Multi-target peak association technique in coherent LIDAR systems

Abstract

The method includes transmitting multiple light beams, each having a different frequency chirp, toward multiple targets within a field of view of a light detection and ranging (LIDAR) system and receiving multiple return signals, each having a different frequency chirp, from the targets. The method then generates a frequency-domain baseband signal based on the return signals, where the baseband signal includes a first set of peaks associated with respective up-chirp frequencies and a second set of peaks associated with respective down-chirp frequencies. The method then generates one or more matching indices associated with each peak in the first set of peaks and each peak in the second set of peaks. The indices are then used to pair each peak in the first set of peaks with each peak in the second set of peaks, and identify the multiple targets based on the pairing.

Description

[Technical field]

[0001] This application claims priority under 35 U.S.C. §119(e) to U.S. patent application Ser. No. 17 / 339,763, filed June 4, 2021, and U.S. Provisional Patent Application Ser. No. 63 / 104,372, filed October 22, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates generally to Light Detection and Ranging (LIDAR) systems, and more particularly to techniques for correlating peaks in multiple target situations in coherent LIDAR systems. [Background technology]

[0003] Frequency-modulated continuous wave (FMCW) LIDAR systems use a tunable infrared laser for frequency-chirp illumination of targets and a coherent receiver to detect the backscattered or reflected light from the targets, which is combined with a local copy of the transmitted signal at the coherent receiver. Mixing the local copy with the return signal delayed by the round-trip time to the target produces a signal at the receiver with a frequency proportional to the distance to each target in the system's field of view. In such LIDAR systems, frequency up- and down-sweeps are sometimes used to detect the range and velocity of detected targets, but problems arise in the presence of multiple targets, where it becomes difficult to accurately associate each corresponding peak with each target. Summary of the Invention [Means for solving the problem]

[0004] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, we discuss aspects of the present invention, namely, a LIDAR system and method for accurately correlating peaks in multiple target situations.

[0005] A method according to one aspect of the present invention includes the following steps a to e. a. Transmitting multiple light beams containing different frequency chirps toward multiple targets within the field of view of a Light Detection and Ranging (LIDAR) system; b. receiving a plurality of return signals based on reflections from the plurality of targets, the plurality of return signals including different frequency chirps; c. generating a frequency domain baseband signal based on the plurality of return signals, the baseband signal including first peaks associated with respective up-chirp frequencies and second peaks associated with respective down-chirp frequencies; d. generating, by a processor, one or more evaluation indices for matching (hereinafter referred to as indices) associated with each peak of the first group of peaks and each peak of the second group of peaks; and e. pairing each peak of the first group of peaks with each peak of the second group of peaks using the one or more indices, and identifying the plurality of targets by the processor based on the pairings.

[0006] In the method of one embodiment of the present invention, the one or more indices include peak shapes similarly calculated between each peak of the first peak group and each peak of the second peak group. The peak shapes calculated in the same manner include the output of a correlator when each peak of the first peak group is compared with each peak of the second peak group. Additionally, the one or more metrics further include at least one of peak intensity, peak width, ego velocity (self-motion velocity), and raw peak frequency.

[0007] The method according to one embodiment of the present invention further comprises the following steps a and b. a. combining the one or more indices for the first group of peaks and the second group of peaks to generate a composite indices; and b. identifying the plurality of targets based on the composite index for the first group of peaks and the second group of peaks; In one embodiment of the present invention, the procedure for combining the one or more indices to generate the composite index comprises the following steps a and b. a. weighting each of the one or more indices to generate a weighted index; and b. adding said one or more weighted indicators to generate a weighted sum of said one or more indicators.

[0008] In a method according to one aspect of the present invention, the procedure of identifying the plurality of targets comprises the following steps. running an optimization algorithm to minimize a cost function associated with pairing each peak in the first set of peaks with each peak in the second set of peaks, where the cost function corresponds to a sum of the one or more metrics for pairing each peak in the first set of peaks with each peak in the second set of peaks;

[0009] The method according to one embodiment of the present invention further comprises the following steps a and b. a. identifying neighboring data points for each peak of the first set of peaks and each peak of the second set of peaks; and b. further identifying the plurality of targets based on the proximate data points for each peak of the first group of peaks and each peak of the second group of peaks.

[0010] In a method of one aspect of the present invention, the group of nearby data points includes one or more data points proximate each peak of the first group of peaks and each peak of the second group of peaks in azimuth space, elevation space, three-dimensional space, or time space. The method according to one embodiment of the present invention further includes the following steps a to c. a. determining that a first number of peaks in the first group of peaks is different from a second number of peaks in the second group of peaks; and The response determined to be different from the number of first peaks to the number of second peaks is: b. identifying the plurality of targets based on an extra peak being detected by either the up-chirp frequency or the down-chirp frequency; c. Alternatively, identifying the plurality of targets based on a lack of detection of either the up-chirp frequency or the down-chirp frequency in response.

[0011] In accordance with one aspect of the present invention, a light detection and ranging (LIDAR) system includes: an optical scanner for transmitting a plurality of optical beams having different frequency chirps toward a plurality of targets within a field of view of the LIDAR system and for receiving a plurality of return signals having different frequency chirps from reflection of the plurality of optical beams; an optical processor coupled to the optical scanner for generating an electrical signal from the plurality of return signals, the electrical signal having a frequency that is dependent on a LIDAR target distance; a signal processor connected to the optical processor, The signal processing device includes: A processor; and a memory storing instructions that, when executed by the processor, cause the LIDAR system to perform the following operations a to c. a. generating a frequency domain baseband signal based on the electrical signal generated from the plurality of return signals, where the baseband signal includes first peaks associated with respective up-chirp frequencies and second peaks associated with respective down-chirp frequencies; b. generating one or more indices for matching associated with each peak of the first set of peaks and each peak of the second set of peaks in the baseband signal; and c. Using the one or more indices, pairing each peak of the first group of peaks with each peak of the second group of peaks, and identifying the plurality of targets based on the pairing.

