We address binary optical communication channels based on phase-shift keyed
coherent signals in the presence of phase diffusion. We prove theoretically and
demonstrate experimentally that a discrimination strategy based on homodyne
detection is robust against this kind of noise for any value of the channel
energy. Moreover, we find that homodyne receiver beats the performance of
Kennedy receiver as the signal energy increases, and achieves the Helstrom
bound in the limit of large noise
