Spatial Modulation in MIMO Spectrum-Sharing Systems with Imperfect Channel Estimation and Multiple Primary Users

In this paper, spatial modulation (SM) is used in multiple-input multiple-output (MIMO) spectrum sharing systems in order to enhance the overall spectral efficiency. In particular, a multi-antenna secondary transmitter, employing SM as a modulator, communicates with a multi-antenna secondary receiver in the presence of multiple primary users. To study the effect of estimation errors on the secondary system performance, we derive a closed-form expression for the average pairwise error probability (PEP) over Rayleigh fading channels assuming limited feedback from the PUs. A tight upper bounded average bit error rate is obtained using the PEP expression. Moreover, simple approximate expressions are obtained to get insights on the system diversity and estimation errors´ effects. Numerical results, which match with simulations, show the efficacy of SM in improving the overall secondary performance in the presence of estimation errors.