Quadrature Spatial Modulation in MIMO Cognitive Radio Systems With Imperfect Channel Estimation and Limited Feedback

Abstract

This paper studies the recent novel multiple-input multiple-output transmission technique called quadrature spatial modulation (QSM), in underlay cognitive radio (CR) systems. In particular, a multi-antenna secondary transmitter (ST) communicates with a multi-antenna secondary receiver (SR) in the presence of a primary receiver (PR). Considering only the statistical knowledge of the ST-PR channel gain, the QSM-CR scheme is investigated using a mean value (MV)-based power allocation strategy referred to as MV-based scheme. Furthermore, assuming that the ST-PR channel gain is perfectly known, the QSM-CR scheme is investigated using a power allocation method based on instantaneous channel state information (CSI), referred to as CSI-based scheme. In each scheme, considering imperfect ST-SR channel estimation, we study the secondary system performance, where closed-form expressions for the average pairwise error probability ( $\rm \overline {PEP}$ ) are derived over Rayleigh fading channels. A tight upper bounded average bit error rate is obtained using the derived $\rm \overline {PEP}$ expression. Moreover, simple approximate expressions are obtained to get insights on the system diversity and channel estimation errors’ effects. Numerical results, which match with simulations, illustrate the robustness of QSM in enhancing the overall system performance in the presence of estimation errors.