Performance Analysis of Decode-and-Forward-Based Mixed MIMO-RF/FSO Cooperative Systems With Source Mobility and Imperfect CSI

This paper investigates a decode-and-forward-based asymmetric dual-hop mixed radio-frequency/free-space optical (RF/FSO) communication link. We consider a moving source user equipment (UE) that communicates with the relay over an RF link and the relay communicates with the serving base station (eNodeB) over an FSO link, assuming there is no direct link between the UE and eNodeB. It is assumed that the source-to-relay link experiences time-selective Rayleigh fading, that arises due to the UE mobility and the relay-destination link is affected by the optical channel impairments, including path loss, atmospheric turbulence, and pointing errors. As the FSO link has a higher data rate in comparison to the RF link, we employ multiple-input multiple-output with zero-forcing (ZF) based linear receiver in the source-to-relay link, in order to enhance the RF link data rate without increasing the transmit power and bandwidth requirements. Moreover, we assume that the relay node has imperfect channel state information (CSI) for the ZF decoding. For the considered system and channel models, novel closed-form expressions for the per-frame average outage probability, bit error rate, and ergodic capacity are derived and verified using Monte Carlo simulations. Additionally, asymptotic floors for the system outage and error probabilities are derived. It is observed that the time-varying nature of the RF link and imperfect CSI at the relay significantly degrades the end-to-end performance of the system.