Photocounting array receivers for optical communication through the lognormal atmospheric channel. 1: optimum and suboptimum receiver structures

The structure of the optimum direct detection array receiver is obtained for a system consisting of an amplitude-stabilized optical source, a lognormal channel, and a bank of photocounting detectors. Additive independent background radiation and detector dark current are taken into account. Both orthogonal and nonorthogonal M-ary signaling formats are considered. Attention is given to detection intervals small in comparison with the correlation time of the atmospherically induced fluctuations. A saddlepoint integration provides an excellent approximation to the optimum processor, resulting in a considerably simplified structure. Suboptimum aperture integration and maximum a posteriori (MAP) receivers are also considered. The performance in related papers (Parts 2 and 3).