EEE 464 EEE 464 Wireless Communications Lecture 9 Shahzad Malik, Ph.D. [email protected]

EEE 464EEE 464 Wireless

Communications

Lecture 9

Shahzad Malik, Ph.D.

[email protected]

Wireless Data Networks

This lecture discusses wireless LANs, IEEE Wireless PANs (Bluetooth) and Wireless

MANs

Shahzad Malik Lecture 9 3Wireless Communications – Wireless Data

WiFi - IEEE 802.11

Bluetooth - IEEE 802.15

WiMax - IEEE 802.16

Mobile IP

MANETs (Routing)

Integration (Cellular + WLAN)

Organization of LectureOrganization of Lecture


Wireless LANs: Characteristics

Advantages Flexible deployment; Minimal wiring problems

More robust against disasters

Historic buildings, conferences, …

Disadvantages Low bandwidth compared to wired networks

Need to follow wireless spectrum regulations


infrared vs. radio transmission

Infrared uses IR diodes, diffuse

light, multiple reflections (walls, furniture etc.)

Advantages simple, cheap, available in

many mobile devices no licenses needed simple shielding possible

Disadvantages interference by sunlight,

heat sources etc. many things shield or

absorb IR light low bandwidth

Example IrDA (Infrared Data

Association) interface available everywhere

Radio typically using the license

free ISM band at 2.4 GHz Advantages

experience from wireless WAN and mobile phones can be used

coverage of larger areas possible (radio can penetrate walls, furniture etc.)

Disadvantages very limited license free

frequency bands shielding more difficult,

interference with other electrical devices

Example WiFi, HIPERLAN, Bluetooth


infrastructure vs. ad-hoc networks

infrastructure network

ad-hoc network

APAP

AP

wired network

AP: Access Point

IEEE 802.11 (WiFi)


IEEE 802.11 Wireless LAN

802.11/802.11b2.4-5 GHz unlicensed

radio spectrumup to 11 Mbpsdirect sequence

spread spectrum (DSSS) in physical layer

all hosts use same chipping code

widely deployed, using base stations

802.11a 5-6 GHz rangeup to 54 Mbps

802.11g 2.4-5 GHz rangeup to 54 Mbps

All use CSMA/CA for multiple access

All have base-station and ad-hoc network versions


802.11 - Architecture of an infrastructure network

Station (STA) terminal with access

mechanisms to the wireless medium and radio contact to the access point

Basic Service Set (BSS) group of stations using the

same radio frequencyAccess Point

station integrated into the wireless LAN and the distribution system

Portal bridge to other (wired)

networksDistribution System

interconnection network to form one logical network (EES: Extended Service Set) based on several BSS

Distribution System

Portal

802.x LAN

Access Point

802.11 LAN

BSS2

802.11 LAN

BSS1

Access Point

STA1

STA2 STA3

ESS


802.11 - Architecture of an ad-hoc network

Direct communication within a limited range

Station (STA):terminal with access mechanisms to the wireless medium

Independent Basic Service Set (IBSS):group of stations using the same radio frequency

802.11 LAN

IBSS2

802.11 LAN

IBSS1

STA1

STA4

STA5

STA2

STA3


IEEE standard 802.11

mobile terminal

access point

fixedterminal

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLC

infrastructurenetwork

LLC LLC


802.11: Channels, association

802.11: 2.4GHz-2.485GHz spectrum divided into 11 channels at

different frequencies

AP admin chooses frequency for AP

interference possible: channel can be same as that

chosen by neighboring AP!

host: must associate with an APscans channels, listening for beacon frames containing

AP’s name (SSID) and MAC address

selects AP to associate with

may perform authentication

will typically run DHCP to get IP address in AP’s subnet


802.11 - Layers and functions

PLCP Physical Layer Convergence Protocol

clear channel assessment signal (carrier sense)

PMD Physical Medium Dependent

modulation, coding PHY Management

channel selection, MIB Station Management

coordination of all management functions

PMD

PLCP

MAC

LLC

MAC Management

PHY Management

MACaccess mechanisms,

fragmentation, encryption MAC Management

synchronization, roaming, MIB, power management

PH

YD

LC

Sta

tion

Man

agem

ent


802.11 - Physical layer

3 versions: 2 radio (typ. 2.4 GHz), 1 IR data rates 1 or 2 Mbit/s

FHSS (Frequency Hopping Spread Spectrum) spreading, despreading, signal strength, typ. 1 Mbit/s min. 2.5 frequency hops/s (USA), two-level GFSK modulation

DSSS (Direct Sequence Spread Spectrum) DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift

Keying), DQPSK for 2 Mbit/s (Differential Quadrature PSK) preamble and header of a frame is always transmitted with 1

Mbit/s, rest of transmission 1 or 2 Mbit/s chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1

(Barker code) max. radiated power 1 W (USA), 100 mW (EU), min. 1mW

Infrared 850-950 nm, diffuse light, typ. 10 m range carrier detection, energy detection, synchonization


802.11 - MAC layer

Traffic services Asynchronous Data Service (mandatory)

exchange of data packets based on “best-effort” support of broadcast and multicast

Time-Bounded Service (optional) implemented using PCF (Point Coordination Function)

Access methods DCF CSMA/CA (mandatory)

collision avoidance via randomized „back-off“ mechanism

minimum distance between consecutive packets ACK packet for acknowledgements (not for broadcasts)

DCF w/ RTS/CTS (optional) Distributed Foundation Wireless MAC avoids hidden terminal problem

