A novel ambiguity search algorithm for high accuracy differential GNSS relative positioning

Abstract It is well understood that the key to high accuracy differential global navigation satellite system (DGNSS) relative positioning is the resolution of the integer ambiguities within the carrier phase measurements and the continuous tracking of them. The resolution process is usually converted into an integer least square optimization problem, e.g., among them is the most notable Least-squares Ambiguity Decorrelation Adjustment (LAMBDA) algorithm. This paper adds additional statistical constraints to the existing LAMBDA approach to improve the performance of ambiguity resolution process when the LAMBDA ratio is below a certain predefined threshold. In order to fix the integer ambiguity as soon as possible, a novel ambiguity search algorithm is proposed, which is like the threshold based algorithm but explicitly exploits the correlation structure of the double difference covariance model and the measurement accuracy difference. To do that, the relationship between global navigation satellite system (GNSS) pseudorange measurement accuracy and the resolution of the integer ambiguity of carrier phase measurements is analyzed based on the GNSS distance measurement equations. Analytic statistical models of the single and double differences of the distance measurements are presented. Based on the analysis, it is found that the conventional choice of the highest elevation satellite as the reference satellite may not be a superior selection in single epoch algorithms. In fact, code phase measurements are used for ambiguity resolution, and the covariance of baseline vector is independent with reference satellite selection when the least square problem is optimally weighted. The novel ambiguity search algorithm is presented to fix the ambiguity as soon as possible. Simulation and field test data validate the analysis and the ambiguity search algorithm.