Spoofing detection for underwater acoustic GNSS-like positioning systems

The need for accuracy, precision, and data registration in underwater positioning and navigation should be viewed as no less stringent than that which exists on the sea surface. In the same way in which GNSS (Global Navigation Satellite System) receivers rely on the signals from multiple satellites to calculate a precise position, undersea vehicles discern their location by ranging to the acoustic signals originating from several fixed underwater acoustic sources using the Time-of-Arrival algorithm (ToA) through the Ordinary Least Squares method (OLS). In this article, the scope has been limited to only considering underwater positioning systems in which the navigation receiver is acoustically passive. The receiver “listens” to the buoys, receives their messages and solves the problem of finding its own position based on the geographical coordinates of the buoys. Often, such systems are called GNSS-like Underwater Positioning Systems (GNSS-like UPS). It is important to note the distinction between general purpose GNSS-like UPS (mainly civil systems) and special purpose GNSS-like UPS (mainly military systems). In this article, only general purpose GNSS-like UPS systems have been considered. Depending on the scale of system’s service areas, GNSS-like UPS are divided into global, regional, zonal and local systems. Only local GNSS-like UPS systems have been considered in this article. The spoofing of acoustic GNSS-like UPS works as follows: the acoustic GNSS signal generator transmits a simulated signal of several satellites. If the level of the simulated signal exceeds the signal strength of the real satellites, the acoustic receiver of an underwater object will “capture” the fake signal and calculate a false position based on it. All receivers that fall into the spoofing zone will calculate the same coordinates, while the receivers located in different places will have a mismatch in the XYZ coordinates.