Modified MMSE receiver for detection of DS-CDMA signals in fading channels

This paper examines the behavior of the MMSE receiver in frequency non-selective fading channels. It is noted that the MMSE receiver will often lose phase lock on the desired signal when that signal dips into a deep fade. A modification to the MMSE receiver is presented which is demonstrated to function quite nicely in flat fading channels. Analytical results for the modified MMSE receiver are presented and found to agree very well with simulation results. These analytical results are then compared to the theoretical performance of the conventional (i.e., correlator) receiver in terms of both BER and capacity. As expected, the modified MMSE receiver is found to offer a substantial improvement in both BER and capacity. Finally, a simple, empirically derived formula is given which will give a good approximation to the BER of the modified MMSE receiver in a Rayleigh fading environment. This formula can also be used to determine the number of users a system can support. It is noted, that as Eb/No grows, it is quite feasible to approach 100% channel utilization with the MMSE receiver, whereas a conventional receiver is typically limited to a utilization of 10-20%.

Modified MMSE receiver for detection of DS-CDMA signals in fading channels Conference Paper