CDMA REVERSE CHANNEL DESCRIPTION

1. REVERSE
CHANNEL

19. 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.

20. 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.

21. 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.

22. Structure of Reverse Channel

23. REVERSE CHANNEL
Reverse Channel
Access Channel Traffic Channel

24. 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

25. Reverse Access Channel

26. Reverse Access Channel

27. Reverse Access Channel

28. Reverse Access Channel

29. Reverse Access Channel

30. Reverse Access Channel

31. Reverse Access Channel

32. Reverse Access Channel

33. Reverse Access Channel

34. Reverse Access Channel

35. Reverse Access Channel

36. Reverse Access Channel

37. Reverse Access Channel

38. Reverse Access Channel

39. Reverse Access Channel

40. Reverse Access Channel

41. Reverse Access Channel

42. Reverse Access Channel

43. Reverse Access Channel

44. Reverse Access Channel

45. Reverse Access Channel

46. Reverse Access Channel

47. Reverse Access Channel

48. Reverse Access Channel

49. Reverse Access Channel

50. Reverse Access Channel

51. Reverse Access Channel

52. Reverse Access Channel

53. Reverse Access Channel

54. Reverse Access Channel

55. Reverse Access Channel

56. Reverse Access Channel

57. 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

58. Reverse Traffic Channel
for fundamental code

59. 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

60. Reverse Traffic Channel
for supplementary code

61. Packets and Frame Formats
In IS-95
 Sync. Channel framing
 Paging channel framing

62. 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.

63. 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

64. 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.

65. Paging Channel Framing
 The channel length is 80ms.

66. 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.

67. 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.