Craig M. Hancock

A Tightly-Coupled GPS/INS/UWB Cooperative Positioning Sensors System Supported by V2I Communication

This paper investigates a tightly-coupled Global Position System (GPS)/Ultra-Wideband (UWB)/Inertial Navigation System (INS) cooperative positioning scheme using a Robust Kalman Filter (RKF) supported by V2I communication. The scheme proposes a method that uses range measurements of UWB units transmitted among the terminals as augmentation inputs of the observations. The UWB range inputs are used to reform the GPS observation equations that consist of pseudo-range and Doppler measurements and the updated observation equation is processed in a tightly-coupled GPS/UWB/INS integrated positioning equation using an adaptive Robust Kalman Filter. The result of the trial conducted on the roof of the Nottingham Geospatial Institute (NGI) at the University of Nottingham shows that the integrated solution provides better accuracy and improves the availability of the system in GPS denied environments. RKF can eliminate the effects of gross errors. Additionally, the internal and external reliabilities of the system are enhanced when the UWB observables received from the moving terminals are involved in the positioning algorithm.

On the improvements of the single point positioning accuracy with Locata technology

This work focuses on the performances of Locata technology in single point positioning using different firmware versions (v2.0 and v4.2). The main difference is that the Locata transmitters with firmware v2.0 are single frequency, whereas in the v4.2, they are dual frequency. The performance of the different firmware versions has been measured in different environments including an urban canyon-like environment and a more open environment on the roof of the Nottingham Geospatial Building. The results obtained with firmware v4.2 show that with more available signals, cycle slips can be more easily detected, together with the improvement of the detection of multipath fading on the received signal. As a result, the noise level on the carrier phase measurements recorded with firmware v4.2 is equal on average to a third of the level of noise on the measurements recorded with firmware v2.0. In addition, with either firmware, the accuracy of the position is at the sub-centimeter level on the East and North coordinates. The Up coordinate accuracy is generally less accurate and more sensitive to the geometry of the network in our experiments. We then show the importance of the geometry of the Locata network on the accuracy of Locata positioning system through the demonstration of the relationship between the dilution of precision value and the confidence ellipse. We also demonstrate that the model of the noise on the Locata coordinates is a white Gaussian noise with the help of the autocorrelation function. To some extent, this technique can help to detect whether the Wi-Fi technology is interfering with the Locata technology and degrades the positioning accuracy.

Locata performance in a long term monitoring

Abstract Today’s monitoring schemes often demand fully or partly automated networks to be established, with the operations done remotely. Ease of use lead to the increasingly dominant position of GNSS within the market. This method’s include limitations includes accuracy, reliability and integrity dependence on the number and geometric distribution of the available satellites. To amend that, pseudolite systems have been suggested as an alternative or companion to GNSS. Pseudolites share characteristics with GNSS and offer deployment flexibility, providing a optimisation of the geometry. Locata is one of such system, capable of centimetre level stand-alone positioning even in difficult environments. Prior research has identified Locata capacity for system for structural monitoring, but focused on planar positioning only. This paper discusses the results of a dedicated five days monitoring trial, without system reinitialisation, focusing on height performance and identification of any biases preventing Locata from being employed as a monitoring system. It performance is tested against the RTK-GPS results.

Indoor multipath effect study on the Locata system

Abstract GNSS has become one of the most wide-spread measurement technologies, allowing cm-level positioning accuracy using RTK or Network RTK. Unfortunately, the systems major drawbacks are the requirement for a clear view of the sky and accuracy dependent on the geometric distribution of the satellites, not only varying throughout the day but also prone to location specific problems. With wide-spread utilisation of GNSS for monitoring of manmade structures and other civil engineering tasks, such shortcomings can be critical. One of possible solution is the deployment of a supporting system, such as Locata – a terrestrial positioning technology, which mitigates the need for a clear view of the sky and provides system integrity control. This paper, part of the proposed integration feasibility study, presents Locata performance indoors, its capacity and mitigation methods.

A theoretical and empirical integrated method to select the optimal combined signals for geometry-free and geometry-based three-carrier ambiguity resolution

Twelve GPS Block IIF satellites, out of the current constellation, can transmit on three-frequency signals (L1, L2, L5). Taking advantages of these signals, Three-Carrier Ambiguity Resolution (TCAR) is expected to bring much benefit for ambiguity resolution. One of the research areas is to find the optimal combined signals for a better ambiguity resolution in geometry-free (GF) and geometry-based (GB) mode. However, the existing researches select the signals through either pure theoretical analysis or testing with simulated data, which might be biased as the real observation condition could be different from theoretical prediction or simulation. In this paper, we propose a theoretical and empirical integrated method, which first selects the possible optimal combined signals in theory and then refines these signals with real triple-frequency GPS data, observed at eleven baselines of different lengths. An interpolation technique is also adopted in order to show changes of the AR performance with the increase in baseline length. The results show that the AR success rate can be improved by 3% in GF mode and 8% in GB mode at certain intervals of the baseline length. Therefore, the TCAR can perform better by adopting the combined signals proposed in this paper when the baseline meets the length condition.