The use of an optical preamplifier in a two laser system for atmospheric line-of-sight optical communication is investigated. Using orthogonal repetition coding is shown to provide diversity. Two different intensity modulation methods, on-off keying (OOK) and binary pulse position modulation (PPM) are analyzed for systems corrupted by background radiation and amplified spontaneous emission noise. Using an optical preamplifier in a MISO channel results in better performance than using an electrical amplifier.

Multiple transmitter and receivers can be used to combat link outage due to the atmosphere turbulence and scattering in an urban 'last-mile' free space optical communication system. We investigate the use of an optical preamplifier in the resulting multiple-input-multiple-output (MIMO) system for atmospheric line-of-sight optical communication, with signal repetition across the laser array. The optically preamplified system has better performance than previous MIMO system relying on electronic amplification. Our focus is on determining symbol error probability for uncoded transmission.

We study the use of multiple laser transmitters combined with multiple photodetectors for atmospheric, line-of-sight optical communication, and focus upon the use of multiple-pulse-position-modulation as a power-efficient transmission format, with signal repetition across the laser array. Ideal (photon counting) photodetectors are assumed, with and without background radiation. The resulting multiple-input/multiple-output channel has the potential for combating fading effects on turbulent optical channels, for which both log-normal and Rayleigh-fading models are treated. Our focus is upon symbol error probability for uncoded transmission, and on capacity for coded transmission. Full spatial diversity is obtained naturally in this application.

The use of multiple laser transmitters combined with multiple photodetectors (PDs) is studied for terrestrial, line-of-sight optical communication. The resulting multiple-input/multiple-output channel has the potential for combatting fading effects on turbulent optical channels. In this paper, the modulation format is repetition Q-ary PPM across lasers, with intensity modulation. Ideal PDs are assumed, with and without background radiation. Both Rayleigh and log-normal fading models are treated. The focus is upon both symbol-/bit-error probability for uncoded transmission, and on constrained channel capacity.

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.