PERFORMANCE OF MMSE RECEIVERS FOR DS - CDMA IN FADING CHANNELS

Abstract

The performance of the minimum mean-squared error (MMSE) receiver for the detection of direct sequence code division multiple access (DS-CDMA) is evaluated in various fading channel models, by the software simulation of the system in the MATLAB environment. The behavior of the MMSE receiver in frequency-nonselective fading channel is examined. The MMSE receiver often loses phase lock on the desired signal when the desired signal dips into a deep fade. A modification to the MMSE receiver is presented which is demonstrated to function well in flat-fading channels. Few modifications to the basic MMSE receiver for frequency-selective fading channels are presented. The performance advantage is gained through the knowledge of the fading parameters of the various transmission paths of each user's signal. Having this knowledge is not particularly useful on a flat fading channel, but is crucial in a multipath fading channel and the inability to learn the fading channel parameters leads to substantial degradation in capacity.