GPS World, September 2013

Algorithms Methods INNOVATION Second the precise relative motion of the antenna during the beam forming interval must be known Again it can be estimated if enough VXI FLHQWO FOHDQ VLJQDOV DUH WUDFNHG 7KH DQWHQQD WUDMHFWRU LV HVWLPDWHG GLUHFWO IURP WKH correlator values as shown later LQ WKLV DUWLFOH Q PRUH VHYHUHO degraded environments the DQWHQQD PD EH PRYHG DORQJ D NQRZQ WUDMHFWRU H DUH developing a rotating antenna displacement unit see FIGURE 1 The rotational unit targets IRUHVWU DQG LQGRRU VXUYH LQJ FIGURE 1 Artists impression of the synthetic aperture GNSS system for surveying in a forest applications The relative motion of the antenna is measured ZLWK VXE PLOOLPHWHU DFFXUDF After beam forming the code pseudoranges and the carrier SKDVHV DUH H WUDFWHG DQG XVHG LQ D FRQYHQWLRQDO ZD 7KDW LV WKH DUH ZULWWHQ LQWR 5HFHLYHU QGHSHQGHQW FKDQJH 51 IRUPDW OHV DQG VWDQGDUG JHRGHWLF VRIWZDUH FDQ EH XVHG WR HYDOXDWH WKHP Q WKH FDVH ZKHUH WKH DUWL FLDO PRYHPHQW DQWHQQD LV XVHG WKH 166 VLJQDO SURFHVVLQJ UHPRYHV WKH NQRZQ SDUW of the movement from the observations and the observations are then like those from a static antenna As a result common VWDWLF SRVLWLRQLQJ DOJRULWKPV LQFOXGLQJ FDUULHU SKDVH DPELJXLW fixing can be applied The presented method therefore SUHSDUHV WKH SDWK IRU 166 VXUYH LQJ DSSOLFDWLRQV LQ QHZ areas An important point is the mechanical realization of the DQWHQQD PRYHPHQW 7KLV KDV WR EH GRQH LQ D FRVW HI FLHQW DQG UHOLDEOH ZD XEULFDWLRQ IUHH DFWXDWRUV DUH XVHG WRJHWKHU ZLWK PDJQHWLF GLVSODFHPHQW VHQVRUV 7KH VHQVRUV DUH V QFKURQL HG to the software receiver front end with better than 1 millisecond DFFXUDF 7KH URWDWLQJ DQWHQQD XVHV VOLS ULQJV WR FRQQHFW WKH antenna elements The rotating antenna can also be used to map the received signal power as a function of elevation and azimuth DQJOHV 7KLV LV EHQH FLDO IRU UHVHDUFKHUV RU H DPSOH LW FRXOG EH XVHG WR HVWLPDWH WKH GLUHFWLRQ RI DUULYDO RI D VSRR QJ VLJQDO or to determine which object causes multipath in an indoor HQYLURQPHQW RU WKH ODWWHU SXUSRVH WKH URWDWLQJ DQWHQQD FDQ EH HTXLSSHG ZLWK OHIW KDQG DQG ULJKW KDQG FLUFXODUO SRODUL HG antennas on both ends of the rotating bar The rotating antenna LV PRXQWHG RQ D JHRGHWLF WULSRG 6HH XUWKHU 5HDGLQJ IRU UHSRUWV of initial studies of the rotating antenna Tracking Modes 7KH V QWKHWLF DSHUWXUH WUDFNLQJ VFKHPH FDQ EH H WHQGHG to different user motion schemes or sensor aiding schemes DOORZLQJ D ZLGH UDQJH RI DSSOLFDWLRQV 7KLV LV UHÀHFWHG LQ WKH algorithm implementation within the modular structure of the VRIWZDUH UHFHLYHU 7KH EDVH PRGXOH WUDMHFWRU ORFN VWLPDWRU LQ FIGURE 2 SUHSDUHV WKH V QWKHWLF DSHUWXUH WUDFNLQJ scheme Different implementations derive from this base class DFK GHULYHG PRGXOH LV XVHG IRU D GLIIHUHQW XVHU PRWLRQ VFKHPH FIGURE 2 Different μ trajectory motion estimators used by the synthetic aperture processing FIGURE 3 Synthetic aperture signal processing FIGURE 4 Triangular test course in a forest and makes use of a different sensor DVLFDOO WKH PRGXOHV GLIIHU LQ WKH ZD WKH HVWLPDWH WKH relative antenna motion over the beam forming interval This UHODWLYH PRWLRQ LV FDOOHG WKH WUDMHFWRU 8VXDOO WKH WUDMHFWRU covers time spans from a few hundreds of milliseconds to a few seconds The μ trajectories have the following characteristics 7KH SHGHVWULDQ PRWLRQ HVWLPDWRU GRHV QRW UHO RQ DQ VHQVRU PHDVXUHPHQWV DQG WV D VHFRQG RUGHU SRO QRPLDO LQWR WKH XVHU WUDMHFWRU RI D ZDONLQJ SHGHVWULDQ VHFRQG RUGHU SRO QRPLDO LV JRRG IRU UHSUHVHQWLQJ WKH PRWLRQ IRU up to a quarter of a second The sensor input to the rotating antenna estimator is the relative angular displacement of the rotating antenna The estimator estimates the absolute direction which is stable LQ WLPH 7KXV WKH QXPEHU RI WUDMHFWRU SDUDPHWHUV HTXDOV one The vertical antenna motion estimator retrieves the vertical position of the antenna and does not estimate www gpsworld com September 2013 GPS World 43