[0012] In accordance with one aspect of the present invention, a light detection and ranging (LIDAR) system includes: an optical scanner for transmitting a plurality of optical beams, each having a different frequency chirp, toward a plurality of targets within a field of view of the LIDAR system and for receiving a plurality of return signals, each having a different frequency chirp, from reflection of the plurality of optical beams; an optical processor coupled to the optical scanner for generating an electrical signal from the plurality of return signals, the electrical signal having a frequency that is dependent on a LIDAR target distance; a signal processor connected to the optical processor, The signal processing device includes: A processor; and a memory storing instructions that, when executed by the processor, cause the LIDAR system to perform the following operations a to c. a. Identifying a first set of peaks in the electrical signal, the first set of peaks being associated with respective up-chirp frequencies and a second set of peaks being associated with respective down-chirp frequencies. b. determining one or more indices for matching associated with each peak of the first group of peaks and each peak of the second group of peaks; and c. generating a plurality of peak pairs by associating each peak of the first group of peaks with each peak of the second group of peaks based on the one or more indicators; d. identifying the one or more targets based on the plurality of peak pairs. [Brief description of the drawings]

[0013] In order to clarify various aspects of the present invention, reference is made to the drawings which are referred to in the following detailed description (embodiments), in which like reference numerals refer to like elements.

[0014] [Figure 1] FIG. 1 is a block diagram illustrating a LIDAR system according to an embodiment of the present invention.

[0015] [Diagram 2] FIG. 2 is a time-frequency diagram illustrating an example LIDAR waveform according to an embodiment of the present invention.

[0016] [Figure 3A] FIG. 1 is a block diagram illustrating a LIDAR system according to an embodiment of the present invention.

[0017] [Figure 3B] FIG. 1 is a block diagram illustrating the electro-optical system of a LIDAR system according to an embodiment of the present invention.

[0018] [Figure 4] 1 is a block diagram showing a signal processing device according to an embodiment of the present invention;

[0019] [Diagram 5] FIG. 2 is a signal strength-frequency diagram illustrating signal peaks for a multiple target situation, in accordance with an embodiment of the present invention.

[0020] [Figure 6] 1 is a signal strength-frequency diagram showing an example of a peak-like waveform of a target used for peak association in accordance with an embodiment of the present invention.

[0021] [Figure 7] FIG. 2 is a block diagram showing a peak association processor using indices computed for each peak according to an embodiment of the present invention.

[0022] [Figure 8] FIG. 2 is a block diagram illustrating a correlation processing system for generating a correlator-based index according to a present embodiment of the present invention.

[0023] [Figure 9]4 is a flow chart illustrating a method for associating signal peaks according to an embodiment of the present invention.

[0024] [Figure 10] FIG. 2 is a block diagram showing a signal processing system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A LIDAR system and method according to an embodiment of the present invention, namely a LIDAR system and method for correlating peaks in a multi-target situation, is described below. The LIDAR system of the embodiments of the present invention can be implemented in any sensing market, including, but not limited to, transportation, manufacturing, metrology, medical, virtual reality, augmented reality, and security systems. Additionally, the LIDAR system described in the embodiments can be implemented as part of the front end of a frequency modulated continuous wave (FMCW) device that aids in the spatial awareness of autonomous driving assistance systems and autonomous vehicles.

[0026] The LIDAR system of the embodiments described herein uses coherent scanning techniques to detect return signals from a target and generate a coherent heterodyne signal from which range and velocity information of the target can be obtained. Such a signal (or signals) may include a frequency up-sweep (up-chirp) and a frequency down-sweep (down-chirp), which may come from a single light source or from separate light sources (i.e., the light source providing the up-sweep may be different from the light source providing the down-sweep). As a result, two distinct frequency peaks, one from the up-chirp and one from the down-chirp, can be associated with a target and used to determine the target's range and velocity. In a multiple target situation, there may be multiple pairs of frequency peaks to be associated in a set, one for each target, however, in such cases, optimally associating the correct peak pairs may be difficult due to the large number of possible peak pair combinations that may be generated from the multiple target situation. According to an embodiment of the present invention, the above problem can be solved by using the technology disclosed in this specification, particularly by setting an index (evaluation index) for each peak and possible peak pair, and executing the association algorithm based on the set index. Several indexes for each peak and possible peak pair can be combined to execute the association algorithm. In this way, by using multiple indexes set for each possible peak pair, the peak pairs can be optimally associated.

[0027] FIG. 1 illustrates a LIDAR system 100 according to one embodiment. The LIDAR system 100 may include any one or more of numerous components, but may include fewer or additional components than those shown in FIG. 1. In one embodiment, one or more of the components shown in FIG. 1 may be implemented on a photonics chip. The optical circuit 101 includes a combination of active and passive optical components. In some examples, the active optical components have light beams of different wavelengths and include one or more optical amplifiers, one or more photodetectors, etc.

[0028] The free-space optics 115 includes one or more optical waveguides for transmitting optical signals and for routing and manipulating the optical signals to the appropriate input / output ports of the active optical circuit. The free-space optics 115 also includes one or more optical components such as taps, wavelength division multiplexers (WDMs), splitters / combiners, polarizing beam splitters (PBSs), collimators, couplers, and non-reciprocal elements such as Faraday rotators. In one embodiment, the free-space optics 115 includes components for converting the polarization state and directing the received polarized light to a photodetector, for example, using a PBS. The free-space optics 115 may also include a diffractive element that deflects light beams having different frequencies at different angles along an axis (e.g., the fast axis).

[0029] The LIDAR system 100 of this embodiment includes an optical scanner 102 having one or more scanning mirrors that are rotatable along an axis orthogonal or substantially orthogonal to the fast axis (e.g., a slow axis) of the diffractive element to direct an optical signal that scans the environment according to a scanning pattern. For example, the scanning mirrors can be rotated by one or more galvanometers. The optical scanner 102 also collects the return light beam reflected by any objects in the environment and directs it back to the passive optical circuit elements of the optical circuit 101. For example, the return light beam is directed by a polarizing beam splitter to a photodetector. Note that the optical scanner 102 may include quarter wave plates, lenses, anti-reflective coated optical windows, etc. in addition to mirrors and galvanometers.

