Exploiting the Doppler effect in GPS to monitor signal integrity and to detect spoofing

We present the results from an analysis of GPS signals, exploiting the Doppler effect to monitor the behaviour and integrity of the GPS signals. The principle is simple: When a receiver is able to precisely determine the Doppler shift of the carrier frequency, the difference with the actually measured shift is the cause of the receiver´s own movement and can then be calculated. When comparing the resultant speed and heading to the same quantities calculated by conventional means, e.g. by Kalman filtering an actual tracked signal results in two similar trajectories, whereas a spoofing signal will generally yield different trajectories. The results of our implementation indicate that the proposed method is able to predict the Doppler shift of a GPS signal with an accuracy of 1 Hz, corresponding with a speed accuracy of 0.2 m/s, showing that the Doppler effect can reliably be used as a method to detect spoofing in received GPS signals.