FMCW radars provide an excellent method for estimating range information of targets... but what about velocity?
The velocity of a target is often obtained using the Doppler frequency shift it incurs. This gets more challenging once you start using frequency information to determine range because it is ambiguous whether the frequency shift is due to the range or velocity.
In this video I introduce two methods for dealing with this issue and provide a python notebook to play around with the methods yourself.
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Resources:
- Interactive python notebook for Range-Doppler processing (fmcw_range_doppler.ipynb) - https://tinyurl.com/doppler-notebook
- Interactive python notebook showing how to use the Fast Fourier Transform (fft.ipynb) - https://tinyurl.com/fft-notebook
- All code for this video - https://tinyurl.com/github-videos
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References:
- Small and short range radar systems (book by Gregory Charvat, p288-291) - https://tinyurl.com/charvat-srr-book
- FMCW Radar Part 2 – Velocity, Angle and Radar Data Cube (Wireless Pi) - https://tinyurl.com/wirelees-pi-doppler
- Texas Instruments Automotive Radar Chip (AWR1642) - https://tinyurl.com/awr1642
- FMCW Chirp Configuration for Short, Medium, and Long-Range Radar (MWRF) - https://tinyurl.com/mwrf-chirp
- RadarSimX simulation of the range-Doppler spectrum - https://tinyurl.com/radarsimx-doppler
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Caveats:
- The "stop-and-hop" assumption is made that assumes the target with a non-zero velocity doesn't move during the chirp duration, then moves by v * T_c by the next chirp. This is not perfectly accurate, but is fine for many cases.
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All animations shown were created using Manim Community (https://docs.manim.community/en/stable/index.html) - a Python animation library written by 3Blue1Brown (https://www.youtube.com/@3blue1brown) and maintained by the community. Huge thanks to everyone working on this incredible project!
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Timestamps:
0:00 - Why is velocity difficult in FMCW radar?
1:25 - Triangular Modulation
4:06 - The problem with Triangular Modulation
4:47 - Range-Doppler Spectrum