[0030] The LIDAR system 100 is provided with a LIDAR controller 110 to control and support the optical circuit 101 and the optical scanner 102. The LIDAR controller 110 includes a processing device, such as a signal processing unit 112. For example, the signal processing unit 112 may be one or more general-purpose processing devices, such as a microprocessor, a central processing unit, or in particular a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets or a combination of instruction sets. Additionally, the signal processing unit 112 may be one or more special purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a network processor, or the like.

[0031] In one embodiment, a digital signal processor (DSP) is used as the signal processing unit 112. Thus, the LIDAR controller 110 outputs a digital control signal for controlling the optical driver 103. The digital control signal is converted into an analog signal via the signal conversion unit 106. For example, the signal conversion unit 106 includes a digital-to-analog converter. The optical driver 103 provides drive signals to the active optical components of the optical circuit 101 to drive light sources such as lasers and amplifiers. In one embodiment, multiple optical drivers 103 and signal conversion units 106 may be provided to drive multiple light sources.

[0032] The LIDAR controller 110 is also configured to output digital control signals to the optical scanner 102. The motion controller 105 can control the galvanometers of the optical scanner 102 based on the control signals received from the LIDAR controller 110. In particular, a digital-to-analog converter can be used to convert the coordinate routing information from the LIDAR controller 110 into signals that can be processed by the galvanometers of the optical scanner 102. In one embodiment, the motion controller 105 may also send information regarding the position or movement of components of the optical scanner 102 back to the LIDAR controller 110. In particular, an analog-to-digital converter may be used to convert the information regarding the galvanometer position into a signal that the LIDAR controller 110 can process.

[0033] The LIDAR controller 110 is further configured to analyze the input digital signal. In this regard, the LIDAR system 100 is provided with an optical receiver 104 for measuring one or more beams received by the optical circuit 101. In particular, the optical receiver 104 as a reference beam receiver measures the amplitude of a reference beam from the active optical components and converts the signal from the reference beam receiver by an analog-to-digital converter into a signal that can be processed by the LIDAR controller 110. The target receiver, as the optical receiver 104, also measures an optical signal carrying information about the range and velocity of the target in the form of a beat frequency modulated optical signal, where the reflected beam of the optical signal may be mixed with a second signal of a local oscillator. The optical receiver 104 may be provided with a high speed analog-to-digital converter to convert the signal from the target receiver into a signal that can be processed by the LIDAR controller 110. In one aspect, the signal from the optical receiver 104 may be subject to signal conditioning by the signal conditioning unit 107 before being received by the LIDAR controller 110. For example, the signal from the optical receiver 104 may be provided to an operational amplifier in the signal conditioning unit 107 for amplification of the return signal, and the amplified signal provided by the operational amplifier to the LIDAR controller 110.

[0034] In some applications, the LIDAR system 100 may additionally be provided with one or more imagers 108 configured to capture images of the environment, a global positioning system (GPS) 109 configured to provide a geographic location of the system, or other sensor inputs. The LIDAR system 100 may also include an image processor 114 that may be configured to receive images and geographic locations from the imager 108 and Global Positioning System (GPS) 109, and to transmit the images and location or related information to the LIDAR controller 110 or other systems connected to the LIDAR system 100.

[0035] In operation according to some embodiments, the LIDAR system 100 is configured to simultaneously measure range and velocity in two dimensions using a non-degenerate optical source. This capability enables real-time, long-range measurements of range, velocity, azimuth, and elevation of the surrounding environment.

[0036] As an example, the scanning process is initiated by the optical driver 103 and the LIDAR controller 110. The LIDAR controller 110 instructs the optical driver 103 to modulate one or more light beams, respectively, and these modulation signals are transmitted through the passive optical circuit of the optical circuit 101 to the collimator of the free space optical system 115. The collimator directs the modulation signals to the optical scanner 102, which scans the environment in a pre-programmed pattern defined by the motion controller 105. The optical circuit 101 may be provided with a polarizing waveplate (PWP) that converts the polarization state of the light as it exits the optical circuit 101. As an example, the polarizing waveplate may be a 1 / 4 waveplate or a 1 / 2 waveplate. A portion of the polarized light beam may be reflected back into the optical circuit 101. For example, a lens or collimating system used in the LIDAR system 100 may have natural reflective properties or a reflective coating that causes a portion of the light beam to be reflected back into the optical circuit 101.

[0037] The optical signal reflected from the environment is sent to the receiver (optical receiver 104) through the optical circuit 101. At this time, the polarization state of the light has been converted, so it is reflected by the polarizing beam splitter along with a portion of the polarized light that was reflected back to the optical circuit 101. As a result, the reflected optical signal does not return to the same optical fiber or waveguide as the light source, but is reflected to different optical receivers. These signals interfere with each other and generate a mixed (combined) signal. Each beam signal returning from the target produces a time-shifted waveform, and the time phase difference between these two waveforms produces a beat frequency that is measured by an optical receiver (photodetector). The mixed signal is then reflected to the optical receiver 104 .

[0038] The analog signal received by the optical receiver 104 is converted to a digital signal by an ADC (analog-to-digital converter), which is then sent to the LIDAR controller 110. A signal processing unit 112 of the device receives the digital signals and processes them. In one embodiment, the signal processing unit 112 receives position data from the motion controller 105 and a galvanometer (not shown) and image data from the image processor 114. This enables the signal processing unit 112 to generate a 3D point cloud with information about the distance and velocity of points in the environment as the optical scanner 102 scans additional points. The signal processing unit 112 may also overlay the 3D point cloud with image data to determine the speed and distance of surrounding objects. The LIDAR controller 110 may also process satellite-based navigation position data to provide precise global position information.

