some time because of the significant infrastructure investmentsmade by operators. All of these systems support circuit data services and may be utilizedfor various forms of mobile VPN, albeit not without difficulties. This section provides a

high-level overview of the air interfaces utilized by most widely deployed 1G systems.

AMPS


11/108



All 1G cellular systems rely on analog frequency modulation for speech and data

transmission and in-band signaling to move control information between terminals and the

rest of the network during the call. Advanced Mobile Phone

System is a good example of first-generation analog technology mostly used in the United

States. AMPS is based on FM radio transmission using the FDMA principle where everyuser is assigned their own frequency to separate user channels within the assigned spectrum

(see Figure 3.2). FDMA is based on narrowband channels, each capable of supporting one

phone circuit that is assigned to a particular user for the duration of the call. Frequencyassignment is controlled by the system, and transmission is usually continuous in both

uplink and downlink directions. The spectrum in such systems is allocated to the user for

the duration of the call, whether it is being used to send voice, data, or nothing at all.

As with other 1G technologies, in AMPS a circuitrepresented by a portion of spectrum

is allocated to the user and must remain available for this user, similar to the telephone

copper pair used for voice communications. Similar to the analog wireline connection, a

modem is also used for data access (see Chapter 4 for more on this). Error correctionprotocols used by wireless modems tend to be more robust than their landline counterparts,

because of the necessity of dealing with a more challenging physical environment withinherently higher interference and signal-to-noise ratios than copper or fiber. The peak datarate for an AMPS modem call under good conditions is usually up to 14.4 Kbps, and as low

as 4.8 Kbps under poor conditions. It can take anywhere up 20 seconds or more to establish

an AMPS data connection.

Fig 1.5 An early AMPS cellular system

Information flow over AMPS channels


12/108



Analog color codes Digital color codes Transponder Signaling tones

Fig 1.6 AMPS forward and reverse control and voice channels

Typical AMPS operations AMPS security and identification Summary of basic AMPS operations

Initialization

Fig 1.7 AMPS mobile phone initialization

AMPS ongoing idle mode tasks


13/108



Mobile-to-land calls Handshaking operations Signaling operations Service requests

Fig 1.8 AMPS mobile originated call

Land-to-mobile and mobile-to-mobile calls

Paging ID information exchange Signaling Control messages


14/108



Fig 1.9 AMPS mobile terminated call

AMPS network operations

Radio base station operations Base station control operations Mobile switching center operations

Fig 1.10 AMPS network operations for a mobile originated call


15/108



Handoff operations

Handshaking operations Signal strength measurements MSC operations during handoff Confirmation messages

Fig 1.11 AMPS handoff operation

2G Cellular Systems

Second-generation (2G) digital cellular systems constitute the majority of cellularcommunication infrastructures deployed today. 2G systems such as GSM, whose rollout

started in 1987, signaled a major shift in the way mobile communications is used

worldwide. In part they helped fuel the transition of a mobile phone from luxury to

necessity and helped to drive subscriber costs down by more efficient utilization of airinterface and volume deployment of infrastructure components and handsets.

Major geographical regions adopted different 2G systems, namely TDMA and CDMA in

North America, GSM in Europe, and Personal Digital Cellular (PDC) in Japan.

cellular systems. It effectively shows how the GSM system has been successful and why it

is now being adopted in geographical areas other than Europe (such as North America,

China, the Asia-Pacific region, and more recently, South America). CDMA, which


16/108



originated in North America, has also proliferated in South America and later in the Asia-

Pacific region. TDMA remains to be widely deployed in North and South America regions,

but it is expected to decline mostly because of the decisions taken by few major NorthAmerican carriers to convert their TDMA networks to GSM.

This second-generation system, widely deployed in the United States, Canada, and SouthAmerica, goes by many names, including North American TDMA, IS-136, and D-AMPS(Digital AMPS). For the sake of clarity, we will refer to it as North American TDMA, as

well as simply TDMA, when the context makes it clear. TDMA has been used in North

America since 1992 and was the first digital technology to be commercially deployed there.As its name indicates, it is based on Time Division Multiple Access. In TDMA the

resources are shared in time, combined with frequency-division multiplexing (that is, when

multiple frequencies are used). As a result, TDMA offers multiple digital channels using

different time slots on a shared frequency carrier. Each mobile station is assigned both aspecific frequency and a time slot during which it can communicate with the base station.

The TDMA transmitter is active during the assigned time slot and inactive during othertime slots, which allows for power-saving terminal designs, among other advantages. North

American TDMA supports three time slots, at 30 kHz each, further divided into three or six

channels to maximize air interface utilization. A sequence of time-division multiplexed

time slots in TDMA makes up frames, which are 40 ms long. The TDMA traffic channeltotal bit rate is 48.6 Kbps. Control overhead and number of users per channel, which is

greater than one, decrease the effective throughput of a channel available for user traffic to

13 Kbps. TDMA is a dual-band technology, which means it can be deployed in 800-MHzand 1900-MHz frequency bands. In regions where both AMPS and TDMA are deployed,

TDMA phones are often designed to operate in dual mode, analog and digital, in order to

offer customers the ability to utilize coverage of the existing analog infrastructure.

Global System for Mobile Communications (GSM)

There are still some analog cellular systems in operations in Europe, but their number is

declining, and some regional networks are being completely shut down or converted to

Global System for Mobile Communications. The GSM cellular system initiative wasinitiated in 1982 by the Conference of European Posts and Telecommunications

Administrations (CEPT) and is currently governed by European Telecommunications

Standards Institute (ETSI), which in turn has delegated GSM specifications maintenance

and evolution to 3GPP (reviewed in part in Chapter 1). The intent behind GSMintroduction was to have a common approach to the creation of digital systems across

European countries, to allowamong other advantages of a common standardeasy

international roaming and better economies of scale by decreasing handset andinfrastructure components costs through mass production. In hindsight, this was a smart

political decision, which contributed to the worldwide success of European cellular

infrastructure providers and equipment manufacturers.


17/108



2.5g Cellular Systems

"2.5G" is an informal term, invented solely for marketing purposes, unlike "2G" or "3G"

which are officially defined standards based on those defined by the InternationalTelecommunication (ITU). The term "2.5G" usually describes a 2G cellular system

combined with General Packet Radio Services (GPRS), or other services not generally

found in 2G or 1G networks.Wireless telecommunication technology like CDMA200 1x-RTT, Enhanced Data Rates for GSM Evolution (EDGE) or Enhanced General Packet

Radio Service (EGPRS), since they have data transmission rates of 144 kbps or higher,

may qualify as 3G technology. However, they are usually classified as 2.5G technology

because they have slower network speeds than most 3G services.

