GSM Air Interface
description
Transcript of GSM Air Interface
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InterfacesBYB S S RaoSDE GSM Faculty
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Physical ChannelThis is the medium over which the information is carried.
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Logical ChannelsThe logical channels consist of the information carried over the physical channel.
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Types of Logical ChannelsTraffic ChannelsControl Channels
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Traffic ChannelThese Channels carries speech or data information.Full Rate Channel Speech ( 13 Kbps net , 22.8Kbps gross). Half Rate Channel Speech ( 12.2 Kbps/net , 22.8Kbps gross)
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Control Channel GroupsBCCH GroupCCCH GroupDCCH Group
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BCCH GroupAll BCCH Channels are in downlink onlySCH carries information for frame synchronizationFCCH provides information for carrier synchronization.
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BCCHThis channel carries the following information:Location area identityCell identityDTX permittedList of frequencies used in Cell etc.
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FCCHFrequency correction channelThis allows the mobile to synchronize its own frequency to that of transmitting BTS
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SCHSCH Carries the following info. Frame Number Base station identity code (BSIC)This allows the MS to synchronize to the TDMA frame
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CCCHThe Common Control Channel Group works in U/L & D/L
RACH (Random Access Channel)PCH (Paging Channel)CBCH ( Cell Broadcast Channel)
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RACHRACH is used by MSs to gain access to the System
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PCHPCH is used by the System to call MS
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CBCHCBCH is used to transmit messages to be broadcasted to all MSs within Cell. For example., road traffic information , sporting results.
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AGCHAccess Grant ChannelThis is used in DownlinkThis is used to assign resources to the MS., such as SDCCH
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DCCHDedicated Control Channels.This Group consists of SDCCH , ACCH ( SACCH and FACCH)
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SDCCHThis supports the transfer of data to and from MS during call set up and validation.
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SACCHSlow associated control channelThis is used for radio link measurement and power control messages.
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FACCHFACCH is used to pass event type messages for example Handover Messages
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FACCH & SACCHBoth channels are operated in U/L & D/L
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Channel combinations and Time Slots
Channel CombinationTim e slotsTrafficAny Time slotBroadcast0,2,4,6 ( 0 first)DedicatedAny Time slotCombined0 only
Channel CombinationChannelsTrafficTCHBroadcastBCCH + CCCHDedicatedDCCHCombinedBCCH + CCCH + SDCCH + SACCH
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THANK YOU ALL