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GPS Adjacent Band Compatibility Assessment

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.

In 2012, the National Executive Committee for Space-Based Positioning, Navigation, and Timing proposed to draft new GPS spectrum interference standards to inform future proposals for non-space, commercial use of the bands adjacent to the GPS signals.

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.

NPEF 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.

The NPEF evaluated five tests performed by the following organizations:

  1. Federal Communication Commission (FCC)-mandated Technical Working Group (TWG)
  2. National Space-Based PNT Systems Engineering Forum (NPEF)
  3. Department of Transportation (DOT)
  4. Roberson and Associates (RAA)
  5. 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.

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

NOTE: If you are seeking information about the National Advanced Spectrum and Communications Test Network (NASCTN) testing of LTE impacts to GPS devices, which was independent of the DOT testing, please visit the NASCTN website.

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.

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.