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​C-V2X and DSRC: Connected car / Autonomous Vehicle Technologies

George Hardesty
17 minute read

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C-V2X and DSRC:

The development and implementation of connected car and autonomous vehicle technology is currently accelerating and carries with it the expectation of a major transformation of how vehicles and transport infrastructure are used. The concept of introducing wireless connectivity into vehicles, highways, and other roadside structures is an ambitious one and is underpinned by the development of Cooperative Intelligent Transport Systems (C-ITS). With the implementation of this type of communication, smart cities and even self-driving cars have the potential to be realized. This digest takes a look at the two competing technologies that support C-ITS: C-V2X, and DSRC and addresses how they work, their key applications and which of the two is most likely to become dominant in the intelligent transport age.

Vehicle Antennas:

What is C-V2X?

Cellular Vehicle to Everything or Cellular V2X is a cellular technology standard devised by the 3rd Generation Partnership Project (3GPP) that specifies cellular connectivity and communications between vehicles and other suitably networked objects.

C-V2X is a form of connected vehicle to everything communication or V2X.

V2X is a short-range, wireless vehicular communication system that involves data transfer between a networked vehicle and the physical objects and environment that it encounters or interacts with. It is an amalgamation of several distinct modules of vehicular communication including:

  • Vehicle to vehicle (V2V) a system of direct connectivity between vehicles for enhancement of on-board sensors and networked early warning mechanisms.
  • Vehicle to network (V2N) providing connectivity between vehicles and the licensed mobile spectrum for 'infotainment': news, streaming music, and entertainment as well as route management and network alerts.
  • Vehicle to infrastructure (V2I) connects a primed automobile to the roadside infrastructure that surrounds it, such as signals, signage, traffic lights, and toll booths.
  • Vehicle to pedestrian (V2P) which allows a vehicle to be alerted to nearby individuals who are wearing or are in possession of a compatible device.

V2X technology was initially devised with the objective of improving road safety and the utility and efficiency of transport infrastructure. In 2016, in a paper entitled 'Vehicle-To-Vehicle Communication Technology For Light Vehicles' the National Highway Traffic Safety Administration (NHTSA) suggested a drop of at least 13% in the annual number of traffic accidents could be achieved with the implementation of this type of technology. By connecting vehicles and creating cooperative intelligent transport systems, agile and responsive solutions to problems such as pollution and traffic congestion can be engineered for significant improvements in road use.

The 3GPP consortium created C-V2X as a cellular driven alternative to the IEEE V2X standard 802.11p which uses W-LAN. C-V2X was preceded by this W-LAN system which is also known as Dedicated Short Range Communications (DSRC).

C-V2X instead uses Long Term Evolution and 5G cellular technology and infrastructure for the necessary connectivity of vehicles in line with V2X requirements. Where LTE is used it is called LTE-V2X, but it is expected to evolve to utilize the global 5G deployment that is in progress. Cellular communication is used to send and receive data packets from traffic signals, other road users, and cloud-based services. It is not dependent on a specific network for operation and has coverage that exceeds one mile.

C-V2X has two key operational modes. The first mode oversees direct communication between compatible vehicles, road users, and infrastructure within the vicinity of the vehicle. This communication does not require cellular network connectivity. Secondly, a mobile phone network can be accessed by the vehicle for access to information alerts about road traffic conditions.

Notable C-V2X applications:

  1. Cooperative driving. C-V2X connectivity can be used to create a vehicular ecosystem where V2V communications between vehicles enabled them to work together by conveying driver intent, promoting optimal spacing and limiting unexpected maneuvers such as sudden braking or lane changes.
  2. Platooning. Semi-autonomous and even autonomously formed convoys of Heavy Goods Vehicles can be formed and controlled using C-V2X. The cellular and wireless connectivity involved can be used to space vehicles closely and synchronously regulate speed, braking, and fuel consumption, making haulage more energy-efficient and cost-effective.
  3. Prevention of collisions. C-V2X use of the Intelligent Transport Systems band aims to improve road safety. V2X communication has the capacity to handle information exchange between multiple vehicles and infrastructure, aggregating data for the creation of real-time maps that can identify collision risk for road users.
  4. Queue warning. Real-time alerts can update road users of upcoming congestion or queuing, meaning that drivers can brake smoothly or change direction or lane in a timely manner.

