Abstract
Cyber–physical systems (CPS) have been widely employed as wireless control networks. There is a special type of CPS which is developed from the wireless networked control systems (WNCS). They usually include two communication links: Uplink transmission and downlink transmission. Those two links form a closed-loop. When such CPS are deployed for time-sensitive applications such as remote control, the uplink and downlink propagation delay are non-negligible. However, existing studies on CPS/WNCS usually ignore the propagation delay of the uplink and downlink channels. In order to achieve the best balance between uplink and downlink transmissions under such circumstances, we propose a heuristic framework to obtain the optimal scheduling strategy that can minimize the long-term average control cost. We model the optimization problem as a Markov decision process (MDP), and then give the sufficient conditions for the existence of the optimal scheduling strategy. We propose the semi-predictive framework to eliminate the impact of the coupling characteristic between the uplink and downlink data packets. Then we obtain the lookup table-based optimal offline strategy and the neural network-based suboptimal online strategy. Numerical simulation shows that the scheduling strategies obtained by this framework can bring significant performance improvements over the existing strategies.
Highlights
In the recent past, applications of the wireless control networks have become more and more extensive, such as drone formations, autonomous vehicles, automatic factories, etc.Some of those scenarios implicate new requirements for remote control technology, which is a sub-topic of communication control co-design
Remote control technology originates from wireless control systems with long propagation delay such as far-sea monitoring and high-efficiency satellite IoT
In order to meet the need of remote control with propagation delay, that is, to maintain stable closed-loop control and reduce control costs, we propose a new framework to design uplink and downlink scheduling strategies
Summary
Applications of the wireless control networks have become more and more extensive, such as drone formations, autonomous vehicles, automatic factories, etc. The scenarios studied above concern mainly short-distance Industrial Internet of Things (IIoT), so the impact of uplink and downlink propagation delay on the closed-loop control performance of a CPS is generally ignored. Some works have studied the design of WNCS optimal control strategy under time-delay scenarios [25,26,27] They do not consider the impact of the code error rate and the scheduling strategy which are issues that cannot be ignored in the design of communication systems in the field of communication engineering. We propose a new framework to obtain the optimal scheduling strategy while considering both the code error rates and propagation delay This strategy can minimize the long-term average control cost.
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