An iterative receiver for differential space-time π/2-shifted BPSK modulation

We consider the issue of blind detection of Alamouti-type differential space-time (ST) modulation in static Rayleigh fading channels, focusing our attention on π/2-shifted BPSK constellation. Applying a novel transformation to the received signal, this binary ST modulation with second-order transmit-diversity, is shown to be equivalent to QPSK with second-order receive-diversity. This equivalent representation allows us to apply a low complexity detection technique specifically designed for receive-diversity; namely, scalar multiple-symbol differential detection (MSDD). To further increase receiver performance, we apply the expectation-maximization (EM) algorithm, which performs joint channel estimation and sequence detection. With receiver complexity proportional to the observation window length, our receiver can achieve the performance of a coherent maximal ratio combining receiver in as little as a single EM-receiver iteration, provided that the window size of the initial MSDD is sufficiently long. We also find that an EM-based iterative receiver initiated by selection-diversity scalar-MSDD has significantly better performance and convergence properties than those initiated by conventional ST differential detection.