Administrations around the world have recognized that today’s Article 22 epfd limits are outdated and require reevaluation. But those administrations also understand the important ITU process that must be followed in order to contemplate any changes to the Article 22 framework. Epfd rules are contained in the Radio Regulations, which can only be modified by the World Radiocommunication Conference, so any update to epfd limits must be considered at WRC-27. The WRC-27 agenda will be adopted at WRC-23, so many administrations at WRC-23 are seeking a Future Agenda Item for WRC-27 to study the current Article 22 rules requiring non-GSO FSS systems to protect GSO FSS and BSS networks from unacceptable interference in certain frequency bands.
Why is a WRC-27 agenda item on epfd necessary? Can’t administrations study any topic they wish at any time?
Epfd rules are contained in the Radio Regulations, which can only be modified by the World Radiocommunication Conference, so any update to epfd limits must be considered at WRC-27. Without an agenda item, the most that studies can lead to is an ITU-R Recommendation or Report, and NGSO systems would still have to meet the Article 22 epfd limits adopted at WRC-2000.
Will an epfd agenda item pose a risk to the operations of GSO operators? Will changing longstanding rules impact the missions GSO satellites fulfill, such as communications, scientific, civic, and defense/security services?
No. First, the proposed epfd agenda item underscores that no matter the outcome of the studies, the core principle of Article 22.2—that NGSO systems must not cause unacceptable interference to GSO networks—will not change. The proposal explicitly states that “Changes to No. 22.2 are beyond the scope of the proposed new agenda item” and resolves to “ensure the protection of GSO networks as required by the ITU Radio Regulations.” Rather, the scope of the agenda item would study more appropriate technical parameters to ensure continued implementation of that fundamental principle.
Second, consistent with customary ITU process, any proposed modifications to epfd rules at WRC-27 will be based on the studies responding to the agenda item. Those studies may or may not support regulatory revisions, and stakeholders should not prejudge today the outcomes of the studies.
What are “aggregate” epfd limits, and why it is more important to study the Article 22 framework before resolving the aggregate issue?
Article 22 of the Radio Regulations contains provisions ensuring the compatibility of NGSO operations with GSO networks. The ITU Radiocommunication Bureau examines NGSO filings and determines whether they comply with the single-entry EPFD limits. Administrations are responsible for ensuring the actual aggregate interference into geostationary satellite networks does not exceed the aggregate EPFD limits (constraints on cumulative interference across all co-frequency NGSO FSS systems).
One agenda item at WRC-23 seeks to establish a consultation process to ensure compliance with aggregate epfd levels. But rather than establish an “aggregate” consultation process now, it is more important to study the entire Article 22 framework (both single-entry and aggregate) for WRC-27. Today’s single-entry and aggregate limits in Article 22 are interconnected: the existing single-entry limits were derived from the aggregate limits, which assumed there would be a maximum of 3.5 NGSO systems operating. We know today this is not accurate. In order to have a modernized single-entry framework, we simultaneously need to ensure that the aggregate framework is correct and consider modern technology and modern spectrum management techniques such as long-term protection limits.
Satellite systems are designed with an interference margin to accommodate spectrum sharing, which is accomplished through coordination or hard limits. Equivalent power flux-density (epfd) limits, as defined in Article 22 of the International Telecommunication Union Radio Regulations, are a mechanism to limit interference from non-geostationary satellite systems into geostationary-satellite networks in certain frequency bands without coordination. The Article 22 epfd limits apply to NGSO emissions, which vary in time and space, and include downlink (into the geostationary earth receiver), uplink (into the geostationary space station receiver), and inter-satellite (also into the geostationary space station receiver) limits.
Geostationary satellite networks generally coordinate their operations if the established criterion (ΔT/T of 6%) is exceeded. A non-geostationary satellite system that meets the epfd limits is considered to have fulfilled its obligation not to cause unacceptable interference to any geostationary-satellite network.
The current epfd limits in use today were adopted provisionally at WRC-97 and revised at WRC-2000. They were based on the characteristics of GSO networks conceived in the early-to-mid 1990s and particular NGSO systems in the Ku and Ka band that were never realized. Satellite technology and spectrum management principles have changed a lot since then, but the rules have not kept pace.
The current epfd limits were already calculated to make sure that no unacceptable interference to GSO satellites occurs. Why do they need to be reevaluated?
Technical studies show that the current epfd limits require that NGSO systems protect GSO networks far beyond the standard used to determine whether coordination between GSO networks is even necessary. Setting the bar for unacceptable interference so low has consequences. The epfd limits constrain NGSO operations at the expense of communities who need broadband access, restricting competition and more intensive use of spectrum resources. To be clear, any revision to the epfd limits would still ensure geostationary networks would be protected from unacceptable interference.
When the limits were determined nearly 25 years ago, satellite technology was vastly different. Modern day NGSOs and GSOs are able to share spectrum more efficiently, and modern day GSOs do not require these legacy restraints from NGSOs in order to be protected. The epfd limits should be re-examined.
How do current epfd limits impact satellite broadband? How will updating epfd limits improve connectivity?
Current epfd limits prevent NGSO satellite constellations from operating at their fullest potential, restricting certain nodes within a constellation and creating an “exclusion zone.” NGSO customers affected by these exclusion zones cannot receive coverage from the closest and most readily available satellites in an NGSO constellation. Without the ability to utilize all of the available satellites in a constellation, the capacity of an NGSO satellite constellation is significantly reduced. The size of this “exclusion zone” could be reduced if WRC-27 revises the epfd limits.
NGSO satellites can provide low-cost, high-speed broadband services across the entire globe, and with updated epfd limits, NGSOs could operate at increased capacity and reach communities that are currently unserved or underserved by existing broadband technology. The ability to operate with more consumers and utilize spectrum more efficiently would also help reduce costs of satellite broadband. This would be a game changer for closing the digital divide.
Will changing longstanding rules impact the missions GSO satellites fulfill, such as communications, scientific, civic, and defense/security services?
Updating epfd limits will not impact the cornerstone of Article 22, which indicates that NGSO systems shall not cause unacceptable interference to GSO networks. Any future studies shall ensure protections to GSO networks.
Agreeing to the future agenda item commits ITU Member States to studying the frequency bands where epfd limits apply and developing potential updates on both technical and regulatory aspects. Based on the results of those studies, the ITU will make recommendations, as appropriate, for addressing epfd limits in time for the next World Radiocommunication Conference, WRC-27. As the limits in Article 22 are part of the international Radio Regulations, they can only be changed by WRC actions, making a WRC Agenda Item on this issue critical.