Wireless Local Loop (WLL)Wireless Local Loop (WLL)

By:By:

Arpit GuptaArpit Gupta

Presentation OutlinePresentation Outline

What is WLL?What is WLL? Why change in the Access Network?Why change in the Access Network? Differences with mobile cellular systemsDifferences with mobile cellular systems

– Why WLL?Why WLL? System AnalysisSystem Analysis

– examplesexamples The future of WLLThe future of WLL

DefinitionDefinition

What is WLL?What is WLL?- - WLL is a system that connects subscribers WLL is a system that connects subscribers to the local telephone station wirelessly.to the local telephone station wirelessly.

Systems WLL is based on:Systems WLL is based on:– CellularCellular– Satellite Satellite – MicrocellularMicrocellular

Other namesOther names– Radio In The Loop (RITL) Radio In The Loop (RITL) – Fixed-Radio Access (FRA).Fixed-Radio Access (FRA).

Change in the Access NetworkChange in the Access Network

The cost of laying Cu line was 3 times that The cost of laying Cu line was 3 times that of the fiber.of the fiber.

A general WLL setupA general WLL setup

WLL servicesWLL services

Desirable:Desirable:– Wireless feature should be transparentWireless feature should be transparent– Wire line Custom featuresWire line Custom features

Other:Other:– Business relatedBusiness related

» Call transfersCall transfers» Conference callingConference calling

– coin phonescoin phones– V.29 (9600bps)V.29 (9600bps)– ISDN (64kbps)ISDN (64kbps)

WLL should provide…WLL should provide…

Toll-quality serviceToll-quality service Expand from a central office to about 5 Expand from a central office to about 5

milesmiles Low license costLow license cost Subscriber costs equivalent or better than Subscriber costs equivalent or better than

coppercopper

Cost ConsiderationsCost Considerations

• Wireless cost is constant over distance for WLL• Wireline depends on distance AND terrain

Situations “made” for WLLSituations “made” for WLL

Environments where it might be cheaper to Environments where it might be cheaper to go wirelessgo wireless

Where it’s impossible to lay copper ( small Where it’s impossible to lay copper ( small islands)islands)

Business parks, industrial areasBusiness parks, industrial areas Speedy deployment, stop gap application Speedy deployment, stop gap application

till wire line is introducedtill wire line is introduced– 90-120 days for activation90-120 days for activation

Connection SetupConnection Setup

PSTN Switch function

WLLController

AMHLR

Transceiver WASU

TrunkAir Interface

UWLL

TWLL

Wireless Access Network Unit(WANU)– Interface between underlying telephone

network and wireless link– consists of

• Base Station Transceivers (BTS)• Radio Controller(RPCU)• Access Manager(AM)• Home Location Register(HLR)

WANU

Wireless Access Subscriber Unit(WASU)Wireless Access Subscriber Unit(WASU)

– located at the subscriberlocated at the subscriber

– translates wireless link into a translates wireless link into a traditional traditional telephone telephone connectionconnection

Important Results of Fixed to Important Results of Fixed to Fixed Propagation in WLLsFixed Propagation in WLLs

Pathloss exponent is considerably smaller Pathloss exponent is considerably smaller ::– 20dB/dec compared to 40dB/dec20dB/dec compared to 40dB/dec

– Decreases cell capacityDecreases cell capacity

– Allows for larger coverage areaAllows for larger coverage area No handoffs necessary:No handoffs necessary:

– Decreases hardware costs and system complexityDecreases hardware costs and system complexity

– Increases quality of service through accurate traffic predictionsIncreases quality of service through accurate traffic predictions Allows usage of directional antennas:Allows usage of directional antennas:

– Can greatly reduce interference and increase cell capacityCan greatly reduce interference and increase cell capacity

In-Cell Interference (CDMA)In-Cell Interference (CDMA)

I = (NI = (Nh h – 1)– 1)S S N NhhSSvoice activity factorvoice activity factor

hh = total number of houses = total number of houses

S = power received at cell site from every houseS = power received at cell site from every house

Out-of-Cell InterferenceOut-of-Cell Interference

Pathloss: 20dB/dec as opposed to 40dB/decPathloss: 20dB/dec as opposed to 40dB/dec

need to take in account more tiersneed to take in account more tiers Only from houses whose antennas are Only from houses whose antennas are

directed at the center cell base stationdirected at the center cell base station

Interference from Another CellInterference from Another Cell

Blue areaBlue area is region of interferers is region of interferers for Cfor C

It is Not a perfect pie shape.It is Not a perfect pie shape.

