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WLL

Wireless local loop

Working in CDMA technology

At present 3 carriers in India.(BSNL)

42, 83 & 160 Range :-824 to 896mhz

824+0.03xN mhz (N=carrier)

Carrier separation is 1.25mhz One pilot for each sector(4,172,340)

Separation is 168

EVDO carrier is 1 (824+0.03x1)

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Advantages of WLL

Quick Installation

Small initial investment

Cheap and easy maintenance Possibility of removing and reinstalling the

system.

Limited mobility Internet/Fax/SMS fecility in FWT

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NETWORK DIAGRAM OF CDMA / WLL SYSTEM

PSTN

BSC

BTS

FAX

FWT

2 MbpsDIGITAL

LINK

..

MS

2 MbpsDIGITAL

LINK2 MbpsDIGITAL

LINK

TelecomNetwork

BTS

BSC : Base Station Controller

MSC : Mobile Switching CentreFWT : Fixed Wireless Terminal at subscriber premises.

MS : Mobile Station

MSC

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EVDO

EVDOEvolution of data only or

Evolution data optimizedSupport asymmetriccommunicationsAllocating a majority bandwidthto downloads

Data transmission speed up to3.1 mbpsIn India now 2.4mbps per carriermax

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NIC (Network interface card)

Speed : 144kbps

Works where ever WLL signal is available.

All Kerala roaming

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HANDOFF TYPES

HARD HANDOFF

SOFT HANDOFF

SOFTER HANDOFF

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Hard & Soft Hand-off

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HARD HANDOFF

In FDMA based cellular systems, neighbor cells usedifferent set of frequencies.

When the signal power received by the mobile unitfrom a neighbor base station exceeds the signalpower of the current cells base station by a certainthreshold, the mobile unit stops communicating withthe current base station and connects to theneighboring station.

This is called HARD HANDOVER.

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SOFT HANDOFF

A mobile unit enters the soft handover statewhen the signal strength of the neighboring cellexceeds a certain threshold but is still below the

current base stations signal strength

The mobile is connected to both base stationsand its transmission power is controlled by thebase station with the higher signal strength

In the uplink two or more base stations canreceive the mobile signal

In the downlink mobile unit can combine signalsfrom different users by a Rake Receiver

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BSC

Base

StationBase

Station

Base

Station

Controlle

r

Mobile

Unit

Soft Handover with Two Base Stations

In the uplink, the mobile station signal is receivedby two base stations which pass the signal to the

combining point called base station controller. In

the downlink same information is transmitted via

both base stations to the mobile unit which treats

them as multipath signals and combine them.

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Hard & Soft Hand-off

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Realistic View of Soft Hand-off

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Advantages of soft handoff

Soft Handoff eliminates the short disruption ofspeech one hears with non-CDMA technologiesduring a handoff.

* Narrow band technologies compete for the signal.In CDMA, the cells come together to obtain the bestpossible combined signal.

* CDMA handoffs do not create the hole in speechthat is heard in other technologies.

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SOFTER HANDOFF

A softer handoff occurs when a subscriber issimultaneously communicating with morethan one sector of the same cell.

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