Automotive FMCW Radar Multiband Chirps for Range-Doppler Ambiguity
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Solution Overview
Problem
Radar systems in autonomous vehicles face challenges such as interference from unsynchronized radars operating in overlapping frequency bands, range cell migration, ambiguity between Doppler velocity and range, and high hardware complexity, which affect range and angle resolution.
Innovation Solution
The system employs multiband chirps with nonlinear start frequency hopping sequences and antenna multiplexing to improve range and angle resolution without increasing hardware complexity, using modified Fourier-based processing to mitigate interference and enhance range resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear FMCW radar with continuous transmission is used, then good short range performance and high accuracy are achieved, but range cell migration and ambiguity between Doppler velocity and range occur
Solution Approach 1:
The patent divides the continuous FMCW transmission into multiple discrete chirps with different frequency slopes and start frequencies. Each chirp is processed independently to generate range-Doppler maps, which are then combined to resolve ambiguities. This segmentation allows the system to distinguish between range cell migration effects and true Doppler shifts by comparing measurements across multiple chirps with varying parameters.
Solution Approach 2:
The patent dynamically varies the start frequency and frequency slope of each chirp in the sequence. By making these parameters dynamic rather than static, the system can differentiate between targets at different ranges and velocities that would otherwise produce identical beat frequencies in a conventional linear FMCW system. The dynamic parameter changes enable the resolution of measurement ambiguities while maintaining high accuracy.
2Measurement precision
If higher bandwidth processing is used to improve range resolution, then range resolution is enhanced, but hardware complexity and cost increase
Solution Approach 1:
The patent achieves high effective bandwidth without requiring high-speed hardware processing by segmenting the measurement into multiple chirps, each with moderate bandwidth. The range resolution is improved through the combination of measurements from multiple chirps with different frequency parameters, rather than requiring a single high-bandwidth chirp. This approach maintains hardware complexity at manageable levels while achieving the desired resolution through computational processing of segmented measurements.
Solution Approach 2:
The patent uses periodic chirp sequences with repeating patterns of frequency slopes and start frequencies. This periodic structure allows the system to accumulate measurements over multiple cycles, effectively synthesizing high resolution from multiple moderate-bandwidth measurements. The periodic action enables high range resolution to be achieved through temporal integration rather than requiring high instantaneous bandwidth hardware.
3Adaptability or versatility
If multiple radars operate in overlapping frequency bands, then spectrum utilization is improved, but mutual interference increases
Solution Approach 1:
The patent makes the radar transmission parameters dynamic by varying start frequencies and frequency slopes across different chirps in a pseudo-random or coded sequence. This dynamic behavior allows multiple radars operating in the same frequency band to be distinguished through their unique parameter sequences, reducing mutual interference while maintaining high spectrum utilization. Each radar's dynamic parameter pattern acts as a signature that enables separation of overlapping signals.
Solution Approach 2:
The patent employs feedback mechanisms where the radar system monitors the received signals to detect and characterize interference from other radars. Based on this feedback, the system can adjust its chirp parameter sequences to avoid or mitigate interference, or use the feedback information to identify and filter out interfering signals. This adaptive feedback approach enables multiple radars to coexist in overlapping frequency bands with reduced mutual interference.
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 achieves improved range and angle resolution with reduced hardware complexity, effectively mitigating interference and enhancing spatial accuracy while maintaining low computational and power consumption.
Implementation Method 1
Frequency Modulated Continuous Wave (FMCW) radar is a type of radar that offers several advantages compared to the others
Implementation Method 2
the Doppler shift to be used to determine velocity
Implementation Method 3
The beat frequency output of a mixer in the receiver due to the range of the target
Implementation Method 4
The beat frequency output of a mixer in the receiver due to the range of the target
Data Source
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AI summary
A novel and useful system and method by which radar angle and range resolution are significantly improved without increasing complexity in critical hardware parts. A multi-pulse methodology is described in which each pulse contains partial angular and range information consisting of a portion of the total CPI bandwidth, termed multiband chirp. Each chirp has significantly reduced fractional bandwidth relative to monoband processing. Each chirp contains angular information that fills only a portion of the 'virtual array', while the full virtual array information is contained across the CPI. This is done using only a single transmission antenna per pulse, thus significantly simplifying MIMO hardware realization, referred to as antenna-multiplexing (AM). Techniques for generating the multiband chirps as well as receiving and generating improved fine range-Doppler data maps. A windowing technique deployed in the transmitter as opposed to the receiver is also disclosed.