A 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 the 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 the BER and capacity. As expected, the modified MMSE receiver is found to offer a substantial improvement in both the BER and capacity. Finally, a simple, empirically derived formula is given which provides 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 the E_b/N₀ 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%