One of the problems that arise in the course of designing a pseudo error monitor (PEM) is the necessity of knowing the relationship between the pseudo error rate (Ppe) and the actual error rate (Pe) in the presence of channel impairments. In the paper, the problem is solved analytically for a fairly general system model. A unified analysis of thePpeand thePeof an M-ary CPSK hard limited multilink system with some hardware imperfections, Gaussian noise and cochannel interference per link, is presented. Extensions of the analysis onM-ary DPSK signals and/or on a linear multilink system are discussed, too.Several types of modern PSK communication systems may be seen as special cases of the model considered in this paper, for example, radio relay link and satellite two-link system.It is shown that knowledge of the asymptotic behaviour of the probabilitiesPpeandPeis very useful for PEM design. To illustrate this, details are given for a one-link quaternary CPSK system.