Motion compensation for fast target detection in automotive radar

Abstract

A motion compensation method for a Doppler radar system includes: for each transmitted pulse in a set of transmitted pulses, receiving a corresponding set of echo signals returned from multiple intervals; performing a Doppler Fourier transform on the set of echo signals of the transmitted pulse set to generate an output including detection signals in multiple velocity frames; and applying a corresponding predetermined compensation phase vector to the detection signal in each of the multiple velocity frames. The corresponding predetermined compensation phase vector applied to the detection signal in each velocity frame includes at least one of a first component proportional to the velocity of the velocity frame or a second component used to compensate for phase compensation errors associated with Doppler velocity aliasing.

Description

[0001] Related applications

[0002] This application claims the benefit of Israeli patent application No. 279457 entitled “Motion Compensation for FastTarget Detection in Automotive Radar”, filed on December 15, 2020, which has been assigned to the assignee of this application and is incorporated herein by reference in its entirety. Background Technology

[0003] This invention relates generally to the field of radar, and more specifically to motion compensation in Doppler radar.

[0004] Radar technology has wide applications across various industries, including automotive, medical, telecommunications, virtual reality (VR), and augmented reality (AR). For example, radar can be used in autonomous vehicles to detect objects in their surroundings. Radar can operate in environments where other types of sensing technologies may fail or be unsuitable. For instance, automotive radar may be able to operate in environments where light-based sensors (e.g., cameras and light detection and ranging (LIDAR) systems) perform poorly, such as during heavy rainfall or reduced visibility.

[0005] Radar can measure round-trip time to determine the distance to an object. Furthermore, the use of Doppler measurement and processing techniques allows radar systems to determine the relative velocity of a target object. For example, a Doppler radar system can use a narrow set of digital filters to perform Doppler frequency detection. By measuring the Doppler frequency and / or phase shift, a Doppler radar system is able to measure the relative velocity of objects that return echoes to the radar system, such as aircraft, vehicles, animals, or other objects. Summary of the Invention

[0006] The techniques disclosed herein generally relate to radar, and more specifically to motion compensation techniques for improving the performance of Doppler radar in detecting high-speed objects. According to some aspects, a motion compensation method for a Doppler radar system may include: for each transmitted pulse in a set of transmitted pulses, receiving a corresponding set of echo signals returned from multiple intervals; performing a Doppler Fourier transform on the set of echo signals of the transmitted pulse set to generate an output comprising detection signals in multiple velocity frames; and applying a corresponding predetermined compensation phase vector to the detection signal in each of the multiple velocity frames. The corresponding predetermined compensation phase vector applied to the detection signal in each velocity frame may include at least one of a first component proportional to the velocity of the velocity frame or a second component for compensating for phase compensation errors associated with Doppler velocity aliasing.

[0007] According to certain aspects, a Doppler radar system may include a Doppler Fourier transform subsystem and a motion compensation subsystem. The Doppler Fourier transform subsystem may be configured to receive a corresponding set of echo signals returned from multiple interval distances for each transmitted pulse in a set of transmitted pulses, and to perform a Doppler Fourier transform on the set of echo signals of that transmitted pulse set. The output of the Doppler Fourier transform may include the detection signals in multiple velocity frames. The motion compensation subsystem may be configured to apply a corresponding predetermined compensation phase vector to the detection signal in each of the multiple velocity frames. The corresponding predetermined compensation phase vector applied to the detection signal in each velocity frame may include at least one of a first component proportional to the velocity of the velocity frame or a second component used to compensate for phase compensation errors associated with Doppler velocity aliasing.

[0008] According to some aspects, an apparatus for motion compensation mainly includes: components for receiving a corresponding set of echo signals returned from a plurality of interval distances for each transmitted pulse in a set of transmitted pulses; components for performing a Doppler Fourier transform on the set of echo signals of the transmitted pulse set to generate an output including probe signals in a plurality of velocity frames; and components for applying a corresponding predetermined compensation phase vector to the probe signal in each of the plurality of velocity frames. The corresponding predetermined compensation phase vector applied to the probe signal in each velocity frame may include at least one of a first component proportional to the velocity of the velocity frame or a second component for compensating for phase compensation errors associated with Doppler velocity aliasing.

[0009] According to certain aspects, a non-transitory computer-readable medium may have instructions embedded therein. When executed by one or more processing units, the instructions may cause the one or more processing units to perform operations including: for each transmitted pulse in a set of transmitted pulses, receiving a corresponding set of echo signals returned from a plurality of spacing distances; performing a Doppler Fourier transform on the set of echo signals of the transmitted pulse set to generate an output comprising probe signals in a plurality of velocity frames; and applying a corresponding predetermined compensation phase vector to the probe signal in each of the plurality of velocity frames. The corresponding predetermined compensation phase vector applied to the probe signal in each velocity frame may include at least one of a first component proportional to the velocity of the velocity frame or a second component for compensating for phase compensation errors associated with Doppler velocity aliasing. Attached Figure Description

[0010] Figure 1A An example of using automotive radar to measure the distance and speed of a vehicle according to an embodiment is shown.

[0011] Figure 1B An example of the phase shift between the transmitted pulse and the echo is shown.

[0012] Figure 2A An example of radar data collection in a pulse-Doppler radar system is shown.

[0013] Figure 2B An example of a Doppler processing subsystem in a pulse Doppler radar system is shown.

[0014] Figure 3A An example of a data matrix including pulse echoes received from different distances is shown.

[0015] Figure 3B It shows that by... Figure 3A The example shown is a distance Doppler map generated by performing a Fast Fourier Transform (FFT) on the data matrix.

[0016] Figure 4A An example of a pulse transmission sequence in an example of a multiple-input multiple-output (MIMO) radar according to certain embodiments is shown.

[0017] Figure 4B An example of a data cube comprising sub-pulse echoes from multiple pulses received by a MIMO radar at different distances is shown.

[0018] Figure 5A This includes images illustrating the measurement of distance and speed of objects in an environment using automotive radar, according to certain embodiments.

[0019] Figure 5B Including what is shown in Figure 5A The example shown is a range-Doppler image of an object's distance and velocity measured by a Doppler radar on a vehicle, illustrating an environment where such images are displayed.

[0020] Figure 5C Including what is shown in Figure 5A An example of a diagram showing the position of a dynamic object in an environment as measured by a Doppler radar on a vehicle.

[0021] Figure 5D Including what is shown in Figure 5A An example of a diagram showing the location of an object in an environment as measured by a Doppler radar on a vehicle.

[0022] Figure 6A This includes an example showing a range Doppler plot of the gain loss of a fast-moving object as measured by Doppler radar.

[0023] Figure 6B An example is shown showing the relationship between the gain and velocity of an object as measured by Doppler radar.

[0024] Figure 7A An example of a method for compensating for residual phase shift in a Doppler radar according to certain embodiments is shown.

[0025] Figure 7B An example of a distance Doppler plot is shown.

[0026] Figure 7C An example of the result of compensating for residual phase in a Doppler radar according to certain embodiments is shown.

[0027] Figure 8 Velocity aliasing is shown in an example of Doppler radar.

[0028] Figure 9 An example is shown of the result of compensating for the first type of residual phase in the presence of Doppler aliasing according to certain embodiments.

[0029] Figure 10 An example is shown of the results of compensating for residual phase in the presence of Doppler aliasing according to certain embodiments.

[0030] Figure 11 An example of a motion-compensated Doppler processing system according to certain embodiments is shown.

[0031] Figure 12 An example of the output of a motion-compensated Doppler processing system according to certain embodiments is shown.

[0032] Figure 13 Includes flowcharts illustrating examples of methods for compensating residual phase in a Doppler radar system according to certain embodiments.

[0033] Figure 14 This is a block diagram of an embodiment of a computer system that can be used in the embodiments described herein.

[0034] Depending on the implementation of certain examples, the same reference numerals in the figures may indicate the same elements. Detailed Implementation

[0035] The technologies disclosed herein generally relate to radar, and more specifically to motion compensation techniques for improving the performance of Doppler radar in detecting high-speed objects. Various embodiments of the invention are described herein, including devices, systems, subsystems, methods, instructions, code, programs, units, engines, computer program products, computer-readable storage media, data carrier signals, etc.

[0036] Doppler radar systems, such as automotive radar systems, may suffer gain loss when detecting moving targets, where the gain loss may be related to the speed of the moving target. Furthermore, pulse-Doppler radar may be ambiguous at either range or Doppler frequency, and the ambiguity may depend on the chosen pulse repetition frequency (PRF). For example, Doppler ambiguity may occur when the target's speed exceeds the maximum Doppler velocity measurement interval, which may be proportional to the PRF. Therefore, pulse-Doppler radar can only effectively detect targets moving at a certain maximum speed. Consequently, fast-moving targets may be detected as very weak targets (e.g., a small vehicle when it is actually a large vehicle), or may not be detected at all, potentially leading to life-threatening risks. Existing techniques can assume that radar output includes inherent ambiguity, and that probabilistic tools in the perception layer can be used to identify this ambiguity. However, the performance of these techniques is limited by the quality of the radar output. If the radar does not detect a target, the perception layer will not be aware of its presence. Therefore, it is desirable to minimize the impact of gain loss from high-speed objects at the radar receiver level.

