GPS World, March 2016
ALTERNATIVE PNT ALTERNATIVE PNT The corresponding SOP state estimates were collaboratively estimated by receivers in the navigating receivers vicinity The pseudoranges and SOP estimates were fed to a leastsquares estimator producing x r and associated P from which the VDOP HDOP and GDOP were calculated and tabulated in TABLE 2 for M GPS SVs and N cellular CDMA SOPs A sky plot of the GPS SVs used is shown in FIGURE 5 The tower locations receiver location and a comparison of the resulting 95th percentile estimation uncertainty ellipsoids of x r for M N 50 and 53 are illustrated in FIGURE 6 The corresponding vertical error was 182 meters and 065 meteres respectively Hence adding three SOPs to the navigation solution that used five GPS SVs reduced the vertical error by 643 percent Although this is a significant improvement over using GPS observables alone improvements for aerial vehicles are expected to be even more significant since they can exploit a full span of observable elevation angles as demonstrated in the simulation section CONCLUSION This article studied the VDOP reduction of a GNSS based navigation solution by exploiting terrestrial SOPs It was demonstrated that the VDOP of a GNSS solution can be reduced by exploiting the inherently small elevation angles of terrestrial SOPs Experimental results using ground vehicles equipped with SDRs demonstrated VDOP reduction of a GNSS navigation solution by exploiting a varying number of cellular CDMA SOPs Incorporating terrestrial SOP observables alongside GNSS SV observables for VDOP reduction is particularly attractive for aerial systems since a full span of observable elevation angles becomes available MANUFACTURERS Two National Instruments universal software radio peripherals were used in the experiment A Trimble 5700 receiver surveyed the experimental receiver location JOSHUA J MORALES is pursuing a Ph D in electrical and computer engineering at the University of California Riverside JOE J KHALIFEH is a Ph D student at the University of California Riverside ZAHER ZAK M KASSAS is an assistant professor at the University of California Riverside He received a Ph D in electrical and computer engineering from the University of Texas at Austin Previously he was a research and development engineer with the LabVIEW Control Design and Dynamical Systems Simulation Group at National Instruments Corp This article is based on a technical paper presented at the 2016 ION ITM conference in Monterey California MARCH 2016 WWW GPSWORLD COM GPS WORLD 29
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