Cognitive MIMO-RF/FSO Cooperative Relay Communication With Mobile Nodes and Imperfect Channel State Information

This paper analyzes the performance of an underlay cognitive radio based decode-and-forward mixed multiple-input multiple-output radio frequency/free space optical cooperative relay system with multiple mobile secondary and primary user nodes. The effect of imperfect channel state information (CSI) arising due to channel estimation error is also considered at the secondary user transmitters (SU-TXs) and relay on the power control and symbol detection processes respectively. A unique aspect of this paper is that both fixed and proportional interference power constraints are employed to limit the interference at the primary user receivers. Analytical results are derived to characterize the exact and asymptotic outage and bit error probabilities of the above system under practical conditions of node mobility and imperfect CSI, together with impairments of the optical channel, such as path loss, atmospheric turbulence, and pointing errors, for orthogonal space-time block coded transmission between each SU-TX and relay. Finally, simulation results are presented to yield various interesting insights into the system performance such as the benefits of a midamble versus preamble for channel estimation.