[0037] The techniques disclosed herein can compensate for or reduce gain loss in pulse-Doppler radars, such as automotive multiple-input multiple-output (MIMO) radars. Gain loss can be at least partially caused by residual phase, which can include at least one of two types. The first type, referred to herein as first-type residual phase, is associated with each moving target and can be proportional to the speed of the moving target. The second type, referred to herein as second-type residual phase, is associated with Doppler ambiguity of targets moving faster than the radar's maximum speed and can be similar for targets with speeds within a certain range. According to certain embodiments disclosed herein, for example, after the received pulse signal has been cross-correlated with the transmitted signal, two compensation phases can be applied to the received pulse signal, or two compensation phases can be applied to the Doppler FFT result of the received pulse signal. These two compensation phases can be selected as opposite phases of the first-type residual phase and opposite phases of the second-type residual phase, respectively. Therefore, if any type of residual phase appears in the received signal, it can be canceled out by the opposite phase in the compensation phase.

[0038] According to some embodiments, in order to determine the appropriate compensation phase to be applied to a received pulse signal or the output signal of a Doppler FFT of the received pulse signal when the target velocity is unknown in advance, a compensation phase corresponding to all possible target velocities can be predetermined and applied to the detection signal (e.g., a cross-correlation pulse or the output signal of a Doppler FFT). Therefore, if a target with a certain velocity is present in the environment, a specific predetermined compensation phase for that velocity can be applied to the corresponding detection signal (e.g., a cross-correlation pulse or the output signal of a Doppler FFT). If there is no target moving at a certain velocity in the environment, and therefore the power of the detection signal associated with that velocity is very low, applying the compensation phase to the detection signal will not cause any harmful side effects. In this way, the residual phase of a target present in the environment can be compensated with little or no side effects.

[0039] Several illustrative embodiments will now be described with reference to the accompanying drawings, which are also part of the embodiments. While some embodiments that may implement one or more aspects of this disclosure have been described below, other embodiments may be used, and various modifications may be made without departing from the scope of this disclosure.

[0040] As used herein, "RF signal" refers to electromagnetic waves that transmit information through space between a transmitter (or transmitting device) and a receiver (or receiving device). As used herein, a transmitter may transmit a single "RF signal" or multiple "RF signals" to a receiver. However, due to the propagation characteristics of RF signals through multipath channels, a receiver may receive multiple "RF signals" corresponding to each transmitted RF signal. The same transmitted RF signal on different paths between the transmitter and receiver can be referred to as a "multipath" RF signal.

[0041] In radar systems, a signal source can transmit RF signals toward a target. The Doppler effect can occur when the signal source and / or the target move relative to each other. For example, as the signal source and target get closer, the arrival time of each wave at the target may be slightly shorter than the previous wave. Therefore, the time between successive wave peaks at the target (or the signal source when reflected back) may decrease, resulting in an increase in the frequency of the received RF signal. Conversely, as the distance between the signal source and the target increases, the arrival time of each wave at the target may be slightly longer than the previous wave. Therefore, the time between successive wave peaks at the target (or the returning signal source) may increase, resulting in a decrease in the frequency of the received signal. The Doppler effect has been used in radar systems to measure target velocity. During radar system operation, a radar beam (e.g., a pulse with a specific carrier frequency) is emitted toward a target, such as a moving vehicle approaching or moving away from the radar system. The Doppler shift can be measured and used to calculate the target's velocity.

[0042] Figure 1AAn example of measuring the distance and speed of a vehicle using Doppler radar according to an embodiment is shown. Vehicle 110 may include an automotive Doppler radar mounted thereon, which can transmit RF signals 130 toward a target vehicle 120. The target vehicle 120 may have a speed v relative to vehicle 110. target The RF signal 130 may include a pulse, which includes a carrier signal modulated by, for example, a chirped signal. The pulse may have a certain pulse width. The target vehicle 120 may reflect a portion of the RF signal 130. Based on the time delay between the transmission of the RF signal 130 by the automotive Doppler radar transmitter at vehicle 110 and the reception of the returned portion of the RF signal 130 by the automotive Doppler radar receiver, the distance between vehicle 110 and the target vehicle 120 can be determined. Based on the frequency and / or phase shift of the returned portion of the RF signal 130 caused by the Doppler effect, the relative speed of the target vehicle 120 relative to vehicle 110 can be determined.

[0043] Because the Doppler shift affects the waves incident on the target and the waves reflected back to the car's Doppler radar, the change in frequency (Δf) observed by the radar transmitting a signal with a carrier frequency (f0) due to the target moving at a relative velocity v can be twice that perceived by the target, and can be determined according to Δf = 2v × f0 / c, where c is the velocity of the electromagnetic wave in free space.

[0044] Pulse Doppler radar can transmit a series of pulses separated from the radar in the radial direction by a distance d. The distance d can be a function of the pulse transmission rate, commonly referred to as the pulse repetition frequency (PRF), where the reciprocal of the PRF is the pulse repetition interval (PRI)T. PRI The spacing d between adjacent pulses can be calculated using d = c / PRF = c × T. PRI To determine this, some energy from the transmitted pulse may be reflected or deflected back to the radar. The maximum distance a pulse can travel and return to before transmitting the next pulse is half the separation distance d. This maximum distance can be defined as R. max = c / (2×PRF). When the target's range is greater than the maximum range, range folding may occur, and the target's pulse echo may not be distinguishable from the pulse echo emitted later by a target at a shorter distance from the radar. One way to mitigate range folding is to reduce the PRF until the maximum range R... max Beyond the entire scattering region. The achievable range resolution (also known as blind range) of pulse Doppler radar can be R... min = cτ / 2, where τ is the pulse width.

[0045] The Doppler velocity resolution Δv (in mph or m / s) of a pulse Doppler radar may depend on the pulse repetition interval T. PRIThe number of pulses N and the wavelength λ of the carrier signal, i.e. Radar may be able to distinguish two targets with a velocity difference greater than Δv. Pulse repetition interval T PRI The product of the pulse number N and the pulse repetition interval T is called the coherent processing interval (CPI). A larger CPI produces better resolution (i.e., smaller Δv). This can be achieved by increasing the pulse repetition interval T. PRI (This may also increase R) max The CPI can be increased by adding and / or increasing the number of pulses N. However, the CPI may not be long enough because the driver or driving system needs to be informed of the target's presence as quickly as possible so that the driver or driving system can respond in a timely manner.

[0046] The maximum Doppler velocity measurement interval V of the Doppler radar system max (Also known as the Nyquist interval) is also related to the radar wavelength λ of the PRF and the carrier signal, i.e., V max = ±PRF×λ / 4. Radar can only definitively measure intervals V at maximum Doppler velocities. max For moving targets, the maximum Doppler velocity measurement interval can also be determined by... Confirmed. In automotive Doppler radar, V max This could be, for example, around 50 mph or higher. Due to Doppler aliasing, compared to V... max A faster-moving target may appear to be moving at a lower speed. When the PRF decreases, V... max It may also decrease, and Doppler velocity aliasing may begin to appear at lower velocities.

[0047] Increasing PRF (or decreasing PRI) may increase V max However, this may reduce the maximum distance R. max This will also reduce velocity resolution (increase Δv). For Doppler radar systems with specific wavelengths, V max and R max The product is constant ±c×λ / 8. Therefore, increasing R... max It may reduce V max Conversely, the same applies. V max and R max The trade-off between the two is known as the "Doppler dilemma".

[0048] Figure 1B An example of the phase shift between the transmitted pulse and the returned echo is shown. Figure 1BIn the example shown, the radar on the first vehicle 140 can transmit a first pulse 160 to the second vehicle 150. The first pulse 160 can be partially reflected by the second vehicle 150, and the reflected portion of the first pulse 160 can later be received by the radar on the first vehicle 140 as an echo pulse 162. When there is a relative velocity V between the first vehicle 140 and the second vehicle 150, when the second pulse 170 is transmitted after a time interval T following the transmission of the first pulse 160, the distance between the first vehicle 140 and the second vehicle 150 can change by a value VT. Therefore, before the second pulse 170 is received by the radar on the first vehicle 140, the second pulse 170 may need to travel a distance 2 × VT longer than the first pulse 160 (or a wavelength 2 × VT / λ longer than the first pulse 160). Thus, the echo pulse 172 of the second pulse 170, reflected by the second vehicle 150 and received by the first vehicle 140, can have a phase shift Δθ = 2π × (2VT / λ) radians compared to the echo pulse 162. (Doppler shift f) d Based on Determined by phase shift.

[0049] The amplitude of the echo pulse received by the radar can be used Let I0 be the amplitude of the pulse returning from the target at V = 0, x0 be the distance between the radar and the target, θ0 be the phase of the first returned pulse, T be the time interval between the first and second transmitted pulses, and Δθ = 4πVT / λ be the relative phase shift of the second returned pulse (e.g., echo pulse 172) relative to the first returned pulse (e.g., echo pulse 162). Therefore, the power of the returned pulse received by the radar receiver can be a function of the phase shift Δθ, which in turn is a function of the velocity V of the target (e.g., the second vehicle 150).

[0050] Figure 2A An example of radar data collection in a pulse-Doppler radar system is shown. For example... Figure 2A As shown, for each of the N pulses 210 in the coherent processing interval, the return pulse (also called the echo) can be sampled at a certain sampling interval during the pulse repetition interval to capture L samples 212 before the radar receiver receives the return pulse of the next transmitted pulse 210. The return pulses can be returned by objects at different distances, and the N return pulses out of the N transmitted pulses returning from the same distance 214 can have different phase shifts due to the relative motion of the target. For example, by performing a Fast Fourier Transform (FFT), the N return pulses out of the N transmitted pulses returning from each distance 214 can be captured and processed to convert the time-domain information into Doppler frequency or velocity.

