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Whatever Happened to DSRC and C-V2X?

Oct. 18, 2021
This new radio, using either of these technologies, will help improve safety for automobiles. So, what’s the holdup?

What you’ll learn:

  • DSRC’s features and specifications.
  • C-V2X’s features and specifications.
  • ·What’s the status of their adoption?

How many radios does your automobile contain? Probably more than you think. You surely have the basic AM and FM broadcast radios, maybe even an HD radio. Many of us also have a SiriusXM satellite radio. Then there’s the embedded Bluetooth for linking to your cell phone. And don’t forget the navigation system tied to the GPS radio. If your car has a hot spot, you have an embedded LTE radio with a Wi-Fi port, too. And for those owning a late model vehicle with an advanced driver-assistance system (ADAS), one or more mmWave radars are in the mix.

Well, you will soon be adding one more radio to further enhance the ADAS capability in your vehicle. Two contestants have been vying for this service: dedicated short-range communications (DSRC) and cellular vehicle-to-everything (C-V2X).

We’ve been hearing about these radios for years and no final decision has come down regarding adoption. In January 2017, the National Highway Transportation Safety Administration (NHTSA) announced in a notice of proposed rulemaking (NPRM) that it would mandate the inclusion of one of these radios in all vehicles. We’re still waiting.

To refresh your memory, here’s a summary of these two systems and how they work to achieve even greater vehicle safety and their current status.

DSRC

This technology comprises a transceiver or onboard unit (OBU) that can communicate directly with other OBUs for vehicle-to-vehicle (V2V) communication. OBUs also can communicate with roadside units (RSUs) or vehicle-to-infrastructure (V2I) that provide information to the vehicle. The communications provide early warnings of heavy traffic, red-light running, potential rear-end collisions, road construction dangers, and weather to prevent accidents.

Data transmissions typically take place up to 10 times per second with a latency in the millisecond range. The data format for the messages includes a vehicle’s location, speed, direction, acceleration or deceleration, turn status, and other such information. The format of this data is defined by the Society of Automotive Engineers (SAE) in standards J2735 and J2945.

The radio technology used in DSRC is called WAVE. It’s a version of the Wi-Fi standard 802.11p that operates in the 5.9-GHz band (5.850 to 5.925 GHz). The band is divided into seven 10 MHz channels; data rate is between 6- to 27-Mb/s half-duplex. Typical range is 300 meters, with 1000 meters maximum.

Though this technology has been around for years, and fully tested and blessed for adoption, it’s never been implemented. Some auto manufacturers started to install DSRC, but they held off mainly due to the introduction of a competing technology called C-V2X. Another confusion factor causing a delay in adoption.

C-V2X

The cellular vehicle-to-everything idea came from Qualcomm. This standard is based on known LTE cell-phone technology. It’s highly developed and widely implemented, plus proven reliable. It can achieve data speeds and a range greater than WAVE, so it’s attractive. Both technologies have been widely tested in V2V and V2I situations and are essentially equally effective. Other options include vehicle-to-pedestrian (V2P) and vehicle-to-cloud (V2C) communication.

While both standards use the same message format, DSRC and C-V2X radios can’t interoperate. Note that C-V2X doesn’t need to communicate through a cell site because the radios can talk to one another directly as well as through a cell site.

The interesting feature of the C-V2X system is that it can follow the development of LTE and 5G. Versions and standards have already been designed and mapped out for the future. This roadmap to improved versions will probably be the deciding factor that determines what technology is eventually mandated.

It appears that auto manufacturers can add this feature whenever possible. Some adoption is expected to take place in 2022. The NHTSA didn’t respond to my inquiries. In the meantime, Qualcomm is geared up to supply its 9150 ASIC or even its backward-compatible 5G NR C-V2X chips.

Other Considerations

The whole V2V and V2I idea is a great one, and if implemented successfully, it can save lives and minimize collisions. It can’t come soon enough. But there are some other factors to consider.

First, I wonder about how all of this information is going to be presented to the driver. Is it on a screen, audible, or what? Will it be just another distraction like texting and driving? The radios will no doubt be tied to the main automotive systems to implement automatic braking or some other evasion. I doubt that most drivers today with ADAS-equipped vehicles really know how to interact with them. Adding one more massive data source may not help.

Second, the system will not really have much efficacy until some critical mass of vehicles integrate this system. The more cars using it, the better the outcome of lower accident rates and lifesaving. Maybe soon.

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