GPS World, April 2014

System Design Test INNOVATION messages MT1 MT2 including all required ADBs MT3 MT4 and MT11 were generated and sent to the telemetry facility via the network Telemetry Official VHF data broadcasts operate in a frequency band between 108 and 118 MHz which is reserved for authorized aviation applications However for our experimental system an alternative data link was used The Institute of Flight Guidance operates a full duplex telemetry system to share data between ground and aircraft Even though the operating frequencies are different the telemetry system allows the generated binary VDB data to be transmitted to research aircraft The airborne telemetry receiver outputs data as if it were a VDB receiver to allow us to switch between a real VDB receiver and the telemetry receiver easily Research Aircraft The Institute of Flight Guidance operates the research aircraft of the Technische Universität Braunschweig The Dornier Do 128 6 with the call sign D IBUF see FIGURE 5 is a twin engine turboprop aircraft without a pressurized cabin and has been used multiple times for GBAS related research over the years The research aircraft allows us to flexibly integrate H SHULPHQWDO HTXLSPHQW IRU VSHFL F ÀLJKW WULDOV RU WKH PXOWL FRQVWHOODWLRQ 6 ÀLJKWV D 9 HOWD 166 receiver capable of multiple constellations and frequencies a telemetry receiver and an experimental cockpit display were installed temporarily Airborne Processing The online GBAS receiver simulator XVHV 166 GDWD IURP WKH 9 HOWD 166 UHFHLYHU together with the VDB data received via telemetry The UHFHLYHU ZDV FRQ JXUHG WR RXWSXW UDZ 36 21 66 and Galileo measurements with an update rate of 10 Hz 7KH VLPXODWRU ZDV FRQ JXUHG WR XVH WKLV GDWD WR FDOFXODWH D multi constellation GAST D solution Based on the selected DSSURDFK GH QLWLRQ WKH UHVXOWLQJ LQIRUPDWLRQ GHYLDWLRQV distance to threshold and so on was displayed in the cockpit using an experimental cockpit display Results 7KH ÀLJKW WHVW ZDV FRQGXFWHG LQ WKH HYHQLQJ RI 1RYHPEHU 87 DW 5HVHDUFK LUSRUW UDXQVFKZHLJ 9 H SHUIRUPHG YH DSSURDFKHV ZLWK D QDXWLFDO PLOH QDO VHJPHQW 7KH ÀLJKW SDWK DV FDOFXODWHG by the GBAS receiver subsystem is shown in FIGURE 6 FIGURE 7 shows the number of satellites used for the GBAS receiver simulation and distinguishes between the different satellite navigation systems used Up to 22 satellites have been used simultaneously for GBAS processing including XS WR 36 VDWHOOLWHV HLJKW 21 66 VDWHOOLWHV DQG IRXU Galileo satellites YHQ WKRXJK QR FHUWL HG 6 HTXLSPHQW ZDV XVHG IRU WKH ÀLJKW WULDOV FIGURE 8 shows the resulting vertical and ODWHUDO SURWHFWLRQ OHYHOV 93 DQG 3 RI WKH RQOLQH PXOWL FRQVWHOODWLRQ 6 UHFHLYHU VLPXODWLRQ RWK YDOXHV ÀXFWXDWH due to the differences between 100 and 30 second smoothing position solutions which have to be added to the protection OHYHOV IRU 67 1HYHUWKHOHVV ERWK VHWV RI YDOXHV UHPDLQ FOHDUO EHORZ WKH FRUUHVSRQGLQJ OHUW LPLWV 6 DWHUDO ODUP LPLW 6 PHWHUV 6 9HUWLFDO ODUP LPLW 69 PHWHUV YDOLG 67 VHUYLFH ZDV achieved continuously FIGURE 9 shows a vertical integrity diagram commonly known as a Stanford plot for the integrity of the multiconstellation GBAS simulation This plot shows the Vertical 3URWHFWLRQ HYHO 93 DV GHWHUPLQHG E WKH 6 UHFHLYHU VLPXODWLRQ DJDLQVW WKH DFWXDO 9HUWLFDO 3RVLWLRQ UURU 93 7KH 9HUWLFDO 3RVLWLRQ UURU LV D GLUHFW PHDVXUH IRU WKH 9HUWLFDO 1DYLJDWLRQ 6 VWHP UURU 9 16 7KLV KDV EHHQ GHWHUPLQHG using a precise point positioning reference trajectory Both YDOXHV DUH QRUPDOL HG E WKH FXUUHQW 9 DV WKHVH YDOXHV FKDQJH GXULQJ WKH DSSURDFKHV XULQJ WKH ÀLJKW WKH 6 RQOLQH SURFHVVLQJ UDQ DW D UDWH RI UHVXOWLQJ LQ GAST D epochs and an availability of 100 percent Of course these results must not be misinterpreted as a multiconstellation GBAS performance assessment The ground facility simulation was highly experimental and lacked any kind RI ORQJ WHUP DQDO VLV YHQ WKH 166 DQWHQQDV XVHG GR QRW meet formal requirements However aside from a quantitative FIGURE 6 Flight trial trajectory Map data OpenStreetMap contributors 35 30 25 20 15 10 5 0 Number of satellites used Combined GPS GLONASS Galileo GPS GLONASS Galileo 166 168 170 172 174 176 178 180 182 Time of day hours FIGURE 7 Number of satellites used by the multi constellation GBAS receiver simulation www gpsworld com April 2014 GPS World 49