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How do V2X communications help connected cars share information?

Connected car communications help safely operate autonomous vehicles. IEEE senior member Alexander Wyglinski discusses the options available.

When connected cars talk to each other or their surrounding infrastructure, this is referred to as vehicle-to-everything, or V2X, communications. When connected cars explicitly communicate with another vehicle, we call this vehicle-to-vehicle (V2V) communications, while connected cars talking to roadside units, traffic lights, road signage and so forth is called vehicle-to-infrastructure (V2I) communications.

In order to support V2X communications -- either V2V or V2I -- there are two approaches to create reliable wireless links between both ends of the communications channel, and each of these approaches has its own pros and cons.

The first approach is referred to as direct V2X, where a connected car directly forms a communications channel with the intended receiver whether it is another connected car or a roadside unit. For direct V2X, the transmitting vehicle literally connects with the intended receiver without the need for any additional infrastructure, such as base stations or relays, thus minimizing the communications delay in the transmission. This can significantly impact the safety applications of autonomous vehicles, which require real-time data.

The major disadvantage of the direct V2X approach is establishing the communication link in the first place, as it takes time and resources for both ends of the communications channel to agree upon a specific transmit frequency, data rate and other essential parameters that support communication.

Conversely, the second connected car communications approach, referred to as cellular V2X, or C-V2X, uses cellphone base station technology to connect all the vehicles and roadside units within the transportation ecosystem. Unlike the direct V2X approach, C-V2X possesses very little overhead when forming wireless links between transmitters and receivers.

On the other hand, the relay nature of the cellular infrastructure incurs a penalty that can potentially be dangerous in time-sensitive vehicle operations, such as safety applications and autonomous vehicle systems.

As a result, it is expected that in the near future a hybrid approach will be employed, where time-critical operations are handled by direct V2X communications while non-time-sensitive operations are handled by a C-V2X framework.

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What do you expect to see in the future of connected car communications?
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I believe the article is a bit misleading/incomplete as it does not mention PC5, the direct V2X technology which is already a part of C-V2X and does not require cellular network.

The other major advantage of C-V2X technology is that it includes V2P, direct communication with pedestrians and other vulnerable road users, thus saving a lot many more lives.

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The state disadvantage of direct V2X is not correct. Those of us who are currently using this technology (we are one of dozens of locations around the country), use dedicated short range communication (DSRC) in the 5.9GHz band. There is no lost time figuring out a transmission frequency or data rate. The DSRC system adheres to specifications of IEEE 802.11 and sends messages in accordance with SAE J2735 and J2945, using spectrum dedicated by the FCC. It already works, and is being used. 
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