Optical MIMO transmission with multipulse PPM

Fading due to atmospheric turbulence is a primary problem in free-space-optical links, and to address this, we consider the use of (noncoherent) optical arrays, analogous to the use of antenna array technology for microwave systems. Specifically, we envision M separate lasers, assumed to be intensity-modulated only, together with N photodetectors, assumed to be ideal noncoherent (direct detection) receivers. The sources and detectors are physically situated so that the fading experienced between source-detector pairs is statistically independent, and thus diversity benefits can accrue from the MIMO channel. Whereas classic single pulse PPM is known to be efficient from an average power perspective, the required peak power from the lasers must become arbitrarily large in this process. This motivates study of multipulse modulation.