Time-varying Clock Offset Estimation in Two-way Timing Message Exchange   in Wireless Sensor Networks Using Factor Graphs
  The problem of clock offset estimation in a two-way timing exchange regime is considered when the likelihood function of the observation time stamps is exponentially distributed. In order to capture the imperfections in node oscillators, which render a time-varying nature to the clock offset, a novel Bayesian approach to the clock offset estimation is proposed using a factor graph representation of the posterior density. Message passing using the max-product algorithm yields a closed form expression for the Bayesian inference problem. 
Aitzaz Ahmad, Davide Zennaro, Erchin Serpedin, Lorenzo Vangelista
cs.IT math.IT