[0051] Figure 2BAn example of a Doppler processing subsystem 200 in a pulse-Doppler radar system for processing measurement pulses is shown. The Doppler processing subsystem 200 may include a Doppler FFT unit 230. The Doppler FFT unit 230 may receive capture samples 220 for each of N transmitted pulses and perform multiple FFTs on the capture samples 220 to convert time-domain information into Doppler frequencies or velocities in different velocity bins 240. For example, if L samples are captured for each of the N transmitted pulses, L one-dimensional Doppler FFTs can be performed in the Doppler FFT unit 230, where the N capture samples corresponding to the N transmitted pulses returning from the same distance can be used for each one-dimensional Doppler FFT. The L one-dimensional Doppler FFTs can be performed as a two-dimensional Doppler FFT.

[0052] Figure 3A An example of a data matrix 300 including pulse echoes from different distances is shown. Figure 3A In the diagram, the horizontal axis of data matrix 300 can correspond to the transmitted pulses in the coherent processing interval. Pulses are transmitted at the pulse repetition frequency described above, where the time delay between two consecutive pulses is the pulse repetition interval. The total time for transmitting N pulses is the coherent processing interval. The vertical axis of data matrix 300 can correspond to the captured echoes, which can be captured at a sampling interval much shorter than the pulse repetition interval. Therefore, the horizontal axis of data matrix 300 can be referred to as slow time, and the vertical axis as fast time. Captured samples from transmitted pulses may fall into different range bins because they return from different range intervals. In the example shown, each column 302 of data matrix 300 can correspond to transmitted pulse n, where n is taken from 1 to N. L samples can be captured for each of the N transmitted pulses. Therefore, each column 302 can include L range bins. Each row 304 of data matrix 300 can correspond to the same range bin for the N transmitted pulses.

[0053] A Doppler FFT can be performed on each row (304) of the data matrix 300. For example, if the N captured samples at a distance of bin l are {x} l,0 x l,1 , ...x l,N-1 Then, an FFT of length N for N captured samples can be obtained as follows:

[0054]

[0055] Where X l,nThe detected signal is located in the distance frame l and the frequency (or velocity) frame n, where n can be -[N / 2], -[N / 2]+1, ..., [(N-1) / 2]-1, or [(N-1) / 2], which can correspond to the first to the Nth frequency frames. In other words, after the Doppler FFT, there can be the same number of output signals as the captured samples, where the output signals can include frequency or velocity information in their phase.

[0056] Figure 3B It shows that by... Figure 3A The example shown is a range-Doppler map 330 generated by performing a Doppler FFT on the data matrix 300. As described above, for a moving target, return echoes corresponding to the same range bin but from different pulses can have different phase shifts, which can be converted into frequency information by a Doppler FFT. As shown, an FFT can be performed on echoes from the same range interval over a coherent processing interval, during which N pulses can be transmitted and returned. The frequency domain information of the FFT result can be filtered into N frequency bins (or velocity bins). In the example shown, two moving targets at the same range interval but with different velocities can be represented by two elements in the same range bin but different velocity bins of the range-Doppler map 330, where the first moving target can move away from the radar at a first velocity (e.g., represented by a negative relative velocity) and can be represented by element 332 in the range-Doppler map 330, while the second moving target can approach the radar at a second velocity (e.g., represented by a positive relative velocity) and can be represented by element 334 in the range-Doppler map 330.

[0057] In many radar systems, range FFT and / or direction-of-arrival (DoA) FFT can also be performed. This allows the generation of a three-dimensional (3D) array of spectral values, also known as a radar 3D image, which can be used to produce range, velocity, and direction-of-arrival estimates for targets within the radar system. In some radar systems, the transmitted pulses can be modulated, for example, by a chirped signal, to distinguish the returning echoes from different transmitted pulses.

[0058] As mentioned above, the range resolution achievable by pulse Doppler radar can be R min = cτ / 2, where τ is the pulse width. Radars using narrower pulses can achieve better range resolution. In Time Division Multiple-Input Multiple-Output (TDM-MIMO) radar, each pulse can include multiple short sub-pulses transmitted over multiple MIMO periods (or time slots). TDM-MIMO radar can transmit short sub-pulses through an antenna subarray in each time slot and can cycle between each antenna subarray of the radar to transmit multiple sub-pulses in each pulse. MIMO radar can achieve better spatial (e.g., range and angle) and Doppler (e.g., velocity) resolution.

[0059] Figure 4A An example of a pulse transmission sequence in an example of a MIMO radar according to certain embodiments is shown. As described above, in a TDM-MIMO radar, each of the N pulses 410 in the coherent processing interval may include a plurality of (e.g., P) MIMO periods 412 (or time slots), wherein short sub-pulses may be transmitted during each MIMO period 412 by, for example, an antenna array or a sub-array. Similarly, as mentioned above regarding... Figure 2A and Figure 3A As described above, the echoes from each short sub-pulse at different distances can be captured by a radar receiver at a certain sampling interval (fast time). Therefore, the above reference can be generated for each of the P MIMO cycles spanning N pulses. Figure 3A The two-dimensional data matrix is ​​described, where one dimension corresponds to the impulse (slow time) and the other dimension corresponds to the distance bin (fast time). Therefore, a three-dimensional data cube can be generated for P MIMO cycles, where the third dimension corresponds to the MIMO cycle (intermediate time).

[0060] Figure 4B An example of a data cube 420 comprising sub-pulse echoes from multiple pulses at different distances is shown. Compared to a two-dimensional data matrix 300, the data cube 420 may include an additional dimension corresponding to the MIMO period (intermediate time). Each layer 422 in the data cube 420 may correspond to the p-th MIMO period of the pulse and may be similar to the two-dimensional data matrix 300 shown in Figure 3. In the illustrated example, there may be N pulses in the CPI, each pulse may include P sub-pulses transmitted in P MIMO periods, and L echo signals may be captured for each sub-pulse transmitted in the MIMO period.

[0061] For reference Figure 3A and 3B As described above, a two-dimensional FFT can be performed on each layer 422 of the data cube 420, where each layer 422 can correspond to one MIMO cycle spanning all N pulses. For example, L one-dimensional FFTs can be performed as described above, where each one-dimensional FFT can be performed on N echoes, each echo corresponding to a sub-pulse in each of the N pulses. The two-dimensional FFT of each layer 422 (or MIMO cycle) can produce, for example,... Figure 3B The corresponding range Doppler image is shown. Then, the P range Doppler images generated using the P-layer data (corresponding to P MIMO cycles) in data cube 420 can be averaged or merged to generate a global range Doppler image. Due to the high resolution and large field of view required for imaging radar in automotive applications, many automotive imaging radars can utilize the aforementioned TDM-MIMO cycles.

[0062] Figure 5A Image 510 is included, illustrating the use of automotive radar to measure the distance and velocity of objects in an environment according to certain embodiments. In the illustrated example, a first vehicle 512 may have an automotive radar mounted thereon, which can be used to detect objects in the surrounding environment and measure the relative velocity of the detected objects. In the illustrated example, two other vehicles 514 and 516 may be traveling on a road, where static objects, such as trees, lampposts, or other stationary objects, may be on either side of the road.

[0063] Figure 5B Including an example at a distance of 520 from the Doppler graph, which shows in Figure 5A The distance and velocity of objects in the environment shown are measured by the Doppler radar on the first vehicle 512. Figure 5B The range and relative velocity of objects detected in the environment are shown, including both static and dynamic objects. For example, Figure 5B Two bright spots 522 and 524, corresponding to vehicles 514 and 516 respectively, are shown. Bright spots 522 and 524 can correspond to different distances and similar speeds. For example, bright spot 522 can indicate that vehicle 514 is approximately 150 meters away from the first vehicle 512 and is approaching the first vehicle 512 at a relative speed of approximately 15 meters per second (m / s). Bright spot 524 can indicate that vehicle 516 is approximately 250 meters away from the first vehicle 512 and is approaching the first vehicle 512 at a relative speed of approximately 15 meters per second (m / s). A static object such as a tree may approach the first vehicle 512 due to the movement of the first vehicle 512 and can be shown by bright spots corresponding to different distances but the same speed (e.g., approximately 8 m / s, which is the speed of the first vehicle 512).

[0064] Figure 5C Including the example in Figure 530, which shows in Figure 5A The image shows the position of a moving object in the environment as measured by a Doppler radar on the first vehicle 512. In Figure 530, the y-axis corresponds to the horizontal direction, and the x-axis corresponds to the vertical (or longitudinal) direction. Figure 530 only shows moving objects. In the example shown, two bright spots 532 and 534 are shown, which could correspond to vehicles 514 and 516, respectively. Figure 530 shows vehicles 514 and 516 approximately aligned with the first vehicle 512 in the horizontal direction and approximately 150 meters and 250 meters away from the first vehicle 512 in the longitudinal direction, respectively.

[0065] Figure 5D Including the example in Figure 540, Figure 540 shows in Figure 5AThe image shows the positions of objects in the environment as measured by Doppler radar on the first vehicle 512. In Figure 540, the y-axis corresponds to the horizontal direction, and the x-axis corresponds to the vertical (or longitudinal) direction. Figure 540 shows all dynamic and static objects detected by the Doppler radar, including objects from different viewpoints.

