Reverse Channel

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CDMA REVERSE CHANNEL DESCRIPTION

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Reverse Channel

  1. 1. REVERSE CHANNEL
  2. 2. 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.
  3. 3. 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.
  4. 4. 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.
  5. 5. Structure of Reverse Channel
  6. 6. REVERSE CHANNEL Reverse Channel Access Channel Traffic Channel
  7. 7. 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
  8. 8. Reverse Access Channel
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  39. 39. Reverse Access Channel
  40. 40. 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
  41. 41. Reverse Traffic Channel for fundamental code
  42. 42. 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
  43. 43. Reverse Traffic Channel for supplementary code
  44. 44. Packets and Frame Formats In IS-95  Sync. Channel framing  Paging channel framing
  45. 45. 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.
  46. 46. 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
  47. 47. 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.
  48. 48. Paging Channel Framing  The channel length is 80ms.
  49. 49. 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.
  50. 50. 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.

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