Research problem:

    Time synchronization for wireless sensor networks


    With the help of recent technological advances in micro-electro-mechanical systems (MEMS) and wireless communications, low-cost, low-power, and multi-functional wireless sensing devices have been developed. When these devices are deployed over a wide geographical region, they can collect information about the environment and efficiently collaborate to process such information by forming a distributed communication network, called the Wireless Sensor Networks (WSN). WSN is a special case of wireless ad-hoc network, and assumes a multi-hop communication framework with no common infrastructure, where the sensors spontaneously cooperate to deliver information by forwarding packets from a source to a destination. The feasibility of WSNs keeps growing rapidly, and WSNs have been regarded as fundamental infrastructures for future ubiquitous communications due to a variety of promising potential applications: monitoring the health status of humans, animals, plants and environment, control and instrumentation of industrial machines and home appliances, homeland security, detection of chemical and biological threats and leaks, etc.

    Time synchronization is a procedure for providing a common notion of time across a distributed system. It is crucial for WSNs in performing a number of fundamental operations, such as Data fusion, Power management and Transmission scheduling.  Moreover, many localization, security and tracking protocols also demand the nodes to timestamp their messages and sensing events.  Therefore, time synchronization appears as one of the most important research challenges in the design of energy-efficient WSNs.

    In general, synchronization is considered a critical problem for distributed wireless ad-hoc networks due to its decentralized nature and the timing uncertainties introduced by the imperfections in hardware oscillators and message delays in physical and MAC-layers.  All these uncertainties cause the local clocks of different nodes to drift away from each other over the course of a time interval. In the context of Internet (a kind of distributed networks), time synchronization has been thoroughly studied and investigated. In the Internet, the Network Time Protocol (NTP) is employed ubiquitously due to its diverse advantages, such as scalability, robustness and self-configurability.  However, NTP presents a number of challenges when applied to WSNs due to the unique nature of sensor networks: limited power resources, wireless channel conditions, and dynamic topology caused by mobility and failure.  Therefore, different types of synchronization schemes have to be explicitly designed for WSN applications to cope with these challenges.

    In this work, we design and analyze existing and new time synchronization protocols for WSN using the statistical signal processing framework.


Representative Publications:

  1. Mei Leng and Yik-Chung Wu, ``Distributed Clock Synchronization for Wireless Sensor Networks using Belief Propagation," IEEE Trans. on Signal Processing, Vol. 59, no. 11, pp. 5404-5414, Nov 2011.[Preprint, IEEE_Xplore]

  2. Mei Leng and Yik-Chung Wu, ``Low Complexity Maximum Likelihood Estimators for Clock Synchronization of Wireless Sensor Nodes under Exponential Delays," IEEE Trans. on Signal Processing, Vol. 59, no. 10, pp. 4860-4870, Oct 2011. [Preprint, IEEE_Xplore]

  3. Yik-Chung Wu, Qasim M. Chaudhari and Erchin Serpedin, ``Clock Synchronization of Wireless Sensor Networks," IEEE Signal Processing Magazine, Vol. 28, no. 1, pp.124-138, Jan. 2011. [IEEE Xplore] (Ranked among top 100 most downloaded IEEE Xplore articles in Jan 2011)

  4. Jun Zheng and Yik-Chung Wu, ``Joint Time Synchronization and Localization of an unknown node in Wireless Sensor Networks," IEEE Trans. on Signal Processing, Vol. 58, no. 3, pp. 1309-1320, Mar 2010.  [PDF]

  5. Mei Leng and Yik-Chung Wu, ``On Clock Synchronization Algorithms for Wireless Sensor Networks under Unknown Delay," IEEE Trans. on Vehicular Technology,  vol. 59, no.1, pp. 182-190, Jan 2010. [PDF]

  6. King-Yip Cheng, King-Shan Lui, Yik-Chung Wu and Vincent Tam, ``A Distributed Multihop Time Synchronization Protocol for Wireless Sensor Networks using Pairwise Broadcast Synchronization," IEEE Trans. on Wireless Communications, vol. 8, no. 4, pp. 1764-1772, Apr 09. [PDF]

  7. Ill-Keun Rhee, Jaehan Lee, Jangsub Kim, Erchin Serpedin, Yik-Chung Wu, ``Clock Synchronization in Wireless Sensor Networks: An Overview." Sensors 9, no. 1: 56-85, 2009. [PDF]

  8. Kyoung-Lae Noh, Yik-Chung Wu, Khalid Qaraqe and Bruce W. Suter, ``Extension of pairwise broadcasting clock synchronization for multi-cluster sensor networks," EURASIP Journal on Advances in Signal Processing, special issue on Distributed Signal Processing Techniques for Wireless Sensor Networks, vol. 2008, Article ID 286168, 10 pages, 2008. doi:10.1155/2008/286168. [PDF]

  9. Kyoung-Lae Noh, Yik-Chung Wu, Khalid Qaraqe and Erchin Serpedin, ``Chapter 13: Time Synchronization for Wireless Sensor Networks," in Adaptive Signal Processing for Wireless Communications, edited by Mohamed Ibnkahla, CRC Press, 2008.