System and method for automotive radar mutual interference reduction - Patents.com

Abstract

A radar system is provided for tracking an object in a scene by transmitting a frequency modulated continuous wave (FMCW), the radar system is configured to collect radar measurements of the scene sampled in a time-frequency domain within an intermediate frequency (IF) bandwidth, reflections of the transmitted FMCW are shifted to the intermediate frequency bandwidth by mixing with a copy of the FMCW, a frequency dimension of the time-frequency domain is quantized into a number of frequency bins forming a frequency bandwidth, and a time dimension of the time-frequency domain is quantized into a number of time points forming a time interval corresponding to a PRI, the radar system is further configured to count a number of amplitude peaks of the radar measurements for each frequency bin at different time points, identify a number of frequency bins for which the count of the number of peaks exceeds a predetermined threshold, and determine at least a distance to the object based on a frequency analysis of the radar measurements.

Description

[Technical field]

[0001] The present disclosure relates generally to radar systems, and more particularly to radar systems and methods for reducing mutual interference. [Background technology]

[0002] Intelligent vehicles are equipped with more and more radar sensors for panoramic and all-weather awareness. New signaling schemes such as phase modulated continuous wave (PMCW) and orthogonal frequency-division multiplexing (OFDM) have been more widely used than the traditional frequency modulated continuous wave (FMCW) scheme. However, PMCW and OFDM operate at very high sampling rates, which increases the requirements for transceiver hardware in radar systems. Nevertheless, FMCW remains the main choice for realizing full 4D (range-velocity-azimuth-elevation) automotive radar with low angular resolution at mass production level.

[0003] However, for FMCW-based automotive radars operating in the same regulated frequency band (e.g., 77-81 GHz), mutual interference of radar signals must be addressed. Otherwise, the mutual interference will raise the noise floor, jam the receiver antenna, trigger false alarms, and cause missed detections. Currently, MIM is widely implemented using fast MIM, which is performed using techniques such as interference zeroing, adaptive noise cancellers, and sparse sampling.

[0004] Current approaches for high-speed MIM exploit the linear chirp characteristic of interference and set the detected interference to zero in the short-time Fourier transform (STFT) domain (also called "STFT zeroing"). However, errors in the interference detection and zeroing steps tend to propagate to the high-speed time domain, resulting in strong residuals. This effect is exacerbated when a low-resolution STFT is used, because current approaches focus on nulling the mutual interference signals.

[0005] Therefore, what is needed is a system capable of performing high speed MIM that minimizes residuals by directly focusing on high speed target signals. Summary of the Invention

[0006] It is therefore an object of some embodiments to provide a radar system and method for directly acquiring high speed target signals.

[0007] Thus, the radar system is configured to transmit an FMCW towards an object (also called a "target") in a scene and receive the FMCW reflected from the object, and the radar system is configured to detect the object in the scene based on the reflected FMCW. In some embodiments, the radar system is configured to track the object in the scene. Thus, the same detection may be performed for multiple objects in the scene.

[0008] To that end, the radar system is configured to generate a fast-time-frequency (fTF) representation of the scene and directly recover the fast-time target signals through a direct fTF mode retrieval (fTFMR), where the fTF representation of the scene includes target ridges corresponding to the objects and interference ridges corresponding to one or more interference signals.

[0009] It is therefore also an objective of certain embodiments of the present disclosure to enable high-precision fTFMR that identifies weaker target ridges among very strong interference ridges that extend linearly across the fTF representation, and maps the fTF representation containing the identified targets to high-speed time samples.

[0010] Therefore, high-resolution fTF representation, robust ridge detection using successive pulses, and direct fTFMR are performed consecutively.

[0011] Some embodiments are based on the realization that a high-resolution fTF representation allows a higher degree of separation between target and interference signals in the fTF representation. A high-resolution fTF representation is particularly important when the interference beat frequency crosses the target signal beat frequency. Therefore, a Fourier synchrosqueezing transform (FSST) based on frequency reassignment is used, which allows a high-resolution fTF representation.

