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

By:By:

Panos TzanosPanos Tzanos

Vladimeros VladimerouVladimeros Vladimerou

Derek StarrDerek Starr

Presentation OutlinePresentation Outline

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

Systems WLL is based on:Systems WLL is based on:– CellularCellular– Satellite (specific and adjunct)Satellite (specific and adjunct)– MicrocellularMicrocellular

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

A general WLL setupA general WLL setup

WLL servicesWLL services

Desirable:Desirable:– Wireless feature should be transparentWireless feature should be transparent– Wireline Custom featuresWireline Custom features

Other:Other:– Business relatedBusiness related

» Hunt groups,Hunt groups,» Call transfersCall transfers» Conference callingConference calling

– Calling cards, coin phonesCalling cards, coin 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

Ideas for U.S. marketIdeas for U.S. market

Supplement Copper LinesSupplement Copper Lines– Easier third telephone lineEasier third telephone line– Data service Data service

Fixed Mobile UsersFixed Mobile Users– Take phone wherever you want / charged on 2 Take phone wherever you want / charged on 2

levelslevels– ““home” could mean neighborhoodhome” could mean neighborhood– Charged regular mobile rate if you’re on the Charged regular mobile rate if you’re on the

roadroad

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 3Environments where 3rdrd line is degraded might line is degraded might be cheaper to go wirelessbe cheaper to go wireless

Where it’s impossible to lay copper (3Where it’s impossible to lay copper (3rdrd world, world, small islands)small islands)

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

wireline is inwireline is in– 90-120 days for activation90-120 days for activation

Developed vs. DevelopingDeveloped vs. Developing

Developed: Wireline serviceDeveloped: Wireline service– Firmly established, cellular penetration is Firmly established, cellular penetration is

relatively highrelatively high– Incumbent operator would use it to install 2Incumbent operator would use it to install 2ndnd, 3, 3rdrd

lines, coverage to rural areaslines, coverage to rural areas– 22ndnd or 3 or 3rdrd competitive operator deploy it for fast competitive operator deploy it for fast

& cost effective deployment& cost effective deployment– Quick way to establish market presenceQuick way to establish market presence

– cellular complement to their offeringscellular complement to their offerings

Developed vs. DevelopingDeveloped vs. Developing

DevelopingDeveloping– Quick & easy to deploy in countries with little Quick & easy to deploy in countries with little

copper line service, so as to accommodate copper line service, so as to accommodate people on enormous waiting lists for basic people on enormous waiting lists for basic serviceservice

– Low maintenance costsLow maintenance costs– Allows more competition in provider marketAllows more competition in provider market

ExamplesExamples

UKUK– 150 PTOs have licenses for wireless150 PTOs have licenses for wireless– Focus on regional networksFocus on regional networks– WLL Commercial servicesWLL Commercial services

» Ionica, Atlantic Telecom, Scottish TelecomIonica, Atlantic Telecom, Scottish Telecom

PolandPoland– Most exciting market in eastern EuropeMost exciting market in eastern Europe– Local loop is the bottleneckLocal loop is the bottleneck– 150,000 WLL lines since 1996 (15% of new)150,000 WLL lines since 1996 (15% of new)– Ericsson, Motorola contractsEricsson, Motorola contracts

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 connectiontelephone connection

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

Signal channel is not a Rayleigh fading channel:Signal channel is not a Rayleigh fading channel:– Power control algorithms are simpler and can be Power control algorithms are simpler and can be

utilized more effectivelyutilized more effectively

Channel Randomness is lost:Channel Randomness is lost:– Makes analysis difficultMakes analysis difficult

Pathloss exponent is considerably smaller Pathloss exponent is considerably smaller (Why?):(Why?):

– 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

Fixed to Fixed Fixed to Fixed Propagation(cont’d)Propagation(cont’d)

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

-30dB

30dB

0o 60o-40dB

10dB

0o 120o 180o

BS antenna Subscriber antenna

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

I = (NI = (Nh h – 1)– 1)αα S S ≈≈ N Nhhαα SS

α = α = voice activity factorvoice activity factor

ΝΝ hh = total # of houses = total # of houses

S = power received at cell site from S = power received at cell site from every houseevery 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 shapeIt is Not a perfect pie shape If w = (1/2)*(antenna width)If w = (1/2)*(antenna width)

(in radians)(in radians) W = w+2sinW = w+2sin-1-1((R/D)sin(w/2))((R/D)sin(w/2)) If w<<1 and R<<D:If w<<1 and R<<D:

W = w (1+(R/D))W = w (1+(R/D))

is the “pie” arc lengthis the “pie” arc length

Per-Tier InterferencePer-Tier Interference

Integration over W and all the cells at tier n yields: Integration over W and all the cells at tier n yields:

IInn = [ = [αα NNhhSw/(3sqrt(3))][1/n]Sw/(3sqrt(3))][1/n]

for n>4for n>4 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

Detail IS-95 CDMA IS-136 TDMA ETSI (GSM)

Mobile WLL Mobile WLL Mobile WLL

Chan. BW (kHz) 1250 1250 30 30 200 200

# channels 4 4 167 167 25 25

Eb/N0 7 dB 6dB 18dB 14dB 12dB 12dB

Freq. Reuse 1 1 7 4 3 3

Effective Chan. Per sect.

