Accuracy Improvements of Pseudolite Systems - First Results

Christian Altmayer

Abstract:	Pseudolites have developed from sole receiver testing purpose to a navigation system for special applications where today's known satellite navigation systems hardly work or fail. The advantage of pseudolite systems is that transmitter of GPS-like signals can be placed wherever GPS navigation is not possible or hampered by a low number of visible GPS satellites. Another benefit is the rather fast change of navigational geometry with pseudolites which aids in carrier phase ambiguity resolution. The main characteristic of pseudolite navigation is the relatively small distance between the signal source and the receiver compared to the GPS satellites. The small distances between pseudolites and the user receivers not only pose the so-called near-far-problem but also require a thorough treatment of the nonlinear observation equations. For simplicity GPS observation equations are linearized and solved e.g. by (iterative) least-squares methods which is valid for common near-earth navigation with satellites. However, most iterative methods show bad convergence properties in case relatively large measurement errors are present depending on the working point of linearization. The solution to this problem is a break with the linearization and instead a consideration of the nonlinear nature of the observation equations. The Institute of Flight Guidance and Control has developed a multi-purpose low-cost pseudolite system which was tested in several flight trials. Also a new method was implemented that is based on the same idea of minimizing the sum of squared residuals as the least-square method. But instead of trying to compute the solution analytically the minimum is seeked. The results are quite promising and show that the region of convergence is expanded.
Published in:	Proceedings of the 2001 National Technical Meeting of The Institute of Navigation January 22 - 24, 2001 Westin Long Beach Hotel Long Beach, CA
Pages:	491 - 500
Cite this article:	Altmayer, Christian, "Accuracy Improvements of Pseudolite Systems - First Results," Proceedings of the 2001 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 2001, pp. 491-500.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In