Cognitive Decode-and-Forward MIMO-RF/FSO Cooperative Relay Networks

This letter considers decode-and-forward (DF) based mixed multiple-input multiple-output radio frequency/free space optical (MIMO-RF/FSO) cooperative relay systems for underlay cognitive radio scenarios. Subsequently, a performance analysis is presented and closed-form expressions are derived for the per-frame outage probability considering both orthogonal space-time block coded transmission and transmit antenna selection at the secondary user. The analysis assumes the RF links between the secondary user-relay and secondary user-primary user to be Nakagami-m fading in nature, while the FSO link between the relay and destination eNodeB is assumed to be affected by optical channel impairments, such as path loss, atmospheric turbulence, and pointing errors, thus incorporating the key characteristics of both the links. Further, the impact of primary user node mobility on the performance of the cognitive radio network is also analyzed. Results demonstrate an improved outage performance of the cognitive MIMO-RF/FSO DF cooperative relay system with multiple antennas in comparison to amplify-and-forward based single-input single-output systems proposed in the existing literature.