Abstract
Quadrature spatial modulation (QSM) is a recent multiple-input-multiple-output (MIMO) digital transmission paradigm. Combining QSM with cooperative relaying in spectrum-sharing systems improves the overall spectral efficiency and enhances the communication reliability. In this paper, we study the performance of QSM-MIMO amplify-and-forward (AF) cooperative relaying spectrum-sharing systems, in which a multiantenna secondary source communicates with a secondary receiver with the help of a secondary AF relay in the presence of multiple primary receivers. In particular, a closed-form expression for the average pairwise error probability (PEP) of the secondary system is derived and used to obtain a tight upper bound of the average bit error probability (ABEP) over Rayleigh fading channels. In addition, a simple asymptotic, yet accurate, expression is derived and analyzed to show the effect of key parameters. Simulation results are presented to validate numerical analysis. Results reveal that QSM with cooperative relaying improves the spectrum-sharing systems' performance.