Forward Traffic Channel of CDMA
Forward Traffic Channel is used to Transmit Data and Signaling Information.
- Symbol repetition makes symbol streams at different rates adapted to those at the rate of 19.2k. The original symbol stream at the rate of 19.2Kbps will not be repeated, 9.6Kbps symbol stream will be repeated once, 4.8Kbps symbol stream will be repeated twice…. Then, after the interleaving, long code scrambling, spreading, etc., the transmitting power of repeated bits is reduced during the transmission. Thus, variable rates can be achieved and the system capacity be increased.
- During the long code scrambling, one chip will be sampled from every 64 long code chips for exclusive-or with a scrambled chip.
- A forward traffic channel includes a power control sub-channel and a power control bit is used to instruct an MS to increase or decrease the transmitting power. Each forward traffic channel frame (20ms) can be divided into 16 power control groups (each group is 1.25ms long).
- Each power control group contains a power control bit , therefore the rate of reverse fast power control is 16* (1s/20ms)=800bps. And the power control bit is embedded right during the long code scrambling.