ADAS Needs V2X to Meet ITS Goals

Connected cars will make a big difference in achieving increased safety.

By Jack Browne, Technical Contributor
[Rohde & Schwarz Sponsored Auto Article]

Advanced Driver Assistance Systems (ADAS) are clearly making a difference in vehicle safety as more cars include them and as drivers learn to use them. However, further gains in safety are possible by adding a communications capability to every vehicle and the surrounding infrastructure. The goal of the Department of Transportation’s (DOT) Intelligent Transportation System (ITS) is to improve U.S. safety and mobility by adding a communications component. We were well on that path thanks to a mandate by the National Highway Transportation Safety Administration (NHTSA) to include the Dedicated Short Range Communications (DSRC) radios in all vehicles by 2023. However, recently that progress has been delayed by two major factors:  the canceled mandate and an alternative radio technology to DSRC. What can we expect in the future?

Direct vehicle-to-vehicle communications should mitigate accidents and help achieve the DOT’s ITS objectives.

Vehicular Communications

The industry and government have defined several versions of vehicular communications. These are vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-to-everything (V2X). V2V is the direct communications between vehicles within range of one another. This link-up is automatic and cars exchange status information. They send and receive a Basic Safety Message (BSM) 10 times per second. The BSM contains data such as GPS location, speed, direction, brake status, and related conditions. This information is communicated to the driver and may also be linked to the ADAS system for automatic control.

V2I sets up communications between the vehicle and nearby roadside units (RSUs) or access points that can provide additional information such as traffic-light status, road conditions, weather alerts, traffic conditions ahead, and any related information. V2I points would provide a link from the vehicle to an external network if needed. Currently that infrastructure is not present. A build-out will take some time.

V2X is a broader term that encompasses V2V and V2I but may include objects such as pedestrians, bicycles, motorcycles, and remote networks that might add to the usefulness of the system.

Intelligent Transportation Systems Using IEEE 802.11p
ADAS Needs V2X to Meet ITS Goals

For several years, automobile makers and government agencies have sought ways to improve safety on roadways and effectively manage traffic flow. As wireless communication systems are advancing, the vision of automobiles talking to each other and to roadside units is becoming a reality.

Download free application note

Mandated V2V: Good News or Bad News?

The recent decision by the Trump administration to drop the V2V mandate was a surprise to many. This administration is essentially anti-regulation despite the fact that most auto companies like the idea of V2V and the proposed benefits are almost obvious. Consumers have already shown a willingness to buy the expensive ADAS packages so should easily get on board with any V2V addition.

The auto manufacturers could go ahead and put V2V into vehicles without a mandate. As long as the dedicated spectrum is still available, that is an option. Most auto makers would have to agree if the critical mass (volume of cars) needed for V2V to be effective is achieved. If that does not happen, other parties such as the telecom and cable companies may try to claim the V2X allocated 5.9 GHz spectrum for cellular and/or broadband connections.

Standard Indecision

Everyone thought that the V2V system had been decided upon years ago. That system, DSRC, has been widely tested and blessed by almost everyone. The DSRC system is defined by the IEEE 802.11p standard. It operates in the 5.9 GHz band in 75 MHz of spectrum using seven 10-MHz channels. Data rates can run from 3 to 27 Mb/s using OFDM and one of several modulation types up to 64 QAM. The range is up about 300 meters. Typical transmit power is 23 dBm. Other characteristics include the CSMA-CA access method of Wi-Fi and a latency of about 10 ms. Security is by way of the IEEE 1609.2 standard that handles encryption and authentication.

The previously mentioned mandate would task auto makers to include DSRC in all vehicles by 2023. Now that is on hold. But that’s not the only issue. Other companies want a different communications technology, namely one based on the current or future cellular standards. Called C-V2X, this technology would use current 4G LTE gear but would eventually phase in the forthcoming 5G New Radio standard being developed by the 3GPP.

The alternate technology C-V2X a variation of the LTE standard as defined by Release 14 of the 3GPP’s guidelines. In addition to communicating with nearby base stations, the new version includes direct device-to-device communications as well as a broadcast mode. C-V2X also uses the 5.9 GHz spectrum but instead of OFDM, it uses single carrier-frequency division multiple access (SC-FDMA), a variation of OFDM that is used in the LTE uplink from cell phone to cell site. This mode of operation has a lower peak to average power ratio (PAPR) feature that is more efficient for battery-powered devices. SC-FDMA also uses a different coding scheme (Turbo) and the hybrid automatic repeat request (HARQ) protocol to enhance the reliability of data transfer. Other benefits are longer-range communications, improved data transfer at higher vehicle speeds, and lower latency. DSRC latency is relatively low (10 ms) but C-V2X latency is much less (< 2 ms). Future versions of C-V2X would presumably use the forthcoming 5G wireless standard.

While the newer C-V2X technology offers some improvement over the older DSRC, DSRC is still a viable option as extensive testing has shown. Some have even proposed a hybrid version that pairs DSRC with C-V2X. The hybrid would probably be more costly, but would enjoy the top benefits of each technology.

Intelligent Transportation Systems Using IEEE 802.11p
ADAS Needs V2X to Meet ITS Goals

For several years, automobile makers and government agencies have sought ways to improve safety on roadways and effectively manage traffic flow. As wireless communication systems are advancing, the vision of automobiles talking to each other and to roadside units is becoming a reality.

Download free application note

V2X and Self-Driving Cars

ADAS and V2V/V2I form the base for fully autonomous vehicles (AVs). While full Level 5 automation (see table) does not seem realistic at this point, no doubt Level 4 can be achieved. The artificial intelligence (AI) software driving the car will make full use of the ADAS and V2X with GNSS/GPS inputs. Full automation is a lofty goal, but perhaps a better target solution is to simply let AI complement the driver rather than replace him or her. While some learning and adaptation will be required by the human, that powerful combination of human/AI should provide the best safety improvement everyone is seeking.

Levels of Vehicle Automation

Level Amount of Automation
0 No automation. Driver performs all functions.
1 Driver performs all functions but ADAS systems provide alerts and partial control.
2 Partial automation. Driver must still monitor actions but automated systems control braking, steering and acceleration.
3 Automated driving systems perform all driving activities driver must still be available to take control in special circumstances.
4 Automated driving systems perform all driving activities. Driver may still control the vehicle if needed or desired.
5 Full automation. No driver needed or possible.

Source: Society of Automotive Engineers

What’s Next?

For the immediate future, the government and industry will be pondering these issues and eventually make some decisions. But instead of waiting around for something to happen, someone needs to take the initiative now to move V2X forward.

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