Analysis of ambiguity resolution in precise pseudolite positioning

Abstract

Global Navigation Satellite Systems (GNSS) positioning technology is vulnerable in a wide range of environments such as indoors or in urban canyons. Even with high sensitivity GNSS receivers, the positioning results are far from being reliable. Therefore, pseudolite positioning technology can be useful as a complement in such environments. Many studies have been carried out for pseudolite positioning in various applications, but for precise pseudolite positioning, the carrier phase measurements must be taken into consideration. Consequently, integer ambiguity resolution issues need to be dealt with. In this contribution, by processing double differenced static and kinematic pseudolite data, ambiguity resolution and validation issues for pseudolite positioning are analyzed. An introduction to pseudolite positioning technologies is presented at first, and then mathematical models for double differenced pseudolites positioning are introduced. Subsequently the parameter estimation procedures by least-squares and integer least-squares are presented. To search for the integer candidate, the efficient LAMBDA method, which is based on the integer least-squares, is utilized. Providing the integer candidates in hand, ambiguity validation procedures are conducted to validate the resolved integer ambiguities. With the validated integer ambiguities, an online stochastic model is implemented to improve the performance of ambiguity resolution in the static and kinematic cases. It has been shown that the integer least-squares is more reliable for ambiguity resolution and validation than integer rounding, and the ambiguity resolution and validation are highly affected by the pseudo-range measurements, the geometry of the pseudolites and the realistic stochastic model used. Moreover, the introduced online stochastic model is very effective for ambiguity resolution and validation in static and kinematic positioning in case of the signal block out occurs.