Control-Aware Distributed Channel Access for Networked Control Systems

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2022-12-19
Degree programme
80 + app. 60
Aalto University publication series DOCTORAL THESES, 184/2022
Modern industrial control environments consist of a multitude of spatially distributed sensors and actuators that form various complex control loops. Networked control systems (NCSs) refer to such systems wherein the communication and information exchange between these distributed components happen over a shared communication network. NCSs offer several advantages over their traditional counterparts, such as higher flexibility and scalability with lower deployment and maintenance costs. However, they also introduce novel challenges that need to be addressed before their full potential can be realized. A major challenge is the limited capacity of the network which necessitates efficient sharing of the available communication resources among control loops based on their real-time needs. In this thesis, we first focus on wired NCSs and advocate using control-aware priority measures by using the concepts of cost of information loss (CoIL) and value of information (VoI). Another challenge is orchestrating channel access without a central network manager which we address by proposing a distributed priority-based channel access method. Next, we turn our attention to wireless NCSs (WNCSs) and consider memoryless erasure channels. Despite the additional complexities that arise due to the unreliability of channels, we prove that the aforementioned priority measures can be utilized for control-aware distributed channel access. We further investigate the stability of the system under the proposed channel access scheme and establish stability conditions. Next, we consider scenarios that necessitate the use of learning methods to evaluate transmission priorities and address how the learning can be done in a distributed way without compromising control performance. Data transmission in certain industrial environments is prone to correlated packet dropouts, which cannot be modeled by the memoryless channel. We investigate such scenarios by considering a more comprehensive channel model, i.e., a two-state Markov chain, and derive the resulting priority measures for control-aware channel access in such settings. The priorities are proved to be a function of the transition probabilities of the underlying channel model which can be unknown in practice. We thus consider practical scenarios without a priori knowledge of these parameters and develop a model-based Bayesian reinforcement learning algorithm to learn them in a distributed control-aware manner.
Supervising professor
Charalambous, Themistoklis, Prof., Aalto University, Department of Electrical Engineering and Automation, Finland
networked control systems, channel access mechanism, wireless communication, Gilbert-Elliott channel, Markov chains, Lyapunov stability
Other note
  • DOI: 10.1109/TCSII.2018.2822871 View at publisher
  • [Publication 2]: Shengquan Wang, Tahmoores Farjam, and Themistoklis Charalam bous. A priority-based distributed channel access mechanism for control over CAN-like networks. In European Control Conference (ECC), Rotterdam, The Netherlands, 7 pages, July 2021.
    Full text in Acris/Aaltodoc:
    DOI: 10.23919/ECC54610.2021.9655068 View at publisher
  • [Publication 3]: T. Farjam, H. Wymeersch and T. Charalambous, "Distributed Channel Access for Control Over Unknown Memoryless Communication Channels," in IEEE Transactions on Automatic Control, vol. 67, no. 12, pp. 6445-6459, Dec. 2022.
    Full text in Acris/Aaltodoc:
    DOI: 10.1109/TAC.2021.3129737 View at publisher
  • [Publication 4]: Tahmoores Farjam and Themistoklis Charalambous. Event-Triggered control in shared networks: How the computational power of sensors affects transmission priorities. In IEEE Conference on Decision and Control (CDC), Austin, Texas, USA, 7 pages, December 2021.
    Full text in Acris/Aaltodoc:
    DOI: 10.1109/CDC45484.2021.9683074 View at publisher
  • [Publication 5]: Tahmoores Farjam, Henk Wymeersch, and Themistoklis Charalambous. Distributed channel access for control over known and unknown Gilbert-Elliott channels. Submitted, 15 pages, July 2022.