Multiple-access interference suppression in CDMA wireless systems

Abstract

This thesis presents techniques that suppress the multiple access interference (MAI) in CDMA wireless systems. MAI is the main factor that influences the communication quality and the capacity in CDMA wireless systems. Hence the suppression of MAI is essential to the performance of a CDMA wireless system. For conventional CDMA systems where matched filters are used as receivers, the only MAI suppression method available is the power control, which allocates each user in the system an appropriate transmitter power level such that the transmitter power is minimized to decrease the MAI, while at the same time each user maintains a given SIR requirement. Another MAI suppression method that has received much attention is the multiuser detection, which employs more complex receivers than the matched filters and uses signal processing techniques to suppress the MAI. These two methods form the basis for MAI suppression in CDMA wireless systems. In this thesis, we first investigate the power control method. A decentralized adaptive power control algorithm which requires only the received signal and the signature sequence of the desired user is discussed. Then the multiuser detection method is discussed. A blind adaptive multiuser detection algorithm that requires the same knowledge as matched filters to demodulate received signals is presented. Both theoretic study and simulation results show the effectiveness of these algorithms. Finally, power control and multiuser detection are combined together within the same system model. A power controlled multiuser detection algorithm is proposed, which preserves the decentralized property and is shown to be effective in simulation studies. Simulation results also show that this algorithm is superior to conventional power control algorithm and multiuser detection algorithm in terms of total transmitter power and more relaxed requirement on the SIR targets of the system.