[0066] Figure 6A An example at a range of 600 Doppler plots illustrates the gain loss of a fast-moving object as measured by Doppler radar. As mentioned above, the power of the returned pulse can be a function of the phase shift, which in turn can depend on the velocity of the object. A moving object can impose a residual phase between sub-pulses in a MIMO cycle, and equivalently between pulses. The residual phase of the echo of the p-th sub-pulse transmitted in the p-th MIMO cycle can be a function of the target velocity and can increase as the target moves faster, according to the following equation:

[0067]

[0068] Where T PRI It is the pulse repetition interval, ν target Δv is the relative velocity of the target, k is the Doppler velocity basket number (or pulse number), and Δv is the Doppler velocity resolution as described above. This can be referred to as the first type of residual phase, and it can be applied to any v. target Both exist. The detection power of a moving target can be a function of the residual phase of the first kind, because the gain can be reduced by a factor. Therefore, the gain loss may only be zero for static targets. For faster targets, the residual phase may be larger, and the gain loss may be even higher. For very fast targets, the gain loss may be too high to detect. Therefore, as... Figure 6A As shown, compared to similar targets at similar distances but with lower speeds, faster targets, such as target 610, may have lower power in the figure, and thus lower brightness.

[0069] Figure 6B Includes Figure 605, which shows an example of the relationship between the gain and velocity of an object as measured by Doppler radar. Figure 6B Curve 620 in the diagram shows that as the target's velocity increases, the power of the detection signal can be gradually reduced to a very small value. For example, point 622 on curve 620 indicates that, at the corresponding velocity, the gain loss can be approximately 10 dB.

[0070] According to some embodiments, the first type of residual phase can be compensated by adding a compensation phase to the phase of the probe signal, wherein the compensation phase can be opposite to the first type of residual phase, thereby removing the first type of residual phase.

[0071] Figure 7A An example of a method for compensating for residual phase in a Doppler radar according to certain embodiments is shown. As illustrated, the phase of the detected signal (e.g., in the case of a reference as shown above) is... Figure 4B The velocity frame of the range-Doppler map generated by performing a Doppler FFT during the MIMO cycle can include two items. The first item It is the phase of the transmitted signal. (Second term) This is the first type of residual phase caused by the target's motion, as described above. Therefore, if the target's velocity v target Given that, it can be done by multiplying the detected signal by... To compensate for the phase This phase is added to the phase of the detected signal. After the phase-compensated signal is cross-correlated with the transmitted signal, the residual phase can be canceled out by the compensated phase. Therefore, for targets at all velocities, the total phase of the detected signal may become...

[0072] However, the target's velocity may not be known in advance, and therefore the compensation phase may also not be known beforehand. Therefore, it is difficult to directly apply residual phase compensation to the captured time-domain signal before knowing the velocity of the target to be compensated. According to some embodiments, the compensation phase can be determined for each column (or velocity basket) of the corresponding range-Doppler plot for each MIMO cycle. Thus, the phase shift of all possible target velocities can be predetermined and applied to the probe signal, such as a cross-correlation pulse or the output signal of a Doppler FFT. If a target with a specific velocity exists in the environment, a specific predetermined compensation phase corresponding to that velocity can be applied to the corresponding probe signal to compensate for the residual phase. If no target is moving at a certain velocity in the environment, and therefore the power of the probe signal associated with that velocity is very low, then applying the predetermined compensation phase for that velocity to the corresponding probe signal will not cause any harmful side effects. In this way, the residual phase of a target moving at any velocity in the environment can be compensated with little or no side effects. Thus, the power of the probe signal can be equalized for similar targets with any velocity.

[0073] Figure 7B An example of a range-Doppler map 700 is shown. Each point in the range-Doppler map 700 can correspond to an object at a certain distance interval from the Doppler radar, which has a certain relative velocity with respect to the Doppler radar. Each distance interval can correspond to a sampling interval, and each velocity interval can correspond to the k-th velocity basket in the N velocity baskets of the Doppler FFT. A compensated phase can be determined for each column in the range-Doppler map 700 (corresponding to the corresponding velocity basket). For example, points 710, 720, and 730 in the range-Doppler map 700 can be in different velocity baskets and can have different associated first-type residual phases.

[0074] In the aforementioned TDM-MIMO Doppler radar, determining the residual phase of the detected signal within the k-th velocity frame of the range-Doppler graph for the p-th MIMO cycle (or corresponding to the p-th MIMO cycle and the k-th pulse) can be... or Therefore, the compensated phase can be opposite to the residual phase, such as - Therefore, as Figure 7A As shown, for the signal detected at the k-th velocity bin in the range Doppler plot during the p-th MIMO cycle, the compensation phase for the first type of residual phase can be set to φ0kp, where φ0 can be a constant, such that:

[0075] φ+Δφ(v target )-φ0kp=φ.

[0076] Since the first type of residual phase can be for the p-th MIMO cycle and the k-th velocity bin... or Therefore, φ0 can be set to because φ0 can be set to

[0077] Figure 7C Figure 740 illustrates the results of an example of compensating for residual phase shift in a Doppler radar according to certain embodiments. In Figure 740, curve 750 shows the power of the radar receiver's detected signal (without motion compensation) as a function of the velocity of the target causing the detected signal. As described above, as curve 750 shows, the power of the detected signal can decrease with increasing target velocity. Line 760 shows the power of the radar receiver's detected signal with the aforementioned first type of residual phase compensation as a function of the velocity of the target causing the detected signal. Figure 7A and Figure 7C As shown in line 760, if the target velocity can be accurately determined, then after the first type of residual phase compensation, the phase and power of the detection signal can remain constant for different target velocities.

[0078] However, as mentioned above, radar can only definitively measure the distance V at maximum Doppler velocity. max The target moving at a speed, among which Due to Doppler aliasing, the moving speed exceeds the maximum speed V. max The target may appear to be moving at a low speed.

[0079] Figure 8 This includes graph 800, which illustrates an example of velocity aliasing in Doppler radar. The horizontal axis of graph 800 corresponds to the actual velocity of the target, and the vertical axis corresponds to the target velocity measured by the Doppler radar. Figure 8 Line 810 shows the expected measured velocity for each corresponding actual velocity of the target. Curve 820 shows the measured velocity for each corresponding actual velocity of the target. Figure 8 In the example shown, the V of the Doppler radar max Approximately 50 mph. Therefore, when the target's actual speed is between 0 and approximately 50 mph, the measured speed can be the same as the actual speed. When the target's actual speed is between approximately 50 and approximately 100 mph, the measured speed can be between approximately -50 and 0 mph. When the target's actual speed is between approximately 100 and approximately 150 mph, the measured speed can be between 0 and 50 mph. For example, when the V of the Doppler radar... max For 50 mph and v target At approximately 130 mph, a target measured by Doppler radar may appear to be moving at only about 30 mph.

[0080] Figure 8 It is shown that for V greater than radar max For a target moving at a speed that differs from its measured speed, the actual velocity of the target may differ from its measured velocity. Therefore, the actual first-type residual phase of the detection signal for a fast-moving target can be... However, the measured speed v measured It can be different from the actual speed v actual Therefore, the compensation phase is determined based on the measured velocity. It can be different Therefore, when the compensation phase determined for the measured velocity is used to compensate for the first type of residual phase, the residual phase after compensation for the first type of residual phase can be:

[0081]

[0082] It is not equal to Because v measured Not equal to v actual Additional items This is caused by Doppler aliasing and can be referred to as the second type of residual phase in this paper. Therefore, the aforementioned first type of residual phase compensation technique may not be able to eliminate velocities greater than the maximum Doppler velocity measurement interval V. max The residual phase of a fast target.

[0083] The second type of residual phase of the probe signal in the p-th range Doppler map (corresponding to the p-th MIMO cycle) can be determined as: Where 'a' is the aliasing factor corresponding to a series of velocities, such as in n×V max and (n+1)×V max The speed between. For speeds greater than V. maxFor fast-moving targets, the residual phase of type II may cause infinite gain loss, thus potentially preventing the target from being detected, regardless of the target's size and / or distance.

[0084] Figure 9 Figure 900 is included, which shows an example of the results of compensating for the first type of residual phase in the presence of Doppler aliasing. Figure 900 includes a first region 910, where the velocity is below V. max Furthermore, the residual phase caused by the target motion can be completely eliminated through the first type of residual phase compensation described above, making the gain loss approximately zero. Figure 900 also includes a second region 920, where the velocity is greater than V. max Furthermore, using the measured velocity to compensate for the first type of residual phase can cause the amplitude of the probe signal to approach zero. Figure 9 Line 930 illustrates an example of a lower threshold power that a radar receiver can detect. When the power of the target's detection signal is below line 930, the target may not be detected. Therefore, a Doppler radar may not detect a target with velocity in the second region 920.

[0085] According to some embodiments, the second phase compensation term φ1p can be used to compensate for a second type of residual phase of the probe signal associated with the p-th MIMO cycle. Since the target velocity is in V... max and 2V max The probability between them may be higher than the target's speed at 2V. max and 3V max The probability between these two values ​​is such that φ1p can be chosen to be close to V. max and 2V max The second kind of residual phase between velocities, thus:

[0086]

[0087] in It can be a very small value. Although the second phase term φ1p may not fully compensate for the second type of residual phase, and for values ​​below V... max The speed may result in some gain loss (because below V) max The velocity detection signal has no second-type residual phase, but the gain loss may be small, such as less than about 3dB. In some embodiments, φ1p can be set as described above. The aliasing factor 'a' can be chosen to be a value less than 1, and φ1 can be set to...

