Improved Distributed Switch and Stay(IDSS) protocol for Amplify and Forward(AF) Relay-Assisted Free-Space Optical communication system

In Free Space Optical (FSO) system to increase overall transmission reach, multi-hop relaying is being used. Decode and Forward (DF) and Amplify and Forward (AF) are two techniques to implement relay assisted FSO systems. In the case of multiple relay systems, relay selection protocols are being used to select the best possible routes between transmitter and receiver. Distributed switch and stay (DSS) protocol is a widely used scheme for relay selection in which all available paths are sorted based on their maximum equivalent distance between either source to relay or relay to destination. However, in AF based relay system, end-to-end distance should be considered to select the best possible route. Hence, in this paper, we proposed a modification in the existing DSS scheme where the best possible route is selected based on end-to-end distances. In order to select two shortest paths between source to destination, the minimization of the total distance between source to relay and relay to destination has been considered. Closed-form expression for outage probability has been computed for the proposed Improved DSS scheme under negative exponentially distributed atmospheric turbulence. The result shows that the proposed scheme outperforms in comparison to existing scheme. Results are verified using Monte Carlo simulation.