Optimum complexity reduction of minimum mean square error DS-CDMA receivers

The near-far problem can be the capacity limiting factor for direct-sequence code division multiple access (DS-CDMA) communication systems. The “classical” near-far resistant receivers are multi-user detectors with rather high complexity requirements. In order to reduce the complexity, a class of minimum mean square error (MMSE) receivers was proposed. These receivers typically use an adaptive filter to suppress the multi-user interference. The length of the filter is equal to the number of chips per bit. To further reduce the complexity, several methods that shorten the length of the adaptive filter have been developed. 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