Optimizing the GPS Ambiguity Search Space by Metaheuristic Techniques

In the Global Positioning System (GPS), the optimal determination of the number of ambiguity candidates to be searched and selected is a crucial factor for improving the computational efficiency of GPS ambiguity resolution. This paper presents a new area of research for effectively optimizing the GPS ambiguity search problem using metaheuristic techniques from the field of Operational Research (OR). OR attempts to provide a systematic and rational approach to the fundamental elements involved in the control of a problem by making decisions which, in some sense, achieves the best results in light of all the information that is available. In most OR applications, researchers are more interested in finding a “good enough” solution than proving the optimality. “Good enough” may of course mean “very good, and much better than would be found by other means”. In discussing the optimality of a solution it is important to realize what is the aim of optimization. Is it seeking the cheapest or the fastest solution, or, that which is most acceptable to use, or, simply any solution that satisfies certain conditions? For example, the aim in GPS surveying network scheduling is to seek the cheapest schedule that satisfies both GPS and metaheuristic requirements. The criterion of acceptability adopted in this research for the GPS ambiguity resolution will include notions such as “How good is the obtained solution?” and “How much computational effort (i.e., cutting down the search space transformation of the ambiguity) will it save?” In this research, the applications of the OR techniques are focused on two major areas. Firstly, developing intelligent and effective approaches to solve GPS ambiguity resolution problems of a realistic size. Secondly, providing information that can be used in the development and dissemination of new theoretical and analytical tools for use in optimising the other GPS applications (e.g., precise orbit determination of low earth orbiters, modelling atmospheric effects, etc). Metaheuristic techniques play an effective role in OR applications by reducing the huge number of evaluations. More recent applications of the proposed metahueristic methodology to GPS surveying show that very good, if not optimal, receiver schedules can be quickly obtained for large and different types of GPS networks. In this paper, the implementation of a metaheuristic technique to optimize the GPS ambiguity resolution problem is presented and developed.