Inside GNSS Media & Research

MAY-JUN 2018

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18 Inside GNSS M A Y / J U N E 2 0 1 8 Final Report On GPS-Protective Power Limits Published N early a year later than expected, federal officials have published the final report of a study on the power levels GPS receivers can tolerate from activities in neighboring bands — a key factor in the kind of new applications that could be approved for those nearby frequencies. e report may also inform the Federal Communications Commission's pending decision on a proposal from Ligado Networks to add a potentially significant ground network to its system using frequencies zoned for satellites. Originally planned for release in May 2017, the Department of Transportation's Adjacent Band Compatibility Assessment (ABC Assessment) tested 80 GPS receivers of six different types — general aviation (non-certified), general location/navigation, high precision, cellular, timing and space based. ese receivers are used for applications ranging from precision agriculture and earthquake monitoring to personal navigation, satellite navigation, weather forecasting, emergency response and the smooth operation of infrastructure like cell phone systems and financial networks. Both the U.S. government and industry provided the GPS/ GNSS receivers for this test. ough a list of the receivers and a great many details about the testing are included in the report some of the data is covered by nondisclosure agreements with industry — a fact that Ligado Networks has taken issue with in public forums. e Department of Defense also conducted tests as part of the overall effort as did the Federal Aviation Administration (FAA). e FAA tested certified aviation receivers, the sort used in passenger and other types of aircra. Civilian hobby drones and commercial unmanned aircra, a huge prospective market for GPS receivers worldwide, typically use non-certified receivers. e National Executive Committee for Space-based Posi- tion, Navigation and Timing (the ExCom) proposed the assess- ment in 2012 aer tests showed a proposed broadband network would overload the vast majority of GPS receivers. at network was the idea of Virginia-based LightSquared, which needed the Federal Communications Commission (FCC) to allow frequen- cies adjacent to the GPS band — frequencies zoned to support satellites — be used for a high-powered terrestrial network. Aer the tests the FCC chose to set the proposal aside and LightSquared soon filed for bankruptcy, emerging a few years later with a modified plan and a new name, Ligado Networks. "We propose to dra new GPS Spectrum interference stan- dards," wrote the ExCom co-chairs, "that will help inform future proposals for non-space, commercial uses in the bands adjacent to the GPS signals and ensure that any such proposals are implemented without affecting existing and evolving uses of space-based PNT services vital to economic, public safety, scientific, and national security needs." e report gathers together results and adds details on how the study team arrived at interference tolerance masks (ITMs) — that is the maximum level of power a GPS receiver can toler- ate from a device in an adjacent band at different frequencies. e tests focused on an LTE signal (i.e. 4G mobile telecom- munications) with researchers assessing the impacts of signals from large (macro) and small (micro) LTE cells in the urban Navigation within Track D: Applications to Automated, Semi-Autonomous, and Fully-Autonomous Systems. Z ak M. Kassas, professor at the University of California-Riverside and chair of Track D, kicked off the track and shared the sad news with attendees before the sessions got underway. "It is wit h de ep s adness t hat I announce the passing of Dr. Per Enge," said Kassas. "Per changed a lot of lives in this community and made tremendous contributions to the field of navigation. I offer my sincere condolences to his family and his colleagues and students at Stanford University." 360 DEGREES Deploy- ment Stand off distance (m) Max Tolerable EIRP (dBW) GLN HPR TIM CEL Macro Urban 10 –31.0 –41.9 –20.6 10.9 100 –11.0 –21.9 –0.6 31 Micro Urban 10 –29.8 –41.2 –20.1 10.7 100 –9.8 –21.1 –0.1 30.8 Deploy- ment Stand off distance (m) Max Tolerable EIRP (dBW) GLN HPR TIM CEL Macro Urban 10 0.8 mW 64 µW 8.7 mW 12.3 W 100 79.4 mW 6.5 mW 0.9 W 1.26 kW Micro Urban 10 1 mW 76 µW 9.8 mW 11.7 W 100 104 mW 7.8 mW 1 W 1.2 kW Table ES-1 Maximum Tolerable Power Level for GPS/GNSS Receivers at 1530 MHz

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