C-V2X has significant support from the automotive industry, who particularly perceive C-V2X to be advantageous for reasons explored further on in this article.

The first LTE-based specification was released in 2016 with subsequent research and development undertaken with the backing of the 60-member 5G Automotive Association (5GAA). The push for C-V2X has been a collaborative effort between the automotive and telecommunications industries and regional governing and regulatory bodies including the US Federal Government and the European Union. Over 800 mobile operators are also participating in facilitating widespread global deployments in compliance with the 3GPP's C-V2X standard. Though the implementation is at a nascent stage, C-V2K has garnered support from automotive manufacturers with numerous pre-commercial projects in progress. The longer-term objective is that C-V2X becomes a globally implemented technology that could pave the way for fully autonomous or self-driving vehicles.

What is DSRC?

Dedicated Short Range Communications is the alternate V2X technology that provides wireless single or bidirectional data transfer designed specifically for the automotive industry. It is based on the IEEE 802.11 standard, 802.12p that specifically refers to Intelligent Transportation Systems (ITS) applications. This Wi-Fi variant specifies a system of communication between vehicles and surrounding infrastructure and objects that is:

  • secure
  • high speed
  • low latency
  • direct

Its most important distinction and the purported advantage is that it is not reliant on cellular networking despite its mobility. The creation of this system of vehicular connectivity goes as far back as 1999 with the Federal Communications Commission designation of 75 MHz in the 5.9 GHz band for use by Intelligent Transport Systems, with similar allocations made internationally. Applications for this W-LAN based connectivity soon followed including toll road collections and traffic network alerts and notification of the emergency services in the event of an accident.

How does DSRC work?

DSRC relies on two key components:

  1. Onboard equipment (OBE): This is the hardware for DSRC that sits within the vehicle and comprises the radio frequency setup needed to run this technology as well as a front-end interface for the driver to use. It is usually installed on the vehicle dashboard.
  2. Roadside equipment (RSE): is installed in close proximity to the road and consists of the radio-communications equipment needed for data exchange with a vehicle's OBE.

Radio signals exchanged between the OBE and RSE can be used for signaling, alerts, or most commonly secure processing of payments on toll roads. Both classes of radio communication devices are licensed and regulated by the FCC.

Two key regional variants of DSRC which are not currently compatible with one another:

  1. The US version of 802.11p known as Wireless Access in Vehicular Environments (WAVE)
  2. ETSI ITS-G5 which is the European Union version covering wireless short-range communications in vehicles.

DRSC communications are favored because of their security and privacy, as communications between vehicles and infrastructure or objects have to be authenticated and cannot be traced back to specific vehicles. However networked vehicles will broadcast their location speed and direction up to 10 times per second. These broadcasts can be picked up by nearby vehicles, pedestrians, or transport infrastructure to help reduce the risk of collision or other hazards.

C-V2X and DSRC:

Key applications that utilize DSRC

Electronic fee collection (EFC). Toll roads are a key means of raising revenue for public and private entities as well as reducing congestion and pollution. In Europe, DSRC has been used successfully for a range of road pricing schemes where drivers have a compatible vehicle. DSRC allows road user charges to be collected automatically, without any need for the vehicle to slow or stop and can support a range of pricing and payment strategies. Electronic parking payments can also be obtained in the same way.

Access control may be necessary on estates or private roads, or in the event of an emergency where traffic needs to be diverted. DSRC can be used to either to alert drivers to restricted stretches of road or as part of an automatic barrier system. DSRC can be used in a similar manner for warnings at highway-rail intersections.

Emergency vehicle signal priority DRSC is desirable as a solution for intelligent traffic control which prioritizes access for Emergency Vehicles. These systems use adaptive traffics lights that can be controlled via DSRC enabled traffic lights and roadside units to warn upcoming drivers that an emergency vehicle is in their vicinity or alter the traffic lights to prioritize an emergency vehicle in transit.

School beacons are a notable example of how DSRC can be used effectively for the benefit of both road users and pedestrians. They are usually strategically positioned and illuminated signs which flash for drivers when they exceed speed limits in place in proximity to schools. DSRC can be used to directly alert drivers at a dashboard interface of the need to slow down via suitably enhanced school zone safety beacons. In June 2020 the FCC granted the US company Applied Information a nationwide ITS license to develop V2I solutions which include school beacons.

