An adaptive DS-CDMA receiver for multipath and multi-user environments

A major limitation to the capacity of direct-sequence code division multiple access systems is multiple access interference produced by the other co-channel users. The optimum multi-user detector is currently too complex to be implemented in commercial systems. In this paper, an adaptive minimum mean square error (MMSE) receiver is introduced which can combat the 'near-far' problem and reject multi-user interference in a multipath fading channel. This type of channel is subject to rapid deep fades and the receiver's performance can be severely degraded by the limited convergence speed of the adaptive algorithm. Here, an equaliser is used to improve the ability of an adaptive MMSE receiver to combat the effect of the multipath fading. Maximal ratio combining (MRC) and an alpha tracker is used to estimate the impulse response of the multipath channel. Results show this technique is effective for rejecting multiple access interference in a multipath fading channel.