Navigating the rocky roads for safe driving: How can V2X be improved?
The difference between a vehicle collision and a near miss may come down to mere milliseconds. According to ASIRT (Association for Safe International Road Travel), over 1.3 million people die in road crashes each year and an additional 20-50 million become injured or disabled. What if those accidents could be prevented? What if the vehicles could speak to each other using cellular technologies that could ensure seamless communications between fast-moving vehicles, in denser traffic conditions, and at longer ranges? 802.11p-based Dedicated Short Range Communications (DSRC)/ITS-G5 established the foundation for V2X communications, though as we look towards the future, an evolved radio technology solution is needed to meet critical safety requirements and deliver functionality necessary to support autonomous driving.
Additionally, today's vehicles are equipped with many sensors such as radar, LIDAR, and camera systems which provide good situational awareness of their surrounding area. Unfortunately, these sensors are limited by their line-of-sight and cannot see around corners or in front of large obstacles like trucks. They can also be impacted by environmental conditions like dense fog, rain, snow, etc. that impair sensor utilization. Radio-based V2X advancements, as part of a sensor fusion, must be made to provide drivers with all-weather, 360-degree Beyond-Line-of-Sight (BLOS) situational awareness, extending a vehicle's ability to detect anomalies beyond their visual horizon to better support safe driving.
Key Research Areas:
Designing C-V2X: Paving a safe path for tomorrow's autonomous vehicles.
Qualcomm Research developed Cellular-V2X (C-V2X) as a modern V2X alternative and a complement to 802.11p, depending on regional deployment scenarios. For example, C-V2X could be deployed in regions that have not yet deployed any V2V technologies. Or, C-V2X can complement 802.11p (DSRC/ITS-G5), serving as a technology evolution to it where there have been V2V deployments.
We designed C-V2X as a transport technology defined in 3GPP Release 14, which can be integrated with the upper layers of SAE and ETSI-ITS to provide superior performance, enhance safety, and bring new capabilities that support situational awareness to usher in the era of enhanced safety and autonomous driving. We engineered C-V2X with better range (approx. twice) than 802.11p, allowing vehicles to exchange data, such as emergency alerts and their location and speeds, as fast as 10 times per second to better avoid collisions.
C-V2X also serves as a crucial part of an overall ADAS portfolio of technologies to achieve unparalleled safety for drivers. C-V2X complements the capabilities of other ADAS sensors by providing 360-degree BLOS awareness, extending a vehicle's ability to “see” further down the road – even at blind intersections or in bad weather conditions – to deliver a more predictable driving experience.
Driving C-V2X standardization and regulation.
To accelerate this technology evolution, Qualcomm Research is actively driving the C-V2X standardization efforts within 3GPP, building on our leadership in LTE Direct and LTE Broadcast to pioneer C-V2X technologies. Additionally, we co-founded the 5G Automotive Association (5GAA) to unite the telecommunications and automotive ecosystems to develop, test, and promote communications solutions, initiate their standardization, and accelerate their commercial availability and global market penetration to address societal needs. Together with our 5GAA partners including Audi, BMW, China Mobile, Continental, Daimler, Denso, Deutsche Telekom, Ericsson, Ford, Huawei, Intel, LG, Nokia, NTT DoCoMo, SAIC Motor, Samsung, SK Telecom, Valeo, Verizon, Vodafone and others, we formed working groups to enhance C-V2X's design and architecture and organize large-scale live trials to demonstrate the technology's capabilities, leading to widespread adoption. 5GAA is creating significant cross-industry momentum surrounding the development and deployment of C-V2X and are actively working to support national and regional regulatory policies around the world.
C-V2X technology is mature enough to be integrated into today's cars, and will soon be integrated into tomorrow's autonomous cars by building on the growing cellular attach rates the automotive segment is experiencing. Recently, citing enormous potential to reduce crashes on U.S. roadways, the U.S. Department of Transportation proposed a rule that would mandate V2V communications in passenger cars, providing 360-degree situational awareness on roads to further bolster safety. Learn more
Overcoming critical C-V2X design roadblocks.
We designed C-V2X to be an evolution of our LTE Direct device-to-device (D2D) communications capability that enabled smartphone users to discover and interact with the world around them. Building on these D2D standards developed in 3GPP Releases 12 and 13, our team grew the technology and applied it to vehicles to support very high speeds (up to 500 km/hr relative), and the high device densities expected in busy roads/freeways, as part of 3GPP Release 14. But this was no easy task. LTE Direct was designed for smartphone users moving at pedestrian speeds. Additionally, it was not a robust communications technology as it could not send large amounts of data within a low latency. Thus, our engineers were challenged with converting a network that talks to users and making it applicable to vehicular use cases, while also creating a scalable system that addressed high relative vehicular speeds, vehicular high node densities, and time synchronization without requiring network infrastructure.
