The effect of interferometer phase error on direct-detection DPSK and DQPSK signals

Based on the well-known Marcum's Q function, closed-form formulae are derived to evaluate the error probability of direct-detected differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) signals with interferometer phase error. For a signal-to-noise ratio penalty less than 1 dB, the phase error must be less than 16/spl deg/ and 6/spl deg/ for DPSK and DQPSK signals, respectively.