###### Abstract  
Vehicle-to-everything (V2X) communications enable real-time information exchange between vehicles and infrastructure, which extends the perception range of vehicles beyond the limits of on-board sensors and, thus, facilitating the realisation of cooperative, connected, and automated mobility (CCAM) services that will improve road safety and traffic efficiency. In the context of CCAM, the successful deployments of cooperative intelligent transport system (C-ITS) use cases, with the integration of advanced wireless communication technologies, are effectively leading to make transport safer and more efficient. However, the evaluation of multi-vendor and multi-protocol based CCAM service architectures can become challenging and complex. Additionally, conducting on-demand field trials of such architectures with real vehicles involved is prohibitively expensive and time-consuming. In order to overcome these obstacles, in this paper, we present the development of a standards-compliant experimental vehicular on-board unit (OBU) that supports the integration of multiple V2X protocols from different vendors to communicate with heterogeneous cloud-based services that are offered by several original equipment manufacturers (OEMs). We experimentally demonstrate the functionalities of the OBU in a real-world deployment of a cooperative collision avoidance service infrastructure that is based on edge and cloud servers. In addition, we measure end-to-end application-level latencies of multi-protocol supported V2X information flows to show the effectiveness of interoperability in V2X communications between different vehicle OEMs. 5G; mobile edge computing; V2X communication; cooperative perception; intelligent transport systems +
Footnote †: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ([[https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/)]([https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/))). Footnote †: This paper is an extended version of our paper published in An Experimental Vehicular On-Board Unit for the Execution of Anticipated Cooperative Collision Avoidance Services in Cross-Border Scenarios. cooperative intelligent transport systems (C-ITS) in the context of cooperative, connected, and automated mobility (CCAM). C-ITS is an emerging use case of intelligent transport systems (ITS) [3; 4] that enables real-time wireless communication and information sharing between ITS stations, e.g., vehicles or roadside units (RSUs), in order to achieve coordinated decisions through cooperation, thus extending the capabilities of a vehicle beyond the scope of a typical stand-alone entity. Modern vehicles are progressively turning into sophisticated computing units able to gather, process, and exchange information with other connected objects [5]. They will be typically equipped with ultra-high-definition cameras, radars, LiDARs, ultrasonic range finders, and other types of sensors, which allow for sensing vehicles' proximity. Additionally, modern vehicles are equipped with an on-board unit (OBU) for V2X communication, which enables vehicles to effectively exchange locally sensed data with the other external entities over wireless connectivity. Such V2X-enabled vehicles are capable of sharing information over vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-pedestrians (V2P), and vehicle-to-network (V2N) communications. V2X connectivity extends the perception range beyond the limits of on-board sensors of a vehicle, thus supporting emerging vehicular services that will increase traffic efficiency and road safety. With the emergence of 5G, the use of cellular V2X (C-V2X) [6; 7] is gaining more attention worldwide through the execution of promising trials of vehicular services [8; 9].