We address binary phase-shift-keyed communication channels based on Gaussian
states and prove that squeezing improves state discrimination at fixed energy
of the channel, also in the presence of phase diffusion. We then assess
performances of homodyne detection against the ultimate quantum limits to
discrimination, and show that homodyning achieves optimality in large noise
regime. Finally, we consider noise in the preparation of the seed signal
(before phase encoding) and show that also in this case squeezing may improve
state discrimination in realistic conditions.Comment: 6 pages, 5 figure