A combined power/rate control scheme for data transmission over a DS/CDMA system

Power control is essential for spread spectrum cellular systems. Perfect power control can result in high intercell interference due to tracking of deep fades. Limiting the user transmitted power will not solve this problem because this will suppress both the interference and the signal itself. We investigate the performance of data users that can tolerate some delay in their transmission. We limit the increase in power to compensate for multipath fading by P_l(dB) and get the extra gain required by reducing the transmission rate. We show that this can result in about a 231% increase in the total transmission rate when the multipath fading consists of a single Rayleigh path. A major issue in this scheme will be tracking the transmission rate by the base station to use it in the demodulation process which is a difficult task when the gain commands can be in error. In this case we propose using only four different transmission rates (R_m, R_m/2, R_m/4, R_m/8) and the base station will demodulate the received signal four times for the four different rates and then pick one data sequence based on metrics like the CRC pass/fail. We show that in such a case, the increase in the total transmission rate can reach 187%