[0088] Thus, both the first and second type of residual phases can be obtained by multiplying the detected signal in the k-th velocity bin of the range Doppler graph of the p-th MIMO cycle by... To compensate, -φ0kp can be opposite to the first type of residual phase mentioned above, and -φ1p can be opposite to the second type of residual phase. For example, φ0 can be constant. or φ1 can be constant After first-type and second-type residual phase compensation, the residual phase of the probe signal can be minimized or canceled.

[0089] Figure 10 Figure 1000 illustrates an example of the results of compensating for residual phase in the presence of Doppler aliasing according to certain embodiments. As described above, this can be achieved by multiplying the detected signal in the k-th velocity bin of the range Doppler map during the p-th MIMO cycle by... To compensate for residual phase. In Figure 1000, curve 1010 shows the power of the radar receiver's detection signal without motion compensation, as a function of the target velocity causing the detection signal. As mentioned above, the power of the detection signal can decrease with increasing target velocity. Dashed line 1020 shows the power of the radar receiver's detection signal with the aforementioned first type of residual phase compensation, as a function of the target velocity causing the detection signal. Dashed line 1020 shows the power of the radar receiver's detection signal for velocities less than V. max For targets with speeds greater than V, residual phase can be completely removed. max For targets with such high gain, the gain loss may be so large that the target may not be detected. Figure 10 Line 1030 illustrates the power of the detection signal from a radar receiver with the aforementioned first and second types of residual phase compensation, as a function of the target velocity causing the detection signal. Line 1030 shows velocities less than V. max The target gain loss and velocity are greater than V max The target gain loss can be flattened and can be a small, constant gain loss of less than approximately 3 dB.

[0090] Figure 11 An example of a motion-compensated Doppler processing system 1100 according to certain embodiments is shown. The Doppler processing system 1100 can be implemented using one or more computer systems, such as those referenced below. Figure 14One or more computer systems 1400 are described in more detail. The Doppler processing system 1100 may include a MIMO radar processing subsystem 1110 similar to the Doppler processing subsystem 200. The MIMO radar processing subsystem 1110 can receive the captured echoes of N pulses, each pulse comprising P subpulses transmitted over P MIMO cycles. The captured echo of each of the P subpulses in each of the N pulses can be cross-correlated with the transmitted subpulses using cross-correlation units 1112-1, 1112-2, ..., or 1112-N to determine the time delay of the echo from the target, thereby determining the target's range.

[0091] The MIMO radar processing subsystem 1110 may further include a Doppler FFT unit 1114. As described above, the Doppler FFT unit 1114 can perform multiple FFTs on the captured echoes of N pulses, each pulse comprising P sub-pulses transmitted in P MIMO cycles, to convert the time-domain signal into Doppler frequencies or velocities in different velocity baskets. For example, as referenced above... Figures 3A-4B As described above, for all N pulses, a two-dimensional Doppler FFT can be performed on the capture echo of the p-th sub-pulse transmitted in the p-th MIMO cycle, where p can be an integer from 1 to P. The output of the two-dimensional Doppler FFT for each MIMO cycle can be filtered to... Figure 3B The N Doppler frequencies or velocity bins are shown. Therefore, a range Doppler map can be generated for each of the P MIMO cycles based on the results of the two-dimensional Doppler FFT for each of the P MIMO cycles.

[0092] The motion compensation subsystem 1120 of the Doppler processing system 1100 can perform the first and second types of residual phase compensation described above using a set of motion compensation engines 1122-1, 1122-2, ..., and 1122-N. Each motion compensation engine 1122-1, 1122-2, ..., or 1122-N can apply residual phase compensation to targets having velocities in the same velocity bin. For example, as described above, the compensation phase -2π(φ0kp+φ1p) can be applied to the probed signal in the k-th velocity bin on the range Doppler graph of the p-th MIMO cycle, where φ0 and φ1 can be constant values ​​as described above. In one example, this can be achieved by multiplying the probed signal by... The compensation phase is then applied to the detection signal. The same compensation phase can be applied to each column (velocity basket) of the range Doppler graph, thus similarly compensating for the residual phase of the detection signal for targets with the same velocity.

[0093] After motion compensation is performed on each of the motion compensation engine sets 1122-1, 1122-2, ..., and 1122-N, the residual phase of the detection signal can be eliminated or minimized, so that the power of the detection signal representing a target with a velocity in any velocity basket can be attenuated or attenuated to a minimum. Then, the range Doppler maps of the P motion-compensated motion cycles can be averaged, or otherwise incorporated into the total range Doppler map, such as... Figure 5B , 6A Or as shown in 7B.

[0094] In some embodiments, phase compensation can be performed before the Doppler FFT. For example, when the number of pulses (N) is equal to the reference above... Figures 3A-3B When describing the length of each one-dimensional Doppler FFT, the received signal corresponding to the p-th MIMO period of the k-th pulse (e.g., after cross-correction) can be multiplied by Where φ′0 and φ′1 are constant values. When the number of pulses (N) is different from the length of the one-dimensional Doppler FFT, the received signal corresponding to the p-th MIMO period of the k-th pulse can be multiplied by... φ″0 and φ″1 are constant values ​​and can be determined based on the number of pulses rather than the length of the one-dimensional Doppler FFT.

[0095] Figure 12 Figure 1200 includes an example of the output of a motion-compensated Doppler processing system (e.g., Doppler processing system 1100) according to certain embodiments. In the illustrated example, a target with velocity v2 may be present in the environment and can be detected. After motion compensation for all velocity bins as described above, the echo from the target can be detected with no gain loss or minimal gain loss due to first-type and second-type residual phase compensation. Since a target with velocity in other frequency bins may not be present in the environment, the signal power of the signal in other velocity bins may be very low, and motion compensation (e.g., multiplying by) It may not, or may only minimally, affect the signal power of signals in other speed baskets.

[0096] Figure 13 Including flowchart 1300, which illustrates an example of a method for compensating for residual phase in a Doppler radar according to certain embodiments. Used for implementation Figure 13 The components illustrating the functions shown in one or more boxes can be implemented by hardware and / or software components of a Doppler processing system or computer system. Example components of a Doppler processing system are described above. Figure 11 The example components of the computer system are shown in [the diagram]. Figure 14 As shown in the diagram, this will be described in more detail below.

[0097] In block 1310, a Doppler processing system, such as Doppler processing system 1100, can receive a corresponding set of echo signals reflected from multiple spacing distances for each transmitted pulse in a transmitted pulse set. The Doppler processing system can be part of a Doppler radar system. The Doppler radar system can include, for example, a MIMO radar system, where each transmitted pulse in the transmitted pulse set can include a set of subpulses transmitted in a MIMO period set, and the corresponding echo signal set can include a corresponding subset of echo signals for each subpulse in the transmitted pulse set. Each echo signal in the corresponding echo signal subset can correspond to a corresponding spacing distance of multiple spacing distances. In some examples, the Doppler radar system can include an antenna array, where each antenna or antenna subarray of the antenna array can be configured to transmit a corresponding subpulse of the subpulse set in a corresponding time slot of the time slot set.

[0098] Optionally, in block 1320, the Doppler processing system, more specifically, one or more cross-correlation units (e.g., cross-correlation units 1112-1 to 1112-N) of the Doppler processing system can cross-correlate each echo signal in the corresponding echo signal set with a transmitted pulse (or sub-pulse). The cross-correlation can determine the distance to a target in the field of view. For example, the target distance can be determined based on the delay of the transmitted pulse (or sub-pulse) to achieve the highest possible cross-correlation value with the echo signals.

[0099] In block 1330, the Doppler processing system, more specifically, the Doppler FFT unit of the Doppler processing system (e.g., Doppler FFT unit 1114), can perform a Doppler Fourier transform on the set of echo signals of the transmitted pulse set. In some implementations, performing the Doppler Fourier transform may include performing a corresponding two-dimensional Doppler Fourier transform on the echo signal of a sub-pulse transmitted in the MIMO period of the transmitted pulse set for each MIMO period of the MIMO period set. In some examples, for each of a plurality of spacing distances, the two-dimensional Doppler Fourier transform may include a corresponding one-dimensional Doppler Fourier transform on the echo signal corresponding to a sub-pulse transmitted in the MIMO period of the transmitted pulse set and returning from the spacing distance. The output of the corresponding two-dimensional Doppler Fourier transform may include a plurality of signals, each of which is associated with a distance basket in a set of distance baskets and a velocity basket in a plurality of velocity baskets. The detection signal in multiple velocity baskets can indicate a target with a measured velocity relative to the Doppler radar system, where the actual velocity of the target can be greater than the maximum Doppler velocity measurement interval of the Doppler radar system.

[0100] In box 1340, the Doppler processing system, more specifically, one or more motion compensation engines of the Doppler processing system (e.g., motion compensation engines 1122-1 to 1122-N), can apply a corresponding predetermined compensation phase vector to the probe signal in each of a plurality of velocity baskets. The corresponding predetermined compensation phase vector applied to the probe signal in each velocity basket may include a first component proportional to the velocity of the velocity basket, and a second component for compensating for phase compensation errors associated with Doppler velocity aliasing. In one example, applying the corresponding predetermined compensation phase vector to the probe signal in the kth velocity basket of the plurality of velocity baskets includes multiplying the probe signal in the kth velocity basket by the output of the two-dimensional Doppler Fourier transform of the pth MIMO period of the MIMO period set. Where φ0 and φ1 are constant values, -φ0kp can be used to compensate for the first type of residual phase, and -φ1p can be used to compensate for the second type of residual phase. In some embodiments, the Doppler processing system can, after applying the corresponding predetermined compensation phase vector to the probe signal in each of the multiple velocity baskets, average the phase compensation output of the two-dimensional Doppler Fourier transform of the MIMO period set to generate a range Doppler map.