Dealing with High Relative Speeds
Although cellular systems and LTE in particular were designed to support high speed vehicles, supporting V2V communications at high relative speeds creates two challenges that must be overcome. First, V2V is expected to operate in the ITS band, harmonized in the 5.9 GHz spectrum ,as opposed to 2 GHz normally used in cellular wide area networks. The higher the frequency, the higher the Doppler effect. Second, in V2V, both sides of the communications link are moving at high relative speed and as cars pass each other, their frequencies shift. To counter these challenges, we increased the number of reference signal symbols to improve frequency alignment and channel estimation, engineering C-V2X with four DMRS signals, as opposed to just two normally utilized in LTE communications. Additionally, we created special properties within our reference signals to make it easier for receivers to detect the condition of the channel and compensate for it.
Managing High Node Densities
Low device density, as standardized in 3GPP Release 12 and 13, was acceptable for LTE Direct as its target use case of public safety typically did not require high densities. In designing C-V2X, Qualcomm Research realized that random resource allocation resulted in excessive resource collisions. To counter this, we enhanced C-V2X's transmission structure by enabling it to transmit control and data on the same sub-frame to reduce in-band emissions. Additionally, we engineered it to allow scheduling assignments and data transmissions to take place at the same unit of time. We also introduced more efficient resource allocation including sensing and semi-persistent resource selection.
A cellular system's performance is partially due to its synchronous nature. In Release 12, a distributed synchronization mechanism was introduced for out-of-coverage D2D communications. However, this design was never intended to support high density and high speed. C-V2X introduces enhancements to the distributed synchronization system and we also incorporated GPS timing to assist with in-coverage areas and leverage satellites (e.g. GNSS) for supporting out-of-coverage areas. V2X already requires GNSS for precise positioning to convey where the vehicle is and help signify where it is going next.
Designing C-V2X for in-coverage and out-of-coverage areas.
To ensure C-V2X's reliability, Qualcomm Research engineered it with a mode of operation that was not dependent on the existence of a cellular network. Luckily, 3GPP had already defined an out-of-coverage mode of operation for public safety use of D2D communications within Release 12. Because C-V2X is based on that earlier specification, it inherited this property and we built on this to enable vehicles to use a common frequency band (5.9GHz) to broadcast their V2V messages. Known as "Direct Communications", this mode assumes that the vehicle has no access to the network or the network may not be available. In addition, we developed C-V2X's in-coverage mode of operation, known as "Network Communications" to be leveraged when vehicles can be connected to the network. Typically, in this case, different cars are connected to different mobile network operators (MNO) but for the purpose of vehicular safety, it is possible for all cars to connect to a single MNO. For both in-coverage and out-of-coverage areas, these two transmission modes work together and vehicles have access to a common frequency channel, permitting direct V2V communications, significantly shortening transmission latency.
The bedrock of our C-V2X system is the PC5 interface which allows cars to communicate directly with each other, breaking the paradigm of solely relying on cellular networks and base stations for communication. We designed C-V2X to enable the exchange of real-time information between vehicles traveling at high speed at hundreds of meters range at a hundred millisecond unicycle, in high-density traffic, outside (or even inside) mobile network coverage areas. This permits safer driving through direct communications on designated ITS spectrum.
We introduced several innovations to allow Direct Communications. For example, we pioneered new techniques for scheduling resources and interference management of C-V2X traffic based on distributed algorithms implemented between vehicles without network assistance. This includes the usage of frequency domain listen-before-talk (LBT) decentralized MAC protocol. In addition, vehicles can use Global Navigation Satellite System (GNSS) receivers for synchronization instead of relying on cellular network coverage. When in coverage, V2X Direct Communications can be augmented by V2N's extended range and network assistance.
To enable C-V2X's second transmission mode, Qualcomm Research optimized our LTE Broadcast technology for vehicular communications. We designed C-V2X Network Communications to send safety messages using unicast transmission to the C-V2X server in the network using a normal Uu interface. The server then aggregates the messages and broadcasts them or other relevant info to the cars via cell towers. This broadcast can be localized down to a single tower or just a few of them if needed, depending on the application. The real benefit of network communications is that vehicles can leverage the ubiquitous coverage of existing LTE networks, which can alert them to an accident a few miles ahead.
The fast and furious road ahead for C-V2X: Tech advancements and trials.
Our team continues to develop future 3GPP Release 15/16 enhancements for C-V2X which will utilize 5G NR to provide vehicular communications with additional optimized functionality suitable for high throughput and very low latency with high reliability.
High Throughput Sensor Communications
Today's vehicles are equipped with a portfolio of sensors (radar, Lidar, cameras, etc.) but they are stove piped within the vehicle. While Release 14 is optimized to allow vehicles to send messages as fast as 10x per second, it is currently limited to only transmitting vehicular speed and trajectory data. We are building a new interface that can also communicate sensor data and HD maps. This interface facilitates high throughput transmissions, allowing many cars to simultaneously share video or other sensor data to further augment safe driving. For example, should a vehicle detect black ice or other road hazard, it could capture that image and forward it to vehicles in the area for dissemination both using Direct and Network Communications.