# GNSS Accuracy Under White Gaussian Noise Jamming +
## 4 Comparison of Theoretical and Measured Results
### Accuracy of the Pseudo-Range Measurements  
In Figure 4, the standard deviations of the pseudo-range measurements are given for GPS C/A (in Figure 4a) and Galileo E1 (in Figure 4b). These standard deviations provide a measure of the accuracy of the DLL and, with it, the pseudo-range for unbiased measurements. The solid lines indicate the predicted standard deviations calculated using (1). In Figure 4a, the standard deviations as predicted using (2) are also given (as dashed lines). These standard deviations of the measurements were determined after detrending the pseudo-range measurements using a third-order polynomial in order to remove the effect of satellite motion. The standard deviations of the measurements with the jammer active were determined in the last minute of measurements. The standard deviation of the measurements without the jammer was determined in the last minute of measurements before the jammer was turned on. Both figures show the results regarding the signals of a single satellite.  
For GPS C/A (Figure 4a), the predictions match the measurements reasonably well with and without the interference of the jammer. Although both models, given by (1) and (2), provide slightly different values, both predict the accuracy well. Again, it is clear that the jammer with the narrowest bandwidth has the largest impact and that the largest jammer bandwidth has the lowest impact, as expected for a BPSK signal (see Figure 1).  
Figure 4: Comparison of the predicted and measured standard deviations of the pseudo-range for **(a)** GPS C/A and **(b)** Galileo E1. The solid lines indicate the prediction made using (1), the dashed lines denote the prediction made using (2), the cross denotes the estimated standard deviation based on the measurements, and the error bar gives the standard deviation of these measurements.  
For Galileo E1 (Figure 4b), the predictions for the situation without the jammer and with the 2 MHz and 4 MHz jammers do match the measurements; however, the predictions for the 1 MHz jammer overestimate the standard deviations found based on the measurements when the jammer is relatively close. Further away from the jammer, the estimations match the measurements well. This overestimation close to the jammer was persistent for all the satellites analyzed, of which only one is given in the figure. Both the predictions and the measurements show that the 1 MHz jammer has the least impact, while the 2 MHz jammer has the largest impact, exactly as expected for CBOC signals (see Figure 1).  
Upon observing Figure 4, it becomes clear that the pseudo-range accuracy significantly deteriorates when closer to the jammer. If, for example, the required accuracy is twice the expected nominal accuracy, the effective range of this 20 mW jammer on a GPS C/A receiver is around 3500 m for the 4 MHz jammer to 7000 m for the 1 MHz jammer. For a Galileo E1 receiver, this range is between 3000 m for the 1 MHz jammer and 4500 m for the 2 MHz jammer. This range is significantly larger than the range in which the receiver will lose its lock on the signal; this range is between approximately 1000 and 1500 m for the receiver used, depending on the bandwidth of the jammer.