[0101] Figure 14 This is a block diagram of an embodiment of computer system 1400, which may be used, in whole or in part, to provide the functionality of one or more processing systems described in this embodiment (e.g., Doppler FFT unit 230, cross-correlation units 1112-1 to 1112-N, Doppler FFT unit 1114, and motion compensation engines 1122-1, 1122-2, ... and 1122-N). It should be noted that... Figure 14 This is intended only to provide a general overview of the various components; any one or all of them may be used appropriately. Therefore, Figure 14 It broadly illustrates how individual system components can be implemented in a relatively discrete or relatively more integrated manner. Furthermore, it can be noted that... Figure 14 The components shown can be limited to a single device and / or distributed across a variety of networked devices that can be located in different geographical locations.

[0102] Computer system 1400 is shown to include hardware elements that can be electrically coupled (or otherwise suitably communicated) via bus 1405. The hardware elements may include processing unit 1410, which may include, but is not limited to, one or more general-purpose processors, one or more special-purpose processors (such as digital signal processing chips, graphics accelerators, etc.), and / or other processing architectures, which may be configured to perform one or more methods described herein. Computer system 1400 may also include one or more input devices 1415, which may include, but is not limited to, a mouse, keyboard, camera, microphone, etc.; and one or more output devices 1420, which may include, but is not limited to, display devices, printers, etc.

[0103] Computer system 1400 may further include (and / or communicate with) one or more non-transitory storage devices 1425, which may include, but are not limited to, locally and / or network-accessible storage devices, and / or may include, but are not limited to, disk drives, drive arrays, optical storage devices, solid-state storage devices such as RAM and / or ROM, which may be programmable, flash-updatable, etc. Such storage devices can be configured to implement any suitable data storage, including but not limited to various file systems, database structures, etc. As described herein, such data storage may include databases and / or other data structures for storing and managing messages and / or other information that will be sent to one or more devices via a hub.

[0104] Computer system 1400 may also include a communication subsystem 1430, which may include wireless communication technologies managed and controlled by wireless communication interface 1433, as well as wired technologies (e.g., Ethernet, coaxial communication, Universal Serial Bus (USB), etc.). Wireless communication interface 1433 may transmit and receive wireless signals 1455 (e.g., signals according to 5G New Radio (NR) or Long Term Evolution (LTE)) via wireless antenna 1450. Therefore, communication subsystem 1430 may include modems, network interface cards (wireless or wired), infrared communication devices, wireless communication devices, and / or chipsets, enabling computer system 1400 to communicate with any device on any or all communication networks described herein, including user equipment (UE), base stations and / or other Tx / Rx points (TRPs) and / or any other electronic devices described herein. Therefore, communication subsystem 1430 may be used to receive and transmit data as described in the embodiments herein.

[0105] In many embodiments, the computer system 1400 will also include working memory 1435, which, as described above, may include RAM or ROM. Software elements shown to be located within working memory 1435 may include operating system 1440, device drivers, executable libraries, and / or other code, such as one or more applications 1445, which may include computer programs provided by various embodiments and / or may be designed to implement methods and / or configure systems provided by other embodiments, as described herein. By way of example only, one or more processes described with respect to the methods above may be implemented as code and / or instructions executable by a computer (and / or processing units within a computer); in one aspect, such code and / or instructions may be used to configure and / or adapt a general-purpose computer (or other device) to perform one or more operations according to the described methods.

[0106] A set of these instructions and / or code may be stored on a non-transitory computer-readable storage medium, such as the storage device 1425 described above. In some cases, the storage medium may be incorporated into a computer system, such as computer system 1400. In other embodiments, the storage medium may be separate from the computer system (e.g., a removable medium such as an optical disc) and / or provided in an installation package, such that the storage medium can be used to program, configure, and / or adapt to a general-purpose computer on which the instructions / code are stored. These instructions may take the form of executable code that can be executed by computer system 1400, and / or may take the form of source code and / or installable code, which, when compiled and / or installed on computer system 1400 (e.g., using any of a variety of generally available compilers, installers, compression / decompression utilities, etc.), then take the form of executable code.

[0107] It will be apparent to those skilled in the art that substantial modifications can be made to suit specific requirements. For example, custom hardware may be used, and / or specific components may be implemented in hardware, software (including portable software such as applets), or both. Furthermore, connections to other computing devices, such as network input / output devices, may be employed.

[0108] Referring to the accompanying drawings, components that may include memory may include non-transitory machine-readable media. As used herein, the terms "machine-readable media" and "computer-readable media" refer to any storage medium that participates in providing data to enable a machine to operate in a particular manner. In the embodiments provided above, various machine-readable media may participate in providing instructions / code to a processing unit and / or other devices for execution. Additionally or alternatively, machine-readable media may be used to store and / or carry such instructions / code. In many implementations, computer-readable media are physical and / or tangible storage media. Such media can take many forms, including but not limited to non-volatile and volatile media. Common forms of computer-readable media include, for example, magnetic and / or optical media, any other physical media with a hole pattern, RAM, programmable ROM (PROM), erasable PROM (EPROM), FLASH-EPROM, any other memory chip or cartridge, or any other medium from which instructions and / or code can be read by a computer.

[0109] The methods, systems, and devices discussed herein are examples. Various processes or components may be appropriately omitted, substituted, or added in various embodiments. For example, features described with respect to certain embodiments may be combined in various other embodiments. Different aspects and elements of embodiments may be combined in a similar manner. The various components of the accompanying drawings provided herein may be implemented in hardware and / or software. Furthermore, technology is evolving, and therefore many elements are examples that do not limit the scope of this disclosure to those particular examples.

[0110] It has been found that, for general reasons, it is sometimes convenient to refer to these signals as bits, information, values, elements, symbols, characters, variables, terms, numbers, tags, etc. However, it should be understood that all these or similar terms are associated with appropriate physical quantities and are merely convenient labels. Unless otherwise stated, it is apparent from the foregoing discussion that throughout this specification, discussions using terms such as “processing,” “computer processing,” “calculation,” “determining,” “identifying,” “ascertaining,” “associating,” “measuring,” and “executing” refer to the actions or processes of a specific device, such as a dedicated computer or similar dedicated electronic computing device. Therefore, in the context of this specification, a dedicated computer or similar dedicated electronic computing device is capable of manipulating or converting signals, generally referred to as physical electronic, electrical, or magnetic quantities in the memory, registers, or other information storage devices, transmission devices, or display devices of the dedicated computer or similar dedicated electronic computing device.

[0111] The terms “and” and “or” as used herein can have a variety of meanings, which depend at least in part on the context in which they are used. Generally, “or” when used to relate a list, such as A, B, or C, is intended to mean A, B, and C, i.e., inclusion, and A, B, or C, i.e., exclusion. Furthermore, the term “one or more” as used herein can be used in the singular to describe any feature, structure, or characteristic, or can be used to describe some combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example, and the claimed subject matter is not limited to this example. Additionally, the term “at least one” when used to relate a list, such as A, B, or C, can be interpreted as meaning any combination of A, B, and / or C, such as A, AB, AA, AAB, AABBCCC, etc.

[0112] Several embodiments have been described, and various modifications, alternative constructions, and equivalents may be used without departing from the scope of this disclosure. For example, the elements described above may simply be components of a larger system, where other rules may take precedence over or otherwise modify the application of the various embodiments. Furthermore, numerous steps may be taken before, during, or after considering the elements described above. Therefore, the above description does not limit the scope of this disclosure.

[0113] In light of this description, embodiments may include different combinations of features. The following numbered clauses describe implementation examples:

[0114] Clause 1. A motion compensation method in a Doppler radar system, the method comprising: for each transmitted pulse in a set of transmitted pulses, receiving a corresponding set of echo signals returned from a plurality of spaced distances; performing a Doppler Fourier transform on the set of echo signals of the transmitted pulse set, wherein the output of the Doppler Fourier transform includes detection signals in a plurality of velocity frames; and applying a corresponding predetermined compensation phase vector to the detection signals in each of the plurality of velocity frames.

[0115] Clause 2. The method according to Clause 1, wherein the corresponding predetermined compensation phase vector applied to the detection signal in each velocity basket comprises: a first component proportional to the velocity of the velocity basket; a second component for compensating for phase compensation errors associated with Doppler velocity aliasing; or both the first component and the second component.

[0116] Clause 3. The method according to Clause 1 or Clause 2, wherein the Doppler radar system includes a multiple-input multiple-output (MIMO) radar system; each transmitted pulse in the transmitted pulse set includes a set of subpulses transmitted in the MIMO period set; and the corresponding echo signal set of each transmitted pulse includes a corresponding echo signal subset of each subpulse in the subpulse set of the transmitted pulse.

[0117] Clause 4. The method according to Clause 3, wherein each echo signal of the respective subset of echo signals corresponds to a respective spacing distance of the plurality of spacing distances; and performing the Doppler Fourier transform comprises, for each MIMO period of the set of MIMO periods, performing a corresponding two-dimensional Doppler Fourier transform on the echo signal of a sub-pulse transmitted in the MIMO period of the set of transmitted pulses.

[0118] Clause 5. The method according to Clause 4, wherein for each of the plurality of spacing distances, the two-dimensional Doppler Fourier transform comprises a corresponding one-dimensional Doppler Fourier transform of the echo signal corresponding to a sub-pulse transmitted in the MIMO period of the set of transmitted pulses and returned from the spacing distance.