PCF (optional) access point polls terminals according to a list


802.11 - MAC layer

Priorities defined through different inter-frame spaces no guaranteed, hard priorities SIFS (Short Inter Frame Spacing)

highest priority, for ACK, CTS, polling response PIFS (PCF IFS)

medium priority, for time-bounded service using PCF DIFS (DCF, Distributed Coordination Function IFS)

lowest priority, for asynchronous data service

t

medium busySIFS

PIFS

DIFSDIFS

next framecontention

direct access if medium is free DIFS


802.11 - CSMA/CA access method

Sending unicast packets station has to wait for DIFS before sending data receivers acknowledge at once (after waiting for

SIFS) if the packet was received correctly (CRC) automatic retransmission of data packets in case of

transmission errors

t

SIFS

DIFS

data

ACK

waiting time

otherstations

receiver

senderdata

DIFS

contention


802.11 – RTS/CTSSending unicast packets

station can send RTS with reservation parameter after waiting for DIFS (reservation determines amount of time the data packet needs the medium)

acknowledgement via CTS after SIFS by receiver (if ready to receive)

sender can now send data at once, acknowledgement via ACKother stations store medium reservations distributed via RTS

and CTS

t

SIFS

DIFS

data

ACK

defer access

otherstations

receiver

senderdata

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)


PCF - Point Coordination Function

PIFS

stations‘NAV

wirelessstations

point coordinator

D1

U1

SIFS

NAV

SIFSD2

U2

SIFS

SIFS

SuperFramet0

medium busy

t1


802.11 - RoamingNo or bad connection? Then perform:Scanning

scan the environment, i.e., listen into the medium for beacon signals or send probes into the medium and wait for an answer

Reassociation Requeststation sends a request to one or several AP(s)

Reassociation Responsesuccess: AP has answered, station can now participatefailure: continue scanning

AP accepts Reassociation Requestsignal the new station to the distribution systemthe distribution system updates its data base (i.e.,

location information)typically, the distribution system now informs the old

AP so it can release resources


WLAN: IEEE 802.11bData rate

1, 2, 5.5, 11 Mbit/s, depending on SNR

User data rate max. approx. 6 Mbit/s

Transmission range 300m outdoor, 30m indoor Max. data rate ~10m indoor

Frequency Free 2.4 GHz ISM-band

Security Limited, WEP insecure, SSID

Cost 100€ adapter, 250€ base

station, droppingAvailability

Many products, many vendors

Connection set-up time Connectionless/always on

Quality of Service Typ. Best effort, no

guarantees (unless polling is used, limited support in products)

Manageability Limited (no automated key

distribution, sym. Encryption)Special

Advantages/Disadvantages Advantage: many installed

systems, lot of experience, available worldwide, free ISM-band, many vendors, integrated in laptops, simple system

Disadvantage: heavy interference on ISM-band, no service guarantees, slow relative speed only


WLAN: IEEE 802.11aData rate

6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNR

User throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54)

6, 12, 24 Mbit/s mandatoryTransmission range

100m outdoor, 10m indoor E.g., 54 Mbit/s up to 5 m, 48 up

to 12 m, 36 up to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60 m

Frequency Free 5.15-5.25, 5.25-5.35,

5.725-5.825 GHz ISM-bandSecurity

Limited, WEP insecure, SSIDCost

280€ adapter, 500€ base station

Availability Some products, some vendors

Connection set-up time Connectionless/always on

Quality of Service Typ. best effort, no

guarantees (same as all 802.11 products)

Manageability Limited (no automated key

distribution, sym. Encryption)Special

Advantages/Disadvantages Advantage: fits into 802.x

standards, free ISM-band, available, simple system, uses less crowded 5 GHz band

Disadvantage: stronger shading due to higher frequency, no QoS


WLAN: IEEE 802.11 – future developments

802.11e: MAC Enhancements – QoSEnhance the current 802.11 MAC to expand support for

applications with Quality of Service requirements, and in the capabilities and efficiency of the protocol.

802.11f: Inter-Access Point ProtocolEstablish an Inter-Access Point Protocol for data exchange

via the distribution system.802.11n: Data Rates > 100 Mbit/s, OFDM , MIMO802.11h: Spectrum Managed 802.11a (DCS, TPC)802.11i: Enhanced Security Mechanisms

Enhance the current 802.11 MAC to provide improvements in security.

Study Groups5 GHz (harmonization ETSI/IEEE) Radio Resource MeasurementsHigh Throughput


ETSI - HIPERLAN ETSI standard

European standard, cf. GSM, DECT, ... Enhancement of local Networks and interworking with fixed

networks integration of time-sensitive services from the early beginning

HIPERLAN family one standard cannot satisfy all requirements

range, bandwidth, QoS support commercial constraints

HIPERLAN 1 standardized since 1996 – no products!

physical layer

channel accesscontrol layer

medium access control layer

physical layer

data link layer

HIPERLAN layers OSI layers

network layer

higher layers

physical layer

medium accesscontrol layer

logical link control layer

IEEE 802.x layers

Bluetooth(IEEE 802.15)


BluetoothIdea

Universal radio interface for ad-hoc wireless connectivity Interconnecting computer and peripherals, handheld devices,

PDAs, cell phones – replacement of IrDAEmbedded in other devices, goal: 5€/device (2002: 50€/USB

bluetooth)Short range (10 m), low power consumption, license-free 2.45

GHz ISMVoice and data transmission, approx. 1 Mbit/s gross data rate

One of the first modules (Ericsson).


