## 2 Related Work  
During the past few years, several solutions for connected vehicles, infrastructure and pedestrians have penetrated the market. These products offer better cooperative perception and are built on top of V2X communication technologies that have been standardized in the last decade. These communication modules typically are closed source, have limited flexibility and only offer support for a single wireless communication technology. They lack an open, modular design to support hybrid communication based solutions. In research, several papers have addressed the topic of hybrid communication for V2X applications. The authors in [7] give an overview of hybrid V2X communications, describe their potentials, identify challenges and discuss main design aspects. As they explain, none of the today's V2X technologies is capable of serving the diverse Quality of Service (QoS) requirements of connected/autonomous driving applications. Hybrid V2X communications may enable Multi-Radio Access Technology (RAT) coordination to efficiently adapt to the conditions of the vehicular environment and serve the QoS requirements by selecting the best suited technologies. The authors introduce different communication profiles consisting of the RAT, its operation mode (e.g., long-range or direct) and other specific configurations. Multiple profiles could either be aggregated for increased throughput or be used concurrently for increased transmission reliability. In addition, the authors state that the dynamic selection of the appropriate communication profiles will be crucial for the overall system's performance and suggest a number of strategies for providing this dynamic selection. The current literature includes several hybrid V2X concepts [8; 9; 10] indicating the importance of combining different V2X technologies in an intelligent way according to the different use case/application requirements. However, to the best of our knowledge these concepts are only implemented and evaluated in simulations and lack the capability to offer a flexible, extendable, technology/service/vendor agnostic hybrid V2X system for real-life operation. In [8], a framework for hybrid V2X communication was developed, which aims to enhance the safety of vulnerable users at 'un-signalized' intersections. Hence, a lightweight communication node has been developed capable to communicate with connected vehicles via LoRa and DSRC technologies, and with pedestrians or unconnected vehicles through Bluetooth. The authors developed a crash prediction algorithm to identify unsafe conditions and warn the users. The VISSIM simulator was used to evaluate the proposed methodology under several traffic and landscape conditions. The authors in [9] propose a V2X simulation framework which allows vehicles to share their profiles and sensor data through V2X communication technologies. This way, researchers can test their V2X solutions for intelligent and autonomous driving at low cost. This framework allows vehicles to exploit received information from neighboring vehicles (e.g., camera feed or LIDAR data) and combine it with their own sensor data through data fusion algorithms. Hence, the vehicles can enhance their environment awareness and select a more optimal driving strategy. According to [10], there is a clear need for virtual test drives for design and testing of automated driving technologies to reduce the overall testing expenditure. Therefore the authors have developed a simulation framework based on the existing vehicle simulator \"CarMaker\", in combination with the middleware platform \"Robot Operating System\". The simulator was fed with real traffic data. To this end, a novel performance evaluation framework for Advanced Driver-Assistance Systems (ADAS) is presented. Furthermore, it allows to analyze the performance of V2X-communication for all kinds of scenarios and input parameters. Regarding the V2X communication, the authors have implemented IEEE 802.11p and C-V2X Mode 4 (without control of the network).