Guest Editors’ Introduction: Cross-Layer Design of Cyber–Physical Systems

Cyber–physical system (CPS) design is characterized by modeling a computer (or cyber) system together with the physical system that the computer controls. This approach differs from both classical control systems design and also embedded systems design. In the former case, given properties of the physical system or the “plant” to be controlled, a control law or strategy is derived, that when applied to the plant enforces the desired behavior on it. Such control laws are described mathematically, and their implementations in software already result in a CPS, viz., the plant together with the software implementation of the controller. But traditionally, the design of the control law did not take into account all the peculiarities of software implementation—such as delays involved in computing the control input based on the state of the plant, or numerical limitations of the processor running the software, or how faithfully the software implements the mathematical description of the controller. When these issues are not accounted for when designing the controller, there might be a deviation in the behavior of the system when analyzing the mathematical description of the controller, versus what would be observed with the software implementation.