Trustworthiness GNSS signal validation by a time-frequency approach

In a short time new demanding applications, as for instance financial and life critical timing and positioning services, will be included in the plethora of uses of new Global Navigation Satellite System (GNSS). They will require the ability to restrict access to some class of protected information by the user position meaning, provided by some GNSS technology. Access control tokens using trusted GNSS receivers will provide the information security core for this kind of applications, including banking, enterprise and secure timestamps. In this paper a Time-Frequency (TF) signal validation algorithm is proposed as valuable tool both to define metrics to quantify the trustworthiness of the navigation signal and to provide countermeasure to the receiver functionalities. This algorithm can work as a subfunction of a signal conditioning stage placed between the Analog-to- Digital Converter and the acquisition block in an innovative secure GNSS receiver. The proposed method is based on a synthesis technique using the so called Orthogonal-Like Gabor Expansion in order to obtain an estimation of the interference to be subtracted to the input signal. Tests have been conducted using Continuous Wave (CW), chirp interference and combination of them added to GNSS signals. Baseline GPS BPSK(1), TMBOC(6,1,4/3,3), BOC(1,1) and Galileo CBOC(6,1,1/11) modulations are simulated for the scope by a software GNSS simulator. The algorithm performance are evaluated at the output of the acquisition stage by means of Receiver Operative Characteristics (ROC) curves, showing encouraging results in terms of mitigation effectiveness.