[0012] In some embodiments, a ridge detection mechanism is used to detect target ridges from the fTF representation of the scene. The proposed ridge detection exploits the fact that target signatures across the fTF domain are consistent across multiple pulses of FMCW, but interference signatures can vary due to incoherence between the interfering radar and the victim radar. The result is robust ridge detection of disappointing two-way attenuated target signals in one-way attenuated interference.

[0013] Some embodiments are based on the realization that fTFMR is guaranteed to converge to a fast time-spaced target signal with sufficient separation between the target signal and interference in the fTF domain. Since FSST places high importance on the sinusoidal target signal, fTFMR can directly recover the target signal in the time domain by integrating the fTR representation over the target-only region and simultaneously removing interference and noise.

[0014] Accordingly, one embodiment of the present disclosure transmits a frequency modulated continuous wave (FMCW) signal within the radio frequency (RF) band as a series of pulse repetition intervals (PRI). a frequency dimension of the time-frequency domain is quantized into a plurality of frequency bins forming a frequency bandwidth; a time dimension of the time-frequency domain is quantized into a plurality of time points forming a time interval corresponding to a PRI; and the instructions, when executed by the processor, cause the radar system to: count a number of amplitude peaks of the radar measurements for each frequency bin at different time points within each PRI; identify a number of frequency bins for which the count of the number of peaks exceeds a predetermined threshold; and determine a distance to the object based on at least a frequency analysis of the radar measurements in the identified frequency bins, while ignoring radar measurements in most other frequency bins within the frequency bandwidth.

[0015] Accordingly, one embodiment of the present disclosure provides a method for tracking an object in a scene by transmitting a frequency modulated continuous wave (FMCW) in a radio frequency (RF) band over a series of pulse repetition intervals (PRIs), the method including collecting radar measurements of the scene sampled in a time-frequency domain within an intermediate frequency (IF) bandwidth, reflections of the transmitted FMCW being shifted into the intermediate frequency bandwidth by mixing with copies of the FMCW, a frequency dimension of the time-frequency domain being quantized into a number of frequency bins forming a frequency bandwidth, and a time dimension of the time-frequency domain being quantized into a number of time points forming a time interval corresponding to the PRI, the method further including counting a number of amplitude peaks of the radar measurements for each frequency bin at different time points within each PRI, identifying a number of frequency bins for which the count of the number of peaks exceeds a predetermined threshold, and determining a distance to the object based at least on a frequency analysis of the radar measurements in the identified frequency bins, while ignoring radar measurements in most other frequency bins within the frequency bandwidth. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 illustrates an FMCW automotive radar system configured to track objects using FMCW, according to an exemplary embodiment of the present disclosure. [Diagram 2] FIG. 1 illustrates a block diagram of a radar system for tracking objects in accordance with an illustrative embodiment. [Figure 3A] FIG. 2 illustrates a diagram of time-frequency domain FMCW radar interference across multiple pulses in an RF band according to an exemplary embodiment. [Figure 3B] FIG. 2 illustrates a diagram of time-frequency domain FMCW radar interference across multiple pulses in the IF band according to an exemplary embodiment. [Figure 4A] FIG. 13 illustrates ridge detection in an fTF representation of a pulse containing only a target signal according to an exemplary embodiment. [Figure 4B]FIG. 13 illustrates a histogram of the number of amplitude peaks within frequency bins of an fTF representation, according to an exemplary embodiment. [Figure 5A] FIG. 1 illustrates ridge detection in an fTF representation of a pulse containing one target signal and two interfering signals according to an exemplary embodiment. [Figure 5B] FIG. 13 illustrates a histogram of the number of amplitude peaks within frequency bins of an fTF representation, according to an exemplary embodiment. [Figure 6] 1 illustrates a flow diagram of a multi-pulse ridge detection method according to an exemplary embodiment. [Figure 7] 5A-5C illustrate steps of a method for tracking an object according to an exemplary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] For purposes of explanation, numerous specific details are set forth in the following to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without these specific details. In other instances, the apparatus and methods are shown in block diagram form solely to avoid obscuring the present disclosure.

