Higher order constellation with simplified minimum mean square error (MMSE) receiver in CDMA channel with tone interference

It has previously been shown that employing a higher order constellation in conjunction with CDMA can improve the performance of the multiuser system in the presence of severe ISI and narrowband Gaussian interference. We study a similar scenario here, except that the narrowband Gaussian interferer is replaced with a tone interferer. It is shown that the use of the higher order alphabet size is also useful in the tone interference case. Also, we derive lower and upper bounds on the performance of an MMSE receiver in a multiuser, flat fading scenario. Later we apply the same technique to a multiuser, frequency selective fading scenario with negligible or mild ISI