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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