On the Joint Impact of Hardware and Channel Imperfections on Cognitive Spatial Modulation MIMO Systems: Cramer–Rao Bound Approach

This paper investigates the performance of spatial modulation for multiple-input multiple-output underlay spectrum-sharing systems in the presence of three practical deleterious effects: (1) transceiver hardware impairments, (2) outdated channel state information (CSI), and (3) imperfect CSI. In particular, for Rayleigh fading channels, a closed-form expression of the average pairwise error probability and a tight upper bound of the average bit error rate (ABER) are derived. In addition, asymptotic and yet simple approximate expressions are obtained, and consequently insightful discussions are manifested on the impacts of channel and hardware imperfections and on the diversity order. Moreover, explicit exact and approximate expressions for the Cramer-Rao bound are computed for assessing the channel estimation accuracy. Numerical results, which are validated through simulations, show that nonzero bounds of the ABER occur in the high power domain because of the effects of channel and hardware impairments.