Positioning Terminal Dynamic SNR Threshold for Multipath Exclusion
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Solution Overview
Problem
In RTK positioning, satellites with low elevation angles experience signal attenuation and scattering, leading to low SNR, making it difficult to distinguish between direct and multipath waves, which reduces positioning accuracy.
Innovation Solution
A positioning method that calculates the elevation angle of each satellite, measures signal strength, and compares it to a threshold that increases with lower elevation angles to identify and exclude satellites with low signal strength, improving positioning accuracy by using signals from other satellites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed SNR threshold is used to exclude satellites, then the exclusion method is simple, but satellites with low elevation angles cannot be correctly identified due to their inherently low SNR causing false exclusions or missed detections
Solution Approach 1:
The patent applies the dynamics principle by making the SNR threshold dynamic rather than fixed. The threshold is adjusted based on the elevation angle of each satellite, with lower elevation angles having higher thresholds. This dynamic adjustment allows the system to correctly identify satellites for exclusion while accounting for the natural SNR variations due to elevation, thereby improving identification accuracy without requiring overly complex fixed-threshold methods
Solution Approach 2:
The patent changes the parameter of the threshold from a constant value to a variable value that depends on the elevation angle parameter. By establishing a relationship where the threshold increases as elevation angle decreases, the system can differentiate between low SNR caused by atmospheric effects (low elevation) and low SNR caused by multipath interference, thus improving satellite identification accuracy
2Measurement precision
If all satellites are used for positioning calculation, then the positioning data quantity is sufficient, but multipath interference from low elevation angle satellites degrades positioning accuracy
Solution Approach 1:
The patent applies the extraction principle by removing (excluding) specific satellites that are likely to cause multipath interference from the positioning calculation. By identifying satellites with low elevation angles and excluding them based on the dynamic threshold method, the system eliminates harmful multipath signals while retaining sufficient valid satellites for accurate and efficient positioning calculations
3Measurement precision
If satellites with low elevation angles are excluded, then multipath interference is reduced, but the number of available satellites for positioning decreases
Solution Approach 1:
The patent changes the exclusion criterion from a fixed SNR threshold to an elevation-angle-dependent dynamic threshold. This allows the system to be more selective about which low elevation angle satellites to exclude, maintaining positioning accuracy by removing only those most likely to cause multipath interference while preserving satellites that can still contribute usefully to the positioning calculation
Data Source
AI summary
A positioning terminal is provided and identifies, as appropriate, a satellite to be excluded, thereby improving positioning accuracy. A processor acquires a signal-to-noise ratio (SNR) and an angle of elevation for each satellite. The processor next identifies a satellite for which the SNR is less than a shielding SNR mask as a multipath satellite and selects the satellite to be excluded. The processor next generates positioning terminal positioning data using a positioning signal from satellites other than the satellite to be excluded. The processor next uses reference station positioning data and positioning terminal positioning data of the selected satellite to execute an RTK calculation.