[0039] 2 is a time-frequency diagram 200 of an FMCW scanning signal 201 that a LIDAR system, such as LIDAR system 100, can use to scan a target environment in one embodiment. FM The scanning signal 201, labeled (t), has a chirp bandwidth Δf C and chirp period T C It is a sawtooth waveform (sawtooth "chirp") with The inclination of the sawtooth is k=(Δf C / T C ). Also shown in FIG. 2 is a target return signal 202 in one embodiment. FM The target return signal 202, denoted (t-Δt), is a time delayed version of the scanning signal 201, where Δt is the round trip time to and from the target illuminated by the scanning signal 201. This round trip time is given by Δt=2R / v, where R is the range of the target and v is the speed of light, c, which is the speed of the light beam. Therefore, the range R of the target can be calculated as R = c(Δt / 2). When the return signal 202 is optically mixed with the scanning signal, a distance-dependent difference frequency ("beat frequency") Δf R (t) is generated. Beat frequency Δf R (t) is linearly related to the time delay Δt by the sawtooth slope k. That is, Δf R (t) = kΔt. Since the target distance R is proportional to Δt, the target distance R is R = (c / 2)(Δf R (t) / k) that is, the distance R can be calculated as the beat frequency Δf R It has a linear relationship with (t). Beat frequency Δf R (t) is generated as an analog signal, for example, in optical receiver 104 of LIDAR system 100. This beat frequency is digitized, for example, by an analog-to-digital converter (ADC) in signal conditioning unit 107 of LIDAR system 100. The digitized beat frequency signal is then digitally processed in a signal processing unit (e.g., signal processing unit 112) in LIDAR system 100. However, it should be noted that the target return signal 202 typically contains a frequency offset (Doppler shift) if the target has a relative velocity with respect to the LIDAR system 100. For simplicity and ease of illustration, the Doppler shift is not shown in FIG. 2 because it is detected separately and used to correct the frequency of the return signal. It is also important to note that the sampling frequency of the ADC is determined by the highest beat frequency that the system can handle without aliasing. Typically, the highest frequency that can be handled is half the sampling frequency (i.e., the "Nyquist limit"). For example, and not by way of limitation, if the sampling frequency of the ADC is 1 GHz, then the highest beat frequency that can be handled without aliasing (Δf Rmax ) is 500 MHz. This limit is the system's maximum target range Rmax = (c / 2)(Δf Rmax / k), which can be adjusted by changing the inclination k of the sawtooth. In one example, the data samples from the ADC may be continuous, but the subsequent digital processing described below may be divided into "time segments" that may be associated with a predetermined periodicity of the LIDAR system 100. For example, and without limitation, the time segments may be divided into "time segments" that are equal to or longer than the chirp period T C or the number of azimuth rotations made by the optical scanner described above. The embodiments of the present disclosure may be applied to FMCW-LIDAR (LiDAR), but are not necessarily limited to FMCW LiDAR, and may also be applied to other types of coherent LIDAR (LiDAR).

[0040] 3A is a block diagram illustrating an FMCW-LIDAR system 300 according to one embodiment. The LIDAR system 300 includes an optical scanner 301 that transmits a FMCW (frequency modulated continuous wave) infrared (IR) light beam 304 and receives a return signal 313 from reflections of the light beam 304, such as from targets 312 within a field of view (FOV) of the optical scanner 301. The LIDAR system 300 also includes an optical processor 302 that generates a baseband signal 314 from the return signal 313, the baseband signal 314 having a frequency dependent on the LIDAR target range in the time domain. The optical processor 302 may include components such as the free space optics 115, the optical circuit 101, the optical driver 103, and the optical receiver 104 described in the LIDAR system 100. The LIDAR system 300 further includes a signal processor 303 that measures the energy of the baseband signal 314 in the frequency domain and compares the energy measurement with an estimate of the LIDAR system noise to determine the likelihood that a signal peak in the frequency domain indicates a detected target. The signal processor 303 may include components such as the signal transformation unit 106, the signal conditioning unit 107, the LIDAR controller 110, and the signal processing unit 112 in the LIDAR system 100.

[0041] Figure 3B is a block diagram illustrating an example of electro-optics 350 of a LIDAR system according to one embodiment. Electro-optics 350 includes an optical scanner 301 similar to optical scanner 102 described in Figure 1. Electro-optics 350 also includes an optical processor 302 that includes components such as free space optics 115, optical circuitry 101, optical driver 103, and optical receiver 104 described in LIDAR system 100, as described above.

[0042] The optical processing device 302 is provided with a light source 305 for generating a frequency modulated continuous wave (FMCW) light beam 304. The light beam 304 from the light source 305 is directed to an optical coupler 306, which sends a portion of the light beam 304 to a polarizing beam splitter (PBS) 307. A sample 308 (reference beam) of the light beam 304 is sent from the optical coupler 306 to a photodetector (PD) 309. The PBS 307 is configured to direct the polarized light beam 304 to the optical scanner 301. The optical scanner 301 is configured to scan the target environment with the light beam 304 at a range of azimuth and elevation angles covering a field of view (FOV) 310 of a LIDAR window 311 within the housing 320 of the electro-optical system 350. Note that only azimuth scanning is shown in FIG. 3B for simplicity of illustration.

[0043] 3B, the light beam 304 passes through the LIDAR window 311 at a predetermined azimuth angle (or range of angles) and is illuminated on the target 312. The return signal 313 from the target 312 passes through the LIDAR window 311 and is returned to the PBS 307 by the optical scanner 301.

[0044] The return signal 313, with a different polarization than the light beam 304 due to reflection from the target 312, is guided through the PBS 307 to the photodetector (PD) 309. In the photodetector (PD) 309, the return signal 313 is optically mixed with the local samples 308 of the light beam 304 to generate a time-domain distance-dependent baseband signal 314. This distance-dependent baseband signal 314 is the frequency difference between the local samples 308 of the light beam 304 and the return signal 313 versus time (i.e., Δf R (t)).

