Free Space Optical Cooperative Communications via an Energy Harvesting Harvest-Store-Use Relay

In this paper, we consider a three-node free space optical (FSO) cooperative network with an energy harvesting (EH) decode-and-forward (DF) relay. The relay is equipped with an energy buffer and implements the harvest-store-use (HSU) architecture where the harvested energy is accumulated and used for forwarding the information from the source node to the destination node. We propose a novel HSU-based relaying strategy based on the simultaneous lightwave information and power transfer (SLIPT) concept where the relay harvests energy from the optical signal transmitted by the source. Firstly, we analyze the performance of the considered system by modeling the energy buffer as a continuous-space Markov chain (MC) for the sake of deriving the limiting distribution of the stored energy. Secondly, we discretize the state space and use the resulting discrete-space MC to derive the steady-state distribution of the buffer content. Thirdly, we propose an approximate discrete-space MC for capturing the energy buffer dynamics in a simple manner. The third approach is useful for relating the outage probability to the channel coefficients and average amounts of harvested energy in a simple closed-form manner. Simulation results validate the presented analytical evaluation and demonstrate the performance improvement that is achieved by the proposed scheme.