[0119] Clause 6. The method according to Clause 5, wherein the output of the corresponding two-dimensional Doppler Fourier transform comprises a plurality of probe signals, each of the plurality of probe signals being associated with a distance basket in a set of distance baskets and a velocity basket in a set of velocity baskets.

[0120] Clause 7. The method according to Clause 6, wherein applying the corresponding predetermined compensation phase vector to the probe signal in the k-th velocity basket of the plurality of velocity baskets comprises multiplying the probe signal in the k-th velocity basket by the output of the two-dimensional Doppler Fourier transform of the p-th MIMO period of the MIMO period set. φ0 and φ1 are constant values.

[0121] Clause 8. The method according to any one of Clauses 4-7 further comprises, after applying the corresponding predetermined compensation phase vector to the probe signal in each of the plurality of velocity baskets, averaging the phase compensation output of the two-dimensional Doppler Fourier transform of the MIMO period set to generate a range Doppler map.

[0122] Clause 9. The method according to any one of Clauses 3-8 further comprises cross-correlating each echo signal of the respective echo signal subset with the subpulse before performing the Doppler Fourier transform.

[0123] Clause 10. The method according to any one of Clauses 1-9, wherein the detection signal in the detection signal of the plurality of velocity baskets indicates a target having a measured velocity relative to the Doppler radar system, and wherein the actual velocity of the target is greater than the maximum Doppler velocity measurement interval of the Doppler radar system.

[0124] Clause 11. A Doppler radar system comprising: a Doppler Fourier transform subsystem configured to: for each transmitted pulse in a set of transmitted pulses, receive a corresponding set of echo signals returned from a plurality of spaced distances; and perform a Doppler Fourier transform on the set of echo signals of the transmitted pulse set, wherein the output of the Doppler Fourier transform includes detection signals in a plurality of velocity frames; and a motion compensation subsystem configured to apply a corresponding predetermined compensation phase vector to the detection signals in each of the plurality of velocity frames.

[0125] Clause 12. The Doppler radar system according to Clause 11, wherein the corresponding predetermined compensation phase vector applied to the detection signal in each velocity frame comprises: a first component proportional to the velocity of the velocity frame; a second component for compensating for phase compensation errors associated with Doppler velocity aliasing; or both the first component and the second component.

[0126] Clause 13. A Doppler radar system according to Clause 11 or Clause 12, wherein the Doppler radar system includes a multiple-input multiple-output (MIMO) radar system; each transmitted pulse in the set of transmitted pulses includes a set of subpulses transmitted in a set of MIMO periods; and the corresponding echo signal set of each transmitted pulse includes a corresponding subset of echo signals for each subpulse in the set of subpulses of the transmitted pulse.

[0127] Clause 14. The Doppler radar system according to Clause 13 further includes an antenna array, wherein each antenna or antenna subarray of the antenna array is configured to transmit a corresponding subpulse of the subpulse set in a corresponding MIMO period of the MIMO period set.

[0128] Clause 15. A Doppler radar system according to any one of Clauses 13-14, wherein each echo signal of the respective subset of echo signals corresponds to a respective spacing distance of the plurality of spacing distances; and the Doppler Fourier transform comprises performing a corresponding two-dimensional Doppler Fourier transform on the echo signal of a sub-pulse transmitted in the MIMO period of the set of transmitted pulses for each MIMO period of the set of MIMO periods.

[0129] Clause 16. The Doppler radar system according to Clause 15, wherein for each of the plurality of spacing distances, the two-dimensional Doppler Fourier transform comprises a corresponding one-dimensional Doppler Fourier transform of the echo signal corresponding to a subpulse transmitted in the MIMO period of the set of transmitted pulses and returned from the spacing distance.

[0130] Clause 17. The Doppler radar system according to Clause 16, wherein the output of the corresponding two-dimensional Doppler Fourier transform comprises a plurality of detection signals, each of the plurality of detection signals being associated with a range basket in a set of range baskets and a velocity basket in a set of velocity baskets.

[0131] Clause 18. The Doppler radar system according to Clause 17, wherein the motion compensation subsystem is configured to multiply the detected signal in the k-th velocity bin of the output of the two-dimensional Doppler Fourier transform of the p-th MIMO period of the MIMO period set by... The corresponding predetermined compensation phase vector is applied to the detection signal in each of the plurality of velocity frames, where φ0 and φ1 are constant values.

[0132] Clause 19. The Doppler radar system according to any one of Clauses 15-18 further includes a graph generator configured to, after the motion compensation subsystem applies the corresponding predetermined compensation phase vector to the detection signal in each of the plurality of velocity frames, average the phase compensation output of the two-dimensional Doppler Fourier transform of the MIMO period set to generate a range Doppler graph.

[0133] Clause 20. The Doppler radar system according to any one of Clauses 13-19 further includes a cross-correlation subsystem configured to cross-correlate each echo signal of the corresponding echo signal subset with the subpulse before the Doppler Fourier transform subsystem performs the Doppler Fourier transform.

[0134] Clause 21. A Doppler radar system according to any one of Clauses 11-20, wherein the motion compensation subsystem comprises a set of motion compensation engines, each of the motion compensation engines being configured to apply the corresponding predetermined compensation phase vector to the detection signal in a corresponding velocity basket of the plurality of velocity baskets.

[0135] Clause 22. A Doppler radar system according to any one of Clauses 11-21, wherein one of the plurality of detection signals in the plurality of velocity baskets indicates a target having a measured velocity relative to the Doppler radar system, and wherein the actual velocity of the target is greater than the maximum Doppler velocity measurement interval of the Doppler radar system.

[0136] Clause 23. An apparatus for motion compensation in a Doppler radar system, the apparatus comprising: means for receiving, for each of a set of transmitted pulses, a corresponding set of echo signals returned from a plurality of spaced distances; means for performing a Doppler Fourier transform on the set of echo signals of the set of transmitted pulses, wherein the output of the Doppler Fourier transform includes detection signals in a plurality of velocity frames; and means for applying a corresponding predetermined compensation phase vector to the detection signals in each of the plurality of velocity frames.

[0137] Clause 24. The apparatus according to Clause 23, wherein the corresponding predetermined compensation phase vector of the detection signal applied to each velocity basket comprises: a first component proportional to the velocity of the velocity basket; and a second component for compensating for phase compensation errors associated with Doppler velocity aliasing.

[0138] Clause 25. The device according to any one of Clauses 23-24, wherein each transmitted pulse in the set of transmitted pulses includes a set of sub-pulses transmitted in a set of periods; the device further includes means for transmitting a corresponding sub-pulse of the set of sub-pulses in a corresponding period of the set of periods; the corresponding echo signal set of each transmitted pulse includes a corresponding subset of echo signals of each sub-pulse of the set of sub-pulses in the transmitted pulse; the Doppler Fourier transform includes, for each period of the set of periods, a corresponding two-dimensional Doppler Fourier transform of the echo signals of the sub-pulses transmitted in the period of the set of transmitted pulses; and the output of the corresponding two-dimensional Doppler Fourier transform includes a plurality of probe signals, each of the plurality of probe signals being associated with a distance basket in a set of distance baskets and a velocity basket in a plurality of velocity baskets.

[0139] Clause 26. The apparatus according to Clause 25, wherein the component for applying the corresponding predetermined compensation phase vector to the probe signal in the kth velocity basket of the plurality of velocity baskets includes a component for multiplying the probe signal in the kth velocity basket by e-2πiφ0kp+φ1p of the output of the two-dimensional Doppler Fourier transform of the pth period of the period set, where φ0 and φ1 are constant values.

[0140] Clause 27. The apparatus according to any one of Clauses 25-26 further includes a component for averaging the phase-compensated output of the two-dimensional Doppler Fourier transform of the period set to generate a range Doppler map.

[0141] Clause 28. The apparatus according to any one of Clauses 25-27 further includes a component for cross-correlating each echo signal of the respective echo signal subset with the subpulse prior to the Doppler Fourier transform.

[0142] Clause 29. A non-transitory computer-readable medium having embedded instructions that, when executed by one or more processing units, cause the one or more processing units to perform operations comprising: for each transmit pulse in a set of transmit pulses, receiving a corresponding set of echo signals returned from a plurality of interval distances; performing a Doppler Fourier transform on the set of echo signals of the set of transmit pulses, wherein the output of the Doppler Fourier transform includes probe signals in a plurality of velocity frames; and applying a corresponding predetermined compensation phase vector to the probe signals in each of the plurality of velocity frames.

[0143] Clause 30. The non-transitory computer-readable medium pursuant to Clause 29, wherein the corresponding predetermined compensation phase vector applied to the detection signal in each velocity basket comprises: a first component proportional to the velocity of the velocity basket; and a second component for compensating for phase compensation errors associated with Doppler velocity aliasing.