[0018] As used in the specification and claims, the terms "for example," "for instance," and "such as," as well as the verbs "comprising," "having," "including," and other forms of these verbs, when used in conjunction with a list of one or more components or other items, should each be construed as open-ended, meaning that the list should not be considered to exclude further components or items. The term "based on" means based at least in part on. Furthermore, it should be understood that the style and terminology used herein are for purposes of illustration and should not be considered limiting. Any headings used herein are for convenience only and should not be considered to have any legal or limiting effect.

[0019] 1 illustrates an FMCW automotive radar system 101 configured to use FMCW to track an object 103, according to an exemplary embodiment of the present disclosure. The FMCW automotive radar system (also referred to as a "radar system") 101 includes a transceiver 101a configured to transmit 105 an FMCW in a radio frequency (RF) band over a series of pulse repetition intervals (PRI) to detect the object 103, which may be located at a distance d from the radar system 101. The transmitted FMCW 105 is reflected by the object 103, and the reflected FMCW 107 is received by the transceiver 101a. The reflected FMCW 107 is analyzed by the radar system 101 to track the object 103 within the scene.

[0020] In some embodiments, the radar system 101 may include a transmitter for transmitting the FMCW 105 and a receiver for receiving the reflected FMCW 107. The radar system 101 is configured to sample radar measurements of a scene in a time-frequency domain and collect sample radar measurements of the scene within an intermediate frequency (IF) bandwidth. The radar system 101 quantizes the frequency dimension of the time-frequency domain into a number of frequency bins that form a frequency bandwidth. Similarly, the radar system 101 quantizes the time dimension of the time-frequency domain into a number of time instants that form a time interval corresponding to a PRI.

[0021] Based on the quantized time and frequency domains, the radar system 101 counts a number of amplitude peaks of the radar measurements for each frequency bin at different times, with each amplitude peak among the number of amplitude peaks corresponding to a maximum energy in each frequency bin at a particular time. The radar system 101 is further configured to identify a number of frequency bins for which the count of the number of peaks exceeds a predetermined threshold, and is further configured to determine at least a range, a velocity, or a combination thereof to the object 103 based on a frequency analysis of the radar measurements in the identified frequency bins, while ignoring radar measurements in most other frequency bins within the frequency bandwidth.

[0022] The radar system 101 may be capable of making the same measurement for multiple objects in a scene by using a different FMCW for each of the multiple objects and performing the corresponding detection described above for each object.

[0023] FIG. 2 illustrates a block diagram 200 of a radar system 101 for tracking an object 103, according to an exemplary embodiment. The radar system 101 includes a processor 201 configured to execute stored instructions. The radar system 101 further includes a memory 203 that stores instructions executable by the processor 201. The processor 201 may be a single-core processor, a multi-core processor, a computing cluster, or any number of other configurations. The memory 203 may include a random access memory (RAM), a read-only memory (ROM), a flash memory, or any other suitable memory system. The processor 201 is connected to one or more input and output devices via a bus 205. Additionally, the radar system 101 includes an FMCW generator 207, which is configured to generate an FMCW over a range of PRIs. The radar system 101 further includes a transmitter 209 configured to transmit the FMCW 105 over a range of PRIs.

[0024] The radar system 101 includes a receiver 211 configured to receive an input signal within an RF bandwidth. The input signal includes a delayed FMCW 107 reflected from an object 103 and one or more interfering signals. The input signal is provided to a mixer 213 configured to mix the input signal with a copy of the FMCW to shift the input signal to an IF bandwidth, such that a series of peak amplitudes at different times of a target beat signal formed by mixing the copy of the FMCW with a coherent input signal forms a ridge in a frequency bin, and a series of peak amplitudes at different times of an interfering beat signal formed by mixing the copy of the FMCW with an incoherent input signal intersects a number of frequency bins at an angle, and an output of the mixer 213 includes a combination of the target beat signal and one or more interfering beat signals. The mixer 213 may include a local oscillator, which is used to convert the RF band FMCW signal to the IF band. The combination of the target beat signal and one or more interference beat signals needs to be sampled at a high rate to obtain an fTF representation of the scene containing the object 103.

