Wireless control systems (WCSs) enable several advantages over traditional wired industrial monitoring and control systems, including self-organization, flexibility, rapid deployment, and lower maintenance. However, wireless network delay and packet loss can result in two main challenges for the control system: instability and performance degradation. This dissertation aims at solving the instability and performance degradation challenges by developing fault-tolerance and real-time approaches for a WCS.
For the instability challenge, we first developed a fault-tolerant network design and a novel model to meet the control system stability requirement for one-way wireless transmission in terms of network delay and packet loss with the minimum number of active nodes. The evaluation results showed that our model was accurate with average 4.1% difference from the simulation result. We scaled the previous work to two-way wireless transmission to meet the control system stability requirement by analyzing the worst-case network end-to-end delay. We carried out an analysis to calculate the maximum number of conflicts that could happen during one message transmission, and then derived the worst-case end-to-end delay. The simulation results showed that our end-to-end delay analysis was accurate within 4.2% of realistic simulation results.
For the performance degradation challenge, we explored a hybrid offline-online network reconfiguration framework with time-varying link failures to improve control system performance for the WCS with a single physical system. Accordingly, a precise network imperfection model and six reconfiguration algorithms had been developed to quantify and improve the performance, respectively. The case study results showed that our network imperfection model was accurate with Pearson correlation 0.993 and our network reconfiguration approach performed better than the state-of-the-art static scheme with less error and longer network lifetime. To improve the overall control system performance for the WCS with multiple physical systems, we studied a dynamic packet assignment approach. Our approach had two steps: packet priority assignment and network path selection. The case study results demonstrated that our approach was effective in improving the overall control system performance.
|Commitee:||Melhem, Rami, Zhang, Youtao, Cole, Daniel|
|School:||University of Pittsburgh|
|Department:||Dietrich School Arts and Sciences|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-B 81/7(E), Dissertation Abstracts International|
|Subjects:||Computer science, Mechanical engineering|
|Keywords:||Cyber physical system, Fault tolerance, Realtime system, Wireless control system, Wireless sensor network|
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