The test, if successful, will show that Starlink satellites can operate at up to eight times the capacity currently allowed by the ITU’s EPFD limit, while still protecting geostationary satellites
Romania’s National Authority for Communications Administration and Regulation (ANCOM), the country’s Ministry of National Defence and SpaceX have conducted the first real-world test to demonstrate whether Starlink’s non-geostationary satellite (NGSO) systems can operate without interfering with geostationary satellite (GSO) networks, even with relaxed power flux density (EPFD) limits.
Aggregate individual EPFD limits were developed and agreed 25 years ago. NGSO systems using certain frequency bands must meet EPFD limits to ensure that they do not cause unacceptable interference to GSO FSS and BSS networks. However, some observers suggest the limits are potentially arbitrary.
The Romanian regulator, decided to contribute to the ongoing EPFD studies – being carried out by the ITU – through a real-world test campaign to demonstrate the protection of GSO networks under more relaxed NGSO limits.
Ahead of the test, Romania reviewed the history of how EPFD limits were set 25 years ago. At that time, ANCOM said administrations agreed on an aggregate protection criterion of 10% for “increased unavailability” of GSO links. The concept of artificial “EPFD masks” was introduced.
These masks are specific limits (in place today) but which introduce spectrum inefficiencies because they are not actually needed, says ANCOM, having been agreed on the basis of compromises made to ensure that they would work for the theoretical non-geostationary systems studied at the time but which never became operational.
ANCOM instead considers that an appropriate protection framework for geostationary networks includes: a complete set of geostationary reference links representing existing modern GSO operations and not just theoretical ones; and protection criteria agreed between the operators of both systems.
With these two fundamental elements it is possible to test any non-geostationary system and check the protection of geostationary communication links.
The test
Based on these considerations, in July ANCOM installed equipment for an EPFD test in real conditions, the first of its kind in the world. The Ministry of National Defense provided the link-budget link characteristics and the C/N unavailability threshold of some of the most sensitive Ku-band communication links in the country. The protection criterion selected to ensure protection is the one agreed 25 years ago, namely a 10% aggregate increase in service unavailability.
In addition, a 3% increase in individual service unavailability will also be tested. SpaceX performed precise computer simulations to extract the operational parameters needed to achieve the 10% and 3% protection margins.
With the agreement of ANCOM and the Ministry of National Defense, SpaceX, has been authorised to exceed the current EPFD limits and reach the agreed operational parameters in a limited area around the test site for a minimum duration of six months. Signal, interference and/or noise level data is being collected through a spectrum analyser and will be shared “in a transparent manner” between the parties involved.
The aim is to demonstrate that the NGSO Starlink satellite network can meet the 10% and 3% protection criteria for the satellite links provided by the Ministry of National Defense through geostationary satellite networks and therefore protect them while exceeding the current EPFD limits under surveillance.
The test will simulate a potential increase in Starlink network capacity in the test area of about 8 times the current limits. “With more efficient limits, all NGSO systems will be able to provide a better service to Romanian citizens in the future while protecting important GSO services,” said ANCOM. The regulator will present the results of the test at ITU meetings at European and international level, as part of Romania’s contribution to the ongoing EPFD studies.
Then back to the ITU
The ITU is the UN body which, through the World Radiocommunication Conference (WRC), is responsible for the analysis and, if necessary, revision of the Radio Regulations (RR), the international treaty governing the allocation of GSO and the use of the related radio spectrum and that allocated for NGSO.
The last WRC was held in Dubai at the end of 2023 and at the meeting the decision was made to invite: “ITU-R to conduct technical studies on the EPFD limits in RR Article 22, including the EPFD limits in RR Article 22.5K, while still ensuring the protection of FSS and BSS geostationary networks, and to present the results, without regulatory area implications, in 4 years time at WRC-27.”
Romania believes that bridging the digital divide and ensuring connectivity requires the joint use of geostationary and non-geostationary communication satellites. ANCOM said it is important for these steps to determine whether the EPFD limits provided for in RR Article 22 are adapted to the new growing allocation requirements, bearing in mind that a balanced and efficient use of orbital and spectrum resources must be ensured.
“Equally important is the adoption of a regulatory framework in line with the new realities, which will continue to ensure the protection of geostationary networks, while at the same time allowing the full potential of non-geostationary networks to be harnessed,” said the regulator.