Ergodic Capacity of Triple-Hop All-Optical Amplify-and-Forward Relaying over Free-Space Optical Channels

In this paper, we propose a comprehensive research over triple hop all-optical relaying free-space optical (FSO) systems in the presence of all main noise sources including background, thermal and amplified spontaneous emission (ASE) noise and by considering the effect of the optical degree-of- freedom (DoF). Using full CSI relaying, we derive the exact expressions for the noise variance at the destination. Then, in order to simplify the analytical expressions of full CSI relaying, we also propose and investigate the validity of different approximations over noise variance at the destination. Finally, we evaluate the the performance of considered triple-hop all-optical relaying FSO system in term of ergodic capacity.