Improved Buffer-Aided Selective Relaying for Free Space Optical Cooperative Communications

This paper tackles the performance analysis and relaying strategies for two-relays buffer-aided (BA) parallel relaying cooperative free space optical (FSO) networks. We first provide an asymptotic analysis of the existing selective relaying scheme that simultaneously activates the strongest source-relay (S-R) and relay-destination (R-D) optical links. We then propose an improvement of this scheme and highlight on its advantages by deriving closed-form accurate expressions for the asymptotic values of the outage probability (OP) and average packet delay (APD). The theoretical evaluation and numerical analysis demonstrate the capability of the improved scheme in enhancing the diversity order with finite buffer sizes unlike the selective relaying scheme that achieves diversity gains only with infinite-size buffers entailing infinite delays. The OP performance is significantly enhanced for all network topologies whether the relays are closer to S, closer to D or placed at the same distance from S and D. On the other hand, the reaped APD gains depend on the positions of the relays.