2019 Volume 23 Issue 3 Pages 105-114
In order to improve tracking capability for fast time-varying channels, this paper proposes maximum-likelihood sequence estimation (MLSE) based on channel prediction employing soft-output Viterbi algorithm (SOVA) for differential space-time coding, e.g., differential encoding and per transmit antenna differential mapping (PADM). Although QPSK is generally demodulated based on LLR (log-likelihood ratio) for its soft decisions, it is difficult for JD (joint detection), which does not explicitly estimate channel state information, to derive LLR. This paper proposes soft decisions for PSP (per-survivor processing), which correspond to metrics difference between the two paths in the VA (Viterbi algorithm) of PSP, where PSP is JD based on the VA. The proposed scheme can improve tracking capability for time-varying channels without an increase of computational complexity. Finally, computer simulation results confirm that the proposed schemes can track four times larger maximum Doppler frequency in fading than the conventional schemes.
