FMCW Radar Sensor Ego Speed Measurement Using Road Surface Doppler Shift
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Solution Overview
Problem
FMCW radar sensors in motor vehicles face challenges in accurately determining ego speed due to calibration errors from wheel-speed sensors and limitations in measuring ego velocity, especially when suitable stationary objects are not available, and existing methods like Doppler radar require angle corrections.
Innovation Solution
The FMCW radar sensor employs special modulation sequences with longer duration and smaller frequency swing, allowing for precise ego speed measurement using radar echoes from the road surface, which enables high velocity resolution and accurate detection of relative velocities from road surface irregularities, effectively eliminating distance measurement and relying on pure Doppler sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional FMCW radar with standard modulation sequences is used, then distance measurement is achieved, but velocity measurement precision is insufficient for accurate ego speed determination
Solution Approach 1:
The measurement process is segmented into two distinct parts: a first modulation sequence dedicated to distance measurement and a second modulation sequence dedicated to velocity measurement. This segmentation allows each sequence to be optimized for its specific purpose, with the second sequence using longer duration and smaller frequency swing to achieve high velocity resolution without compromising distance measurement capabilities
Solution Approach 2:
The patent changes the parameters of the modulation sequences by varying their duration and frequency swing characteristics. The second modulation sequence specifically uses a longer duration and smaller frequency swing compared to conventional sequences, which directly improves velocity measurement precision while maintaining the ability to perform distance measurement with the first sequence
2Measurement precision
If Doppler radar with oblique direction to road surface is used, then ego velocity measurement is possible, but angle correction is required reducing measurement simplicity
Solution Approach 1:
Instead of directing the radar beam obliquely to the road surface as in conventional Doppler radar, this patent directs the beam parallel to the road surface (α=0). This inversion of the conventional approach eliminates the need for angle corrections while maintaining measurement accuracy, as the cosine effect is maximized when the beam is parallel to the surface
3Productivity
If wheel-speed sensors are used for ego velocity measurement, then velocity data is obtained, but calibration errors and accuracy degradation at low speeds occur
Solution Approach 1:
The patent uses the road surface as an intermediary target for velocity measurement. By measuring the Doppler shift from the road surface reflection, the system obtains accurate ego velocity data without relying on wheel-speed sensors, thereby eliminating calibration errors and maintaining accuracy across all speed ranges including low speeds
4Measurement precision
If FMCW radar measures relative velocity of stationary objects, then ego speed can be determined, but suitable stationary objects must be available
Solution Approach 1:
The radar system uses the road surface itself as the measurement target, which is always available during vehicle operation. This self-service approach eliminates the need for external stationary objects, making the measurement method universally applicable in all driving situations without dependency on environmental conditions or object availability
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 enhances the precision and reliability of ego speed measurement by increasing signal density and clarity, allowing for clear detection of ego velocity without angle corrections, even in situations lacking suitable stationary objects.
Implementation Method 1
The signal also has a velocity-dependent component because of the Doppler effect
Implementation Method 2
Due to the frequency modulation, this intermediate frequency signal is a function of the signal propagation time and thus of the distance of the object
Data Source
AI summary
An FMWC radar sensor for motor vehicles, having a high-frequency oscillator, which is developed to generate a frequency-modulated transmit signal that has a periodically repeating series of modulation sequences having different modulation patterns, and having an evaluation device for evaluating the received radar echo according to the FMCW principle, wherein the series of the modulation sequences includes a special class of modulation sequences whose duration is longer than that of any other modulation sequence not belonging to this class and whose frequency swing is smaller than that of any other modulation sequence, and the evaluation device is developed to carry out a measurement of the ego velocity of the vehicle on the basis of a radar echo that is received from non-moving objects during the modulation sequences that belong to the special class.