Mapping of a stationary scene using radar

Abstract

To provide a method for mapping using a floor-mounted type radar unit in a quiesce scene.SOLUTION: A floor mounted type radar unit (100) includes one set of receiver antennas (102a-h) which are configured to detect a radar signal from any direction, and measures a target speed in an individual speed jar. In the method, the set of the receiver antennas are used for continuously and chronologically collecting the radar signal for detecting a quiesce scene, then constructing an occupancy map of the quiesce scene by using confirmed detection which is determined on the basis of the collected radar signals. The detections are: detection in which, radar signal strength exceeds a detection threshold value, and the speed is within a zero speed jar; and detection in which, the radar signal strength exceeds the detection threshold value, the speed is not zero, and is the detection being low enough to store overflow information in a same jar, and in a zero speed jar.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention generally relates to the field of radar imaging, and more particularly, to a method and a control unit for mapping a stationary scene using a stationary radar unit.

Background Art

[0002] The principle of radar detection is that the transmitted radar signal is reflected by an object and detected by the radar antenna. By appropriate signal processing, properties such as the object speed and the position relative to the radar can be estimated.

[0003] Radar mapping of stationary installations may be performed using a scanning radar, where the radar antenna is moved spatially so that the detection area is detected from various angles. In some applications, the radar is necessarily in motion. For example, in the automotive industry, the radar is mounted on a vehicle to detect the surroundings of that vehicle.

[0004] A common type of radar is based on what is called range-Doppler measurement. Typically, a range-Doppler measurement radar detects a specific combination of the distance and speed of a target. However, this type of measurement is most suitable for detecting moving objects in the detection area and is not suitable for detecting stationary, non-moving objects.

[0005] A common approach to increasing the resolution of a stationary image detected by radar is to significantly increase the number of antennas and employ complex and computationally expensive signal processing. Increasing the number of antennas is costly and generally not desirable, and computationally expensive signal processing is not desirable as it increases the requirements for the processor.

[0006] As a result, there is room for improvement with respect to detecting stationary installations using radar.

Summary of the Invention

[0007] In view of the above and other drawbacks of the prior art, it is an object of the present invention to provide a method for mapping a stationary scene using a stationary radar unit that mitigates at least some of those drawbacks of the prior art.

[0008] According to a first aspect of the present invention, there is thus provided a method for mapping a stationary scene using a stationary radar unit operative to transmit radar signals towards the scene. The stationary radar unit includes a set of receiver antennas configured to detect radar signals from any direction. The stationary radar unit is configured to measure target velocity in individual velocity bins. The method includes the following steps. Continuously collect radar signals over time using this set of receiver antennas to detect a stationary scene. In a further step, construct an occupancy map of the stationary scene using confirmed detections determined from the collected radar signals. Confirmed detections are detections where the radar signal intensity exceeds a detection threshold and the velocity falls within the zero velocity bin, and detections where the radar signal intensity exceeds the detection threshold, the velocity is non-zero, and the overflow information is made to occur as a detection within the same bin and within the zero velocity bin, and is low enough to be considered as a detection within the zero velocity bin.

[0009] The present invention is based on the realization that in order to construct a map of stationary objects in a scene, it includes not only the detection of stationary objects but also the detection of objects that are almost stationary. Information regarding the detection of almost stationary objects is often discarded. This is because it may be information that is already considered to form part of the detection of stationary objects, i.e., overflow information in the region of almost stationary objects from the detection of stationary objects. Furthermore, radar detection of moving objects can also cause overflow information to occur in the same region of almost stationary objects. Thus, the information in the region of almost stationary objects includes the sum of the overflow information from stationary objects and from moving objects.

[0010] The inventors have realized that information regarding the detection of targets having non-zero speeds is used to construct a map of a stationary scene.

[0011] The radar measures the speed in individual steps such that the detected speed falls within one of several bins. The detection of speed is thus performed, for example, for a speed of 0 and speeds of -ΔV and +ΔV where ΔV is the bin size. Thus, the radar unit operates to include detections where the signal strength exceeds a threshold and the speed is zero or, although non-zero, within + / -ΔV according to the threshold setting. Due to the overflow, each of the detections regarding the zero bin, the -ΔV bin, or the +ΔV bin may include detections from stationary objects and detections from moving objects.

[0012] A speed that is low enough to cause overflow information may be interpreted as a speed that is low enough such that there is a correlation or linear dependence between the frequencies corresponding to targets at zero speed and targets at non-zero speed.

[0013] In addition to measuring the speed in individual speed bins, a stationary radar unit may also measure the target range in individual range bins and, optionally, also measure the angle of arrival of the radar signal in individual bins. This causes overflow information between target range bins and between angle of arrival bins.

[0014] Overflow information may be regarded as spectral leakage, i.e., in signal processing including a discrete Fourier transform or the like, the lobes or "tones" in the discrete Fourier transform regarding the detected speed spread to other frequencies such as speed. Similarly, in signal processing including a discrete Fourier transform or the like, the lobes or "tones" in the discrete Fourier transform regarding the detected range or the angle of arrival of the detected signal spread to other frequencies such as other neighboring range bins or angle of arrival bins.

[0015] A stationary radar should be interpreted as a radar without a moving part that sweeps a scene. Instead, the radar is adapted to signals detected from all directions without using beamforming or sweeping. Further, a stationary radar is placed in a stationary position and not on a moving entity such as a vehicle. Thus, a stationary radar unit is not moving with respect to a stationary scene.

