Gao, Yang
(2017)
Robust cooperative positioning using DGPS and UWB for V2X applications.
PhD thesis, Nottingham Geospatial Institute, University of Nottingham.
Abstract
Road transportation injuries, environmental pollution, and traffic congestion have resulted in a considerable cost to society annually. They have led to an increasing demand for a new generation of Intelligent Transportation Systems (ITS) road applications, which promise to tackle these widespread issues. A common element of such applications is the positioning system, and its performance has been highlighted as one of the key enablers. With the rapid expansion of Global Navigation Satellite Systems (GNSS), satellite-based positioning and navigation will continue to be the predominant positioning solution for most of ITS road applications. GNSS positioning systems offer global coverage, they are primarily free of charge, operate in all weather conditions, and are available all day, every day. However, there are challenges for GNSS-based positioning for ITS applications; in particular, the limited availability and degraded performance of GNSS signals in urban canyons. These challenges could impede the adoption of ITS applications, such as collision avoidance systems, lane departure warning systems, connected and autonomous vehicles. There is a gap between the positioning performance of GNSS-based systems and the positioning performance demanded by ITS applications.
To bridge this gap, this research considers multi-sensor integration and cooperative positioning based on vehicle-to-vehicle, vehicle-to-infrastructure, and vehicle-to-pedestrian communications (collectively known as V2X communication). In comparison to other radio frequency augmentation techniques, Ultra-Wideband (UWB) is of particular interest for multi-sensor integration due to its fine time resolution and robust performance in high signal multipath environments. In addition to this benefit, Dedicated Short Range Communication (DSRC), as a key enabling communication component in V2X communication, not only allows vehicles to exchange their position information but also to share traffic safety-related information such as real-time congestion, accident and incident details, and variable speed limits. By taking advantage of DSRC, a vehicle in a GNSS hostile environment can calculate its position based on data shared from surrounding road users.
This thesis utilises Global Positioning System (GPS) as a representative of GNSS and proposes to augment Differential GPS (DGPS) with UWB ranging observations attained from surrounding vehicles and infrastructure. It is accomplished by tightly integrating double-difference (DD) code pseudo-range GPS observations and UWB ranging observations using a Robust Kalman Filter. The performance of the proposed Robust Cooperative Positioning (RCP) method is evaluated using real and simulated GPS code pseudo-range and UWB ranging observations supported by assumed DSRC transmission.
This thesis carries out a thorough assessment of the ranging performance, error sources and positioning performance of the Thales UWB Lock-on Model LD2. The assessment is completed by conducting a series of tests in different static and dynamic situations.
In addition to this in-field assessment of the UWB device, the positioning performance of the proposed RCP method is demonstrated in both favourable and hostile GPS environments. The proposed RCP method effectively eliminates the impact of observed outliers, and the integrated RCP solution outperforms the DGPS-only solution, especially when the GPS signal is partially or fully obstructed.
The results based on simulated UWB ranging observations and real GPS code pseudo-range observations on the roof of the Nottingham Geospatial Building achieve sub-metre three-dimensional accuracies when three DD code pseudo-ranges and four UWB ranging observations are available.
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