With connected vehicle technology, vehicles exchange messages directly with each other (i.e., vehicle to vehicle or V2V), and with roadside infrastructure (i.e., vehicle-to-infrastructure or V2I). V2V and V2I communications support applications that could save lives by reducing the number of vehicle crashes, as well as enabling applications that bring new services to drivers and passengers. These communications can occur without involvement from any cellular operator, but they require access to spectrum. Most countries have allocated a band of spectrum exclusively for this purpose. In the U.S., this is called the Intelligent Transportation Systems (ITS) band. Both government agencies and companies in the transportation sector have argued that the ITS band is insufficient to meet the spectrum needs of connected vehicles.
This paper proposes an approach that allows connected vehicles to share spectrum with Wi-Fi and possibly other unlicensed devices, rather than use only ITS spectrum allocated exclusively for connected vehicles. This approach requires no changes to Wi-Fi, and only modest changes to connected vehicle technology. It prevents harmful interference through implicit and backwards-compatible beaconing.
Our approach is significant for two reasons. First, it provides a useful strategy to meet the needs of connected vehicles, and eliminates a difficult dilemma that confronted spectrum regulators. The U.S. Federal Communications Commission (FCC) took 45 MHz away from ITS and made it unlicensed, because doing so created a contiguous unlicensed spectrum band wide enough for the next generation of Wi-Fi. The FCC had to choose between two compelling uses. If connected vehicles and Wi-Fi could share those 45 MHz or other unlicensed bands in a way that protects quality of service, the needs of both would be met.
Second, this approach is significant as a case study for a form of spectrum sharing that is different from what we see today. Our approach can give one class of devices a form of priority, although priority is not absolute. Spectrum access is governed by a backward-compatible form of implicit beaconing rather than by traditional spectrum sensing or by accessing a database. Thus, sharing is based on cooperation, rather than coexistence.
Whether used in the context of connected vehicles or for other purposes, the proposed spectrum-sharing approach has a number of advantages. This form of sharing can achieve far greater spectrum efficiency than today’s approaches. It can protect quality of service for both types of devices, which in this case means supporting safety-critical communications for vehicle crash prevention while preventing starvation of Wi-Fi. It requires no centralized control, so there is no need to rely on any kind of database operator or cellular operator, or to build out infrastructure to communicate with that centralized controller. It gives spectrum regulators the ability to admit a new kind of device into a band without disrupting legacy devices, even when the new devices have priority. In this particular case, the legacy devices are Wi-Fi, and the new devices are for connected vehicles. The principal disadvantage of this spectrum-sharing approach is that it introduces rigidity which may limit future technologies operating in the band.