Secrecy capacity of the degraded Poisson wiretap channel

Providing security guarantees for the information “traveling” through the air is of critical importance for today's applications. Previous research concentrated on studying this problem when the medium used for communication is radio frequency (RF) channels. However, providing security guarantees on RF channels is a complicated task as RF channels' conditions are prone to rapid variations due small scale fading and at a given moment it is difficult to predict which of the main or wiretapper's channel has a better quality. Wireless optical communication is inherently more secure than regular RF communication. Despite this fact, optical communication is not completely immune against wiretapping and signal interception. The purpose of this paper is to study the secrecy capacity of a direct detection optical communication system. For the degraded Poisson wiretap channel, we give a complete characterization of the secrecy capacity in terms of the system parameters.