Security-reliability analysis and power allocation in multiuser SIMO mixed RF/FSO relay networks

Abstract

In this paper, we study the performance of multiuser (MU) single-input-multiple-output (SIMO) mixed radio frequency (RF)/free space optical (FSO) relay network with transmit opportunistic scheduling. The considered system includes multiple users, one amplify-and-froward (AF) relay, one destination and a multiple-antenna eavesdropper. The users are connected with a multi-antenna relay through RF link and the relay is connected with the destination through an FSO link. Maximal ratio combining (MRC) scheme is used at the relay node to combine the received signals at its different antennas. In the analysis, the first hop channels are assumed to follow Nakagami-m fading model and the second hop channel is assumed to follow Gamma-Gamma fading model with considering the effect of pointing errors. Closed-form expressions are derived for the outage probability, average symbol error probability (ASEP) and ergodic channel capacity. Furthermore, the system performance is studied at high signal-to-noise ratio (SNR) regime where the diversity order and coding gain are derived and analyzed. Using the asymptotic results, the power of the selected best user is determined to minimize the system outage probability under the dominant RF or FSO link. Then, the considered system secrecy performance is investigated and an exact closed-form expression for the intercept probability is derived. Monte-Carlo simulations are provided to validate the achieved exact and asymptotic results.