Bluetooth Characteristics

2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacingChannel 0: 2402 MHz … channel 78: 2480 MHzG-FSK modulation, 1-100 mW transmit power

FHSS and TDDFrequency hopping with 1600 hops/sHopping sequence in a pseudo random fashion,

determined by a masterTime division duplex for send/receive separation

Voice link – SCO (Synchronous Connection Oriented)FEC (forward error correction), no retransmission, 64 kbit/s

duplex, point-to-point, circuit switched Data link – ACL (Asynchronous ConnectionLess)

Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched

TopologyOverlapping piconets (stars) forming a scatternet


Piconet

Collection of devices connected in an ad hoc fashion

One unit acts as master and the others as slaves for the lifetime of the piconet

Master determines hopping pattern, slaves have to synchronize

Each piconet has a unique hopping pattern

Participation in a piconet = synchronization to hopping sequence

Each piconet has one master and up to 7 simultaneous slaves (> 200 could be parked)

M=MasterS=Slave

P=ParkedSB=Standby

M

S

P

SB

S

S

P

P

SB


Forming a piconetAll devices in a piconet hop together

Master gives slaves its clock and device ID Hopping pattern: determined by device ID (48 bit,

unique worldwide) Phase in hopping pattern determined by clock

AddressingActive Member Address (AMA, 3 bit)Parked Member Address (PMA, 8 bit)

SB

SB

SB

SB

SB

SB

SB

SB

SB

M

S

P

SB

S

S

P

P

SB


Scatternet

Linking of multiple co-located piconets through the sharing of common master or slave devices

Devices can be slave in one piconet and master of anotherCommunication between piconets

Devices jumping back and forth between the piconets

M=MasterS=SlaveP=ParkedSB=Standby

M

S

P

SB

S

S

P

P

SB

M

S

S

P

SB

Piconets(each with a capacity of < 1 Mbit/s)


Bluetooth protocol stack

Radio

Baseband

Link Manager

Control

HostControllerInterface

Logical Link Control and Adaptation Protocol (L2CAP)Audio

TCS BIN SDP

OBEX

vCal/vCard

IP

NW apps.

TCP/UDP

BNEP

RFCOMM (serial line interface)

AT modemcommands

telephony apps.audio apps. mgmnt. apps.

AT: attention sequenceOBEX: object exchangeTCS BIN: telephony control protocol specification – binaryBNEP: Bluetooth network encapsulation protocol

SDP: service discovery protocolRFCOMM: radio frequency comm.

PPP


Baseband link types

Polling-based TDD packet transmission 625µs slots, master polls slaves

SCO (Synchronous Connection Oriented) – Voice Periodic single slot packet assignment, 64 kbit/s full-duplex,

point-to-point ACL (Asynchronous ConnectionLess) – Data

Variable packet size (1,3,5 slots), asymmetric bandwidth, point-to-multipoint

MASTER

SLAVE 1

SLAVE 2

f6f0

f1 f7

f12

f13 f19

f18

SCO SCO SCO SCOACL

f5 f21

f4 f20

ACLACLf8

f9

f17

f14

ACL


L2CAP - Logical Link Control and Adaptation Protocol

Simple data link protocol on top of baseband

Connection oriented, connectionless, and signalling

channels

Protocol multiplexing

RFCOMM, SDP, telephony control

Segmentation & reassembly

Up to 64kbyte user data, 16 bit CRC used from baseband

QoS flow specification per channel

Follows RFC 1363, specifies delay, jitter, bursts, bandwidth

Group abstraction

Create/close group, add/remove member


Additional protocols

Service Discovery Protocol (SDP)

Inquiry/response protocol for discovering services

RFCOMM Emulation of a serial port (supports a large base of legacy

applications)

Allows multiple ports over a single physical channel

Telephony Control Protocol Specification (TCS) Call control (setup, release)

Group management

OBEX Exchange of objects, IrDA replacement

WAP Interacting with applications on cellular phones


Profiles

Represent default solutions for a certain usage model Vertical slice through the protocol stack Basis for interoperability

Generic Access ProfileService Discovery Application ProfileCordless Telephony Profile Intercom ProfileSerial Port ProfileHeadset ProfileDial-up Networking ProfileFax ProfileLAN Access ProfileGeneric Object Exchange ProfileObject Push ProfileFile Transfer ProfileSynchronization Profile

Additional ProfilesAdvanced Audio DistributionPANAudio Video Remote ControlBasic PrintingBasic ImagingExtended Service DiscoveryGeneric Audio Video DistributionHands FreeHardcopy Cable Replacement

Profiles

Pro

toco

ls

Applications


WPAN: IEEE 802.15-1Data rate

Synchronous, connection-oriented: 64 kbit/s

Asynchronous, connectionless

433.9 kbit/s symmetric 723.2 / 57.6 kbit/s

asymmetricTransmission range

POS (Personal Operating Space) up to 10 m

with special transceivers up to 100 m

Frequency Free 2.4 GHz ISM-band

Security Challenge/response

(SAFER+), hopping sequenceCost

50€ adapter, drop to 5€ if integrated

Availability Integrated into some

products, several vendors

Connection set-up time Depends on power-mode Max. 2.56s, avg. 0.64s

Quality of Service Guarantees, ARQ/FEC

Manageability Public/private keys needed,

key management not specified, simple system integration

Special Advantages/Disadvantages

Advantage: already integrated into several products, available worldwide, free ISM-band, several vendors, simple system, simple ad-hoc networking, peer to peer, scatternets

Disadvantage: interference on ISM-band, limited range, max. 8 devices/network&master, high set-up latency


WPAN: IEEE 802.15 – future developments

802.15-2: CoexistanceCoexistence of Wireless Personal Area Networks

(802.15) and Wireless Local Area Networks (802.11), quantify the mutual interference