[0025] To that end, the processor 201 is configured to use an analog-to-digital converter (ADC) 215. The ADC 215 is configured to generate radar measurements providing an fTF representation of the scene by sampling the output of the mixer at a high time rate. The processor 201 is further configured to generate a high-resolution fTF representation of the scene based on the fTF representation obtained from the ADC 215 by using a Fourier synchrosqueezed transform (FSST) based on frequency reassignment. The high-resolution fTF representation of the scene includes a target ridge corresponding to the object 103 and an interference ridge corresponding to one or more interference signals. The interference ridge is stronger than the target ridge.

[0026] Some embodiments are based on the recognition that a high-resolution fTF representation allows for a higher degree of separation between target and interference ridges. To detect target ridges, the radar system 101 includes a ridge detector 217. The ridge detector 217 is configured to sequentially detect the strongest signal ridges in the fTF representation. The radar system 101 stores a count of the number of peaks corresponding to detection of a ridge signal in each of the pulses of the FMCW in each PRI.

[0027] Additionally, the radar system 101 may include an output interface 219. In some embodiments, the radar system 101 is further configured to provide a set of control forces to a controller 221 via the output interface 219, the control forces being generated based on the detection of the object 103. The controller 221 may be configured to control a load, such as an autonomous vehicle in which the radar system 101 is mounted, based on the set of control forces. Mathematical Implementation Target and Interferer Signal Models

[0028] FIG. 3A illustrates time-frequency domain FMCW radar interference across multiple pulses in an RF band 300a, according to an exemplary embodiment. For ease of illustration, only two FMCW pulses are illustrated in FIG. 3A. FIG. 3A illustrates two pulses corresponding to a reference signal 301 and two corresponding pulses of a backscattered target signal 303. The reference signal 301 corresponds to the FMCW 105 transmitted to detect an object 103, and the backscattered target signal 303 corresponds to the reflected FMCW 107. As illustrated in FIG. 3A, the FMCW is affected by two interfering pulses, interference 1 305 and interference 2 307.

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[0038] 4A illustrates ridge detection in an fTF representation 400a of a pulse containing only a target signal, according to an exemplary embodiment. The frequency dimension of the time-frequency domain in the fTF representation 400a is quantized into a number of frequency bins (e.g., from −15 MHz to 15 MHz, with each frequency bin having a size of 5 MHz) forming a frequency bandwidth, and the time dimension of the time-frequency domain in the fTF representation 400a is quantized into a number of time points forming a time interval corresponding to a PRI (e.g., from 0 μs to 30 μs, with each time interval or time bin having a size of 5 μs).

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[0041] FIG. 5A illustrates ridge detection in an fTF representation 500a of a pulse containing one target signal and two interfering signals according to an exemplary embodiment. A maximum energy 501 is detected according to the plot representation 500a. The time-frequency dimensions of the fTF representation 500a are quantized similarly to the time-frequency dimensions of the fTF representation 400a. As shown in FIG. 5A, the target ridge 503 remains the same across multiple pulses in the CPI, but the FMCW interference ridge (corresponding to the maximum energy detection 501) may vary across multiple pulses due to non-coherence between the interfering radar and the victim radar.

[0042] Figure 5B illustrates a histogram 500b of the number of amplitude peaks in frequency bins of the fTF representation 500a, according to an exemplary embodiment. Figure 5B is described below in conjunction with Figure 5A. Because the target ridges remain the same across multiple pulses in the CPI, but the FMCW interference ridges vary across multiple pulses, the number of amplitude peaks (or ridges) 505 accumulated at the beat frequency of the target signal, i.e., 5 MHz, is still much higher than the number of amplitude ridges at any other frequency.

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[0052] 7 illustrates steps of a method 700 for tracking an object, according to an exemplary embodiment. The method 700 is performed by the radar system 101. In step 701, an FMCW in an RF band is transmitted over a series of pulse repetition intervals (PRI) to detect the object 103, which may be located at a distance d from the radar system 101. The transmitted FMCW 105 is reflected by the object 103, and the reflected FMCW 107 is received by the radar system 101 and analyzed by the radar system 101 to track the object 103 in the scene.

