Pentagon and Ligado clash over claims of satellite interference

A new commercial 5G mobile broadband scheme from Ligado Networks has raised hackles in the DoD, which argues that it encroaches on parts of the L-band spectrum that are essential for military SATCOM and GPS operations.

The licencing proposal from Ligado was approved by the Federal Communications Commission (FCC) in 2020, prompting the Pentagon to block it.

Press reports in September 2022 indicated that the company’s network could be operationalised as early as October — but a recent DoD-backed study from the National Academies of Science, Engineering and Medicine (NASEM) outlined multiple problems.

If Ligado deploys its low-powered terrestrial services, the commercial network would ‘interfere with GPS capabilities essential for DoD’s mission execution’ and harm ‘high-precision DoD GPS receivers’, NASEM concluded.

It added that the commercial 5G network would threaten the military Iridium SATCOM service ‘along with equipment transmitting in the Uplink 1 band’.

The FCC has not responded to the analysis. ‘We were not asked to comment on the FCC’s [position] and did not,’ a NASEM study contributor told Shephard.

Neither side is open to correcting or modifying the Ligado system. 

Ligado had not responded to requests for comment at the time of writing, but on its website the company insists that its monitoring GPS satellites and receivers ‘can co-exist’ with military systems and will actually minimise dangers to national security.

The DoD, in contrast, believes that in-house interference measuring and testing capabilities are ‘more comprehensive and informative’ than others.

The NASEM report also dismissed mitigation measures as ‘impractical, cost prohibitive, and possibly ineffective’, although Ligado countered that only a few ‘poorly-designed and very old [circa 2012] GPS devices’ may need upgrading.

The Association of Old Crows (AOC), an EW and RF organisation, is concerned over the power levels from Ligado’s signals. ‘Weak GPS signals travelling through the Earth’s atmosphere from satellites are easily interfered with, or overcome, by the higher power “noise” of signals from Ligado’s ground stations,’ it asserted.  

Changes will compel the DoD to ‘redesign and rebuild its GPS infrastructure, [costing] taxpayers billions … and taking years to complete’, the AOC added.

Ligado still hopes that the DoD will remove its block and cooperate instead on resolving what it describes as ‘potential impacts relating to all [DoD] systems, including but not limited to GPS’.

The company is urging federal agencies to contact Ligado under existing legacy repair-or-replace agreements.

A compromise is not impossible even if Legado and the Pentagon seem willing to move from their core positions. One of the co-authors of the NASEM report told Shephard that ‘dialogue between potentially affected parties and Ligado is going to be necessary’.