Edge-Cloud Architectures for Urban Mobility and Safety

<ns3:p> This paper introduces the NOUS Smart City Architecture (NSCA), an extensible middleware designed to enable intelligent, interoperable urban services across the edge–cloud continuum. Developed within the NOUS project, NSCA addresses a central challenge in urban digitalization: supporting scalable, efficient communication among heterogeneous actors while integrating with emerging data space infrastructures. On the <ns3:bold>edge side</ns3:bold> , NSCA builds on the lightweight and widely adopted MQTT protocol, enabling reliable, low-latency, and semantically structured communication among distributed assets such as edge devices, vehicles, roadside units, and localized digital services. On the <ns3:bold>cloud side</ns3:bold> , it integrates a Data Space Ecosystem based on the SIMPL Open architecture, providing a scalable foundation for cross-stakeholder data exchange and governance. The two layers are bridged through a standard MQTT inter-broker connector that can be deployed on either edge nodes or cloud hosts, offering flexibility in how topics are forwarded, filtered, and federated. NSCA supports both real-time data dissemination and service composition at scale, allowing new applications to be integrated with minimal configuration. This makes the architecture suitable for a wide range of smart city verticals, including road safety, mobility management, environmental monitoring, and citizen services. The platform’s practical value is demonstrated through two operational services deployed in a real-world smart city testbed. The <ns3:bold>Vulnerable Road User (VRU) Safety Service</ns3:bold> leverages edge-to-cloud communication to detect pedestrians, cyclists, and other users at risk, issuing proactive collision warnings based on real-time situational awareness. The <ns3:bold>GeoPerception Service</ns3:bold> enables cooperative sensing by sharing localized perception among vehicles and smart infrastructures, improving environmental understanding and mobility intelligence. Together, these services showcase NSCA’s ability to integrate IoT data flows, edge analytics, and data-space–enabled cloud services, supporting next-generation, interoperable urban applications. </ns3:p>