Ultra Tight Coupling Implementation Using Real Time Software Receiver

Aleksandar Jovancevic, Andrew Brown, Suman Ganguly, Joseph Noronha and Brijesh Sirpatil

Abstract:	Ultra Tightly Coupled (UTC) INS systems offer numerous advantages in terms of robustness, under high dynamics, improved A/J performance, use of inexpensive INS, minimization of clock error etc. In Ultra Tight Coupling (UTC), all the GPS satellites are tracked through one composite filter, instead of separate tracking filters used in conventional GPS systems. The filter operates on the I and Q correlator outputs and the pseudoranges and the delta ranges can be obtained from the internal states of the Kalman Filter. The simultaneous and composite tracking of different satellites provides aiding to each other resulting in improved accuracies, improved jamming immunity, and high dynamics. We are adopting the Federated Filter Approach, where multiple pre-filters are used (one per satellite) at a relatively high data rate working with the I and Q of the correlator outputs. The outputs from these pre-filters are next used in one composite Kalman Filter operations at a relatively low data rate. This approach provides improved J/S performance by about 15 to 20 dB under high dynamics conditions. The UTC coupling will provide J/S performance around 70 dB. Under high dynamics and jamming conditions, the transition from acquisition to tracking needs to be fast and robust. Direct transition from acquisition to tracking is achieved using the block processing approach pioneered by us, which is further enhanced through INS aiding of the doppler. One of the major benefits of CRS’s approach is the use of “software radio” architecture for overall system design and development. The software system allows easy and convenient simulation of different architectures and once the simulations are satisfactory, the same codes can be used for rapid prototyping of real-time systems. This offers improved performance, flexibility, upward growth and upgrade and modest cost. The UTC coupling scheme combined with the software radio platform developed by us will allow a truly versatile UTC and GNSS system.
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:	1575 - 1586
Cite this article:	Jovancevic, Aleksandar, Brown, Andrew, Ganguly, Suman, Noronha, Joseph, Sirpatil, Brijesh, "Ultra Tight Coupling Implementation Using Real Time Software Receiver," 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. 1575-1586.
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