Optical signal detection in the turbulent atmosphere using p-i-n photodiodes

Performance of signal detection for intensity modulated direct detection optical communications systems through the turbulent atmosphere is studied considering statistics of photoelectron count in p-i-n photodiodes. The effect of atmospheric turbulence is modeled as a lognormal process. In this system, the photoelectron count is a conditional Poisson process, where the mean count is lognormal. A normal approximation is derived for this conditional Poisson process, which results in a simple calculation for the probability of miss. The probabilities of miss for quantum-limited detection and detection in the presence of thermal electronic noise are simulated and compared with calculations using the normal approximation. Simulation results match the analytical results. For the thermal noise case, the probability of miss is compared with the probability of false alarm to determine appropriate signal length and detection threshold settings for a required performance. Applying results in this paper, a system designer can determine appropriate signal length and detection threshold settings.