4 4 7.95 13.92 2.78 2.78

Erlangs per cellPer MHz

38.3 48.7 9.84 19.6 9.12 9.12

ComparisonComparisonWLL Mobile Wireless Wireline

Good LOS component

Mainly diffuse components

No diffuse components

Rician fading Rayleigh fading No fading

Narrowbeam directed antennas

Omnidirectional antennas

Expensive wires

High Channel reuse Less Channel reuse Reuse Limited by wiring

Simple design, constant channel

Expensive DSPs, power control

Expensive to build and maintain

Low in-premises mobility only, easy access

High mobility allowed, easy access

Low in-premises mobility, wiring of distant areas cumbersome

Weather conditions effects

Not very reliable Very 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

ForecastsForecasts

800M projected new lines by 2002685M in developing countries

QuestionsQuestions??

Basie station

ReferencesReferences

http://www.tenet.res.in/Papers/wll/iete1.htmlhttp://bicsi.org/Wireless2/index.htmhttp://sss-mag.com/wlltutor.htmlhttp://www.cdg.org/http://www.voicendata.com/may98/will.htmlhttp://www.cdg.org/tech/wll.asphttp://www.motorola.com/NSS/Press/press_archive_1997/19970826a.htmlhttp://www.mobilemark.com/WLL_antennas.htmlhttp://www.atdi.co.uk/t_wll.htmhttp://www.lucent.com/wireless/http://www.art-telecom.fr/communiques/pressrelease/98-13a.htmhttp://www.fcr.fr/en/savoirfaire/blr.htmhttp://www.citi.columbia.edu/wireless/col_1096.htmhttp://www.telecomresearch.com/tutorials.htmlhttp://www.kyocera.co.jp/frame/product/telecom/english/wll/index.htmhttp://www.americasnetwork.com/issues/96issues/961101/110196_wll.htmlhttp://208.220.133.42/issues/199803/tci/bout.html

ReferencesReferences

http://www.smartrunk.com/WLL/SSIWLL.htmlhttp://www.amd.pl/products/cpd/prodover/wllsol.htmlhttp://www.biz.uiowa.edu/class/6K251_park/Student-Reports/ymao/index.htmlhttp://ieeexplore.ieee.org/iel3/5002/13722/00632520.pdfhttp://www.ece.queensu.ca/dept/vpoor.pdfhttp://www.mprg.ee.vt.edu/tech_xfer/ppt/EmergingTechnology.pdfhttp://www.carlsontech.com/manual15.htmlhttp://www.corporateinformation.com/data/statusa/china/chinavsat.htmlhttp://www.hindubusinessline.com/2001/01/09/stories/14096802.htmhttp://www.tradeport.org/ts/countries/brazil/mrr/mark0115.htmlhttp://www.atdi.com/99/p_wll.htmhttp://www.marconi.com/html/news/libertywlltrials.htmhttp://citeseer.nj.nec.com/359563.htmlhttp://www.corporateinformation.com http://www.stanford.edu/class/ee359/http://www.alcatel.com/telecom/asd/products/groups/access/wireless/wllacc1.htmhttp://www.goodwin.ru:8086/products/wll/http://www.goodwin.ru:8086/dect.html (DECT standard)

ReferencesReferences

Wideband CDMA personal communications system featuring IDSN compatibilityReed Fisher, Henri Suyderhoud, Toshiro Kato, Atushi Fukasawa and Takuro Sato ©1997 IEEE

Performance Analysis of WCDMA WLL ProtocolSeong Won Shum, Sang Hwan Lee, Minsoo Suk, Hang Gu Bahk Hyundai Electronics ICCT’98 Beijing, China

Capacity of a Wireless Local Loop Network based on GSMThomas Klingenbrunn, Preben MogensenCenter for Person Kommukation, Aalborg University© 1998 IEEE

Network Management Applications for wireless local loopJelena Vucetic Paul KlineDynamic Telecomminications, Inc. 1998

Implementation of code acquisition and code tracking loop for CDMA wireless localloop systemJae-Wook Chung, Jin-Su Kim, Young-Gyun Jeong, Jeong-Suk HaElectronics and Telecommincations Research Institute, Yusong, Taejon, Korea©1998 IEEE

Implementation of Base Station Receiver for CDMA Wireless Local Loop SystemJae W. Chung, Jin S. Kim, Y. G. Jeong, J. S. HaElectronics and Telecommincations Research Institute, Yusong, Taejon, Korea©1997 IEEE

Wireless Local Loop – Propagation Environment Measurements and analysisLevin M., Katz E., Gil A., Freedman A., Matityahu I., Dilmon D.Wireless Systems Tadiran Telecommunications, Israel1996 IEEE

Issues and challenges of implementing a wireless local loop based telephone access networkT.Minero, T. Babji NEC cororation, JAPAN© 1997 IEEE

ReferencesReferences

Wireless local loop: why the slow take up?Andrian May, Electronics Communication Engineering Journal 1998

A Wideband CDMA based Wireless Local Loop ProtocolMehmet Ulema and Young Ki YoonDaewoo Telecom R&D Center © 1999 IEEE

An Implementation of Wireless Local Loop fixed StationSang Sik Lim, Mobile Telecommunication DivisionElectronics and Telecommunications Research Institute, Taejon, Korea© 1998 IEEE

A comparison of wireless local loop with competing access technologiesW. Webb, Electronics & Communication Engineering Journal 1998

Estimate of Uplink in Overlaid Macrocell/Multi-Microcell CDMA WLL SystemsJ. S. Roh, S. Y. Kim, S. J. Cho, S. C. Son, S. E. Cho H. J. Kang

ReferencesReferences

ReferencesReferences

Wireless Local Loop Made For the USA?

David Kopf, Peter Meade, America’s Network November 1996

The Performance of DS-CDMA For Wireless Local Loop

Q. Bi, D.R. Pulley

1996 IEEE

Wireless Local Loop: Architecture, Technologies and Services

Anthony R. Noeprel, Hughes Network Systems, Yi-Bing Lin

CSIE/NCTU 1998 IEEE