BIOGRAPHIES Daniel Gerbeth received a Bachelor and Master's degree in Electrical Engineering and Information Technology from Karlsruhe Institute of Technology in 2014. During Master studies he specialized in aerospace technology and navigation. After working in the field of sensor fusion and navigation aiding at Fraunhofer IOSB he joined German Aerospace Center (DLR) in May 2015 and is involved in the research on GBAS now. Michael Felux received a diploma in Technical Mathematics from the Technische Universität München in 2009. The same year he joined the German Aerospace Center (DLR) where he has was working on the development of the GBAS GAST C testbed at the research airport in Braunschweig and its upgrade to GAST D. He was involved in flight testing and ground validation of the station and the approach procedures. Since 2015 he is coordinating DLRs research on GBAS-based navigation.
In this work an overview of numerous possible processing modes in future dual frequency, dual constellation GBAS is given and compared to the current GAST D standard. We discuss the individual error contributions to GBAS protection levels and give an overview of the general processing. Based on this the consequences when adding a second constellation as well as frequency are investigated. Geometrical implications and changes to the residual differential error bounds are studied separately first. In terms of geometry a comparison between the single and dual constellation case is presented using dilution of precision as metric. The influence on the different sigma contributions when using new satellites (Galileo) and signals (E1, L5, and E5a) is individually discussed based on recent measurements. Final simulations for different varying parameters are carried out to compare relevant processing modes in terms of achieved nominal protection levels. A concluding discussion compares the outcomes and analyzes the implications of choosing one or the other mode.
Ground transportation systems demand accurate and robust localization functions. Satellite navigation is considered a key element in those systems, but its position determination can be highly corrupted in urban environments because of the presence of reflected signals (i.e. multipath). This paper deals with the detection of multipath in the code measurements of GNSS receivers for mobile users in urban scenarios. First, we discuss the different alternatives and limitations to properly isolate multipath autonomously at the receiver based on Code-Minus-Carrier (CMC) techniques in challenging GNSS applications. We then propose a practical methodology to design a suitable multipath detector based on the time difference of CMC. All the analysis and evaluations are supported with real measurements collected in Railway scenarios.
In this paper we describe a method to monitor for a difference in the ionospheric delay observed by a ground station of a Ground Based Augmentation System (GBAS) and an airborne user. In case of detection the affected satellite can be excluded or a switch to an ionospheric free processing mode can be triggered. As it is not possible to estimate the absolute ionospheric delay at the ground station from the transmitted corrections directly, we compare a pseudo-ionospheric delay estimate from the corrections with an ionospheric estimate after removing biases. We then show the performance of the proposed monitoring architecture in flight trials from our GBAS test environment for different scenarios. In order to obtain results for a full constellation we considered an L1/L2 dual frequency combination where the expected noise and multipath is larger than in the L1/L5 case which will be used in an operational GBAS. Results show that even with the larger test statistic and in the single constellation case the monitor is feasible and provides good results. Furthermore, we also show results using the available L5/E5a signals collected during flight tests. Also in this case the performance is good and the threshold was not exceeded despite the low threshold of the monitor due to the marginal geometry. In order to test the reaction of the monitor to ionospheric gradients we injected a simulated error into the airborne measurements. As the monitoring threshold depends on the satellite geometry we show some exemplary results of the impact of different gradient slopes on the test statistic of the affected satellites.
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