Low complexity joint demodulation and decoding of DPSK systems in correlated Rayleigh fading channel

In this paper, joint demodulation and decoding of a DPSK system in a time-varying flat Rayleigh fading channel is considered. Knowing that the optimal design or even the truncated optimal design has an exponential complexity which hinders the practicability, a reduced complexity approach is proposed. This approach keeps the differential demodulation/decoding and the channel decoding schemes separate, while applying the turbo or iterative processing principle to enable information exchange between them. As a result, the complexity is rendered linear, and the filter adaptability can be easily established. As a coded DPSK system can be seen as having serially concatenated differential code and channel code, we start by investigating the effects of channel code structure and channel interleaver on the performance assuming perfect channel state information (CSI). The results are then used to predict and explain the performance of the proposed design. In general, the proposed design achieves very good performance when the fading rate is not too high. When the fading rate is high, the performance gain of the proposed design over conventional DPSK demodulation is not so evident