Analysis of Potential Interference Issues Related to FCC Order 20-48

On April 19, 2020, the Federal Communications Commission (FCC) adopted order 20-48 authorizing Ligado Networks, LLC, to move forward with the deployment and operation of a low-power terrestrial nationwide radio network. The complexity of this region of the spectrum, including its adjacency to Global Positioning System (GPS) and other satellite services and the variety of commercial, economic, and national security interests involved has led some parties to question the analyses and assumptions underlying the FCC order. The motivation for this study and report is the possibility that emissions by the Ligado system as it would be deployed in accordance with the terms authorized in FCC 20-48 might disrupt GPS or MSS services. At issue are two simple facts: (1) radio-frequency transmitters do not operate with arbitrarily sharp cutoff frequencies and thus, depending on how rapidly (as a function of frequency) their emitted power spectrum falls off, may emit power beyond their authorized spectral bands; and (2) receivers of electromagnetic spectrum do not "listen" only within a band defined with arbitrarily sharp boundaries and thus may receive power from frequencies outside their designed band. The FCC's goal is to enable as much productive use of valuable spectrum resources as possible, balanced against the deleterious impacts that may arise when adjacent signals cause receivers to experience interference