Official U.S. government information about the
Global Positioning System (GPS) and related topics
GPS Adjacent Band Compatibility Assessment
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Demand for commercial spectrum to support broadband wireless communications has led the government to consider repurposing various radio frequencies, including the satellite communications bands next to GPS.
The Department of Transportation's (DOT) approach to this task was to develop power limit criteria for transmitters in the bands near GPS.
Final Report
In April 2018, DOT released the final report of its GPS Adjacent Band Compatibility Assessment.
View final report at transportation.gov
Return to top of pageNPEF Gap Analysis
In March 2018, the National Executive Committee released an assessment by its National Space-Based PNT Systems Engineering Forum (NPEF) of testing methodologies used to analyze the impacts of adjacent band interference on GPS receivers.
View NPEF gap analysis (900 KB PDF)The NPEF evaluated five tests performed by the following organizations:
- Federal Communication Commission (FCC)-mandated Technical Working Group (TWG)
- National Space-Based PNT Systems Engineering Forum (NPEF)
- Department of Transportation (DOT)
- Roberson and Associates (RAA)
- National Advanced Spectrum and Communications Test Network (NASCTN)
The gap analysis concluded that the results from three of the five tests are sufficient and appropriate to inform spectrum policy makers on the major impacts of a proposed LTE network on GPS receivers. The DOT test results revealed the power levels that GPS and GNSS receivers can tolerate from interference sources in the adjacent band in an effort to inform the enforcement of a GPS interference protection criterion.
Assessment Plan
The 2012 GPS Adjacent-Band Compatibility Assessment Plan provided the framework for DOT's development of power limit criteria for transmitters in the bands near GPS.
View assessment plan, Dec 2012 (bts.gov)The plan identified the processes to (a) derive power limit criteria to ensure new adjacent-band applications do not disrupt current GPS services and (b) determine similar levels needed for future GPS equipment using modernized and interoperable GNSS signals. These processes were used to develop and specify adjacent-band transmitter power limits needed to protect GPS/GNSS signals for civil applications.
Device Testing
DOT began testing GPS/GNSS receivers in April 2016 pursuant to the final test plan published in March 2016. Device testing took place at the U.S. Army Research Laboratory at the White Sands Missile Range (WSMR) facility in New Mexico. All GPS device manufacturers had an opportunity to participate in the testing.
View test plan, Mar 2016 (500 KB PDF)Go there
A second round of testing occurred in July 2016 at Zeta Associates in Fairfax, Virginia, and MITRE Corporation in Bedford, Massachusetts. The goals of the additional lab testing were:
- (1) Receiver characterization for comparison with results obtained in April at the anechoic chamber at the U.S. Army Research Laboratory;
- (2) Evaluation of Out Of Band Emission (OOBE) interference at prescribed and proposed levels with Long Term Evolution (LTE) uplink and downlink signals;
- (3) GPS/GNSS signal acquisition characterization; and
- (4) Antenna characterizations.
Anechoic chamber test setup
Additional Information:
- July 2017 Letter from PNT Advisory Board to National Executive Committee
- Air Force paper on 1 dB interference threshold (178.4 KB PDF)
- Sept 2016 presentation to CGSIC (821 KB PDF)
- July 2016 testing notice (federalregister.gov)
- April 2016 testing notice (federalregister.gov)
- Draft test plan (bts.gov)
- Public comments on draft test plan (regulations.gov)
Public Workshops
The U.S. Department of Transportation hosted six workshops on the GPS Adjacent Band Compatibility Assessment effort from 2014 to 2017.
- Workshop I, September 2014
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To discuss implementation of the Adjacent-Band Compatibility Assessment Plan, including development of GPS receiver use cases, identification of representative GPS receivers, and development of a test and analysis program.
- Workshop II, December 2014
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Focused on the following topics: (i) GPS "use case" information, with emphasis on non-government applications; (ii) identification of current GPS receivers which are representative of the current categories of GPS applications and which should be considered for testing; and (iii) feedback on the GPS Adjacent Band Compatibility Assessment program implementation plan presented during the September 2014 workshop.
- Workshop III, March 2015
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Focused on the following topics: (i) Identification of GPS and Global Navigation Satellite System (GNSS) receivers to be considered for testing that are representative of the current categories of user applications; and (ii) discussion of a GPS/GNSS receiver test plan.
- Workshop IV, October 2015
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To discuss the draft test plan and provide an opportunity for questions prior to the close of the comment period.
- Workshop V, October 2016
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To discuss the results from testing of various categories of GPS/GNSS receivers to include aviation (non-certified), cellular, general location/navigation, high precision and networks, timing, and space-based receivers. Also included a discussion on the development of use-case scenarios for these categories.
- Workshop VI, March 2017
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To discuss the results from testing of various categories of GPS/GNSS receivers to include aviation (non-certified), cellular, general location/navigation, high precision and networks, timing, and space-based receivers, as well as use-case scenarios for these categories.
