Inside GNSS Media & Research

JUL-AUG 2018

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22 Inside GNSS J U L Y / A U G U S T 2 0 1 8 Push to Change the Rules e "empirical testing" Ligado referred to are studies done by Roberson and Associates and the National Advanced Spectrum and Communications Test Net work (NASCTN). Ligado spon- sored those studies and, in the case of NASCTN, helped frame the research itself. e tests, however, did not meet the minimum criteria to be useful for judg- ing interference according to the Nation- al Space-Based PNT Systems Engineer- ing Forum (NPEF), a panel of technical experts drawn from more than a dozen agencies. e NPEF report was released in March by the nation's leading GPS policy body — the National Executive Committee (ExCom) for Space-Based Positioning, Navigation, and Timing (PNT). It was the ExCom that requested the NPEF study. The NPEF team found the scope and framework of the Roberson and NASCTN tests were insufficient when evaluated against a set of minimum criteria. A key element in that criteria was the use of the globally accepted 1 dB degradation Interference Protection Criterion (IPC) — that is problematic interference exists when there is a one- decibel (1 dB) decrease in C/N 0 , the car- rier-to-noise power density ratio. Ligado has been seeking to redefine the yardstick for determining interfer- ence to a much more favorable metric: a change in positioning and timing accu- racy as experienced by the user. They laid out what was at stake in getting the FCC to adopt their approach over the internationally-accepted 1 dB IPC standard — hinting at the possibility of a fight over compensation and asserting that a decision in favor of the 1 dB stan- dard could undermine sharing in other bands aimed at supporting 5G telecom applications. Sticking with the 1 dB IPC stan- dard would "preclude Ligado's use of this spectrum in a manner consistent with its existing ATC authorization," the firm wrote, adding in a footnote t hat "use of t he IPC would destroy any commercial utility of the Lower Downlink Band, constructively nulli- fying Ligado's authorization to use of the spectrum without affording Ligado the required administrative procedures or compensation." Ligado then asserted there was more at stake than just the fate of its network proposal. "Use of the IPC would be inconsis- tent with spectrum regulations," the Ligado team wrote, and "also would block use of spectrum adjacent to GNSS on either side of the allocation for more than 60 megahertz for any commercial purpose, and imperil spectrum identi- fied in the Spectrum Pipeline Act of 2015." In response to a question from Inside GNSS, Ligado said it was referring to uses for 5G applications. e firm explained in a footnote that using the 1 dB IPC standard could limit the use of the 1300-1370 MHz band, which is under study for use for ter- restrial wireless service. "is "Pipeline Spectrum" could enable the commercial wireless sector to expand into additional spectrum and provide additional ser- vice," the firm said. "The Commission is considering authorizing use of the Galileo GNSS system in the U.S., including one sig- nal at 1260-1300 MHz, directly adja- cent to the Pipeline Spectrum," Ligado wrote. "Transposing DOT's applica- tion of the 1 dB standard to the L-band to Galileo, if spectrum regulators use the 1 dB metric to protect Galileo, it will render substantial portions of the Pipeline Spectrum essentially unus- able." GPS Manufacturers Say 'No' Ligado's asser t ion t hat i mpac ts to receiver accuracy are the better yard- stick for measuring interference has been rejected by the Air Force, which runs the GPS system; the DOT, which did the ABC Assessment and relies on GPS to support air, rail and other sys- tems; and the National Space-Based Positioning, Navigation, and Timing Advisory Board (PNTAB), the nation's leading satellite navigation experts. e PNTAB set the minimal criteria used by the NPEF to assess NASCTN, Rob- erson and three government studies. Perhaps as importantly from a pol- icy-making perspective, Ligado's posi- tion in favor of using accuracy impacts — so called key performance indicators (KPIs) — has been rejected by the three GPS manufacturers Ligado settled a $1.9 billion lawsuit with in 2015. Ligado has repeatedly pointed to its deals with GPS receiver manufacturers as evidence that it's worked out interfer- ence issues with the GPS community as a whole. "The agreements with the major GPS device manufacturers, along with t he t housa nds of hou rs of test i ng, show that GPS devices will not experi- ence harmful interference as a result of Ligado's revised power and out of band emissions levels," the firm said in its July 9 comments. That sa me day Trimble Nav iga- tion, John Deere and Garmin told the FCC that, while they had agreed not to oppose Ligado's terrestrial plan as long as certain criteria were met, their agree- ments did not include backing Ligado's KPI-based interference standard. Deere said "its position with respect to Ligado's Amended Modif ication Applications must not be interpreted as acquiescence in, or in any way agree- ment with, Ligado's continued efforts to depart from long-accepted practice and establish a new metric for determining potential harm to GPS and other GNSS systems based on Key Performance Indicators ("KPIs"). Deere does not agree with this approach and reaffirms its staunch support for application of WASHINGTON VIEW Ligado has been seeking to redefine the yardstick for determining interference to a much more favorable metric : a change in positioning and timing accuracy as experienced by the user.

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