GNSS Carrier Ambiguity Fixing for Robust Centimeter Positioning
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Solution Overview
Problem
Existing GNSS positioning techniques face challenges in accurately resolving carrier-phase ambiguities, particularly in urban environments, which affect positioning accuracy and reliability due to multipath effects and ionospheric errors.
Innovation Solution
A method involving multiple strategies for fixing carrier range ambiguities, including individual and linear combinations, such as widelane ambiguities, is employed, with Kalman filters and ambiguity resolution units to enhance accuracy and robustness, utilizing algorithms like LAMBDA for integer ambiguity estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If carrier-phase measurements are used to achieve centimeter-level positioning accuracy, then measurement precision is improved, but the inherent ambiguity in carrier phase measurements makes the ranging measurement non-unique
Solution Approach 1:
The patent applies preliminary action by fixing carrier range ambiguities to integer values before using them in positioning calculations. The ambiguity resolution unit determines and fixes the ambiguous integer terms in advance, allowing the carrier phase measurements to be used for high-precision positioning without the ambiguity affecting the final result. This is achieved through methods such as LAMBDA (Least squares AMBiguity Decorrelation Adjustment) and other ambiguity resolution techniques that constrain the ambiguous terms to their correct integer values.
2Measurement precision
If individual carrier range ambiguities are fixed to achieve better positioning, then measurement precision is improved, but the complexity of resolving multiple ambiguities increases
Solution Approach 1:
The patent applies segmentation by dividing the ambiguity resolution process into separate functional components: an ambiguity resolution unit that handles the mathematical complexity of resolving ambiguities, and a positioning unit that uses the resolved ambiguities for calculations. The ambiguity resolution unit can process multiple ambiguities independently and in parallel, reducing the overall complexity burden on the positioning system. Different ambiguity fixing strategies (individual ambiguity fixing, linear combination fixing, widelane ambiguity fixing) can be applied selectively based on the specific positioning scenario.
Solution Approach 2:
The patent introduces an intermediary ambiguity resolution unit that acts as a mediator between the carrier phase measurements and the positioning calculations. This intermediary component专门 handles the complex task of resolving ambiguities by applying various fixing strategies, thereby isolating the complexity from the main positioning algorithm. The resolved ambiguities are then passed to the positioning unit as simplified input data, separating the complexity of ambiguity resolution from the positioning computation.
3Reliability
If multiple ambiguity fixing strategies are employed to improve positioning reliability, then reliability is improved, but the computational processing requirements increase
Solution Approach 1:
The patent applies dynamics by making the ambiguity fixing strategy adaptive rather than static. The system can dynamically select which ambiguity fixing strategy to apply (individual ambiguity fixing, linear combination fixing, widelane ambiguity fixing, or a combination) based on the current positioning conditions, satellite geometry, and measurement quality. This dynamic approach allows the system to use computational resources more efficiently by applying complex resolution methods only when necessary, while using simpler methods when conditions permit, thereby balancing reliability improvement with processing requirements.
Data Source
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AI summary
A method and apparatus are provided for calculating a position based on GNSS signals. The method comprises estimating (202) a first state vector comprising a first set of float carrier range ambiguities using a first estimator (102), based on first observations of the GNSS signals; and estimating (204) a second state vector comprising a second set of float carrier range ambiguities using a second estimator (104), based on second observations of the GNSS signals. It further comprises fixing (212) one or more first carrier range ambiguities, using a first strategy, based on the first set of float carrier range ambiguities; and fixing (214) one or more second carrier range ambiguities, using a second strategy, based on the second set of float carrier range ambiguities. The first strategy for fixing the one or more first carrier range ambiguities is different from the second strategy for fixing the one or more second carrier range ambiguities. The method further comprises: selecting (220) a set of fixed carrier range ambiguities from among a plurality of different sets of fixed carrier range ambiguities, the plurality including at least the one or more fixed first carrier range ambiguities and the one or more fixed second carrier range ambiguities; and estimating (230) the position based on the selected set of fixed carrier range ambiguities.