TDM FMCW radar apparatus and signal processing method of apparatus
A method and structure for solving a Doppler ambiguity problem in a time-division-multiplexed (TDM) frequency modulated continuous wave (FMCW) radar apparatus are proposed. In a frame of a waveform signal transmitted by one transmitting antenna in the TDM FMCW radar apparatus, at least three consecutive chirps having different periods are included for each chirp loop. A Doppler frequency may be determined from phase difference values between the three consecutive chirps measured from an FMCW radar signal received at a receiving antenna. The at least three consecutive chirps having different periods are configured to differ in at least one of an idle time between the chirps or a ramp time of the chirp.
1. A signal processing method of a time-division-multiplexed (TDM) frequency modulated continuous wave (FMCW) radar apparatus, the method comprising:
a wireless transmission operation of transmitting an FMCW radar waveform signal configured such that at least three consecutive chirps included in a chirp loop of a radar signal have different periods;
a wireless reception operation of demodulating a baseband FMCW radar signal from an FMCW radar waveform signal reflected by a target, sampling a difference signal between the baseband FMCW radar signal and the transmitted signal, transforming the difference signal into a digital signal, and outputting the digital signal;
a spectrum analysis operation of determining and outputting a beat frequency and a Doppler frequency from the signal output in the wireless reception operation; and
a Doppler frequency determination operation of measuring phase differences between the at least three consecutive chirps having different periods, which are received in the wireless reception operation, and determining and outputting a true Doppler frequency from the measured phase differences and the Doppler frequency output in the spectrum analysis operation,
wherein the at least three consecutive chirps have a same frequency,
wherein both a ramp time and an idle time of a first chirp are same with a ramp time and an idle time of a last chirp, and
wherein both a ramp time and an idle time of an intermediate chirp are different from the ramp time and the idle time of both the first chirp and the last chirp.
2. The method of claim 1 , wherein the FMCW radar waveform signal transmitted in the wireless transmission operation is configured such that the at least three consecutive chirps differ in at least one of an idle time between the chirps and a ramp time of the chirp.
3. The method of claim 2 , wherein the at least three consecutive chirps are configured such that a sum of an inter-chirp difference value of the idle time and an inter-chirp difference value of the ramp time is limited by a maximum moving velocity of the target.
4. The method of claim 1 , wherein the spectrum analysis operation includes:
a range fast Fourier transform (FFT) processing operation of transforming the digital signal output in the wireless reception operation into a frequency-domain signal in units of chirps and outputting the frequency-domain signal;
a Doppler FFT processing operation of transforming the same frequency components of the frequency-domain signal output in the range FFT processing operation into a frequency-domain signal again and outputting the frequency-domain signal;
a range estimation operation of determining and outputting a beat frequency from the signal output in the range FFT processing operation; and
a Doppler estimation operation of determining and outputting a Doppler frequency from the signal output in the Doppler FFT processing operation.
5. The method of claim 1 , wherein in the Doppler frequency determination operation,
from at least three consecutive chirp signals output in the wireless reception operation, the phase differences between the chirps are measured, and the Doppler frequency at which theoretically calculated phase difference values have values most similar to the measured phase difference values is determined and output as a true Doppler frequency.
6. The method of claim 1 , wherein the Doppler frequency determination operation includes:
a phase difference measurement operation of measuring phase differences between at least three consecutive chirp signals which have different periods and are included in the chirp loop;
a search range calculation operation of determining a search range of Doppler frequencies of an aliased spectrum by a ratio of a maximum Doppler frequency of the target to be detected and a maximum Doppler frequency obtained from a range-Doppler spectrum; and
a Doppler frequency search operation of determining and outputting a Doppler frequency at which a theoretically calculated phase difference value is most similar to a measured phase difference value, among the Doppler frequencies of the aliased spectrum.
7. A time-division-multiplexed (TDM) frequency modulated continuous wave (FMCW) radar apparatus, comprising:
a wireless transmitter configured to transmit an FMCW radar waveform signal configured such that at least three consecutive chirps included in a chirp loop of a radar signal have different periods;
a wireless receiver configured to demodulate a baseband FMCW radar signal from an FMCW radar waveform signal reflected by a target, sample a difference signal between the baseband FMCW radar signal and the transmitted signal, and transform the difference signal into a digital signal and output the digital signal;
a spectrum analyzer configured to determine and output a beat frequency and a Doppler frequency from the signal output from the wireless receiver; and
a Doppler frequency determiner configured to measure phase differences between the at least three consecutive chirps having different periods, which are received at the wireless receiver, and determine and output a true Doppler frequency from the measured phase differences and the Doppler frequency output from the spectrum analyzer,
wherein the at least three consecutive chirps have a same frequency,
wherein both a ramp time and an idle time of a first chirp are same with a ramp time and an idle time of a last chirp, and
wherein both a ramp time and an idle time of an intermediate chirp are different from the ramp time and the idle time of both the first chirp and the last chirp.
8. The TDM FMCW radar apparatus of claim 7 , wherein the FMCW radar waveform signal transmitted from the wireless transmitter is configured such that the at least three consecutive chirps differ in at least one of an idle time between the chirps and a ramp time of the chirp.
9. The TDM FMCW radar apparatus of claim 8 , wherein the at least three consecutive chirps are configured such that a sum of an inter-chirp difference value of the idle time and an inter-chirp difference value of the ramp time is limited by a maximum moving velocity of the target.
10. The TDM FMCW radar apparatus of claim 7 , wherein the spectrum analyzer includes:
a range fast Fourier transform (FFT) processor configured to transform the digital signal output from the wireless receiver into a frequency-domain signal in units of chirps and output the frequency-domain signal;
a Doppler FFT processor configured to transform the same frequency components of the frequency-domain signal output from the range FFT processor into a frequency-domain signal again and output the frequency-domain signal;
a range estimator configured to determine and output a beat frequency from the signal output from the range FFT processor; and
a Doppler estimator configured to determine and output a Doppler frequency from the signal output from the Doppler FFT processor.
11. The TDM FMCW radar apparatus of claim 7 , wherein the Doppler frequency determiner, from at least three consecutive chirp signals output from the wireless receiver, measures the phase differences between the chirps, and determines and outputs the Doppler frequency at which theoretically calculated phase difference values have values most similar to the measured phase difference values as a true Doppler frequency.
12. The TDM FMCW radar apparatus of claim 7 , wherein the Doppler frequency determiner includes:
a phase difference measurer configured to measure phase differences between at least three consecutive chirp signals which have different periods and are included in the chirp loop;
a search range calculator configured to determine a search range of Doppler frequencies of an aliased spectrum by a ratio of a maximum Doppler frequency of the target to be detected and a maximum Doppler frequency obtained from a range-Doppler spectrum; and
a Doppler frequency searcher configured to determine and output a Doppler frequency at which a theoretically calculated phase difference value is most similar to a measured phase difference value, among the Doppler frequencies of the aliased spectrum.