Inside GNSS Media & Research

NOV-DEC 2018

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www.insidegnss.com N O V E M B E R / D E C E M B E R 2 0 1 8 InsideGNSS 53 reference, the comparison of both D-FE inputs is presented. e D-FE has one clock which is used for the sampling of both inputs. Here the best performance is expected as no clock synchronization is needed. Secondly, the clock synchro- nization with the WR hardware is tested (described earlier). e clock synchro- nization performance will be measured by comparing the ΔPR Phase and ΔPR Code performance under each synchro- nization approach. As before, we use the SIS (Galileo OS PRN 3, E1C) for the synchronization performance measure- ments. e processing, described in the Con- cept section, of the code and phase PR of the signals D-FE1 and D-FE2 (same clock; no external clock sync.), is dis- played in Figure 7 and yields the ΔPR for code (Figure 8a) and phase (Figure 8b). e top plots of (a) and (b) show ΔPR(t) and ΔGR(t) (the satellite movement was approximated and removed by a qua- dratic polynomial fit of the ΔPRP). e bottom plots of (a) and (b) show the dif- ference of ΔPR – ΔGR and represent the remaining residual error ε 1 – ε 2 . For the ΔPR code (ΔPRC) a standard deviation of 0.664 meters and for the ΔPR phase (ΔPRP) a standard deviation of 0.58 cen- timeters is observed. ese values are in the expected range of the Galileo OS SIS and prove the basic working principle. In Figure 9 the ΔPRC (a) and the ΔPRP (b) of the signals S-FE and D-FE2 (diff. clocks; WR clock sync.) are presented. e ΔPRC standard deviation is 0.659 meters and the ΔPRP standard deviation is 0.62 cen- timeters. Comparing the ΔPRP plots of Figure 8 and Figure 9, a clear phase jitter is visible under the usage of the WR syn- chronization. e 16.6 picoseconds devia- tion of the WR synchronization yield an estimated range error of approximately 0.5 centimeters. is was calculated by 16.6 ✴ 10 -9 ✴ c. is range error is clearly visible in the magnitude of the jitter in Figure 9b. e plots for the ΔPRC in Fig- ure 8a and Figure 9a are almost identical. e values for the standard deviation are equal within the error margin. erefore it is shown that the WR clock synchro- nization is sufficient for the code perfor- mance evaluation. However, the observed WR clock synchronization deviation of 16.6 picoseconds can become a relevant disturbance for phase processing pur- poses and needs further investigation, e.g. smoothing of the clock adjustments. FIGURE 7 Tracking performance of ground system. Tracking Galileo OS PRN 3 SIS. From left to right: S-FE, D-FE1, and D-FE2; from top to bottom, C/N 0 , discriminators, and the Code Minus Carrier (CMC) GPS time - t 0 = 310280.001 s[s] GPS time - t 0 = 310280.001 s[s] Signal Power [dB-Hz] 0 50 100 150 200 250 300 350 200 250 300 350 S-FE 51 50 49 48 47 46 45 44 43 42 e DLL [subchip] 0 50 100 150 200 250 300 350 0.2 0 –0.2 e PLL [cyc] 0 50 100 150 200 250 300 350 0.1 0 –0.1 e FLL [Hz] 0 50 100 150 200 250 300 350 50 0 –50 GPS time - t 0 = 310280.001 s[s] Code minus carrier [m] 0 50 100 150 2 1.5 1 0.5 0 –0.5 –1 –1.5 –2 GPS time - t 0 = 310280.077 s[s] GPS time - t 0 = 310280.077 s[s] Signal Power [dB-Hz] 0 50 100 150 200 250 300 350 200 250 300 350 D-FE1 51 50 49 48 47 46 45 44 43 42 0 50 100 150 200 250 300 350 0.2 0 –0.2 0 50 100 150 200 250 300 350 0.1 0 –0.1 0 50 100 150 200 250 300 350 50 0 –50 GPS time - t 0 = 310280.077 s[s] Code minus carrier [m] 0 50 100 150 2 1.5 1 0.5 0 –0.5 –1 –1.5 –2 GPS time - t 0 = 310280.077 s[s] GPS time - t 0 = 310280.077 s[s] Signal Power [dB-Hz] 0 50 100 150 200 250 300 350 200 250 300 350 D-FE2 51 50 49 48 47 46 45 44 43 42 0 50 100 150 200 250 300 350 0.2 0 –0.2 0 50 100 150 200 250 300 350 0.1 0 –0.1 0 50 100 150 200 250 300 350 50 0 –50 GPS time - t 0 = 310280.077 s[s] Code minus carrier [m] 0 50 100 150 2 1.5 1 0.5 0 –0.5 –1 –1.5 –2

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