Implementation of Zero Forcing Linear Algorithm for CDMA-Based Multiuser Detection Technique Using MATLAB

Abstract

Multiuser Detection (MUD) is the estimation/demodulation of transmitted bits in the presence of Multiple Access Interference (MAI). Matched filter-based conventional detectors treat the MAI as Additive White Gaussian Noise (AWGN). However, MAI has a nice correlative structure that is quantified by the cross-correlation matrix of the signature sequences. Hence, multiuser detectors taking advantage of this correlation would perform better than the conventional matched filter bank. MUD is a concept which brings improvement over the conventional Code Division Multiple Access (CDMA) receiver. Spread spectrum CDMA uses certain coding properties to accommodate many users. MUD technique is employed to improve the performance of Direct-Sequence (DS)-CDMA. The performance of DS-CDMA is limited by MAI and multipath distortion. This paper shows the linear MUD Zero Forcing (ZF) Technique which involves matrix inversion operations. The computation time of matrix inversion increases if the number of users become large because the size of matrix to be inverted increases. By varying the users from 1 to 64, it is concluded that if the number of users increases, the Bit Error Rate (BER) also increases. ZF operator is given by (R)–1, which is the operator for ZF.

Keywords: Multiple Access Interference (MAI), Zero Forcing (ZF), Multiuser Detection (MUD)