Time and frequency transfer between master and slave clocks

The problem of time and frequency transfer between remotely located clocks is investigated for the case when internal and external disturbances are present. A model based on the maximum-likelihood (ML) estimation of the carrier phase and the transmission path delay in the face of white Gaussian noise is suggested. In this model, path delay estimation and, consequently, clock synchronization is achieved by tracking a pseudonoise (PN) code phase-modulated onto the carrier. Phase and frequency estimation are obtained through a closed-loop phase tracking model. The performance of the maximum-likelihood model under high and low signal-to-noise ratio (SNR) is established in terms of probability density functions of the phase increment processes in space and time. Factors which influence performance include external and internal disturbances. These include additive thermal noise, range delay, clock drift, etc. Numerical results are presented to explain the influence of system parameters on performance