Detection of GSM and GSSK Signals with Soft-Output Demodulators

A special case of conventional spatial modulation (SM) is demonstrated in space shift keying (SSK) modulation, where the amplitude and/or phase modulation symbols are eliminated from the transmission process so as to reduce system complexity. However, the spectral efficiencies of both schemes increase only logarithmically. Hence, large antenna arrays are required to achieve high spectral efficiencies. To reduce the transceiver overhead, while achieving improved spectral efficiencies in both SM and SSK, generalised SM (GSM) and generalised SSK (GSSK), respectively, were proposed. Typically, in coded channels, soft-output detection coupled with soft-input channel decoding yields significant signal-to-noise ratio (SNR) gain. Hence, in this paper, we propose soft-output maximum-likelihood (ML) detectors (SOMLDs) for the GSM and GSSK schemes, with an aim to further improve the error performance of the systems. Monte Carlo simulation results demonstrate that the error performance of the proposed SOMLD schemes closely match with that of their hard-decision ML detector counterparts in uncoded channels; while significant SNR gains are yielded in coded channels.