A report by the National Academies of Sciences (NAS) found that while most GPS receivers won’t face interference from Ligado’s wireless network, Iridium’s mobile satellite services used by the DoD would likely see “harmful interference.” The congressionally mandated report assessed the likelihood of harmful interference from Ligado Networks’ authorized use of the L-band near frequencies used by GPS and other satellite services.
The FCC authorized Ligado, a private satellite communications company, to use the L-band in 2020, over the objections of the DoD and other federal agencies, Inside Towers reported. Ligado has 40 MHz of spectrum licenses in the 1500 MHz to 1700 MHz of the L-Band. L-band is one of the chief operating ranges used by various applications such as radars, GPS, radio, telecommunications and aircraft surveillance.
The report says Ligado’s wireless network operations won’t cause most commercially produced general navigation, timing, cellular, or certified aviation GPS receivers to experience harmful interference. However, some high-precision receivers sold before 2012 can be vulnerable to what the NAS calls “significant” harmful interference. In addition, certain mobile satellite services provided by Iridium Communications Inc. and used by the DoD and others will experience harmful interference under certain conditions.
Because of the commercial, economic, and national security interests involved, and questions over whether signals from Ligado transmitters could disrupt critical services, Congress, through the DoD, requested a study from NAS. The committee’s task did not include consideration of whether the FCC reached a correct outcome in authorizing the Ligado system.
The report recommends that the FCC and NTIA take a more collaborative approach to resolving spectrum issues, such as joint study and testing of proposed changes to spectrum use. The NAS also recommends the development of definitive receiver performance standards, and establishment of specific time spans with adherence to those standards.
In response to the report, NTIA said the NAS notes that a number of the FCC’s mitigations to prevent interference would be practically unworkable. “NTIA will review this detailed report more carefully, but we believe this offers the Commission an important opportunity to reconsider Ligado’s authorization,” it said in a statement.
By Leslie Stimson, Inside Towers Washington Bureau Chief
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