Energy-efficient time synchronizations for wireless sensor networks (WSNs) have been put under the spotlight for years. A promising technique among which is the timestamp-free approach where no timestamps are required to establish the synchronization, thereby sparing the transmissions of the timing messages for conserving significant transmission energy. In this paper, we first investigate the feasibility of adopting timestamp-free time synchronization in practical resource-constrained WSNs; we then identify the issue of inaccuracy in maintaining the pre-defined response interval which affects the foundations of most existing timestamp-free schemes. Based on the investigation and our previously proposed reverse asymmetric time synchronization framework, we further propose an asymmetric timestamp-free time synchronization scheme with two estimation methods tailored for resource-constrained WSNs. We as well introduce the centralized and distributed multi-hop extension methods for the proposed scheme to cover diverse multi-hop scenarios. Experimental results on a real WSN testbed consisting of TelosB motes running TinyOS demonstrate that the proposed scheme achieves high energy efficiency while maintaining microsecond-level time synchronization accuracy compared to three other conventional schemes.

中文翻译：

---

基于反向非对称框架的实用资源受限无线传感器网络无时间戳时间同步方案

多年来，无线传感器网络 (WSN) 的节能时间同步一直备受关注。其中一种很有前途的技术是无时间戳方法，其中不需要时间戳来建立同步，从而节省定时消息的传输以节省大量传输能量。在本文中，我们首先研究了在实际资源受限的 WSN 中采用无时间戳时间同步的可行性；然后，我们确定了维护预定义响应间隔的不准确性问题，这会影响大多数现有无时间戳方案的基础。基于调查和我们之前提出的反向不对称时间同步框架，我们进一步提出了一种非对称无时间戳时间同步方案，该方案具有两种针对资源受限的 WSN 量身定制的估计方法。我们还介绍了所提出方案的集中式和分布式多跳扩展方法，以覆盖各种多跳场景。在由运行 TinyOS 的 TelosB 微粒组成的真实 WSN 测试平台上的实验结果表明，与其他三种传统方案相比，所提出的方案在保持微秒级时间同步精度的同时实现了高能效。