FMCW Radar Distance Measurement Asynchronicity Correction
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Solution Overview
Problem
Conventional active FMCW radar systems face errors in distance and velocity measurements due to asynchronicity of local oscillators and relative frequency drift between terminals, which existing methods do not account for, especially when these deviations are small compared to the duration or bandwidth of radar pulses.
Innovation Solution
A method involving two measurement cycles where terminals exchange FMCW radar signals, analyzing the frequency spectra of beat signals to determine distance and relative velocity, accounting for effects of asynchronicity and frequency drift by calculating beat frequencies and their differences across multiple measurement cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional FMCW radar signal analysis is used, then distance and velocity can be determined, but measurement precision deteriorates due to asynchronicity and frequency drift of local oscillators
Solution Approach 1:
The patent segments the measurement process into two distinct measurement cycles: first cycle where terminal A transmits and terminal B receives, second cycle where terminal B transmits and terminal A receives. This segmentation allows separate analysis of beat frequencies from each direction, enabling mathematical isolation of distance-related frequency shifts from Doppler and oscillator drift effects, thereby resolving the measurement precision issue under asynchronicity conditions
Solution Approach 2:
The patent changes the measurement parameters by performing frequency spectrum analysis on beat signals from two different measurement cycles and calculating specific combinations of beat frequencies. By analyzing the sum and difference of beat frequencies from bidirectional measurements, the method isolates the frequency component proportional to distance while eliminating components related to Doppler shift and oscillator drift, thus improving measurement precision despite oscillator asynchronicity
2Ease of operation
If synchronized replica transmission is assumed, then simple beat frequency analysis works, but measurement accuracy deteriorates when local oscillators are asynchronous or experience frequency drift
Solution Approach 1:
The patent implements a feedback mechanism where the system performs measurements in both directions (A→B and B→A), analyzes the beat frequencies from each direction, and uses mathematical relationships between these frequencies to isolate and eliminate the effects of oscillator asynchronicity and frequency drift. This bidirectional feedback approach allows the system to compensate for oscillator imperfections without requiring complex synchronization mechanisms, maintaining ease of operation while improving accuracy
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
Enables accurate determination of distance and relative velocity between FMCW radar terminals despite asynchronicity and frequency drift, improving measurement precision by isolating and calculating individual frequency shifts related to distance, Doppler, and oscillator drift.
Implementation Method 1
terminal A transmits a first locally generated periodic FMCW transmit signal to terminal B
Implementation Method 2
terminal B receives the first transmit signal from terminal A as a first receive signal, and mixes it with a locally generated replica of the first transmit signal to produce a first beat signal
Implementation Method 3
the signals mixed at terminal A will include a mutual time-shift that is equal to twice the round trip time. As a result, the mixed signal will define a beat signal at a so-called beat frequency, which is proportional to the distance between the two terminals A and B
Implementation Method 4
In case the two terminals A and B move at a mutual radial velocity, the above procedure requires adjustment to enable correction for the fact the signal received by terminal A includes a Doppler frequency-shift
Data Source
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AI summary
Disclosed is a method that enables the determination of the distance and/or relative radial velocity between two terminals A, B of an active FMCW radar system irrespective of a-synchronicity and relative frequency drift of the respective local signal generators.