Research On GNSS Anti-spoofing Technology Based On Subspace Projection

In recent years, with the development and prosperity of GNSS(Global Navigation Satellite System), it is used in people’s life and applications in the military as one kind of infrastructure. As GNSS is applied in more and more key services, its accuracy and reliability have attracted more and more attentions. Due to the low power and public signal structure of GNSS signals, the system is very vulnerable to all kinds of interference which mainly includes blanket jamming and spoofing jamming. For blanket jamming, it can affect all devices in the target area and is very easy to be found, which extremely limit its applications. While spoofing jamming has no distinct difference with authentic signals which is difficult to be discovered, the receiver can be spoofed to move along the specific trajectory. Because spoofing jamming is more flexible and threatening, this paper focuses on anti-spoofing technology.Now the anti-spoofing technology mainly includes spoofing detection and spoofing mitigation. And spoofing detection is more such as power comparison and signal quality monitoring, while the spoofing mitigation is less including multi-antenna technology and RAIM(Receiver Autonomous Integrity Monitoring), whose reliability are low. The anti-spoofing technology proposed in this paper is based on the characteristics of the space and the code that includes spatial processing and data processing, which can conduct both spoofing detection and spoofing mitigation.The traditional multi-antenna technology is only suitable for one spoofing source. This paper proposes the algorithm in the space domain first, which can not only deal with one spoofing source but also conduct more jamming sources. It can estimate the DOA(Direction of Arrival) of the spoofing signals by RELAX algorithm, then set the threshold according to the false alarm probability, and construct the subspace projection of the spoofing signals to eliminate the jamming. And it is proved that the subspace projection can completely eliminate the spoofing signals. In spatial processing, the compensation matrix is also derived in this paper, which can compensate the authentic signals’ power to maximize the output. In the simulation, it is found that spatial processing can remove the high power spoofing signals with high detection probability and low false alarm probability, which can also decrease the effect of cross-correlation in the data domain. And the compensation matrix can maximize the authentic signals ’ power without affecting the spoofing signals.Data processing proposed in this paper constructs the subspaces by the pseudo code of the spoofing signals, which can conduct the signals with low p ower that cannot be removed by spatial processing. It can get the spoofing signals’ parameters such as the signal power, the Doppler frequency, PRN(Pseudo Random Noise) and so on by the acquisition and tracking part of the receiver, then the subspace can be constructed. It is proved that data processing can eliminate spoofing signals completely and has little effect on authentic signals. Data processing also optimizes the parameters by theoretical derivation, it is proved that the subspace is independent of the signal power. In specific conditions, the subspace is also proved to be independent with the navigation data and carrier initial phase. And it also evaluates the effects of Doppler estimation error. Meanwhile data processing gives the multipath decision part to decrease the multipath signal’s influence, which increases the reliability greatly. In the simulation, the performance of data processing is proved to be better when there is no high cross-correlation. And the receiver’s structure including spatial processing and data processing is also designed, whose process is also given. The two parts aim at two different parts of the spoofing signals, and spatial processing also helps data processing to suppress the signals with high power. So the new receiver has high robustness.