Methods for Aiding Height Determination in Pseudolite-Based Reference Systems Using Batch Least-Squares Estimation

There are many situations in which GPS is either unable to provide the desired level of accuracy or is unavailable. Use of a pseudolite-based reference system for navigation can be a means for positioning during these times. While there are advantages in using a pseudolite-based reference system, there are still implementation issues and deficiencies that must be addressed. In many cases, a pseudolite system with ground-based transmitters has difficulty determining the height of the receiver accurately. This is due to the poor vertical observability inherent in the geometry of the system. A common approach in naval applications for solving the problem of poor vertical observability is to use a height constraint, which is well known when travelling on a surface of water. For a ground-based vehicle, knowledge of the surface topography can be obtained, but it cannot be readily used in the same manner as in marine cases, since the height is often a varying function of position. This research investigates and develops five methods of incorporating the known surface topography in a non-linear batch least squares estimation algorithm using carrier-phase measurements from pseudolites. The floating point carrier-phase ambiguities are estimated in this process. Real and simulated data sets are used to evaluate the performance of the five algorithms. In simulation, all methods performed equally well on a flat surface. When simulating a hill, constraining the solution to lie in a plane tangent to the surface topography appeared to aid the solution with the best knowledge of the terrain. Use of a pseudo-measurement, a commonly used approach, did not provide the best results, and indicates the inadequacy of using this method for pseudolite-based systems. Results using data from a real system on a ground-based vehicle demonstrated sub-decimeter level positioning accuracy in all three dimensions

GPS/Pseudolites technology based on EMD-wavelet in the complex field conditions of mine

AbstractTo increase the number and improve the geometric condition of visual satellites of GPS in complex environment of mine areas, GPS and pseudolite (PLs) positioning technologies will be integrated in this paper. Integration of GPS/Pseudolites(PLs) positioning technology can be applied to increase the number of visible satellites, strengthen the intensity of the geometry condition of the satellites, and provide an effective solution for precision measurement in the mine. However, the un-modeled systematic errors are still the main restrictive factors for high precision baseline solution. The Empirical Mode Decomposition (EMD)-Wavelet model was proposed for analysing non-linear time series. The EMD decomposes the time series to high-frequency and low-frequency part with the standards of the scale selection for the systematic errors elimination which is given in terms of the mean of the accumulated standardized modes, and the tendency of high-frequency part is extracted by Wavelet. Then low-frequency part and the tendency of high-frequency are reconstructed based on EMD theory and the systematic errors mitigation model is demonstrated as well. Thereafter, the scheme of the GPS/PLs baseline solution based on the EMD-Wavelet is suggested. The experiment shows that the proposed scheme dramatically improves the reliability of ambiguity resolution and the precision of baseline vector after systematic error eliminated

An Integration of GPS with INS Sensors for Precise Long-Baseline Kinematic Positioning

Integrating the precise GPS carrier phases and INS sensor technologies is a methodology that has been applied indispensably in those application fields requiring accurate and reliable position, velocity, and attitude information. However, conventional integration approaches with a single GPS reference station may not fulfil the demanding performance requirements, especially in the position component, when the baseline length between the reference station and mobile user’s GPS receiver is greater than a few tens of kilometres. This is because their positioning performance is primarily dependent on the common mode of errors of GPS measurements. To address this constraint, a novel GPS/INS integration scheme using multiple GPS reference stations is proposed here that can improve its positioning accuracy by modelling the baseline-dependent errors. In this paper, the technical issues concerned with implementing the proposed scheme are described, including the GPS network correction modelling and integrated GPS/INS filtering. In addition, the results from the processing of the simulated measurements are presented to characterise the system performance. As a result, it has been established that the integration of GPS/INS with multiple reference stations would make it possible to ensure centimetre-level positioning accuracy, even if the baseline length reaches about 100 km

Indoor multipath effect study on the Locata system

GNSS has become one of the most wide- spread measurement technologies, allowing cm-level positioning accuracy using RTK or Network RTK. Unfortunately, the system’s major drawbacks are the requirement for a clear view of the sky and accu- racy 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 man- made structures and other civil engineering tasks, such shortcomings can be critical. One of possible solution is the deployment of a sup- porting system, such as Locata – a terrestrial posi- tioning technology, which mitigates the need for a clear view of the sky and provides system integrity control. This paper, part of the proposed integration feasibil- ity study, presents Locata performance indoors, its capacity and mitigation methods