Chirp Receiver Phase Precession Multipath Separation
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Solution Overview
Problem
Current GNSS ranging systems face limitations in accurately distinguishing direct path signals from multipath signals that arrive very close in time, leading to errors in positioning, especially in environments like construction sites where reflectors cause signal overlap within 4 meters, resulting in suboptimal tracking and accuracy.
Innovation Solution
A chirp receiver processes broadcast chirp signals using a Fast Fourier Transform (FFT) after phase adjustment and concatenation, enabling the separation of multipath signals from direct path signals with up to 1 millimeter accuracy by converting pulsed frequency sweeps into sine waves and identifying the direct path signal frequency bin above a noise threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If narrow correlators are used to reduce multipath effects, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces the traditional time-domain narrow correlator approach with a frequency-domain processing method using FFT. Instead of using multiple narrow correlators with reduced delay spacing, the invention transforms the correlation operation into the frequency domain where multipath components can be separated and eliminated more efficiently, reducing the computational complexity and hardware requirements while maintaining or improving measurement precision.
2Measurement precision
If multipath mitigation techniques are applied, then positioning accuracy is improved, but processing time increases
Solution Approach 1:
The patent performs preliminary transformation of the received signal into the frequency domain using FFT before conducting correlation operations. By pre-processing the signal to identify and separate multipath components in the frequency domain, the system eliminates multipath effects earlier in the processing chain, allowing for faster subsequent correlation and positioning calculations compared to iterative time-domain multipath mitigation methods.
3Measurement precision
If wider bandwidth signals are used to improve multipath separation, then measurement precision is improved, but loss of substance increases
Solution Approach 1:
The patent changes the processing domain from time to frequency, allowing effective multipath separation using the inherent frequency domain characteristics of chirp signals. This approach enables precise multipath mitigation without requiring excessive bandwidth expansion, as the frequency domain processing efficiently separates multipath components based on their different time delays translated into frequency shifts, maintaining signal power while improving separation capability.
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 achieves high fidelity frequency measurements, allowing for precise clock phase difference determination and pseudorange calculation, significantly improving accuracy in environments with closely arriving multipath signals, surpassing the 4-meter separation limit of existing methods.
Implementation Method 1
A chirp receiver processes broadcast chirp signals in the frequency domain using a Fast Fourier Transform (FFT) to distinguish the direct path signal from the respective multipath signals.
Implementation Method 2
chirp receiver utilizing phase precessed chirp signals
Data Source
AI summary
A system for determining precise position includes a chirp receiver that processes broadcast chirp signals in the frequency domain to distinguish direct path signals from multipath signals. The chirp receiver processes the received chirp signals, which consist of respective pulsed frequency sweeps, by combining a received chirp signal with a synchronized locally generated chirp signal and phase adjusting and concatenating the results over multiple sweeps, based on estimated clock phase errors and expected phase rotations of the direct path signals, to produce a sine wave. The phase adjustment and concatenation allows the use of longer Fast Fourier Transforms (FFTs) that, in turn, provide increased accuracy of frequency estimation and separate component signals that are very close in frequency. The phase adjustment and concatenated signals are processed in the frequency domain using an FFT and a frequency corresponding to the direct path signal is identified by the lowest frequency bin in which power is above a predetermined noise threshold. The receiver then determines a time delay based on the identified frequency and uses the time delay to calculate accurate clock phase error. The system may then determine position based on associated pseudorange measurements.