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Protecting the Skies: GNSS-less Aircraft Navigation with Terrestrial Cellular Signals of Opportunity

This paper shows how to protect our skies from harmful radio frequency interference (RFI) to global navigation satellite system (GNSS) signals, by offering terrestrial cellular signals of opportunity (SOPs) as a viable aircraft navigation system backup. An extensive flight campaign was conducted by the Autonomous Systems Perception, Intelligence, and Navigation (ASPIN) Laboratory in collaboration with the United States Air Force (USAF) to study the potential of cellular SOPs for high-altitude aircraft navigation. A multitude of flight trajectories and altitudes were exercised in the flight campaign in two different regions in Southern California, USA: (i) rural and (ii) semi-urban. Samples of the ambient downlink cellular SOPs were recorded, which were fed to ASPIN Laboratory’s MATRIX (Multichannel Adaptive TRansceiver Information eXtractor) software-defined receiver (SDR), which produced carrier phase measurements from these samples. These measurements were fused with altimeter data via an extended Kalman filter (EKF) to estimate the aircraft’s trajectory. This paper shows for the first time that at altitudes as high as about 11,000 ft above ground level (AGL), more than 100 cellular long-term evolution (LTE) eNodeBs can be reliable tracked, many of which were more than 100 km away, with carrier-to-noise ratio ( C/N 0 ) exceeding 40 dB-Hz. The paper shows pseudorange and Doppler tracking results from cellular eNodeBs along with the C/N 0 and number of tracked eNodeBs over the two regions, while performing ascending, descending, and grid maneuvers. In addition, the paper shows navigation results in the rural and semi-urban regions, showing a position root mean-squared error of 9.86 m and 10.37, respectively, over trajectories of 42.23 km and 56.56 km, respectively, while exploiting an average of about 19 and 10 eNodeBs, respectively.