Download - Wireless in local loop
By:- Mustahid Ali
Presentational OutlineDefinition of WLL Two important issue Capacity and EfficiencyThe Future TechnologiesWireless StandardsDisadvantages of WLLScope of WLL
What is WLL ?
“In telephone network, a Wireless Local Loop is a generic term for an access system that uses a wireless link to connect subscriber to their local exchange in place of conventional copper cable. Using a wireless link shortens the construction period and also reduces installation and operating cost.”
Difference between WLL and mobile system . Mobile systemMobile system
- - connect people on the moveconnect people on the move
- universal coverage- universal coverage
- moderate voice quality - moderate voice quality
- Traffic per subscriber is supposed to be not - Traffic per subscriber is supposed to be not very high. very high.
Wireless in Local LoopWireless in Local Loop -- Serve subscribers at homes or offices.Serve subscribers at homes or offices. -Voice quality must be high. -Voice quality must be high. -Long conversation facility-Long conversation facility -High Traffic support.-High Traffic support.
Difference between WLL Difference between WLL and mobile Systemand mobile System
Efficiency Efficiency ConsiderationConsiderationDepends on use and reuse of spectrum which is
governed by the following :
channel pay load signaling overhead modulation efficiency cell-radius choice of multiple access interference reduction techniques
Channel Pay LoadHigher bit rate pay load large frequency
resourcesVoice Communication required lower bit rate
voice codec
Signaling OverheadUsed in setting up, monitoring and tearing
down of a callCarried out between subscriber and base
stationsMore sophisticated system more signaling
requirementIt is an overhead
Modulation EfficiencyDirect bearing on efficient use of spectrumQAM, QPSK, MSK techniques are usedEfficient techniques are expensive
Cell Radius
N – Channels Availablee – Traffic / Subscriber in
Erlangr – Radius of a cell
Subscriber Density is
FTDMA
- Frequency signal is divided into frequency channels
- Channels are assigned to users on demand
- Used for both analog and digital signals
TDMA
- Careers used for transmission of multiple time
multiplexed channels
- provided batter reuse factor for digital signal
CDMA
- Each bit is uniquely coded
- Receiver use decoder to separate data
- Interference is very small
MC-TDMA
- Use dynamic channel selection
- Frame is divide into time slots
Sectorization
Voice Activity Detection
Frequency Hopping
Capacity of WLL System
Capacity = C = Number of Subscriber/ sq. km. is
S – Total spectrum availableM – Multi Access Efficiency + Modulation
Efficiency + Effect of Overhead R – Reuse Efficiencyx – Payload in bps Required / SubscriberTe – Trunking Efficiencye– Erlang Traffic / Subscriberns – Number of Non Overlapping Sector used per Cellr – radius in KM. for each Cell
Space-Time processing
- Smart Antenna Technology - Transmit Diversity Schemes
Turbo Codes
Multi User Detection
Wireless StandardsFirst Generation Standards -Promised Wide – Scale Mobile communication -AMPS(USA), NTT (Japan), NMT (Europe)
Second Generation Standards -Marked as late eighties and early nineties -Technology used TDMA,GSM -Wireless Standards Used AMPS,IS-95,DECT
Third Generation Standards -DECT Evaluation towards third Generation
DisadvantagesRelatively new technologyNetwork capacity needs improvementHas yet to be fully implemented to maximize
utilization and economy
Developed vs. DevelopingDeveloped: Wire line 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 presencecellular complement to their offerings
Developed vs. DevelopingDeveloping
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 costsAllows more competition in provider market
PotentialWithout the need to have a physical link in
the last mile, WLL offers us a variety of applications that will further enhance our capability to communicate and transfer information
PotentialSuitable for the deployment of
communication facilities in provinces where tele-density is low and geographical terrain is unsuitable for the setting-up of infrastructure
Abbreviation UsedFDMA - Frequency Division Multiple AccessTDMA – Time Division Multiple AccessCDMA – Code Division Multiple AccessMC-TDMA – Multi Career TDMAQAM – Quadrature Amplitude ModulationQPSK - Quadrature Phase Shift KeyingMSK – Minimum Shift KeyingAMPS – Advance Mobile Phone ServiceGSM – Global Service Mobile communicationDECT – Digital European Cordless Telephone
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