Since the U.S. Federal Communications Commission (FCC) in 2020 authorized Ligado Networks to use radio frequency spectrum near GPS and satellite service bands, aviation and other industry groups have asked the FCC to rescind the order. However, a report requested by Congress raises new questions about whether Ligado’s operation in the L-band will deleteriously affect GPS receivers used in aviation and by the military. The report was conducted by the National Academies of Sciences, Engineering, and Medicine.
Although fairly detailed and filled with complex calculations of the possible effects of Ligado’s broadcasts in the L-band, the report concludes that “use of radio frequency bands…by Ligado Networks…will not cause most commercially produced general navigation, timing, cellular, or certified aviation GPS receivers to experience harmful interference. However, some high-precision receivers, used for applications such as farming, geodesy, and surveying and sold before about 2012, can be vulnerable to significant harmful interference. In addition, certain mobile satellite services provided by Iridium Communications Inc. and used by the U.S. Department of Defense and others will experience harmful interference under certain conditions.”
The report further concluded: “It is within the state-of-the-practice of current technology to build a receiver that is robust to Ligado signals for any GPS application, and all GPS receiver manufacturers could field new designs that could coexist with the authorized Ligado signals and achieve good performance even if their existing designs cannot.”
Military GPS remains vulnerable, the report concluded. “The terrestrial network authorized by FCC Order 20-48 will create unacceptable harmful interference for DoD missions. The mitigation techniques and other regulatory provision in FCC Order 20-48 are insufficient to protect national security missions,” it says.
The report also notes: "This study was not charged with considering whether the FCC reached a correct outcome in authorizing the Ligado system."