22 Uplink channelization and spreading operations.
I-Channel
PN
Code
X
X
LPF
LPF Q-Channel
Dedicated
Channel
QPSK
Modulator
Walsh
X
Complex
Multiplication
FIGURE 1.23 Downlink channelization and spreading operations.
The baseband, low-pass filter is a square root??“raised cosine (SRC) with a roll-off factor of
0.22. This filter is used at both the transmitter and receiver sections. The power control update
rate is given as 1500 Hz. As indicated above, the maximum number of power control bits per time
slot is 8. These will all be transmitted with the same sign to aid the receiver in detecting the transmit
power control (TPC) command reliably.
An example of transport channel multiplexing is given in Fig. 1.24. We show an example of how a
data-based transport channel (DTCH) and low-rate control transport channel (DCCH) are each encoded,
interleaved, and segmented into frames. Then, they are multiplexed into a physical channel to be interleaved
and time slot segmented. The downlink multiplexing operations are shown in Fig. 1.24.
As we can see in the figure, the downlink spreading factor for the data-based service is 32, and
the associated uplink spreading factor is 16. This was obtained from the fact that there are 160 bits
per time slot (140 data plus 20 control) that become 80 QPSK symbols.
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