Optimization of Cascade Integer Resolution with Three Civil GPS Frequencies

Jaewoo Jung, Per Enge and Boris Pervan

Abstract:	In the near future, there will be two more civil GPS signals in addition to the current one at the L 1 frequency (1575.42 MHz). The second civil signal will be broadcast at the L2 frequency (1227.60 MHz), and the third civil signal will be broadcast at the recently-selected Lc frequency (I 176.45 MHz). With three civil frequencies, a user can generate three beat frequency signals. The LI and L2 carrier frequencies are processed to create the Widelane (WL) with wavelength of 86 centimeters. The combination of the L 1 and Lc carrier frequencies yields the second beat frequency with 75 centimeters in wavelength (Medium Lane, ML). The combination of the L2 and Lc carrier frequencies yields the third beat frequency with 5.9 meters in wave-length (Extra Widelane, EWL). In earlier research [8], an instantaneous geometry-free carrier-phase DGPS integer ambiguity resolution technique was developed utilizing the multiple available beat frequencies. This technique, known as Cascade Integer Resolution (CIR), resolves the integer ambiguities successively from the longest to the shortest beat wavelength. The performance of CIR was examined in the earlier study, and it was shown that CIR can be used to resolved the Lc integer ambiguity with probability of wrong integer resolution of IE-4 up to 2.4 kilometers from a reference station. It can also resolve the WL integer ambiguity up to 22 kilometers, and the EWL integer ambiguity beyond that, with the same probability of incorrect integer resolution. Performance degradation of the CIR over distance mainly comes from the spatial decorrelation of ionospheric error (residual differential troposphere error is eliminated by the geometry-free CIR process). This paper focuses on recent improvements to CIR performance to extend service volume and reduce the probability of incorrect integer resolution. First, effect of decrease in measurement error on performance of the CIR is examined. Then, the spatial gradient of the residual differential ionosphere error, which was assumed to have a fixed standard deviation of 2 parts per million in the earlier research, is estimated by using measurements from two different user locations. Estimation of ionospheric spatial decorrelation is integrated into the CIR process. With these enhancements, performance of the CIR increased. With the probability of incorrect integer ambiguity resolution of IE-4, the optimized CIR can resolve the Lc integer up to 4 km (increases of 2.4 km) and the WL integer up to 40 km (increase of 22 km).
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	2191 - 2200
Cite this article:	Jung, Jaewoo, Enge, Per, Pervan, Boris, "Optimization of Cascade Integer Resolution with Three Civil GPS Frequencies," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 2191-2200.
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