In order to reduce the computation complexity in flops for multiple symbol differential unitary space-time modulation systems, this paper presents a new algorithm called M-BID algorithm. This algorithm uses the BID to search the best part branches firstly, and then computes their decision metrics to each retained node in the M algorithm that differs from the M algorithm which need compute decision metrics for all paths. So the M-BID algorithm can reduce the computation numbers of Frobenius norm greatly, which can impel the complexity in flops decreased. Simulation results show that the computation num bers of the M algorithm keep unchanging with the signalnoise-ratio increasing, but the M-BID algorithm decreases very quickly, and the average numbers of each block in the M-BID algorithm a re lower very much than the 1\1 algorithm, this is in the computation complexity aspect. Tn the performance way, the M-BID algorithm is close to the M algorithm. So the M-BID algorithm has good performance with lower complexity.
In view of the shortcoming of large-capacity storage requirements and high computational complexity for most multisymbol differential detection (MSDD) algorithm, we propose PMCTS (Pruning Memory Constrained Tree Search) algorithm based on Memory Constrained Tree Search (MCTS), which uses a threshold for node cutting operation. The nodes whose metrics are greater than the threshold value will be deleted directly. Simulation results show that the proposed algorithm solves the problem of relatively high computational complexity with a small PMCTS storage in the low SNR region, but its performance loss less than 0.2dB. For example, under the condition of the RA channel model and the observation window length is 6, the average visited notes of PMCTS can be reduced up to 47.8% than the MCTS algorithm, 87.8% lower than the ML, and 36% lower than PASD (Pruning Automatic Sphere Decoding).
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