Diversity Coherent Receivers for Optical Communication over the Clear Turbulent Atmosphere

Optical communication through the atmosphere possibly enables high data rate communication. However, the optical field undergoes fades or outages due to air turbulence. Spatial diversity is an attractive technique to mitigate these fades. The outage probability of a system that uses diversity has been analyzed for diversity incoherent detection. This paper investigates the benefit of coherent detection with spatial diversity for fade mitigation. We also compare the performance improvement of diversity coherent detection over diversity incoherent detection. We find that coherent detection provides power gain of at least a few more dB for typical background noise limited applications (e.g. 2.86 dB at an error probability threshold of 0.1 and average received background noise photons per bit of 1).