# Virtual Validation of In-Flight GNSS Signal Reception during Jamming for Aeronautics Applications
## 4 Full-Scenario Simulation
### Scenario 2: GNSS Reception during jamming  
In the next scenario, we modeled the downlink portion of satellite transmission for GNSS transmitters as shown in Figure 13. GNSS transmitters are responsible for transmitting signals from GPS satellites to an aircraft receiver. This simulation allows us to study and analyze the behavior of the GNSS signal power level during jamming events. Both in the measurement campaign and in the virtual simulation, signals from 12 GPS satellites were received (see Figure 14). Figure 12: Simulation and Measurement results for the flight route. (**a**) Ant.1. (**b**) Ant.2. (**c**) Ant.3. (**d**) Ant.4. Figure 13: Simulated view of earth with GPS satellites (Yellow lines indicate the orbit of the satellites and pink lines indicate the connections between the GNSS satellites and the receiver). To evaluate the quality of the GNSS signals, we used the metric called C/N\({}_{0}\), which stands for carrier-to-noise-density ratio. This metric is expressed in decibel-Hertz (dB-Hz) and represents the ratio of the carrier power (the power of the transmitted signal) to the noise power (unwanted signal components) per unit bandwidth. C/N\({}_{0}\) changes according to the mutual orientation of GPS satellites and receiving antenna. Moreover, in the case of jamming events, it will strongly decrease (as jamming effectively increases the not-wanted part of the signal). By measuring C/N\({}_{0}\), we can assess the signal strength and quality in the presence of interference. The simulated and measured results, including the C/N\({}_{0}\) values at L1, are depicted in Figure 15. The figure depicts the congruent reception of signals from corresponding satellites during measurement and simulation. Figure 16 illustrates the specific time period when the jammer becomes effective. It is evident that during the time interval between 120 and 160 s, all (single) antennas experience a loss of signal tracking to the satellites. This loss of connection occurs because jamming is overpowering the signal. The receiver employs a tracking threshold of 30 dB-Hz to monitor the satellites. When the signal strength drops beneath a predefined threshold, especially in the presence of jamming, the reception diminishes to zero, signifying a complete loss of signal. This decline is evident in the plots. Furthermore, the received carrier-to-noise ratio (C/N\({}_{0}\)) values in the simulation setup also experience a significant decrease during the same time frame. This indicates that the simulation accurately reproduces the real-life scenario, as the observed loss of signal during the jamming period aligns with the simulation results. The obtained results are shown in Figure 17 for some exemplary satellites and compared with the results of our method and with the measurement. To compare the different approaches quantitatively, we have calculated the approximate cumulative integral of the deviation of the simulation results of each approach from the measured data. The integral is defined as:  
\[\int_{a}^{b}f(x)dx\approx\frac{b-a}{2N}\sum_{n=1}^{N}(f(x_{n})+f(x_{n+1})), \tag{1}\]  
where  
\[f(x_{n})=|(\text{C/N${}_{0}$Meas}-\text{C/N${}_{0}$Sim})|, \tag{2}\]  
\(a=x_{1}<x_{2}<...<x_{N}<x_{N+1}=b\), and \((x_{n+1}-x_{n})\) is the spacing between each consecutive pair of points. C/N\({}_{0}\)Meas denotes the measured C/N\({}_{0}\) values with Ant. 4 while C/N\({}_{0}\)Sim denotes the simulated values with Ant. 4 (as in our approach), GPS patch antenna or isotropic antenna. The integral results for the selected satellites with all intermediate values are shown in Figure 18. From Figure 17 it can be seen that in this case the isotropic antenna incorrectly predicts the signal drop before it actually occurs and Figure 18 confirms this as the integral value becomes very high (2.5-3 times) over the period analyzed as compared to our approach.