[0053] In step 703, radar measurements of a sampled scene in the time-frequency domain within the IF bandwidth where reflections of the transmitted FMCW are shifted by mixing with copies of the FMCW can be collected. The frequency dimension of the time-frequency domain is quantized into a number of frequency bins that form a frequency bandwidth. Similarly, the time dimension of the time-frequency domain is quantized into a number of time instants that form a time interval corresponding to a PRI.

[0054] In step 705, the number of amplitude peaks of the radar measurements for each frequency bin at different times may be counted, with each peak in this number of amplitude peaks corresponding to the maximum energy in each frequency bin at a particular time, and in step 707, the number of frequency bins for which the number of peaks exceeds a predetermined threshold is identified.

[0055] In step 707, the range to at least the object 103 is determined based on a frequency analysis of radar measurements in the identified frequency bin, while ignoring radar measurements in most other frequency bins within the frequency bandwidth. Embodiment

[0056] The above description provides only exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the above description of exemplary embodiments provides one of ordinary skill in the art with an enabling description for implementing one or more exemplary embodiments. What is intended is various changes that may be made in the function and arrangement of elements without departing from the spirit and scope of the disclosed subject matter, as set forth in the appended claims.

[0057] Specific details are provided in the above description to provide a thorough understanding of the embodiments. However, those skilled in the art will appreciate that the embodiments may be practiced without these specific details. For example, systems, processes, and other elements in the disclosed subject matter may be shown as components in block diagram form in order to avoid obscuring the embodiments in unnecessary detail. In other instances, well-known processes, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. Additionally, like reference numbers and names in the various drawings refer to like elements.

[0058] Also, the individual embodiments may be described as a process that is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe operations as a sequential process, many of the operations may be performed in parallel or simultaneously. Moreover, the order of operations may be rearranged. A process may be terminated when its operations are completed, but may have other steps not discussed or included in the diagram. Moreover, not all operations in any process specifically described may occur in all embodiments. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, or the like. When a process corresponds to a function, the end of the function may correspond to a return of the function to a calling function or to the main function.

[0059] Furthermore, embodiments of the disclosed subject matter may be implemented, at least in part, either manually or automatically. The manual or automated implementation may be performed or at least assisted through the use of machines, hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, program code or code segments to perform the necessary tasks may be stored on a machine-readable medium. A processor may perform the necessary tasks.

[0060] The various methods or processes outlined herein may be coded as software executable on one or more processors employing any one of a variety of operating systems or platforms. In addition, such software may be written using any of a number of suitable programming languages ​​and / or programming or scripting tools, and may be compiled as executable machine language code or intermediate code that runs on a framework or virtual machine. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

[0061] The embodiments of the present disclosure may be implemented as a method, an example of which is provided. The order of operations performed as part of the method may be determined in any suitable manner. Thus, the embodiments may be configured to perform operations in an order different from that illustrated, which may include performing some operations simultaneously, even though in the illustrated embodiments they are shown as a series of operations. Although the present disclosure has been described with reference to certain preferred embodiments, it should be understood that various other adaptations and modifications may be made within the spirit and scope of the present disclosure. It is therefore the object of the appended claims to cover all such variations and modifications that fall within the true spirit and scope of the present disclosure.

Claims

1. 1. A radar system for tracking objects in a scene by transmitting a frequency modulated continuous wave (FMCW) signal in a radio frequency (RF) band over a series of pulse repetition intervals (PRIs), the radar system comprising: a processor and a memory having instructions stored thereon, the instructions, when executed by the processor, causing the radar system to: The instructions, when executed by the processor, further cause the radar system to: collect radar measurements of the scene sampled in a time-frequency domain within an intermediate frequency (IF) bandwidth, where reflections of the transmitted FMCW are shifted into the intermediate frequency bandwidth by mixing with copies of the FMCW, a frequency dimension of the time-frequency domain is quantized into a number of frequency bins forming the frequency bandwidth, and a time dimension of the time-frequency domain is quantized into a number of time points forming a time interval corresponding to the PRI; and counting the number of amplitude peaks of the radar measurements for each frequency bin at different times within each PRI; identifying a number of frequency bins in which the peak count exceeds a predetermined threshold; A radar system that performs at least the following steps: determine a distance to the object based on a frequency analysis of the radar measurements within the identified frequency bin, while ignoring radar measurements in most other frequency bins within the frequency bandwidth.

