DSC and universal bit-level combining for HARQ systems

This paper proposes a Dempster -Shafer theory based combining scheme for single-input single-output (SISO) systems with hybrid automatic retransmission request (HARQ), referred to as DSC, in which two methods for soft information calculations are developed for equiprobable (EP) and non-equiprobable (NEP) sources, respectively. One is based on the distance from the received signal to the decision candidate set consisting of adjacent constellation points when the source bits are equiprobable, and the corresponding DSC is regarded as DSC-D. The other is based on the posterior probability of the transmitted signals when the priori probability for the NEP source bits is available, and the corresponding DSC is regarded as DSC-APP. For the diverse EP and NEP source cases, both DSCD and DSC-APP are superior to maximal ratio combining, the so-called optimal combining scheme for SISO systems. Moreover, the robustness of the proposed DSC is illustrated by the simulations performed in Rayleigh channel and AWGN channel, respectively. The results show that the proposed DSC is insensitive to and especially applicable to the fading channels. In addition, a DS detection-aided bit-level DS combining scheme is proposed for multiple-input multiple-output–HARQ systems. The bit-level DS combining is deduced to be a universal scheme, and the traditional log-likelihood-ratio combining is a special case when the likelihood probability is used as bit-level soft information.