Traditional spectrum policy is mostly a two-dimensional problem. It talks about license areas (not volumes) and protection contours (not bubbles). The key determinant in managing interference between radios is the horizontal distance between them.
It’s not quite flatland, of course. Many signal propagation models (key to interference analysis) include the heights of transmitters and receivers as well as intervening obstacles, but typically horizontal distances are much, much larger than vertical ones. Satellite systems are an exception, but even here one could call it essentially 2 ½ dimensional: satellites up high, strung out like pearls along a geostationary orbit, beaming down 2D patches of coverage onto the earth. And the propagation is essentially a line: geostationary satellites are roughly 1,000 times as high as continents are wide.
This two dimensionality started breaking down with the dense urban deployment of cellular systems. The vertical position of handsets in tall building relative to base stations started to matter, not only in positioning and pointing antenna systems appropriately but even in the requirements for locating emergency calls: the FCC’s E911 requirement now calls for vertical location information for calls originating in multi-story buildings.
New plans for constellations of low earth orbiting satellites (the last generation mostly failed: remember Teledesic?), high altitude broadband platforms like Facebook’s Aquila and Google’s Loon, and the prospect of the mass deployment of drones and clouds of cubesats are leading to spectrum management becoming a 3D world. Radios will not just be on the earth’s surface and in geostationary orbit (and a few airplanes), but at a whole range of altitudes between zero and 36,000 km.
We need to start thinking seriously about a 3D Wireless World. If that’s is the vision, the three major tasks are:
- Build: the design and engineering challenge of creating the devices and systems to realize the vision; and the policy challenge of creating a new regulatory framework, encompassing aeronautical, aviation and communications agencies
- Manage: the measurements, operations, and government regulations to ensure the effective and beneficial operation of the components and systems
- Use: all the applications that use the 3D wireless infrastructure, from earth science and weather forecasting to navigation to delivering broadband services in new ways, to name a few.
The FCC has thought about 3D spectrum management in a piecemeal way over the years
- Coexistence between “horizontal” and “vertical” services, e.g. Northpoint’s (failed) broadband distribution service in the satellite TV broadcast band; unlicensed Wi-Fi networks and Globalstar satellite uplinks in the 5 GHz band; and cellular point-to-point links and satellite earth stations in the millimeter wave bands
- Allowing terrestrial operation in bands planned for satellite services, e.g. adding terrestrial transmitters for audio broadcast (SiriusXM) or cellular service (LightSquared)
- And most recently, work at the ITU on command-and-control links for drones
The time has come to think holistically about the 3D wireless world we’re busily building.