Impact of Cochannel Interference on the Performance of Quadrature Spatial Modulation MIMO Systems

Quadrature spatial modulation (QSM) was proposed recently as a viable multiple-input multiple-output (MIMO) communication technique for future wireless systems. QSM expands spatial modulation to include both real and imaginary spatial constellation symbols. In this letter, we consider an arbitrary QSM MIMO system operating over Rayleigh fading channels and in the presence of additive white Gaussian noise and cochannel interference (CCI). The performance of the system is analyzed mathematically and numerically. In particular, a closed-form expression for the pairwise error probability is derived assuming arbitrary number of CCIs and used to calculate an upper bound on the average error probability. As well, an asymptotic expression, which is shown to be tight at practical SNR values is derived. Analytical results are sustained through Monte Carlo simulations and impact of different system parameters is studied. In addition, performance comparison between QSM, spatial modulation, spatial multiplexing, and single antenna transmission schemes for the same spectral efficiency and in the presence of CCI is presented.