  Several proposed techniques for distinguishing between optical coherent
states are analyzed under a physically realistic model of photodetection.
Quantum error probabilities are derived for the Kennedy receiver, the Dolinar
receiver and the unitary rotation scheme proposed by Sasaki and Hirota for
sub-unity detector efficiency. Monte carlo simulations are performed to assess
the effects of detector dark counts, dead time, signal processing bandwidth and
phase noise in the communication channel. The feedback strategy employed by the
Dolinar receiver is found to achieve the Helstrom bound for sub-unity detection
efficiency and to provide robustness to these other detector imperfections
making it more attractive for laboratory implementation than previously
believed.