[0045] 4 is a detailed block diagram illustrating one embodiment of a signal processor 303 for processing the baseband signal 314. As previously described, the signal processor 303 may include components such as the signal transformation unit 106, the signal conditioning unit 107, the LIDAR controller 110, and the signal processing unit 112 of the LIDAR system 100.

[0046] The signal processing device 303 includes an analog-to-digital converter (ADC) 401, a time domain module 402, a block sampler 403, a discrete Fourier transform (DFT) module 404, a frequency domain module 405, and a peak search module 406. Each component block of the signal processing device 303 can be implemented, for example, in hardware, firmware, software, or a combination of hardware, firmware, and software.

[0047] As shown in Fig. 4, the baseband signal 314, which is a time-domain continuous analog signal, is sampled by the ADC 401 to generate a series of time-domain samples 315. The time-domain samples 315 are processed by the time-domain module 402 to condition it for further processing. For example, the time-domain module 402 may apply weighting or filtering to remove undesired signal components or make it suitable for further processing. The output signal (time-domain samples) 316 of the time-domain module 402 is then sent to the block sampler 403. The block sampler 403 divides the output signal (time domain samples) 316 into groups of N samples 317 (N is an integer greater than 1) and sends them to the DFT module 404. The DFT module 404 converts the groups of N time domain samples 317 into N frequency bins or sub-bands 318 in the frequency domain that cover the bandwidth of the baseband signal 314. The N sub-bands 318 are sent to the frequency domain module 405 to be conditioned for further processing. For example, the frequency domain module 405 may resample and / or average the sub-bands 318 for noise reduction. The frequency domain module 405 may also calculate signal statistics and system noise statistics. The processed sub-bands 319 are then sent to the peak search module 406 to search for signal peaks that represent targets within the field of view (FOV) of the LIDAR system 300.

[0048] FIG. 5 is an example of a signal strength-frequency diagram 500 showing signal peaks for multiple targets in one embodiment. In one embodiment, the FMCW-LIDAR system can generate frequency modulations of up-chirps and down-chirps (also referred to herein as up-sweeps and down-sweeps) to scan an environment and determine the range and velocity of targets within the environment. In one example, both the up-chirps and down-chirps can be generated by a single light source, and in another example, the LIDAR system can include a light source that generates a light beam including the up-chirps and a different light source that generates a light beam including the down-chirps. Using the beat frequencies (i.e., peak frequencies) generated in response to the return signals from the up-chirps and down-chirps, a signal processor (e.g., signal processing unit 112 and signal processor 303 shown in FIG. 1) can determine both the range and velocity of the targets. In some embodiments, the signal processing unit 112 can determine the range of the target (i.e., the distance of the target from the LIDAR system) by summing the two frequencies of the two peaks and dividing the sum by 2. The signal processing unit 112 can also determine the velocity of the target by dividing the difference between the frequencies of the two peaks by 2. However, as shown in FIG. 5, when determining the target as described above, a situation may arise in which multiple targets are present, resulting in a situation in which multiple peak pairs are generated.

[0049] 5, the signal processing unit 112 may identify multiple peak frequencies (e.g., peak frequencies in subband 319) from two targets in the field of view of the LIDAR system. For example, the signal processing unit 112 may identify a first downsweep target peak 520A and a second downsweep target peak 520B from the downsweep signal and a first upsweep target peak 525A and a second upsweep target peak 525B from the upsweep signal. Thus, the signal processing unit 112 can match the potentially matching peaks using one of a variety of means, and in order to properly associate the pairs, the signal processing unit 112 can calculate multiple indices (evaluation indices) for each potentially matching peak and each peak pair, as described in more detail below in Figures 7-9. For example, as shown in FIG. 6, peaks corresponding to the same target may have very similar shapes, and therefore the signal processing unit 112 may calculate an index related to the peak shape and use the calculated index to optimally correlate the peaks of the targets. However, as will be described below, the signal processing unit 112 can calculate many other indices for these peaks and use these indices to make associations for each peak. 5, the signal processing unit 112 can identify a first target pair 505 including a first downsweep target peak 520A and a first upsweep target peak 525A based on the calculated metrics (e.g., peak shape, intensity, etc.). In addition, the signal processing unit 112 can identify a second target pair 510 including a second downsweep target peak 520B and a second upsweep target peak 525B based on the calculated metrics (e.g., peak shape, intensity, etc.).

[0050] 6 is a signal strength-frequency diagram 600 showing peaks due to upsweep and downsweep signals for multiple targets. As shown, the subband frequency distribution (e.g., subband 319) is shown separated into upsweep and downsweep signals, each with a corresponding peak associated with each target. Peaks in the upsweep and downsweep signals corresponding to the same target may have similar characteristics. For example, the first peak 601 in the upsweep and the first peak 602 in the downsweep have similar characteristics including shape and intensity, and are offset from each other in the frequency spectrum. Similarly, the second peak 603 in the upsweep and the second peak 604 in the downsweep have common characteristics including shape and intensity, and are also offset in frequency. Therefore, the signal processing device (e.g., the signal processing unit 112 in FIG. 1) can generate an index for each detected peak based on the characteristics of each peak, and the index can be used to optimally perform peak association.