Claims

1. A motion compensation method in a Doppler radar system, the method comprising: For each transmitted pulse in the set of transmitted pulses, receive the corresponding set of echo signals returned from multiple interval distances; Perform a Doppler Fourier transform on the echo signal set of the transmitted pulse set, wherein the output of the Doppler Fourier transform includes the probe signals in multiple velocity baskets; as well as The corresponding predetermined compensation phase vector is applied to the detection signal in each of the plurality of velocity frames. The corresponding predetermined compensation phase vector applied to the detection signal in each velocity basket includes: A first component proportional to the velocity of the velocity basket; or The second component is used to compensate for the phase compensation error associated with Doppler velocity aliasing; or Both the first component and the second component, The execution of the Doppler Fourier transform includes: for each MIMO cycle of the multi-input multi-output MIMO cycle set, performing a corresponding two-dimensional Doppler Fourier transform on the echo signal of the sub-pulse transmitted in the MIMO cycle of the transmitted pulse set, and applying the corresponding predetermined compensation phase vector to the probe signal in the k-th velocity frame of the plurality of velocity frames includes: multiplying the probe signal in the k-th velocity frame from the output of the two-dimensional Doppler Fourier transform of the p-th MIMO cycle of the MIMO cycle set by... ,in and It is a constant value.

2. The method according to claim 1, wherein: The Doppler radar system includes a MIMO radar system; Each transmit pulse in the transmit pulse set includes a set of sub-pulses transmitted within the MIMO period set; and The corresponding echo signal set for each transmitted pulse includes the corresponding echo signal subset for each sub-pulse in the set of sub-pulses within the transmitted pulse.

3. The method according to claim 2, wherein: Each echo signal of the corresponding subset of echo signals corresponds to a corresponding spacing distance of the plurality of spacing distances.

4. The method according to claim 3, wherein, For each of the plurality of spacing distances, the two-dimensional Doppler Fourier transform includes a corresponding one-dimensional Doppler Fourier transform of the echo signal, which corresponds to a sub-pulse transmitted in the MIMO period of the set of transmitted pulses and returned from the spacing distance.

5. The method according to claim 4, wherein, The output of the corresponding two-dimensional Doppler Fourier transform includes multiple detection signals, each of which is associated with a distance basket in the set of distance baskets and a velocity basket in the set of velocity baskets.

6. The method of claim 3, further comprising, after applying the corresponding predetermined compensation phase vector to the probe signal in each of the plurality of velocity frames, averaging the phase compensation output of the two-dimensional Doppler Fourier transform of the MIMO period set to generate a range Doppler map.

7. The method of claim 2, further comprising cross-correlating each echo signal of the corresponding echo signal subset with the subpulse before performing the Doppler Fourier transform.

8. The method according to claim 1, wherein, The detection signal in the plurality of velocity baskets indicates a target having a measured velocity relative to the Doppler radar system, wherein the actual velocity of the target is greater than the maximum Doppler velocity measurement interval of the Doppler radar system.

9. A Doppler radar system, comprising: The Doppler Fourier transform subsystem is configured as follows: For each transmitted pulse in the set of transmitted pulses, receive the corresponding set of echo signals returned from multiple interval distances; and Perform a Doppler Fourier transform on the echo signal set of the transmitted pulse set, wherein the output of the Doppler Fourier transform includes the probe signals in multiple velocity baskets; as well as A motion compensation subsystem is configured to apply a corresponding predetermined compensation phase vector to the detected signal in each of the plurality of velocity frames. The corresponding predetermined compensation phase vector applied to the detection signal in each velocity basket includes: A first component proportional to the velocity of the velocity basket; or The second component is used to compensate for the phase compensation error associated with Doppler velocity aliasing; or Both the first component and the second component, The execution of the Doppler Fourier transform includes: for each MIMO cycle of the multi-input multi-output MIMO cycle set, performing a corresponding two-dimensional Doppler Fourier transform on the echo signal of a sub-pulse transmitted in the MIMO cycle of the transmitted pulse set, and the motion compensation subsystem is configured to multiply the probe signal in the k-th velocity bin of the output of the two-dimensional Doppler Fourier transform of the p-th MIMO cycle of the MIMO cycle set by... The corresponding predetermined compensation phase vector is applied to the detection signal in each of the plurality of velocity frames, wherein and It is a constant value.

10. The Doppler radar system according to claim 9, wherein: The Doppler radar system includes a MIMO radar system; Each transmit pulse in the transmit pulse set includes a set of sub-pulses transmitted within the MIMO period set; and The corresponding echo signal set for each transmitted pulse includes the corresponding echo signal subset for each sub-pulse of the sub-pulse set in the transmitted pulse.

11. The Doppler radar system of claim 10, further comprising an antenna array, wherein each antenna or antenna subarray of the antenna array is configured to transmit a corresponding subpulse of the subpulse set in a corresponding MIMO period of the MIMO period set.

12. The Doppler radar system according to claim 10, wherein: Each echo signal of the corresponding subset of echo signals corresponds to a corresponding spacing distance of the plurality of spacing distances.

13. The Doppler radar system according to claim 12, wherein, For each of the plurality of spacing distances, the two-dimensional Doppler Fourier transform includes a corresponding one-dimensional Doppler Fourier transform of the echo signal, which corresponds to a sub-pulse transmitted in the MIMO period of the set of transmitted pulses and returned from the spacing distance.

14. The Doppler radar system according to claim 13, wherein, The output of the corresponding two-dimensional Doppler Fourier transform includes multiple detection signals, each of which is associated with a distance basket in the set of distance baskets and a velocity basket in the set of velocity baskets.

15. The Doppler radar system of claim 12, further comprising a graph generator configured to, after the motion compensation subsystem applies the corresponding predetermined compensation phase vector to the detection signal in each of the plurality of velocity frames, average the phase compensation output of the two-dimensional Doppler Fourier transform of the MIMO period set to generate a range Doppler graph.

16. The Doppler radar system of claim 10, further comprising a cross-correlation subsystem configured to cross-correlate each echo signal of the corresponding echo signal subset with the subpulse before the Doppler Fourier transform subsystem performs the Doppler Fourier transform.

17. The Doppler radar system according to claim 9, wherein, The motion compensation subsystem includes a set of motion compensation engines, each of which is configured to apply the corresponding predetermined compensation phase vector to the detection signal in the corresponding velocity basket of the plurality of velocity baskets.

18. The Doppler radar system according to claim 9, wherein, The detection signal in the plurality of velocity baskets indicates a target having a measured velocity relative to the Doppler radar system, wherein the actual velocity of the target is greater than the maximum Doppler velocity measurement interval of the Doppler radar system.

19. A device for motion compensation in a Doppler radar system, the device comprising: A component for receiving a set of corresponding echo signals returned from multiple spacing distances for each transmitted pulse in a set of transmitted pulses; A component for performing a Doppler Fourier transform on the set of echo signals of the set of transmitted pulses, wherein the output of the Doppler Fourier transform includes the probe signals in a plurality of velocity baskets; as well as A component for applying a corresponding predetermined compensation phase vector to the detection signal in each of the plurality of velocity frames. The corresponding predetermined compensation phase vector applied to the detection signal in each velocity basket includes: A first component proportional to the velocity of the velocity basket; or The second component is used to compensate for the phase compensation error associated with Doppler velocity aliasing; or Both the first component and the second component, The Doppler Fourier transform includes: for each MIMO cycle of the multi-input multi-output MIMO cycle set, a corresponding two-dimensional Doppler Fourier transform of the echo signal of a sub-pulse transmitted in the MIMO cycle of the transmit pulse set; and the component for applying the corresponding predetermined compensation phase vector to the probe signal in the kth velocity frame of the plurality of velocity frames includes: multiplying the probe signal in the kth velocity frame of the output of the two-dimensional Doppler Fourier transform of the pth MIMO cycle of the MIMO cycle set by... The components, among which and It is a constant value.

20. The apparatus according to claim 19, wherein: Each transmit pulse in the transmit pulse set includes a set of sub-pulses transmitted in the period set; The device also includes components for transmitting a corresponding sub-pulse of the sub-pulse set in a corresponding period of the period set; The corresponding echo signal set for each transmitted pulse includes the corresponding echo signal subset for each sub-pulse of the sub-pulse set in the transmitted pulse; and The output of the corresponding two-dimensional Doppler Fourier transform includes multiple detection signals, each of which is associated with a distance basket in the set of distance baskets and a velocity basket in the set of velocity baskets.

21. The apparatus of claim 20, further comprising means for averaging the phase-compensated output of the two-dimensional Doppler Fourier transform of the period set to generate a range Doppler map.

22. The apparatus of claim 20, further comprising means for cross-correlating each echo signal of the respective echo signal subset with the subpulse prior to the Doppler Fourier transform.

23. A non-transitory computer-readable medium having instructions embedded thereon, the instructions causing the one or more processing units to perform an operation when executed by the one or more processing units, the operation including: For each transmitted pulse in the set of transmitted pulses, receive the corresponding set of echo signals returned from multiple interval distances; Perform a Doppler Fourier transform on the set of echo signals of the set of transmitted pulses, wherein the output of the Doppler Fourier transform includes the probe signals in multiple velocity baskets; as well as The corresponding predetermined compensation phase vector is applied to the detection signal in each of the plurality of velocity frames. The corresponding predetermined compensation phase vector applied to the detection signal in each velocity basket includes: A first component proportional to the velocity of the velocity basket; or The second component is used to compensate for the phase compensation error associated with Doppler velocity aliasing; or Both the first component and the second component, The execution of the Doppler Fourier transform includes: for each MIMO cycle of the multi-input multi-output MIMO cycle set, performing a corresponding two-dimensional Doppler Fourier transform on the echo signal of the sub-pulse transmitted in the MIMO cycle of the transmitted pulse set, and applying the corresponding predetermined compensation phase vector to the probe signal in the k-th velocity frame of the plurality of velocity frames includes: multiplying the probe signal in the k-th velocity frame from the output of the two-dimensional Doppler Fourier transform of the p-th MIMO cycle of the MIMO cycle set by... ,in and It is a constant value.

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