The Capacity of the Optical Broadcast Channel with Peak and Average Intensity Constraints

This paper addresses a two-user intensity-modulation direct-detection discrete memoryless free space optical broadcast channel (DM-FSOBC) with nonnegativity, peak and average intensity constraints at the transmitter. It is shown that superposition coding along with generating the codebooks of both users according to discrete distributions with a finite number of mass points, achieve the capacity region of the DM-FSOBC. Although the capacity-achieving distributions are not necessarily unique, it is established that only discrete distributions with a finite number of mass points can achieve the points on the boundary of the capacity region.