Adaptive cruise radar and front radar do not conflict. FMCW radar is smaller and consumes less power. It is usually used in automobile adaptive cruise system (ACC), and usually occupies a frequency band of about 77GHz. The radar system constantly estimates the distance between the vehicle mounted on it and the vehicle in front of it, and warns the driver when they become too close.

Fb is called beat frequency. The received signal is a delayed copy of the transmitted signal, where the delay is related to the distance. Because the signal always sweeps across the frequency band, the frequency difference between the transmitted signal and the received signal is constant at any time during scanning. Usually called beat frequency. Because the scanning is linear, the time delay can be obtained from the beat frequency, and then the delay can be converted into a range. Under the ACC setting, the maximum range that radar needs to monitor is about 200 meters, and the system needs to be able to distinguish two targets with a distance of 1 meter. According to these requirements, the waveform parameters can be calculated.

Fc = 77e9 (set RF frequency) c = 3e8；; (light speed) λ = c/fc; ; The (wavelength) scanning time can be calculated according to the time required for the signal to propagate to the determined maximum range. Generally speaking, for FMCW radar system, the scanning time should be at least 5 to 6 times of the round-trip time. In this example, a factor of 5.5 is used.

range _ max = 200tm = 5.5 * range2time(range_max，c)； The scanning bandwidth can be determined according to the range resolution, and the scanning bandwidth and scanning time can be used to calculate the scanning slope.

range _ RES = 1； bw = range2bw(range_res，c)； (The formula is in another blog in my collection) sweep _ slope = bw/tm; ; (The slope is the scanning bandwidth divided by the period) Since FMCW signals usually occupy a lot of bandwidth, blindly setting the sampling rate to twice the bandwidth usually emphasizes the capability of the ADC hardware. In order to solve this problem, people can usually choose a lower sampling rate. There are two things to consider here:

1. For complex sampling signals, the sampling rate can be set to be the same as the bandwidth.

2.FMCW radar uses the beat frequency embedded in the signal to estimate the target distance. The maximum beat frequency that radar needs to detect is the sum of the beat frequency corresponding to the maximum distance and the maximum Doppler frequency. Therefore, the sampling rate only needs to be twice the maximum beat frequency.

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