Round Robin, Centralized and Distributed Relay Selection for Free Space Optical Communications

In this paper, we derive the Symbol Error Probability (SEP) of Round Robin (RRS), Centralized (CRS) and Distributed Relay Selection (DRS) techniques for Free Space Optical communications. RRS consists to randomly select a node as relay with equal probability. It does not consider the SNR value for relay selection. In CRS, the SNRs of different relays are sent to a Central Node (CN) for detecting the relay with highest SNR. The CN selects the best relay with largest SNR. We propose a new DRS where each relay is allowed to transmit only when its SNR is higher than a given threshold T. The threshold T is optimized with the Gradient algorithm to guarantee the lowest SEP. The suggested DRS with optimal threshold allows close performance to CRS and better performance than RRS. DRS is less complex than CRS since no signalization is needed.