Implementation of DSRC has been mainly US-led with V2V and V2I communication, but in 2017 Toyota became the world's first automobile manufacturer to build cars with DSRC connectivity for the Japanese marketplace. Chrysler followed with a DSRC equipped Cadillac in 2018.

Frequencies used for Vehicle to Everything communication.

Both C-V2X and DSRC operate at the 5.9 GHz frequency in a band that has been internationally designated the Intelligent Transportation System band. Regulators have set aside a specific portion of this frequency band, typically between 5 875 and 5 905 MHz for the safety-related radio communications undertaken by V2X. A frequency band below 6 GHz is suitable for the wide-area coverage needed for V2X connectivity.

In 2017, the Global System for Mobile Communications (GSMA) insisted that the frequency band designation should be technology-neutral and able to cope with the rapid pace developments in Intelligent Transport solutions. Presently, neither C-V2X nor DSRC have been mandated by regional regulators, and solutions for the functional coexistence of both forms of V2X within the ITS band are currently being explored.

3.4 to 3.8 GHz

The suggestion has been made of utilizing spectrum on the 3.4 to 3.8 GHz range for safety-based automotive applications as it has yet to be assigned for a specific purpose in a number of countries. Using this frequency band would also allow more spectrum in the 5-6GHz range to be used for expansion and enhancement of WiFi. This lower frequency is also considered more favorable and robust for applications that require mobility, where one or both connected parties are in transit, and the line of sight is limited. Also, ITS antennas used for this frequency would not be prohibitively large. But the use of the 3.4 to 3.8 GHz band in preference to 5.9 GHz which has already been associated with ITS could reduce the bandwidth available for upcoming 5G deployments.

5.9 GHz

This frequency also has some key limitations that will need to be overcome to gain the maximum utility of V2X in a complex 'real-world' setting.

Firstly, the high carrier frequency of this band is susceptible to optical behaviors during propagation such as:

  • reflections
  • refraction
  • diffraction
  • polarization
  • scattering
  • absorption

The 5cm wavelength of radio frequency signals at this band can be affected by obstructions while in transmission with poor penetration of buildings and dense vegetation. Line of sight between sending and receiving V2X antennas is preferable but not always achievable, especially in urban environments. Without a line of sight and with the added challenge of mobility, V2X at this frequency is highly reliant on strong multipath for effective data transfer.

V2x Antenna Considerations

It's best to use a Combo Antenna that has multiple internal antennas; each internal antenna has an antenna cable with a connector that you can connect to your device. This saves a lot of space on your vehicle surface or enclosure surface. Combo antennas can have, for examples, one or two internal LTE antennas, one internal GPS antenna, and one or two 5.9 GHz antennas for C-V2X and/or DSRC. Data Alliance offers Combination Antennas that include from two up to seven internal antennas with two to seven cables to SMA or connectors or your choice.

Antenna installation is critical for V2X to perform optimally at 5.9 GHz.

Wavelength and propagation of the RF signal at 5.9 GHz are the factors that affect antenna placement rather than the use of C-V2X or DSRC technology.

Appropriately locating the antenna on many types of vehicles may be difficult due to the size of the vehicle or curvature of their roofs. For example, Heavy Goods Vehicles (HGVs) have a trailer that has a greater height than the cab may have limited radio coverage if an antenna is mounted on the cab as the trailer will obstruct line of sight from behind the antenna. Multiple antennas may be needed to provide adequate coverage in this scenario.

The curved roofs of many models of cars are known for the problems they cause with antenna deployment especially when sited near the base of the roof. The shark fin antenna in many models of vehicle does not provide the performance necessary for acquiring and broadcasting signals between moving objects. Like GPS antennas, the middle of the roof would be a preferable position for a V2X antenna. High signal attenuation rates at this frequency also mean that the distance between an installed antenna and the vehicle's receiver must be kept to an absolute minimum. Use of automotive-grade radio frequency connectors such as FAKRA connectors that can support frequencies up to 6 GHz, will also be imperative.

Common Connector Types Used in V2X Systems

U.FL and MHF4 Connectors: Small, low-profile connectors commonly used due to space constraints.

SMA Connectors: Threaded connectors offering better durability and higher power handling compared to U.FL and MHF4.

RP-SMA Connectors: Reverse polarity variation of SMA connectors to prevent accidental mismatches.

