The Federal Communications Commission is asking for further comment about spectrum sharing between connected vehicle and Wi-Fi uses in the 5.865 GHz to 5.925 GHz band, illustrating a shift in thinking about spectrum allocation generally, and providing yet one more example of how all spectrum decisions are inherently political and contentious.

In this case, growing demand for additional spectrum for Wi-Fi–in a band logical for Wi-Fi use–clashes with a prior licensing decision intended to support connected vehicles.

Supporters of vehicle-to-vehicle communications generally prefer that dedicated Short Range Communications (DSRC) operations in the 5.850-5.925 GHz (U-NII-4) band not be shared with “Unlicensed National Information Infrastructure” (U-NII) devices. In other words, the argument is “no sharing of dedicated DSRC spectrum with Wi-Fi.”

Proponents of Wi-Fi sharing in that band cite growing needs for Wi-Fi bandwidth, the fact that no services yet are provided, after 15 years, as well as advances in sharing technology that allow dual use.

The DSRC spectrum at 5.850-5.925 GHz consists of seven 10-Megahertz channels and a 5 MHz segment of spectrum reserved to accommodate future developments.

The current FCC rules designate two of the seven 10 megahertz channels (5.855-5.865 GHz and 5.915-5.925 GHz) for safety of life and property applications and one of the 10 megahertz channels (5.885-5.895 GHz) is designated as a control channel.

Two sets of the 10 megahertz channels may be combined to create a two 20 megahertz channel (5.865-5.885 GHz and 5.895-5.915 GHz)

Advocates of spectrum sharing often say as little as five to 10 percent of licensed spectrum actually is used, at any given moment, pointing out the value of allowing spectrum sharing, instead of exclusive use that actually means most communications spectrum lies fallow, most of the time.

Communications policy advocates often point out that much allocated spectrum is not in use, years after being awarded. Sometimes that is alleged to be an example of deliberate hoarding, intended mostly to deny its use to rivals.

“The auto industry wants to retain near-exclusive use of the full 75 megahertz, without an auction and at no charge, but most of it would be used for commercial applications unrelated to safety,” said Michael Calabrese, director of the Wireless Future Project at New America think tank. The same functions could be supplied by Wi-Fi apps and devices, he has argued.

There are more benign explanations. The Dedicated Short Range Communications (DSRC) band, featuring 75 MHz, was allocated for vehicle-to-vehicle communications more than a decade ago, but only now are the first commercial applications coming to market. Sometimes it takes that long for an ecosystem to develop.

DSRC was intended to enable short range, wireless links to transfer information between vehicles and roadside systems. But some argue Wi-Fi, in nearby bands, also requires more spectrum, and that sharing mechanisms now are feasible that allow connected car apps and Wi-Fi to coexist, while making more efficient use of available spectrum.

Disputes over use of spectrum always will be part of the regulatory landscape. What is new is the ability to allow shared access. Considering that perhaps 90 percent of spectrum is not used, most of the time, shared spectrum is a major tool for increasing the availability of spectrum at relatively low cost.