[0051] FIG. 7 shows a peak association processor 700 for optimizing peak association. The peak association processor 700 may be included in the signal processing unit 112 of FIG. 1, and may be included in a configuration the same as or similar to the peak search module 406 of FIG. In one embodiment, the index computation module 705 receives N upsweep peaks (peaks 701A-N) and N downsweep peaks (peaks 702A-N), where N is a positive non-zero integer. The index computation module 705 may also receive multiple frequency bins proximate to the peaks 701A-N and 702A-N. In some embodiments, the index computation module 705 generates one or more indices 715 for each peak 701A-N and 702A-N, and for each peak pair combination of peaks 701A-N and 702A-N. The index computation module 705 may generate the one or more indices 715 based on characteristics of the peaks 701A-N and 702A-N, and characteristics of frequency bins proximate to these peaks. For example, the index computation module 705 can generate indices 715 for peaks 701A-N and 702A-N and other potentially matching peak pairs based on, but not limited to, peak shape, peak intensity, raw frequency of the peak, SNR, reflectivity, ego velocity of the LIDAR system, and / or any other characteristics of the target, peak, and LIDAR system. That is, the index computation module 705 can generate multiple indices 715 for the N×N number of potentially matching peak pairs.

[0052] In one embodiment, the index computation module 705 can take each of the indices 715 calculated individually and combine them into a composite index. For example, the index computation module 705 can generate a weighted sum of the indices 715 for each peak or pair of peaks that may be a match. Each index 715 can be weighted in a manner that corresponds to the relevance or confidence of that index. For example, an index such as peak shape can be weighted more heavily than other indices with lower confidence scores because it provides a higher confidence in the correct association. It should be noted that the individual indices may be combined in any combination and manner to generate a composite index. In one example, the weighting of each index may be determined statically, while in another example, the weighting may be determined dynamically based on feedback from the peak association algorithm. In one embodiment, the weighting may be determined by a machine learning model to optimize the performance of the peak association algorithm.

[0053] The index computation module 705 can provide the generated index or indices 715 to a peak association module 710. The peak association module 710 can optimize peak association based on an algorithm that uses the index or indices 715 as input, and subsequently output one or more peak pairs 720 based on the peak association algorithm. In one example, the peak association module 710 may implement a greedy algorithm that first selects the most correlated peak pair based on the index 715, associates and removes that pair, and moves on to the next most correlated. In another example, a more complex algorithm (e.g., the Hungarian algorithm) may be implemented to find an overall cost optimization based on the index 715.

[0054] In some embodiments, the number of upsweep peaks and downsweep peaks may differ. In such cases, the index computation module 705 may generate N×M indexes 715, where N is the number of upsweep peaks and M is the number of downsweep peaks, or vice versa. In some embodiments, the peak association module 710 may execute multiple algorithms to account for situations where the number of peaks from the upsweep and the number of peaks from the downsweep do not match. For example, the peak association module 710 may execute a first peak association algorithm when the number of peaks from the upsweep and the downsweep are the same. However, if the number of peaks are not the same, the following algorithms may be executed depending on two situations: The first situation is when a target is missed by one sweep, resulting in a mismatch, in which case the peak association module 710 can run a second peak association algorithm to match all but a few peaks (i.e., not forcibly match all peaks) into pairs. The second situation is when a false positive causes an extra peak to be associated with an upsweep or downsweep peak, in which case the peak association module 710 can run a third peak association algorithm to match all peaks as pairs except for the extra false positive peak (i.e., weak peaks that are potential false positive peaks can be excluded from the peak association algorithm).

[0055] FIG. 8 illustrates an example correlation processor 800 for determining correlations (eg, cross-correlations) between peak shapes performed according to embodiments of the present disclosure. In some embodiments, the correlation processor 800 may be included in the signal processing unit 112 of FIG. 1, or the correlation processor may be included in the index computation module 705 of FIG. 8, each upsweep peak 810A-N, along with each downsweep peak 820A-N, is input to a correlator 830A-(N×N) to generate a correlation value for each possible combination of upsweep and downsweep peak pairs. Input to each correlator 830A-(N×N) are K samples (or frequency bins) around each input peak, where K is a positive, non-negative integer. In one example, the correlation processor may convolve the two peaks and K samples input to the correlator 830A-(N×N) to generate 2K+1 correlation samples. The correlator 830A-(N×N) may then select the maximum correlation sample from the 2K+1 correlation outputs to be the output of the correlator 830A-(N×N). This generates a maximum correlation for each possible matching peak pair, which is provided (output) to the peak association module 710 described in FIG. 7 above.

[0056] FIG. 9 is a flow chart illustrating a method 900 for correlating peaks of multiple target scenes in a LIDAR system, such as LIDAR system 100 or LIDAR system 300.

[0057] The method 900 begins with operation 902, where an optical scanner (e.g., optical scanner 301) transmits multiple light beams containing different frequency chirps toward a target within a field of view of the LIDAR system. In operation 904, an optical scanner (eg, optical scanner 301) receives multiple return signals containing different frequency chirps based on reflections from a target.

[0058] In operation 906, an optical processor (e.g., optical processor 302) generates a frequency domain baseband signal based on the return signal, the baseband signal including a first set of peaks associated with respective up-chirp frequencies and a second set of peaks associated with respective down-chirp frequencies.

[0059] In operation 908, an index calculation module (e.g., index calculation module 705) of the signal processing device (e.g., signal processing device 303) generates one or more indexes (evaluation indexes) for matching associated with the first peak set (first group of peaks) and the second peak set (second group of peaks). In some embodiments, the one or more metrics include a similarly calculated peak shape between each peak in the first group of peaks and each peak in the second group of peaks. In some embodiments, the one or more indices also include a correlation value between each upsweep peak and each downsweep peak based on similarity in peak shape, peak intensity, peak width or other peak characteristics. The one or more metrics may also include external metrics such as ego / sensor speed. In one example, the similarity of peak shapes can be determined by applying a correlator to generate a correlation value (the output of the correlator) when comparing each peak in the first group of peaks with each peak in the second group of peaks.

[0060] In some embodiments, the index computation module (e.g., index computation module 705) can combine one or more indices for the first and second peak groups to generate a composite index and associate the peaks based on such composite index. As an example, an index computation module (e.g., index computation module 705) may assign a weight to each of one or more indexes and add these weighted indexes to generate a weighted sum of the one or more indexes.