C-V2X versus DSRC

Despite both forms of V2X being operable at 5.9 GHz, the use of this frequency by both systems simultaneously is likely to cause harmful interference, so there is pressure, particularly from automobile manufacturers, to settle on one or other form of automotive technology that can be deployed internationally. In addition, the development and adoption of a single standard or any necessary licensing is likely to accelerate once regulators, governments and manufacturers are agreed on which type of V2X is preferred.

In the USA, DSRC has been in development for over two decades, with spectrum reserved for its use in ITS in accordance with the Transportation Equity Act for the 21st Century. However, there has been little progress in the widespread implementation of DRSC systems in consumer vehicles or the transport infrastructure, beyond specialized traffic-related projects that have not been widely used. In the meantime, stagnancy in DSRC has led to other automobile safety technologies coming to the fore, often developed by manufacturers and using a range of unlicensed frequencies. Technologies such as long-range radar, LiDAR, and cameras used for emergency braking, adaptive cruise control, and enhanced parking have become widespread and GPS-integrated dashboard systems with on-board entertainment software such as Android Auto and Apple Car Play are the norm. Safety features and functionality that was expected to be the domain of DSRC such as lane-keeping alerts have been achieved independently of this technology and threatens to render DSRC obsolete.

Now the automotive industry is seeking to lead in harmonizing ITS communication by throwing its weight behind C-V2X.

C-V2X is coming to the forefront as a technology capable of providing a not only functional but scalable vehicle safety ecosystem while utilizing existing bandwidth set aside in the ITS band. The combination of automotive industry expertise and cellular communication innovation has proven a formidable one and there is a joint determination to see this technology fully established.

Advantages of cellular network operator involvement in C-V2X

  • Mobile operators bring considerable resources, infrastructure, and intellectual property to C-V2X which DSRC has found difficult to replicate.
  • A major advantage is the use of the existing cellular network which LTE-V2X, and later the 5th generation form, will piggyback on.
  • Along with the network infrastructure comes the expertise in maintaining the network and ensuring the robust and secure mobile communications needed for a widespread roll-out of V2X.
  • Data management, processing, and storage in itself is a considerable investment that has hampered progress with DSRC, but again mobile operators already are advantaged by having this critical infrastructure in place already.
  • The mobile telecommunications industry already has established a dialogue with the radio communications regulators which will be needed to take full advantage of ITS bandwidth and ensure the technology is compliant.

These unique benefits of the cellular network make it easier to direct to working with transport safety technology than building the entirely new communications network that would be required for DSRC implementation. The cellular network can be readily used to provide the timely alerts and updates needed for hazards outside of a driver's view and can partner with the data acquisition from a vehicle's onboard sensors, radar, or optics, especially where conditions are poor.

Partnership with GNSS / GPS

Global Navigational Satellite Systems such as GPS are necessary for the location and navigational services that are now standard for modern vehicles and are also expected to play a critical role in the advancement of autonomous vehicle technologies. However, all forms of GNSS are known to be limited in their visibility in urban environments or dense vegetation, leading to delays or failure in pinpointing vehicle location in a range of environments. The cellular network has already provided a solution to improve the Time To First Fix (TTFF) of GPS with the development of Assisted-GPS which relies on cellular network positioning to locate or zone in on a GPS-enabled device or in this case vehicle. This technology, also known as Augmented GPS, is heavily reliant on cell tower and ISP data and will greatly accelerate GPS start-up in typically poor conditions where there may be significant reflection and multipath.

A-GPS technology standards and protocols are authored by 3GPP, possess the capabilities needed to adapt and integrate this existing technology into C-V2X, enhancing its performance and potentially its accuracy

A-GPS has already been made a requirement for GPS-capable phones by the FCC so that location data can be made available to the emergency services if needed. The European E-call system in cars is based on similar principles and also utilizes GPS.

In conclusion

Both C-V2X and DSRC are recognized as offering significant utility as vehicle connectivity technologies that serve a range of safety, informational, and navigation purposes that can make transport infrastructure safer and more efficient. C-V2X is currently edging ahead of DSRC with a consensus of opinion in favor of its deployment from the automotive and telecommunications industries. As explored above it appears to offer scalable connectivity for transport with the capacity to evolve and interface with concurrently developed automotive technologies. With sound protocols and standards that appear to meet the requirements of Intelligent Transport Systems worldwide, C-V2X seems likely to be the contender through which autonomous vehicles will be realized.

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