Ergodic capacity of decode-and-forward (DF) relay-assisted free-space optical (FSO) communication systems when line of sight is available is analyzed over gamma-gamma fading channels with pointing errors. Novel closed-form approximate ergodic capacity expression is obtained in terms of the H-Fox function for a 3-way FSO communication system when the α-μ distribution to efficiently approximate the probability density
function (PDF) of the sum of gamma-gamma with pointing errors variates is considered. Moreover, we present a novel asymptotic expression at high signal-to-noise ratio (SNR) for the ergodic capacity of DF relay-assisted FSO systems. The main contribution
in this work lies in an in-depth analysis about the impact of pointing errors on the ergodic capacity for cooperative FSO systems. In order to maintain the same performance in terms of capacity, it is corroborated that the presence of pointing errors
requires an increase in SNR, which is related to the fraction of the collected power at the receive aperture, i.e. A 0 . Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. The authors wish to acknowledge the financial support given by Spanish MINECO Project TEC2012-32606
