Presented By:
Panos Tzanos
Vladimeros Vladimerou
Derek Starr

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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
 Situations “made” for WLL
 Environments where 3rd line is degraded might be cheaper to go wireless
 Where it’s impossible to lay copper (3rd 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
 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
 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
 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
Þ 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
 Comparison
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