GPS World, June 2009
INNOVATION GPS Modernization both cases For the central three hour interval during which the L5 signal was received with normal signal strength the achieved tracking accuracy clearly outperforms that of the L1 C A code signal for the given receivers For further comparison FIGURE 10 shows sample results of GIOVE B E5a tracking with receiver type J Again the GPS L5 signal at medium to high elevation angles is fully competitive and a notable degradation is only evident when the signal strength is well below the values to be expected in the future operational system Legacy Signal Anomaly While the GPS L5 signal transmission by SVN49 is clearly designated as experimental the legacy signals that is the C A and P Y code on L1 as well as L2Cand P Y code on L2 were expected to achieve the same level of performance as observed on other satellites of the existing constellation This is not the case however in the L1 band where both the C A code measurements and the semicodeless P Y code pseudoranges exhibit a systematic elevation angle dependent bias This bias is not specific to any of our test receivers and can be similarly observed in heritage receivers employed at the stations of the International GNSS Service IGS As an example FIGURE 11 illustrates the variation of the C A code error for high elevation angle passes of SVN49 over western Canada and Germany The bias varies between approximately 05 meters near the horizon and 1meter near zenith The cause of the bias is unclear but resides apparently in the design of the transmitter antenna or signal generation chain It is exclusively seen on SVN49 and not on other GPS or GIOVE satellites which excludes a possible problem of the receiver antenna or environment Furthermore data collected at UNB using the UNBJ IGS station a few days after launch clearly demonstrate that the elevation angle dependent L1 bias existed well before L5 signal activation and therefore might not be related to the signal generator It is unclear to what extent the L1 signal bias can be corrected on the spacecraft and how it will affect the declaration of SVN49 as a fully healthy satellite Conclusions Tracking and analysis of SVN49 s L5 signal using both the 30 meter dish and code correlating receivers reveals that it possesses improved signal characteristics with respect to the legacy signals in particular with regard to its bandwidth and therefore will allow even more accurate and reliable positioning when the signal is deployed on the future Block IIF constellation Acknowledgments We thank NovAtel and JAVAD GNSS for supplying special firmware Sébastien Carcanague at UNB and DLR colleagues at Weilheim for their help The L5 signal description comes from the Innovation article by A J Van Dierendonck and C Hegarty PRN G01 2009 04 16 PRN G01 6h 9h 12h 15h 2009 04 16 20 10 00 10 20 MP C1C meters 20 10 00 10 20 MP C1C meters 18h 21h 17 3h GPS Time Å FIGURE 11 Pseudorange errors of SVN49 L1 C A code tracking for high elevation angle passes using a type A receiver at IGS station DRAO in Penticton Canada top and a type J receiver at Oberpfaffenhofen bottom The satellite achieved peak elevation angles of about 70 and 80 respectively at the two sites September 2000 issue of GPS World MICHAEL MEURER received a Ph D in electrical engineering from the University of Kaiserslautern Germany He is director of the Department for Navigation in the Institute for Communications and Navigation of the German Aerospace Center DLR STEFAN ERKER received his diploma degree in information technology from the Technical University of Kaiserslautern and works at DLRs Institute for Communications and Navigation STEFFEN THÖLERT received his diploma degree in electrical engineering from the University of Magdeburg and works at DLR OLIVER MONTENBRUCK works at DLRs German Space Operations Center Oberpfaffenhofen where he is head of the GPS Technology and Navigation Group He holds a Dr rer nat degree in physics ANDRÉ HAUSCHILD received his diploma degree in mechanical engineering from the Technical University of Braunschweig Germany and is a Ph D candidate at DLRs German Space Operations Center Manufacturers Receiver N is the NovAtel www novatel com EuroPak 15a Receiver J is the JAVAD GNSS www javad com Triumph Delta G2T Receiver A is an Allen Osborne Associates AOA Benchmark ACT www itt com Space Engineering www space it Galileo Experimental Sensor Station antenna Trimble www trimble com Zephyr Geodetic II antenna and AOA D MT antennas were used MORE ONLINE Further Reading For references related to this article go to gpsworld com and click on Innovation under Resources in the left hand navigation bar COPYRIGHT 2009 QUESTEX MEDIA GROUP INC All rights reserved No part of this publication may be reproduced or transmitted in any form or by any means electronic or mechanical including by photocopy recording or information storage and retrieval without permission in writing from the publisher Questex Media Group Inc 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