A new ambiguity resolution method based on searching in both geometric and ambiguity spaces

Effective ambiguity resolution methods are crucial for GPS carrier phase positioning, particularly for Real-Time Kinematic (RTK) operation. Ambiguity resolution is based on search methods, and the search can be either in geometric or ambiguity spaces. For example, the ambiguity function method is based on geometric space search. For ambiguity resolution validation, majority algorithms are based on the comparison of the smallest and the second smallest sum of residuals. Success Rate of ambiguity resolution can also be used for the validation process. However, the existing methods are difficult to answer the question of why the ambiguity cannot be fixed if the validation test is not passed. In this paper, we propose a new ambiguity resolution method which searches both geometric and ambiguity spaces. With this new approach, we can clearly identify the reasons why the ambiguity cannot be fixed, with the following possible reasons: Weak geometry, outliers in carrier phase measurements, or the measurement errors are too large. For the geometry reason, we have to wait for more time for ambiguity resolution. When there are outliers in the measurements, RAIM methods can be used to detect those measurements with errors are significantly larger than others. If the carrier phase measurements noise level is too high, the ambiguity fixing solution will not be available for the positioning solution.