Abstract: Time synchronization is one of the most important protocols in Wireless Sensor Networks（WSN）, and it is the key mechanism to ensure the cooperative work of each node in the WSN. According to the reference node, time synchronization algorithm is divided into two-way message exchange time synchronization algorithm and the distributed consensus time synchronization algorithm, the two-way message synchronization algorithm is divided into the two-way message exchange algorithm based on sender-receiver synchronization, pairwise broadcast message exchange algorithm and time synchronization algorithm based on ACK frames according to the decrease of the energy loss. The time synchronization message sending number of these three kinds of two-way message time synchronization algorithm is gradually decreasing, so energy consumption is also reduced. However, distributed consensus time synchronization algorithm abandons the selection of reference nodes, and simultaneously synchronizes all the sensor nodes, which avoids the failure of reference nodes and other nodes cannot be synchronized. Based on the analysis of the existing research, this paper concludes the possible future research directions of the time synchronization algorithm.

Key words: Wireless Sensor Network（WSN）, time synchronization, two-way message exchange, distributed consensus clock synchronization

摘要： 时间同步技术是无线传感器网络中非常重要的协议之一，是保证传感器网络中各个节点协同工作的核心机制。根据有无参考节点将时间同步算法分为双向消息交换时间同步算法和分布式一致时间同步算法，其中双向消息同步机制广播消息交换算法和基于ACK帧的时间同步算法。这三类双向消息时间同步算法的时间同步消息发送数目逐级递减，能耗相对应降低；而分布式一致时间同步算法摒弃了参考节点的选择，同时同步所有的传感器节点，避免了参考节点失效而无法进行时钟同步的情况。基于现有研究的分析及归纳，最后给出了时间同步算法未来可能的研究方向。

关键词: 无线传感器网络, 时间同步, 双向消息交换, 分布式一致时钟同步