On December 27, 2024, the National Telecommunications and Information Administration (NTIA) issued a Request for Comment (“RFC”)that seeks public input on the potential impacts on the Global Positioning Satellite (GPS) L1 signal by the growth of satellite-based direct-to-device (D2D) operations that use frequencies between 1610-1660.5 MHz (the “L-band”). As the lead spectrum advisor to the Executive Branch on spectrum issues, NTIA serves as the advocate for other agencies including the Department of Transportation (DOT) before the FCC. NTIA issued its Request for Comment (RFC) in response to analysis prepared by DOT and states that its interest in D2D usage stems from the increasing deployment of services in which mobile devices like smartphones and Internet of Things (IoT) devices connect directly to satellite systems in the L-band, a portion of which is located near spectrum allocated to GPS. NTIA invited comments to be filed by February 10, 2025.
In its RFC, NTIA asked parties to discuss the DOT technical analysis as well as options for mitigating any potential impacts on GPS systems while “facilitating the potential benefits” of a growing D2D ecosystem. The FCC has exclusive authority over requirements on L-band operators and their devices, but NTIA could use information gleaned from the comment process to make recommendations to the FCC on whether new spectrum rules are needed. As such, satellite industry stakeholders, device manufacturers, and wireless network providers may want to share their views and educate NTIA about how this band is (and will be) used as well as its potential for coexistence with GPS devices.
The DOT technical analysis included in the RFC builds on a study conducted by DOT in 2018 to analyze Ligado Network’s proposed terrestrial system. In 2020, after receiving comments on the 2018 study, the FCC unanimously concluded that sufficient conditions – such as limited power levels and guard bands – were in place to protect against interference between GPS signals in the 1559-1610 MHz band and a terrestrial wireless network. The technical analysis recently prepared by DOT and included in the NTIA RFC borrows heavily from the 2018 study and largely extrapolates from that study to conclude that D2D operations using the 1610-1660.5 MHz band may cause changes to the carrier-to-noise ratio (e.g., a 1 dB C/No) that could impair GPS receivers operating in the adjacent 1559-1610 MHz band. (It bears mention that DOT for many years has urged the FCC to protect GPS devices from a 1 dB change in the carrier-to-noise ratio, but the FCC has not agreed with that recommendation and instead has applied its rules on harmful interference. See generally In the Matter of Lightsquared Technical Working Group Report et al., 35 FCC Rcd. 3772 ¶¶ 37-59 (2020).The RFC seeks comment on this DOT analysis and encourages stakeholders to file any alternative technical analyses relevant to D2D operations in the L-band and the potential effects on the GPS L1 signal.
NTIA’s request comes in the context of satellite companies using this band for nearly thirty years to provide mobile satellite services (“MSS”). And for the past few years, some L-band satellite companies have been working with prominent wireless companies and device manufacturers to provide satellite-based mobile services to widely deployed wireless handsets. NTIA’s request for comments indicates a concern that the current emissions standards for D2D L-band devices are based on the historical “expectation that comparatively few user devices would be deployed relative to ubiquitous terrestrial mobile handsets.”. Specifically, the RFC notes that NTIA and other U.S. Government departments and agencies assumed there would be relatively few mobile receivers operating in the L-band.
NTIA asks for comment on the concern that that the “wide deployment of devices subject to the [current emissions standards] thus presents an unexpected increase in the risk of interference to nearby GPS receivers.” One of the “situations of greatest concern” to NTIA is the use of D2D-capable L-band devices on airplanes, which the RFC references as a scenario in which these devices would be operating in relative proximity to certified GPS devices supporting aircraft navigation systems.
NTIA’s RFC solicits feedback on several key areas related to D2D operations in the L-band frequencies, their potential impacts on the GPS signal adjacent to these MSS systems, and potential mitigation options. Specifically, the RFC seeks the following input:
- From parties deploying or planning to deploy D2D service in the L-band, the RFC asks for comments on:
- Current out-of-band emissions and potential mitigations to address impact on GPS devices;
- L-band transmission characteristics;
- expected geographic deployment patterns for initial D2D service offerings, planned service expansions, and typical use environments;
- other information relevant to an evaluation of the likelihood that an L-band device will cause “harmful interference” to a nearby GPS receiver; and
- measures to mitigate harmful interference to nearby GPS receivers and user education on the risks of operating near critical GPS receivers.
- From GPS manufacturers and users, the RFC seeks information about:
- Any documented instances of harmful interference from MSS L-band devices;
- their concerns regarding the increased probability of harmful interference; and
- any mitigations that might be effective in reducing the risk of harmful interference while minimizing impacts on MSS service delivery.
- And from all interested parties, the RFC requests input:
- On what industry standards and improvements have been put in place by the GPS industry over the last ten years to protect GPS receivers and minimize receiver blocking and overload. Protective improvements include:
- separation distances due to receiver selectivity, in contrast to the separation distances due to MSS L-band MES OOBE, and
- GPS receiver overload limits.
- On the Department of Transportation technical analysis.
- On what industry standards and improvements have been put in place by the GPS industry over the last ten years to protect GPS receivers and minimize receiver blocking and overload. Protective improvements include: