Reference Broadcast Time Synchronization

Reference Broadcast Time synchronization is a method in which the receiver uses the physical layer broadcasts for comparing the clocks. This is slightly different from traditional methods which synchronize the sender's with the receiver's clock.

RBS allows nodes to synchronize their clocks to the resolution necessary for example for wireless sensor network applications. Rather than broadcasting a time stamp in a synchronization packet as in protocols such as NTP, RBS allows the nodes receiving the synchronization packets to use the packet’s time of arrival as a reference point for clock synchronization. Because most of the non-deterministic propagation time involved in transmitting a packet over a wireless channel lies between construction of the packet and the sender’s transceiver (e.g., sender’s queue delay, MAC contention delay, etc.), RBS removes most delay uncertainty involved in typical time synchronization protocols. For single-hop networks, the RBS algorithm is very simple. First, a transmitter broadcasts some number M as reference broadcasts. Each receiver that receives these broadcasts exchanges the time that each reference broadcast was received locally with its neighbors. Nodes then calculate phase shifts relative to each other as the average of the difference of the time stamps of the node’s local clocks for the M reference broadcasts. In multihop networks, time synchronization can be performed hop by hop between two nodes as long as the nodes on each link along the path have a common node whose reference broadcasts they can synchronize to.^[1]

References

1. J. Elson, L. Girod, and D. Estrin. "Fine-grained network time synchronization using reference broadcasts". ACM SIGOPS Operating Systems Review - OSDI '02: Proceedings of the 5th symposium on Operating systems design and implementation. Volume 36 Issue SI, Winter 2002. Pages 147-163.