Spoofing Mitigation Using Multiple GNSS-Receivers

Sammanfattning: Global Navigation Satellite Systems (GNSS) are used in a multitude of civilian as well as security related applications. GNSS-receivers are vulnerable to different types of spoofing attacks where the receiver is ``tricked'' to provide false position and time estimates. These attacks could have serious implications; hence, it is important to develop GNSS-receivers that are robust against spoofing attacks. This thesis investigates the use of multiple GNSS-receivers that exchange information such as pseudorange or carrier phase measurements in order to perform spoofing mitigation. It has previously been shown that carrier phase measurements from multiple receivers can be used to identify spoofing signals. The focus in this thesis is on investigating the possibility of using pseudorange measurements from two receivers to perform spoofing mitigation. The use of pseudoranges to perform spoofing mitigation is compared to the use of carrier phases. The spoofing attack is assumed to be performed using a single transmission antenna. This is exploited in order to identify the spoofing signals. The spoofing mitigation algorithms compute, for a pair of receivers, either pseudorange or carrier phase double differences. A double difference is the difference of two single differences for a satellite pair, where the single difference is the difference of pseudoranges or carrier phases measured from one satellite by a pair of receivers. The spoofing mitigation involves the identification of spoofing signals based on these calculated pseudorange or carrier phase double differences. The measurements obtained from identified spoofing signals are not used by the receivers in subsequent computations of position, velocity and time, thereby mitigating the effects of the spoofing attack. The spoofing mitigation algorithms were evaluated with the help of the software-defined GNSS-receiver GNSS-SDR, which was modified to acquire and track both authentic signals and spoofed signals. The spoofing mitigation algorithms were implemented and evaluated in MATLAB. Simulated meaconing attacks were created using a Spirent GNSS simulator. The evaluations indicate that spoofing mitigation is possible using pseudorange measurements from two receivers. However, the performance of the spoofing mitigation algorithms deteriorates for short distances between the receivers when pseudorange measurements are used. The use of carrier phase measurements for spoofing mitigation appears to be more appropriate for short distances between the receivers. The use of pseudoranges enabled quite fast identification of the spoofing signals for larger distances between the receivers. Most spoofing signals are identified within 30 seconds using pseudoranges and for distances larger than 20 meter between the receivers.