FMCW Ranging Device Ring-Down Interference Subtraction
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Solution Overview
Problem
Conventional FMCW ranging devices face challenges in accurately determining distance due to severe interference from ring-down effects at close ranges, where interference frequencies are not constant and vary with environmental factors, leading to degraded performance and a 'blanking zone' starting from 1 meter away from the device.
Innovation Solution
A method that learns and tracks the stationary or slowly changing ring-down pattern, extracting the interference profile from the low-frequency portion of the echo profile using FFT, and subtracts it to isolate the target signal, allowing for accurate distance measurement even at close ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional FMCW ranging devices use standard FFT-based echo profile analysis, then distance measurement is straightforward for far targets, but measurement accuracy severely degrades at close ranges due to ring-down interference
Solution Approach 1:
The patent extracts the ring-down interference component from the echo profile by identifying and isolating the low-frequency portion (below a threshold frequency) that corresponds to ring-down. This extracted interference profile is then subtracted from the total echo profile, effectively removing the harmful ring-down component and enabling accurate target detection at close ranges.
Solution Approach 2:
The patent dynamically adapts the interference removal process by continuously updating the interference profile based on current measurements. The system adjusts the threshold frequency and re-estimates the interference profile in real-time, allowing the measurement system to adapt to changing environmental conditions and maintain accuracy at close ranges.
2Reliability
If a reference measurement is made in an empty container to record interference components, then interference suppression can be applied, but the method requires a special set-up and assumes constant interference frequencies which is not valid in practice
Solution Approach 1:
The patent enables the system to automatically characterize and remove its own ring-down interference without requiring external reference measurements or special setup procedures. The interference profile is extracted directly from the measured echo profiles using automated threshold-based identification and iterative refinement, making the system self-sufficient and eliminating the need for separate calibration procedures.
Solution Approach 2:
The patent performs preliminary interference characterization by identifying and storing the ring-down interference profile before target detection. The system pre-processes the echo profile to extract the interference component, which is then used in subsequent target detection operations, enabling consistent interference suppression without requiring reference measurements at different times.
3Length of stationary object
If the measurement range is extended to close ranges, then more applications become possible, but the received signal is severely distorted by huge interference factors
Solution Approach 1:
The patent converts the harmful ring-down interference into a useful characteristic by identifying its specific frequency signature (low-frequency portion of the spectrum) and using it as a basis for selective removal. By characterizing the interference's frequency distribution and systematically subtracting it, the system transforms the previously unusable close-range region into a valid measurement zone.
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 effectively removes close-range interferences, improving measurement accuracy and extending the reliable measurement range closer to the device by learning and updating the interference profile over time, enhancing performance and reducing errors.
Implementation Method 1
a transmitted signal is modulated to periodically sweep over a predetermined frequency range
Implementation Method 2
A received signal, which comprises echo signal portions from the object of interest and other obstacles, is mixed down with the transmitted signal
Implementation Method 3
the frequency difference signal obtained is analyzed by, e.g., a Fast Fourier Transform (FFT) to obtain a frequency spectrum in which the echoes appear as peaks
Implementation Method 4
A received signal, which comprises echo signal portions from the object of interest and other obstacles
Data Source
AI summary
A method for determining a distance between a ranging device and target, wherein a valid interference profile, if already available, is subtracted from a frequency-domain echo profile that is analyzed to determine the distance of the target, where to obtain or update the valid interference profile, a low-frequency portion of the frequency-domain echo profile is stored as a temporary interference profile after each measurement, and if the target is not proximal to the ranging device and the valid interference profile is not available, the temporary interference profile is saved as the valid interference profile, otherwise if the valid interference profile is available, the valid interference profile is updated via the temporary interference profile, otherwise if the target is distal and the valid interference profile is not yet available, the temporary interference profile is first subjected to a quality check before being saved as the valid interference profile.