What are equivalent power flux-density (EPFD) limits?

Satellite systems are designed with an interference margin to accommodate spectrum sharing, which is accomplished either through coordination between the concerned systems or hard limits. EPFD limits, as defined in Article 22 of the International Telecommunication Union (ITU) Radio Regulations, are a mechanism to limit interference from NGSO systems to GSO systems in certain frequency bands without coordination. The Article 22 EPFD limits apply to NGSO emissions and include downlink (into the geostationary earth receiver), uplink (into the geostationary space station receiver) and inter-satellite limits. An NGSO satellite system that meets the EPFD limits is considered to have fulfilled its obligation not to cause unacceptable interference to any GSO network.  

The current EPFD limits in use today were adopted provisionally at WRC-97 and revised at WRC-2000. The limits were based on the characteristics of GSO networks conceived in the early-to-mid 1990s and theoretical NGSO systems in the Ku and Ka bands that were never developed. Satellite technology and spectrum management principles have changed a lot since then, but the rules have not kept pace.

WRC-23 invited the ITU to perform studies of EPFD limits and asked for results to be presented to WRC-27 — a win for innovation. Regulators from around the world are now conducting these technical studies. The next step is to objectively consider the results of these studies at WRC-27 and then modernize the limits accordingly.

EPFD rules are contained in the Radio Regulations and can be modified by the WRC on a global basis. ITU members can submit proposals for modernizing EPFD limits based on the results of studies that will be reported to WRC-27.

No. The core principle of Article 22.2 – that NGSO systems must not cause unacceptable interference to GSO networks – is uncontested. The scope of the studies mandated by WRC-23 would address more appropriate technical parameters to ensure the continued implementation of Article 22.2. Any proposed modernization to EPFD rules will be based on the objective consideration of studies put forth before the conference. Modernized EPFD limits would still protect GSO systems. 

What are “aggregate” EPFD limits?

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 individually comply with the single-entry EPFD limits. In addition, ITU member states are responsible for ensuring the actual aggregate interference from all NGSO systems into GSO networks does not exceed the aggregate EPFD limits (constraints on cumulative interference across all co-frequency NGSO systems). The single-entry limits were historically derived from the aggregate limits and WRC-23 called for studies of both. The ITU-R, in accordance with a separate mandate, is also studying the process for ensuring that the different NGSO systems comply with aggregate limits.

The current EPFD limits were conceived based on GSO operations from over 25 years ago and decades before today’s NGSO operators even launched, making them truly obsolete. The current EPFD limits are overly conservative and require that NGSO systems protect GSO networks far beyond the standard used to calculate interference between GSO networks. Setting the bar for interference so low is not only an inefficient use of spectrum but also has consequences. The EPFD limits constrain NGSO operations and restrict competition at the expense of communities that need broadband access. To be clear, any revision to the EPFD limits would still ensure GSO networks would be protected from unacceptable interference. 

Modernized EPFD limits can help to realize the full potential of NGSO networks, enabling all regions to expand connectivity in four ways: 

  1. Rural and remote coverage: In areas where deploying terrestrial networks is not feasible, satellite broadband delivers a fast and reliable service directly to consumers who might otherwise wait years for costly fiber trenching or base station construction.
  2. Backhaul connectivity: Broadband needs to be connected via “middle-mile” infrastructure that connects a local network to national and international networks. NGSO satellites can provide more robust and cost-effective network operations by acting as the middle mile.
  3. Network redundancy: When major network systems come under stress from overuse, natural disasters or technology problems, NGSO internet is an option to turn to. This is especially crucial to customers in regions where internet services are unstable.
  4. Affordability: NGSO satellites increase competition and capacity, making broadband more affordable through competitive pricing, community networks and other delivery models. In areas without terrestrial infrastructure, the cost of GSO broadband has often been too high for public services (such as schools and hospitals), households and small businesses.

No. Many countries have projects including satellites in low Earth orbit. 

Modernized EPFD limits would enable more efficient use of spectrum and satellite capacity. Outdated EPFD limits force NGSO operators to under-utilize their satellites, which means more satellites are needed to achieve the same coverage and capacity.  

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.  

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. 

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.

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. 

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. 

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.

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.