As the world continues to embrace technological advancements, few innovations hold as much promise for revolutionizing transportation as autonomous vehicles (AVs). Autonomous vehicles, or self-driving cars, have the potential to significantly improve road safety, reduce traffic congestion, and enhance mobility for people of all ages and abilities.
One of the key pillars supporting this transformative technology is the number of sensors, machine learning, and the use of cellular technology.
Unlike traditional vehicles, AVs are capable of sensing their surroundings using a variety of sensors, such as LiDAR, cameras, radar, and GPS, to make informed decisions without human intervention. The potential benefits of AVs are far-reaching, with safety being the primary concern.
Vehicle-to-everything (V2X) is seen as a key technology to provide complete environmental awareness around the vehicle by exchanging messages with other vehicles, roadside units (RSU), and pedestrians with low latency and high reliability.
We will explore two technologies that facilitate V2X, with a primary focus on the evolutionary progress of C-V2X (Cellular Vehicle-to-Everything) for autonomous vehicles.
A Vision of Safer Roads
Autonomous Vehicles are categorized into six defined levels, each representing a different degree of autonomy.
- Level 0: 100% human, no driving automation
- Level 1: Some drive assistance (cruise control, lane keep assist)
- Level 2: Partial automation (vehicles can control steering & speed)
- Level 3: Conditional automation (vehicle can drive itself under ideal conditions)
- Level 4: High automation (does not require human intervention)
- Level 5: 100% automation (does not have steering wheel nor pedals)
The essential capabilities needed to attain the mentioned levels through V2X technologies include:
- NLOS (Non-Line of Sight) Sensing: Ensuring 360-degree awareness even in situations with obstructed visibility, functioning effectively during nighttime and adverse weather conditions.
- Conveying Intent: Facilitating the sharing of intent, sensor data, and path planning information to enhance predictability and coordination.
- Situation Awareness: Providing an extended electronic horizon to support soft safety alerts and gradual warnings.
Supporting V2X communications are two emerged technologies: DSRC (Dedicated Short-Range Communications) and C-V2X (Cellular Vehicle-to-Everything).
#1: DSRC
In 1999, the FCC allocated a 75MHz spectrum block ranging from 5.85GHz to 5.925GHz for Intelligent Transport Systems (ITS). Subsequently, in 2004, the USDOT (US Department of Transportation) and the ITS working group decided to adopt the IEEE 802.11a variant for L1/L2 communication.
As a result, the IEEE 802.11p working group was established, marking the beginning of Dedicated Short-Range Communication (DSRC) – an open-source protocol designed for vehicular wireless communications.
These ITS standards are commonly referred to as WAVE (Wireless Access in Vehicular Environment), DSRC, or Wi-Fi 802.11p. For a considerable period, DSRC served as synonymous with V2X (Vehicle-to-Everything) communications.
DSRC enables V2V (Vehicle-to-Vehicle) and V2I (Vehicle-to-Infrastructure) communications via wireless broadcasts, occurring every 3 seconds within a hundred-meter range providing approx. 2ms of latency. It acts as a non-line of sight sensor, penetrating walls and facilitating the exchange of crucial information like heading, direction, and speed among vehicles.
#2: C-V2X: Cellular Technology in Autonomous Vehicles
Cellular V2X is an emerging technology that enhances LTE and 5G features to enable vehicle-to-vehicle and vehicle-to-infrastructure communication. Vehicles can use cellular technology to share their status (e.g., position, speed) with nearby vehicles, infrastructure, and pedestrians.
The table below provides a summary of the progress made in various cellular technology standards.
3GPP has used LTE ProSe (Proximity Services) as a starting point for the definition of C-V2X.
C-V2X employs two complementary transmission modes:
- Short-range direct communications: between vehicles (V2V), V2I (vehicle-to-infrastructure), and V2P (vehicle-to-Pedestrian). C-V2X works independently of the cellular networks in the dedicated ITS 5.9GHz spectrum (5.875-5.905)
- Long-range network communications Vehicle-to-Network (V2N) leverages conventional mobile networks to enable vehicles to receive real-time information about road conditions and local traffic.
LTE sidelink (SL) technology was introduced to facilitate Device-to-Device (D2D) communications. Sidelink refers to the direct connection between terminal nodes or User equipment (UE) without data going through the network.
Sidelink defines four resource allocation modes: 1, 2, 3, and 4. Modes 1 and 2 apply to D2D, while modes 3 and 4 apply to LTE V2X. Mode 3 is for resource allocation scheduled by eNB. Mode 4 is for UE autonomous resource selection.
Additionally, 3GPP R14 introduces two new Physical channels for sidelink communication, PSSCH & PSCCH. PSSCH carries data and PSCCH carries control information for decoding the data channel.
Comparing DSRC & C-V2X
C-V2X offers longer transmission time for the same number of bits, resulting in improved energy per bit due to accumulated energy over a longer period.
C-V2X with Turbo Codes (TC) is designed to enable decoding even at a lower Signal-to-Noise Ratio (SNR), while DSRC with convolution codes requires a higher SNR for successful decoding.
Protocol Stack
The main difference in protocol stacks lies in the lower two layers: PHY and MAC layers. The top layers across both stacks have somewhat similar implementations.
