See current research theme 'Algorithms & Software'

'Third Generation', Precise, Kinematic GNSS Positioning
Over Short, Medium and Long-Ranges

This project was a continuation of the research undertaken by Shaowei Han during his PhD studies, and a collaboration with the world renowned GPS researcher Prof. Peter Teunissen and his colleagues. Peter Teunissen was the leader of the then Mathematical Geodesy & Positioning Group at the Delft University of Technology, The Netherlands, and has made significant contributions to ambiguity resolution search techniques through development of the LAMBDA method of transforming ambiguities. Download a PDF file giving further information on this project .

Carrier phase measurements are ambiguous, requiring that ambiguity resolution (AR) be incorporated as an integral part of the data processing software. The first generation of carrier phase-based GPS positioning systems used GPS receivers capable of making C/A-code pseudo-range, L1 carrier phase and (usually) half wavelength L2 carrier phase measurements. Carrier phase ambiguity simply involved "rounding-off" to the nearest integer of the real-valued parameter estimate. This required real-valued ambiguity estimates that were accurate, and hence typically an observation period of 0.5 to 1 hour for short baseline static positioning was required. GPS "rapid static" (keeping GPS antenna static for a few minutes) or kinematic positioning was rarely used, due to the inefficiency of the system, but such techniques as "stop & go", antenna swap, etc., were introduced in the late 1980s.

The second generation carrier phase-based GPS positioning systems were a product of improvements in GPS receiver hardware as well as data processing algorithms, especially the AR techniques developed in the early 1990s. As a result, GPS rapid static positioning systems, and GPS real-time kinematic (RTK) positioning systems, using "on-the-fly" (OTF) ambiguity resolution algorithms, have progressively been released onto the market. The observation span normally required is just a few minutes for short-range (<15km) static positioning, and up to a few minutes of data are required to determine the integer ambiguities using OTF-AR techniques for short-range kinematic positioning. With the development of the latest generation of GPS receivers instantaneous carrier phase-based positioning becomes feasible on a routine basis. The techniques of AR, and validation and 'quality control', are being extended so that they are also applicable for combined GPS + GLONASS data processing. (The term 'GNSS' is nowadays used as an umbrella term to cover both the current GPS and GLONASS satellite-based positioning systems, the 'modernised' GPS system from about 2005 onwards, and the proposed European 'Galileo' system planned for operation from 2008 onwards.)

One of this project aims was to develop and test a new generation of GNSS data processing techniques, especially quality control procedures, appropriate for the latest generation of GPS receiver hardware, which can routinely deliver centimetre (or sub-centimetre) level accuracy using a single epoch of GPS observations. Network-based configurations allow for longer baselines between reference receivers and user receiver.

Variations of the single-epoch ambiguity resolution technique can be used in applications such as attitude determination using multiple GPS antennas. In addition, modified algorithms and procedures were tested on single-frequency and dual-frequency GPS+GLONASS data. Important studies were undertaken into improving the stochastic models for GPS (and GLONASS) observations.

Parallel studies were undertaken in the integration of GPS with pseudolites, and GPS/INS(PL) integration -
see Theme 3 & Theme 4.