Wireless Local Loop (WLL), Deployment issues

1. Wireless Local Loop (WLL)

2. Wireless Local Loop (WLL)
• Providing wireless connections to stationary or near stationary stations within a
small service area
• Generally targeted at the “last mile” or from a point in the neighborhood to the user
Advantages of Wireless local loop:
• ease of installation
• reducing digging, reduce poles, ducts/conduits, …
• quick installation of new links (i.e., rapid provisioning)
• largely distance insensitive pricing - at least up to some limit
• concentration of resources (especially at the multiplexer to the high
bandwidth backbone)

3. Deployment issues
• Spectrum
• licensed - limited interference, but requires licensing
• unlicensed - more interference, but no licensing - generally limited in (maximum
and average) power
• Service Quality
• Users expect it is going to be the same as wireline service
• high reliability
• low risk of fraud (due to others “hijacking” the link)
• Network planning
• should support very high penetration levels (for example >90%)
• exploits the fact that users are not moving (or rarely move)
• antenna height, etc. is generally derived from user density
Very popular in the former “East block” of Europe - since there was no need to
install a local loop cable to bring users to the local exchange of the PSTN;
enabled very rapid provisioning to very large numbers of subscribers.

4. WLL Technologies
• Satellite
• a great chance for the satellite operators (Hughes Network Systems,
Inmarsat International Circular Orbit (ICO), Iridium, Globestar, Odyssey,
American Mobile Satellite Corporation (AMSC), Asia Cellular Satellite
(ACeS), Thuraya, …)
• note that some of these operators (such as Hughes) used terrestrial
versions of their system
• Cellular-based
• used in rural and sparse urban settings
• Low Tier PCS or Microcellular based systems
• PACS, PHS, DECT, …
• Fixed Wireless Access (FWA)
• some times proprietary point-to-point links
• increasingly LMDS

5. 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).

6. 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)

7. 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

8. Wireless Local Loop
• Wired technologies responding to need for reliable,
high-speed access by residential, business, and
government subscribers
– ISDN, xDSL, cable modems
• Increasing interest shown in competing wireless
technologies for subscriber access
• Wireless local loop (WLL)
– Narrowband – offers a replacement for existing telephony
services
– Broadband – provides high-speed two-way voice and data
service

9. WLL Configuration

10. Advantages of WLL over Wired
Approach
• Cost – wireless systems are less expensive due to cost
of cable installation that’s avoided
• Installation time – WLL systems can be installed in a
small fraction of the time required for a new wired
system
• Selective installation – radio units installed for
subscribers who want service at a given time
– With a wired system, cable is laid out in anticipation of
serving every subscriber in a given area

11. Wireless Local Loop (WLL)
• Providing wireless connections to stationary or near stationary
stations within a small service area
• Generally targeted at the “last mile” or from a point in the
neighborhood to the user Advantages of Wireless local loop:
• ease of installation
• reducing digging, reduce poles, ducts/conduits, …
• quick installation of new links (i.e., rapid provisioning)
• largely distance insensitive pricing - at least up to some limit
• concentration of resources (especially at the multiplexer to the
high bandwidth backbone)

12. IS-54 architectural reference model for
WLL:
WANU = Wireless Access Network Unit
WASU = Wireless Access Subscriber Unit
PSTNWASU WANU
UWLL
Switch
Function
AWLL
Trunk
transceiver
AM
HLR
WLL
controller

13. Connection Setup
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)
PSTN
Switch
function
WLL
Controller
AM
HLR
Transceiver WASU
Trunk
Air
Interface
UWLL
TWLL
WANU
Wireless Access Subscriber Unit(WASU)
– located at the subscriber
– translates wireless link into a
traditional telephone connection

14. Deployment issues
• Spectrum
• licensed - limited interference, but requires licensing
• unlicensed - more interference, but no licensing - generally limited in
(maximum and average) power
• Service Quality
• Users expect it is going to be the same as wireline service
• high reliability
• low risk of fraud (due to others “hijacking” the link)
• Network planning
• should support very high penetration levels (for example >90%)
• exploits the fact that users are not moving (or rarely move)
• antenna height, etc. is generally derived from user density
• Very popular in the former “East block” of Europe - since there
was no need to install a local loop cable to bring users to the local
exchange of the PSTN; enabled very rapid provisioning to very large
numbers of subscribers.

15. WLL Technologies
Satellite
• a great chance for the satellite operators (Hughes Network Systems, Inmarsat
International Circular Orbit (ICO), Iridium, Globestar, Odyssey, American Mobile
Satellite Corporation (AMSC), Asia Cellular Satellite (ACeS), Thuraya, …)
• note that some of these operators (such as Hughes) used terrestrial versions of their
system
Cellular-based
• used in rural and sparse urban settings
Low Tier PCS or Microcellular based systems
• PACS, PHS, DECT, …
Fixed Wireless Access (FWA)
• sometimes proprietary point-to-point links
• increasingly LMDS

16. Propagation Considerations for WLL
• Most high-speed WLL schemes use millimeter wave
frequencies (10 GHz to about 300 GHz)
– There are wide unused frequency bands available above 25
GHz
– At these high frequencies, wide channel bandwidths can be
used, providing high data rates
– Small size transceivers and adaptive antenna arrays can be
used

17. Propagation Considerations for WLL
• Millimeter wave systems have some undesirable
propagation characteristics
– Free space loss increases with the square of the frequency;
losses are much higher in millimeter wave range
– Above 10 GHz, attenuation effects due to rainfall and
atmospheric or gaseous absorption are large
– Multipath losses can be quite high

18. Comparison
WLL 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