Ambiguity Resolution in GPS-based, Low-cost Attitude Determination

Abstract. Reliable determination of integer ambiguities is a critical issue in high-precision global positioning system (GPS) applications such as kinematic positioning, fast control surveying and attitude determination. This paper discusses the integer ambiguity resolution procedures in attitude determination using single frequency carrier phase measurements. An optimised ambiguity search algorithm is proposed. This method can not only improve the computation efficiency and reduce the time for resolving ambiguities, but also improve the reliability of the ambiguity solution. The ambiguity search space is determined using float solutions and their variance and covariance matrices estimated by applying Kalman filter algorithm. The integer Gaussian transformation is then used to reduce the size of the search space and Cholesky factorisation algorithm is used to improve the efficiency of the integer ambiguity searching process. Finally, an ambiguity validation method by using the known baseline length and the relationship between the primary and secondary ambiguity groups is presented. The algorithms have been implemented within two low-cost Allstar GPS OEM boards. A number of field experiments have been conducted and the results show that a valid integer ambiguity solution in cold start mode can be identified within 3 minutes. Key words: Ambiguity resolution, attitude determination, carrier phase, GPS