GNSS Signal Acquisition Using Frequency Multi-Correlation Feedback
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Solution Overview
Problem
The acquisition of satellite signals in GNSS systems is prolonged due to inconsistencies in code generation rates caused by Doppler shift compensation errors in frequency-shifted carriers, especially in the presence of interference or low signal-to-noise ratios, leading to reduced effectiveness of correlators and increased acquisition times.
Innovation Solution
A method that corrects the error induced by frequency shifts by summing the results of frequency-increased correlators at specific instants during integration, transferring these results between correlators to maintain code alignment, and implementing Doppler shift compensation for each channel to ensure consistent code generation speed with the nominal frequency, thereby optimizing the use of correlators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If post-detection frequency multicorrelation is implemented to reduce acquisition time, then the number of hypotheses tested simultaneously increases, but code generation rate inconsistencies cause code slippage and reduce the number of usable correlators
Solution Approach 1:
The patent implements feedback by calculating the induced error at the output of each frequency-increased correlator and using this error information to transfer results between correlators. The error calculation is based on the frequency shift and integration duration, and this feedback mechanism allows the system to maintain code alignment accuracy while using multiple frequency-shifted correlators simultaneously, thus resolving the contradiction between reduced acquisition time and maintained reliability
Solution Approach 2:
The patent changes the operating parameters of the correlators by introducing frequency shifts relative to the center frequency. By carefully selecting and managing these frequency parameters, the system can test multiple hypotheses simultaneously (reducing acquisition time) while the induced error from frequency shifts is compensated through the feedback mechanism, maintaining code alignment accuracy
2Reliability
If integration time is increased to improve signal detection in low signal-to-noise ratio conditions, then detection reliability improves, but code slippage due to frequency offset increases
Solution Approach 1:
The feedback mechanism calculates the induced error as a function of frequency shift and integration duration. By providing feedback about the accumulated error over the integration period, the system can transfer results to appropriate correlators, maintaining code alignment precision even when integration time is extended for low signal-to-noise ratio conditions
3Productivity
If the number of frequency-augmented correlators is increased to reduce acquisition time, then search coverage increases, but the induced error from frequency offset reduces the number of usable correlators
Solution Approach 1:
The feedback mechanism allows the system to use frequency-increased correlators shifted by larger frequency offsets (which would normally be unusable) by calculating their induced error and transferring results appropriately. This feedback-enabled approach increases the number of usable correlators and expands search coverage while maintaining frequency measurement precision
Solution Approach 2:
The patent introduces an additional dimension of frequency shifting beyond the nominal Doppler compensation. By operating correlators at multiple frequency offsets from the center frequency and managing the induced errors through feedback, the system expands the search space in the frequency dimension, increasing productivity while maintaining precision through error compensation
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
This approach significantly reduces satellite signal acquisition times by maintaining code alignment and increasing the number of usable correlators, even under low signal-to-noise conditions, enhancing the efficiency of GNSS signal detection.
Implementation Method 1
The acquisition of signals from a satellite of a satellite positioning system consists of aligning the signal coming from a satellite with a replica signal generated locally by the receiver... This alignment is confirmed when the result of the correlation, integrated over a more or less long period, exceeds a detection threshold
Implementation Method 2
Implementing compensation for the Doppler shift of the carrier of the satellite signal which is sought with respect to the nominal frequency of said carrier of the satellite signal; this offset is a function of the apparent speed of the satellite relative to the receiver
Data Source
Figure 1
Figure 2~3
AI summary
The method involves summing successive results of frequency-augmented correlators (14) at instants during an integration period of results of multi-frequency correlation. The summated results of one of the correlators are transferred to the summated results of the other correlator if an error induced at an output from the correlator expressed as an integer number of code spaces between code correlators (12) at each of the instants has increased relative to an induced error expressed as an integer number of code spaces between the code correlators at the output valid in previous instant. An independent claim is also included for a receiver of satellite positioning system.