by Françoise Lamnabhi-Lagarrigue, Maria Domenica Di Benedetto and Erwin Schoitsch
Embedded systems - some visible, others integrated into every day equipment and devices – are becoming increasingly pervasive, and increasingly responsible for ensuring our comfort, health, services, safety and security. In combination and close interaction with the unpredictable real-world environment and humans, they become “Cyber-Physical Systems” (CPS), which act independently, co-operatively or as “systems-of-systems” composed of interconnected autonomous systems originally independently developed to fulfill dedicated tasks. Some of these systems may be older legacy systems.
The elements of the physical system are connected by the exchange of material or energy, while the elements of the control and management system are connected by communication networks which sometimes impose restrictions on the exchange of information, with software as a critical core element. Dependability - particularly resilience, safety and security - is a more complex issue than ever before for embedded distributed systems in the conventional sense. Prototype systems are the electrical grid, a power plant, an airplane or a ship, a manufacturing process with many cooperating elements, e.g., robots, machines, warehouses, conveyer belts, a large processing plant with many process units, a building with advanced distributed HVAC control, etc.
From the German Agenda CPS, Intermediate Results, Acatech, 2010: “Cyber-physical systems typically comprise embedded systems (as parts of devices, buildings, vehicles, routes, production plants, logistics and management processes etc.) that
- use sensors and actuators to gather physical data directly and to directly affect physical processes
- are connected to digital networks (wireless, wired, local, global)
- use globally available data and services
- possess a range of multi-modal human-machine interfaces (dedicated interfaces in devices, or unspecific interfaces accessed through browsers, etc.).”
The extreme importance of CPS for industrialized countries was highlighted in the August 2007 Report of the President's Council of Advisors on Science and Technology (PCAST) presenting a formal assessment of the Federal Networking and Information Technology R&D (NITRD). This report led the National Science Foundation to create the Cyber-Physical Systems Program in 2009, a major cross-cutting initiative at NSF. CPS-related conferences have been integrated into a major annual event, CPS WEEK, which rotates between the United States and Europe.
During the Workshop on Control of Cyber-Physical Systems held at the University of Notre Dame London Centre, 20-21 October 2012, organized by Panos Antsaklis, Vijay Gupta and Karl Henrik Johansson, the following definition was adopted: “Cyber-Physical Systems (CPS) are physical, chemical, biological and engineered systems whose operations are monitored, coordinated, controlled and integrated by a computing and communication core.” Desired characteristics or descriptive words of well-designed and engineered Cyber-Physical Systems include: coordinated, distributed, connected, heterogeneous, robust and responsive, providing new capability, adaptability, resiliency, safety, security, and usability, with feedback loops including often humans and the environment and related systems. This intimate coupling between the cyber and physical will be manifested across a broad range of length scales, from the nano-world to large-scale wide-area systems of systems. Correspondingly, CPSs will often have dynamics at a wide range of time-scales, such as at the discrete clock scale for some computational aspects to multi-day or even year-long time scales for system-wide properties and evolution.
Applications with enormous societal impact and economic benefit will be created. Cyber-Physical Systems will transform how we interact with the physical world just as the Internet transformed how we interact with one another. After several FP7 related projects or supporting actions, CPSs are now a targeted research area in Horizon 2020 (http://ec.europa.eu/programmes/horizon2020/) and public-private partnerships such as ECSEL (Electronic Components and Systems for European Leadership (http://ec.europa.eu/digital-agenda/ en/time-ecsel), which integrates the former ARTEMIS (http://www.artemis-ju.eu), ENIAC (http://www.eniac.eu) and EPoSS (http://www.smart-systems-integration.org), which are dedicating great effort to this area of research. The importance of “Systems of Cyber-Physical Systems” is highlighted by EU-Roadmap activities such as the CPSoS project (see article on page 21), developing a strategic policy document “European Research and Innovation Agenda on Cyber-Physical Systems of Systems” (http://www.cpsos.eu/).
The design of such systems requires understanding the joint dynamics of computers, software, networks, physical, chemical and biological processes and humans in the loop. It is this study of joint dynamics that sets this discipline apart. Increasingly, CPSs are autonomous or semi-autonomous and cannot be designed as closed systems that operate in isolation; rather, the interaction and potential interference among smart components, among CPSs, and among CPSs and humans, requires coordinated, controlled, and cooperative behaviour. Very difficult challenges are posed for control of CPS owing to a variety of factors, such as very broad time and length scales, the presence of network communication and delays, coordination of many components (with an associated increased risk of component failure as the number of components grows to be very large), model reduction, tractability, etc.
Cyber-physical systems (of systems) cannot be designed and managed using theories and tools from only one domain, see the FP7 NoE HYCON2 deliverable D3.4.1 “Roadmap: From distributed and coordinated control to the management of cyber-physical systems of systems”. The behaviour of the large coupled physical part of the system must be modelled, simulated and analysed using methods from continuous systems theory, e.g. large-scale simulation, stability analysis, and the design of stabilizing control laws. On the other hand, methods and tools from computer science for the modelling of distributed discrete systems, for verification and testing, assume-guarantee methods, contract-based assertions etc. are indispensable to capture both the behaviour on the low level (discrete control logic, communication, effects of distributed computing) and global effects, in the latter case based on abstract models of complete subsystems. Logistic models as well as models and tools for performance analysis of discrete systems will be useful for system-wide performance analysis. Finally, theories from physics, e.g. structure formation in large systems, and from economics and social science (market mechanisms, evolution of beliefs and activity in large groups) may also prove to be useful.
The emphasis of this special issue is on an integrated perspective of real-time computing, communication, dynamics, and control of CPS, particularly of non (extra-) functional properties. A first set of contributions are dedicated to the representation and foundations of CPS including:
- Analysis, estimation, synthesis, design, and verification of CPS
- Platforms for smart infrastructure connecting the three layers : the Cloud layer, the Middle layer and the Physical layer
- Dependability (safety, security, reliability etc.) and resilience of CPS, including the Systems of Systems aspects
- Specification formalisms, including languages and software tools
- Real-time computing and resource-aware control for CPS
- Networks and protocols for CPS.
Several contributions are dedicated to specific applications:
- Smart Electric Grid
- Water Management
- Autonomous Vehicles and Smart Transportation
- Next-generation Port and Air Traffic Management
- Smart Medical Technologies.
As stated in the previous cited NoE HYCON2 Deliverable, “the size of cyber-physical systems of systems and their ‘multimodality’ or hybrid nature consisting of physical elements as well as quasi-continuous and discrete controls, communication channels, and local and system-wide optimization algorithms and management systems, implies that hierarchical and multi-domain approaches to their simulation, analysis and design are needed. These methods are currently not available. In individual domains, e.g. dynamic modelling and simulation, verification of discrete systems, design of controllers for guaranteed system stability on different system levels, and optimization of flows across the system, further progress can be expected that will have a high impact on the engineering of systems of systems. However, the simultaneous use and the integration of heterogeneous models and tools to capture system-wide properties reliably and with firm guarantees are currently completely open issues. The critical properties of cyber-physical systems of systems go beyond what can be analysed and designed systematically today: dynamic reconfiguration of complex systems, large-scale dynamics, waves of events or alarms, interaction of autonomous, selfish systems, and coupling of physical and computational elements via communication channels.”
Maria Domenica Di Benedetto
University of L’Aquila, Center of Excellence DEWS, EECI, Italy
CNRS-Laboratoire des Signaux et Systèmes, EECI, France
AIT Austrian Institute of Technology/AARIT, Austria