A British government agency is concerned that OneWeb, SpaceX’s Starlink and similar broadband systems for low Earth orbit (LEO) satellites could block each other’s signals.
Ofcom, the UK’s telecoms regulator, proposed new rules today in a report detailing its interference concerns. Ofcom also said it intends to amend satellite licenses already issued to SpaceX and OneWeb to require coordinated frequency use. Ofcom said that without new requirements, the risk of interference could prevent competition by excluding new players from the market.
Ofcom noted that non-geostationary satellite orbit (NGSO) systems are more complex than the traditional geostationary type because they use hundreds or thousands of satellites. Ofcom’s report stated that “satellite dishes need to track these satellites as they move across the sky, unlike current satellite networks, where the dishes are mounted toward a single satellite fixed in the sky.” Because many LEO satellites are launched, “there is a risk that satellites from different operators will appear in the same part of the sky,” causing interference known as “connected events” in which multiple operators occur. Satellites line up in the sky.
This interference can affect uplink and downlink transmissions between satellites and user stations serving individual homes, the report said. Interference can also affect links between satellites and Gateway Earth stations that connect to the Internet backbone.
“Because the NGSO satellites are moving relative to each other relative to the Earth, individually synchronized events may only be short, perhaps a few seconds,” Ofcom wrote. “However, if an event occurs on the line and causes interference, it may take longer to reconnect the terminal to the network. The interference can continue to repeat over time, repeating in a regular pattern that depends on the orbits of both systems.”
interruption of interference
Users may lose service when there is interference at the user station or gateway ground stations, but interference with the gateway station may affect many users. “[T]The impact of interference on gateway links will be much greater than on individual user links as each gateway provides connectivity to many users (maybe hundreds or thousands of users depending on the design of the system), so the connection loss due to interference in the gateway will be experienced more widely across the network, Ofcom wrote.
Ofcom wrote that Gateway Earth stations operated by various companies are “likely to require large minimum separation distances” of tens of kilometers to avoid interference. In contrast, ‘Multiple GSO [geostationary satellite orbit] Gates can be located in one location” without causing harmful interference with each other.
Ofcom’s report listed five groups of NGOs that were already planned or nearly operational. The biggest example is SpaceX, which offers a trial service of 1,500 satellites already launched and has more than 4,400 satellites planned in its initial phase. The report noted that Amazon’s Kuiper division has not yet launched a satellite, but it has 3,236 satellites planned in its initial phase.
OneWeb – jointly owned by the UK government and Bharti Global – has launched more than 200 satellites and has plans for 648 satellites in its initial phase. Telesat and Kepler supplement the list with plans for 298 and 140 satellites, respectively.
Here is an Ofcom chart listing LEO satellite networks:
The US Federal Communications Commission in 2017 adopted rules, including power limits, to reduce the risk of interference in NGSO systems. The FCC has adopted different rules for different segments of the spectrum. In the 17.8 to 18.3 GHz band, for example, the FCC said, “While terrestrial use of this band is significant, there are areas, particularly rural areas, where terrestrial deployment is less intense and using mitigation techniques such as positioning considerations, hub rejection, And protection, we expect FSS [fixed-satellite service] Earth stations will be able to operate successfully without receiving harmful interference…in the event of interference, earth stations can switch to other bands not shared with terrestrial users or use alternative mitigation techniques. “
The FCC has also imposed specific requirements to prevent interference and space debris on licenses granted to SpaceX, OneWeb, Amazon, and others.
Ofcom is concerned that the Global Coordination Satellite System is being overseen by the International Telecommunication Union [ITU], is not good enough to prevent NGSO problems. “The potential for harmful interference between different satellite systems is usually managed by operators cooperating with each other under the International Telecommunication Union’s satellite coordination procedures,” Ofcom wrote.
The agency added:
However, coordination between NGSO systems is proving more difficult due to the dynamic nature of these systems, along with operators that have different deployment rates (some operators with outdated files will not publish their systems for a few years) and change their architecture over time. We are therefore concerned that non-GSO satellite services could be deployed before an appropriate level of coordination is possible with other operators.
Ofcom is also concerned about the coexistence of user terminals when two or more companies offer LEO satellite service in the same area:
Lack of agreement on how user stations of different systems can coexist in the same area, and scope can limit competition as a result of earlier deployed systems hindering later systems. Once an operator starts deploying user terminals, other operators who wish to launch services using the same band may expect harmful interference from existing user terminals. In the worst case, this could mean that the quality of broadband services will not be reliable enough to enter the market. However, the founding player can have an incentive to cooperate since the overlap is likely to be reciprocal, i.e. its services can deteriorate as well.
New rules, license changes
Ofcom said its goal in issuing new rules is to reduce interference while encouraging competition. The agency proposed, among other things, an “additional express licensing clause requiring NGO licensees to cooperate so that they can coexist and operate within the UK without causing harmful radio interference to each other.” Ofcom said it also intends to “[i]Provide checks when we issue new NGSO licenses so that they are granted only if all systems (existing and new) are able to co-exist and provide services to end users “and implement new terms allowing Ofcom” to take action to resolve service degradation if this is to occur at the site or site(s) specific in the UK. “
To maintain competition, Ofcom said it will introduce a “competition check” into its licensing process to take into account “technical limitations that portal or user terminals may impose on future licensees.” Ofcom said:
In particular, in a market that has been concentrated, if there is a limited potential for the licensee system and future systems (applicants) to be technically able to coexist, then this can present a barrier to future entry into the market. As a result, we suggest that the basic information that applicants must provide when applying for a network license be reliable evidence of the technical ability of their system and future systems to coexist. This will include evidence of the flexibility of their system and/or reasonable steps that new licensees can easily take to protect them. This information may also be used when evaluating whether it is reasonable for new applications and existing services to coexist, to understand the reasonableness of mitigation measures undertaken by existing licensees.
Ofcom said it plans to review all NGSO licenses to identify companies using the same frequencies. The agency said it will also modify existing licenses held by SpaceX Starlink, OneWeb and Kepler. The changes would “require NGO licensees to cooperate with other NGO licensees operating on the same frequencies so that they can coexist,” and allow Ofcom to require operators to take action in cases of overlap between NGO systems that affect on providing services to users at certain UK location(s).
Ofcom said it will receive comments on its proposals until September 20, 2021.
We contacted SpaceX regarding the Ofcom report and will update this article if the company provides a response.