  Differential distributed space-time coding (D-DSTC) technique has been
considered for relay networks to provide both diversity gain and high
throughput in the absence of channel state information. Conventional
differential detection (CDD) or two-symbol non-coherent detection over slow
-fading channels has been examined and shown to suffer 3-4 dB loss when
compared to coherent detections. Moreover, it has also been shown that the
performance of CDD severely degrades in fast-fading channels and an irreducible
error floor exists at high signal-to-noise ratio region. To overcome the error
floor experienced with fast-fading, a nearly optimal "multiple-symbol"
differential detection (MSDD) is developed in this paper. The MSDD algorithm
jointly processes a larger window of received signals for detection and
significantly improves the performance of D-DSTC in fast-fading channels. The
error performance of the MSDD algorithm is illustrated with simulation results
under different fading scenarios.
