Performance of Two-Way Relaying over α-μ Fading Channels in Hybrid RF/FSO Wireless Networks
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In this paper, the performance of two-way relaying in mixed RF/FSO communication system with a backup RF link is investigated. Uplink RF channels are used to send data of K users to a two-way relay, R, whereas FSO link is mainly used to exchange data between a base station S and R. We propose to have a backup RF link between the relay R and the node S to improve reliability under certain conditions. All uplink RF channels follow Rayleigh fading model while α-μ is adopted to model both backup RF and FSO links. We approximate the widely used Gamma-Gamma fading model using the α-μ distribution based on moments-based estimator technique assuming perfect alignment between transmitter and receiver antennas. This approximation shows good agreement under certain atmospheric turbulence conditions. Then, we derive exact closed-form expressions for the outage and average symbol error probabilities and derive approximations at high signal-to-noise ratio (SNR). We corroborate our analytical expressions with extensive Monte-Carlo simulations and demonstrate exact match. Furthermore, we analyze the effect of number of nodes, opportunistic scheduling among K nodes, and α-μ parameters on the overall performance of mixed RF/FSO and backup RF systems. Our numerical results illustrate an achievable coding gain when increasing K; however, performance degradation occurs as the relay applies selection that favors the domination of specific links in the system.
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