FMCW Radar Phase Difference Distance Calculation
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Solution Overview
Problem
FMCW radar systems face ambiguity in determining the distances and relative speeds of multiple objects simultaneously due to overlapping frequency peaks, leading to incorrect identification of 'decoy targets' and increased computational effort with increasing object count, especially when relative speeds exceed the condition for unambiguous phase change determination.
Innovation Solution
The method employs a modulation pattern with two groups of ramps, one without and one with frequency offset, nested alternately, where intermediate frequency signals are evaluated separately to determine phase differences, allowing for accurate object distance calculation by selecting the closest approximate value from multiple possibilities, thus reducing ambiguity and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple frequency ramps are used to resolve ambiguity in distance and velocity measurement, then measurement reliability improves, but device complexity and computational effort increase
Solution Approach 1:
The measurement process is segmented into two distinct phases: first using frequency-shifted ramps to obtain an approximate distance value, then using conventional ramps to refine the measurement. This segmentation allows each phase to specialize in its strength while avoiding the weaknesses of the other approach alone.
Solution Approach 2:
The frequency-shifted ramps perform a preliminary measurement to establish an approximate distance value before the main measurement phase. This preliminary action constrains the search space for the subsequent conventional ramps, reducing the computational complexity of resolving ambiguities.
2Reliability
If the ramp duration is reduced to maintain unambiguous velocity measurement at high speeds, then velocity measurement reliability improves, but distance measurement precision deteriorates
Solution Approach 1:
The measurement process is segmented into two distinct phases: first using frequency-shifted ramps to obtain an approximate distance value, then using conventional ramps to refine the measurement. This segmentation allows each phase to specialize in its strength while avoiding the weaknesses of the other approach alone.
Solution Approach 2:
The approximate distance value obtained from frequency-shifted ramps acts as an intermediary that bridges the gap between the two measurement requirements. It provides a preliminary constraint that enables the subsequent precise measurement without requiring the first measurement to be perfectly accurate.
3Productivity
If frequency-shifted ramps are used to determine approximate distance, then distance measurement speed improves, but velocity measurement accuracy deteriorates due to phase periodicity
Solution Approach 1:
The measurement process is segmented into two distinct phases: first using frequency-shifted ramps to obtain an approximate distance value, then using conventional ramps to refine the measurement. This segmentation allows each phase to specialize in its strength while avoiding the weaknesses of the other approach alone.
Solution Approach 2:
The frequency-shifted ramps perform a preliminary measurement to establish an approximate distance value before the main measurement phase. This preliminary action constrains the search space for the subsequent conventional ramps, reducing the computational complexity of resolving ambiguities.
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 provides clear and accurate measurements of object distances and relative speeds by exploiting the phase difference independence from relative speed at short time intervals, enabling correct identification of object distances and speeds even at higher velocities, while maintaining unambiguous results within a defined distance range.
Implementation Method 1
However, due to the Doppler effect, the frequency difference also includes a component caused by the object's relative velocity.
Implementation Method 2
the frequency difference depends on the signal's travel time from the radar sensor to the object and back, and thus on the object's distance
Data Source
Figure 1~2
Figure 3(A)~3(C)
Figure 4(A)~4(C)
AI summary
The invention relates to a method for determining distances and relative speeds of a plurality of objects that are located at the same time by means of a FMCW radar, in which the frequency of an emitted signal in the form of ramps (24, 30) repeating in periodic intervals is modulated, the emitted signal combined with a received signal to an intermediate frequency signal and for determining the distance and/or the relative speed of the objects the modification of the phase of the intermediate frequency signal is evaluated from ramp to ramp, characterized in that the modulation pattern comprises at least two ramps (24, 30) which differ in one fixed frequency offset (fs) only and which are consecutive in a determined time distance (T'c), and in that a unique approximate value (R0) for the object distance is calculated on the basis of the phase difference (φ1- φ2) the intermediate frequency signals for these two ramps.