GNSS Receiver Frame Synchronization via Geometric Range Convergence
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Solution Overview
Problem
GPS receivers face challenges in achieving accurate position and time calculations in degraded signal environments, such as urban areas and tunnels, due to weak satellite signals, which leads to inaccurate navigation data.
Innovation Solution
The method involves using acquisition channel results from multiple satellites to achieve composite weak acquisition, identifying correlation peaks, and performing a position domain search to determine the point of convergence of ranges, thereby solving for GPS position and time without data demodulation or preamble matching, effectively achieving frame synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If GPS receivers use conventional data demodulation or preamble matching for frame synchronization, then synchronization can be achieved in strong signal environments, but the method fails in degraded signal environments such as urban canyons and tunnels
Solution Approach 1:
The patent changes the fundamental parameter of synchronization from data-based (requiring successful demodulation) to geometry-based (using pseudorange and code phase measurements). This parameter change allows the system to achieve frame synchronization through geometric convergence of satellite ranges rather than through data bit synchronization, making it effective in degraded signal environments where conventional data demodulation fails.
Solution Approach 2:
The patent replaces the electronic signal processing mechanism (data demodulation and preamble matching) with a geometric/mathematical mechanism (position domain search and range convergence). By substituting the mechanical/electronic synchronization approach with a geometric calculation approach, the system can achieve synchronization without relying on strong signal conditions required for data demodulation.
2Duration of action of stationary object
If GPS receivers rely on last-known position with navigation filters in degraded signal environments, then continuous positioning can be maintained, but position calculation accuracy deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the geometric convergence result provides accurate position and time information that feeds back to correct the navigation filter's accumulated errors. By periodically obtaining accurate position fixes through geometric convergence even in degraded environments, the system can reset and correct the drift that occurs during signal outages, maintaining both continuous positioning and accuracy.
3Measurement precision
If GPS receivers use conventional acquisition methods for each satellite independently, then acquisition can be achieved in strong signal environments, but the method is insufficient for composite weak acquisition from multiple satellites
Solution Approach 1:
The patent merges the acquisition results from multiple independent satellite channels into a composite position domain search. By combining the pseudorange and code phase measurements from multiple satellites that individually have weak signals, the system achieves composite weak acquisition where the collective geometric information provides sufficient precision for synchronization, enabling processing capability that exceeds the sum of individual channel performances.
Data Source
AI summary
According to certain aspects, the invention includes using acquisition channel results from a number of satellites to achieve composite weak acquisition. According to certain other aspects, the invention also includes solving for an improved position estimate and, with a sufficiently accurate, either initial or improved position estimate, also solving for GPS system time using a composite of acquired signals from a plurality of satellites. Within commonly experienced initial position and time uncertainties, the geometric range changes are fairly linear, which allows the point of convergence of ranges to solve for GPS position and subsequently for time with reasonable accuracy, which is the equivalent to obtaining frame sync without any data demodulation or preamble matching.