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Distributed Sampling, Filtering and Synchronization in Wireless Sensor Networks Open Access


Other title
signal processing
clock synchronization
sampled data control
multi-agent systems
filter banks
control systems
time synchronization
Type of item
Degree grantor
University of Alberta
Author or creator
Ahmed, Salman
Supervisor and department
Zhao, Qing (Electrical and Computer Engineering)
Chen, Tongwen (Electrical and Computer Engineering)
Lynch, Alan (Electrical and Computer Engineering)
Examining committee member and department
Leung, Henry (Electrical and Computer Engineering, UoC)
Chen, Tongwen (Electrical and Computer Engineering)
Zhao, Qing (Electrical and Computer Engineering)
Qiu, Tony (Civil and Environmental Engineering)
Lynch, Alan (Electrical and Computer Engineering)
Department of Electrical and Computer Engineering
Control Systems
Date accepted
Graduation date
Doctor of Philosophy
Degree level
A wireless sensor network (WSN) consists of spatially distributed sensor nodes which are deployed to monitor some process of interest. Although WSNs are very promising, the distributed nature, attributes of wireless networks, and availability of limited resources in WSNs introduce significant theoretical and practical challenges. First, the cooperative control of sensor nodes requires to consider subsystems instead of a single system. Second, the communication capabilities and connectivity of the sensor nodes are limited. Third, the information exchange in the wireless sensor network may be unreliable and suffer transmission delays. Fourth, the availability of limited resources imposes constraints on the sampling rates and time synchronization of sensor nodes. Motivated by these challenges, this thesis studies the design of distributing filtering and sampling techniques in resource constrained WSNs. For distributed filtering, one of the most promising techniques are the linear consensus protocols. A motivating example for studying the application of consensus protocols is to investigate the distributed time synchronization problem in WSNs. In this thesis, we study and propose distributed time synchronization protocols which consider an asynchronous framework where the sensor nodes can have different time-periods, starting times and input update times. The clocks in a WSN are modeled by a time-varying system with time-delay terms. By employing tools from nonnegative matrix and graph theories, the convergence analysis is presented. Most of the standard control and monitoring techniques rely on uniform and synchronized sampling. A sensor node has limited battery resources and their efficient utilization imposes constraints on the time synchronization of the sensor nodes which introduces sampling jitters. In this thesis, we model WSNs employing distributed sampling using filter banks and present the design of synthesis filters to minimize the effects of sampling jitters. We consider two cases for the design of synthesis filters. In the first case, we consider a hybrid filter bank and assume that the sampling jitter is known for each sensor. We employ tools from sampled-data control theory and present a procedure to design optimal H2 synthesis filter bank to handle sampling jitters and reconstruct uniformly sampled measurements. In the second case, we consider a discrete-time filter bank and allow the sampling jitters to be time-varying. Using polytopic matrices to encompass all possible representations of the system matrices, the problem is reduced to an Hinfty optimization problem and the design of pre-processing filters is presented. All the theoretical development and the proposed techniques in this thesis are validated using simulation examples.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
S. Ahmed and T. Chen. Minimizing the effects of sampling jitters in wireless sensors networks. IEEE Signal Processing Letters, 18(4):219-222, 2011.S. Ahmed, F. Xiao, and T. Chen. Achieving relative time synchronization in wireless sensor networks. Journal of Control Science and Engineering, 2013:Article ID 538181, 7 pages, 2013S. Ahmed, F. Xiao, and T. Chen. Asynchronous consensus-based time synchronization in wireless sensor networks using unreliable communication links. submitted to IET Control Theory and Application

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