Error-Rate Considerations for Digital Phase-Modulation Systems

The performance of digital phase-modulation systems has been investigated by many authors, and we first present a simple and alternate method of evaluating the character error rates of
m
-phase coherent and differentially coherent phase-shift keyed (DCPSK) systems when the receiver is ideal. An ideal receiver is assumed to operate with zero-width decision thresholds, but in any practical receiver, the voltage (or current) in question must differ from the threshold value by a finite amount in order for the device to respond properly and reliably. This finite-width decision threshold for any practical receiver can be expressed in terms of a certain parameter γ, and we give methods of evaluating the character error rates of coherent phase-shift keyed (CPSK) and differentially coherent phase-shift keyed systems when the receiver has a finite nonzero γ. The receiver may also introduce a certain phase perturbation δ in the detected phase of the signal because of imperfections present in various parts of the receiver. The methods of evaluating its effect on both CPSK and DCPSK systems have also been given in this paper.