This paper presents the most thorough study to date of vehicular carrier-phase differential GNSS (CDGNSS) positioning performance in a deep urban setting unaided by complementary sensors. Using data captured during approximately 2 hours of driving in and around the dense urban center of Austin, TX, a CDGNSS system is demonstrated to achieve 17-cm-accurate 3D urban positioning (95% probability) with solution availability greater than 87%. The results are achieved without any aiding by inertial, electro-optical, or odometry sensors. Development and evaluation of the unaided GNSS-based precise positioning system is a key milestone toward the overall goal of combining precise GNSS, vision, radar, and inertial sensing for all-weather high- integrity high-absolute-accuracy positioning for automated and connected vehicles. The system described and evaluated herein is composed of a densely-spaced reference network, a software-defined GNSS receiver, and a real-time kinematic (RTK) positioning engine. A performance sensitivity analysis reveals that navigation data wipeoff for fully-modulated GNSS signals and a dense reference network are key to high-performance urban RTK positioning. A comparison with existing unaided systems for urban GNSS processing indicates that the proposed system has significantly greater availability or accuracy.

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Cite and download the paper:
Todd E. Humphreys, Matthew J. Murrian, and Lakshay Narula "Deep-Urban Unaided Precise Global Navigation Satellite System Vehicle Positioning," in IEEE Intelligent Transportation Systems Magazine, doi: 10.1109/MITS.2020.2994121.

January 2021: FAA pilot reports have revealed that military tests are interfering with airline flights. The military is presumably generating GPS interference to test their latest positioning technology, but the interference is reaching beyond the test sites and jamming passenger aircraft that routinely rely on GPS for navigation and landing. Although pilots are trained for such scenarios, the loss of GPS is so rare that it can still cause disorientation and confusion in the cockpit. In this article from IEEE Spectrum, Dr. Humphreys explains: 

"I don’t blame pilots for getting a little addicted to GPS. When something works well 99.99 percent of the time, humans don’t do well in being vigilant for that 0.01 percent of the time that it doesn’t."