Wireless Local Loop (WLL)

Presentation Outline
◼ What is WLL?
◼ Differences with mobile cellular systems
– Why WLL?
◼ System Analysis
– examples
◼ The future of WLL
 Definition
◼ What is WLL?
- WLL is a system that connects subscribers
to the local telephone station wirelessly.
◼ Systems WLL is based on:
– Cellular
– Satellite (specific and adjunct)
– Microcellular
◼ Other names
– Radio In The Loop (RITL)
– Fixed-Radio Access (FRA).
A general WLL setup
 WLL services
◼ Desirable:
– Wireless feature should be transparent
– Wireline Custom features
◼ Other:
– Business related
» Hunt groups,
» Call transfers
» Conference calling
– Calling cards, coin phones
– V.29 (9600bps)
– ISDN (64kbps)
 WLL should provide…
◼ Toll-quality service
◼ Expand from a central office to about 5
miles
◼ Low license cost
◼ Subscriber costs equivalent or better than
copper
 Ideas for U.S. market
◼ Supplement Copper Lines
– Easier third telephone line
– Data service
◼ Fixed Mobile Users
– Take phone wherever you want / charged on 2
levels
– “home” could mean neighborhood
– Charged regular mobile rate if you’re on the
road
 Cost Considerations

• Wireless cost is constant over distance for WLL

• Wireline depends on distance AND terrain
 Situations “made” for WLL
◼ Environments where 3rd line is degraded
might be cheaper to go wireless
◼ Where it’s impossible to lay copper (3 rd
world, small islands)
◼ Business parks, industrial areas
◼ Speedy deployment, stop gap application
till wireline is in
– 90-120 days for activation
 Developed vs. Developing
◼ Developed: Wireline service
– Firmly established, cellular penetration is
relatively high
– Incumbent operator would use it to install 2nd,
3rd lines, coverage to rural areas
– 2nd or 3rd competitive operator deploy it for fast
& cost effective deployment
– Quick way to establish market presence
– cellular complement to their offerings
 Developed vs. Developing
◼ Developing
– Quick & easy to deploy in countries with little
copper line service, so as to accommodate
people on enormous waiting lists for basic
service
– Low maintenance costs
– Allows more competition in provider market
 Examples
◼ UK
– 150 PTOs have licenses for wireless
– Focus on regional networks
– WLL Commercial services
» Ionica, Atlantic Telecom, Scottish Telecom
◼ Poland
– Most exciting market in eastern Europe
– Local loop is the bottleneck
– 150,000 WLL lines since 1996 (15% of new)
– Ericsson, Motorola contracts
 Connection Setup
UWLL
WANU Transceiver WASU

Trunk
Air TWLL
Switch WLL AM
PSTN function Controller HLR Interface

Wireless Access Network Unit(WANU) Wireless Access Subscriber Unit(WASU)

– Interface between underlying telephone – located at the subscriber
network and wireless link
– translates wireless link into a
– consists of traditional telephone connection
• Base Station Transceivers (BTS)
• Radio Controller(RPCU)
• Access Manager(AM)
• Home Location Register(HLR)
 Important Results of Fixed to
Fixed Propagation in WLLs
◼ Signal channel is not a Rayleigh fading channel:
– Power control algorithms are simpler and can be
utilized more effectively
◼ Channel Randomness is lost:
– Makes analysis difficult
◼ Pathloss exponent is considerably smaller (Why?):
– 20dB/dec compared to 40dB/dec
– Decreases cell capacity
– Allows for larger coverage area
 Fixed to Fixed
Propagation(cont’d)
◼ No handoffs necessary:
– Decreases hardware costs and system complexity
– Increases quality of service through accurate traffic predictions
◼ Allows usage of directional antennas:
– Can greatly reduce interference and increase cell capacity