2. 2. The radar system of claim 1, wherein each amplitude peak of the number of amplitude peaks corresponds to a maximum energy within each frequency bin at a particular time.

3. The radar system includes: a transmitter configured to transmit the FMCW over the range of PRIs; a receiver configured to receive an input signal within an RF bandwidth, the input signal including a delayed FMCW reflected from the object and one or more interference signals; and a mixer configured to mix the input signal with a copy of the FMCW to shift the input signal to the IF bandwidth, wherein a series of peak amplitudes at different times of a target beat signal formed by mixing the copy of the FMCW with a coherent input signal forms a ridge in a frequency bin, and a series of peak amplitudes at different times of an interference beat signal formed by mixing the copy of the FMCW with an incoherent input signal intersects a number of frequency bins at an angle, and an output of the mixer includes a combination of the target beat signal and one or more interference beat signals; and 2. The radar system of claim 1, further comprising an analog-to-digital converter (ADC) configured to sample the output of the mixer at a fast time to generate radar measurements that provide a fast time-frequency (fTF) representation across each PRI of the scene.

4. The radar system of claim 3 , wherein the processor is further configured to convert high speed time samples in each PRI to the high speed time-frequency representation.

5. 4. The radar system of claim 3, wherein the processor is further configured to identify, for a plurality of objects, a number of frequency bins in which the count of the number of peaks exceeds the predetermined threshold.

6. The processor further comprises: recovering interference-reduced high speed time samples from the high speed time-frequency representation restricted to each of the identified frequency bins across each PRI; The radar system of claim 3 configured to group the interference-reduced high speed time samples from the same frequency bin across all PRIs.

7. The radar system of claim 6 , wherein the processor is further configured to process the grouped interference-reduced samples to identify a range, a velocity, or a combination thereof, of the object.

8. The processor further comprises: obtaining the fTF representation of the scene from the ADC; 4. The radar system of claim 3, configured to generate a high-resolution fTF representation of the scene by using a Fourier synchrosqueezed transform (FSST) based on frequency reassignment, the high-resolution fTF representation of the scene including a target ridge corresponding to the object and an interference ridge corresponding to the one or more interference signals, the interference ridge being stronger than the target ridge.

9. 10. The radar system of claim 8, wherein the processor is further configured to detect the weaker target ridge from the stronger interference ridge in each pulse of the plurality of pulses of the FMCW using a multi-pulse ridge detection mechanism.

10. 10. The radar system of claim 9, wherein the multipulse ridge detection mechanism is implemented using a maximum energy ridge detector configured to sequentially detect strongest signal ridges using a penalized forward-backward greedy algorithm.

11. 10. The radar system of claim 9, wherein the processor is configured to determine that a ridge detected by the multipulse ridge detection corresponds to a target ridge when the ridge is constant over multiple pulses of the FMCW within a coherent processing interval (CPI), the CPI being indicative of a group of multiple pulses of the FMCW having the same pulse repetition frequency (PRF) and frequency.

12. 12. The radar system of claim 11, wherein the processor is further configured to recover a fast time target signal corresponding to the object from the high-resolution fTF representation and the detected target ridge through direct fTF mode search (fTFMR).

13. 2. The radar system of claim 1, wherein the processor is configured to maintain an identifier of a current frequency bin with a highest peak number count across multiple PRIs and to switch the identifier to a next frequency bin when the peak number count in the next frequency bin within a predetermined number of time intervals is greater than the peak number count in the current frequency bin.

