A hybrid free space optical-millimeter wave cooperative system

In this paper, a hybrid free space optical (FSO)–millimeter wave (mmWave) cooperative system is proposed. Specifically, a cooperative dual-hop decode-and-forward (DF) relaying system coexists with a direct communication link and two scenarios are considered. In the first scenario, the direct link is used for FSO transmission while the DF dual-hop relaying system is used for mmWave transmission. On the contrary, in the second scenario, the direct link is used for mmWave communication whereas the relaying link is used for FSO communication. In both scenarios, the mmWave link experiences Nakagami-m fading while the FSO link suffers gamma–gamma turbulence fading. At the destination, the two signals, i.e., the mmWave and the FSO signals, are jointly detected using an optimum maximum likelihood receiver. To investigate the performance of the proposed systems, novel analytical expressions for the overall average bit error rate (BER) and outage probability are derived. The impact of different system and channel parameters on the overall average BER is investigated. Additionally, the performance of the proposed systems is compared with other setups where only direct mmWave or FSO link exists. Monte Carlo simulation results are provided to corroborate the accuracy of the analysis.