DOT Prepping for L-Band GPS Interference

Ligado's terrestrial L-band plans came up multiple times during the meeting. Board First Vice Chairman Bradford Parkinson said neither Congress nor the FCC has acted to undo the agency's approval of Ligado's terrestrial use of spectrum adjacent to GPS, but he remains "hopeful." "Hats off to DOD" for its heavy lobbying against Ligado, he said.

Currently, the federal government relies on user identification and reporting of global navigation satellite system (GNSS) interference, based on subjective user assessment of operational disruption, said James Aviles, a spectrum engineer in the DOT Office of the Assistant Secretary for Research and Technology. The aim is to move toward independent, dedicated technology for automated monitoring of GPS intelligence signals to augment that current process, he said.

That would entail getting data feeds from legions of distributed network GNSS devices acting as sensors for signal disruptions, and that data being used to create a publicly available visualization, perhaps accessed via an app, Aviles said. The idea comes from something similar to what DOD's Defense Innovation Unit is implementing, he said. Aviles said DOT is experimenting now with possible visualizations -- a "GPS weather map." He said DOT has done some data curation work and is working on incorporating an Automatic Dependent Surveillance-Broadcast data source from aviation. Beyond that will be incorporation of a terrestrial data source into the modeling, he said.

GPS interests are seeking toughening of receivers via removing International Traffic in Arms Regulations restrictions on some equipment. Those ITAR restrictions on multi-element anti-jamming enhancements mean civilians lack access and "that's got to change," said Parkinson. He said there's a particular need on civilian ships and aircraft. Robert Hampshire, DOT deputy assistant secretary-research and technology, said DOT backs that route for toughening receivers and said there needs to be more inter-agency conversation along those lines.

A growing number of GNSS satellites are being put into orbit, but a GNSS spectrum crunch doesn't seem likely soon thanks to signal isolation techniques available, as well as that numerous signals can fit in the allocated spectrum, Parkinson said. Today about 900 million active GPS devices are in the U.S., and 7 billion receivers worldwide, with that number to grow due to such applications as drones, connected vehicles and IoT, said Stormy Martin, director-National Coordination Office for Space-Based PNT.

Providing some satellite data and atmospheric corrections over the internet in a High Accuracy and Robustness Service system could make GPS far less vulnerable to spoofing, said Google Distinguished Engineer Frank van Diggelen. A HARS system would take data vulnerable to spoofing and cryptographically "sign" and deliver it, he said. For commonplace GPS applications like auto and smartphone navigation, that could improve accuracy from around 3 meters to less than a meter -- good enough for car lane-level accuracy, he said. Encrypted digital signatures would address GPS' vulnerability to data spoofing, he said. It also would enable signal processing for the relatively weak GPS signals and add robustness that makes signal spoofing harder, he said. He said it could prevent chipmakers from designing chips that favor use of the EU's Galileo system over GPS, he said. Without improving GPS features and performance, "the writing is on the wall" for the U.S. having the premier satellite navigation system, he said.

The growing trend of lunar activity points to the need for a coordinates reference system for the moon, Parkinson said. How that would look is still to be determined, he said. "I wouldn't even try" to extend the GPS reference system to the moon, as it would introduce a number of errors and have to deal with the moon's orbital wobble, he said.