Energy Efficient Quadrature Spatial Modulation MIMO Cognitive Radio Systems with Imperfect Channel Estimation

Quadrature spatial modulation (QSM) in cognitive radio (CR) is a new spectral and energy efficient multiple-input multiple-output (MIMO) transmission paradigm. In QSM, the spatial constellation diagram of conventional spatial modulation (SM) system is extended to include both in-phase and quadrature components of the data symbol. As such, QSM combined with CR techniques achieve significant improvement in the overall spectral efficiency while inherent advantages of SM are retained. In this paper, we study the performance of QSM-MIMO-CR systems in the presence of channel estimation errors (CEEs) and limited feedback. A closed-form expression for the average pairwise error probability (PEP) of CR system is derived and used to calculate a tight upper bound of the average bit error rate (ABER) over Rayleigh fading. In addition, a simple asymptotic expression is derived and analyzed. Simulation results, which corroborate the numerical ones, show the importance of QSM in improving the overall secondary performance and its robustness to CEEs with reduced signal power.