Of the hundreds of papers researchers presented this year at the Institute of Navigation’s annual ION GNSS+ conference, which took place virtually Sept. 21–25, the following three focused on navigation in urban environments. Papers are available at www.ion.org/publications/browse.cfm.
Low-Cost Single-Frequency PPP System
Featuring multi-constellation global availability, fast convergence and continuous navigation solutions, Instant PPP (IP3) was developed as an ideal precise positioning solution for mass-market applications in urban environments. The low-cost single-frequency PPP system demonstrates 50-cm accuracy in open-sky and suburban environments, and is further enhanced to support precise positioning in urban environments. The IP3 library is uniquely designed and enhanced. For instance, the instant receiver velocity based on the Doppler observations and the coordinate changes calculated from the carrier-phase differences between two consecutive epochs are integrated for the one-step prediction of the receiver positions in the Kalman filter.
Meanwhile, the weight of carrier phase, pseudorange and Doppler observations are smartly tuned as a function of signal-to-noise ratio (SNR) respectively. Additionally, quality control adapts to different scenarios, such as open-sky or urban environments. The receiver clock drifts for different constellations are specifically modelled in the velocity estimation to increase the degrees of freedom, which further enhances the solution availability in these extreme challenging situations.
To evaluate the IP3 library in urban environments, real-time vehicle-based field tests were carried out with an IP3 evaluation kit in Calgary, Canada. Results indicate the IP3 library can provide 50-cm accuracy in suburban areas with 100% solution availability. In an urban environment with numerous high buildings, the positioning root-mean-square error (RMS) of IP3 degrades to meter level while the solution availability remains 100%. IP3 can provide precise positioning solutions with low-cost GNSS receivers even in urban environments.
Citation. Hongzhou Yang, Fei Liu and Yang Gao, Profound Positioning Inc., Canada, “Precise Positioning into Urban Environments: A Low-Cost Single-Frequency PPP System.”
A Sub-Meter Real-time Positioning Service for Smartphones
A real-time positioning service for smartphones that meets a target threshold of 50 centimeters in urban environments is evaluated. The evaluation is possible through the Flamingo service, an API library for smartphone developers that enables higher accuracies than standard Google location services. The API is offered in a format that simply replaces Android location, streamlining its integration into new and existing applications that require better positioning. The service provides reference station infrastructure and correctional data products through a modified version of traditional NTRIP services. Duty cycling, low-quality clocks and high RF interference are common in a smartphone, so pre-filtering algorithms have been designed and calibrated to reject and de-weight poor measurements.
Based on proximity to a local base station, the service decides whether to use RTK or PPP-like processing. Performance is assessed on positioning accuracy, reliability and availability. Different operational environments are tested, such as pedestrian navigation in a congested area, and cycling scenarios. These are chosen to closely correspond to various applications. Rather than proving ideal test conditions and post-processing to optimize performance, the study focuses on realistic, real-time processing inside a smartphone.
Results are collected through a simple logging app that uses the Flamingo API. A target is set for 50 cm or better accuracies, where current smartphone positioning is within only a few meters. This enables mass-market location services to be applied in new markets such as augmented reality, lower accuracy surveying, GIS asset collection, and navigation assistance applications.
Citation. Joshua Critchley-Marrows, William Roberts, Malgorzata Siutkowska, Maria Ivanovici, NSL, UK; Valentin Barreau, Soufian Ayachi, Laurent Arzel, Telespazio, France, “A Sub-Meter Real-Time Positioning Service for Smartphones.”
The Path to Robust Municipal PNT
This research identifies where municipal governments fit in the positioning, navigation and timing (PNT) ecosphere, their awareness of PNT-related issues, whether and how they are approaching these issues, and actions they can take to improve their services to citizens and travelers. Lessons from other areas are applied, such as the resource typing construct used in FEMA’s National Incident Management System, to develop best practices for city PNT activity. This work will guide cities in addressing this important area and assist policy makers in efforts to involve cities in the development and implementation of PNT processes.
Citation. Steven Polunsky, Alabama Transportation Policy Research Center, University of Alabama, “The Path to Robust Municipal PNT.”
