Optimum Complexity Reduction of Minimum Mean Square ErrorDS - CDMA

|The near-far problem can be the capacity limiting factor for a direct-sequence code division multiple access (DS-CDMA) communication systems. The \classical" near-far resistant receivers are multiuser detectors with rather high complexity requirements. In order to reduce the complexity, the class of minimum mean square error (MMSE) receivers was recently proposed. These receivers typically use an adaptive lter to suppress the multiuser interference. The length of the lter is equal to the number of chips per bit. To further reduce the complexity, several methods that shorten the length of the adaptive lter have been developed. In this paper, we present a common mathematical framework in which these receivers can be evaluated in terms of their probability of bit error. The form of the optimum complexity reduction is derived. Two new structures are proposed and are shown to outperform previously proposed receivers.