Vehicle Radar FMCW Ramp Timing for Doppler Bin Separation
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Solution Overview
Problem
Vehicle radar systems struggle to distinguish ground stationary objects from approaching vehicles due to under-sampling of target velocities, leading to ambiguity in Doppler bins and difficulty in separating them based on angle of arrival.
Innovation Solution
A vehicle radar system that generates and transmits FMCW signals with varying ramp period times for different pluralities of frequency ramps, allowing differentiation of ground stationary and approaching vehicles by altering the Nyquist velocity and reducing azimuth jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the radar system uses a relatively rapid sequence of ramps to track phase from one ramp to the next, then phase tracking is improved, but velocity under-sampling occurs making it difficult to distinguish ground stationary objects from approaching vehicles
Solution Approach 1:
The patent applies dynamics by making the ramp period time variable rather than fixed. The control unit adapts the ramp period time based on detected target velocities, switching between different ramp period values to optimize both phase tracking and velocity measurement. This dynamic adjustment allows the system to maintain accurate phase tracking while avoiding velocity under-sampling aliases.
Solution Approach 2:
The patent changes the parameter of ramp period time to resolve the contradiction. By varying the ramp period time between different radar cycles based on target velocity detection, the system can adjust the Nyquist velocity to match the actual target velocities, thereby preventing velocity under-sampling while maintaining phase tracking accuracy.
2Speed
If the radar system travels at high velocity, then detection range is improved, but ground stationary objects and following targets appear in the same Doppler bin making them indistinguishable
Solution Approach 1:
The system dynamically adjusts the ramp period time based on the ego vehicle's velocity and detected target velocities. When traveling at high speeds that cause Doppler bin overlap, the control unit modifies the ramp period to shift the Doppler frequency scaling, thereby separating ground stationary objects from approaching vehicles into different Doppler bins for accurate classification.
Solution Approach 2:
The patent employs feedback by using the detected target velocities and ego vehicle velocity information to continuously adjust the ramp period time. The control unit monitors the Doppler bin distribution and adapts the ramp period to optimize the separation between different target types, ensuring accurate target classification even at high velocities.
3Device complexity
If a single ramp period time is used for all radar cycles, then system simplicity is maintained, but velocity ambiguity occurs where different targets occupy the same Doppler bin
Solution Approach 1:
The system transitions from a static single ramp period time to a dynamic multi-ramp period time approach. The control unit selects from multiple predefined ramp period values based on the detected velocity conditions, providing the flexibility needed to resolve velocity ambiguities while maintaining relatively simple system architecture through pre-defined ramp period options.
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 system effectively separates ground stationary objects from approaching vehicles by ensuring they occupy different Doppler bins, eliminating ambiguity and maintaining consistent sample counts for FFT processing.
Implementation Method 1
A vehicle radar system comprises at least one transceiver arrangement arranged to generate, transmit a least one FMCW (Frequency Modulated Continuous Wave) chirp signal
Implementation Method 2
The received signals, thus constituted by reflected radar echoes, are mixed with the transmitted chirp signal in order to convert the received signals to baseband signals
Implementation Method 3
The digital signals are used for retrieving an azimuth angle of possible targets by simultaneously sampling and analyzing phase and amplitude of the received signals
Data Source
AI summary
A vehicle radar system (3) adapted to be placed in an ego vehicle (1) and comprising a control unit (4) and at least one transceiver arrangement (5) arranged to generate and transmit an FMCW signal (6; 6a, 6′a; 6b, 6′b) and to receive reflected signals (7) that have been reflected by one or more target objects (14, 15), each target object having an associated determined target object velocity (v2, v3). The FMCW signal (6) comprises a corresponding plurality of frequency ramps (r1, r2), where each one has a certain duration time (tr1, tr2). The control unit (4) is adapted to control the transceiver arrangement (5) to generate at least two pluralities (6a, 6′a; 6b, 6′b, 6c, 6′c) of ramps (r1, r2). The ramps (r1) in each plurality (6a, 6′a) of ramps (r1) are adapted to have a ramp period time (tT1) that differs from the ramp period time (tT2, tT3, tT4) in all other pluralities (6b, 6′b, 6c, 6′c) of ramps (r1, r2). The ramp period times (tT1, tT2, tT3, tT4) are based on a determined ego vehicle velocity (v1), the determined target object velocity (v2, v3), or a combination of both.