Capacity analysis of cooperative amplify and forward–quadrature spatial modulation MIMO system

Quadrature spatial modulation (QSM) multiple-input multiple-output system attracted substantial research interests lately driven by the several promised advantages. As well, cooperative communication is well-known to enhance the diversity gain and the overall system performance. In this paper, the theoretical capacity of amplify and forward (AF)-QSM system is derived and analyzed. In particular, the mutual information is first obtained and used to obtain the capacity. Derived formulas are corroborated through Monte Carlo simulation results over wide range of system and channel parameters. Besides, the impact of various parameters on the capacity and the mutual information of the studied system is investigated. The performance of AF-QSM is compared with AF-spatial modulation system and superior gains are reported. It is revealed that the capacity of AF-QSM is independent of the channel fading distribution where Rayleigh, Rician and Nakagami-m fading channels are considered. It is also reported that increasing the number of transmit antennas enhances the performance whereas increasing the number of relays degrades the performance.