By Lukasz Bonenberg and Craig Hancock
One-hundred-twenty meters of test track, designed for repeatable dynamic position testing, run along the roof of the new Nottingham Geospatial Building at the University of Nottingham, UK. The figure-eight track provides an optimal controlled environment with test equipment aboard a remote-controlled, multi-sensor 7¼-inch gauge locomotive platform with a top speed of 7 kilometers per hour, a dedicated power supply, and five antenna mounts. Simulation of the track using Spirent GSS8000 hardware (GPS and Galileo) provides additional planning and testing capacity.
The combination of these tools creates the ideal environment for our new project: augmentation of GNSS systems with ground-based Locata positioning technology. This pseudolite-like system, described in the March issue of GPS World, works in a GNSS-like fashion, using code and carrier phase. The major advantage, apart from utilization of the licensee-free 2.4 GHz frequency band, is the precise time synchronization of the network to the nanosecond level.
The proposed integration addresses Locata’s weak vertical coordinates (due to relative coplanarity of transceivers) and GNSS’s requirement for a clear view of the sky and location-specific weak geometric distribution of the satellites. Prior research and analysis suggests considerable improvement in 3D positioning accuracy when combining ground-based positioning devices (pseudolites) with GNSS, but the current project pushes the research forward by attempting to create on-the-fly ambiguity resolution.
Combination of hardware and software simulation has provided an initial assessment of the proposed integration, optimization of equipment location, and test of the mathematical model to be used. Practical tests, using the roof lab on top of the NGB, will further verify the method and allow comparisons between the predicted and real-life results. This will aid the assessment of noise, multipath, and in-bound interference. The test design minimizes the tropospheric effect, while track flexibility and repeatability offer the possibility of implementing and simulating obstructions and areas of GNSS outage. This will provide a full assessment of the mathematical model and the integrated system’s capacity.
This project offers new opportunities in civil engineering, specifically monitoring and machine control. GPS is currently widely used for those applications, with Locata also proven successful. The integrated solution can provide not only enhanced positioning capacity but lower the required number of visible GNSS satellites, and offer improved integrity and quality control, ultimately increasing the safety of life.
The intended utilization is for positioning in dense urban areas and essential structures (airports, seaports, factory sites, bridges) where sky visibility or correct satellite distribution cannot be guaranteed.
The track is available for other projects. Funded by East Midlands Development Agency, hosted by the Institute of Engineering Surveying and Space Geodesy, the Centre for Geospatial Science, and the GNSS Research and Applications Centre of Excellence (GRACE).