Outage Probability of the MIMO Gaussian Free-Space Optical Channel with PPM

The main drawback in communicating via the freespace optical channel is the detrimental effect the atmosphere has on a propagating laser beam. Atmospheric turbulence causes random fluctuations in the irradiance of the received laser beam, commonly referred to as scintillation. The authors investigate the mitigation of scintillation through the use of multiple lasers and multiple apertures, thereby creating a Multiple Input Multiple Output (MIMO) channel. They adopt a quasi-static block fading model and study the outage probability of the channel under the assumption of orthogonal pulse-position modulation. Non-ideal photodetection is also assumed such that the combined shot noise and thermal noise are considered as signal-independent additive Gaussian white noise.