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.
What happened at WRC-23 regarding EPFD limits? And what will happen at WRC-27?
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 and then modernize the limits accordingly at WRC-27.
How can EPFD limits be changed at WRC-27?
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.
Will modernizing EPFD limits 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. 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 already calculated to make sure that no unacceptable interference to GSO satellites occurs. Why do they need to be reevaluated?
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.
How will updating EPFD limits improve connectivity?
Modernized EPFD limits can help to realize the full potential of NGSO networks, enabling all regions to expand connectivity in four ways:
- 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.
- 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.
- 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.
- 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.
Will modernized EPFD limits only benefit American companies?
No. Many countries have projects including satellites in low Earth orbit.
What is the relationship between EPFD limits and space sustainability?
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.
