以節點同步狀態為基礎的感測網路時間同步協定

State-Based Time Synchronization Protocol in Sensor Networks

徐尚誌(Shang-Chih Hsu)

指導教授 ： 嚴威

大同大學/電機資訊學院/資訊工程學系所/碩士(2006年)

摘要

在最近這幾年來，無線感測網路(wireless sensor networks)成為了一門重要的研究領域。可以想像的是，這類型的網路應用會需要大量的感測節點(sensor nodes)，靠著彼此間互相的合作來執行任務。其中有些應用，利用各個感測節點內的本地時間戳記，來做為節點間彼此的訊息交換來實現。這是因為即時的要求或者是其他應用所需，所以在這類的系統中，時間的同步是一重要議題。
感測網路的時間同步協定(Time-sync Protocol for Sensor Network, TPSN)與以標準重量式及樹狀為基礎的同步協定(Lightweight Tree-based Synchronization, LTS)已經為感測網路提供了廣域網路(network-wide)的時間同步協定。然而這兩個協定還是可以利用消除重複的封包、最佳化收斂時間與減少同步的誤差發生等方法來改進。因此我們提出了一個以節點同步狀態為基礎的感測網路時間同步協定(State-Based Time Synchronization Protocol, STSP)，它是利用感測節點狀態的不同，來決定同步的動作。我們的目標是希望在感測網路中，能改善其時間同步收斂的時間、減少電源的消耗與降低同步錯誤的發生。
我們把這些協定與STSP做一比較，並對它們的效能作了三方面的檢查。其中包括了同步的收斂時間、訊息的交換數量與同步的誤差。我們將展現STSP是可以同步每個節點，而與TPSN和LTS比較下，它增進了48%與40%的平均精確度。此外，STSP的平均訊息交換量與TPSN、LTS相比，減少了大約67%與51%。以結論來說，我們相信STSP在感測網路中提供了一加強的穩固效能。

關鍵字

時間漂移 ； 感測網路 ； 同步誤差 ； 同步周期 ； 時間同步

並列摘要

Wireless sensor networks are an important research area in the last few years. The applications envisioned for such networks require collaboration execution among a large set of nodes. Some of them may be realized by message exchanges with timestamp of the local clock in the sensor node. Because of the real time or other application specific requirements, time synchronization is an important issue in such systems.
The time-sync protocol for sensor networks (TPSN) and lightweight tree-based synchronization (LTS) protocols have provided network-wide time synchronization in sensor networks. However, these two protocols can still be improved by eliminating duplicated packets, optimizing convergence time, and reducing synchronization error. Therefore, we propose a state-based time synchronization protocol (STSP), which uses states to decide the synchronization actions of the sensor nodes. Our goals are to improve convergence time, reduce power consumption, and decrease synchronization error in the sensor network.
We compare these protocols with the STSP and examine their performance in three key metrics including synchronization convergence time, the number of message exchanges, and the synchronization error. We will show that the STSP can synchronize every node to an average accuracy of less than 48% and 40% of TPSN and LTS, respectively. Moreover, the average number of message exchanges of the STSP reduces about 67% and 51% that compare with TPSN and LTS. In summary, we believe the STSP provides solid performance enhancement in the sensor network.

並列關鍵字

Clock Drift ； Sensor Networks ； Synchronization Error ； Synchronization Period ； Time Synchronization

參考文獻

[2] Fikret Sivrikaya and Bülent Yener,“Time Synchronization in Sensor Networks：A Survey,”IEEE Network, v18, n4, July/August, 2004, p 45-50.

[3] Liang Cheng, Yuecheng Zhang, Tina Lin, and Qing Ye,“Integration of Wireless Sensor Networks, Wireless Local Area Networks and the Internet,” IEEE International Conference on Networking, Sensing and Control, 2004, p 462-467.

[5] Santashi PalChaudhuri and Amit Kumar Saha, and David B. Johnson,“Adaptive Clock Synchronization in Sensor Networks,”Third International Symposium on Information Processing in Sensor Networks, IPSN’04 April 26-27, 2004, Berkeley, California, USA.

[6] Len J. Sciacca and Robin J. Evans,“Cooperative Sensor Networks with bandwidth constraints,”Proceedings of SPIE – The International Society for Optical Engineering, v 4741, 2002, p 192-201.

[9] Saurabh Ganeriwal, Ram Kumar, and Mani B. Srivastava,“Timing-sync Protocol for Sensor Networks,” Proceedings of the 1st international conference on Embedded networked sensor systems, November 5-7, ACM 2003, Los Angels, California, USA.