SIMULATION OF MULTISTAGE PARALLEL INTERFERENCE CANCELLATION SCHEMES FOR CDMA

Abstract

system using conventional single user correlator or matched filter receivers. Previous research has shown that multiuser receivers that employ interference cancellation techniques can significantly improve the capacity of a CDMA system. The focus of this dissertation is the study of some multiuser interference cancellation techniques in Direct Sequence Code Division Multiple Access communications. Multistage parallel interference cancellation has been identified as a practical and robust approach for mitigating the effects of MAI. Although the complete parallel interference cancellation detector is simple in structure, its performance degrades when number of active users becomes large. In some cases the performance is even worse than that without cancellation, due to the lack of the exact knowledge of the interfering signal in cancellation [1]. Partial interference cancellation tries to remedy this weakness by reducing cost of wrong interference estimation through a weight in each stage. A more improved version of partial cancellation is adaptive, multistage structure based on partial interference cancellation approach. In this structure, the weights are obtained by minimizing the mean square error between the received signal and its estimate through Least Mean Square (LMS) algorithm. Neither a training sequence nor a pilot signal is needed in this scheme. In this dissertation, parallel interference cancellation schemes have been simulated for both, Additive White Gaussian Noise (AWGN) channel and multipath fading channel. Performance curves are plotted between Bit Error Rate (BER) and number of users. The performance of each of these interference cancellation iii schemes is compared with the performance of conventional receiver and relative performance comparison of various interference cancellation schemes is also plotted. iv