Performance of CP-FSK systems with tight IF filtering

A report is presented on a rigorous bit-error-rate analysis appropriate to continuous-phase frequency shift keying (CPFSK) coherent optical receivers with delay demodulation and an integrating IF filter with integration time less than or equal to the delay time. An important result of the analysis is that IF filtering for CPFSK modulation reduces the phase swing due to modulation at the detector, and this leads to a degradation in system performance both with regard to phase noise and receiver noise influence. For a modulation index of 0.5, a minimum 2.4-dB penalty relative to matched filter detection is found under shot-noise-limited conditions and without any phase noise.<>