Optimal power allocation for decode-and-forward based mixed MIMO-RF/FSO cooperative systems

This paper investigates a decode-and-forward (DF) based dual-hop mixed radio-frequency/free-space optical (RF/FSO) communication link, where the source and relay communicate with each other over a RF link and the relay and destination communicate over a FSO link. The RF channel experiences Rayleigh fading whereas the optical channel is affected by path loss, atmospheric turbulence, and pointing errors. Since, the FSO link has a higher data rate in comparison to the RF link, we employ multiple-input multiple-output (MIMO) with zero-forcing based linear receiver in the source-to-relay link, to enhance the RF link data rate. For the considered system and channel models, novel closed form expressions for the outage probability and average bit error rate are derived and verified using Monte Carlo simulations. Furthermore, a framework for optimal source-to-relay power allocation is presented, which significantly improves the end-to-end performance of the system.