There is growing interest around the world in unmanned aerial vehicles (UAVs), often called “drones” for both military and civilm use. In International Civil Aviation Organization (ICAO) jargon, they are called remotely piloted aircraft (RPA), while in the International Telecommunication Union (ITU) they are called unmanned aeronautical systems (UAS). The civil use includes both commercial use as well as noncommercial use, e.g. a new platform for photography. A major U.S. newspaper reported recently:
“The next time you go to a wedding, be sure your hair is done, your lipstick is on, and your (underwear isn’t) sticking out of your pants. You never know if a drone is lurking in the sky about to zoom in and take your picture.”[i]
UAVs range in size from military units with mass of over 1000 kg to consumer units of about 1 kg. Similarly the range and endurance time of these units vary significantly from minutes to hours. While autonomous UAVs without radio links are theoretically possible, for a variety of reasons radio links are generally used for vehicle control and often to downlink information such as imagery or video.
At the international level, the spectrum needs of UAVs have been under consideration at ITU deliberations for more than a decade. A 2009 ITU Radio Sector (ITU-R) report[ii] found that:
“Communications are key in UAS systems due to the remote nature of human presence. Safety-of-flight is the driving factor when the seamless flight of UAS within civilian air traffic is at stake. In the end, safe operation of UAS relies on communications which represents a critical step in enabling UAS operations in non-segregated airspaces.”
The report listed a wide variety of applications for UAVs, including:
- Movie making, sports games, popular events like concerts.
- Cargo planes with reduced man power (one-man-cockpit).
- Inspections for industries, e.g. oil fields, oil platforms, oil pipelines, power line, rail line.
- Provision of airborne relays for cell phones in the future.
- Commercial agricultural services like crop dusting.
- Earth science and geographic missions (e.g. mapping and surveying, aerial photography) biological, environmental missions (e.g. animal monitoring, crop spraying, volcano monitoring, biomass surveys, livestock monitoring, tree fertilization).
- Coast line inspection, preventive border surveillance, drug control, anti-terrorism operations, strike events, search and rescue of people in distress, and national security.
- Public interest missions like remote weather monitoring, avalanche prediction and control, hurricane monitoring, forest fires prevention surveillance, insurance claims during disasters and traffic surveillance.
- Famine relief, medical support, aid delivery. Search and rescue activities.
Note that this long list from ITU-R include neither the military use of UAVs that has become a regular news item nor wedding photography.
The same report estimated the spectrum needs for UAVs to be “34 MHz for terrestrial systems (and) 56 MHz for satellite systems.” However, in view of the rapid recent changes in UAV technology it is not clear if these 2009 estimates are still relevant.
This month, the ITU World Radio Communication Conference (2-27 November, Geneva, Switzerland) is considering “the use of frequency bands allocated to the fixed-satellite service ” for the control and non-payload communications of unmanned aircraft systems (UAS) in non-segregated airspaces, in accordance with Resolution 153[iii] (WRC-12).”[iv]
But while formal reallocations are being considered, the “marketplace” is making way for rapidly expanding private sector UAV use using existing spectrum in ways that might cause long-range pragmatic problems. In particular, unlicensed (“Part 15”) spectrum and cellular land mobile spectrum are both readily, if not formally legally, used for modest UAV applications such as photography for weddings and marketing houses and land for sale. Already one U.S. cellular carrier has announced the marketing of a UAV controlled by smartphones via a Bluetooth link.[v] Whether this is a brilliant marketing decision or an event that “opens Pandora’s box” remains to be seen. Why? Jamming of both cellular spectrum and GPS spectrum is an unfortunate growing trend in the United States. While the sociology of this jamming is complex, a key motivator appears to be perceptions that some of today’s wireless technology that we are so proud of is seen by others in our communities as invading personal privacy. Indeed, GPS jammers are sometimes marketed as “privacy protection devices.” Jamming motivated by direct personal gain, on the other hand, appears to be rare, although there have been a few cases of hotels and conference centers blocking unaffiliated Wi-Fi signals to collect fees for their own networks[vi].
“Peeping drones” — UAVs that provide imagery from locations that were previously thought private such as bedroom windows and backyards — are a growing concern.[vii] Public perception of UAVs as privacy invasion could escalate interest in illegal but hard-to-suppress jamming of the spectrum supporting the imagery.
While ITU and FCC provide for the Aeronautical Mobile Service, which is planned for communications to/from airborne systems, cellular and unlicensed bands are not planned for transmitters well off the ground. Thus, transmitters more than 50-100m off the ground can impact the band much more than terrestrial users, since height has a significant impact on propagation loss. Widespread use of imagery transmission from UAVs in cellular or unlicensed spectrum may congest that spectrum much more than the expected terrestrial use that the systems in those bands were designed for.
Thus, poorly planned use of cellular and unlicensed spectrum for drone control and imagery downlinks might have adverse impacts on both cellular and unlicensed spectrum hosting the transmission. Many uses of drones are clearly beneficial and will contribute to economic growth. In view of the growing interest in drone use in the United States, it is amazing how little attention FCC has paid to the related spectrum issues. It is hoped that FAA and FCC will join forces and deal with airspace and spectrum issues related to drones in a transparent and consistent manner.
Michael J. Marcus (mjmarcus@marcus-spectrum.com) (S ’66, M ’72, SM ’01, F “04) is Director of Marcus Spectrum Solutions, Cabin John, Maryland, adjunct professor at Virginia Tech’s Department of Electrical & Computer Engineering. He retired from the Federal Communications Commission in 2004 after nearly 25 years in senior spectrum policy positions. While at FCC, he proposed and directed the policy developments that resulted in the bands used by Wi-Fi, Bluetooth, ZigBee and unlicensed millimeter wave systems. He was an exchange visitor to the Japanese Ministry of Posts and Telecommunications and has been a consultant to the European Commission and the Singapore regulator. In 2013 he was awarded the IEEE ComSoc Award for Public Service in the Field of Telecommunications. He received S.B. and Sc.D. degrees in electrical engineering from MIT. In 2012-13 he was chair of the IEEE-USA Committee on Communication Policy.