GPRS is a service commonly associated with 2.5G technology. It has data transmissionrates of 28 kbps or higher. GPRS came after the development of the Global System for

Mobile (GSM) service, which is classified as 2G technology, and it was succeeded by thedevelopment of the Universal Mobile Telecommunication Service (UMTS), which is

classified as 3G technology.A 2.5G system may make use of 2G system infrastructure, but

it implements a packet-switched network domain in addition to a circuit-switched domain.This does not necessarily give 2.5G an advantage over 2G in terms of network speed,

because bundling of timeslots is also used for circuit-switched data services (HSCSD).

The services and infrastructure of a 2.5G network may be used on a per-transaction basis

rather than a per-minute-of-use basis, thanks to its packet-switched domain. This makes its

infrastructure more efficient and improves the service delivery. This impetus is known asthe "always-on" capability.2.5G networks may support services such as WAP, MMS, SMSmobile games, and search and directory.

3G Cellular Systems

Cell phones and systems are classified by the generation they belong to. Third generation

(3G) phones were developed in the late 1990s and 2000s. The goal was to improve the data

capability and speed. 3G phones were defined by the Third Generation Partnership Project

(3GPP) and later standardized by the ITU-T. Generally known as the Universal MobileTelecomunications System (UMTS), this 3G system is based on wideband CDMA that

operates in 5 MHz of bandwidth and can produce download data rates of typically 384 kb/sunder normal conditions and up to 2 Mb/s in some instances. Another 3G standard,

cdma2000, was developed by Qualcomm. It uses 1.25 MHz bands to produce data rates to

2 Mb/s. Another version of cdma2000 is an improved IS-95 version. It is a 3GPP2

standard. It can transmit data at a rate to 153 kb/s and up to 2 Mb/s in some cases.


18/108



3G phone standards have been expanded and enhanced to further expand data speed and

capacity. The WCDMA phones have added high speed packet access (HSPA) that use

higher level QAM modulation to get speeds up to 21 or 42 Mb/s downlink (cell site tophone) and up to 7 and/or 14 Mb/s uplink (phone to cell site). AT&T and T-Mobile use

HSPA technology. The cdma2000 phones added 1xRTT as well as Rev. A and Rev B

modifications that boost speed as well. Verizon and Sprint use cdma2000 3G standardtechnology. Virtually all standard and smartphone models and most tablets still use someform of 3G.

Fig 1.12 3G operating environments


19/108



Table 1.1 3G characteristics by cell size and mobile speed

4G Cellular Systems and Beyond

The fourth generation has been defined but we are not in it, yet. Yes, many if not most ofthe mobile carriers and the various phone and equipment manufacturers actually advertise

4G now. The formal definition of 4G as declared by the 3GPP and the ITU-T is something

called Long Term Evolution-Advanced (LTE-A). The standard has not been fullycompleted but basically it is an improved and enhanced version of LTE that uses wider

bandwidth channels and a greater number of MIMO antennas. The theoretical upper data

rate is 1 Gb/s. That remains to be seen in practice.

As for what the various companies are calling 4G, Verizon says that their LTE network is

4G. AT&T promotes their LTE and HSPA networks as 4G. T-Mobile indicates that their

HSPA+ networks are 4G. Furthermore Sprint and Clearwire say that their WiMAXnetwork is 4G. As mentioned, WiMAX is actually defined as a 3G technology by ITU-T

like LTE.


20/108



UNIT - 2

Common Cellular System components, Common cellular network components, Hardware

and software, views of cellular networks, 3G cellular systems components, Cellularcomponent identification Call establishment.

6 Hours

TEXT BOOK:


REFERENCE BOOKS:



Edition Thomson learning 2007.3. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath,

Cambridge 2005.


21/108



UNIT-2

COMMON CELLULAR SYSTEM COMPONENTSIt is very much essential to implement increased system functionality to meet the demands

of the increasing number of subscribers with the more sophisticated wireless cellular

network. To achieve this the various hardware network elements used to create the wireless

cellular network plays an important role.The network element scan be divided into three basic groups

1.The mobile or subscriber device (providers the user link to the wireless network.

2.Base station ( provides wireless system links to the subscriber over air interface)3.Network switching system (provides interface to the PSTN and PDN )

2.1 COMMON CELLULAR NETWORK COMPONENTS

Fig 2.1 Typical wireless cellular system componentsDuring 1G wireless cellular system , it consists of several subsystems to perform certain

operations in support of the entire system. For 2G and 2.5G cellular networks , the air

interface functions are performed by fixed Radio Base Station and Mobile Station orSubscriber device that provide user mobility. The radio base station is controlled by a base

station controller which is referred as base station system.The base station system is connected to a fixed switching system that handles the routing of

both voice calls and data services to and from the mobile switching centre and various

databases and functional nodes to support the mobility management and security operations

of the system. The switching system is usually connected to the PSTN , the PDN , otherpublic land mobile networks(PLMN ) and various data messaging networks through gate

way switches.


22/108



The various network elements that make up the wireless system are interconnected by

communication links that transport system messages between network elements to facilitate

network operations and deliver the actual voice call or data services information.SUBSCRIBER DEVICES:

The subscriber device is the link between the customer and the wireless network. The SD

must be able to provide a means for the subscriber to control and input information to thephone and display its operation status.

Fig 2.2 subscriber device

The subscriber device must be able to sample , digitize and process audio and othermultimedia signals, transmit and receive RF signals, process system control messages and

provide the power needed to operate the complex electronics subsystems .

A SD consists of man machine interface, an RF transceiver section a signal processingsection , a system control processor and a power supply/ management section.

BASE STATION SYSTEM COMPONENTS:

The Base station system handles all radio interface related functions for the wirelessnetwork .The BSS consists of several to many radio base stations , a base station

contr5oller , Transcoder controller .The radio equipment required to serve one cell is

typically called a base transceiver system. A single radio base station might contain three

base transceiver systems which is used to serve a cell site that consists of three 120 degreesectors or cells.


23/108



Fig 2.3 components of base station system

Typical CDMA wireless system

The base station controller functions as the interface between mobile switching centre and

packet core network and all the radio base stations controlled by BSC. The BSC systemprovides timing signals and connectivity to every subsystem within it and computer

interfaces to the entire system. The BSC will supply signaling towards the MSC using

message transfer part protocol to transfer the message over a PCM link connected to SS7signaling terminals located within MSC and the BSC.

