Vertical Dilution Of Precision Research Articles

Flight Test Results of an Integrated Wideband Airport Pseudolite for the Local Area Augmentation System

ABSTRACT: This paper details the first real-time integration of a wideband airport pseudolite (WBAPL) into the Local Area Augmentation System (LAAS) and illustrates the benefits accrued from this integration. Flight test results obtained using two pulsing formats (1/11th and a modified RTCA pulsing format), a full GPS satellite vehicle (SV) constellation, and a reduced SV set are presented. While WBAPL bias-value (B-value) averages were generally higher than those obtained for GPS SVs (the standard deviations were comparable), inclusion of the WBAPL still provided an improvement in performance for a reduced GPS SV constellation set. With a healthy constellation (11 SVs), integration of the WBAPL into the differential solution resulted in little difference in the final solution over the last 2.5 to 0.2 nmi of the approaches. However, with a reduced constellation available (˜4–5 SVs), inclusion of the WBAPL resulted in a significant improvement in the LAAS system performance in terms of an increase in availability, decrease in vertical dilution of precision (VDOP), and increase in position accuracy over the differential GPS (DGPS)-only case.

Relationship between navigation vertical error, VDOP, and pseudo-range error in GPS

At a specified position and time, vertical position error is related to satellite ranging errors by the relationship Z=VDOP*URE where URE is the user range equivalent error, VDOP is the vertical dilution of precision, and Z is the vertical position error. This relationship is developed and it is shown that it is statistically correct even when position and time are variables. Expressions are given for the density, cumulative distribution, and standard deviation of Z in terms of the distributions of VDOP and URE. Vertical position error is investigated at several locations and the results compared with published work. A simple method for converting VDOP distributions to distributions of vertical accuracy as an alternative to computer simulation is presented. >