802.15-3: High-RateStandard for high-rate (20Mbit/s or greater) WPANs,

while still low-power/low-cost Data Rates: 11, 22, 33, 44, 55 Mbit/s Quality of Service isochronous protocol Ad hoc peer-to-peer networking Security Low power consumption Low cost Designed to meet the demanding requirements of

portable consumer imaging and multimedia applications


WPAN: IEEE 802.15 – future developments

802.15-4: Low-Rate, Very Low-PowerLow data rate solution with multi-month to multi-year

battery life and very low complexityPotential applications are sensors, interactive toys, smart

badges, remote controls, and home automation Data rates of 20-250 kbit/s, latency down to 15 ms Master-Slave or Peer-to-Peer operationSupport for critical latency devices, such as joysticks CSMA/CA channel access (data centric), slotted (beacon) or

unslottedAutomatic network establishment by the PAN coordinator Dynamic device addressing, flexible addressing formatFully handshaked protocol for transfer reliability Power management to ensure low power consumption 16 channels in the 2.4 GHz ISM band, 10 channels in the

915 MHz US ISM band and one channel in the European 868 MHz band

IEEE 802.16 (WiMax)

Fixed Broadband Wireless Access StandardFixed Broadband Wireless Access Standard


IEEE 802.16

The standard IEEE 802.16 defines the air interface,

including the MAC layer and multiple PHY layer options,

for fixed Broadband Wireless Access (BWA) systems to

be used in a Wireless Metropolitan Area Network

(WMAN) for residential and enterprise use. IEEE 802.16

is also often referred to as WiMax. The WiMax Forum

strives to ensure interoperability between different

802.16 implementations - a difficult task due to the

large number of options in the standard.

IEEE 802.16 cannot be used in a mobile environment.

For this purpose, IEEE 802.16e has been developed.


What is 802.16

Commonly referred to as WiMAX or less commonly as WirelessMAN™ or the Air Interface Standard, IEEE 802.16 is a specification for fixed broadband wireless metropolitan access networks (MANs) just like wireless local loop (WLL) that use a point-to-multipoint architecture.

Published on April 8, 2002, the standard defines the use of bandwidth between the licensed 10GHz and 66GHz and between the 2GHZ and 11GHz (licensed and unlicensed) frequency ranges and defines a MAC layer that supports multiple physical layer specifications customized for the frequency band of use and their associated regulations.

802.16 supports very high bit rates in both uploading to and downloading from a base station up to a distance of 30 miles to handle such services as VoIP, IP connectivity and TDM voice and data.


Properties of IEEE Standard 802.16

Broad bandwidth Up to 134 Mbit/s in 28 MHz channel (in 10-66 GHz air interface) Supports multiple services simultaneously with full QoS Efficiently transport IPv4, IPv6, ATM, Ethernet, etc. Bandwidth on demand (frame by frame) MAC designed for efficient used of spectrum Comprehensive, modern, and extensible security Supports multiple frequency allocations from 2-66 GHz ODFM and OFDMA for non-line-of-sight applications TDD and FDD Link adaptation: Adaptive modulation and coding Subscriber by subscriber, burst by burst, uplink and downlink Point-to-multipoint topology, with mesh extensions Support for adaptive antennas and space-time coding Extensions to mobility are coming next.


Different versions of 802.16

802.16a 802.16a, approved in January 2003, specified non-line-of-sight

extensions in the 2-11 GHz spectrum, delivering up to 70 Mbps at distances up to 31 miles.

802.16 Revd Consolidates revisions of 802.16a and 802.16c into a single

standard that will replace 802.16a as the base standard. 802.16-2004

The IEEE 802.16-2004 standard subsequently revised and replaced the IEEE 802.16a and 802.16REVd versions. This is designed for fixed-access usage models. This standard may be referred to as "fixed wireless" because it uses a mounted antenna at the subscriber's site. The antenna is mounted to a roof or mast, similar to a satellite television dish.

802.16e 802.16e will add mobility in the 2 to 6 GHz licensed bands,

while 802.20 aims for operation in licensed bands below 3.5GHz.


Comparisons of Different Versions of 802.16


Working of 802.16

• Wireless broadband access is set up like cellular systems, using base stations that service a radius of several miles/kilometers.

• A customer premise unit, similar to a satellite TV setup, is all it takes to connect the base station to a customer.

• The signal is then routed via standard Ethernet cable either directly to a single computer, or to an 802.11 hot spot or a wired Ethernet LAN.


IEEE 802.16 basic architecture

BS SS

SS

SS

Point-to-multipoint transmission

AP

AP

802.11 WLANBS = Base Station

SS = Subscriber Station

Fixed network

Subscriber line replacement


Uplink / downlink separation

IEEE 802.16 offers both TDD (Time Division Duplexing) and FDD (Frequency Division

Duplexing) alternatives.

Wireless devices should avoid transmitting and receiving at the same time, since duplex filters

increase the cost:

TDD: this problem is automatically avoided

FDD: IEEE 802.16 offers semi-duplex operation as an option in Subscriber Stations.


Uplink / downlink separation

TDDTDD

FDDFDD

Semi-duplex

FDD

Semi-duplex

FDD

DownlinkDownlink

UplinkUplink

… …

Adaptive

Frequency 1

Frequency 2

…

…

…

…

…

…

…

…

Frame n-1 Frame n Frame n+1


WiMAX

The WiMax (Worldwide Interoperability for Microwave Access)

certification program of the WiMax Forum addresses

compatibility of IEEE 802.16 equipment

=>

WiMax ensures interoperability of

equipment from different vendors.