The TRC consists of subsystems that perform transcoding and rate adaptation which can be

either stand alone or combined.REGISTERS IN WIRELESS SYSTEMS:VISITOR LOCATION REGISTER:It is a database that temporarily stores information about any mobile station that attaches to

a RBS in the area services by a particular MSC. This temporary subscriber information is

required by the MSC to provide service to a visiting subscriber .HOME LOCATION REGISTER:

It is a data base that stores information about every user that has a cellular service contractwith specific wireless service provider . This database stores permanent data about the

networks subscribers, information about the subscribers present location. The HLR alsoplays a major role in the process of handling calls terminating at the MS. The HLR

analyzes the information about the incoming call and controls the routing of the call.

AUC Interconnection:

The AUC provides authentication and encryption information for the MS being used in thecellular network. Upon a request from a VLR the HLR will be delivered a triplet for a

particular mobile subscriber .the HLR receives the triplet information in response to a


24/108



request to the AUC for verification of a subscriber. The HLR forwards the random

number and returns it to the MSC/VLR and from there to the HLR .The AUC contains a

processor, a database for the storage of key information for each subscriber maintenancefunctions for subscriber and an interface fro communication with HLR.

EQUIPMENT IDENTITY REGISTER:

Then EIR database is used to validate then status of mobile equipment . This globaldatabase is updated daily to reflect the current status of an MS. The MS can be black listedindicating that it has been reported stolen or missing and does not approve for network

operation.

INTERWORKING UNITS:

IWUs are required to provide an interface to various data networks. These nodes are used

to connect the base station controller and hence the radio base stations to various data

services networks.

GATEWAYS and its types

1. Gateway MSC: (GMSC)gateway MSC is an MSC that interfaces the wirelessmobile network to other telecommunication networks. A cellular network will have

numerous MSCs to facilitate coverage of large area but all switching centers need to

be connected to other wireline network .to support its function as gateway the

GMSC will have ability to reroute a call to an MS using the information provided

by the HLR of a subscriber.

2. Billing gateway : (BGW) this collects billing information from various wireless

network elements which becomes a file use by customer administrative system to

generate billing information for the system subscribers like monthly access fees,

home usage , roaming , data and special services etc.,

3. Service order Gateway :(SOG) It is used to connect a customer administrative

system to the switching system. This system is used to input new subscriber data to

the HLR or to update current subscriber data already contained in the HLR. The

SOG allows access to the AUC and EIR for equipment administration. When a

customer signs a service contract with cellular service provider the information

about the contract is entered into the customer administrative system.

2.2 HARDWARE AND SOFTWARE VIEWS OF CELLULAR NETWORK: Hardware view of a cellular network

Serving areas

Cells

MSC boundaries


25/108



Fig 2.4 Hardware view of cellular network

Software view of a cellular network

Location area identity

Cell global identity

Mobile country code and network code

Fig 2.5 Software view of Cellular system

2.3 3G Cellular System Components Core network

Radio access network


26/108



Radio network controller

Radio base station

Fig 2.6 The 3G radio network controller

2.4

Cellular Component Identification

Subscriber device identification

Mobile station ISDN identification number

North American version

The rest of the world


27/108



Fig 2.6 Formation of MSISDN number Cellular Component Identification

International mobile subscriber identity

Fig 2.7 Formation of IMSI number

International mobile equipment identity

Fig 2.8 Formation of IMEI number

Cellular system component addressing

Location area identity

Cell global identity

Radio base station identity code


28/108



Location numbering

Addressing cellular network switching nodes

Global title and global title translation

2.5 Call Establishment

Mobile-terminated call

PSTN messages

GMSC operations

MSC/VLR operations

BSC operations

Fig 2.9 Mobile terminated call operations

Mobile-originated call

Mobile operations

Radio base station operations

Base station controller operations

MSC operations


29/108



Fig 2.10 Mobile originated call operations Call release

Connection management operations

Radio resource operations


30/108



Fig 2.11 Call release

The above figure shows the operation during release of a mobile call through MSC . the

steps involved as shown in detail which is self explanatory.


31/108



UNIT - 3

Wireless network architecture and operation, Cellular concept Cell fundamentals, Capacity

expansion techniques, Cellular backbone networks, Mobility management, Radio resources

and power management Wireless network security

6 Hours

TEXT BOOK:


REFERENCE BOOKS:





Cambridge 2005.


32/108



UNIT-3

WIRELESS NETWORK ARCHITECTURE AND OPERATION

3.1 The Cellular ConceptSolves the problem of spectral congestion and user capacity,Offer very high capacity ina limited spectrum without major technological changes,Reuse of radio channel in

different cells.Enable a fix number of channels to serve an arbitrarily large number of

users by reusing the channel throughout the coverage region.Simplex and duplex

Each cellular base station is allocated a group of radio channels within a smallgeographic area called a cell.Neighboring cells are assigned different channel groups.

By limiting the coverage area to within the boundary of the cell, the channel groups

may be reused to cover different cells.Keep interference levels within tolerable limits.Frequency reuse or frequency planning seven groups of channel from A to G.footprint

of a cell - actual radio coverage ,omni-directional antenna v.s. directional antenna

Steps for frequency reuse:

Consider a cellular system which has a total of Sduplex channels. Each cell is allocated a group of kchannels, . The Schannels are divided amongNcells. The total number of available radio channels

TheNcells which use the complete set of channels is called cluster. The cluster can be repeated M times within the system. The total number of

channels, C, is used as a measure of capacity

The capacity is directly proportional to the number of replicationM. The cluster size,N, is typically equal to 4, 7, or 12. SmallNis desirable to maximize capacity. The frequency reuse factor is given by Hexagonal geometry has

exactly six equidistance neighbors

the lines joining the centers of any cell and each of its neighbors areseparated by multiples of 60 degrees. Only certain cluster sizes and cell layout are possible. The number of cells per cluster,N, can only have values which satisfy Co-channel neighbors of a particular cell, ex, i=3andj=2.

The Cellular Concept Cellular hierarchy


33/108



Picocells Microcells Macrocells Megacells and femtocells

Fig 3.1 Cellular concept

3.2 Cell Fundamentals The use of hexagons

Reuse number Cellular reuse patterns

Fig 3.2 Frequency reuse concept

Frequency reuse scheme increases capacity


34/108



minimize interference Channel assignment strategy

fixed channel assignment dynamic channel assignment

Fixed channel assignment

each cell is allocated a predetermined set of voice channel any new call attempt can only be served by the unused channels the call will be blockedif all channels in that cell are occupied

Dynamic channel assignment channels are not allocated to cells permanently. allocate channels based on request. reduce the likelihood of blocking, increase capacity.

