# A Method of Detections' Fusion for GNSS Anti-Spoofing
## 3 Performance Evaluation
### Simulation Results
#### 3.2.2 Test Results on TEXBAT  
Simulations of multiple detections' fusion based on the proposed method are provided next. The test data are from TEXBAT, which is a public dataset of eight high-fidelity digital recordings of live static and dynamic GPS L1 C/A spoofing tests. It is conducted by the Radio Navigation Laboratory of the University of Texas at Austin, and each scenario in TEXBAT has been described in detail in [18]. In Scenario 1 of TXBAT, the counterfeit signals substitute all authentic GNSS signals instantaneously; the power of counterfeit signals is much weaker than the authentic. In Scenario 2, the spoofer increases the power of the counterfeit signal, and it has a 10-dB power advantage; this is an obvious power attack. Moreover, the spoofer changes the counterfeit signals' carrier phase proportionally when it shifts the code phase to induce a position or timing deviation in the target receiver. The power advantage of counterfeit signals is common in the next scenarios, but it is reduced. In Scenario 3, the spoofer fixes the carrier phase offset between the counterfeit signals and the authentic signals when it shifts the code phase of counterfeit signals. Scenario 4 is identical to Scenario 3, except that the power advantage of the counterfeit signal is reduced again. Static Scenarios 1\(\sim\)4 are tested, and the results are discussed in this section. In each scenario, the detection results of just one satellite, GPS PRN 6, is discussed because the results of most satellites in the same scenario are similar. In the following tests, a software-defined GPS receiver is employed. Common acquisition and tracking algorithms of GPS signals are implemented in the receiver where a phase-locked loop (PLL) is used for carrier tracking and a common delay lock loop (DLL) is used for code tracking. The coherent integration time is 1 ms in the receiver, and a measurement is obtained per one millisecond. The detection time is 50 milliseconds as the sample size is K = 50. The time interval of two sample sets, X and Y, is 1 s. This time interval can be set according to the application scenario. Herein, the short interval is conducive to improve the real-time capability of detectors. Besides, false alarm probabilities or significance levels are set as \(P_{fa}=0.005\) in both detections. Figure 6 shows the test results of the clean static dataset where the GPS signals are not disturbed by counterfeit signals. It can be observed that there is a small number of false alarms in both two detections, and they disappear in the fused results. Reduction of false alarms is coincident with the curve in Figure 4, and it suggests that higher \(P_{fa}^{(i)}\) can be adopted to obtain a lower \(P_{md}^{(i)}\) in each detector before the fusion. Test results of Scenario 1 for GPS PRN 6 are shown in Figure 7. The sudden replacement of the signals and the power difference disturbed the correlator and tracking loop. It can be observed that an obvious change of correlator outputs occurs at about 125 s in the time history, and an anomaly between carrier Doppler and code Doppler is detected at the same time, although the signal is tracked and locked by the receiver in the whole process. Figure 8 shows the fused results of two detections of Scenario 2. They are similar to the results of Scenario 1; the appearance of counterfeit signals with the power advantage makes two detectors issue alarms simultaneously at about 110 seconds. Moreover, with the shift of the carrier phase and code phase, the consistency of carrier Doppler and code Doppler is not met. Meanwhile, correlator outputs are not stationary because the tracking loop is disturbed. These are reflected in the figure. Figure 8: Detections fusion of the Scenario 2 dataset. Figure 6: Detections’ fusion of the clean static dataset. Figure 7: Detections’ fusion of the Scenario 1 dataset. The fused results based on Scenarios 3 and 4 are shown in Figures 9 and 10, respectively.