GNSS Signal Acquisition Using FFT Correlation for Faster Tracking
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Solution Overview
Problem
Conventional GNSS signal acquisition methods are slow, especially for modern GNSS signals with longer PRN codes and finer code shift hypotheses, requiring significant time to determine the correct frequency and code shift, which can take up to 60 seconds for signals like Galileo-E1B/E1C.
Innovation Solution
A method involving discrete Fourier transforms (DFT) and correlation techniques to quickly acquire GNSS satellite signals by generating samples, correlating them with local pseudorandom codes, and performing DFT on correlation values to determine tracking frequency and code shift, utilizing iterative techniques to handle longer PRN codes with smaller buffer sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional guess-and-check methods are used to determine frequency and code shift hypotheses, then the receiver can systematically search for the correct signal parameters, but the acquisition time becomes excessively long (up to 60 seconds for Galileo-E1B/E1C signals)
Solution Approach 1:
The patent replaces the conventional mechanical guess-and-check search method with an accelerated search algorithm that uses correlation techniques and frequency domain processing. The system performs correlation between received signal and local pseudorandom code, then applies Fast Fourier Transform (FFT) to quickly identify frequency and code shift hypotheses, reducing acquisition time from 60 seconds to a fraction of that time while maintaining measurement precision.
2Measurement precision
If longer PRN codes are used in modern GNSS systems, then the code uniquely identifies the satellite with higher precision, but the number of code shift hypotheses increases, making acquisition slower
Solution Approach 1:
The patent segments the correlation processing into manageable portions by dividing the PRN code into segments and processing them in blocks. The system correlates received signal segments with local code segments, then uses FFT to process the correlation results. This segmentation approach allows the system to handle longer PRN codes (4092 chips for Galileo-E1B/E1C) by processing them in manageable portions rather than attempting to process the entire code at once, thus maintaining both precision and acquisition speed.
3Measurement precision
If finer code shift hypotheses are required for BOC modulation, then the measurement precision improves, but the number of hypotheses to test increases, extending acquisition time
Solution Approach 1:
The patent replaces the exhaustive mechanical testing of each code shift hypothesis with an accelerated search using correlation and FFT techniques. The system performs correlation between received signal and local code, then applies FFT to the correlation results to quickly identify peaks that indicate correct frequency and code shift hypotheses. This substitution of the search method allows the system to handle the increased number of hypotheses required for BOC modulation while maintaining fine measurement precision without proportionally increasing acquisition time.
Data Source
AI summary
A method is provided for acquiring a signal from a satellite in a global navigation satellite system. The signal includes a pseudorandom code. The method includes, for each time period of a plurality of time periods: generating samples of the signal, segments of the samples of the signal are correlated with a local copy of the pseudorandom code, thereby producing correlation values for the time period. A discrete Fourier transform is performed using, as inputs, the correlation values for the respective time period, thereby producing a frequency representation of the correlation values for the time period. The frequency representations of the correlation values for the plurality of time periods are combined according to a data hypothesis. When a magnitude of the combined frequency representations meets predefined criteria, a frequency corresponding to the magnitude is selected as a tracking frequency for the satellite.