Cell Fundamentals Reuse number

Frequency reuse distance The reuse distance can be calculated by using the equation:

Fig 3.3 Frequency Reuse number

Cell Fundamentals Cellular interference issues

Signal-to-interference ratio Channel assignments

Fig 3.4 Cellular calculations

3.3 Capacity Expansion Techniques

Cell splitting


35/108



Split congested cell into smaller cells. Preserve frequency reuse plan. Reduce transmission power.

Transmission power reduction from to Examining the receiving power at the new

and old cell boundary

If we take n = 4and set the received power equal to each other

The transmit power must be reduced by 12 dB in order to fill in the originalcoverage area.

Problem: if only part of the cells are splited Different cell sizes will exist simultaneously

Handoff issues - high speed and low speed traffic can be simultaneouslyaccommodated

Fig 3.5 cell splitting

Capacity Expansion Techniques Cell sectoring

Sectoring concept

Decrease the co-channel interference and keep the cell radiusRunchanged Replacing single omni-directional antenna by several directional antennas Radiating within a specified sector


36/108



Fig 3.6 Cell sectoring

Capacity Expansion Techniques Overlaid cells

Overlay concept

Fig 3.7 Cell overlaid

Capacity Expansion Techniques Channel allocation Other capacity expansion schemes

Lees microcell technology Smart antenna technology Migration to digital technology

3.4 Cellular Backhaul Networks Introduction Standards for PSTN carriers


37/108



Fig 3.8 cellular backhaul network

Fig 3.9 cellular backhaul network

3.5 Mobility Management

Location management Need Frequency Location updating


38/108



Fig 3.10 Location management in cellular network

Mobility Management Paging messages Different paging schemes Transmission of the location information between network elements

Mobility Management Handoff management

Handoff control Handoff operation

Handoff algorithm

When a mobile moves into a different cell while a conversation is in progress, theMSC automatically transfers the call to a new channel belonging to the new base

station.

Handoff operation identifying a new base station re-allocating the voice and control channels with the new base station.

Handoff Threshold Minimum usable signal for acceptable voice quality (-90dBm to -100dBm) Handoff margin cannot be too large or too small.

If it is too large, unnecessary handoffs burden the MSC If it is too small, there may be insufficient time to complete handoff before

a call is lost.


39/108



Fig 3.10 Mobility management in cellular network

Handoff must ensure that the drop in the measured signal is not due to momentaryfading and that the mobile is actually moving away from the serving base station.

Running average measurement of signal strength should be optimized so thatunnecessary handoffs are avoided.

Depends on the speed at which the vehicle is moving. Steep short term average -> the hand off should be made quickly The speed can be estimated from the statistics of the received short-term

fading signal at the base station

Dwell time: the time over which a call may be maintained within a cell withouthandoff.

Dwell time depends on propagation interference distance speed


40/108



Handoff measurement In first generation analog cellular systems, signal strength measurements

are made by the base station and supervised by the MSC. In second generation systems (TDMA), handoff decisions are mobile

assisted, called mobile assisted handoff (MAHO)

Intersystem handoff: If a mobile moves from one cellular system to a differentcellular system controlled by a different MSC. Handoff requests is much important than handling a new call.

Different type of users

High speed users need frequent handoff during a call.

Low speed users may never need a handoff during a call.

Microcells to provide capacity, the MSC can become burdened if high speed users

are constantly being passed between very small cells. Minimize handoff intervention handle the simultaneous traffic of high speed and low speed users.

Large and small cells can be located at a single location (umbrella cell) different antenna height different power level

Cell dragging problem: pedestrian users provide a very strong signal to the basestation

The user may travel deep within a neighboring cell

Handoff for first generation analog cellular systems ,10 secs handoff time, is in theorder of 6 dB to 12 dB,Handoff for second generation cellular systems, e.g., GSM 1 to

2 seconds handoff time, mobile assists handoff , is in the order of 0 dB to 6 dB

Handoff decisions based on signal strength, co-channel interference, and adjacentchannel interference.

IS-95 CDMA spread spectrum cellular system ,Mobiles share the channel in every

cell.No physical change of channel during handoff ,MSC decides the base station withthe best receiving signal as the service station Handoff within a cell, No channel re-

assignment, Switch the channel to a different zone site, Reduce interference, Low

power transmitters are employed

Frequency reuse - there are several cells that use the same set of frequencies co-channel cells co-channel interference

To reduce co-channel interference, co-channel cell must be separated by aminimum distance.

When the size of the cell is approximately the same


41/108



co-channel interference is independent of the transmitted power co-channel interference is a function of

R: Radius of the cell D: distance to the center of the nearest co-channel cell

Increasing the ratio Q=D/R, the interference is reduced.

Qis called the co-channel reuse ratio

Fig 3.11 Handoff management


42/108



Fig 3.12 analysis of handoff operation

3.6 Radio Resources and Power Management

Power control Power saving schemes

Discontinuous transmission Sleep modes

Energy efficient designs Radio resource management

Need Schemes

3.7 Wireless Network Security

Wireless network security requirements Network security requirements Network security


43/108



UNIT - 4

GSM and TDMA techniques, GSM system overview, GSM Network and systemArchitecture, GSM channel concepts, GSM identifiers

6 Hours

TEXT BOOK:


REFERENCE BOOKS:1. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002.




Cambridge 2005.


44/108



Unit-4

GSM AND TDMA TECHNOLOGIES

4.1 Introduction to GSM and TDMA

Global System for Mobile Communications (GSM) servicesare a standard collection of

applications and features available to mobile phone subscribers all over the world. TheGSM standards are defined by the 3GPP collaboration and implemented in hardware andsoftware by equipment manufacturers and mobile phone operators. The common standard

makes it possible to use the same phones with different companies' services, or even roam

into different countries. GSM is the world's most dominant mobile phone standard.

The design of the service is moderately complex because it must be able to locate a moving

phone anywhere in the world, and accommodate the relatively small battery capacity,

limited input/output capabilities, and weak radio transmitters on mobile devices.

In order to gain access to GSM services, a user needs three things:

A billing relationship with a mobile phone operator. This is usually either where

services are paid for in advance of them being consumed (prepaid), or where billsare issued and settled after the service has been consumed (postpaid).

A mobile phone that is GSM compliant and operates at the same frequency as the

operator. Most phone companies sell phones from third-party manufacturers.

A Subscriber Identity Module (SIM) card, which is activated by the operator oncethe billing relationship is established. After activation the card is then programmed

with the subscriber's Mobile Subscriber Integrated Services Digital Network

Number (MSISDN) (the telephone number). Personal information such as contactnumbers of friends and family can also be stored on the SIM by the subscriber.

