Non-terrestrial spectrum sharing

Will we have global standards for Internet satellite spectrum sharing one day?

Four companies, SpaceX, OneWeb, Boeing and Leosat have announced ambitious plans to put thousands of Internet-service satellites in non-geostationary low-Earth orbit (NGSO) and other companies like ViaSat and SES are currently operating hundreds of communication satellites in medium-Earth and higher, geostationary orbits.

With so many satellites orbiting in different planes and at different altitudes, there are bound to be frequent "inline events" when two satellites are simultaneously above an area both are communicating with -- causing potential radio interference.

Terrestrial radio interference has historically been handled by setting limits on transmitter power and granting exclusive rights to organizations, so, for example, in the Los Angeles area radio station KPCC has the exclusive right to broadcast at 89.3 MHz. Since transmitter power is also regulated, KPCC does not interfere with stations broadcasting at the same frequency in distant cities.

Technology has improved since the early days of radio and we are entering an era when smart radios can be programmed to cooperatively share the same spectrum (range of frequencies) by quickly changing frequencies, power levels, antenna focus, etc. (You can see a quick overview of the frequency ranges these companies wish to use here).

Last month, the US Federal Communication Commission (FCC) voted to delay SpaceX's application to launch satellites, saying they would defer to the International Telecommunication Union (ITU) on how these new satellite systems should coordinate and share spectrum. Since OneWeb had already been granted permission to launch their satellites, Bloomberg and others speculated that the issue of potential interference might pose a significant problem for SpaceX.

It would have been a problem in the past, but today's regulators recognize that we need new rules for the spectrum-sharing era. In 2015, the ITU came out in favor of coordination between operators stating that they did not intend "to state an order of priorities for rights to a particular orbital position and the coordination process is a two way process" and last month FCC chairman Ajit Pai agreed, saying "given recent trends in the satellite industry and changes in satellite technology, the Commission began a review last year of the rules governing NGSO fixed-satellite service operations to better accommodate this next generation of systems."

What this means is that OneWeb and other early applicants who have been approved by the ITU and FCC as having priority access to frequency bands do not have exclusive rights to that spectrum, just that SpaceX will have to negotiate and define a sharing mechanism that satisfies them.

OneWeb technique to avoid inference
with geostationary satellites (source)

That process has begun. For example, OneWeb has a patent pending on progressive pitch technology, a technique to avoid interference between their low-Earth orbit constellation and geostationary satellites, which orbit around the equator at relatively high altitudes. Their satellites will automatically change orientation and power level as they pass over the equator to avoid interference with geostationary satellites orbiting above them.

SpaceX has proposed that NGSO operators share data to indicate the steering angle of each beam within a satellite's footprint. As shown below, they assert that this data sharing would drastically reduce the occurrence of inline events between their 4,425 satellites and a ViaSat geosynchronous satellite.

Inline events (red dots) without and with information sharing

This effort to enable efficient spectrum sharing by OneWeb, SpaceX, Boeing and operators of other satellites (and one day perhaps balloons, drones and other high altitude platforms) reminds me of the proposal for the Ethernet standard for local area networks by three companies -- DEC, Intel and Xerox. A major difference, in this case, is that the Ethernet standard was adopted by a professional engineering organization and a satellite communication standard would be approved by the ITU, a United Nations agency. It may be too soon, but might engineers from OneWeb, Boeing and SpaceX one day define global standards for non-terrestrial spectrum sharing?