Adaptive Decentralized MAC for Event-Triggered Networked Control Systems

Abstract

Control over shared communication networks is a key challenge in design and analysis of cyber-physical systems. The quality of control in such systems might be degraded due to the congestion while accessing the scarce communication resources. In this paper, we consider a multiple-loop networked control system (NCS), where all control loops share a communication network. Medium Access Control (MAC) is performed in contention-based fashion using a multi-channel slotted ALOHA protocol, where each control loop decides locally whether to attempt a transmission based on some error thresholds. We further introduce a local event-based resource-aware scheduling design with an adaptive choice of the error thresholds for a transmission. This leads to a hybrid channel access mechanism where the control loops are deterministically categorized into two sets of eligible and ineligible sub-systems for transmission in an event-based fashion, before a random process to select the available channels. In addition, employing the introduced policy, we show the stability of the resulting NCS in terms of Lyapunov stability in probability. We illustrate numerically the efficiency of our proposed approach in terms of reducing the average networked-induced error variance, and show the superiority of the adaptive event-based scheduler compared to the scheduling design with non-adaptive thresholds.

Decentralized event-triggered medium access control for networked control systems

“…factor α i k ′ equals 77.51, shows that the selected waiting times are concentrated at the beginning of the macro slot, which leads to a collision rate of 3.47%, and error variance of 2.71. By tuning the parameters in (18) properly, the mean of α i k ′ changes to 163, which results in a better use of the entire channel range in one slot. This leads to less collisions (1.35%) and consequently lower error variance (2.50).…”

“…On the other hand, setting the thresholds high implies that sub-systems with relatively high errors are blocked, which also leads to performance deficiency. Hence, there should be optimal values of error thresholds which maintain a balance between optimizing performance and maximizing transmission chance for sub-systems with critical real-time conditions [18]. Deriving optimal thresholds is out of this paper's scope.…”

Wireless Network Design for Control Systems: A Survey

“…On the other hand, [173] derives experimental based models by using curve fitting techniques and validation through extensive experiments. An adaptive algorithm was also proposed to adjust the coefficients of these models by introducing a learning phase without any explicit information about data traffic, network topology, and Contention-based Access [212], [213], [175], [174], [214], [129], [84], [107], [215], [173], [125] [166], [202], [194], [195], [216], [196], [217] [204], [211], [206], [207], [208], [209], [210] Schedule-based Access [126], [127], [176], [177], [178] [4], [190], [203], [202], [192], [193] [81], [218], [205], [62], [83] Physical Layer Extension [6], [87], [183], [219], [220], [221] --Network Resource Schedule Scheduling Algorithm …”

“…Contention-based Access: The tradeoff between the level threshold crossings in the control system and the packet losses in the communication system have been analyzed in [204], [211], [206], [207], [208], [209], [210]. [204] studies the eventtriggered control under lossy communication.…”

“…However, this introduces extra delay between the triggering of an event and a transmission in its assigned slot. [206] analyzes the event-based NCS consisting of multiple linear time-invariant control systems over a multichannel slotted ALOHA protocol. The multichannel slotted ALOHA system is considered as the random access model of the Long Term Evolution [226].…”