The Effect of a Finite-Width Decision Threshold on Binary Differentially Coherent PSK Systems

A binary differentially coherent phase shift keyed (DCPSIv) system is one in which the two (binary) states -- "mark" and "space" -- are transmitted as phase changes between adjacent time slots. In such a system, optimum results are obtained when the expected values of the two possible signal states in a given time slot differ in phase by t radians. For clarity it will be assumed in the following discussion that the expected value of phase change is 0 or ir, respectively, according to whether a space or a mark was transmitted, even though phase changes of 6 + 0 and 0 + ir (6 an arbitrary but fixed angle) are equally suitable. 307 308 THE B E L L SYSTEM TECHNICAL JOURNAL, FEBRUARY 1966 Such a system mechanism and a in adjacent time phase difference to usually consists of a limiter, followed by a storage product demodulator, as shown in Fig. 1. If the signals slots have amplitudes A and B, respectively, and a the output of the product demodulator is proportional v = AB cos f/. (1)