Seamless Outdoor-to-Indoor Pedestrian Navigation using GPS and UWB

David S. Chiu, Kyle P. O’Keefe

Abstract:	GPS is often used in hostile signal conditions. At the same time, users want a certain degree of accuracy and reliability from the system. This is not always achievable due to effects such as attenuation, fading, multipath and a GPS receiver’s ability to even detect a satellite signal. To assist in maintaining a position when the GPS solution degrades, GPS may be augmented from another ranging source such as ultra wideband (UWB) ranging radios. In this paper, several tests are performed to study the benefits of UWB integration with GPS. However, before these effects are studied, it is necessary to understand the accuracy of UWB ranges alone. Studying UWB range accuracy reveals that as the distance that ranges were measured increased, the number of measurements made by the UWB radio decreased. However, no such correlation was found between range and number of data outliers. Comparing the mean error between measured UWB ranges and truth distances showed that UWB was immune to multipath effects in this test. Plotting UWB mean error also showed that UWB measurements suffer from a scale factor and bias, and thus, need to be corrected or calibrated, prior to further UWB data analysis or augmentation with GPS. Once UWB range accuracy was confirmed, UWB measurements were combined with Code DGPS measurements in a static and kinematic test. In the static test, the UWB augmented Code-DGPS solution reported more accurate and precise results compared to the Code DGPS-only solution. Standard deviation values for Northing and Easting decreased and converged once UWB measurements were added into the solution. For the kinematic test, a simulation of “indoor” or hostile signal conditions was created by removing all but two GPS satellites in the solution. UWB measurements integrated with Code DGPS (two satellite constellation) reported meter-level deviations from the UWB-Code DGPS (full constellation) and Code DGPS-only solutions. Horizontal Dilution of Precision (HDOP) values showed that UWB-Code DGPS (full constellation) had the lowest DOP values and was resistant to sudden DOP increases observed by the Code DGPS-only solution. The final test in this paper studies whether or not a solution was able to be maintained between outdoor to indoor navigation. Several points outdoors and indoors were surveyed by a total station so that their absolute positions would be known and could be used to compare the UWB-GPS rover trajectory. While outdoors, only GPS measurements and no UWB ranges were observed. However, once the rover traveled indoors, only UWB measurements were made and GPS suffered from a complete outage. The solution whilst indoors reported accuracies in the sub-meter level. A position solution was maintained as the rover traveled outdoors, to indoors, then back outdoors. In all tests where UWB was used to augment GPS, meterlevel or better accuracies were observed and thus, sufficient for most pedestrian navigation applications.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	2626 - 2637
Cite this article:	Chiu, David S., O’Keefe, Kyle P., "Seamless Outdoor-to-Indoor Pedestrian Navigation using GPS and UWB," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 2626-2637.
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