Turbulence-induced scintillation is the principal impairment to Gbps laser communication over clear-weather atmospheric paths. This paper, plus its companion [A. Puryear, J. H. Shapiro, and R.R. Parenti, "ReciprocityEnhanced Optical Communication through Atmospheric Turbulence-Part II: Communication Architectures and Performance"], introduce and analyze the exploitation of atmospheric reciprocity for combating turbulence. Part I presents reciprocity proofs that apply under rather general conditions and underlie the communication performance analysis in Part II.

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Free-space optical communication provides rapidly deployable, dynamic communication links that are capable of very high data rates compared with those of radio-frequency systems. As such, free-space optical communication is ideal for mobile platforms, for platforms that require the additional security afforded by the narrow divergence of a laser beam, and for systems that must be deployed in a relatively short time frame. In clear-weather conditions the data rate and utility of free-space optical communication links are primarily limited by fading caused by micro-scale atmospheric temperature variations that create parts-per-million refractive-index fluctuations known as atmospheric turbulence. Typical communication techniques to overcome turbulence-induced fading, such as interleavers with sophisticated codes, lose viability as the data rate is driven higher or the delay requirement is driven lower. This paper, along with its companion [J. H. Shapiro and A. Puryear, "Reciprocity-Enhanced Optical Communication through Atmospheric Turbulence-Part I: Reciprocity Proofs and Far-Field Power Transfer"], present communication systems and techniques that exploit atmospheric reciprocity to overcome turbulence which are viable for high data rate and low delay requirement systems. Part I proves that reciprocity is exhibited under rather general conditions, and derives the optimal power-transfer phase compensation for far-field operation. The Part II paper presents capacity-achieving architectures that exploit reciprocity to overcome the complexity and delay issues that limit state-of-the art free-space optical communications. Further, this paper uses theoretical turbulence models to determine the performance-delay, throughput, and complexity-of the proposed architectures.