GPS Receiver Phase Tracking via Doppler-Aided Correlation
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Solution Overview
Problem
GPS receivers face challenges in accurately determining the phase of the C/A code under weak signal conditions due to Doppler shift and low signal strength, leading to positioning inaccuracies.
Innovation Solution
A positioning device and method that includes a phase calculation section for correlating a positioning base code, an estimated phase calculation section to account for Doppler shift and elapsed time, and a phase difference evaluation section to determine if the phase difference is within a specific allowable range, ensuring accurate positioning even under weak signal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the GPS receiver uses correlation process to determine the phase of the C/A code, then the positioning function can be achieved, but under weak signal conditions the phase determination accuracy deteriorates due to insufficient signal strength
Solution Approach 1:
The patent applies preliminary action by calculating an estimated phase in advance based on the previous phase and Doppler shift before performing the correlation process. This estimated phase serves as a reference to guide the correlation search, enabling accurate phase determination even when signal strength is weak. The estimated phase is computed using the formula: estimated_phase = previous_phase + Doppler_shift × elapsed_time, which provides a head start for the correlation process without requiring strong signal accumulation.
2Measurement precision
If the GPS receiver coherently combines multiple signal segments to improve signal-to-noise ratio, then the detection capability improves, but the synchronization becomes difficult due to continuous Doppler shift causing frequency mismatch
Solution Approach 1:
The patent applies dynamics by making the correlation frequency adaptive rather than fixed. The correlation process uses the estimated phase that incorporates Doppler shift compensation, allowing the receiver to dynamically track the changing frequency. This dynamic adjustment enables coherent combination of multiple signal segments while maintaining synchronization despite continuous Doppler shift, as the correlation frequency is continuously updated based on the estimated phase evolution.
Solution Approach 2:
The patent implements feedback by using the previously determined phase information to calculate the estimated phase for the current correlation process. This feedback loop allows the system to continuously adjust to Doppler shift effects. The phase from the previous measurement cycle feeds into the estimation formula, creating a self-correcting mechanism that maintains synchronization accuracy over time despite frequency drift.
3Adaptability or versatility
If the GPS receiver performs correlation process over a wide frequency range to account for Doppler shift, then the frequency acquisition capability improves, but the processing time and computational complexity increase
Solution Approach 1:
The patent applies local quality by concentrating the correlation process around the estimated phase frequency rather than distributing it uniformly across a wide frequency range. The estimated phase provides a local focus point where the correlation energy is most likely to be found. This localized approach maintains frequency acquisition capability by using the Doppler shift estimation to identify the relevant frequency region, while significantly reducing processing time by avoiding unnecessary correlations at frequencies far from the estimate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables accurate verification of the phase of the positioning base code and precise location determination under weak electric field conditions by filtering out phases with low accuracy and using the most reliable frequency sequences, thereby improving GPS positioning accuracy.
Implementation Method 1
a phase calculation section which performs a correlation process of a specific positioning base code replica and a positioning base code from a specific transmission source to calculate a present phase of the positioning base code
Implementation Method 2
an estimated phase calculation section which calculates an estimated phase when estimating the present phase based on the phase used during preceding positioning, a Doppler shift of a frequency of a radio wave carrying the positioning base code, and an elapsed time from the preceding positioning
Data Source
AI summary
A positioning device includes a phase calculation section which performs a correlation process of a specific positioning base code replica and a positioning base code from a specific transmission source to calculate a present phase of the positioning base code, an estimated phase calculation section which calculates an estimated phase when estimating the present phase based on the phase used for preceding positioning, a Doppler shift of a frequency of a radio wave carrying the positioning base code, and an elapsed time from the preceding positioning, a phase difference evaluation section which determines whether or not a phase difference between the calculated present phase and the estimated phase is within a phase difference allowable range specified in advance, and a positioning section which locates a present position using the phase within the phase difference allowable range.