Further results on the capacity of free-space optical channels in turbulent atmosphere

In recent studies, the average capacity for optimal rate adaptation (ORA) of free-space optical channels in turbulent atmosphere has been derived in closed form, mainly based on the application of Meijer´s G-function. To this end, the channel was assumed to be memoryless, stationary and ergodic, with independent and identically distributed fading statistics. It was also assumed that scintillations follow a gamma´gamma distribution so as to appropriately describe moderate-to-strong turbulence conditions. In the current contribution, the author will extend this work in two aspects: (i) using the properties of Meijer´s G-function, it is shown that the average capacity provides also a closed-form solution for adaptation policies other than ORA, namely optimal power and rate adaptation, channel inversion with fixed rate and truncated channel inversion with fixed rate; (ii) if the additional loss caused by a misalignment between transmitter and receiver (pointing error) is taken into account, it is demonstrated that the developed analytical framework applies straightforwardly.