Anomalous GPS Signals from SVN49

摘要

Fabio Dovis, Nicola Linty, Mattia Berardo, Calogero Cristodaro, Alex Minetto, Lam Nguyen Hong, Marco Pini, Gianluca Falco, Emanuela Falletti, Davide Margaria, Gianluca Marucco, Beatrice Motella, Mario Nicola and Micaela Troglia Gamba Researchers at the Navigation Signal Analysis and Simulation (NavSAS) Group of the Politecnico di Torino detected in mid-May the presence of anomalous spikes in the LI signal spectrum. The origin of the spikes was identified to be transmission of a nonstandard code from a non-operational GPS satellite (GPS IIF-9, SVN49). Here we report on signal observations and address possible impacts on GNSS signal processing. On May 17, 2017, during outdoor data collection, NavSAS researchers detected two spikes in the LI spectrum, with sufficient power to be clearly visible on a display processing raw digital samples at the receiver's intermediate frequency An initial check looked for a possible interfering source in the experimental set-up, since it was quite complex with multiple pieces of electronic equipment. The likelihood of this source was soon dispelled as the same kind of spectrum was visible on a spectrum analyzer (SA) connected to an active survey-grade GNSS antenna on the lab roof; results shown in FIGURE 1. The spectrum is centered at 1575.42 MHz, with the SA set to a frequency span of 5 MHz. Connecting the SA to different survey-grade antennas on the roof, we found no remarkable differences. The spikes continued to appear on subsequent days, becoming clearly visible around 13:00 UTC and disappearing around 19:00 UTC. U.S. Air Force Response The 2nd Space Operations Squadron is performing maintenance on a presently non-operational satellite. SVN49 is broadcasting non-standard C/A and nonstandard Y codes as described in IS-GPS-200. Space professionals continue to conduct safe and responsible command and control of the constellation to continue to provide accuracy that exceeds established system requirements.