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.
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
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
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
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.
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.