Equivalent power flux density

Equivalent power flux density (EPFD) is a quantity used in satellite spectrum-sharing regulation to express the total radio frequency interference that a satellite constellation of non-geostationary orbit (NGSO) satellites produces at a geostationary orbit (GSO) receiving station. It generalizes the simpler concept of spectral flux density to systems with many simultaneously visible transmitters.

EPFD weighs each transmitter's contribution according to the receiving antenna's gain in that transmitter's direction and adding the result across every satellite in view. It is defined in Article 22 of the Radio Regulations of the International Telecommunication Union (ITU) and in corresponding national rules, such as FCC regulations in the United States, where it has historically been used to determine whether an NGSO fixed-satellite service (FSS) system may share frequencies with GSO satellites without individually negotiated coordination agreements.