Facebook Vision of Drones for Universal Net Coverage Unclear on Spectrum Sources, Interference

Internet.org wants drones to fly as close to the ground as possible to maximize signal strength, Zuckerberg’s paper said. The aircraft should have the cheapest structure so many can be built, and reusable structures to make them more cost-effective, the paper said. Based on those and other constraints, drones operating at around 65,000 feet are ideal, the paper said. Unlike satellites, drones won’t burn up in the atmosphere and can be brought down and reused when their mission is complete.

It’s unclear what spectrum is being considered for the drones, said GSM Association Senior Director of Spectrum Policy Wladimir Bocquet. International radio regulations make most commercial mobile spectrum unsuitable because aeronautical use is prohibited, he told us. Most unlicensed bands are also likely to be unsuitable due to regulatory issues surrounding aeronautical uses, and, more important, because the altitude of the drones would put them out of the range of ground-based systems, he said.

It won’t be possible for each market sector to have its own spectrum for its drones, said Thomas Weber, who deals with spectrum management in the European Communications Office, which advises the European Conference of Postal and Telecommunications Administrations. The idea of exclusive access to spectrum for such applications may not be good, if the spectrum opportunity costs in each case are also considered, he said. The use scenario could be similar to the sort of wireless, cordless cameras helicopters use for such things as covering the Tour de France or for police activities, he said. In that case, it may not matter with regard to spectrum usage whether it’s a helicopter or an unmanned drone, he said.

Such scenarios are already under study in Europe, mostly in the 3 GHz-10 GHz range, but higher frequencies could also be of interest, Weber said. Higher frequencies need line-of-sight communications, but the spectrum opportunity costs for reservation of such spectrum for airborne applications will decrease, he said.

Drones could possibly use Wi-Fi spectrum in the 2.4 GHz band and maybe spectrum in the 5 GHz band as well, said Director-Spectrum Consulting Richard Womersley of LStelcom, which designs and develops software and systems for the wireless telecom market. Those bands are typically license-exempt, he said, but would need regulatory permission. If they're low enough to the ground and have the right equipment, drones could potentially run standard Wi-Fi to tablets, with no need for users to buy special devices, he said in an interview.

Weber, however, said use of the 2.4 GHz band would be feasible from a regulatory perspective, but the quality of service might be lower than drone operators would like due to interference from many other users of the spectrum. The 5 GHz band has a “major problem” because of the dynamic frequency selection (DFS) requirement for protection of military and weather radars, he said. DFS doesn’t work when airborne, but detects radar signals only when stationary, he said. The license-exempt regulations may not provide enough of an emission level to cover a sufficiently large distance, and there might be non-line-of-sight conditions as well, Weber said.

Interference Potential

The internet.org vision “is indeed a challenge,” said Weber. Due to the location of the drones, their airborne receivers are vulnerable to incoming interference, and on the reverse link to the ground, “this has high potential to interfere [with] other terrestrial applications,” he said.

Satellite broadband services demonstrate that the height of the antennas isn’t a fundamental barrier for service delivery, said Bocquet, but altitude “certainly presents complications that make interference a challenge.” It’s especially complex because drones will be moving at high speed, which will affect the cost of ground equipment because the antenna will have to move to track the signal, he said. Most commercial mobile spectrum can’t be used for aeronautical use precisely because of interference issues, he said.

Womersley said if there’s a Wi-Fi network on the ground, a drone could possibly link into it to avoid interference. If no such network exists, there shouldn’t be any interference issues, he said. The bigger question is whether the drone could interfere with Wi-Fi transmissions because it would have large antennas underneath broadcasting to the ground, he said. But Wi-Fi isn’t a protected service, and is designed to operate with a lot of interference, so someone running another Wi-Fi network likely couldn’t claim interference, he said.

Zuckerberg’s idea of delivering last-mile Internet services with drones and other equipment, “though light on details,” has “generated a fair amount of buzz” and “only a few critical comments about how developing countries may not be excited about a fleet of U.S.-company-supported drones circling their airspace,” emerging markets analyst Vital Wave said in an April 14 newsletter (http://bit.ly/1mh9F0p). Even fewer have considered the implications of Facebook’s drones bypassing network operators completely and putting the keys to Internet access firmly in the hands of advertising giants, it said. “It’s notable that the advertising, e-commerce and mobile phone crowd is making the most noise” about global Internet coverage, the newsletter said. “They have a lot to gain from Bushmen friending Sherpas."

Asked if the broadband drones will be a disaster for telecom companies, GSMA’s Bocquet said, “Certainly not.” The mobile industry wants to provide ubiquitous high-speed mobile broadband coverage and is particularly focused on connecting people in developing markets, he said. This has proved complex because the business case for rural services, especially in developing countries, can be “extremely challenging” due to the type of spectrum operators are allowed to use, and base station economics, he said.

This is changing, as the availability of lower frequencies, such as digital dividend spectrum, means rural areas can be covered with fewer base stations, lowering the costs of providing services, said Bocquet. Mobile operators are more willing to share infrastructure to make mobile broadband access more affordable in developing regions, he said. Eight major operators groups agreed in March to cooperate on infrastructure-sharing initiatives in Africa and the Middle East, a GSMA news release said.