Joint Minimum Variance Unbiased and Maximum Likelihood Estimation of Clock Offset and Skew in One-Way Packet Transmission

In distributed systems like large wireless sensor networks, dense indoor small cell networks, maintaining each node´s logical clock synchronized to a common reference is challenging. Increasing data rates and required cooperation among nodes for high spectral efficiency, further exacerbate the required clock synchronization accuracy. Here, we propose a one way timing information distribution mechanism simplifying existing two way information exchange for clock synchronization. We view the problem at the synchronizing node as a Peer-to-Peer (P2P) continuously running process. A node with stable clock (master) transmits regular packets embedded with transmit time stamps. All synchronizing nodes within the master´s communication range can listen and apply receive time stamp. Efficient Passive Minimum Variance Unbiased Estimator (PMVUE) or Passive Maximum Likelihood Estimator (PMLE) are applied to jointly estimate clock offset and skew to correct the local clock. Random component of the link delay is assumed to be Gaussian distributed. Cramer-Rao Lower Bound (CRLB) guarantees that PMVUE and PMLE are efficient. We also propose a less accurate PMLE method, Independent PMLE (IPMLE) to remove dependency on random delay distribution parameter and show through simulations the high accuracy of our algorithms.