# How Does C-V2X Help Autonomous Driving to Avoid Accidents?
###### Abstract  
Accidents are continuously reported for autonomous driving vehicles including those with advanced sensors installed. Some of accidents are usually caused by bad weather, poor lighting conditions and non-line-of-sight obstacles. Cellular Vehicle-to-Everything (C-V2X) radio technology can significantly improve those weak spots for autonomous driving. This paper describes one of the C-V2X system solutions: Vulnerable Road User Collision Warning (VRUCW) for autonomous driving. The paper provides the system architecture, design logic, network topology, message flow, artificial intelligence (AI) and network security feature. As a reference it also includes a commercial project with its test results. C-V2X autonomous driving; PC5; RSU; OBU; VRUCW; AI 20  
vehicle movements and road conditions, detecting potential non-line-of-sight (NLOS) problems before a catastrophe happens. Today, a serial of advanced sensors including IP Camera, Radar/LiDAR, and Advanced Driver Assistance Systems (ADAS) have been installed in autonomous driving vehicle. Sensors in the vehicle provide the basic functionalities of autonomous driving, it is crucial for safety and will not change in the near future, but these sensors are easily impacted by bad weather, poor lighting conditions or non-line-of-sight obstacles. Apparently, the automotive industry has recognized that connectivity is necessary to further increase the safety and comfort of Level 3 or Level 4 driving. Going beyond a certain level of driving autonomy will definitely require vehicles to be connected with each other or with network as mentioned in [6]. The cooperative C-V2X systems are known as vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-pedestrian (V2P) or vehicle-to-network (V2N) communications. C-V2X can enable vehicle to communicate with other vehicle, infrastructure, pedestrian and network to improve road safety and road efficiency, as introduced in [7]. Our work is inspired by a number of prior studies on the applications of C-V2X. A brief summary of relatedness is shown in Table 2.  
In [8; 9], the authors shared function and performance tests in V2V/V2I whose aim was to review how the automated driving benefits on PC5/Uu connected in LTE-V2X network to improve road safety and traffic efficiency. Moreover, V2X platform or MEC was used to send messages to RSU, and then RSU could broadcast them to vehicles through the PC5 interface. RSU also might send messages to network through the Uu interface. In [10], author solved problems of Uu interface based C-V2X and verified the performance of the solution in both LTE-V2X and NR-V2X networks. Then, ref. [11] suggested some pricing and investment strategies which may be helpful for a successful deployment of V2N. Refs. [12; 13] focused on vulnerable road users (VRU) scenario, collision prediction algorithms were proposed based on pedestrian-to-vehicle (P2V) or vehicle-to-pedestrian (V2P) communication. In terms of network topology, they involved remote cloud-based cellular architecture and MEC infrastructure to decrease E2E communication latency. Refs. [14; 15; 16] concluded that Artificial Intelligence (AI) technology could make the collision avoidance system adapt to the environment and facilitate fast and accurate decisions. Edge analytics architecture was proposed to reduce AI computing time. With the popularity of C-V2X technology in recent years, on the one hand, automobile manufacturers would like to bind C-V2X function to the future electric vehicles in order to strengthen safety. On the other hand, current driver does not need to wait until these C-V2X products are initially embedded in new manufactured vehicle models after few years. Instead, as the global automotive aftermarket, external C-V2X On-Board Unit (OBU) equipment can be installed flexibly in a traditional vehicle or autonomous vehicle that have left the factory already, to pioneerly experience C-V2X services based on existed Road-Side Unit (RSU) or telecommunication cellular network as mentioned in [17; 18].