Cyber-Physical Systems
The term cyber-physical systems (CPSs) refers to an evolving generation of systems with integrated computational and physical capabilities that can interact with humans in a number of ways (Baheti & Gill, 2011; Song, Rawat et al.,2017; Romanovsky & Ishikawa, 2017). The term CPS was originally introduced in 2006 at a National Science Foundation (NSF) workshop in Austin, TX, where it was defined as “a system composed of collaborative entities, equipped with calculation capabilities and actors of an intensive connection with the surrounding physical world and phenomena, using and providing all together services of treatment and communication of data available on the network” (Quintanilla, Cardin et al., 2016). Some researchers now see a CPS as an orchestration of computers and physical systems where embedded computers monitor and control physical processes, usually making use of feedback loops, and where the physical processes affect computations, and vice versa (Lee, 2015; Sivakumar, Sadagopan et al., 2016; Hua, Lua et al., 2016). Thus, CPSs are systems of collaborating computational entities that are intensively connected with the surrounding physical world and its on-going processes, simultaneously providing and using data-accessing and data-processing services available on a cloud and/or on the Internet (Monostori, 2014; Zanero, 2017; Yu & Xue, 2016). CPSs therefore consist of computer networks and devices with built-in controllers that control (possibly, with human participation) physical processes by means of feedback; that is, physical processes exert influence on computations and computations exert influence on the choice and course of physical processes (Letichevsky, Letychevsky et al., 2017; Stankovic, 2017; Müller, Litoiu et al., 2016). Documented applications include but are not limited to: Vehicular Ad hoc Networks (VANETs), Intelligent Transportation Systems (ITSs), automotive systems, biomedical and healthcare systems, smart grid and renewable energy systems, manufacturing process control, military systems, air traffic control and safety systems, aircraft instrumentation, water management systems, physical security systems(access control and monitoring), asset management, and distributed robotics and drones (Baheti & Gill, 2011; Lee, 2015; Zanero, 2017; Letichevsky, Letychevsky et al., 2017; Massey, 2017). While some researchers consider CPSs as distinct from Internet of Things (IoT) systems, others broadly equate the two concepts, e.g., (Wang, Zhu et al., 2018, Thramboulidis & Christoulakis, 2016, Burg, Chattopadhyay et al., 2018, Antonino, Morgenstern et al., 2018, He, Maple et al., 2016, Blasch, Kadar et al., 2017), as a short list of references -- in fact, the National Institute for Standards and Technology (NIST) observes that “CPS and related systems (including the Internet of Things, Industrial Internet, and more) are widely recognized as having great potential to enable innovative applications and impact multiple economic sectors in the world-wide economy”, thus drawing a relationship between the two concepts (Griffor, 2017).
As seen above, the basic concept of CPSs is to provide intelligent capabilities to dispersed devices in order to support automated (machine-to-machine or people-to-machine) data aggregation, and also, as appropriate, to reliably transmit configuration files or commands to end-systems. CPSs comprise interacting digital, analog, physical, and human components engineered for functionality through integrated physical elements and logic capabilities (Griffor, 2017). The data can be end-system data (e.g., device status, patient monitoring), near-environment sampled data (e.g., site temperature, vehicle or device location and/or proximity, traffic patterns, site parameters), or interactive data (e.g., one- or two-way multimedia streams, video surveillance). The commands can be actuation information, for example, resetting a device or system parameter, or performing some action (e.g., for a road signal, a dam door, a grid transfer switch, a drone function, or a remote robot action). The devices can be stationary or mobile, simple or complex (Wang, Lei et al., 2016; Koutsoukos, Karsai et al., 2018; Minoli, 2013). The applicable CPS technology spans (i) sensors; (ii) access networks -- especially wireless systems for personal area networks, or more generally, Wireless Sensor Networks (WSNs); (iii) edge networks (also called fogs by some), which include VANETs; (iv) core networks -- such as metro Ethernet systems, 5G cellular; (v) cloud and/or Internet services; and (vi) data anal3ytics/big data systems.