A New Approach for Fast and Reliable Ambiguity Search Technique

C. Kee, D. Kim, J. Jang

Abstract:	Real-Time Kinematic GPS positioning is widely used for many applications. It can provide static & kinematic positioning accuracy to centimeter level. Resolving ambiguities is the key to precise positioning. Integer ambiguity resolution is the process of resolving the unknown cycle ambiguities of double difference carrier phase data as integers. Two important issues of resolving are efficiency and reliability. In real-time positioning, the reliability of solution is a very critical problem that is directly related to safety. In the conventional search techniques, we generally used chi-square random variables for decision variables. Mathematically, a chi-square random variable is the sum of mutually independent, squared zero-mean unit-variance normal (Gaussian) random variables. With this base knowledge, we can separate decision variables to several normal random variables. We showed it with related equations and conceptual diagrams. With this separation, we can improve the computational efficiency of the process without losing the needed performance. In general, ambiguity search process is repeated epoch by epoch independently. This inevitably causes problems of removing true candidate that has exceptionally large errors of measurements temporarily. Separated normal random variables can be the solution of this problem. If we average separated normal random variables sequentially, averaged values are also normal random variables. So we can use them as decision variables, which prevent from a sudden increase of some decision variable. In the case of wrong candidates, their biases will be accumulated and their decision variables may be increased relatively fast. Eventually, true candidate will remain safely and wrong candidates will be removed fast. With the method using averaged decision values, we can get the solution more quickly and more reliably. To verify the performance of our proposed algorithm, we conducted simulations. We used some visual diagrams that are useful for intuitional approach. We analyzed the performance of the proposed algorithm and compared it to the conventional methods.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	2112 - 2119
Cite this article:	Kee, C., Kim, D., Jang, J., "A New Approach for Fast and Reliable Ambiguity Search Technique," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 2112-2119.
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