What's in a spectrum allocation? Aero bods talk drone radio links

Preparing the ground for remotely flown and autonomous aircraft – drones – of the near future is a challenge. How much effort has gone into clearing radio spectrum for vital command-and-control links?

That question was addressed at a recent Royal Aeronautical Society workshop on drone command and control, where Alastair Munro, chairman of the EUROCAE WG-105 unmanned aircraft system working group, spoke about frequency allocations for vital aviation control links.

"We have a persistent problem that fails to attract sufficient effort to solve," said Munro, "which is understanding what performance is required, what disruption is tolerable and how does it play out across the different services required?"

He said there is "an increasing amount of uncoordinated standards activity" around defining radio links for drone command and control (C2) transmissions: "People's expectations about how quickly they can do it are very optimistic."

Although the International Telecommunications Union (ITU) has set aside bands for use by unmanned aerial vehicles (PDF), and has previously mused about whether to dedicate the 5,030-5,091MHz block for drone C2 links, there was uncertainty in the room as to what the currently allocated bands were. The Register has heard more than one story about (probably hypothetical) operators who simply installed and used drone C2 kit on any old band, on the basis that if it caused a problem, sooner or later someone would probably complain.

The 960-1.164MHz band was allocated by the International Civil Aviation Organization (ICAO) to C2 links for RPAS* in 2012, as well as the 5,030-5,091MHz band for BVLOS* drone flights. Of interest will be the potential conflict with the 5GHz Wi-Fi frequencies, which overlap from 5.035GHz upwards. While the theory is that indoor-grade Wi-Fi devices should only ever be low-power transmitters incapable, in practice, of causing interference to the sort of gear needed to control a remotely flown aircraft that may be tens or even hundreds of miles away, this appears to El Reg to be a bit of a trusting assumption to make for a safety-critical service.

"In terms of spectrum use you'll find a lot of ISM band (industrial, scientific and medical) users... and also short-range devices. Anecdotally, you hear people talking about 868MHz and others where there's an awful lot of users, including some safety critical devices," mused Munro, who added, in reference to the common 2.4GHz and 5GHz bands: "There’s more users of Wi-Fi than [many] think."

He continued: "We've not really met expectations in terms of band planning... who is going to pay for the amount of work [needed] for consumer systems? Where's the balance point? Can you afford to have a collection of small services that somehow coordinate with each other or does it have to be managed nationally?"

There are other problems as well to consider when designing drone C2 links, and high up on that list, as Munro said, is security.

"Cybersecurity we all know will be a difficult thing to address," he said. "I personally think attacks on UAS links will be the least of the problems... there's a very large number of things that are vulnerable. Most important, I think, is authentication of the equipment and accountability. If you say somebody did something, how are you going to prove that?" ®