The Effect of Intersymbol Interference on Error Rate in Binary Differentially-Coherent Phase-Shifted-Keyed Systems

This paper presents a summary of calculations which were performed before and during the construction of a 300-Mb/s repeater for a guided millimeter-wave communication system. Consequently, the problems which are considered are oriented toward problems which arise in connection with these high-speed systems, e.g., finite-width decision thresholds, imperfect phase shifts in the modulators, etc. Because of the nature of the channels envisioned for these systems, only 1149 1150 T H E BELL SYSTEM TECHNICAL JOURNAL, J U L Y - A U G U S T 19(57 intersymbol interference from adjacent time slots is significant and the treatment of intersymbol interference will include only adjacent timeslot interference. 1.1 Summary of Previous Results Several authors1'2,3,4 have calculated the error rate as a function of signal-to-noise ratio, S/N, for an ideal differentially-coherent phaseshift-keyed (DCPSK) system, i.e., a system in which intersymbol interference can be ignored and in which regeneration is assumed to be ideal. The well-known result is n0 = | exp (--S/N), (1) 5 where n0 is the probability of error for the ideal case. The author has considered the effects of nonideal regeneration. Sections II and III of this paper extend these error-rate calculations to include the effects of intersymbol interference for two types of DCPSK signals. These signals are discussed and compared in the next paragraph. 1.2 Comparison of AM-DCPSK and FM-DCPSK Signals In a DCPSK system the information is carried in the phase of the signal at the sampling point in one time slot relative, to the phase of the signal at a time, T, earlier where T is the reciprocal of the bit rate B.