Ultra Tightly Coupled GPS/INS Receiver for TSPI Applications

Lars Dyrud, Bill Woessner, Aleksandar Jovancevic, and Suman Ganguly

Abstract:	Time and Space Position Information (TSPI) is an aviation environment demands stringent performance requirements from navigational receivers. The high dynamics and varying attitude pose a highly dynamic environment for conventional receivers to be able to acquire and track GPS satellites. The signal environment is often further degraded by interference, jamming, and multipath. TSPI receivers must provide a highly accurate estimate of the relevant parameters, such as position, velocity, and acceleration orientation, as well as basic observables such as pseudorange, phase, bias, and drift (satellites, receiver, IMU). In order to meet these demands, the Center for Remote Sensing, Inc. (CRS) has designed and developed an Ultra Tightly Coupled (UTC) receiver for TSPI applications. The UTC receiver utilizes MEM-based IMUs yet provides cm-level accuracies under difficult environments. UTC GNSS-INS systems enable high precision navigation in high-dynamics, high-jamming environments. The systems move away from the traditional GNSS receivers that use tracking loops to maintain lock on satellite signals. The navigation filter itself provides error estimates of position and velocity that are provided as feedback to the INS, code generation and correlators. This approach essentially uses base level GPS measurements to calibrate and correct an INS, improving accuracy of navigation by elimination of tracking loops and constraining the INS with IMU error corrections. The use of a software-reconfigurable receiver enables the receiver to dynamically reconfigure to respond to changing scenarios, i.e. the presence of a jammer or high G conditions. In this manner continuous tracking of the satellites is assured with precise navigation capabilities. This approach provides improved J/S performance significantly higher under high dynamic conditions. The paper describes the UTC architecture and TSPI receiver developed at CRS and compares its performance against a conventional GNSS receiver. Several issues associated with precision are also addressed. The tests are carried out using a CRS GNSS Signal Simulator to generate the trajectories and signal dynamics. The software based approach allows rapid prototyping and can accommodate a variety of IMUs ranging from MEM based systems to highly specialized units.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	2563 - 2572
Cite this article:	Dyrud, Lars, Woessner, Bill, Jovancevic, Aleksandar, Ganguly, Suman, "Ultra Tightly Coupled GPS/INS Receiver for TSPI Applications," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 2563-2572.
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