Space-time receivers for CDMA multipath signals

We consider the problem of receiving CDMA multipath signals at a receiver with an antenna array. We derive the space-time matched filter for the multipath signals arriving at the array and show that this space-time matched filter consists of a front-end spatial matched filter or a bank of beamformers (one for each multipath component), followed by a temporal matched filter, or a bank of correlators (one for each multipath component). Then we derive the optimum (maximum likelihood) sequence detector that can be implemented via a Viterbi algorithm. We also present a sub-optimal space-time decorrelating receiver structure and discuss its limitations. Based on this space-time matched filter framework, we briefly discuss conventional space-time receiver structures for CDMA multipath signals. Analysis results for a space-time receiver with DPSK signaling show improved bit error rate performance due to the exploitation of the spatial dimension in the received signal