I. Introduction
A popular method for clock synchronization in a coherent communication system consists of passing the incoming signal, either at intermediate frequency (IF) or at baseband, through a zero-memory device with an even nonlinearity and then feeding the resulting waveform to a phase-locked loop or, equivalently, to a bandpass filter centered at the pulse repetition frequency so that a discrete tone is generated at the symbol rate frequency as shown in Fig. 1. Many forms of nonlinearities may be used for this purpose. The most common are square law [1], absolute value [2], and fourth law [3]. In a high signal-to-noise ratio case, the recovered clock is mainly contaminated by a data-dependent noise, which is called self-noiseor pattern noise. Gardner has pointed out that the self-noise component that is in-phase with the recovered clock plays a different role from the component that is quadrature [4]. To properly analyze the contribution of each of these noise components to phase jitter, the power spectra of the two noise components must be found separately. Block diagram of a clock recovery system