Positioning for Range-Based Land Navigation Systems Using Surface Topography

摘要

There are many situations in which GPS is either unable to provide the desired level of accuracy or is unavailable. Use of a pseudolite-based system (possibly at non-GPS frequencies) for navigation can be a means for positioning during these times. In many cases a pseudolite system with ground based transmitters has difficulty in determining the height of the receiver accurately, due to the poor vertical observability inherent in the geometry of the system.rnThis paper investigates and develops five methods of incorporating the known surface topography in a nonlinear batch least squares estimation algorithm using carrier-phase measurements from pseudolites. While the specific carrier-phased pseudolite example is used throughout this paper, the height constraint methods would apply to any range-based positioning systems for surface use.rnReal and simulated data sets are used to evaluate the performance of the five algorithms. In simulation, all methods performed equivalently well on a flat surface. When simulating a hill, constraining the solution to lie inrna plane tangent to the surface topography appeared to aid the solution with the best knowledge of the terrain. Use of a pseudo-measurement, a commonly used approach, did not provide the best results. Analysis of data from a real pseudolite system on a ground-based vehicle demonstrated sub-decimeter level positioning accuracy in all three dimensions.