GPS World, April 2014

INNOVATION System Design Test Configuration GNSS receivers Approach definitions GBAS ground facility simulation VDB Recording Status Telemetry GNSS receiver Configuration GBAS receiver simulation Cockpit CDI Recording FIGURE 4 Schematic data processing for the flight experiments ground components in orange airborne components in blue FIGURE 5 Research aircraft D IBUF Dornier Do 128 6 transmittable corrections can be calculated easily for different numbers of assigned slots for GAST C as well as for GAST D services see TABLE 4 The exact distribution of VDB messages for the maximum number of differential corrections 18 is shown in FIGURE 3 IRU DQ 07 07 FRQ JXUDWLRQ and two assigned slots Experimental Realization of Multi Constellation GBAS The experimental GBAS multiconstellation extensions described earlier have been implemented in software for further testing As these enhancements are purely experimental and might change in the future we have ensured WKDW WKHVH GH QLWLRQV FDQ EH FKDQJHG easily Navigation Software The Institute of Flight Guidance at Technische Universität Braunschweig has been developing an experimental navigation framework for many years This software called TriPos can handle and combine different navigation Number of slots GAST C MT1 only GAST D MT 1 and MT 11 2 32 18 3 36 30 4 36 36 TABLE 4 Number of differential corrections that can be broadcast technologies TriPos can be used for simulations post processing of recorded data and even for live online processing It is written in C and supports various platforms The navigation framework can be extended easily Originally only GPS was supported within the software but support for GLONASS and Galileo as well as augmentation systems like SBAS and GBAS were added over the past few years Additionally the software handles GNSS data of multiple frequencies internally and can thus be used for multi constellation and multi frequency applications TriPos includes decoders for the binary protocols of most GNSS receivers currently available For GBAS research two components can be simulated using the software On the one hand the Ground Facility simulation calculates the differential corrections and provides simulated VDB data On the other hand the GBAS receiver simulation emulates the behavior of an airborne GBAS receiver and uses VDB data and GNSS measurements to calculate a GBAS solution Both simulations can use either recorded data in post processing or live data for online processing This allows complete simulation of GBAS Multi Constellation GBAS Ground Facility Simulation The GBAS ground facility simulation uses raw binary data from multiple stationary GNSS receivers to calculate binary VDB data The simulation can be freely configured to process either live or pre recorded GNSS data Even though it features all algorithms required by the standards it does not contain additional monitor algorithms at the moment Nevertheless it can provide a valid VDB signalin space SIS which can be used by GBAS receivers and simulation tools such as Eurocontrols PEGASUS tool The ground facility simulation supports legacy GBAS CAT I GAST C as well as GAST D including all additional VDB information required using GPS and GLONASS Support for Galileo has been added according to WKH H SHULPHQWDO GH QLWLRQV GHVFULEHG earlier In addition to FAS data blocks the ground facility simulation is also capable of providing curved approaches using TAP data blocks Multi Constellation Airborne GBAS Receiver Simulation The GBAS receiver simulation has been used for various GBAS related projects It supports GAST C as well as GAST D and can be configured flexibly to use GPS GLONASS and or Galileo using the experimental enhancements as described earlier For GAST D all airborne monitoring algorithms required DUH SUHVHQW 7KXV WKH DLUFUDIW VSHFL F parameters for example for the airborne JHRPHWU VFUHHQLQJ FDQ EH FRQ JXUHG together with the other parameters Flight Trials The practicability of the multiconstellation GBAS approach has been WHVWHG LQ ÀLJKW WULDOV 7R HQVXUH WKDW DOO four Galileo satellites were in view and capable of providing valid data during our trials an orbit prediction tool and the Notice Advisory to Galileo Users NAGU service of the European GNSS Service Center GSC were used prior to WKH ÀLJKW 7KH GDWD SURFHVVLQJ FRQ JXUDWLRQ LV shown in FIGURE 4 and includes the GBAS simulation components explained earlier All processing is done in real time while recording all data for later post processing Ground Processing On the ground two Septentrio AsteRx3 GNSS receivers connected to two roof top antennas were used The GNSS receivers were connected to the GBAS ground facility simulation via a network and provided binary GPS GLONASS and Galileo raw measurements with an update rate of 2 Hz as well as navigation data Using this data the ground facility simulation generated binary VDB data The GBAS ground facility simulation was configured to generate multiconstellation GAST D VDB data for D WKUHH VORW FRQ JXUDWLRQ OO UHTXLUHG GPS World April 2014 www gpsworld com 48