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Zero-forcing equalization of space-time block coded transmissions over frequency selective channels

Recently, a polyphase approach was proposed for the analysis of space-time block coded (STBC) transmissions over frequency selective channels. Using this approach, we study the zero-forcing (ZF) equalization of these systems. In this study, we consider only the two transmit antennas case. For the receiver, the single and multiple receive antennas cases are both considered. For the case of single receive antenna, the ZF receiver is a unique infinite impulse response (IIR) filter whereas for the case of multiple receive antenna, there exist finite impulse response (FIR) ZF receivers. We will derive the general form of the ZF receiver. Then the optimal ZF solution that minimizes the output noise variance will be derived. Simulation results show that the performance of STBC system with two transmit and one receive antenna is better than the conventional system with one transmit and one receive antenna. When there are multiple receive antennas, it is found that there can be significant improvement if we optimize the ZF receiver.