The 3GPP platform was first expanded to the automotive industry by the introduction of support for V2V and V2X services in Release 14. This support forms Phase 1 of 3GPP's ongoing project relating to V2X, and was intended to support a set of requirements sufficient for basic road safety services. Vehicles containing UEs with these features can use the uplink, downlink and sidelink to exchange information on their own status, such as position, speed, and heading with other nearby vehicles, infrastructure nodes, and pedestrians. Phase 2 of the V2X project was standardised in Release 15, and adds a number of new features to the sidelink intended to enhance efficiency and exploit developments in UE and network designs. These enhancements include sidelink carrier aggregation, higher-order modulation, and reduced latency. Phase 3 of V2X, in Release 16, adds support to NR (and also 5GC, not addressed in this TR) for advanced V2X use cases, and includes introduction of the NR sidelink. The use-cases are broadly grouped to enable vehicular platooning, exchange of extended sensor information, advanced driving, and remote driving. Phase 3 also allows either RAT's sidelink to be operated under control of the other RAT's Uu interface, as well as permitting connection to EPC or 5GC, to enable usage in the main MR-DC deployment scenarios. In the following clauses, LTE-V2X is described first, then NR-V2X, and finally certain aspects which have a degree of commonality to both RATs. Although this TR deals with RAN aspects, note that the core network architectures also have many adaptations to support V2X in both EPC and 5GC. These are referred to only as needed for other explanations in this TR, and details can be found in the relevant specifications.

The present document provides an overall description of the features introduced by 3GPP to LTE and NR in support of V2X services, starting from Rel-14. The purpose of this TR is to give an overview across the RAN specifications of how the features have been designed, and how they operate together. This document addresses LTE V2X and NR V2X via both sidelink, i.e. the PC5 interfaces, and via the cellular uplink/downlink, i.e. the Uu interfaces. It covers V2V, V2I/N, and V2P, as well as the eNB/gNB, UE, and RSU nodes. The intention is to provide descriptions at approximately the Stage 2 level of detail, and thus references are provided to RAN specifications for the reader to obtain precise details. The document is a 'living' document, i.e. it is permanently updated and presented to TSG-RAN meetings.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

LTE-V2X is designed with BSM, CAM, and DENM particularly in mind. BSMs and CAMs have the characteristic of generating periodic messages at intervals, whereas DENMs are event-triggered. As an illustration of the different message types, in TR 36.885, BSM/CAM were modelled, for evaluation purposes, as periodically occurring sets of one 300-byte message followed by four 190-byte messages. These types of message regularly broadcast information such as the vehicle's heading, speed, latitude/longitude, etc. ETSI EN 302 637-2 [3], SAE J2735 [4]. In TR 36.885, DENMs were modelled, for evaluation purposes, as Poisson distributed initiations of six 800-byte messages spaced by 100 ms. DENMs can contain various different messages depending on the cause for their transmission, such as imminent collision, sudden braking, or detection of a traffic jam, amongst others ETSI EN 302 637-3 [5]. The requirements relating to traffic size and pattern for LTE-V2X set in TS 22.185 can be summarized as follows, although they do not limit the usage of LTE-V2X. Other requirements relating to general system function are also included in TS 22.185.

• Support for periodic broadcast messages with payloads of 50-300 bytes.
• Support for event-triggered messages with payloads of up to 1200 bytes.
• Up to 10 messages per second transmitted by a UE.
• V2V and V2P latency of maximum 100 ms, or for V2V pre-crash sensing, maximum 20 ms.
• V2I latency, i.e. between a UE and RSU, of maximum 100 ms.
• V2N latency, i.e. when transferring messages via the cellular network, of maximum 1000 ms.
• Maximum relative velocity between two vehicles of 500 km/h, and maximum absolute velocity of 250 km/h for V2V and V2P UEs, and of a UE communicating with an RSU.
• Requirements relating to security, integrity, authorization, and privacy.

NR V2X is designed with a broader set of more advanced V2X use cases in mind. These were specified in TS 22.186, and are broadly arranged into four use case groups: vehicular platooning, extended sensors, advanced driving, and remote driving.

1. Vehicles Platooning enables the vehicles to dynamically form a platoon travelling together. All the vehicles in the platoon obtain information from the leading vehicle to manage this platoon. These information allow the vehicles to drive closer than normal in a coordinated manner, going to the same direction and travelling together.
2. Extended Sensors enables the exchange of raw or processed data gathered through local sensors or live video images among vehicles, road site units, devices of pedestrian and V2X application servers. The vehicles can increase the perception of their environment beyond of what their own sensors can detect and have a more broad and holistic view of the local situation. High data rate is one of the key characteristics.
3. Advanced Driving enables semi-automated or full-automated driving. Each vehicle and/or RSU shares its own perception data obtained from its local sensors with vehicles in proximity and that allows vehicles to synchronize and coordinate their trajectories or manoeuvres. Each vehicle shares its driving intention with vehicles in proximity too.
4. Remote Driving enables a remote driver or a V2X application to operate a remote vehicle for those passengers who cannot drive by themselves or remote vehicles located in dangerous environments. For a case where variation is limited and routes are predictable, such as public transportation, driving based on cloud computing can be used. High reliability and low latency are the main requirements.

The most demanding requirements set in TS 22.186 are for a maximum sidelink range of 1000 m, a maximum throughput of 1 Gbps, a shortest latency of 3 ms, a maximum reliability of 99.999%, and a maximum transmission rate of 100 messages/second. However, there is not a use case which, on its own, demands all of these bounding requirements. The communication scenarios described in TS 22.186 include a mixture of periodic and aperiodic services. Similar to LTE-V2X, there are also requirements relating to security, integrity, authorization, and privacy.