GPS World, September 2013

INNOVATION Algorithms Methods Synthetic Aperture Antenna Pattern With the same methodology as referenced previously it is possible to estimate the synthetic antenna gain pattern We assume that the pattern simply maximizes the line of sight signal power for an assumed satellite elevation angle of 45 and an azimuth of 135 We use a rotation radius of 50 cm The antenna has a really high directivity eliminating scattered signals from trees The gain pattern is symmetric with respect to the horizon and ground multipath of perfectly flat ground would not be mitigated by the synthetic aperture Ground multipath is only mitigated by the antenna element itself for example a small ground plane can be used RZHYHU PRVWO WKH JURXQG LV QRW ÀDW and in that case the rotating antenna also mitigates the ground multipath Results with a Simulator The rotating antenna has been tested with simulated GNSS signals using an RF signal generator The signal generator was FRQ JXUHG WR VWDUW ZLWK WKH DQWHQQD DW rest and at some point the antenna starts rotating with a speed of 15 revolutions per minute Six GPS L1 C A code signals have been simulated The signal processing unit has to estimate the antenna state static or rotating and the north direction The quality of the estimation can be visualized by comparing the complex argument of the prompt correlator values to the modeled correlator values Two examples are shown in FIGURES 8 AND 9 In Figure 8 the differences are at the millimeter level corresponding to the carrier phase thermal noise This indicates that the absolute heading and receiver clock parameters have been estimated to a high precision I PXOWLSDWK IURP D UHÀHFWLRQ SODQH is present see Figure 9 the phase UHVLGXDOV VKRZ WKH PXOWLSDWK UHÀHFWLRQ For example around t 065 seconds in WKH JXUH WKH DQWHQQD LV PRYLQJ SDUDOOHO WR WKH UHÀHFWLRQ SODQH DQG WKH SKDVH residuals are constant over a short time span As the distance of the antenna to WKH UHÀHFWLRQ SODQH FKDQJHV WKH SKDVH residuals start to oscillate Generally the estimation of the absolute heading and of the receiver clock parameters works even with strong multipath signals but the parameters are not as stable as in the multipath free case In the case when the antenna is rotating signal processing has to remove the rotation from the code and carrier observations To check if this HOLPLQDWLRQ RI WKH DUWL FLDO PRWLRQ LV done correctly we use carrier smoothed code observations to compute a singlepoint positioning solution Only if the antenna is rotating can the system estimate the absolute heading and refer the observations to the rotation center Before that point the observations refer to the antenna position The antenna position and the rotation center differ by the radius of 05 meters Since the position is stable for t 100 seconds we conclude that the elimination of the DUWL FLDO PRWLRQ KDV EHHQ GRQH FRUUHFWO Conclusion We are in the process of developing positioning solutions for degraded environments based on principles of synthetic aperture processing The tools target operational use as an end goal supporting standard geodetic form factors tripods and the software receiver running on standard laptops and producing data in standardized formats such as RINEX or the National Marine Electronics Association NMEA standards Acknowledgments The research leading to the results reported in this article received funding from the European Communitys Seventh Framework Programme FP7 2007 2013 under grant agreement No 287226 This support is gratefully acknowledged It also received funding from the Upper Bavarian Administration Aerospace Support Program under the contract number 20 8 34102 14 2012 FAUSST which is also thankfully acknowledged This article is based on the paper Concept of Synthetic Aperture GNSS Signal Processing Under Canopy presented at the European Navigation Conference 2013 held in Vienna Austria April 23 25 2013 Manufacturer The research described in this article used an IFEN www ifen com SXNSR GNSS software receiver and an IFEN NavX NCS RF signal generator The rotating antenna displacement unit was designed and manufactured by Blickwinkel Design Development www blickwinkel at THOMAS PANY works for IFEN GmbH in Munich Germany as a senior research engineer in the GNSS receiver department He also works as a lecturer Priv Doz at the University of the Federal Armed Forces FAF Munich and for the University of Applied Science in Graz Austria His research interests include GNSS receivers GNSS INS integration signal processing and GNSS science NICO FALK received his diploma in electrical engineering from the University of Applied Sciences in Offenburg Germany Since then he has worked for IFEN GmbH in the receiver technology department focusing on signal processing hardware and field programmable gate array development BERNHARD RIEDL received his diploma in electrical engineering and information technology from the Technical University of Munich Since 1994 he has been concerned with research in the field of real time GNSS applications at the University FAF Munich where he also received his Ph D In 2006 he joined IFEN GmbH where he is working as the SX NSR product manager JON O WINKEL is head of receiver technology at IFEN GmbH since 2001 He studied physics at the universities in Hamburg and Regensburg Germany He received a Ph D Dr Ing from the University FAF Munich in 2003 on GNSS modeling and simulations FRANZ JOSEF SCHIMPL started his career as a mechanical engineer and designer at Wigl Design while studying mechanical engineering In 2002 he founded Blickwinkel Design Development with a focus on prototyping and graphic design MORE ONLINE Further Reading For references related to this article go to gpsworld com and click on Innovation in the navigation bar COPYRIGHT 2013 NORTH COAST MEDIA LLC All rights reserved No part of this publication may be reproduced or transmitted in any form by any means electronic or mechanical including by photocopy 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