Diffusive clock synchronization in highly dynamic networks

Abstract

Abstract-This paper studies the clock synchronization problem in highly dynamic networks. We show that diffusive synchronization algorithms are well adapted to environments in which the network topology may change unpredictably. In a diffusive algorithm, each node repeatedly (i) estimates the clock difference to its neighbors via broadcast of zero-bit messages, and (ii) updates its local clock according to a weighted average of the estimated differences. The system model allows for drifting local clocks, running at possibly different frequencies.We show that having a rooted spanning tree in the network at every time instance suffices to solve clock synchronization. We do not require any stability of the spanning tree, nor do we impose that the links of the spanning tree be known to the nodes. Explicit bounds on the convergence speed are obtained. In particular, our results settle an open question posed by Simeone and Spagnolini to reach clock synchronization in dynamic networks in the presence of nonzero clock drift. We also identify certain reasonable assumptions that allow for a significant higher convergence speed, e.g., bidirectional networks or random graph models.

Pulse Synchronization for Vehicular Networks

“…In [24], round numbers are assumed to be known for all vehicles, which is not always realistic, because rounds estimated by vehicles can be faster or slower. In our new algorithm, vehicle i broadcast a round value s i ∈ Z, 0 ≤ s ≤ s max − 1.…”

“…The overall benefit of the method is that vehicles do not need to identify their neighboring vehicle and their pulses, so the message is short and robust. 1) Offset compensation: The term corr 1 i is used for correcting the offset for all the vehicles in previous work [24]. corr 1 i is a time difference between the average pulse of the neighboring vehicles and the pulse of vehicle i itself in round k:…”

“…The second algorithm is our improvement of the work published by [24] and the third is our new proposed technique. We take corr 2 i into account after at the sixth round.…”

“…The convergence properties of [22] is studied in [23] through graph theory. The dynamic and bi-directional properties of [22] is analyzed in [24]. Idle listening is introduced in [25] to reduce total energy consumption.…”

“…A pulsecoupled frequency synchronization proposed by [27] but it only synchronizes the frequency of nodes without aligning offsets. Our goals are to adapt the algorithm to vehicle network and to improve the pulse-coupled approach proposed by [24]. We apply both corrections for offset and frequency to local clocks of nodes.…”