How automotive radar measures the velocity of objects
Automotive radar uses chirp signals for distance and velocity measurement. Frequency shifts in reflected chirps indicate object velocity. Phase data is crucial for accurate measurements, analyzed through Doppler FFT for precise results.
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Automotive radar utilizes chirp signals to measure distance and velocity. The frequency modulated chirp signals are transmitted and reflected off objects, generating beat frequencies proportional to distance. Doppler effect causes frequency shifts in received chirps, indicating object velocity. Phase information is crucial for resolving range and velocity ambiguities. Phase changes with distance and object movement, providing sensitive measurements. Multiple chirps in succession form a frame for velocity estimation of multiple objects. Doppler FFT analyzes phase changes over chirps to determine velocities and directions. Chirp design factors include bandwidth, chirp duration, and number of repetitions in a frame, impacting range and velocity resolution. Practical examples of chirp parameters for automotive radar applications illustrate trade-offs between range and velocity measurements. Memory capacity is essential for storing radar data to compute range-doppler plots accurately. Automotive radar systems rely on complex signal processing techniques to extract precise distance and velocity information for various applications.
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8 commentsYes. That's a neat property of superhetrodyning - phase is preserved. Both the outgoing and incoming signals are down-converted by mixing with the local oscillator. The phase angle difference between out and in is the same at both the transmitted/received frequency and the IF frequency. But down at the IF frequency, you get to work at a lower frequency where it's easier to do A/D conversion and counting. Most software defined radios still have a superhetrodyne front end, so the digital stuff is working at the IF frequency.
This is less necessary than it used to be, now that digital circuits can work well into gigahertz ranges.
>> The time between two consecutive chirps is called the pulse repetition rate (PRT), and plays a key role in the accuracy of doppler velocity estimation.
This is actually known as the pulse-repetition interval (PRI), or time (PRT). A "rate" is describable by a frequency. An interval is described with a unit of time between repetitions. Radar signal characteristics are a rabbit hole of such definitions. They really do matter once one switches from theoretical discussion to actual math. Confuse a rate with a period and your math for calculating ambiguity zones will fall apart.
> With a PC with Intel Wi-Fi sensing capabilities in sleep mode, the PC Wake-on-Approach is activated as it detects human presence. Even when a user forgets to lock the PC, a count-down to lock starts with no human present. False detection is prevented even with human presence behind and next to the PC.
https://www.viksnewsletter.com/p/how-automotive-radar-uses-c...
If the author is here I would be curious to know your process and tools to generate the graphs and figures?
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