Extended MMSE receiver for multiuser interference rejection in multipath DS-CDMA channels

The conventional minimum mean squared error (MMSE) receiver which actively suppresses multiuser interference (MUI), outperforms the RAKE receiver for direct sequence code division multiple access (DS-CDMA) in multipath slow fading channels. However the performance gap between the conventional MMSE receiver and the theoretical bound is still large. We therefore propose an extended MMSE receiver which spans three symbol intervals the desired symbol interval as well as the previous and the next symbol interval. The extended MMSE receiver outperforms the conventional MMSE receiver especially for large system load and large number of propagation paths in the channel. Its computational complexity is approximately three times the complexity of the conventional MMSE receiver but still independent of the number of active users and the number of paths in the channel. As a consequence the extended MMSE receiver allows a low-complexity low-power implementation in the mobile user-terminal for communication over multipath slow fading channels in the forward link.