Performance of Multiuser Mixed RF/FSO Relay Networks with Generalized Order User Scheduling and Outdated Channel Information

Abstract

The generalized order user scheduling is among the efficient user selection schemes which can be used in conditions where the opportunistic scheduling could fail. The opportunistic scheduler could erroneously select a user other than the best user for data transmission or reception due to imperfect channel estimation or outdated channel information issues. In this paper, we study the performance of multiuser mixed radio frequency (RF)/free-space optical (FSO) relay network with generalized order user scheduling. Due to its importance on the system performance, the outdated channel information problem is also addressed in this paper. The considered system includes K sources or users, one decode-and-forward relay and one destination. The users are connected with the relay node through RF links, and the relay is connected with the destination through an FSO link. In the analysis, the first-hop channels are assumed to follow Rayleigh fading model and the second-hop channel is assumed to follow Gamma–Gamma fading model including the effect of pointing errors. Closed-form expressions are derived for the outage probability, average symbol error probability and ergodic channel capacity. Moreover, in order to get more insights about the system behavior, the system is studied at the high signal-to-noise ratio regime where the diversity order and coding gain are provided and studied. Monte Carlo simulations are given to validate the achieved exact and asymptotic results. Main findings illustrate that under weak atmospheric turbulence conditions, the system performance is dominated by the RF links and a diversity order of K − N + 1 is achieved by the system, whereas under sever atmospheric turbulence conditions, the system is dominated by the FSO link and the diversity order is related to the minimum value of the turbulence fading and pointing error parameters.