Electronic Version

Today, GPS is the most popular and widely used three-dimensional positioning technology in the world. However, in many everyday environments such as indoors or in urban areas, GPS signals are not available for positioning (due to the very weak signals). Even with high sensitivity GPS receivers, positioning for urban and indoor environments cannot be guaranteed in all situations, and accuracies are typically of the order of tens to hundreds of meters at best. Other emerging technologies obtain positions from systems that are not designed for positioning, such as mobile phones or television. As a result, the accuracy, reliability and simplicity of the position solution is typically very poor in comparison to GPS with a clear view of the sky. Locata is a new positioning technology, developed to address the failure of current technologies for reliable ubiquitous (outdoor and indoor) positioning. In this paper key aspects of the new technology are discussed, with particular emphasis on the positioning network (LocataNet). An innovative characteristic of the LocataNet is its ability to propagate (autonomously) into difficult environments and over wide areas. Through an experimental LocataNet installation, a key mechanism for achieving this is tested, and real-time stand-alone positioning (without a base station and additional data link) with sub-centimetre precision is demonstrated.

To take advantage of the existing GPS tracking networks established primarily for surveying, geodesy and navigation purpose for meteorology studies, this research effort is made to use hourly surface temperature and pressure (T & P) observations from in Australia for GPS Precipitable Water Vapour (PWV) estimation. After some necessary technical basises are given, the paper presents the experimental results to show: the comparison between the interpolated and observed T and P values, and agreement between the GPS-PWV estimates using the surface meteorological data and the radiosonde PWV results. Data analysis with 36 data points from the Victoria region in Australia has demonstrated that the Ordinary Kriging method with is preferable to pressure interpolation, resulting in an overall standard deviation of 0.40 mbar in pressure or 0.15mm in PWV estimation. We use the interpolated T and P measurements for four Australian IGS GPS sites to estimate GPS-PWV and compare against the radiosonde PWV results for the closely located radiosonde observations. 195 comparisons from all the sites have shown that GPS-PWV estimates agree with the Rad-PWV solutions at an average mean difference of -0.604 mm and RMS of 1.74mm for the tested stations. This agreement level is considered very reasonable. The experimental study shows a possible way to develop GPS meteorology and applications with the existing meteorological data network. This could save significant costs in installation of GPS-Met sensors.

GPS is essential in applications that require high (sub centimeter) positioning precision, such as in the velocity field estimation of tectonic plates. Normally, GPS relative positioning is used for this kind of application. However, GPS Precise Point Positioning (PPP) is a very simple and efficient method, which, as shown in this paper, can also be applied. This paper outlines the use of PPP for processing GPS data. Station coordinates and velocity vectors are inferred, and an estimation of the South American Plate rotation parameters is given. The PPP repeatability of station coordinates is better than 9mm, and comparisons of the final solution with other sources, such as ITRF, NNR-NUVEL 1A and APKIM 2000 generally show good agreement. The formal precision of the station velocity is in the order of 0.6 mm/year, for horizontal and vertical components, which appears to be an optimistic value, and the quality of the estimated rotation parameters is better than those from other sources.

This paper presents the multiple reference station approach to wide area (and regional) instantaneous RTK GPS, implemented in the MPGPS (Multi Purpose GPS Processing Software) software, developed at The Ohio State University. A weighted free-net approach (WFN) was applied in the instantaneous RTK software module, which enabled optimal estimation of the rover coordinates, properly reflecting the accuracies of the observations and the coordinates of the CORS stations. The effect of using the distance-dependent weighting scheme in the WFN approach on the final rover solution is analyzed. The influence of the different weights was studied by introducing the distance-dependent weights as a function of the CORS station separation L to the rover (1/L2). The results show that almost 100% of the differences between the computed horizontal rover coordinates and the known reference coordinates are below a decimeter, and 95% of the differences in the vertical coordinate are below 20 cm, when using the suggested approach. In addition, the accuracy analysis of two other solutions, with different datum definition (minimum constraint and over-constrained), is presented. This analysis verifies the suitability of the stochastic models used in the RTK module and the rigorous approach, taking into account inter-baseline correlation as well as the correlation in-between each baseline components.

The integrated GPS/INS system has become an indispensable tool for providing precise and continuous position, velocity, and attitude information for many positioning and navigation applications. Therefore, it is important to gain insights into the characteristics of the integrated GPS/INS system performance, particularly their relationships with key operational factors, such as the trajectory and dynamics. Such knowledge can be used to improve the quality of positioning and navigation results from the integrated GPS/INS systems. In order to analyse the influence of vehicle dynamics and trajectory, simulation and field tests have been carried out in this research. The test results show that the vehicle dynamic changes significantly affect the Kalman filter initialisation time and estimation performance depending on the system operational environments.

The probability of correct integer estimation, the success rate, is an important measure in the case of fast and high precision positioning with a Global Navigation Satellite System. Integer ambiguity estimation is the process of mapping the least-squares ambiguity estimates, referred to as the float ambiguities, to an integer value. It is namely known that the carrier phase ambiguities are integer-valued, and it is only after resolution of these parameters that the carrier phase observations start to behave as very precise pseudorange measurements. The success rate equals the integral of the probability density function of the float ambiguities over the pull-in region centered at the true integer, which is the region in which all real values are mapped to this integer. The success rate can thus be computed without actual data and is very valuable as an a priori decision parameter whether successful ambiguity resolution is feasible or not. The pull-in region is determined by the integer estimator that is used and therefore the success rate also depends on the choice of the integer estimator. It is known that the integer least-squares estimator results in the maximum success rate. Unfortunately, it is very complex to evaluate the integral in the case of integer least-squares. Therefore, approximations have to be used. In practice, for example, the success rate of integer bootstrapping is often used as a lower bound. But more approximations have been proposed which are known to be either a lower or upper bound of the actual integer least-squares success rate. In this contribution an overview of the most important lower and upper bounds will be given. These bounds are compared theoretically as well as based on their performance. The performance is evaluated using simulations, since it is then possible to compute the ’actual’ success rate. Simulations are carried out for the two-dimensional case, since its simplicity makes evaluation easy, but also for the higher-dimensional geometry-based case, since this gives an insight to the performance that can be expected in practice.