[0061] In operation 910, a peak association module (eg, peak association module 710) identifies each target based on pairing each peak in the first group of peaks with each peak in the second group of peaks using one or more indices. To identify a target from the first and second groups of peaks, a peak association module (e.g., peak association module 710) can execute an optimization algorithm that minimizes a cost function that corresponds to the difference between the matched peaks. As an example, a peak association module (e.g., peak association module 710) can identify neighboring data points for each peak in the first set of peaks and each peak in the second set of peaks, and associate the peaks based on the neighboring data points. Such neighboring data points can include one or more of data points that are proximate to each peak in azimuth space, elevation space, three-dimensional space, or time space.

[0062] The peak association module (e.g., peak association module 710) may further determine that the number of peaks in the first group of peaks (the first number) is different from the number of peaks in the second group of peaks (the second number) (e.g., detecting missing or extra peaks). In some embodiments, a peak association module (eg, peak association module 710) may implement a variation of the peak association algorithm that accounts for missing and extra peaks. For example, if it is determined that the number of peaks in the first group of peaks does not match the number of peaks in the second group of peaks, the peak association module (e.g., peak association module 710) may perform peak association based on a first algorithm related to the detection of an extra peak (e.g., an extra peak detected due to an up-chirp or down-chirp). In another example, if it is determined that detection of a target is missed due to an up-chirp or down-chirp, the peak association module (e.g., peak association module 710) can perform peak association based on a second algorithm for missed detection.

[0063] FIG. 10 is a block diagram of a signal processing system 1000 (e.g., similar to signal processing device 303 in FIG. 4) in a LIDAR system such as LIDAR system 100 or LIDAR system 300. Signal processing system 1000 includes processor 1001, which may be any type of general-purpose processor or a specialized processor designed for use in LIDAR systems (see also, e.g., signal processing unit 112 in FIG. 1). The processor 1001 is operatively coupled to a memory 1002. The memory 1002 is any type of non-transitory computer-readable medium (e.g., RAM, ROM, PROM, EPROM, EEPROM, flash memory, magnetic disk memory, or optical disk memory) that contains instructions that, when executed by the processor 1001 in the LIDAR system, cause the LIDAR system to perform the methods described herein. Specifically, the memory 1002 includes: instructions 1004 for transmitting a plurality of light beams having different chirp frequencies (frequency chirps) toward a target within a field of view of the LIDAR system; instructions 1006 for receiving a plurality of return signals having different chirp frequencies (frequency chirps) based on reflections from the target; instructions 1008 for generating a frequency domain baseband signal based on the return signal, the baseband signal including a first set of peaks associated with different up-chirp frequencies and a second set of peaks associated with different down-chirp frequencies; instructions 1010 for generating one or more metrics associated with each peak in the first set of peaks and each peak in the second set of peaks; and The method includes instructions 1012 for pairing each peak in the first peak set (first group of peaks) with each peak in the second peak set (second group of peaks) using the one or more indices, and identifying each target based on the pairing.

[0064] In the above description, a number of specific examples of specific systems, components, methods, etc. are shown to facilitate understanding of the embodiments of the present invention, but those skilled in the art may practice the present invention without the description of these specific examples. In addition, details of known components and methods may be omitted or shown in the form of simple block diagrams, but this is for the purpose of facilitating understanding of the present invention. Therefore, the contents disclosed are merely examples, and even if one example differs from other examples, it is considered to be included within the scope of the present invention.

[0065] When the phrase "one embodiment" or "an embodiment" is used in this specification, it means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places in this specification do not necessarily refer to the same embodiment.

[0066] Although the operations of the methods described herein are shown in a particular order, the order of operations of each method may be changed, certain operations may be performed in reverse order, at least some operations may be performed simultaneously with other operations, and instructions for different operations or auxiliary operations may be performed intermittently or alternately.

[0067] The above-described description of the embodiments of the invention (including those described in the Abstract) is not intended to be detailed or exhaustive, nor is it intended to limit the invention to the specific forms disclosed. While specific embodiments and examples of the invention are described herein for illustrative purposes, various equivalent modifications will occur to those skilled in the art. The word "example" or "exemplary" is used herein to mean serving as an example, illustration, or illustration. Any aspect or design described herein as "example" or "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word "example" or "exemplary" is intended to illustrate concepts in a concrete manner. The term "or" as used herein is intended to be interpreted as an inclusive "or" rather than an exclusive "or." That is, unless otherwise specified or clear from the context, the phrase "X contains A or B" refers to any of the natural inclusive permutations: if X contains A, if X contains B, or if X contains both A and B, then in any of the above cases, the condition "X contains A or B" is satisfied. Furthermore, the articles "a" and "an" as used in this specification and the appended claims are to be construed to mean "one or more" unless otherwise specified and unless the singular form is clear from the context. Furthermore, when terms such as "first," "second," "third," and "fourth" are used in this specification, these terms are used as identifiers to distinguish different elements and do not necessarily indicate an order according to the numerical designation.

Claims

1. A method comprising the steps of: a. Transmitting multiple light beams containing different frequency chirps toward multiple targets within a field of view of a Light Detection and Ranging (LIDAR) system; b. receiving a plurality of return signals based on reflections from the plurality of targets, the plurality of return signals including different frequency chirps; c) generating a frequency domain baseband signal based on the plurality of return signals, the baseband signal including a first set of peaks associated with respective up-chirp frequencies and a second set of peaks associated with respective down-chirp frequencies; d. generating, by a processor, one or more evaluation indices for matching (hereinafter referred to as indices) associated with each peak of the first group of peaks and each peak of the second group of peaks, where the indices include similarly calculated peak shapes between each peak of the first group of peaks and each peak of the second group of peaks, and the similarly calculated peak shapes include the output of a correlator when comparing each peak of the first group of peaks with each peak of the second group of peaks; e. using the one or more indices to pair each peak of the first group of peaks with each peak of the second group of peaks, and identifying, by the processor, the plurality of targets based on pairings associated with similar peak shapes.

