Outage Analysis of Relay-Based Dual-Hop Hybrid FSO-mmWave Systems

Bearing in mind the high data rate and volume requirements of 5G and beyond networks, millimeter wave (mmWave) systems can be utilized with the assistance of free-space optical (FSO) systems since both technologies exhibit distinctive behaviors under different weather conditions. Therefore, in this study, we investigate a relay-based dual-hop hybrid FSO-mmWave systems from an outage performance point of view, where the communication in each hop is established on both FSO and mmWave links simultaneously. Specifically, Nakagami-m distribution is used for mmWave fading channels, while gamma-gamma distribution is assumed for FSO turbulence channels. Two well-known amplify-and-forward (AF) relaying schemes are examined during data transmission, in which the power amplification operation is based on partial and full channel state information of the system, namely, fixed-gain and variable-gain AF relaying methods. The effects of fundamental system variables on the outage analysis of the relay-based hybrid transmissions are investigated by obtaining exact closed-form derivations of the outage probability and effective throughput. Based upon the results, it is shown that the proposed closed-form expressions are in good match with the Monte-Carlo simulations.