1. A method for estimating a deviation between a free-running transmitter clock and a reference clock, the method comprising: at a receiver stationary with respect to a transmitter, receiving a transmitter signal generated by the transmitter on the basis of the transmitter clock; on the basis of the reference clock determining a time of arrival of the transmitter signal and a beat phase of the transmitter signals carrier; and on the basis of a clock error model, the time of arrival and the beat phase, estimating the deviation between the transmitter clock and the reference clock, wherein the clock error model is derived by fitting a correlation function of a stochastic model to a measured auto correlation function of the transmitter clock and wherein the correlation function of the stochastic model is the correlation function of a second order Markov process.