Impact of LTE Signals on GPS Receivers

Summary

The National Advanced Spectrum and Communications Test Network (NASCTN) has completed the Impacts of LTE Signals on GPS Receivers project and has released the NASCTN report LTE Impacts on GPS  along with the measurement data associated with this project.

Description

To better understand the potential impact of adjacent-band LTE signals on GPS receiver performance, NASCTN developed a draft test plan designed to measure how the performance of GPS receivers changed as a function of increasing LTE signal power relative to a baseline with no LTE emissions.

NASCTN testing included several measurands: carrier-to-noise density (C/N₀), 3D position error, timing error, number of GPS satellites in view, time to first fix and time to first reacquisition.  

The NASCTN test plan focused on GPS devices from four different receiver classes – general location and navigation (GLN), high-performance positioning (HPP), real-time kinematic (RTK), and GPS-disciplined oscillator (GPSDO). 

A cross-section of regulators, Federal agencies and GPS manufacturers reviewed the NASCTN test plan and provided technical comments, which NASCTN used to prepare a revised test plan, which was released in July of 2016.

Over a three-month period, NASCTN performed the radiated measurements associated with this project at two facilities – a semi-anechoic chamber at National Technical Systems (NTS) in Longmont, CO and at a fully-anechoic chamber at the NIST Broadband Interoperability Testbed (NBIT) facility in Boulder, CO.

NASCTN relied on technical staff from NIST and the U.S. Army’s Electronic Proving Grounds to perform and validate the measurements and collect the data. The team was multi-disciplinary, including expertise in GPS devices and simulation, radiated radio-frequency measurements, timing measurements, microwave metrology, statistical analysis and data processing.

In total, NASCTN performed 1,476 hours of testing and collected over 19,000 data files for a variety of measurands that were collected from a number of GPS devices. These data were collected at a baseline condition (no LTE signals present) and over a large range of LTE signal power levels.  Subsequent data processing yielded a set of 3,859 anonymized data files (780 MB) that is available along with the NASCTN report.

The project was conducted under a Cooperative Research and Development Agreement (CRADA) between NIST and Ligado Networks. A CRADA is the principal mechanism used by Federal laboratories to engage in collaborative efforts with non-Federal entities and allow the exchange of resources with private industry to advance technologies that can then be commercialized for the benefit of the public and the U.S. economy.

 

Project Time Table

Framework Stage	Information
Spectrum Community Engagement and Awareness	Due to the significant interest of regulators, Federal agencies, and the GPS community in these measurements for assessing LTE signals on performance of GPS devices, NASCTN held a Public Brief on the project in May 2017, as well as a brief for the PNT advisory board in June 2017.  NASCTN GPS Project Final Briefing June 2017 Briefing to PNT Advisory Board
Stage 4:  Summarize Findings	NASCTN Report 1 - Impact of LTE on GPS
Stage 3:  Test Execution	LTE Impacts on GPS Data Set
Stage 2:  Test, Metrology, and Implementation Plan	Revised Test Plan Draft Test Plan Adjudicated Comments Supplemental Information
Stage 1:  Proposal Screening	A proposal was submitted and approved by the NASCTN Steering Committee.

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