Abstract
In the design of multi-loop Networked Control Systems (NCSs), wherein each control system is characterized by heterogeneous dynamics and associated with a certain set of timing specifications, appropriate metrics need to be employed for the synthesis of control and networking policies to efficiently respond to the requirements of each control loop. The majority of the design approaches for sampling, scheduling, and control policies include either time-based or event-based metrics to perform pertinent actions in response to the changes of the parameters of interest. We specifically focus in this article on Age-of-Information (AoI) as a recently-developed time-based metric and threshold-based triggering function as a generic Event-Triggered (ET) metric. We consider multiple heterogeneous stochastic linear control systems that close their feedback loops over a shared communication network. We investigate the co-design across the NCS and discuss the pros and cons with the AoI and ET approaches in terms of asymptotic control performance measured by Linear-Quadratic Gaussian (LQG) cost functions. In particular, sampling and scheduling policies combining AoI and stochastic ET metrics are proposed. It is argued that pure AoI functions that generate decision variables solely upon minimizing the average age irrespective of control systems dynamics may not be able to improve the overall NCS performance even compared with purely randomized policies. Our theoretical analysis is validated through several simulation scenarios.
Highlights
Networked Control Systems (NCSs) generally refer to multiple dynamical systems controlled by possibly remotely located controllers with information exchange supported by a wired or wireless communication infrastructure
We consider an NCS consisting of N heterogeneous stochastic Linear Time-Invariant (LTI) controlled dynamical processes that synchronously exchange their sensory information with their corresponding controllers via a common resource-limited communication network; see Figure 1
The major goal is to propose a co-design networked control architecture of sampling, scheduling, and control for NCSs comprised of multiple heterogeneous LTI stochastic control systems that close their sensor-to-controller loops over a shared capacity-limited communication network
Summary
Networked Control Systems (NCSs) generally refer to multiple dynamical systems controlled by possibly remotely located controllers with information exchange supported by a wired or wireless communication infrastructure. Considering state-of-the-art communication technology, there is a need for novel approaches to the modeling, analysis, and design of network protocols and control mechanisms capable of jointly supporting information exchange required to make decisions at the right component and at the right time. This is the basic motivation behind employing appropriate utility functions to coordinate the process of data exchange in a network of many dynamical users. To fill this research void, it is essential to develop systematic and applicable co-design principles for NCSs that bring both QoC and QoS together by studying novel architectures that take into account the requirements, limitations, and tolerances of both network and control systems
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