After subscribers sign up, information about their identity (telephone number) and whatservices they are allowed to access are stored in a "SIM record" in the Home Location

Register (HLR).

Once the SIM card is loaded into the phone and the phone is powered on, it will search for

the nearest mobile phone mast (also called a Base Transceiver Station/BTS) with the

strongest signal in the operator's frequency band. If a mast can be successfully contacted,

then there is said to be coverage in the area. The phone then identifies itself to the networkthrough the control channel. Once this is successfully completed, the phone is said to be

attached to the network.

The key feature of a mobile phone is the ability to receive and make calls in any area where

coverage is available. This is generally called roaming from a customer perspective, but

also called visiting when describing the underlying technical process. Each geographic areahas a database called the Visitor Location Register (VLR), which contains details of all the

mobiles currently in that area. Whenever a phone attaches, or visits, a new area, the Visitor

Location Register must contact the Home Location Register to obtain the details for thatphone. The current cellular location of the phone (i.e., which BTS it is at) is entered into


45/108



the VLR record and will be used during a process called paging when the GSM network

wishes to locate the mobile phone.

Every SIM card contains a secret key, called the Ki, which is used to provide authentication

and encryption services. This is useful to prevent theft of service, and also to prevent "over

the air" snooping of a user's activity. The network does this by utilising the AuthenticationCenter and is accomplished without transmitting the key directly.

Every GSM phone contains a unique identifier (different from the phone number), calledthe International Mobile Equipment Identity (IMEI). This can be found by dialing *#06#.

When a phone contacts the network, its IMEI may be checked against the Equipment

Identity Register to locate stolen phones and facilitate monitoring.

TDMA

It can be easily adapted to the transmission of data and voice communication.TDMA offers the ability to carry data rates of 64 kbps to 120 Mbps (expandable in

multiples of 64 kbps). This enables operators to offer personal communication-likeservices including fax, voiceband data, and short message services (SMSs) as well as

bandwidth-intensive applications such as multimedia and videoconferencing.

It will not experience interference from other simultaneous transmissions

Unlike spread-spectrum techniques which can suffer from interference among the

users all of whom are on the same frequency band and transmitting at the same time,TDMAs technology, which separates users in time, ensures that they will not

TDMA is the only technology that offers an efficient utilization

of hierarchical cell structures (HCSs) offering pico, micro, and macrocells. HCSsallow coverage for the system to be tailored to support specific traffic and service


46/108



needs. By using this approach, system capacities of more than 40-times AMPS can

be achieved in a cost-efficient way. TDMA allows service compatibility with the use of

dual-mode handsets because of its inherent compatibility with FDMA analog systems.

4.2 GSM Network and System ArchitectureMobile station

Subscriber identity module

Base station system

Network switching system

SMS gateway

Flexible numbering register

Operation and support system and other nodes

Administrative and control system

Fig 4.1 components of GSM network

GSM network interfaces and protocols

GSM interfaces

Abis interface

A interface


47/108



Um interface

Layered structure/OSI model

Fig 4.2 interfaces in GSM

GSM network interfaces and protocols

GSM protocols and signaling model

Um interface

Abis interface

A interface

Ater interface

The network structure is defined within the GSM standards. Additionally each interface

between the different elements of the GSM network is also defined. This facilitates the

information interchanges can take place. It also enables to a large degree that network

elements from different manufacturers can be used. However as many of these interfaceswere not fully defined until after many networks had been deployed, the level of

standardisation may not be quite as high as many people might like.

1. Um in terf ace The "air" or radio interface standard that is used for exchangesbetween a mobile (ME) and a base station (BTS / BSC). For signalling, a modified

version of the ISDN LAPD, known as LAPDm is used.

2. Abis interf ace This is a BSS internal interface linking the BSC and a BTS, and ithas not been totally standardised. The Abis interface allows control of the radio

equipment and radio frequency allocation in the BTS.

3. A interf ace The A interface is used to provide communication between the BSSand the MSC. The interface carries information to enable the channels, timeslots

and the like to be allocated to the mobile equipments being serviced by the BSSs.


48/108



The messaging required within the network to enable handover etc to be undertaken

is carried over the interface.

4. B in terf ace The B interface exists between the MSC and the VLR . It uses aprotocol known as the MAP/B protocol. As most VLRs are collocated with an

MSC, this makes the interface purely an "internal" interface. The interface is used

whenever the MSC needs access to data regarding a MS located in its area.5. C in terf ace The C interface is located between the HLR and a GMSC or a SMS-G.When a call originates from outside the network, i.e. from the PSTN or another

mobile network it ahs to pass through the gateway so that routing information

required to complete the call may be gained. The protocol used for communicationis MAP/C, the letter "C" indicating that the protocol is used for the "C" interface. In

addition to this, the MSC may optionally forward billing information to the HLR

after the call is completed and cleared down.

6. D in terf ace The D interface is situated between the VLR and HLR. It uses theMAP/D protocol to exchange the data related to the location of the ME and to the

management of the subscriber.

7. E in terf ace The E interface provides communication between two MSCs. The Einterface exchanges data related to handover between the anchor and relay MSCsusing the MAP/E protocol.

8. F interface The F interface is used between an MSC and EIR. It uses the MAP/Fprotocol. The communications along this interface are used to confirm the status ofthe IMEI of the ME gaining access to the network.

9. G interf ace The G interface interconnects two VLRs of different MSCs and usesthe MAP/G protocol to transfer subscriber information, during e.g. a locationupdate procedure.

10.H interface The H interface exists between the MSC the SMS-G. It transfers shortmessages and uses the MAP/H protocol.

11.I interf ace The I interface can be found between the MSC and the ME. Messagesexchanged over the I interface are relayed transparently through the BSS.

Although the interfaces for the GSM cellular system may not be as rigorously defined asmany might like, they do at least provide a large element of the definition required,

enabling the functionality of GSM network entities to be defined sufficiently.


49/108



Fig 4.3 GSM network interfaces and protocols

4.3 GSM Channel Concept Time division multiple access

Frames

Multiframes

A single GSM RF carrier can support up to eight MS subscribers simultaneously. Eachchannel occupies the carrier for one eighth of the time.

This is a technique called Time Division Multiple Access. Time is divided into discreteperiods called timeslots . The timeslots are arranged in sequence and are

conventionally numbered 0 to 7. Each repetition of this sequence is called a TDMA

frame . Each MS telephone call occupies one timeslot (07) within the frame until the

call is terminated, or a handover occurs.

