February 17, 2017–Ligado Networks LLC said that a 428-page report released this week by the National Advanced Spectrum and Communications Test Network (NASCTN) on the impacts of LTE signals on GPS receivers validates that the LTE network Ligado wants to deploy can operate without harming the performance of GPS devices. Company representatives said the report completes the record in the FCC’s Ligado proceeding, and they said the agency should move ahead to act on its authorization request.
“Ligado’s very pleased that NASCTN has issued its report on the compatibility of GPS devices with LTE deployed in adjacent bands. We’re looking forward to reviewing fully this comprehensive and extensive collection of data, but our initial review indicates that this data supports the conclusion reached by the major GPS companies over the last 14 months: And that conclusion is that a Ligado network built to the specifications proposed in the pending FCC application can operate alongside GPS devices without harming the performance of GPS,” Valerie Green, Ligado’s executive vice president and chief legal officer, told reporters during a conference call.
“The NASCTN report is really the last piece of information that the regulatory decision-makers like the FCC need to move forward with Ligado’s pending application. This government report is objective, and it is impartial,” she said.
“This report completes the technical evaluation of how Ligado proposes to use its spectrum for ground-based services, and is the last in a long line of testing by multiple stakeholders,” Doug Smith, the company’s president and chief executive officer, said in a statement. “The regulatory decision-makers now have the information they need to make this 35 MHz of vital mid-band spectrum available to serve critical American infrastructure needs and deliver substantial economic benefits to our nation.”
The NASCTN testing was conducted under a Cooperative Research and Development Agreement. NASCTN was established in 2015 by the National Institute of Standards and Technology, the National Telecommunications and Information Administration, and the Department of Defense to look for ways to increase access to spectrum for commercial and federal government entities (TRDaily, March 25, 2015).
“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,” a summary of the project noted. “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).”
“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,” the summary noted. “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.”
“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,” the summary said. “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 report presents a huge amount of data, including numerous plots of test results, but it does not reach conclusions about whether LTE signals would cause harmful interference to GPS devices.
“The two primary goals of this report were to document a test methodology that allows the measurement on the impact to global positioning system (GPS) receivers from adjacent band long-term evolution (LTE) waveforms and to provide data from a set of GPS receivers subject to the test methodology,” the report stressed. “Data was presented without defining or use of pass/fail criteria as the establishment of those [criteria] was not part of this project.”
The report also does not include findings on the performance of individual devices or antennas. The DUT [device under test] and antenna product identifiers are anonymized in the data presentation,” it noted. “This allows the reader to make informed decisions on DUT performance independent of manufacturer knowledge. Although the GPS receiver products are listed in the report, product names will not be reported in conjunction with the data. Moreover, the intent of this report is to focus on the effects of LTE signals on GPS based receivers as classified by device functional capability of devices instead of by manufacturer. Therefore, devices are simply given an identification number as well as an antenna identification letter.”
Ms. Green said that in showing that Ligado’s proposed LTE network would be able to operate without degrading GPS devices, the report confirms Ligado’s argument that a 1 dB increase in the noise floor is not the appropriate standard for assessing harmful interference to GPS receivers. What matters is the actual performance of the devices in the presence of LTE signals, Ms. Green said.
For example, she pointed to findings in the report that indicate that large changes in the carrier-to-noise density ratio don’t impact the performance of GPS devices and seem unrelated to the power levels of LTE signals. However, the Department of Transportation and GPS manufacturers such as Trimble Navigation Ltd., Garmin International, Inc., and Deere & Company have supported the 1 dB standard, even though those companies and two other GPS manufacturers have reached agreements with Ligado on the operating parameters for its planned LTE network.
Trimble, Garmin, and Deere and DoT did not respond to TRDaily requests for comment on the NASCTN report.
Gerry Waldron, an attorney for Ligado, drew a distinction between LTE-GPS testing done by DoT and the NASCTN testing. “One looked to a proxy for impact, and that’s change in the noise level … and the other one directly measured the performance of the device,” he said, with DoT’s study using the proxy. “We think this test is, frankly the gold standard of testing because it is repeatable and verifiable,” he said.
The Ligado representatives were asked about when they hope the FCC will act in its proceeding. “Chairman [Ajit] Pai has clearly shown a willingness to take action” on issues, Mr. Waldron said. “We also know that he is very serious about the Commission deciding things as opposed to lingering for a long time.”
“Obviously, they’re on their own timing, but, you know, we think that this … gives them the information that they need to make a decision,” Mr. Waldron added.
Mike Wendy, president of MediaFreedom, said of the NASCTN report, “A preliminary reading of the lengthy, multi-stakeholder technical evaluation reveals that Ligado [Networks’] proposed satellite/ground-based LTE network would be compatible with GPS devices in adjacent spectrum bands. This finding would go a long way toward boosting Ligado Networks’ broadly-endorsed proposal. With NIST’s new evaluation, the FCC now has the information needed to move forward on Ligado’s important, spectrum-crunch-alleviating plan.” – Paul Kirby, firstname.lastname@example.org