The term Cyber-Physical System (CPS) is used to describe dynamic systems which combine components characterized by a physical state (e.g., the location, power level, and temperature of a mobile robot) with components (mostly digital devices empowered by software) characterized by an operational state or mode (e.g., on/off, transmitting/receiving). From a modeling point of view, physical states evolve according to time-driven dynamics commonly described through differential (or difference) equations, while operational states have event-driven dynamics where events may be controllable (e.g., a turn on command) or uncontrollable (e.g., a random failure). Imparting intelligence to a CPS implies the presence of multiple additional events that correspond to actions such as “start moving” for a mobile robot or “change sampling rate” for a sensor. These physical and operational states generally interact to give rise to a hybrid dynamic system. For example, a sensor with autonomous control capabilities may switch to a data transmitting mode as a result of a particular physical state change (e.g., its residual energy drops below a certain threshold).
Smart Cities are an example of CPS currently attracting considerable attention, as 66% of the world’s population is projected to be concentrated in urban areas by 2050.