# V2X Communications in Highway Environments: Scheduling Challenges and Solutions for 6G Networks
## 1 Introduction  
Advances in wireless communication standards have started to systematically address the communication requirements of vertical industries such as the automotive sector. The development of 5G communications systems for vehicular use cases (UC), referred to as 5G-V2X, has enabled several automotive services that significantly improve the safety, efficiency, and comfort experienced by traffic participants. The International Society of Automotive Engineers (SAE) in [1] describes vehicle driving automation systems that sustainably perform part or all the dynamic driving tasks. It provides a taxonomy with detailed definitions for six levels of driving automation, ranging from no driving automation (Level 0) to full driving automation (Level 5), in the context of vehicles and their operation on roadways. Cellular Vehicle-to-Everything (C-V2X) is a promising connected mobility platform that allows vehicles to interact with their surroundings, such as other vehicles, cyclists, pedestrians, road infrastructure, or mobile networks. C-V2X provides one unified solution for vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-to pedestrian (V2P) operation with vehicle-to-network (V2N) by leveraging existing cellular network infrastructure. * Device-to-device encompasses V2V, V2I, and V2P direct communications without necessarily relying on network involvement for scheduling. * Device-to-cell tower is another communication link that enables network resources and scheduling and utilizes existing operator infrastructure. Device-to-cell tower communications constitute at least part of the V2I proposition and are essential to end-to-end solutions. * Device-to-network is the V2N solution, which uses traditional cellular links to enable cloud services to be part of the end-to-end solution. The 5G Automotive Association (5 GAA) has provided a visionary roadmap of the expected timelines for mass deployments of the C-V2X UCs [2]. The detailed UCs in the 5 GAA roadmap include the Service Level Requirements (SLR) listed in the 5 GAA's C-V2X Technical Report [3], and in the white paper [4]. Furthermore, the Third Generation Partnership Project (3 GPP) identifies UCs and potential service requirements in [5] to enhance 3 GPP's support for V2X services. The authors in [6] examine the key requirements for advanced autonomous driving UCs, as provided by the main standards organizations 3 GPP and 5 GAA. A comprehensive capacity and delay analysis was conducted for these UCs, taking into account the performance characteristics and features of both Fourth Generation Long-Term Evolution (LTE) and 5G cellular networks. According to the analysis presented, although V2X communication is typically considered within the context of Ultra Reliable Low-Latency Communication (URLLC), adopting V2X services by multiple vehicles in an area poses significant challenges in terms of capacity. Increased network load can lead to reduced throughput, increased packet latency, and degradation in packet reception rate (PRR), falling well below the required performance levels. These severe performance issues have been particularly noted on the uplink (UL) path. Servicing V2X UCs, especially in highway environments, comes with several challenges:  
1. High Mobility and Speed: Vehicles on highways typically travel at high speeds, creating a demanding environment for mobile communications. Maintaining stable and low-latency communication between fast-moving vehicles and infrastructure is difficult. Moreover, high speeds reduce the time window for exchanging critical information, such as collision warnings or traffic updates, making it crucial for the system to operate with minimal latency. 2. Network Coverage and Connectivity: Highway environments often span rural and remote areas with sparse network coverage. The lack of reliable connectivity, e.g., 4G, 5G, or dedicated short-range communication (DSRC), can hinder continuous communication.