Radar system with monitoring of the frequency position of a sequence of similar transmission signals
A method for detecting the environment of a motor vehicle utilizing a radar system includes bringing about frequency modulation utilizing an oscillator and generating a sequence of transmission-frequency-modulated transmit signals, which each having the same nominal frequency profile, apart from a variation in frequency position. Received signals for object detection are evaluated. A one time-discrete signal per transmit signal is used which includes information about the frequency profile of the transmit signal and which is generated by sampling of an analog signal or by reading out of a free-running counter at predetermined points in time. These time-discrete signals are unnormalized by way of the transmit signals with regard to the position of their phase and/or their initial value.
1. A method of controlling a radar system, the method comprising:
generating a sequence of K 0 (K 0 >1) transmission-frequency-modulated transmit signals, each transmission-frequency-modulated transmit signal among the K 0 transmission-frequency-modulated transmit signals having a same nominal frequency profile, apart from a variation in frequency position;
determining a deviation of a frequency position of a transmission-frequency-modulated transmit signal among the K 0 transmission-frequency-modulated transmit signals
from a nominal profile of a frequency position of the K 0 transmission-frequency-modulated transmit signals; and
correcting frequency modulation of an oscillator of the radar system for generating the K 0 transmission-frequency-modulated transmit signals based on the deviation of the frequency position of the transmission-frequency-modulated transmit signal from the nominal profile of the frequency position of the K 0 transmission-frequency-modulated transmit signal.
2. The method according to claim 1 , wherein determining the deviation of the frequency position of the transmission-frequency-modulated transmit signal from the nominal profile of the frequency position of the K 0 transmission-frequency-modulated transmit signals comprises:
generating a low-frequency signal reduced in frequency relative to the transmission-frequency-modulated transmit signal by frequency division by a division factor and/or by mixing;
filtering and sampling the low-frequency signal;
determining a complex value after further filtering of the low-frequency signal in one or more time intervals, and
wherein the correcting the frequency modulation of the oscillator of the radar system comprises:
correcting sampled values of the one or more time intervals at least approximately by an expected phase advance, which results from the nominal frequency profile of the frequency position of the K 0 transmission-frequency-modulated transmit signals; and
accumulating phase-corrected sampled values per interval among the one or more time intervals,
wherein the one or more time intervals have at least approximately a same position over the K 0 transmission-frequency-modulated transmit signals, and
wherein the nominal profile of the frequency position of the K 0 transmission-frequency-modulated transmit signals is characterized by the complex value on the basis of a phase angle of the complex value.
3. The method according to claim 2 , wherein the filtering and sampling the low frequency signal comprises:
converting the low-frequency signal at least approximately into an analytical signal; and
applying first level Hilbert filters with a zero point at about a negative or a positive of a respective center frequency.
4. The method according to claim 3 , wherein applying the first level Hilbert filters comprises accumulating the phase-corrected sampled values over the one or more time intervals by a scalar product between the low-frequency signal and a parameter vector.
5. The method according to claim 2 , determining the deviation of the frequency position of the transmission-frequency-modulated transmit signal from the nominal profile of the frequency position of the K 0 transmission-frequency-modulated transmit signals comprises:
generating a phase difference between pairs of complex values,
wherein the complex values belong to time intervals of similar positions over the K 0 transmission-frequency-modulated transmit signals and a same time period and a same frequency profile is at least approximately present between the time intervals, and
wherein the deviation of the frequency position of the transmission-frequency-modulated transmit signal from the nominal profile of the frequency position of the K 0 transmission-frequency-modulated transmit signals is determined absolutely or relatively from the phase difference.
6. The method according to claim 5 , wherein the phase difference is formed from a same transmission-frequency-modulated transmit signal among the K 0 transmission-frequency-modulated transmit signals.
7. The method according to claim 5 , wherein the phase difference is formed from different transmission-frequency-modulated transmit signals among the K 0 transmission-frequency-modulated transmit signals.