Reduced-Complexity Coherent Versus Non-Coherent QAM-Aided Space-Time Shift Keying

A novel reduced-complexity near-optimal detection algorithm is proposed for enhancing the recent Coherently-detected Space-Time Shift Keying (CSTSK) scheme employing arbitrary constellations, such as {cal L}-point Phase-Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM). The proposed detector relies on a modified Matched Filter (MF) concept. More specifically, we exploit both the constellation diagram of the modulation scheme employed as well as the Inter-Element-Interference (IEI)-free STSK architecture. Furthermore, we generalize the Pulse Amplitude Modulation (PAM)- or PSK-aided Differentially-encoded STSK (DSTSK) concept and conceive its more bandwidth-efficient QAM-aided counterpart. Then, the proposed reduced-complexity CSTSK detector is applied to the QAM-aided DSTSK scheme, which enables us to carry out low-complexity non-coherent detection, while dispensing with channel estimation. It is revealed that the proposed detector is capable of approaching the optimal Maximum Likelihood (ML) detector´s performance, while avoiding the exhaustive ML search. Interestingly, our simulation results also demonstrate that the reduced-complexity detector advocated may achieve the same performance as that of the optimal ML detector for the specific STSK scheme´s parameters. Another novelty of this paper is that the star-QAM STSK scheme tends to outperform its square-QAM counterpart, especially for high number of dispersion matrices. Furthermore, we provided both the theoretical analysis and the simulations, in order to support this unexpected fact.