Discreteness of Sum-Capacity-Achieving Distributions for Discrete-Time Poisson Multiple Access Channels with Peak Constraints

This letter introduces the discrete-time Poisson (DTP) multiple access channel (MAC) which is applicable to a number of optical wireless links, most notably intersatellite laser communications. It is shown that the sum-capacity-achieving distributions of the DTP MAC under peak amplitude constraints are discrete with a finite number of mass points.