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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