Interference determination method and FMCW radar using the same
Occurrence of interference is detected using sampled amplitude data obtained by oversampling a beat signal. It is detected by comparing the absolute value (|VD|) of variation in the sampled data with a threshold value (TH). When interference occurs, a wideband signal is superposed on the beat signal, and this disturbs the signal waveform of the beat signal to drastically varies its amplitude. Therefore, occurrence of interference can be detected without fail regardless of the scheme on which a radar as the source of an interference wave is based and even when the amplitude of the interference wave is low. In addition, when low-frequency noise is superposed on the beat signal, erroneous detection of occurrence of interference can be prevented.
1. An interference determination method for FMCW radars, the method comprising the steps of:
generating a beat signal by mixing a transmission signal of a radar wave and a received signal of a reflected wave, wherein the transmission signal is frequency-modulated to vary linearly with time and the received signal is the radar wave reflected by a target;
sampling the beat signal to produce sampled data;
calculating a variation in the sampled data; and
determining occurrence of interference with some other radar when the variation exceeds a preset upper limit value.
2. The interference determination method according to claim 1 ,
wherein the beat signal contains a signal component higher than a maximum frequency determined based on a maximum relative speed or maximum distance that can be detected with the radar wave.
3. The interference determination method according to claim 2 ,
wherein the beat signal is sampled at a sampling frequency higher than the maximum frequency of the beat signal.
4. The interference determination method according to claim 3 ,
wherein the sampling frequency is higher than twice the maximum frequency of the beat signal.
5. An FMCW radar comprising:
a transmitting and receiving means that transmits a radar wave frequency-modulated to vary linearly with time, receives a reflected wave that is the radar wave reflected by a target, and mixes a transmission signal of the radar wave and a received signal of the reflected wave to generate a beat signal;
a sampling means that samples the beat signal;
a variation computing means that computes variation in sampled data obtained by the sampling means; and
a determining means that determines interference with some other radar, when the variation computed by the variation computing means exceeds a preset upper limit value,
wherein the beat signal generated by the transmitting and receiving means contains a signal component higher than a maximum frequency of the beat signal determined based on a maximum relative speed or maximum distance that can be detected with the radar wave of the transmitting and receiving means.
6. The FMCW radar according to claim 5 ,
wherein the sampling means samples the beat signal at a sampling frequency higher than the maximum frequency of the beat signal.
7. The FMCW radar according to claim 6 ,
wherein the sampling frequency is higher than twice the maximum frequency of the beat signal.