Assessment of GPS Signal Quality in Urban Environments Using Deeply Integrated GPS/IMU

This research evaluates the quality of GPS signals and their usability for localization in urban environments using GPS data collected in urban canyons. GPS signals collected on a Software Defined Radio (SDR) platform in urban canyons in downtown Athens, Ohio and Columbus, Ohio are processed using a deeply integrated GPS/INS scheme. This deep integration architecture allows for coherent signal integration over time intervals as long as 1 second. The deep integration mode that provides continuous carrier phase tracking is used herein. Performance of the deep integration scheme in urban canyons is compared to performance characteristics of commercially available low-sensitivity GPS receivers. Results characterize the received signals in urban environments in terms of signal strength, tracking continuity and multipath influence on signal tracking performance. Results attained show that signals from 5 to 6 Space Vehicles (SVs) are available for processing, even in dense urban canyons. Deep GPS/INS integration enables continuous carrier phase tracking, thus allowing for accuracies on the cm/s level in velocity in urban environments. In contrast, velocity performance of the commercial low-sensitivity GPS receivers considered yielded errors on the level of 1 m/s. Additionally, the results demonstrate that continuous carrier phase tracking is possible, even for those cases where buildings block the satellite Line Of Sight (LOS). Further, consistent carrier phase tracking is performed for at least 2 SVs for a test scenario where all LOS vectors are blocked by buildings, and up to 6 SVs for all other urban canyon scenarios. Tracking remains consistent for weak signals with Carrier-to-Noise Ratios (CNRs) down to 12 dB-Hz.