Inside GNSS Media & Research

JUL-AUG 2018

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36 Inside GNSS J U L Y / A U G U S T 2 0 1 8 www.insidegnss.com simulated scenario settings, including the receiver location, the start time, the duration, the GNSS signal power and the interference power levels for the different test methodologies. When performing the tests, an elevation mask of 5° is applied for the Position, Velocity and Time (PVT) computation. e RUT's default C/N 0 mask is used in all cases. e RUT set- tings are summarized in Table 2 . Results is section presents the results of the standardized tests of a mass-market and a professional grade receiver against one of the most frequently detected interference types at STRIKE3 monitoring sites. e spectrum and the spectrogram of such interference signal are shown in Figure 1. e accuracy and availability of the receiver's position solution during the interference interval is analyzed in the sensitivity tests. As the interference power increases, the receiver perfor- mance continues to degrade and at some point the RUT loses the position fix. e East-North-Up (ENU) devia- tions of the position solution for the mass-market (top) and the professional grade receiver (bottom) are shown in Figure 5 . Both receivers offer inaccurate position solutions in the beginning, especially in the vertical component. is is due to the cold start and the resulting unavailability of ionospheric parameters, and to the convergence of the navigation filter. It can be seen that the mass-market RUT prioritizes the availability of the position solution over its accuracy. In particular, during the interference interval, there are only a few epochs at which the receiver does not yield a solution, but this high yield comes with degraded positioning accuracy. On the other hand, the professional grade RUT prioritizes the accuracy over the availability. It does not offer the position solution as oen during the interference interval, but when it does the position errors are minor. In order to have a better under- standing of the interference impact on the RUT, a comparison with respect to the baseline test case is also carried out. Figure 6 shows the drop in the average C/N 0 of the satellites used in position fix with respect to the baseline for the entire duration of the test. As expected, in the presence of interference, the signal quality worsens as the interfer- ence signal's power increases. Given the wideband nature of the interfering signal, GPS and Galileo are affected similarly. e difference between the mass- market and the professional grade receivers' behavior is also visible here. While the former continues to use very low quality signals in order to provide a position solution, even if inaccurate, for as long as possible, the professional grade RUT stops computing the solu- tion when the signal quality decreases by about 20 dB. A summary of the results is given in Table 3 . e maximum horizontal and vertical errors are computed for the interval in which the interference is present when the receiver offers a valid position fix. As already discussed, the position fix availability during the interference interval for the mass-mar- ket receiver is high at the expense of position accuracy. On the other hand, the professional grade RUT preserves the position accuracy at the expense of solution availability: the maximum horizontal and vertical errors in the test case are only slightly larger than in the baseline case. e J/S at which the position solu- tion is no longer available, J/S PVT_lost , is also determined. It can be observed from Table 3 that the mass market RUT has much higher sensitivity as compared to professional grade RUT, when manufacturer's default receiver settings are used. Finally, it can be observed that TTRP values are much better for mass-market RUT than pro- fessional grade RUT. FIGURE 5 East-North-Up deviations 50 0 –50 –100 –150 –200 389100 12:05 389700 12:15 390300 12:25 390900 12:35 391500 12:45 392100 12:55 GPS Time (s) UTC Time (HH:MM) Mass-market RUT Coordinate variations [m] 70 60 50 40 30 20 10 0 Jamming/GNSS signal power ratio [dB] 16 14 12 10 8 6 4 2 0 –2 389100 12:05 389700 12:15 390300 12:25 390900 12:35 391500 12:45 392100 12:55 GPS Time (s) UTC Time (HH:MM) Professional grade RUT Coordinate variations [m] 70 60 50 40 30 20 10 0 Jamming/GNSS signal power ratio [dB] GNSS SOLUTIONS

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