Nikos Piperigkos ¹ Alexandros Gkillas ^1* Gerasimos Arvanitis ² Stavros Nousias ³ Aris Lalos ¹ Apostolos Fournaris ¹ Panagiotis Radoglou-Grammatikis ^4,5 Panagiotis Sarigiannidis ⁴ Konstantinos Moustakas ²

• ¹ Industrial Systems Institute, Athena Research Center, Patras, Greece, Patras, Greece
• ² Department of Electrical and Computer Engineering, University of Patras, Patras, Greece, Patras, Greece
• ³ Technical University of Munich, Arcisstrasse 21, 80333 Munich, Germany, Munich, Germany
• ⁴ Department of Electrical and Computer Engineering, University of Western Macedonia, Kozani, Greece, Kozani, Greece
• ⁵ K3Y Ltd, William Gladstone 31, Sofia, 1000, Bulgaria, Sofia, Bulgaria

Cyber-Physical Systems (CPSs) have been transforming from individual systems to collectives of systems that collaborate to achieve a highly complex cause, realizing a Cyber-Physical Systems of Systems (CPSoS) approach. They are heterogeneous systems, comprising of various, autonomous, CPSs, each one of them having unique performance capabilities, priorities and pursued goals. In practice, there are significant challenges in CPSoS applicability and usability to be addressed. Decentralization of CPSoS appoints tasks to individual CPSs within the System of Systems. All CPSs should harmonically pursue system-based achievements and collaborate to make system-of-system based decisions and implement the CPSoS functionality.The automotive domain has been making a transition to the system of system approach aiming to provide a series of emergent functionality like traffic management, collaborative car fleet management or large-scale automotive adaptation to the physical environment thus providing significant environmental benefits and achieving significant societal impact. Similarly, large infrastructure domains, are evolving into global, highly integrated cyber-physical systems of systems covering all parts of the value chain. This survey provides a comprehensive review of current best practices in connected cyber-physical systems and investigates a dual-layer architecture entailing perception and behavioural components. The presented perception layer entails object detection, cooperative scene analysis, cooperative localization and path planning, human-centric perception. The behavioural layer focuses on human-in-the-loop-centric decision making and control where the output of the perception layer assists the human operator to make 1 Nikos Piperigkos et al.decisions while monitoring the operator's state. Finally, an extended overview of Digital Twins paradigms is provided, so as to simulate, realize and optimize large-scale CPSoS ecosystems.