30dB 10dB

-30dB -40dB
0o 60o 0o 120o 180o

BS antenna Subscriber antenna

 In-Cell Interference (CDMA)
◼ I = (Nh – 1)aS  NhaS
a = voice activity factor
Nh = total # of houses
S = power received at cell site from every house
 Out-of-Cell Interference
◼ Pathloss: 20dB/dec as opposed to 40dB/dec
 need to take in account more tiers
◼ Only from houses whose antennas are
directed at the center cell base station
 Interference from Another Cell
◼ Blue area is region of interferers
for C
◼ It is Not a perfect pie shape
◼ If w = (1/2)*(antenna width)
(in radians)
◼ W = w+2sin-1((R/D)sin(w/2))
◼ If w<<1 and R<<D:
W = w (1+(R/D))
is the “pie” arc length
 Per-Tier Interference
◼ Integration over W and all the cells at tier n yields:
In = [aNhSw/(3sqrt(3))][1/n]
for n>4
◼ Interference is proportional to antenna width w and
inversely proportional to the tier number.
◼ Decreasing the antenna width can greatly reduce
interference.
◼ As the number of tiers approaches infinity, so does the total
interference. Therefore, system capacity is a function of
the total number of tiers in the system.
 Capacity comparison
for 5 MHz spectrum allocation
Detail IS-95 CDMA IS-136 TDMA ETSI (GSM)
Mobile WLL Mobile WLL Mobile WLL
Chan. BW 1250 1250 30 30 200 200
(kHz)
# 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. 4 4 7.95 13.92 2.78 2.78
Per sect.
Erlangs per cell 38.3 48.7 9.84 19.6 9.12 9.12
Per MHz
 Comparison
WLL Mobile Wireline
Wireless
Good LOS Mainly diffuse No diffuse
component components components
Rician fading Rayleigh fading No fading
Narrowbeam Omnidirectional Expensive wires
directed antennas antennas
High Channel reuse Less Channel reuse Reuse Limited by
wiring
Simple design, Expensive DSPs, Expensive to build
constant channel power control and maintain
Low in-premises High mobility Low in-premises
mobility only, easy allowed, easy mobility, wiring of
access access distant areas
cumbersome
Weather conditions Not very reliable Very reliable
effects
 Examples of services provided
◼ Marconi WipLL (wireless IP local loop)
– Based on Frequency hopping CDMA
– Internet Protocol 64kbps to 2.4Mbps rates Committed
Information Rate or best effort service
◼ Lucent WSS (wireless subscriber system)
– 800 to 5000 subscribers per switch
– Uses FDMA/FDD 12 Km to 40Km coverage
◼ GoodWin WLL
– DECT standards
– 9.6 kbps rate
– Specified conditions -5°С...+55°С, 20...75% humidity
 Future of WLL / Overview
◼ Depends on
– economic development
– existing infrastructure of a region
◼ Offers
– market competition
– quick deployment
– relatively reliable service at low costs
 Forecasts

800M projected new lines by 2002

685M in developing countries
 Questions?

Basie station
 References

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

http://www.smartrunk.com/WLL/SSIWLL.html
http://www.amd.pl/products/cpd/prodover/wllsol.html
http://www.biz.uiowa.edu/class/6K251_park/Student-Reports/ymao/index.html
http://ieeexplore.ieee.org/iel3/5002/13722/00632520.pdf
http://www.ece.queensu.ca/dept/vpoor.pdf
http://www.mprg.ee.vt.edu/tech_xfer/ppt/EmergingTechnology.pdf
http://www.carlsontech.com/manual15.html
http://www.corporateinformation.com/data/statusa/china/chinavsat.html
http://www.hindubusinessline.com/2001/01/09/stories/14096802.htm
http://www.tradeport.org/ts/countries/brazil/mrr/mark0115.html
http://www.atdi.com/99/p_wll.htm
http://www.marconi.com/html/news/libertywlltrials.htm
http://citeseer.nj.nec.com/359563.html
http://www.corporateinformation.com
http://www.stanford.edu/class/ee359/
http://www.alcatel.com/telecom/asd/products/groups/access/wireless/wllacc1.htm
http://www.goodwin.ru:8086/products/wll/
http://www.goodwin.ru:8086/dect.html (DECT standard)
 References
Wideband CDMA personal communications system featuring IDSN compatibility
Reed Fisher, Henri Suyderhoud, Toshiro Kato, Atushi Fukasawa and Takuro Sato
©1997 IEEE

Performance Analysis of WCDMA WLL Protocol

Seong 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 GSM

Thomas Klingenbrunn, Preben Mogensen
Center for Person Kommukation, Aalborg University
© 1998 IEEE

Network Management Applications for wireless local loop

Jelena Vucetic Paul Kline
Dynamic Telecomminications, Inc. 1998
 References
Implementation of code acquisition and code tracking loop for CDMA wireless local
loop system
Jae-Wook Chung, Jin-Su Kim, Young-Gyun Jeong, Jeong-Suk Ha
Electronics and Telecommincations Research Institute, Yusong, Taejon, Korea
©1998 IEEE

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

Wireless Local Loop – Propagation Environment Measurements and analysis

Levin M., Katz E., Gil A., Freedman A., Matityahu I., Dilmon D.
Wireless Systems Tadiran Telecommunications, Israel
1996 IEEE

Issues and challenges of implementing a wireless local loop based telephone

access network
T.Minero, T. Babji NEC cororation, JAPAN
© 1997 IEEE
 References

Wireless local loop: why the slow take up?

Andrian May, Electronics Communication Engineering Journal 1998

A Wideband CDMA based Wireless Local Loop Protocol

Mehmet Ulema and Young Ki Yoon
Daewoo Telecom R&D Center © 1999 IEEE

An Implementation of Wireless Local Loop fixed Station

Sang Sik Lim, Mobile Telecommunication Division
Electronics and Telecommunications Research Institute, Taejon, Korea
© 1998 IEEE

A comparison of wireless local loop with competing access technologies

W. Webb, Electronics & Communication Engineering Journal 1998

Estimate of Uplink in Overlaid Macrocell/Multi-Microcell CDMA WLL Systems

J. S. Roh, S. Y. Kim, S. J. Cho, S. C. Son, S. E. Cho H. J. Kang
 References
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