This letter proposes a timing recovery scheme for transmission systems with baud-rate sampling allowing the use of an all digital phase-locked loop. The impact of the numerically controlled oscillator on the attainable signal-to-noise ratio and jitter under conditions of the European Telecommunications Standardization Institute (ETSI) HDSL standard is discussed.

An analytical model for Rayleigh backscattering from a single-mode fiber which takes into account the coherence properties of the optical source, the modulation of the source field and the polarization state changes during propagation along the fiber is presented. It allows a full description of the statistical properties of the backscattered signals. Expressions for the power spectral densities and for the probability density functions of Rayleigh backscattered intensity and of the corresponding detector current are derived from the autocorrelation function of the optical source field. The measurements are shown to correspond to the theoretical results.>