ATMtransport

ATMtransport

IPtransport

IPtransport

Service Specific ConvergenceSublayer (CS)


MAC Common Part Sublayer(MAC CPS)


Privacy sublayerPrivacy sublayer

Physical Layer (PHY)Physical Layer (PHY)

WiMax


IEEE 802.16 PHY

IEEE 802.16-2004 specifies three PHY options for the 2-11 GHz band, all supporting both TDD and FDD:

WirelessMAN-SCa (single carrier option), intended for a line-of-sight (LOS) radio environment where multipath

propagation is not a problem

WirelessMAN-OFDM with 256 subcarriers (mandatory for license-exempt bands) will be the most popular option

in the near future

WirelessMAN-OFDMA with 2048 subcarriers separates users in the uplink in frequency domain (complex

technology).


WirelessMAN-OFDM PHY

WirelessMAN-OFDM is based on 256 subcarriers, of which 200 subcarriers are used: 192 data subcarriers + 8 pilot subcarriers. There are 56 ”nulls” (center carrier,

28 lower frequency and 27 higher frequency guard carriers).


Modulation and coding affect user data rate

The 192 data subcarriers carry 192 data symbols in parallel (= transmitted at the same time). Each symbol carries 1 bit (BPSK), 2 bits (QPSK), 4 bits (16-QAM), or 6 bits (64-QAM) of channel information (corresponding to

the channel bit rate after channel coding, not to be confused with the user bit rate before channel coding).

The inner convolutional coding reduces the usable number of bits to 1/2, 2/3, or 3/4 of the channel

information.

The outer Reed-Solomon block coding furthermore reduces the usable number of bits about 10 %.


Subcarrier signal in time domain (1)

Time

Guard time for preventing intersymbol interference

In the receiver, FFT is calculated only during this time

Next symbol

TbTg

IEEE 802.16 offers four values for G = Tg/Tb: G = 1/4, 1/8, 1/16 or 1/32. (802.11a/g offers only one value: G = 1/4)

Ts


Subcarrier signal in time domain (2)

IEEE 802.16 offers various bandwidth choices. The bandwidth is typically an integer multiple of 1.25, 1.5 or

1.75 MHz. (802.11a/g offers only a fixed channel bandwidth: 16.25 MHz)

Since the number of subcarriers is fixed, a certain bandwidth is translated into a certain subcarrier spacing

f = 1/Tb.

Time

Next symbol

TbTg


Four primitive parameters

WirelessMAN-OFDM defines four "primitive parameters" that characterize the OFDM symbol:

The nominal channel bandwidth BW

The number of used subcarriers Nused = 200

The sampling factor n. This parameter depends on the bandwidth. For instance, when the bandwith is a

multiple of 1.25, 1.5 or 1.75 MHz, n = 144/125, 86/75 or 8/7, respectively.

The guard time to useful symbol time ratio G.


Derived parameters

Using the four primitive parameters shown on the previous slide, the following additional parameters can

be derived:

NFFT (the smallest power of two greater than Nused) = 256

Sampling frequency fs = floor(n.BW/8000)x8000

Subcarrier spacing f = fs/NFFT

Useful symbol time Tb = 1/f

Guard time Tg = G.Tb

OFDM symbol time Ts = Tg + Tb.


Example

For BW = 5 MHz, BPSK, G = 1/32, calculate peak bit rate:

fs = floor(144/125 x 5 MHz / 8000) x 8000 = 5.76 MHz

f = fs/NFFT = 5.76 MHz / 256 = 22.5 kHz

Tb = 1/f = 44.44 s

Tg = G.Tb = 1.39 s

Ts = Tg + Tb = 45.83 s

Peak bit rate = (192 bits x 0.5 x 0.9) / 45.83 s = 1.89 Mb/s

86.4 info bits / OFDM symbol


Modulation

BPSKQPSKQPSK

16-QAM16-QAM64-QAM64-QAM

Info bits / subcarrier

0.51

1.5234

4.5

Info bits /symbol

88184280376568760856

Peak data rate (Mbit/s)

1.893.956.008.0612.1816.3018.36

Coding rate

1/21/23/41/23/42/33/4

Depends on chosen bandwidth (here 5 MHz is assumed)

Modulation and coding combinations


Example (cont.)

The peak bit rate does not take into account the MAC layer overhead (MAC PDU header and trailer) and PHY layer overhead (contention slots and burst preamble in

UL, DL PHY PDU preamble and header in DL).

Consequently, the user data rate is substantially smaller (even if the SS is the only user of the WMAN).


ATMtransport

ATMtransport

IPtransport

IPtransport



IEEE 802.16 protocol layering





MA

C

Like IEEE 802.11, IEEE 802.16 specifies the

Medium Access Control (MAC) and PHY layers of the wireless transmission system.

The IEEE 802.16 MAC layer consists of three

sublayers.


ATMtransport

ATMtransport

IPtransport

IPtransport








MA

C

CS maps data (ATM cells or IP packets) to

a certain unidirectional

connection identified by the Connection Identifier (CID) and associated with a

certain QoS.

CS adapts higher layer protocols to MAC CPS.

May also offer payload header suppression.


ATMtransport

ATMtransport

IPtransport

IPtransport








MA

C

MAC CPS provides the core MAC

functionality:

• System access

• Bandwidth allocation

• Connection controlNote: QoS control is applied dynamically to every connection

individually.


ATMtransport

ATMtransport

IPtransport

IPtransport








MA

C

The privacy sublayer provides

authentication, key management and

encryption.


ATMtransport

ATMtransport

IPtransport

IPtransport








MA

C IEEE 802.16 offers three PHY options for the 2-11 GHz band:

• WirelessMAN-SCa

• WirelessMAN-OFDM

• WirelessMAN-OFDMA


Overall TDD frame structure (1)

Frame n-1Frame n-1 Frame nFrame n Frame n+1Frame n+1 Frame n+2Frame n+2

Frame length 0.5, 1 or 2 ms

The following slides present the overall IEEE 802.16 frame structure for TDD.

