By Onn Haran
Published on eeTimes Europe

Vehicle-to-everything (V2X) communication is a vehicular sensor that collects data from nearby road users by exchanging wireless information to prevent accidents that no other sensor can detect, specifically risks from hidden road users located around the corner or behind another vehicle. V2X is designed for real-time safety by ensuring the integrity of the wireless connectivity, the authenticity of the messages and the accuracy and freshness of the information.

The V2X system is illustrated with the relevant elements in the vehicle architecture. Although there are slight variations, the core concept of a V2X system remains the same for all road users, including trucks, cars, motorcycles and eBikes.

The V2X system consists of three primary subsystems: wireless, security and processing. These subsystems interact with four key systems within the vehicle: ADAS, which receives data on detected road users from V2X; the head unit, which receives warnings from V2X; vehicle data, which is transmitted via V2X; and positioning.

Wireless subsystem

Many people consider the wireless subsystem to be the entirety of the V2X system, but this is a limited perspective. The wireless subsystem converts signals from the antennas into data. Due to the popularity of full glass roofs, two 5.9-GHz V2X antennas, typically placed at the front and rear of the roof, are required to ensure consistent, 360° wireless coverage. These antennas are connected to an RF front-end module (FEM). In cases where the cable between the antenna and FEM exceeds 4 meters, an additional FEM is needed at the antenna to compensate for cable attenuation. The FEM is a monolithic device that includes a power amplifier for amplifying the transmitted signal and a low-noise amplifier for amplifying the received signal.

The FEM is connected to the RF transceiver, which down-converts the received signal to a baseband signal and up-converts the transmitted signal by adding a 5.9-GHz carrier. The RF transceiver has two independent paths, one for each antenna. The modem controls the gain and functionality (transmit or receive) of both the FEM and the RF transceiver.

The modem receives the baseband signals from both antennas and demodulates the incoming bits. For optimal receiver performance, the signals from the two antennas need to be combined. The receiver tracks the wireless channel to compensate for the rapid movements of the transmitting and receiving vehicles, as well as reflections from metal objects between them (i.e., multipath). The quality of this equalization determines the practical communication range. High-quality implementations can consistently achieve ranges exceeding 1 km on highways and 400 meters at obstructed urban intersections in real-world measurements.

The modem must support all V2X wireless technologies. DSRC (IEEE802.11p) is based on Wi-Fi and is deployed in European road infrastructure and Volkswagen vehicles, continuing to be used as a legacy system. LTE-V2X (3GPP Rel. 14/15) is used in the U.S. and China. The latest technology, 5G-V2X (3GPP Rel. 16/17), is aimed at enabling new services in Europe. Unfortunately, these technologies are neither backward-compatible nor capable of coexisting with each other, necessitating a full implementation of all. Integrating all technologies into a single chip complicates the design but enhances system performance and cost efficiency. This integration is particularly beneficial when multiple technologies need to operate concurrently, as planned in Europe for DSRC and 5G-V2X.

Security subsystem

The security subsystem consists of the security stack within the processing system along with dedicated hardware components. The hardware-secure module (HSM) stores the private keys used to sign messages. Protecting the HSM is crucial, as the integrity of these keys underpins the trustworthiness of the messages. The signature algorithm used in Europe and the U.S. is based on the elliptic-curve digital-signature algorithm, whereas China employs local algorithms. Additionally, security certification is region-specific, necessitating the HSM to pass three certifications: the Federal Information Processing Standard in the U.S., Common Criteria in Europe and the Office of State Commercial Cryptography Administration in China. Another key hardware component in the security subsystem is the verification engine. Because verifying signatures is computationally intensive and thousands of messages need to be verified per second, a dedicated hardware engine is necessary. For enhanced protection of information exchange, it is preferable to integrate the security subsystem with the processing subsystem.

Processing subsystem

The processing subsystem can operate on a dedicated CPU for maximum isolation and security or share a CPU with other functions. The more vehicle safety decisions rely on V2X, the greater the need for isolation, particularly from the telematics processor, which also communicates with the cloud and is exposed to more attack vectors. The V2X stack is responsible for composing transmitted messages and decomposing received ones. The format of these messages varies by region, requiring interoperability tests for each specific region.

The transmitted message embeds the latest positioning information from the positioning system and relevant vehicle data, such as speed, heading and acceleration. Accurate positioning is crucial for reliable warnings, as it reduces the probability of false warnings and missed true warnings. Therefore, the most accurate positioning technology should be used, such as an L1/L5 dual-band GNSS receiver, augmented by visual cues or other algorithms. The vehicle data is obtained from the vehicle bus.

V2X applications are responsible for issuing safety warnings related to infrastructure information, such as road work ahead or traffic light timing, as well as warnings about other road users, such as a bicycle crossing an intersection or a vehicle stopped in the lane. Currently, a single CPU handles both the V2X stack and applications, with warnings forwarded to the head unit. In the future, ADAS will process V2X data like any other vehicle sensor data, receiving information about road users from the V2X stack and fusing it with detected objects from other vehicle sensors.

System variation

The partitioning of V2X subsystems can differ across various system designs. For instance, a system designed for a specific region with a single radio may differ from a global system that integrates multiple radios. Another example is a system intended to support ADAS, where V2X would be separated from other non-safety elements, including processing. System integration and testing efforts, as well as risk considerations, can also influence the partitioning. Therefore, maximum flexibility is required to meet diverse system and regional demands.