The TDMA frames are then built into further frame structures according to the type ofchannel. We shall later examine how the information carried by the air interface builds into

frames and multi-frames and discuss the associated timing. For such a system to work

correctly, the timing of the transmissions to and from the mobiles is critical. The MS or

Base Station must transmit the information related to one call at exactly the right moment,or the timeslot will be missed. The information carried in one timeslot is called a

burst . Each data burst, occupying its allocated timeslot within successive TDMA

frames, provides a single GSM physical channel carrying a varying number of logicalchannels between the MS and BTS.


50/108



Fig 4.4 TDMA time frame structure

GSM Channel Concept

Logical channels

Broadcast channels

Broadcast control channel

Frequency correction channel

Synchronization channel

Logical channels

Common control channels

Paging channel

Random access channel

Access grant channel

Dedicated control channels

Stand-alone dedicated control channel

Slow associated control channel

Fast associated control channel

Cell broadcast channel

Speech processing

Operations

Bit rate

GSM speech processing


51/108



Fig 4.5 GSM processing of speech

Timeslots and TDMA frames

TDMA frames

TDMA multiframes

Hyperframes

Superframes

Multiframes

26 frame

51 frame

Timeslot bursts

Normal burst

Frequency correction burst

Synchronization burst

Access burst

Dummy burst


52/108



Fig 4.6 TDMA Hyperframe structure

A hyperframe is a multiframe sequence that is composed of 2048 superframes and is

largest time interval in the GSM system (3 hours, 28 minutes, 53 seconds). Every time slotduring a hyperframe has a sequential number (represented by an 11 bit counter) that is

composed of a frame number and a time slot number. This counter allows the hyperframe

to synchronize frequency hopping sequence, encryption processes for voice privacy ofsubscribers' conversations. The hyperframe in an IS-136 TDMA system consists of 192

frames.

The basic GSM frame defines the structure upon which all the timing and structure of theGSM messaging and signalling is based. The fundamental unit of time is called a burst

period and it lasts for approximately 0.577 ms (15/26 ms). Eight of these burst periods are

grouped into what is known as a TDMA frame. This lasts for approximately 4.615 ms(i.e.120/26 ms) and it forms the basic unit for the definition of logical channels. One

physical channel is one burst period allocated in each TDMA frame.

In simplified terms the base station transmits two types of channel, namely traffic andcontrol. Accordingly the channel structure is organised into two different types of frame,

one for the traffic on the main traffic carrier frequency, and the other for the control on thebeacon frequency.

GSM multiframe


53/108



The GSM frames are grouped together to form multiframes and in this way it is possible to

establish a time schedule for their operation and the network can be synchronised.

There are several GSM multiframe structures:

Traff ic multifr ame: The Traffic Channel frames are organised into multiframesconsisting of 26 bursts and taking 120 ms. In a traffic multiframe, 24 bursts are used

for traffic. These are numbered 0 to 11 and 13 to 24. One of the remaining bursts is

then used to accommodate the SACCH, the remaining frame remaining free. Theactual position used alternates between position 12 and 25.

Control mul tif rame: the Control Channel multiframe that comprises 51 bursts and

occupies 235.4 ms. This always occurs on the beacon frequency in time slot zero

and it may also occur within slots 2, 4 and 6 of the beacon frequency as well. Thismultiframe is subdivided into logical channels which are time-scheduled.

GSM Superframe

Multiframes are then constructed into superframes taking 6.12 seconds. These consist of 51traffic multiframes or 26 control multiframes. As the traffic multiframes are 26 bursts long

and the control multiframes are 51 bursts long, the different number of traffic and control

multiframes within the superframe, brings them back into line again taking exactly the

same interval.

GSM Hyperframe

Above this 2048 superframes (i.e. 2 to the power 11) are grouped to form one hyperframewhich repeats every 3 hours 28 minutes 53.76 seconds. It is the largest time interval within

the GSM frame structure.

Within the GSM hyperframe there is a counter and every time slot has a unique sequential

number comprising the frame number and time slot number. This is used to maintainsynchronisation of the different scheduled operations with the GSM frame structure. These

include functions such as:

Frequency hopping: Frequency hopping is a feature that is optional within the

GSM system. It can help reduce interference and fading issues, but for it to work,

the transmitter and receiver must be synchronised so they hop to the samefrequencies at the same time.

Encryption: The encryption process is synchronised over the GSM hyperframe

period where a counter is used and the encryption process will repeat with eachhyperframe. However, it is unlikely that the cellphone conversation will be over 3

hours and accordingly it is unlikely that security will be compromised as a result.


54/108



UNIT - 5

GSM system operation, Traffic cases, Cal handoff, Roaming, GSM protocol architecture.

TDMA systems

6 Hours

TEXT BOOK:


REFERENCE BOOKS:1. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002.



Cambridge 2005.


55/108



UNIT-5

GSM SYSTEM OPERATIONS

5.1 GSM IdentitiesTo switch a call to a mobile subscriber, the right identities need to be involved. It istherefore important to address them correctly. Followings are those identities;

Mobile Station ISDN Number (MSISDN)

The MSISDN is a number, which uniquely identifies a mobile telephone

subscription in the public switched telephone network numbering plan. These arethe digits dialed when calling a mobile subscriber.

The MSISDN is consisted with followings;

Country Code (CC)

National Destination Code (NDC)

Subscriber Number (SN)

MSISDN = CC + NDC + SN

International Mobile Subscriber Identity (IMSI)

The IMSI is a unique identity allocated to each subscriber to allow correct

identification over the radio path and through the network and is used for allsignaling in the PLMN. All network-related subscriber information is connected to

the IMSI. The IMSI is stored in the SIM, as well as in the HLR and in the serving

VLR.

The IMSI is consisted with followings;

Mobile Country Code (MCC)

Mobile Network Code (MNC)

Mobile Subscriber Identification Number (MSIN)

IMSI = MCC + MNC + MSIN

Temporary Mobile Subscriber Identity (TMSI)

The TMSI is a temporary number used instead of IMSI to identify an MS. The

TMSI is used for the subscribers confidentiality on the air interface. The TMSI has

only local significance (that is, within the MSC/VLR area) and is changed at certain

events or time intervals.


56/108



International Mobile Equipment Identity (IMEI)

The IMEI is used for equipment identification and uniquely identifies a MS as a

piece or assembly of equipment.

The IMEI is consisted with followings;

Type Approval Code (TAC), determined by a central GSM body

Final Assembly Code (FAC), identifies the manufacture

Serial Number (SNR), uniquely identifies all equipment within each TAC &

FAC

Spare, a spare bit for future use.

IMEI = TAC + FAC + SNR + Spare

Mobile Station Roaming Number (MSRN)

A MSRN is used during the call setup phase for mobile terminating calls. Each

mobile terminating call enters the GMSC in the PLMN. The call is then re-routedby the GMSC, to the MSC where the called mobile subscriber is located. For this

purpose MSRN is allocated by the MSC and provided to the GMSC.