It is assumed that the PHY option is WirelessMAN-OFDM, since this presumably will be the most popular PHY

option (in the near future). The general frame structure is applicable also to other PHY options, but the details

may be different.


Overall TDD frame structure (2)

Frame n-1Frame n-1 Frame nFrame n Frame n+1Frame n+1 Frame n+2Frame n+2

DL PHYPDU

DL PHYPDU

Contentionslot A

Contentionslot A

Contentionslot B

Contentionslot B

UL PHYburst 1UL PHYburst 1

UL PHYburst kUL PHYburst k

…

DL subframe UL subframe

TDMA bursts from different subscriber stations (each with its own preamble)

TDM signal in downlink

For initial ranging

For BW requests

Adaptive


Modulation and coding combinations

Modulation

BPSKQPSKQPSK

16-QAM16-QAM64-QAM64-QAM

Info bits / subcarrier

0.51

1.5234

4.5

Info bits /symbol

88184280376568760856

Peak data rate (Mbit/s)

1.893.956.008.0612.1816.3018.36

Coding rate

1/21/23/41/23/42/33/4

Depends on chosen bandwidth (here 5 MHz is assumed)


Example: Efficiency vs. Robustness Trade-off

Large distance => high attenuation => low bit rate

BS64 QAM

16 QAM

QPSK

SS

SS

SS


Four service classes The IEEE 802.16 MAC layer defines four service

classes:

• Unsolicited Grant Service (UGS)• Real-time Polling Service (rtPS)

• Non-real-time Polling Service (nrtPS)• Best Effort (BE) service

The scheduling algorithms needed for implementing the three first types of services are implemented in

the BS (while allocating uplink bandwidth to each SS) and are not defined in the 802.16 standard. Each SS

negotiates its service policies with the BS at the connection setup time.

QoS increasesQoS increases

Dynamic QoS management


Unsolicited grant service (UGS)

UGS offers fixed size grants on a real-time periodic basis, which eliminates the overhead and latency of SS requests and assures that

grants are available to meet the flow’s real-time needs. The BS provides fixed size bursts in the uplink at periodic intervals for the service flow.

The burst size and other parameters are negotiated at connection setup.

Typical UGS applications: E1/T1 links (containing e.g. delay-sensitive speech signals), VoIP

(without silence suppression).

UGSUGS

rtPSrtPS

nrtPSnrtPS

BEBE


Real-time Polling Service (rtPS)

The Real-time Polling Service (rtPS) is designed to support real-time service flows that generate variable size data packets on a periodic basis,

such as VoIP (with silence suppression) or streaming video.

This service offers real-time, periodic, unicast request opportunities, which meet the flow’s real-time needs and allow the SS to specify the size of

the desired uplink transmission burst. This service requires more request overhead than

UGS, but supports variable grant sizes for optimum data transport efficiency.

UGSUGS

rtPSrtPS

nrtPSnrtPS

BEBE


Non-real-time Polling Service (nrtPS)

The Non-real-time Polling Service (nrtPS) is designed to support non-real-time service flows that require variable size bursts in the uplink on

a regular (but not strictly periodic) basis.

Subscriber stations contend for bandwidth (for uplink transmission) during contention request

opportunities. The availability of such opportunities is guaranteed at regular intervals (on the order of one second or less) irrespective

of network load.

UGSUGS

rtPSrtPS

nrtPSnrtPS

BEBE


Best Effort (BE) service

The Best Effort service is intended to be used for best effort traffic where no throughput or delay

guarantees are provided.

Subscriber stations contend for bandwidth (for uplink transmission) during contention request

opportunities. The availability of such opportunities depends on network load and is

not guaranteed (in contrast to nrtPS).

UGSUGS

rtPSrtPS

nrtPSnrtPS

BEBE


Dynamic QoS management in practice

The request-response mechanism described on the previous slides is designed to be scalable, efficient, and

self-correcting.

While extensive bandwidth allocation and QoS mechanisms are specified in the IEEE 802.16 standard, the

details of scheduling and reservation management have not been standardized and thus provide an important

mechanism for vendors to differentiate their equipment.

(There is a similar situation regarding standardization of a transmission system in general: the transmitted signal is standardized in detail, whereas receivers can process the

received signal as they like, using innovative technology.)


Three types of management connections

When a subscriber station accesses the network, three types of management connections are established

between the SS and the BS (before transport connections can be established):

Basic management connection for exchange of short, delay-critical MAC management messages

Primary management connection for exchange of longer, more delay tolerant MAC management

messages

Secondary management connection for exchange of delay tolerant IP-based messages, such as used

during DHCP transactions.


Summary: Dynamic QoS management

In summary, IEEE 802.16 offers the following mechanisms for dynamically managing QoS and

bandwidth:

In the PHY layer by adjusting the DL and UL burst profiles (modulation and coding combination) on a per-frame

basis.

In the MAC layer through fragmentation and packing (both can be done at the same time).

At higher protocol layers by using scheduling algorithms in the base station. These algorithms are not specified in

the IEEE 802.16 standard.

Mobile IP


Motivation for Mobile IP

Routing based on IP destination address, network prefix (e.g.

