An Experimental Receiver for Positioning by Triangulating on Non-Cooperating Cell Towers
G. Poberezhskiy, D. Lewis, P. Grobert, P. Quinn, W. Wallace, Raytheon Space and Airborne Systems
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An experimental receiver for positioning by triangulating on non-cooperating cell towers is described in this paper. This receiver utilizes the analog and digital hardware of an existing GNSS receiver using an antenna array. It can provide a backup when GNSS navigation is disrupted, or work as a complementary navigation sensor. Most positioning methods using cell towers are cooperative, i.e. cell sites actively assist a registered user who belongs to their network. However, cell sites continuously transmit various signals (pilot, broadcast, user data, etc.) that are sufficiently above background noise (SNR > 20 dB) in a proper frequency band. Therefore, array direction finding allows a receiver to use non-cooperating cell towers transmitting signals of various standards for accurate positioning. Such a receiver is particularly beneficial for low- to medium-altitude (100–2000 m), low- to medium-speed aerial vehicles. It also can be useful for terrestrial vehicles, especially in rural areas. Hardware calibration and direction-finding (DF) algorithms have been implemented and sufficiently refined to demonstrate good positioning accuracy consistent with rms azimuth DF error close to 1 degree in good propagation conditions. This method can be combined with other positioning, navigation, and timing (PNT) methods. Field testing has also shown that the receiver can be used for accurate geolocation of cell sites. A basic concept of receiver operation has been developed. Current and potential issues have been identified, and workarounds and coping strategies have been proposed. Further concept refinements have been suggested.