Evaluation of Coupled GPS/INS Integration Using Software GPS Receiver Model

Eng-Kee Poh, Alvin Koh, and Gabriel Wong

Abstract:	The ability to simulate GPS receivers is crucial in the validation of new algorithms. In particular, to simulate tight and deep integration of GPS/INS schemes, the software GPS model should include the sampling and quantization processes and the receiver tracking loops should be able to generate I-Q and pseudorange/deltarange measurements. The software model should also be of reasonable fidelity so that objective evaluation of GPS/INS integration schemes can be performed. In this paper, we will present the development of a software GPS simulator and GPS receiver model which could perform signal conditioning, sampling, quantization, carrier and code-wipeoff, carrier and code tracking and generate measurements of I-Q samples, pseudo-ranges and deltaranges. A software GPS simulator was first developed to generate a GPS signal based on actual satellite and receiver dynamics. The GPS signal simulator is used to test the effectiveness of the GPS receiver algorithms under various dynamics and external noise conditions. The simulator produces samples of the signal that would be received at the receiver after signal conditioning, down-conversion, sampling and quantization. The effects of different interference sources, sampling rates and number of bits used to quantize could also be modelled. The GPS signal simulator also provides an estimate of carrier-to-noise power ratio. The software GPS receiver model allows the user to adjust the code and carrier loop filter bandwidths and predetection time intervals. This is to optimize the carrier/code-tracking performance in the presence of noise and receiver-satellite dynamics. The software model also facilitates velocity loop aiding which is implemented in tight GPS/INS integration schemes. The model also provides raw data at all steps of the receiver demodulation and signal tracking process. This allows the user to implement and evaluate the ultra-tight GPS/INS algorithm which, generally requires access to in-phase (I) and quadrature (Q) data measurements. Both these software modules were used together to evaluate the performances of loosely-coupled, tightly coupled and ultra-tight GPS/INS integration schemes under different operating scenarios. To facilitate the performance comparison of loosely-coupled, tightlycoupled, and ultra-tight GPS/INS integration, a Kalman filter model was designed and simulated. The simulation results validate the benefit of velocity loop aiding scheme used in tightly coupled GPS/INS techniques to provide good dynamics tracking and interference noise rejection. The merit of a single centralized Kalman filter in an ultratight configuration in adaptively modifying the loop filter bandwidth based on the carrier to noise ratio in the individual channels is also demonstrated.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2443 - 2450
Cite this article:	Poh, Eng-Kee, Koh, Alvin, Wong, Gabriel, "Evaluation of Coupled GPS/INS Integration Using Software GPS Receiver Model," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2443-2450.
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