Multifrequency GNSS Line Bias Estimation for Ambiguity Resolution
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Solution Overview
Problem
Traditional GNSS positioning systems face challenges in achieving centimeter-level accuracy due to integer cycle ambiguities in carrier phase measurements, especially when using multiple frequencies, as the delay cycles for different frequencies are not matched, requiring additional satellites and complex clock synchronization.
Innovation Solution
A system utilizing multiple GNSS receivers with multifrequency antennas and a common clock to process phase information, resolving integer cycle ambiguities by comparing residual functions derived from carrier phase measurements and fractional cycle delays, and storing line bias information for each transmission path to facilitate accurate positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple GNSS frequencies are used to improve positioning accuracy, then measurement precision is improved, but device complexity increases due to unmatched delay cycles and clock synchronization requirements
Solution Approach 1:
The patent introduces line bias parameters as intermediary variables that mediate between the multiple frequency signals and the positioning calculation. These line bias parameters represent the unknown delay differences for each frequency signal path, allowing the system to account for frequency-specific delays without requiring complex synchronization mechanisms. By treating these delays as estimable parameters rather than requiring precise control, the patent simplifies the system architecture while maintaining multi-frequency positioning accuracy.
Solution Approach 2:
The patent transforms the problem from one of time synchronization to one of parameter estimation. Instead of attempting to synchronize clock phases across multiple frequencies (which would require complex hardware control), the patent changes the approach to estimating line bias parameters that capture the effective delay differences. This parameter transformation allows the system to handle frequency mismatches through mathematical modeling rather than hardware synchronization.
2Measurement precision
If integer cycle ambiguities are resolved to achieve centimeter-level positioning, then measurement precision is improved, but loss of time increases due to the complexity of resolving ambiguities
Solution Approach 1:
The patent performs preliminary estimation of line bias parameters using available measurements before attempting integer ambiguity resolution. By pre-estimating the line biases from the multi-frequency observations, the system creates a more accurate initial state for the ambiguity resolution process. This preliminary action reduces the search space and improves the convergence speed of subsequent ambiguity resolution algorithms, thereby reducing the time required to achieve centimeter-level accuracy.
Solution Approach 2:
The patent implements an iterative feedback process where line bias estimates are continuously refined using carrier phase measurements. The estimated line biases are fed back into the positioning calculation, which in turn provides updated measurements for further bias refinement. This feedback loop allows the system to progressively reduce errors and resolve ambiguities more quickly, transforming a potentially time-consuming process into an efficient iterative convergence.
3Productivity
If fewer satellites are used to reduce resource requirements, then productivity is improved, but reliability decreases due to insufficient geometric diversity
Solution Approach 1:
The patent changes the mathematical parameters of the positioning problem by introducing line bias estimators that effectively add degrees of freedom to the solution. By modeling the transmission path delays as estimable parameters rather than unknown constants, the system can achieve reliable positioning with fewer satellites. The parameter expansion allows the system to compensate for reduced geometric diversity through enhanced mathematical modeling of the signal propagation characteristics.
Data Source
AI summary
A differential carrier phase global navigation satellite system (GNSS) receiver with multiple antennas uses multiple GNSS carriers to determine position, which can improve the speed of integer searches, for example. In the system, an estimate of delays associated with the transmission paths between the antennas and receiver for at least one of the GNSS frequencies is stored. Typically, these are measures of the phase delay in the transmission paths for two or more of the GNSS frequencies such as in fractional cycles of the GNSS frequencies. Having this information solves problems associated with using multiple carrier frequencies. While cable delays typically have a fixed time delay, the signal paths for the different frequencies are not completely common—even if they were perfectly matched in time, the number of fractional cycles would still be different. Thus, the number of cycles a radio frequency (RF) signal is delayed is different for different frequencies.