Reciprocity-enhanced optical communication through atmospheric turbulence — Part I: Reciprocity proofs and far-field power transfer optimization

Deep (>;10 dB) long-duration (>;1 ms) scintillation fades, caused by propagation through refractive-index turbulence, are the principal impairment that must be overcome to realize Gbps-class laser communication over line-of-sight atmospheric paths in clear-weather conditions. Spatial diversity reception can ameliorate such fades, to a degree, but current systems typically rely on forward error-correction and interleaving to achieve reliable communication over the atmospheric channel. This paper, together with its companion [A. L. Puryear, J. H. Shapiro, and R. R. Parenti, “Reciprocity-enhanced optical communication through atmospheric turbulence - Part II: Communication architectures and performance,” to be submitted to J. Opt. Commun. Netw.], comprise a two-part study that introduces and analyzes an alternative approach, in which atmospheric reciprocity is exploited to eliminate the need for interleaving and minimize the amount of forward error-correction required. The present work (Part I) first describes the problem setting and then presents proofs for reciprocity principles - with and without phase compensation - that apply under rather general conditions. By specializing to the far-field regime, the optimum (power-transfer maximizing) phase compensation is identified. These results underlie the communication architectures and performance analysis that will be reported in the Part II paper.