Rate determination algorithms in IS-95 forward traffic channels

According to the IS-95 CDMA standard, the transmit data rate can vary from frame to frame depending on the speech activity. However, the receiver does not know the data rate of the received frames. Conventionally, the receiver has to decode the received frame four times corresponding to the four possible data rates in rate set 1 or rate set 2 so as to obtain the correct decoded frame. Two rate determination algorithms for using 8 kbps (rate set 1) and 13 kbps (rate set 2) speech codecs in the forward traffic channel are introduced. The idea of maximum-likelihood estimation is employed in these two algorithms to determine the data rate. By using these algorithms, the received frame can be decoded once only corresponding to the determined rate instead of four times. Consequently, the decoding complexity and the power consumption at the receiver can be significantly reduced. From our analysis, the worst-case complexity and the average power consumption can be saved by a factor of 2 and 5, respectively