Specifications
Here is a summary of the key technical differences between both V2X technologies.
| 802.11P / DSRC | C-V2X: PC5 | |
| Synchronization | Asynchronous | Synchronous |
| Resource multiplexing across vehicles | TDM only | FDM & TDM |
| Channel coding | Convolutional | Turbo |
| Retransmission | No HARQ | HARQ |
| Waveform | OFDM | SC-FDM |
| Resource selection | Carrier sense multiple access with collision avoidance (CSMA-CA) | Semi-persistent transmission with relative energy-based selection channel |
| l BW | 10/20 MHz | R14-10/20 MHz
R16-10/20 & N*20MHz |
| LOS Range | 675m | 1175m |
| NLOS Blocker (5G AA)
NLOS Blocker (Camp) | 125m
400m | 425m
>1350m |
| NLOS Intersection | 375m | 875m |
| Co-existence with Wi-Fi 80MHz BW in UNII-3 | 300m | 625m |
| Co-existence of V2X with adjacent DSRC carrier | 400m | 1050m |
| FEC | Convolutional | Turbo |
| MIMO & Diversity | 1Tx/2Rx | 1TX/2Rx and 2TX/2RX |
R16: 5G-NR Based C-V2X Sidelink Technology
In Release 16, V2X includes support for advanced use cases in NR (New Radio), introducing the NR sidelink. The goal of NR V2X SL is to support enhanced V2X (eV2X) use cases related to connected and automated driving and not to replace LTE V2X. The use cases encompass various applications related to vehicle-to-everything communication.
- Vehicle Platoon enables vehicles to form a coordinated platoon, traveling closely together in the same direction, with information shared from the leading vehicle.
- Extended Sensors allow vehicles to exchange raw or processed data, including live video, among themselves, pedestrians’ devices, roadside units, and V2X application servers enhancing their perception beyond onboard sensors with a high data rate.
- Advanced Driving enables semi or full-automated driving, with vehicles sharing their perception data to synchronize and coordinate trajectories and maneuvers, along with communicating driving intentions.
- Remote Driving allows a remote driver or V2X application to operate vehicles in dangerous environments or for passengers who cannot drive. Cloud-based computing can be utilized for predictable cases like public transportation, demanding high reliability and low latency.
NR-V2X introduces new features like Groupcast and unicast communication, a novel feedback channel, and a redesigned control channel.
C-V2X Safety Applications
Below are some of the applications of C-V2X for autonomous vehicles:
Vehicle to infrastructure
- Redlight violation warning
- Stop sign violation warning
- Stop sign gap assist
- Pedestrian in crosswalk warning
- Curve speed warning
- Spot whether impact warning
- Reduced speed/work zone warning
Vehicle-to-vehicle
- Forward collision warning
- Emergency electronic brake light
- Left turn assist
- Do not pass the warning
- Blind spot lane change
Vehicle-to-pedestrian
- Mobile accessible pedestrian signal system
- Pedestrian signalized crosswalk
- Intelligent pedestrian traffic signal
- Intelligent pedestrian protectors
Other Aspects of C-V2X for Autonomous Vehicles
While AVs are designed to be intelligent machines, they cannot operate in isolation. Connectivity is paramount for their successful deployment, and this is where cellular technology plays a crucial role. Cellular technology empowers autonomous vehicles in:
Data Transmission and Communication
Autonomous vehicles generate vast amounts of data from their sensors and internal systems. To ensure seamless communication between AVs, other vehicles, and infrastructure elements like traffic lights and road signs, cellular networks provide the necessary bandwidth and low-latency connectivity for the exchange of real-time information. This enables AVs to make well-informed decisions based on the most up-to-date data.
Over-The-Air (OTA) Updates
OTA updates are essential for keeping AVs up-to-date with the latest software improvements, bug fixes, and security patches. Cellular technology allows AV manufacturers to remotely update their vehicles’ software, ensuring that the cars are equipped with the latest advancements and remain compliant with changing regulations.
HD Mapping and GPS
Accurate and up-to-date mapping is vital for AVs to navigate their environment safely and efficiently. Cellular networks facilitate high-definition (HD) mapping by providing constant access to GPS and real-time mapping services. This ensures that AVs can navigate complex road networks and adapt to changes in real time.
Significant Potential
Human error is a leading cause of road accidents, and AVs have the potential to significantly reduce the number of fatalities and injuries on our roads. By leveraging advanced algorithms and real-time data processing, self-driving cars can detect and respond to potential hazards with unmatched precision and speed, making roads safer for all road users.
From a technology adoption viewpoint, cars may be equipped with two radio modules DSRC and C-V2X where the incumbent solution would operate in the 5.9GHz band while C-V2X may use some LTE/5G bands. Some countries have gone ahead with C-V2X as their preferred choice for autonomous vehicles while some countries and manufacturers still have debates on DSRC vs. C-V2X.
Autonomous vehicles, coupled with cellular technology, are poised to redefine transportation as we know it. From increased safety and reduced traffic congestion to improved accessibility and environmental benefits, AVs offer a glimpse into the future of mobility.
The ongoing collaboration between the automotive and telecommunications industries will undoubtedly play a pivotal role in unlocking the full potential of autonomous vehicles and shaping a smarter, safer, and more efficient transportation landscape for generations to come.
There is a need to have critical mass adoption and policy changes, wireless spectrum availability, cybersecurity and privacy, and research funding. Data will fuel future vehicle innovations as the automotive industry shifts focus from horsepower to compute power. V2X is helping to make the driving experience safer and more efficient.
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