Gsm Handoff 1 [Compatibility Mode]

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T.KartheeswaranVavuniya Campus

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Outline

• What is GSM• GSM History• GSM System Architecture• GSM Call Operations• Features of GSM• What is Handoff• Hand of Features• GSM Handoff• Handoff Architecture • Type of Handoff• Performance of Handoff

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Ready !!! To Handover

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What is GSM?

• Global System for Mobile (GSM) is a secondgeneration cellular standard developed tocater voice services and data delivery usingdigital modulation

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GSM History

• 1982 Conference of European Posts and Telegraphs (CEPT) GSM (Group Special Mobile) group was formed to study and develop a pan-European public land mobile system

• GSM Criteria –– Good subjective speech quality, Low terminal and service cost– Support for international roaming –,one system for all of Europe– Ability to support handheld terminals, Support for range of new

services and facilities, Enhanced Features, ISDN compatibility– Enhance privacy, Security against fraud

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GSM History Cont...

• 1980-GSM transferred to European Telecom• 1991-Comerciallized • 1992-First Customer• 1993-36 GSM networks -22 Countries• 1994-1.3 Million Subscribers• 1996-25 Million Subscribers• 1997-55 Million Subscribers

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System Architecture

• Mobile Station (MS)Mobile Equipment (ME)Subscriber Identity Module (SIM)

• Base Station Subsystem (BBS)Base Transceiver Station (BTS)Base Station Controller (BSC)

• Network SubsystemMobile Switching Center (MSC)Home Location Register (HLR)Visitor Location Register (VLR)Authentication Center (AUC)Equipment Identity Register (EIR) 7

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System Architecture Cont...

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GSM Operations

Speech decoding

Channel decoding

De-interleaving

Burst Formatting

De-ciphering

DemodulationModulation

Ciphering

Burst Formatting

Interleaving

Channel Coding

Speech coding

Radio Interface

Speech Speech

13 Kbps

22.8 Kbps

22.8 Kbps

33.6 Kbps

33.6 Kbps

270.83 Kbps

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Basic Features of GSM

• Call Waiting• Call Hold• Call Barring• Call Forwarding• Multi Party Call Conferencing

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Advanced Features Of GSM

• Calling Line ID• Alternate Line Service• Closed User Group• Advice of Charge• Fax & Data• Roaming

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What is Hand off

• What happens when mobile move to one areato another???

• In a cellular telephone network, handoff is thetransition for any given user of signaltransmission from one base station to ageographically adjacent base station as theuser moves around

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Tor K Moseng, Handoff in Wireless Internet Access

Hand Off

BSC

BS1 BS2 BS3

1. Connect to BS1 and start conversation2. Moving out of BS1’s coverage – connect to BS23. Moving out of BS2’s coverage – connect to BS34. Conversation ended – still within BS3’s coverage

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Hand Off

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BTS Signal Distribution

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Hand Off Must be!!!!

• Perform Quickly• Perform infrequently• Imperceptible for users• Perform Successfully

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Hand Off Features

• Maximize– Performance– Reliability

• Maintain– Seamless– Load Balancing

• Minimize– Interference– No of Handoff

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When hand off occur??

• Initiated when received signal level dropsbelow a certain threshold value.

• Not as simple as it seems• Actually consider a time average of the

received signal instead of the instantaneouslevel.

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When hand off occur??

• Define – PMIN_USABLE as the minimum usable signal level – PHANDOFF as the threshold received signal level at

which a handoff will be initiated – ∆ = PHANDOFF – PMIN_USABLE

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Handoff - Successful

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Handoff - Unsuccessful

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Why Handoff Fails?

• ∆ Too small (i.e. PHANDOFF too low)• High mobile speeds • Excessive delay at MSC

– High traffic level– Unavailability of channels

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When hand off occur??...

• Must optimize ∆. – Too large => too many handoffs – Too small => too many lost calls

• Value of ∆ depends on – Environment – Expected mobile speeds – Time required to perform a handoff

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• Within the GSM system there are four types of handover that can be performed for GSM only systems:– Intra-BTS handover

– Changing frequency /slot due to the traffic same BS

– Inter-BTS Intra BSC handover– Different BTS same BSE switch frequency and slot before release old

– Inter-BSC handover– From one BSC to Another BSC controlled by MSC

– Inter-MSC handover– between networks. Two MSCs control.

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GSM Hand off

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Tor K Moseng, Handoff in Wireless Internet Access

Three types of handover Intra-BSC handover Inter-BSC handover Inter-MSC handover

BSCBSC BSC

MSC

MSC

BSC

GSM Hand off

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Handoff

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Type of Hand Off

• Soft Hand off– Hand off where a new connection is established before

the old one is released

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Type of Hand Off

• Hard Hand off– Hard handoff is one where an existing connection

must be broken before the new one is established

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Type of Hand Off

• Softer Hand off– It may also occur when a signal is replaced by a stronger

signal from a different sector under the same basestation

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• Vertical Handoff• Horizontal Handoff

Type of Hand Off

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Vertical Hand Off

• This handoff process of a mobile terminaltakes place among access points supportingdifferent network technologies. For example,the changeover of signal transmission from anIEEE 802.16 WiMax base station to a cellularGPRS network is considered as a verticalhandoff process

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Vertical Hand Off

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Horizontal Hand Off

• In this handoff process, the handoff of a mobileterminal takes place between base stationssupporting the same network technology. Forexample, the changeover of signaltransmission due to the mobility of the mobileterminal from an IEEE 802.11bbase station toa neighbouring IEEE 802.11b base station isconsidered as a horizontal handoff process

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Horizontal Hand Off

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Performance

• Priority Schemes for Handoffs – Goal is to minimize rate of handoff failure

• Guard Channel Concept – reserve set of channels for handoffs only

• Queuing of Handoffs – queue Serves handoffs on a FCFS basis

• Giving handoffs priority over call requests– reduces rate of handoff failure desirable from user’s

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Sri Lankan GSM Network

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Shall We Discuss????

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References(web)

• 3GPP, [Online]: www.3gpp.org• Jacques De Kegel, IBM & Wireless 2004, Presentation

WIreless e-business EBO, [Online]: http://www.ti.kviv.be/Ittelecom/EBO_overview.pdf

• Charles Perkins, Presentation at an IEEE 802 Handoff Tutorial, November 2002, [Online]: http://ieee802.org/16/tutorial/T80216-02_04.zip

• Wikipedia, The Free Encyclopedia, [Online]: http://en.wikipedia.org

• GSM Handoff http://www.radio-electronics.com/info/cellulartelecomms/gsm_technical/handover-handoff.php

• Handoff http://www.authorstream.com/Presentation/belide-1343819-my-tech-semivar/ 39

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Thank You

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