Exploring V2X in 5G networks: A comprehensive survey of location-based services in hybrid scenarios

Vehicle-to-Everything (V2X) communications are constrained by both 3GPP technical specifications, as well as by country-specific spectrum regulations. The world's largest economies, such as the USA, EU and China have self-imposed regulations regarding the specific bandwidths and central spectrum frequencies where both safety and non-safety related V2X communication services are allowed to occur (always aligned with the aforementioned 3GPP technical specifications). Although the channels used for safety, non-safety, and control packets differ, what all of these countries have in common is that V2X shall occur mostly on New Radio Unlicensed (NR-U) spectrum, i.e., by means of private networks. A specific bandwidth in the public spectrum is also available, but since public spectrum is purchased through auctions, it is quite common the case that one particular operator will own the entirety of this spectrum, leading to a monopoly in V2X operations. Besides, this public spectrum is quite limited in bandwidth. This of course includes all of the Intelligent Transportation Systems (ITS) services, even location-based services, such as the ones that require the usage of positioning technologies, like autonomous vehicles, that require said services in order to support complex maneuvers and cooperative driving. Global Navigation Satellite Systems (GNSS) such as GPS or Galileo, currently already offer high-accuracy location to vehicles. However, this form of stand-alone position estimation of the vehicle has several drawbacks, as the information is constrained to the individual vehicle and not shared with others in a secure manner. This exchange of position information between other entities (not only vehicles, but also other infrastructure nodes) is vital for actions such as cooperative maneuvers and to counter loss of satellite sight (e.g., when entering a tunnel). Taking these facts into consideration, it is therefore expected that in the mid to long-term, municipalities and highways will possess dedicated private 5G networks for V2X operations with the aim of offering a plethora of vehicular services, including positioning ones. Since the existent scientific literature lacks an integrated analysis of precise positioning services for ITS in 5G private networks, we propose in this paper, to provide a comprehensive review connecting these diverse elements, examining the role of 5G private networks in transmitting positioning messages in V2X scenarios. Additionally, the paper shall explore hybrid positioning systems that combine 5G and GNSS technologies, illustrating their potential to enhance V2X communications. This study offers a roadmap for the evolution of ITS and V2X communications by showcasing current trends and identifying areas for further research.