Google is trying to test a 6 GHz network across much of the United States – in 17 states, to be exact, according to filings with the FCC. It is currently unclear what, exactly, the web giant is trying to test, but it is important to remember that in America it also has an important role as a network operator, both mobile with Fi and fixed with Fiber.
The tests, again according to the documentation, should last 24 months and, the text explains laconically, aim at "produce technical information regarding the usefulness of these frequencies to create reliable broadband connections"In total, 26 cities, large and small, will be required to conduct the tests.
Unfortunately, the mere definition of 6 GHz is too broad to narrow it down significantly. The new Wi-Fi 6E operates at 6 GHz, probably the same could do the IoT division dedicated to communication between vehicles (V2V), and the same hypothesize some prototype specifications of 5G.
In addition to the things that are already there, it's worth remembering that Google is one of the world's leading tech companies: between cars that drive themselves (or drones, for that matter) and balloons that bring the internet to remote areas, not it can certainly be ruled out that he is developing something entirely new.