2. A method according to claim 1, comprising: The method, wherein the one or more metrics further include at least one of peak intensity, peak width, ego velocity (self-motion velocity), and raw peak frequency.

3. 2. The method of claim 1, further comprising the steps of: a. a. combining the one or more indices for the first group of peaks and the second group of peaks to generate a composite indices; and b. identifying the plurality of targets based on the composite index for the first group of peaks and the second group of peaks.

4. The method according to claim 3, The method, wherein the procedure of combining the one or more indices to generate the composite index comprises the following steps a and b: a. weighting each of the one or more indices to generate a weighted index; and b) adding the one or more weighted indicators to generate a weighted sum of the one or more indicators.

5. 2. The method of claim 1 , The method, wherein identifying the plurality of targets comprises the steps of: running an optimization algorithm that minimizes a cost function associated with pairing each peak in the first set of peaks with each peak in the second set of peaks, where the cost function corresponds to a sum of the one or more metrics for pairing each peak in the first set of peaks with each peak in the second set of peaks.

6. 2. The method of claim 1, further comprising the steps of: a. a. identifying neighboring data points for each peak in the first set of peaks and for each peak in the second set of peaks; and b) further identifying the plurality of targets based on the neighboring data points for each peak of the first set of peaks and each peak of the second set of peaks.

7. The method of claim 6, comprising: The method of claim 1, wherein the group of nearby data points includes one or more data points proximate each peak of the first group of peaks and each peak of the second group of peaks in azimuth space, elevation space, three-dimensional space, or time space.

8. 2. The method of claim 1, further comprising the steps of: a) determining that a first number of peaks in the first group of peaks is different from a second number of peaks in the second group of peaks; and The response in which the first peak number is determined to be different from the second peak number is: b) identifying the plurality of targets based on an extra peak being detected by either the up-chirp frequency or the down-chirp frequency; or c) identifying the plurality of targets based on a lack of detection of either the up-chirp frequency or the down-chirp frequency in response to the response.

9. 1. A light detection and ranging (LIDAR) system comprising: an optical scanner for transmitting a plurality of optical beams having different frequency chirps toward a plurality of targets within a field of view of the LIDAR system and for receiving a plurality of return signals having different frequency chirps from reflection of the plurality of optical beams; an optical processor coupled to the optical scanner for generating an electrical signal from the plurality of return signals, the electrical signal having a frequency that is dependent on a LIDAR target distance; a signal processor connected to the optical processor, The signal processing device includes: A processor; A LIDAR system including: a memory storing instructions that, when executed by the processor, cause the LIDAR system to perform the following operations a to c. a) generating a frequency domain baseband signal based on the electrical signal generated from the plurality of return signals, where the baseband signal includes a first set of peaks associated with respective up-chirp frequencies and a second set of peaks associated with respective down-chirp frequencies; b. generating one or more matching indices associated with each peak of the first group of peaks and each peak of the second group of peaks in the baseband signal, where the indices include similarly computed peak shapes between each peak of the first group of peaks and each peak of the second group of peaks, and the similarly computed peak shapes include the output of a correlator when comparing each peak of the first group of peaks with each peak of the second group of peaks; c) pairing each peak of the first set of peaks with each peak of the second set of peaks using the one or more indices and identifying the plurality of targets based on pairings associated with similar peak shapes.

10. The system of claim 9, The one or more metrics further include at least one of a peak intensity, a peak width, an ego velocity, and a raw peak frequency.

11. The system of claim 9, The LIDAR system further includes the processor performing the following processes a and b. a. combining the one or more indices for the first group of peaks and the second group of peaks to generate a composite indices; and b. identifying the plurality of targets based on the composite index for the first group of peaks and the second group of peaks.

12. The system of claim 11, The processor performs the following processes a and b to combine the one or more indices to generate the composite indices. a. weighting each of the one or more indices to generate a weighted index; and b) adding the one or more weighted indicators to generate a weighted sum of the one or more indicators.

13. The system of claim 9, The processor, and executing an optimization algorithm to minimize a cost function associated with pairing each peak in the first set of peaks with each peak in the second set of peaks to identify the plurality of targets, where the cost function corresponds to a sum of the one or more metrics for pairing each peak in the first set of peaks with each peak in the second set of peaks.

14. 1. A light detection and ranging (LIDAR) system comprising: an optical scanner for transmitting a plurality of optical beams, each having a different frequency chirp, toward a plurality of targets within a field of view of the LIDAR system and for receiving a plurality of return signals, each having a different frequency chirp, from reflection of the plurality of optical beams; an optical processor coupled to the optical scanner for generating an electrical signal from the plurality of return signals, the electrical signal having a frequency that is dependent on a LIDAR target distance; a signal processor connected to the optical processor, The signal processing device includes: A processor; A LIDAR system including: a memory storing instructions that, when executed by the processor, cause the LIDAR system to perform the following operations a to c. Identifying a first set of peaks in the electrical signal, the first set of peaks being associated with respective up-chirp frequencies and a second set of peaks being associated with respective down-chirp frequencies. b. determining one or more indices for matching associated with each peak of the first group of peaks and each peak of the second group of peaks, where the indices include similarly computed peak shapes between each peak of the first group of peaks and each peak of the second group of peaks, and the similarly computed peak shapes include the output of a correlator when comparing each peak of the first group of peaks with each peak of the second group of peaks; c) pairing each peak of the first group of peaks with each peak of the second group of peaks based on the one or more indices to generate a plurality of peak pairs associated with similar peak shapes. d. identifying the one or more targets based on the plurality of peak pairs.

15. The system of claim 14, The one or more metrics include at least one of a peak intensity, a peak width, an ego velocity, and a raw peak frequency.

16. The system of claim 15, The processor performs the following processes a and b to generate the plurality of peak pairs. a. combining the one or more indices for the first group of peaks and the second group of peaks to generate a composite indices; and b. Associating each peak of the first group of peaks with each peak of the second group of peaks based on the composite index for the first group of peaks and the second group of peaks.

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