Performance of Single- and Multiple-Dish Laser Communications Systems

A comparison is given of three potentially useful types of laser communications systems. These are the incoherent direct detection systems (DDS), the transmitted reference system (TRS) and the coherent local heterodyning system (LHS). Both signle- and multiple-dish receiver systems are considered. In all cases a photomultiplier receiver detector is assumed. In the analysis the wave interference noise (or equivalently, classical noise) has been taken into account. The results are given for the case where the background noise arises from a point source, from rnanv point sources or from a uniformly radiating background. Also, the case where the receiving aperture is not diffraction limited/ is considered. Convenient curves are given which permit one to determine the performance of the three systems for various background conditions and system parameters. It is pointed out that the transmitter power required for a communications system using a multiple-dish receiver complex does not decrease always in direct proportion to the reciprocal of the increase in the number of receiver dishes used. Curves are given showing the receiver collecting aperture loss as a function of the number of collecting apertures