Increasing the DS/CDMA system reverse link capacity by equalizing the performance of different velocity users

Abstract

The capacity of the reverse link DS/CDMA system has been investigated by many researchers. Power control is essential for such systems to increase the capacity. Power control based on equalizing the received power levels from different users was proposed. The user's bit error rate (BER) depends on its received signal to noise ratio (SNR). Since the user's required SNR to achieve a given BER depends on its velocity, low mobility users are expected to have a lower BER compared to high mobility ones. Hence, the BER performance of a high mobility user is investigated when determining the system capacity. We propose a power control algorithm based also on power level measurements but where the required threshold is determined according to the user velocity where slow users thresholds are lower than fast ones. This results in increasing the slow users BER but lower the interference they cause to other users and hence increases the system capacity. This increase in capacity is found to be about 30% for a three resolvable Rayleigh fading paths channel and a path-loss exponent of four.