ECEF Position Accuracy and Reliabilityin the Presence of Differential Correction LatencyPhase B Technical Reportfor Sirius XM
Many applications, including connected and autonomous vehicles, would benefit from navigation technologies reliablyachieving sub-meter position accuracy with high reliability on moving platforms. Commercial on-vehicle implementation ofEarth-referenced positioning at submeter accuracy with 99% probability would require widely and reliably available differentialcorrections; however, such corrections delivered on a nationwide or global scale via satellite systems will incur latency betweentheir time-of-applicability and their time-of-reception at the vehicle.Phase 1 of this project presented a differential correction computation methodology designed to be robust to latency andstudied position accuracy as a function of differential correction latency for stationary receivers –. The study showed thatsubmeter accuracy at 95% probability was achievable when a sufficient number and diversity of satellites were available.This report summarizes the conclusions of the Phase 2 of the work performed by University of California, Riverside (UCR).There were two main goals for this effort. For moving platforms, Phase 2 investigates:1) the feasibility of achieving meter-level positioning accuracy on at least 95% of epochs using Global Navigation SatelliteSystem (DGNSS) based state estimation; and,2) the sensitivity of that positioning accuracy to communication latency.The study uses the utilizes the local based station design presented in .The study presents and experimentally analyzes two state estimation approaches suitable for moving platforms. The Position,Velocity, Acceleration (PVA) approach uses DGNSS data only within a Kalman filter framework. The Inertial Navigation System(INS) approach uses DGNSS and inertial measurement data within an extended Kalman filter implementation. Section VIIshows that both approaches have performance exceeding the SAE J2945 specification (1.5 meter horizontal accuracy and 3.0meter vertical accuracy at 68%) with PVA achieving 1m horizontal at 90% and 2 m vertical accuracy at 95% while the INSapproach using a consumer-grade IMU achieves 1m horizontal at 98% and 2 m vertical accuracy at 95%.Section VIII presents an analysis of position estimation accuracy, for moving platforms, as a function of communicationlatency, which shows that, using the DGNSS correction computation approach presented in , position estimation accuracyis robust to correction latency exceeding 500 seconds.The results herein used a local base station approach. National or global implementations would be more efficient usingnetworks of base stations working collaboratively to estimate parameters usable by user receivers to reconstruct corrections.Such methods are the focus of Phase 3 of this study.This study focuses on single frequency, single constellation results. The availability of multiple constellations and multiplefrequencies per constellations will facilitate compensation of ionospheric error, accommodation of outliers, and accommodationof multipath, while still having a set of satellites with appropriate geometry to reliably achieve the performance specification.