Performance Analysis and Experimental Validation of a Doppler-Aided GPS/INS Receiver for JPALS Applications

Tsung-Yu Chiou, Santiago Alban, Sarah Atwater, Jennifer Gautier, Sam Pullen, Per Enge, Dennis Akos, Demoz Gebre-Egziabher and Boris S. Pervan

Abstract:	The Joint Precision Approach and Landing System (JPALS) is the next generation aircraft precision approach and landing system being sponsored by US Department of Defense. This GPS-based system will provide joint operational capability for military users to perform assigned conventional and special operations missions from fixed-base, tactical, shipboard, and austere environments under a wide range of meteorological and terrain conditions. JPALS is expected to operate in the presence of significant radio frequency interference (RFI) and hostile jamming, the presence of which will reduce the effective received signal power, and thus degrade navigation accuracy and integrity of the system. Previous research has proposed using Doppler-aided carrier-tracking loops as a component of the anti-jam solution. Since Doppler aiding removes platform dynamic stress, the required bandwidth of the carrier-tracking loop can be reduced to mitigate wide-band interference. Thus, Doppler aiding via an inertial measurement unit (IMU), can improve the robustness of the GPS receiver for operation in extreme RFI environments as well as in high dynamical situations. To validate the benefits of Doppler aiding, three experimental data sets consisting of Intermediate Frequency (IF) samples from a GPS receiver and time-synchronized IMU measurements are collected. Three clock sources are used to drive a software GPS receiver for collecting the GPS data sets: a rubidium atomic standard, an oven-controlled crystal oscillator (OCXO) and a temperature-compensated crystal oscillator (TCXO). The inertial measurements are obtained from an automotive grade IMU (i.e., gyro in-run stability on the order of 180deg/hr) and a tactical grade IMU (i.e., gyro in-run stability between 1 and 10 deg/hr). Hence, six GPS/IMU data sets are collected to allow a comprehensive analysis on the impacts of the different combinations of critical components. The software receiver processing incorporates both the GPS and IMU measurements, and tracks the GPS carrier with a third order carrier-tracking loop. One of the metrics used for judging the carrier-tracking loop performance is the measured phase-error, which is evaluated with varying tracking-loop noise bandwidths. The results of this investigation show that for high-quality GPS oscillators (OCXO or atomic clocks) the bandwidth of the carrier-tracking loops can be reduced to about 1Hz with the use of Doppler-aiding from a GPS/INS navigation filter. Further reduction of the bandwidth is expected with more optimized navigation filters. Keywords: JPALS, anti-jamming, Doppler aiding, GPS/INS integration
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1609 - 1618
Cite this article:	Chiou, Tsung-Yu, Alban, Santiago, Atwater, Sarah, Gautier, Jennifer, Pullen, Sam, Enge, Per, Akos, Dennis, Gebre-Egziabher, Demoz, Pervan, Boris S., "Performance Analysis and Experimental Validation of a Doppler-Aided GPS/INS Receiver for JPALS Applications," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1609-1618.
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