The MSRN is consisted with followings;

Country Code (CC)

National Destination Code (NDC)

Subscriber Number (SN)

MSRN = CC + NDC + SN

Location Area Identity (LAI)

The LAI is used for paging, to indicate to the MSC in which Location Area (LA)the MS is currently situated and also for location updating of mobile subscribers.

The LAI is consisted with followings;



Location Area Code (LAC)

LAI = MCC + MNC + LAC


57/108



Cell Global Identity (CGI)

Each cell is identified by cell identity (CI). A CI is unique within a location area(LA).

CGI is consisted with following;



Location Area Code (LAC)

Cell Identity (CI)

CGI = MCC + MNC + LAC + CI

Base Station Identification Code (BSIC)

In GSM, the mobile station uses BSIC to distinguish between neighboring basestation.

The BSIC is consisted with

Network Colour Code (NCC)

Base Transceiver Colour Code (BCC).

5.2 GSM System Operations (Traffic Cases)Registration, call setup, and location updating

Call setup

Interrogation phase

Radio resource connection establishment

Service request

Authentication

GSM System Operations (Traffic Cases)

Call setup

Ciphering mode setting

IMEI check

TMSI reallocation

Call initiation procedure


58/108



Assignment of a traffic channel

Call confirmation, call accepted, and call release


Other aspects of call establishment

Location updating

Normal location updating (idle mode)

IMSI detach/attach location updating

Periodic location updating

Fig 5.1 GSM channel assignment


59/108



Fig 5.2 GSM channel establishment


Call handoff

Intra-BSC handover

The process that occurs during the handover intra BSC as follows:

A). During the call, MS will measure the strength and quality of the signal on the

TCH and the signal strength from the neighboring cell. MS to evaluate and assessthe average for each cell.

MS send the results to the BTS measurements every two times in one second cell

not only on their own but also the results of measurements from the BTS

neighboring cell.

B). The BTS will send the results of measurements on the TCH to the BSC. In the

BSC, the function is activated when the placement is required to handover to

another cell.

C). When the handover is done, BSC will check whether the channel had requested

be met by another cell, if not the BSC will be the new BTS to enable TCH.

D). BSC will ask the BTS for a long time to send a message to MS with information

about the frequency, time slot, and the output power for the change.

E). MS choose a new frequency handover and access to the appropriate time slot.

F). When the BTS to detect the handover, the BTS will send the informationcontains the physical "timing advance" (the distance between MS to the BTS) to


60/108



MS. BTS also inform the BSC to send a "message HO detection" so that point on

the new GS is connected.

G). MS send a "HO complete message."

H). Last time the BTS ordered not to activate the old TCH.

Fig 5.3 Intra BSC handover

Inter-BSC handoverIn this case BSC1, (old BSC) does not control the better cell which is the target for

the handover. This means that the MSC will be part of the link procedure between

BSC1 and BSC2 (new BSC).Handover request - BSC1 will use the MSC to send a handover request to

BSC2. The MSC will know which BSC controls that cell.Activation of new channel - BSC2 will allocate a TCH in the targetcell and thenorder the BTS to activate it. The chosen HO ref. no. will be part of the activation

message. The BTS will acknowledge that the activation has been made.

Handover command - After the activation the new BSC commands the MS tochange to the new channel. The message is sent on FACCH via the old channel and

will contain a full description of the new channel and the HO ref. no.


61/108



3. Handover bursts - When the MS has changed to the new channel, it will send

handover bursts on the new channel. The information content is the HO ref. no.

The bursts are as short as the access bursts. This is because the MS does not knowthe new Timing Advance (TA) value yet. On the detection of the handover bursts,

and check of HO ref. no., the new BTS will send the new TA.

4. Handover complete - Now the MS is ready to continue the traffic and willsend a handover complete message, which will be addressed to the old BSC as

a clear command.

5. Release of old channel - When the old BSC receives the clear command

from the MSC, the BSC knows that the handover was successful. The BSC

orders the BTS to release the TCH and the BTS will acknowledge.

Fig 5.4 Inter BSC handover

Inter-MSC handover

Handing over a GSM call is a complicated procedure. It is even more so when thesource and target GSM cells are controlled by different MSCs. The following call flows

analyze the different steps involved in a inter-MSC handover:

The source BSC analyzes the signal quality measurement reports and initiates a

handover.

The source MSC finds that the call needs to be handed over to a cell controlled by adifferent MSC.


62/108



The source MSC and target MSC interact and then command the UT to move to the

new cell.

The target MSC informs the source MSC when the call has been successfullyhanded over.

The source MSC releases the radio resources for the call. Note that the call is still

routed via the source MSC

Fig 5.5 Inter MSC handover

GSM Infrastructure Communications (Um Interface)

A GSM network is a bearer data communication protocol families. Any protocol stackfor data communication, for example TCP/IP, can be implemented to use a bearer.

GSM protocol architecture is - as for ISDN - structured into three independent planes .

User plane ,Control plane,Management plane

The user plane defines protocols to carry connection oriented voice and user data. At

the radio interface Um, user plane data will be carried by the logical traffic channel

called TCH. The control plane defines a set of protocols for controlling these

connections with signalling information, for example signalling for connection setup.Such signalling data is carried over logical control channels called D-channels (Dm-


63/108



channels). As the control channels often have spare capacities, also user data, the

packet oriented SMS data, is transported over these channels (see Figure gsm8). All

logical channels, however, will be finally multiplexed onto the physical channel.

Management plane function are:

plane management functions related to the system as a whole including planecoordination

functions related to resources and parameters residing in the layers of the control

and/or user plane.

Management of network element configuration and network element faults are

examples of management plane functionality

The basic GSM bearer service, Circuit Switched Data (CSD), simply consists of

transmitting and receiving signals representing data instead of voice across the airinterface. Modems are used for the conversion between data bit streams and modulated

radio signals. Data transmission is either transparent or non-transparent.


64/108



Fig: 5.6 Three layers of interface in GSM


65/108



Fig: 5.7 Linking of Three layers of interface in GSM


Layer 3: Networking layer operations

Connection management

Mobility management

Radio resource management


66/108



Fig: 5.8 Linking of RR, RM and MM in GSM


Layer 2: Data Link layer operations

LAPD operations

Service access points

Data link procedures

Physical services required by the Data Link layer

Data link timers

North American TDMA

TIA/EIA-136 basics

TIA/EIA-136 channel concept

TIA/EIA-136 timeslots and frame details


67/108



Fig: 5.9 NA -TDMA structure


68/108



UNIT - 6

CDMA technology, CDMA overview, CDMA channel concept CDMA operations.

