Navigating the Road Ahead: A Comprehensive Survey of Radio Resource Allocation for Vehicle Platooning in C-V2X Communications

Vehicle-to-everything (V2X) communications have emerged as an indispensable component of the Intelligent Transportation Systems (ITS), fostering innovations that enhance road safety and traffic efficiency. Within this transformative landscape, vehicle platooning has been identified by the Cellular-V2X (C-V2X) standards as an advanced V2X use case with the potential to reshape the future of ITS. However, the stringent requirements of such applications necessitate an optimized spectrum efficiency. Consequently, Radio Resource Allocation (RRA) has emerged as a critical and central component in addressing this challenge. This paper provides a comprehensive examination of RRA tailored specifically to the context of vehicle platooning. It presents an overview of fundamental concepts, including V2X communications, vehicle platooning, and RRA standards, which is followed by an in-depth review of the state-of-the-art, categorized based on the underlying communication technologies, RRA modes, and coverage conditions. By analyzing the existing literature, this paper identifies several key research challenges and potential opportunities, offering insightful guidance for shaping future research in this field.