129.13.42) determines physical subnet change of physical subnet implies change of IP address to

have a topological correct address (standard IP) or needs special entries in the routing tables

Specific routes to end-systems? change of all routing table entries to forward packets to the

right destination does not scale with the number of mobile hosts and

frequent changes in the location, security problems Changing the IP-address?

adjust the host IP address depending on the current location almost impossible to find a mobile system, DNS updates

take to long time TCP connections break, security problems


Mobile IP - Terminology

Mobile Node (MN) system (node) that can change the point of connection

to the network without changing its IP address Home Agent (HA)

system in the home network of the MN, typically a router registers the location of the MN, tunnels IP datagrams to the COA

Foreign Agent (FA) system in the current foreign network of the MN, typically a

router forwards the tunneled datagrams to the MN, typically also the

default router for the MN Care-of Address (COA)

address of the current tunnel end-point for the MN (at FA or MN) actual location of the MN from an IP point of view can be chosen, e.g., via DHCP

Correspondent Node (CN) communication partner


Example network

mobile end-system

Internet

router

router

router

end-system

FA

HA

MN

home network

foreign network

(physical home networkfor the MN)

(current physical network for the MN)

CN


Data transfer to the mobile system

Internet

sender

FA

HA

MN

home network

foreignnetwork

receiver

1

2

3

1. Sender sends to the IP address of MN,HA intercepts packet (proxy ARP)2. HA tunnels packet to COA, here FA, by encapsulation3. FA forwards the packet to the MN

CN


Data transfer from the mobile system

Internet

receiver

FA

HA

MN

home network

foreignnetwork

sender

1

1. Sender sends to the IP address of the receiver as usual, FA works as default router

CN


Overview

CN

routerHA

routerFA

Internet

router

1.

2.

3.

homenetwork

MN

foreignnetwork

4.

CN

routerHA

routerFA

Internet

router

homenetwork

MN

foreignnetwork

COA


Network integration

Agent AdvertisementHA and FA periodically send advertisement messages into

their physical subnetsMN listens to these messages and detects, if it is in the

home or a foreign network (standard case for home network)

MN reads a COA from the FA advertisement messages Registration (always limited lifetime!)

MN signals COA to the HA via the FA, HA acknowledges via FA to MN

these actions have to be secured by authentication Advertisement

HA advertises the IP address of the MN (as for fixed systems), i.e. standard routing information

routers adjust their entries, these are stable for a longer time (HA responsible for a MN over a longer period of time)

packets to the MN are sent to the HA, independent of changes in COA/FA


Encapsulation

original IP header original data

new datanew IP header

outer header inner header original data


Encapsulation I

Encapsulation of one packet into another as payloade.g. IPv6 in IPv4 (6Bone), Multicast in Unicast (Mbone)here: e.g. IP-in-IP-encapsulation, minimal encapsulation or

GRE (Generic Record Encapsulation) IP-in-IP-encapsulation (mandatory, RFC 2003)

tunnel between HA and COA

Care-of address COAIP address of HA

TTLIP identification

IP-in-IP IP checksumflags fragment offset

lengthDS (TOS)ver. IHL

IP address of MNIP address of CN

TTLIP identification

lay. 4 prot. IP checksumflags fragment offset

lengthDS (TOS)ver. IHL

TCP/UDP/ ... payload


Optimization of packet forwarding

Triangular Routingsender sends all packets via HA to MNhigher latency and network load

“Solutions”sender learns the current location of MNdirect tunneling to this locationHA informs a sender about the location of MNbig security problems!

Change of FApackets on-the-fly during the change can be lostnew FA informs old FA to avoid packet loss, old FA now

forwards remaining packets to new FA this information also enables the old FA to release

resources for the MN

Mobile Ad-hoc Networks (MANETs)


Multi-Hop wireless networks

May need to traverse multiple links to reach destination

Mobility causes route changes


Mobile Ad Hoc Networks (MANET)

Host movement frequent Topology change frequent

No cellular infrastructure. Multi-hop wireless links. Data must be routed via intermediate nodes.

A B AB

Source: Vaidya


MANETs

Do not need backbone infrastructure support Are easy to deploy Useful when infrastructure is absent, destroyed or

impractical Infrastructure may not be present in a disaster area or war

zone Applications

Military environments soldiers, tanks, planes

Emergency operations search-and-rescue policing and fire fighting

Civilian environments taxi cab network meeting rooms sports stadiums


MAC in MANET

IEEE 802.11 DCF is most popular Easy availability Uses RTS-CTS to avoid hidden terminal problem Uses ACK to achieve reliability

802.11 was designed for single-hop wireless Does not do well for multi-hop ad hoc scenarios Reduced throughput Exposed terminal problem


Routing in MANET

Mobile IP needs infrastructure Home Agent/Foreign Agent in the fixed network DNS, routing etc. are not designed for mobility

MANET no default router available “every” node also needs to be a router


MANET routing protocols

Reactive protocols Determine route if and when needed Example: DSR (dynamic source routing)

Proactive protocols Traditional distributed shortest-path protocols Example: DSDV (destination sequenced distance

vector) Hybrid protocols

Adaptive; Combination of proactive and reactive Example : ZRP (zone routing protocol)


MANET variations

Fully symmetric environment all nodes have identical capabilities and responsibilities

Asymmetric Capabilities transmission ranges, battery life, processing capacity may

differ at different nodes Asymmetric Responsibilities

only some nodes may route packets Mobility patterns may differ from one scenario to another Mobility characteristics (speed, predictability) may be

different for different applications Traffic characteristics may differ

timeliness constraints reliability requirements


MANET summary

Routing is the most studied problem

Interplay of layers is being researched

Large number of simulation based expts

Small number of field trials

Very few reported deployments

Fertile area for imaginative applications

Integration of Cellular Networks and WLANs


Why Cellular + WLAN?

