<title>Free-space optical communication: detector array aperture for optical communication through thin clouds</title>

Abstract

Optical communication must contain clouds as parts of communication channels. Propagation of optical pulses through clouds causes widening in the spatial domain and attenuation of the pulse radiant power. These effects decrease the received signal and increase bit error rate (BER). One way to improve the BER of the communication system is by using adaptive methods to obtain more signal relative to noise power. Based on mathematical models of spatial widening of optical radiation derived by Monte-Carlo simulation in part 1, a mathematical model for optimum performance of digital optical communication through clouds is developed. The purpose of the optimum adaptive communication system suggested here is to improve the BER by optimizing according to meteorological conditions the spatial distribution of the detected radiation beam using a detector array where the external amplification of each detector is adaptable. Comparison and analysis of three models of communication systems in fog cloud channels are presented: (1) the optimum adaptive detector array aperture, (2) an ordinary single detector aperture of the same size, and (3) a small detector aperture. Improvement of more than four orders of magnitude in bit error rate under certain conditions is possible with the new adaptive system model.