Low Complexity Detection for an AF Relay Assisted MIMO QSM System

This paper presents a low complexity near maximum likelihood (Near-ML) detection algorithm for an amplify and forward (AF) relay assisted multiple input-multiple output (MIMO) quadrature spatial modulation (QSM) transmission system. The proposed low complexity detection algorithm is based on a tree search and a spherical detection strategy. First, we analyze the performance of the relay assisted AF-MIMO-QSM system for a different number of relays and compare the bit error rate (BER) performance of the proposed scheme with the conventional relay assisted AF-MIMO system considering the optimal ML criterion. Then, we compare the performance and complexity of the proposed algorithm with the optimal ML detector for the AF-MIMO-QSM system. Results show that the system's BER performance can be significantly improved as the number of relays increases. The AF-MIMO-QSM system has up to 8 dB gain in BER performance compared with the conventional AF-MIMO system for the analyzed cases. Mainly, the proposed low complexity detection algorithm performs very near to the optimal with the advantage of a reduction in complexity of 45% and 61% for a spectral efficiency of 4 bits per channel use (bpcu) and 6 bpcu respectively.