Inside GNSS Media & Research

MAR-APR 2018

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46 Inside GNSS M A R C H / A P R I L 2 0 1 8 R AILWAY APPLIC ATIONS are able to provide two frequencies and therefore, can be included in a dual- constellation with dual-frequency iono- spheric correction. It is obvious that the rising number of available Galileo sat- ellites just enables the exclusive use of dual-frequency satellites, when apply- ing dual-constellation in combination with GPS. e corresponding Horizon- tal Dilution of Precision (HDOP) of the dual-constellation and for comparison of all available GPS satellites (within our elevation mask) is presented in the third sub-figure. In some instances, the available dual-constellation set of sat- ellites only provides poor geometrical constellation. The vehicle velocity is given in the lower plot. Compared to the results mentioned earlier from Zweigel et alia and Gehrt et alia, the 2D accuracy resulting in this last test campaign with respect to all three filter modes is of a slightly lower level. As expected, the accuracy of the EK F w it h GPS L1 obser vables a nd Klobuchar ionospheric correction is permanently in the range of more than 2 meters. Due to a temporary low num- ber of available satellites and a resulting poor satellite constellation at i.e. second 1850, second 1930 and thereaer, the dual-constellation loses the high accu- racy. It gets worse around second 2150, where only three satellites are available and HDOP rises towards infinity. Nev- ertheless, the total average accuracy is still below 1 meter and along some sections even better than the naviga- tion filter with differential correction mode, which is in accordance with for- mer measurement campaigns. Summary and Outlook e present work introduces the techni- cal developments for the GNSS process- ing of an existing tightly coupled naviga- tion filter as part of the ongoing research project Galileo Online: GO!. It presents Galileo enhancements with a dual-con- stellation approach and processing of differential data. e advantages of using GPS and Galileo in dual-constellation and processing two frequencies of each satellite are discussed and evaluated in extensive measurement campaigns in harsh railway environments. Obtained results prove that both the differential aided filter and the multi-constellation aided filter provide track-resolved posi- tion estimation, even under worst condi- tions. Moreover, results show that both modes are almost complementary. e huge advantage of the dual-constellation mode consists in the independency of differential corrections broadcasted via mobile radio. For future works, a state machine, which enables switching between the available filter modes regarding current conditions, is in progress. Poor GNSS reception, signal damping, and multi- path effects in combination with high requirements on the position estimation, reveal a wide field for future research on GNSS signal integrity determination. Developments, basing on well-known Receiver Autonomous Integrity Moni- toring (RAIM) algorithms, applied on dual constellations with Fault Detection and Identification (FDE), methods are in progress. Manufacturers e RCP real-time hardware referenced in the Results section is a MicroAutoBox II, with a 900 megahertz single core sys- tem from dSPACE, Paderborn, Germa- ny. For inertial measurement, the setup FIGURE 4 Evaluation of the navigation filter results using different GNSS settings along a test environment LEO in Bavaria, Germany.

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