Resolving doppler ambiguity in multi-input multi-output radar using digital multiple pulse repetition frequencies
A system and method to detect a target with a radar system of a vehicle involve transmitting two or more chirps, in turn, from two or more transmit elements. Each chirp is a continuous wave liner frequency modulated waveform. The method also includes receiving reflections generated by each of the two or more chirps from each of the two or more transmit elements at two or more receive elements, and processing the reflections based on a Doppler sampling frequency corresponding with a period of each of the two or more chirps to determine velocity of each detected target relative to the vehicle.
1. A method of detecting a target with a radar system of a vehicle, the method comprising:
transmitting two or more chirps, in turn, from two or more transmit elements, wherein each chirp is a continuous wave linear frequency modulated waveform;
receiving reflections generated by each of the two or more chirps from each of the two or more transmit elements at two or more receive elements; and
processing the reflections based on performing a Doppler fast Fourier transform (FFT) corresponding with each of the two or more chirps, each Doppler FFT using a Doppler sampling frequency corresponding with a period of each of the two or more chirps to determine velocity of each detected target relative to the vehicle, wherein the processing the reflections includes performing a range FFT to obtain a range-chirp map as a matrix of FFT results for each range bin and each chirp for every combination of the two or more transmit elements and the two or more receive elements, the processing the reflections further includes performing the Doppler FFT on the range-chirp maps to obtain a range-Doppler map as a matrix of FFT results for each range bin and each Doppler bin for every combination of the two or more transmit elements and the two or more receive elements, and the processing the reflections also includes performing two beamforming processes to determine corresponding directions of arrival of each target, each of the two beamforming processes being associated with a different range of target velocities.
2. The method according to claim 1 , wherein the processing the reflections further includes performing target detection using the range-Doppler maps.
3. The method according to claim 2 , wherein the processing the reflections further includes comparing a result of the performing the target detection with a result of performing a second Doppler FFT on the range-chirp maps, wherein the performing the second Doppler FFT involves obtaining FFT results for each range bin and each Doppler bin associated with all of the two or more transmit elements for each of the two or more receive elements.
4. The method according to claim 3 , wherein the comparing is used to resolve ambiguity in the velocity of each detected target relative to the vehicle.
5. The method according to claim 2 , wherein the processing the reflections further includes comparing a result of the performing the target detection with results of performing two second Doppler FFT processes on the range-chirp-maps, wherein the performing each of the second Doppler FFT processes involves obtaining FFT results for each range bin and each Doppler bin associated with all of the two or more transmit elements for each of the two or more receive elements.
6. The method according to claim 5 , wherein the performing the two second Doppler FFT processes is associated with two different ranges of target velocities, and the comparing is used to resolve ambiguity in the velocity of each detected target relative to the vehicle.
7. The method according to claim 1 , wherein the processing, the reflections further includes correcting the directions of arrival to remove relative phase differences among the two or more transmit elements.
8. A system to detect a target with a radar system of a vehicle, the system comprising:
two or more transmit elements configured to transmit two or more chirps, in turn, wherein each chirp is a continuous wave linear frequency modulated waveform;
two or more receive elements configured to receive reflections generated by each of the two or more chirps from each of the two or more transmit elements; and
a processor configured to process the reflections based on performing a Doppler fast Fourier transform (FFT) corresponding with each of the two or more chirps, each Doppler FFT using a Doppler sampling frequency corresponding with a period of each of the two or more chirps to determine velocity of each detected target relative to the vehicle, wherein the processor is further configured to perform a range FFT to obtain a range-chirp map as a matrix of FFT results for each range bin and each chirp for every combination of the two or more transmit elements and the two or more receive elements, the processor is further configured to perform the Doppler FFT on the range-chirp maps to obtain a range-Doppler map as a matrix of FFT results for each range bin and each Doppler bin for every combination of the two or more transmit elements and the two or more receive elements, and the processor is also configured to perform two beamforming processes to determine corresponding directions of arrival of each target, each of the two beamforming processes being associated with a different range of target velocities.
9. The system according to claim 8 , wherein the processor is further configured to perform target detection using the range-Doppler maps.
10. The system according to claim 9 , wherein the processor is further configured to obtain a comparison of a result of performing the target detection with a result of performing a second Doppler FFT on the range-chirp maps, wherein the performing the second Doppler FFT involves obtaining FFT results for each range bin and each Doppler bin associated with all of the two or more transmit elements for each of the two or more receive elements.
11. The system according to claim 10 , wherein the processor is further configured to use a result of the comparison to resolve ambiguity in the velocity of each detected target relative to the vehicle.
12. The system according to claim 9 , wherein the processor is further configured to obtain a comparison of a result of the performing the target detection with results of performing two second Doppler FFT processes on the range-chirp-maps, wherein the performing each of the second Doppler FFT processes involves obtaining FFT results for each range bin and each Doppler bin associated with all of the two or more transmit elements for each of the two or more receive elements.
13. The system according to claim 12 , wherein the performing the two second Doppler FFT processes is associated with two different ranges of target velocities, and the processor is further configured to use a result of the comparison to resolve ambiguity in the velocity of each detected target relative to the vehicle.
14. The system according to claim 8 , wherein the processor is further configured to correct the directions of arrival to remove relative phase differences among the two or more transmit elements.