14. 14. The radar system of claim 13, wherein the processor is configured to switch the identifier when a difference between a count of the number of peaks in the next frequency bin and a count of the number of peaks in the current frequency bin is greater than a threshold.

15. 1. A method for tracking an object in a scene by transmitting a frequency modulated continuous wave (FMCW) signal in a radio frequency (RF) band over a series of pulse repetition intervals (PRI), the method comprising: collecting radar measurements of the scene sampled in a time-frequency domain within an intermediate frequency (IF) bandwidth, where reflections of the transmitted FMCW are shifted into the intermediate frequency bandwidth by mixing with copies of the FMCW, a frequency dimension of the time-frequency domain is quantized into a number of frequency bins forming the frequency bandwidth, and a time dimension of the time-frequency domain is quantized into a number of time points forming a time interval corresponding to the PRI, the method further comprising: counting the number of amplitude peaks of the radar measurements for each frequency bin at different times within each PRI; identifying a number of frequency bins in which the peak count exceeds a predetermined threshold; determining a distance to the object based on at least a frequency analysis of the radar measurements in the identified frequency bin, while ignoring radar measurements in most other frequency bins within the frequency bandwidth.

16. The method of claim 15 , wherein each amplitude peak of the number of amplitude peaks corresponds to a maximum energy within each frequency bin at a particular time.

17. transmitting the FMCW over the range of PRIs using a transmitter; and receiving, using a receiver, an input signal within an RF bandwidth, the input signal including a delayed FMCW reflected from the object and one or more interference signals, the method further comprising: using a mixer to mix the input signal with a copy of the FMCW to shift the input signal to the IF bandwidth, a series of peak amplitudes at different times of a target beat signal formed by mixing the copy of the FMCW with a coherent input signal forms a ridge in a frequency bin, a series of peak amplitudes at different times of an interference beat signal formed by mixing the copy of the FMCW with an incoherent input signal intersects a plurality of frequency bins at an angle, an output of the mixer includes a combination of the target beat signal and one or more interference beat signals, the method further comprising:

16. The method of claim 15, comprising using an analog-to-digital converter (ADC) to sample the output of the mixer at a fast time to generate radar measurements that provide a fast time-frequency (fTF) representation across each PRI of the scene.

18. obtaining the fTF representation of the scene from the ADC; and 20. The method of claim 17, further comprising: generating a high-resolution fTF representation of the scene by using a Fourier synchrosqueezed transform (FSST) based on frequency reassignment, wherein the high-resolution fTF representation of the scene includes a target ridge corresponding to the object and an interference ridge corresponding to the one or more interference signals, the interference ridge being stronger than the target ridge.

19. 20. The method of claim 18, further comprising detecting the weaker target ridge from the stronger interference ridge in each pulse of the plurality of pulses of the FMCW using a multi-pulse ridge detection mechanism.

20. 20. The method of claim 19, wherein the multi-pulse ridge detection mechanism is implemented using a maximum energy ridge detector that uses a penalized forward-backward greedy algorithm to sequentially detect the strongest signal ridges.

21. 20. The method of claim 19, further comprising determining that a ridge detected by the multi-pulse ridge detection corresponds to a target ridge when the ridge is constant across multiple pulses of the FMCW within a coherent processing interval (CPI), the CPI being indicative of a group of multiple pulses of the FMCW having the same pulse repetition frequency (PRF) and frequency.

22. 22. The method of claim 21, further comprising recovering a high-speed time target signal corresponding to the object from the high-resolution fTF representation and the detected target ridges through direct fTF mode retrieval (fTFMR).

23. 16. The method of claim 15, further comprising: maintaining an identifier of a current frequency bin with the highest peak number count across a plurality of PRIs; and switching the identifier to a next frequency bin when the peak number count in the next frequency bin within a predetermined number of time intervals is greater than the peak number count in the current frequency bin.

24. 24. The method of claim 23, further comprising: switching the identifier when a difference between a count of the number of peaks in the next frequency bin and a count of the number of peaks in the current frequency bin is greater than a threshold.

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