8 Hours

TEXT BOOK:


REFERENCE BOOKS:




Cambridge 2005.


69/108



UNIT- 6

CDMA TECHNOLOGY

6.1 Introduction to CDMA

Cellular services are now being used every day by millions of people worldwide. Thenumber of customers requiring such services is increasing exponentially, and there is a

demand for integration of a variety of multimedia services. The range of services includes

short messaging, voice, data, and video. Consequently, the bit rate required for the services

varies widely from just 1.2 kbps for paging up to several Mbps for video transmission.Furthermore, supporting such a wide range of data rates with flexible mobility management

increases network complexity dramatically.

The CDMA is a digital modulation and radio access system that employs signature codes(rather than time slots or frequency bands) to arrange simultaneous and continuous access

to a radio network by multiple users. Contribution to the radio channel interference inmobile communications arises from multiple user access, multipath radio propagation,

adjacent channel radiation and radio jamming.

The spread spectrum systems performance is relatively immune to radio interference. Cell

sectorisation and voice activity used in CDMA radio schemes provide additional capacity

compared to FDMA and TDMA. However, CDMA still has a few drawbacks, the main onebeing that capacity (number of active users at any instant of time) is limited by the access

interference. Furthermore, Near-far effect requires an accurate and fast power control

scheme. The first cellular CDMA radio system has been constructed in conformity with IS-95 specifications and is now known commercially as cdmaOne.

Fig 6.1 comparison of different techniques


70/108



Fig 6.2 channel allocation

6.2 CDMA Network and System Architecture

There is increasing demand for data traffic over mobile radio. The mobile radio industry has toevolve the current radio infrastructures to accommodate the expected data traffic with the efficientprovision of high-speed voice traffic. The General Packet Radio Service (GPRS) is being introduced

to efficiently support high-rate data over GSM. GPRS signalling and data do not travel throughGSM network. The GPRS operation is supported by new protocols and new network nodes:Serving GPRS support node (SGSN) and Gateway GPRS support node (GGSN). One prominentprotocol used to tunnel data through IP backbone network is the GPRS tunnel protocol (GTP).GPRS obtains user profile data using location register database of GSM network. GPRS supportsquality of service and peak data rate of up to 171.2 kbps with GPRS using all 8 timeslots at thesame time. GPRS uses the same modulation as that used in GSM, that is Gaussian Minimum ShiftKeying (GMSK) with 4 coding schemes. GPRS packetises the user data and transports it over 1 to8 radio channel timeslots using IP backbone network.

The Enhanced Data Rates for GSM Evolution (EDGE) employs an Enhanced GPRS (EGPRS) tosupport data rate up to 384 kbps through optimised modulation. EGPRS support 2 modulationschemes, namely GMSK with 4 coding schemes and 8-PSK with 5 coding schemes. Unlike GPRS

where header and data are encoded together, headers are encoded separately in EGPRS.

Fig 6.3 Network architecture of CDMA

CDMA Network and System Architecture


71/108



Mobile-services switching center and visitor location register Interworking function Mobile positioning system Unified messaging/voice mail service HLR/AC, PPCS, and other nodes

Fig 6.3 Packet Network architecture of CDMA

6.2 CDMA Network and System Architecture

Base station subsystem Base station controller Radio base station

PLMN subnetwork Circuit core network CDMA radio access network

CDMA Network and System Architecture

PLMN subnetwork Packet core network

AAA server Home agent Packet data serving node Foreign agent


72/108



Fig 6.5 Packet core Network architecture of CDMA

CDMA Network and System Architecture Network management system

Network management Subnetwork management and element management

System communications links

Fig 6.6 Network interface architecture of CDMA

6.3 CDMA Channel Concept


73/108



Introduction to Walsh codes

Characteristics Other pseudorandom noise codes Short and long PN codes

Spreading procedure

Fig 6.7 CDMA channel concept

The IS-95 CDMA system is a narrow band radio system. Bandwidth is limited to 1.25 MHzand a chip rate of 1.2288 Mcps. The system is intended to provide voice and low bit ratedata service using circuit-switching techniques. Data rate varies from 1.2 kbps to 9.6 kbps.

Forward (base station to mobile) and reverse (mobile to base station) link structures are

different and each is capable of distinctive capacity. Forward transmission is coherent andsynchronous while the reverse link is asynchronous. The 'chanellisation' in each link is

achieved by using 64- chip orthogonal codes, including provision for pilot,

synchronisation, paging, and network access. Consequently, the number of active users

able to simultaneously access the network is limited by the level of interference, serviceprovisions and the number of 'channels' available. In IS-95B, an active mobile always has a

fundamental code channel at 9.6 kbps and when high data rate is required, the base station

assign the mobile up to 7 supplementary code channels.

The Wideband CDMA (W-CDMA) system is the major standard in the next-generation

Global Mobile Telecommunications standard suite IMT-2000. The W-CDMA supports


74/108



high data rate transmission, typically 384 kbps for wide area coverage and 2 Mbps for local

coverage for multimedia services. Thus W-CDMA is capable of offering the transmission

of voice, text, data, picture (still image) and video over a single platform. However, inaddition to the drawbacks arising from the mobile environment and multiple access

interference, high bit rate transmission causes Inter-symbol interference (ISI) to occur. The

ISI therefore has to be taken into account during transmission. The W-CDMA has 2versions: frequency division duplex (FDD) and time division duplex (TDD).

The FDD version of W-CDMA will operate in either of the following paired bands:

Uplink: 1920 - 1980 MHz Downlink: 2110 - 2170 MHz

Uplink: 1850 - 1010 MHz Downlink: 1930 - 1990 MHz

The 3GPP architecture of the Universal Mobile Telecommunications System (UMTS) iscomposed of IP-based core network (CN) connected to the user equipment through UMTS

Terrestrial Radio Access Network (UTRAN). The UTRAN consists of a set of radionetwork subsystem comprising a radio controller and one or more node base station. Thenetwork controller is responsible for the handover decisions that require signalling to the

user equipment. Each subsystem is responsible for the resources of its set of cells and each

node B has one or more cells.

Fig 6.8 Walsh code in CDMA

CDMA Channel Concept

Forward logical channels Pilot channel Synchronization channel Paging channel Traffic/power control channels


75/108



Fig 6.9 I channel pilot signals

Fig 6.10 Power control systems

CDMA Channel Concept

Reverse logical channels Differences from forward channel


76/108

Documents

Ece Viii Wireless Communication [10ec81] Notes