Improvements of GNSS Receiver Performance Using Deeply Coupled INS Measurements

Christian Kreye, Bernd Eissfeller and Jón Ólafur Winkel

Abstract:	Beside of influences from space and control segments the GNSS performance depends on several parameters, e.g. signal properties, multipath, signal interruptions, signalto- noise ratio, dynamics and receiver errors like thermal noise and oscillator instabilities. The effects of these influences are based on the behaviour of the Phase Lock Loop (PLL) and the Delay Lock Loop (DLL) implemented in the GNSS receiver. To guarantee a precise navigation solution the loop errors have to be significantly low in comparison to the lock thresholds. The first part of the paper presents investigations about the interaction of loop bandwidth, signal-to-noise ratio, accelerations, oscillator Allan variance and oscillator vibrations. A discussion is presented concerning satellite signals in L- and C-band. C-band is currently discussed in Europe for the governmental service in GALILEO. Consequently under high dynamic conditions or in a jamming environment the dynamics of the pseudoranges have to be removed from the loop signal to keep them in lock. If the receiver dynamics on the other hand are measured by an low cost INS, the range accelerations can be computed. In this context investigations about the tightly and deeply coupling principles between GNSS and INS are presented. After filtering the INS-data is added to the GNSS receiver DLL and PLL directly. A possible filter design for low cost INS-data and its properties are described. In opposite of the unaided receiver the tightly coupled sensors are no longer depending on the accelerations but on the accelerometer bias and gyro drift behavior of the INS. The Schuler frequency dominates the jitter value of the loops. The paper demonstrates that a gyro rate of approximately 1°/h is necessary to support the phase lock loop. Concerning the delay lock loop a gyro rate of 10°/h is sufficient. In next part of the paper a simulation tool for a deeply coupled GPS/INS-Sensor is described. Used algorithms and sensor models are specified. The data flow beginning with original data and ending with the integrated navigation solution is presented. Advantages and problems of the combined sensor system are mentioned. Finally the plannings of a deeply coupled GPS/INS system are presented. Hardware and software aspects concerning data procession and time synchronisation are noted.
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:	844 - 854
Cite this article:	Kreye, Christian, Eissfeller, Bernd, Winkel, Jón Ólafur, "Improvements of GNSS Receiver Performance Using Deeply Coupled INS Measurements," 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. 844-854.
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