Vehicular User Equipment

Description

A Vehicular UE is a specific type of User Equipment (UE) defined in 3GPP specifications, particularly in the context of 5G NR (New Radio). It refers to a UE that is integrated into a vehicle and is permanently connected to an antenna system that is embedded in the vehicle and radiates externally. This is in contrast to a regular UE (e.g., a smartphone) that may be brought into a vehicle and connected to the vehicle's antenna system via a temporary connection, or that uses its own internal antennas. The Vehicular UE is designed to operate in NR operating bands, which include both frequency range 1 (FR1) and frequency range 2 (FR2). The permanent external antenna connection allows for better radio performance, as the antenna can be placed optimally on the vehicle exterior, reducing penetration loss and improving coverage. This is crucial for vehicular communication applications such as V2X (Vehicle-to-Everything), which require reliable and low-latency connectivity.

The concept of Vehicular UE was introduced in 3GPP Release 15, the first release of 5G NR. It is specified in technical specifications such as TS 38.101 (UE radio transmission and reception), TS 38.521 (UE conformance specification), and TS 38.785 (vehicle-mounted mobile relay). The definition has evolved slightly over releases. In Release 15 and 16, it was simply defined as "A UE embedded in a vehicle". In Release 17, the definition was expanded to explicitly mention the permanent connection to an embedded antenna system that radiates externally for NR operating bands. This change likely aimed to clarify the distinction between a Vehicular UE and other UEs used in vehicles, emphasizing the permanent and external nature of the antenna. In Release 18, the definition reverted to the shorter form, but the technical requirements for Vehicular UEs continue to be specified. The Vehicular UE is an important enabler for connected car services, including safety, traffic efficiency, and infotainment.

From an architectural perspective, a Vehicular UE communicates with the Radio Access Network (RAN) via the Uu interface, just like any other UE. However, due to its permanent external antenna, it may have different radio frequency (RF) requirements, such as higher transmit power or different antenna gain patterns. These are captured in the specifications. The Vehicular UE can also act as a relay for other UEs inside the vehicle, providing connectivity to passengers' devices. This is known as a vehicle-mounted mobile relay (VMR), which is specified in TS 38.785. The VMR functionality allows the Vehicular UE to relay traffic between the network and UEs inside the vehicle, potentially using a different radio interface (e.g., Wi-Fi or Bluetooth) for the in-vehicle devices. This can improve coverage and capacity for passengers.

In terms of network procedures, a Vehicular UE performs cell selection, registration, and mobility management like any other UE. However, its mobility pattern may be different, as it moves at vehicular speeds and may traverse multiple cells quickly. The network may need to handle handovers efficiently to maintain connectivity. Additionally, Vehicular UEs may support specific features like high-speed train scenarios or V2X sidelink communication (PC5 interface) for direct vehicle-to-vehicle communication. The sidelink allows vehicles to communicate directly without going through the network, which is essential for low-latency safety applications. The Vehicular UE can support both Uu and PC5 interfaces simultaneously.

Overall, the Vehicular UE is a key element in the 3GPP ecosystem for connected vehicles. It ensures that vehicles can have reliable, high-performance cellular connectivity, enabling a wide range of services from autonomous driving to infotainment. As 5G evolves towards 5G-Advanced and 6G, the requirements for Vehicular UEs will continue to evolve, supporting higher data rates, lower latency, and enhanced reliability.

Purpose & Motivation

The Vehicular UE concept exists to address the specific needs of vehicles that require robust and reliable cellular connectivity. Unlike smartphones, vehicles have unique constraints: they operate in diverse environments, often at high speeds, and require continuous connectivity for safety and non-safety applications. A standard UE placed inside a vehicle suffers from penetration loss through the vehicle's metal body, which can degrade signal strength and quality. By defining a Vehicular UE with a permanently connected external antenna, 3GPP ensures that vehicles can achieve better radio performance, leading to more reliable connections. This is particularly important for V2X communications, where latency and reliability are critical for safety.

Historically, before the introduction of Vehicular UE in Release 15, vehicles relied on aftermarket solutions or integrated telematics units that may not have been optimized for cellular performance. These solutions often used internal antennas or required complex installations. The 3GPP standardization of Vehicular UE provides a clear specification that manufacturers can follow, ensuring interoperability and performance. It also enables new business models, such as vehicles acting as mobile relays to provide connectivity to passengers, or as edge computing nodes. The evolution of the definition in Release 17 to explicitly mention the external antenna highlights the importance of this aspect in distinguishing Vehicular UEs from other UEs.

Furthermore, the Vehicular UE concept supports the broader 3GPP vision of connected vehicles, which includes enhanced mobile broadband (eMBB) for infotainment, ultra-reliable low-latency communication (URLLC) for safety, and massive machine-type communication (mMTC) for vehicle diagnostics. By providing a standardized UE type, 3GPP facilitates the development of a vibrant ecosystem of automotive and telecom vendors, accelerating the deployment of connected car services.