Residual Versus Suppressed-Carrier Coherent Communications

This article addresses the issue of when to suppress or not to suppress the transmitted carrier in designing a coherent communication system employing a carrier tracking loop for carrier synchronization. Assuming that a phase-locked loop (PLL) is used whenever there exists a residual carrier and a Costas loop is used whenever the carrier is suppressed, the regions of system parameters that delineate these two options are presented based on the desire to minimize the average probability of error of the system.