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Sensors 2007, 7(11), 2548-2564; doi:10.3390/s7112548

Flexible Time-Triggered Sampling in Smart Sensor-Based Wireless Control Systems

1,*  and 2
1 College of Computer Science and Technology, Zhejiang University, Hangzhou 310027, China 2 Precision Engineering Laboratory, Zhejiang University of Technology, Hangzhou 310014, China
* Author to whom correspondence should be addressed.
Received: 15 October 2007 / Accepted: 31 October 2007 / Published: 31 October 2007
(This article belongs to the Special Issue Intelligent Sensors)
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Wireless control systems (WCSs) often have to operate in dynamic environmentswhere the network traffic load may vary unpredictably over time. The sampling in sensors isconventionally time triggered with fixed periods. In this context, only worse-than-possiblequality of control (QoC) can be achieved when the network is underloaded, whileoverloaded conditions may significantly degrade the QoC, even causing system instability.This is particularly true when the bandwidth of the wireless network is limited and sharedby multiple control loops. To address these problems, a flexible time-triggered samplingscheme is presented in this work. Smart sensors are used to facilitate dynamic adjustment ofsampling periods, which enhances the flexibility and resource efficiency of the system basedon time-triggered sampling. Feedback control technology is exploited for adapting samplingperiods in a periodic manner. The deadline miss ratio in each control loop is maintainedat/around a desired level, regardless of workload variations. Simulation results show that theproposed sampling scheme is able to deal with dynamic and unpredictable variations innetwork traffic load. Compared to conventional time-triggered sampling, it leads to muchbetter QoC in WCSs operating in dynamic environments.
Keywords: adaptive sampling; smart sensors; flexible time-triggered; wireless control systems; sensor/actuator networks. adaptive sampling; smart sensors; flexible time-triggered; wireless control systems; sensor/actuator networks.
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Xia, F.; Zhao, W. Flexible Time-Triggered Sampling in Smart Sensor-Based Wireless Control Systems. Sensors 2007, 7, 2548-2564.

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