# Advancing C-V2X for Level 5 Autonomous Driving from the Perspective of 3 GPP Standards
## 2 Background
### An Overview of 3 GPP Releases  
The ongoing efforts for smarter management of traffic and use of transport networks require ITS-enabled innovative services. Amongst others, these services assist road users (vehicles, pedestrians, cyclists, etc.) in making informed decisions about safety and mobility. For instance, traffic intensity in road segments may be controlled by dynamically adapting the traffic light control timers and adjusting the speed limits, enabling an AV to proactively plan a maneuver to avoid a collision with an object(s) on the road, etc. Although work in ITS has been focusing on standardizing the communication interfaces, security and privacy are some of the main issues associated with the development and deployment of ITS applications. To support the ITS applications, 3 GPP started including major elements for vehicular communications i.e., \"Internet on Wheels\" [10]. Starting from _Rel-14_[11], the communication technologies of 3 GPP i.e., 4G (before) and 5G (now) have had a great influence on the success of C-V2X applications. The 3 GPP contains technical specification groups (TSG) i.e., core network & terminals (CT), service & system aspects (SA), and radio access network (RAN). These TSGs provide specifications and technologies as a result of technical reports, which are released from time to time. In release 14, 3 GPP started supporting V2X services and the current releasesnow discuss the intelligence for V2X use-case scenarios. Following the 3 GPP standardized technologies and their selection can be challenging due to the sheer number of technical documents and the difficulty of navigating through each one of them. Hence, it can become a daunting task. Therefore, we reduce the complexity by finding the relevant standard documents for V2X services. The current releases of 3 GPP standards are realizing the successful transition from 802.11p or DSRC to 4G-V2X communication. _Rel-14_ was one of the early releases, which focused on vehicular communication. Although the need for 5G was initially discussed in _Rel-14_, 5G Phase-1 of 5G system (5 GS) started in _Rel-15_[12]. _Rel-14_ supports V2X communication through enhancing the 4G technology by evolved packet system (EPS) [13]. Since the V2X gained support from EPS in _Rel-14_, some technical specifications from _Rel-15_ introduced enhancements to V2X (eV2X) considering the future of V2X with 5G New-Radio (NR). Furthermore, advanced driving, remote driving, extended sensors, and vehicle platooning are supported in _Rel-14_ and _Rel-15_. The updated version of the 5G system (5 GS: 5G Phase 2) presented in _Rel-16_ (_TR 21.916_) extends the 5G specifications i.e., architectural aspects and service-oriented functionalities for V2X. Hence, _Rel-16_'s 5G supports the advanced V2X services and the authors from [13] analyzed the architectural status of _Rel-16_. The _Rel-16_ (current) [14] and _Rel-17_ (future) [15] releases discuss NR sidelink communication and its improvements [1], which targets important aspects i.e., resource allocation, power efficiency, high QoS, etc., for successful V2X communication. In addition, new use-case scenarios are under study in _Rel-17_ and _Rel-18_[16] e.g., AI-based sidelink communication for devices, communication between robots and machines. The C-V2X evolution is presented in Figure 1. The V2V standards and basic safety services are delivered in _Rel-14_ phase 1. To provide support for eV2X services complementary to _Rel-14_, the _Rel-15_ phase 2 built a stable LTE-V2X (4G-V2X) ecosystem by providing services i.e., platooning, extended sensors, advanced driving, and remote driving. In addition, the _Rel-15_ introduced various new technical features such as longer range, higher-order modulation (64 QAM), lower latency (10 ms min), higher reliability, and carrier aggregation up to eight component carriers. Advancement to 5G NR-V2X (5G-V2X), phase 3 is designed to deliver support for the advanced V2X (aV2X) services with lower latency, ultra-reliability, and higher throughput.