An algorithm for clock synchronization with the gradient property in sensor networks

We introduce a distributed algorithm for clock synchronization in sensor networks. Our algorithm assumes that nodes in the network only know their immediate neighborhoods and an upper bound on the network’s diameter. Clock-synchronization messages are only sent as part of the communication–assumed to be reasonably frequent–that already takes place among nodes. The algorithm has the gradient property of [R. Fan, N. Lynch, Gradient clock synchronization, Distributed Computing 18 (2006) 255–266], achieving an O(1)O(1) worst-case skew between the logical clocks of neighbors. The algorithm’s actions are such that no constant lower bound exists on the rate at which logical clocks progress in time, and for this reason the lower bound of [R. Fan, N. Lynch, Gradient clock synchronization, Distributed Computing 18 (2006) 255–266; L. Meier, L. Thiele, Brief announcement: Gradient clock synchronization in sensor networks, in: Proceedings of the Twenty-Fourth Annual ACM Symposium on Principles of Distributed Computing, 2005, p. 238] that forbids a constant clock skew between neighbors does not apply.