Vehicle-to-Everything (V2X) Evolution From 4G to 5G in 3GPP: Focusing on Resource Allocation Aspects

Cellular Vehicle-to-everything (V2X) is evolving from a communication technology for safety messages towards a platform for advanced V2X services such as platooning and autonomous driving. The development of technical specifications for V2X communications is done across several task specification groups (TSGs) and working groups (WGs) within 3rd Generation Partnership Project (3GPP). In this paper, we focus on radio access network (RAN) aspects for direct communication between user equipments (UEs), which is known as sidelink (SL) communication. Resource allocation for SL communication can be performed in one of two modes. In the first mode, resource allocation is centralized in the network. In the second mode, resource allocation is performed in a distributed manner among UEs, where resource selection is performed at a transmitting UE, i.e., the transmitting UE determines time and frequency resources for a SL transmission without the assistance of a base station. In this paper, we review V2X evolution from 4G to 5G in 3GPP focusing on resource allocation aspects defined in Long-Term Evolution (LTE) and New Radio (NR) specifications, with particular attention given to the difference in design and performance of each. We highlight the key 3GPP standard developments on V2X resource allocation which includes enhanced resource reselection mechanisms and partial sensing schemes. It is observed that NR V2X resource reselection mechanism can provide up to 20% of reliability improvement over LTE V2X and NR V2X partial sensing scheme can provide up to 95% of reduced power consumption over full sensing scheme.