Cellular

Outdoor

Wide area mobility

Moderate to high

mobility

Moderate bandwidth

High cost

Good for everywhere

except hotspots

WLAN

Indoor

Small area mobility

Low mobility

High bandwidth

Low cost

Good for hotspots of

high-bandwidth activity


3G UMTS Architecture

MSC

VLR

PSTN

BS

BS

BS

RNC

RNC

BS

GGSN InternetSGSN

• GGSN• connected to the Internet• IP address assignment• session management

• SGSN• manage mobility context• interact with RNC to perform RAB setup• perform inter-RNC handover

GnIu

Iu

Gi

Gs


802.11 WLAN Infrastructure Mode

Association Point (AP) Base station

Basic Service Set Cell 100-300 meters

Every MN is associated to at most one AP

MACDistributed Coordinated

Function (DCF) CSMA/CA

Point Coordinated Function (PCF)

Polling IAPP for Roaming

BSS1

MN1

AP1

BSS2

MN2

AP2

Distribution System


Integration ScenariosScenario 1:

Common Billing and Customer Care No real inter-working

Scenario 2: 3GPP System-based Access Control and Charging Common AAA service – Reusing GPRS AAA

Scenario 3: Access to 3GPP GPRS-based Services E.g. WAP, Location-base service etc

Scenario 4: Service Continuity No stringent requirement on handover

Scenario 5: Seamless Services Service continuity without any noticeable difference

Scenario 6: 3GPP Circuit Switched Services E.g. Voice service should be available in WLAN network


Integration – At GGSN

SGSN GGSN

Internet

BS

BS

RNC

WLAN Network

AR1 AR2Macro Cell (UMTS)

Micro Cell (802.11)

AAA


Integration – At SGSN

SGSN GGSN

Internet

BS

BS

RNC

WLAN Network


Micro Cell (802.11)


Integration – At RNC

SGSN GGSN

Internet

BS

BS

RNC

WLAN Network


Micro Cell (802.11)


Integration


IA: FeaturesWLAN is an IP network

All IETF standard protocols IP Local Mobility Management

(LMM) IP level integrationSGSN is the integration point

SGSN maintains mobility context that can be modified to include MN’s mobility state in WLAN

No need to update HLR/VLR when MN is in WLAN

MN in a BSS with multiple interfaces can access:

Packet switched services through WLAN

Circuit switched services through UMTS

WLAN IP Network

AR AR

BR BR

SRNS SGSN

Packet Data Signallling

Packet Data Bearer Voice (CS)

GGSN

Internet


IA: ChallengesSynchronization between SGSN

and WLAN For mobility management For session management

GPRS is connection oriented, whereas WLAN network is connection-less

GPRS is a single-hop IP network and WLAN is a multi-hop IP network

Mobility management in WLAN network is qualitatively different

GPRS is essentially tunneled-based

WLAN could be tunnel-based or routing-based

Terminal Model How to maintain connection

between MN and SGSN through WLAN?

WLAN IP Network

AR AR

BR BR

SRNS SGSN

Packet Data Signallling

Packet Data Bearer Voice (CS)

GGSN

Internet


Terminal ArchitectureMobile Node is equipped with

two interfaces UMTS-GPRS interface 802.11 WLAN interface

GPRS specific protocols are implemented at the device driver level

Applications GPRS applications can

access GPRS-aware services through GPRS service layer

IP applications use IP protocols through IP stack

Mobility Management and QoS signaling protocols

LMM and RSVP

ICMPIGMP

Internet Protocol (IP)

TCPUDP

LMM RSVP

GMMSM

RRC PDCP

RLC

MAC

L1 802.11 PHY

802.11 MAC

802.2 LLC

UMTS Device Driver

GPRS Service Layer

802.11 Device Driver

Application Layer


Mobility Management

LMM state machine is

augmented with two new states

WLAN-attached stated: a

transition point from GPRS to

WLAN network

GPRS-attached state:

representing the MN is

disassociated from WLAN

GPRS state machine is

augmented with one new state

WMM-connected state: MN is

receiving PS service from

WLAN, hence no RAB is set

up for PDP contexts in UTRAN

PMM-IDLE

PMM-DETACHED

PMM-CONNECTED

WMM-CONNECTED

GPRS MM Context

Handover Points

GPRS -ATTACHED

WLAN-ATTACHED

LMM States

WLAN LMM Context

Handover Points


UMTS-WLAN Handover Handover signalling through WLAN

Avoid keeping separate signalling connection through UTRAN

Support abrupt disconnection SGSN can implement modified

mobility agent functionality to allow Mobile IP signalling between AR and SGSN

W_Route Area Update may not be a new signalling protocol, it may be BU with some extensions

It is shown differently here to show explicit transaction between WLAN and UMTS

Resource Reservation following HO may be required to adjust QoS parameters and acquire resources in WLAN network including 802.11 radio resources when it offers QoS

UMTS – WLAN Handover

MN AR SGSN SRNC

Beacon Association Request

Router Advertisement

Binding Update

[W_Route Area Update] RAB

Release

RAB Release Complete

[W_Route Area Update Accept]

Binding Update Ack

[W_Route Area Update Complete]

RSVP Path

RSVP Resv

Association Response

Authentication & COA Assignment

RSVP Path RSVP Path

RSVP Resv RSVP Resv


Concluding RemarksAn Integration Architecture is discussed:

UMTS macro cells overlaid on 802.11 micro cells Access services through the networks that optimize their

delivery Seamless handover between two networks SGSN as integration point

Modifications only in SGSN inside the network No gateway functionality in WLAN network

• Incurs no additional cost to WLAN network deployment IP level inter-system handover

No GPRS specific layer-2 level inter-working function in WLAN network

Transparency to IP applications IETF standardized protocols in WLAN networks

Reuse UMTS AAA infrastructure

Documents

EEE 464 EEE 464 Wireless Communications Lecture 9 Shahzad Malik, Ph.D. [email protected]