Per-Tier InterferencePer-Tier Interference

Interference is proportional to antenna width w and Interference is proportional to antenna width w and inversely proportional to the tier number.inversely proportional to the tier number.

Decreasing the antenna width can greatly reduce Decreasing the antenna width can greatly reduce interference.interference.

As the number of tiers approaches infinity, so does the As the number of tiers approaches infinity, so does the total interference. Therefore, system capacity is a function total interference. Therefore, system capacity is a function of the total number of tiers in the system.of the total number of tiers in the system.

Capacity comparisonCapacity comparison for 5 MHz spectrum allocationfor 5 MHz spectrum allocation

ParameterParameter IS-95 CDMAIS-95 CDMA IS-136 TDMAIS-136 TDMA ETSI (GSM)ETSI (GSM)

MobileMobile WLLWLL MobileMobile WLLWLL MobileMobile WLLWLL

Chan. BW Chan. BW (kHz)(kHz)

12501250 12501250 3030 3030 200200 200200

Number of Number of channelschannels

44 44 167167 167167 2525 2525

Spectral Spectral Density( EDensity( Ebb/N/N0)0)

7 dB7 dB 6dB6dB 18dB18dB 14dB14dB 12dB12dB 12dB12dB

Freq. ReuseFreq. Reuse 11 11 77 44 33 33

Effective Chan. Effective Chan. Per sect.Per sect.

44 44 7.957.95 13.9213.92 2.782.78 2.782.78

Erlangs per cellErlangs per cell

Per MHzPer MHz

38.338.3 48.748.7 9.849.84 19.619.6 9.129.12 9.129.12

ComparisonComparisonWLLWLL Mobile Mobile

WirelessWirelessWirelineWireline

Good LOS Good LOS componentcomponent

Mainly diffuse Mainly diffuse componentscomponents

No diffuse No diffuse componentscomponents

Narrowbeam Narrowbeam directed antennasdirected antennas

Omnidirectional Omnidirectional antennasantennas

Expensive wiresExpensive wires

High Channel reuseHigh Channel reuse Less Channel reuseLess Channel reuse Reuse Limited by Reuse Limited by wiringwiring

Simple design, Simple design, constant channelconstant channel

Expensive DSPs, Expensive DSPs, power controlpower control

Expensive to build Expensive to build and maintainand maintain

Low in-premises Low in-premises mobility only, easy mobility only, easy accessaccess

High mobility High mobility allowed, easy allowed, easy accessaccess

Low in-premises Low in-premises mobility, wiring of mobility, wiring of distant areas distant areas cumbersomecumbersome

Rician fadingRician fading Rayleigh fadingRayleigh fading No fadingNo fading

Weather conditions Weather conditions effectseffects

Not very reliableNot very reliable Very reliableVery reliable

Examples of services providedExamples of services provided

Marconi WipLLMarconi WipLL (wireless IP local loop) (wireless IP local loop)– Based on Frequency hopping CDMABased on Frequency hopping CDMA– Internet Protocol 64kbps to 2.4Mbps rates Committed Internet Protocol 64kbps to 2.4Mbps rates Committed

Information Rate or best effort serviceInformation Rate or best effort service Lucent WSSLucent WSS (wireless subscriber system) (wireless subscriber system)

– 800 to 5000 subscribers per switch800 to 5000 subscribers per switch– Uses FDMA/FDD 12 Km to 40Km coverageUses FDMA/FDD 12 Km to 40Km coverage

GoodWin GoodWin WLLWLL– DECT standardsDECT standards– 9.6 kbps rate9.6 kbps rate– Specified conditions -5°С...+55°С, 20...75% humiditySpecified conditions -5°С...+55°С, 20...75% humidity

Future of WLL / OverviewFuture of WLL / Overview

Depends onDepends on– economic developmenteconomic development– existing infrastructure of a regionexisting infrastructure of a region

OffersOffers– market competitionmarket competition– quick deploymentquick deployment– relatively reliable service at low costsrelatively reliable service at low costs

QuestionsQuestions??

Basie station

BibliographyBibliographyWireless in local loop – some fundamentalsWireless in local loop – some fundamentals

paper by Ashok Jhunjunwala (IIT Madras)paper by Ashok Jhunjunwala (IIT Madras)

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THANK YOUTHANK YOU