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Reverse Channel
 

Reverse Channel

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CDMA REVERSE CHANNEL DESCRIPTION

CDMA REVERSE CHANNEL DESCRIPTION

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    Reverse Channel Reverse Channel Presentation Transcript

    • REVERSE CHANNEL
    • REVERSE CHANNEL  CDMA reverse channel is the information passed from mobile to Base station.  CDMA reverse channel is fundamentally different from the forward channel.  In forward channel, QPSK is employed.  In this channel, OQPSK is employed.
    • REVERSE CHANNEL OQPSK  Orthogonal Quadrature Phase Shift Keying  OQPSK is closer to a constant envelop modulation  A constant envelop modulation technique provide for a more power efficient implementation of the transmitter at the MS.
    • REVERSE CHANNEL  Bandwidth is 1.25MHz and the frequency range is 869-894 MHz.  Compared with the forward channel, there is no spreading of the data symbols since orthogonal codes are used for waveform encoding.  The orthogonal modulation consumes B.W. but reduces the error rate performance of the system.
    • Structure of Reverse Channel
    • REVERSE CHANNEL Reverse Channel Access Channel Traffic Channel
    • Access Channel  Used to transmit the ctrl info such as call origination, response to a page from MS to the BS.  The data rate is fixed at 4800bps
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    • Reverse Traffic Channel  Supports Voice data at 2 rate sets RS1 and RS2 i.e., fundamental code channel and supplementary code channel.  In both the cases, the data burst before the 64-ary orthogonal modulation and after the coding & interleaving is at a rate of 28.8kbps
    • Reverse Traffic Channel for fundamental code
    • Reverse Traffic Channel  Data burst randomizer is used only in fundamental code channel to mask the redundant data during symbol repetition.  After spreading by long PN code by factor 4, the chip rate= 307.2x4 =1.2288Mcps
    • Reverse Traffic Channel for supplementary code
    • Packets and Frame Formats In IS-95  Sync. Channel framing  Paging channel framing
    • Sync. Channel Framing  Provides the MS info about the >system identification (SID) >the n/w ID (NID) >PN short sequence offset >the PN long code state >system timings.
    • Sync. Channel Framing  Every 32 bits is simplified as 2, >SOM (Start of the message) >Data  The SOM consists of the msg length, data, CRC, padding
    • Paging Channel Framing  Used to send some info to MS.  These info are traffic channel info, temp mobile subscriber identity, response, list of neighbouring BS and their parameters.
    • Paging Channel Framing  The channel length is 80ms.
    • Paging Channel Framing  It contains msg length, data, CRC and padding.  Data rate is 4800 or 9600 bps and txed over a paging channel half frame (10ms)  Half frame has 1 bit->SCI (Synchronization capsule indicator) is used IIlar to SOM bit.
    • Soft handoff  By simultaneously evaluating the Rxed. Signal from a single subscriber at several BS, the MSC may decide which signal is the best one.