Accurate Clock Synchronization for IEEE 802.11-Based Multi-Hop Wireless Networks

摘要

Clock synchronization is an essential building block for many control mechanisms used in wireless networks, including frequency hopping, power management, and packet scheduling. Although the IEEE 802.11 standard [1] provides a clock synchronization mechanism for multi-hop wireless networks, it has well-documented accuracy problems [2], [3] because the beacon frames transmitted by nodes with faster clock are not prioritized at the MAC layer. This paper describes the design and implementation of the first known software-only solution that successfully eliminates the deficiency of IEEE 802.11's clock synchronization mechanism when operating on multi-hop wireless networks without requiring any hardware/protocol modifications. The key idea of this solution is to periodically arrange for a node to become the fastest node in the network by jumping its clock with a substantial amount, and force other nodes to synchronize their clocks with this leading node by virtue of IEEE 802.11's native clock synchronization mechanism. Empirical measurements of a working implementation of the proposed algorithm on a multi-hop wireless network testbed conclusively demonstrates its effectiveness in removing IEEE 802.11's clock synchronization accuracy problem.