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 Authorization to photocopy items for internal educational or personal use or the internal educational or personal use of specific clients is granted by Questex Media Group Inc for libraries and other users registered with the Copyright Clearance Center 222 Rosewood Dr Danvers MA 01923 978 750 8400 fax 978 750 4470 For uses beyond those listed above please direct your written request to questexpermissions@ reprintbuyer com or 800 494 9051 Ext 100 PRIVACY NOTICE Questex Media Group provides certain customer contact data such as customers names addresses phone numbers and e mail addresses to third parties who wish to promote relevant products services and other opportunities which may be of interest to you If you do not want Questex Media Group to make your contact information available to third parties for marketing purposes simply call toll free 866 344 1315 or 1 847 763 9594 Outside the US between the hours of 8 30 am and 5 pm CT and a customer service representative will assist to remove your name from Questexs lists GPS WORLD ISSN 1048 5104 is published monthly 12 issues yr by Questex Media Group Inc 306 W Michigan St Ste 200 Duluth MN 55802 SUBSCRIPTION RATES U S and possessions 1 year 12 issues 67 2 years 24 issues 117 Canada and Mexico 87 1 year 137 2 years All other countries 127 1 year 232 2 years International pricing includes air expedited service Single copies prepaid only 7 in the United States 9 all other countries Back issues if available are 19 in the U S and possessions 23 all other countries Include 650 per order plus 2 per additional copy for U S postage and handling Periodicals postage paid at Duluth MN 55806 and additional mailing offices POSTMASTER Please send address changes to GPS WORLD P O Box 1270 Skokie IL 60076 8270 USA Canadian G S T number 840 033 278 RT0001 Publications Mail Agreement Number 40017597 Printed in the U S A GPS World June 2009 www gpsworld com 58