[0016] The continuous collection of radar signals should be interpreted as being performed at regular intervals defined by a time frame or simply a "frame".

[0017] Measuring speed is preferably done by periodically transmitting radar signals. Suitable transmitted signals are pulsed signals that are repeated periodically, frequency modulation sequences, in particular the linear frequency sweep used for frequency-modulated continuous-wave radar (FMCW), phase modulation signals, or multi-carrier signals such as orthogonal frequency division multiplexing (OFDM).

[0018] The signal processing of radar signals may be performed in various known ways. Some examples include range compression using a matched filter. For FMCW signals using stretch processing, this may be performed by a Fourier transform or other frequency estimation algorithms (such as MUSIC, CAPON, etc.). Other suitable implementations may be correlation with the transmitted signal or a frequency domain implementation of a matched filter.

[0019] Furthermore, Doppler compression may be performed including analyzing the periodicity of the transmitted signal and detecting the Doppler shift. This is generally done using a fast Fourier transform (FFT) or other frequency estimation algorithms described above.

[0020] Furthermore, the estimation of the angle of arrival in an antenna array may be performed by estimating the phase steering vector between antennas using an FFT. Other techniques may be the frequency estimation techniques described above.

[0021] Using the embodiments of the present invention, the method described below provides mapping using a radar with a relatively small number of antennas for a stationary scene and signal processing with low computational cost.

[0022] In each of the embodiments, the number of receiver antennas does not exceed 16, preferably does not exceed 10, and more preferably does not exceed 8. As a result, the radar unit can be of a relatively simple and low-cost type. The receiver antenna may be a physical antenna or a virtual antenna. The antenna may be implemented as a virtual antenna of a multiple-input multiple-output (MIMO) radar.

[0023] In each of the embodiments, constructing the occupancy map may include, over time, including in the occupancy map all detections where the radar signal intensity exceeds the detection threshold and the speed is zero, and all detections where the radar signal intensity exceeds the detection threshold and the speed is non-zero, for each of a set of individual radii from the position of the radar. As a result, the radar unit is configured to mark all detections that satisfy the detection and speed thresholds for each of the set of individual radii. For example, all detections where the speed falls within the thresholds of 0, -ΔV, +ΔV, - are marked in the occupancy map.

[0024] In a more specific example, the occupancy map is constructed by including one radar detection for each combination of an individual radius from the position of the radar and detections associated with the velocity bins in the vicinity of the zero velocity bin.

[0025] In each of the embodiments, constructing the occupancy map may include increasing the occupancy probability value in the corresponding first region of the occupancy map for each of the confirmed detections, and decreasing the probability value in the region between the first region in the occupancy map and the position of the radar. This is an efficient method for constructing an occupancy map that takes into account the detection of moving objects. Preferably, it enables the construction of the map by averaging the detections over time, where stationary objects appear and moving objects are averaged. The degree of increase and / or decrease of the probability value is a tuning parameter that may be tuned to a particular implementation. The tuning parameter effectively controls the speed at which the occupancy map is constructed, i.e., how quickly the probability value approaches the set limit.

[0026] Preferably, the region between the first region in the occupancy map and the position of the radar intersects the straight line between the first region in the occupancy map and the position of the radar. This straight line represents the line of sight between the radar unit and the first region. Since there are no additional objects in the line of sight, the probability value in the region between the first region and the radar unit can be reliably decreased, which may improve the contrast between the region with stationary objects and the region without stationary objects in the occupancy map. Objects located on the straight line that are seen as coming from the radar unit position and beyond the first region are completely or partially covered by the shadow.

[0027] Furthermore, while constructing the occupancy map, it may be included to increase the occupancy probability value in the regions adjacent to the first region. This may account for the uncertainty in the measured target range and arrival angle in the occupancy map. This increase may be performed according to a probability function. For example, the closer to the first region, the higher the increase in probability, and the probability of decrease increases as the distance from the first region increases.

[0028] To construct an accurate occupancy map, the occupancy map may be constructed as a collection of probability values over time. Since the occupancy map is effectively a collection of estimates of the detected environment, the differences in these estimates are reduced by averaging over many measurements over time.

[0029] In each of the embodiments, constructing the occupancy map may include determining, using the selection of the frequency with the most energy content of the Fourier transform of the phase difference between radar signals collected by various receiver antennas divided along a first axis, the azimuth angle of the confirmed detection. The first axis corresponds to the horizontal axis of the scene when the radar unit is in use.

[0030] In each of the embodiments, constructing the occupancy map may include determining, using the selection of the frequency with the most energy content of the Fourier transform of the phase difference between radar signals collected by various receiver antennas divided along a second axis, the elevation angle of the confirmed detection. The second axis corresponds to the vertical axis of the scene when the radar unit is in use.

[0031] Each of the embodiments of the present invention is applicable to various types of stationary radar units. In one preferred embodiment, the stationary radar unit is a frequency modulated continuous wave radar. Further, the stationary radar unit may be operative to transmit radar signals in all directions.

[0032] According to a second aspect of the present invention, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to perform any one of the methods of the embodiments described herein.

[0033] Each of the further embodiments of this second aspect of the present invention, and the effects obtained through them, are very similar to those described above for the first aspect of the present invention.

[0034] According to a third aspect of the present invention, there is provided a control unit for mapping using radar signals collected by a stationary radar unit that operates to transmit radar signals towards a scene of a stationary scene and detect radar signals from any direction using a set of receiver antennas. The stationary radar unit is configured to measure the target velocity in individual velocity bins. The control unit is configured to acquire data indicative of radar signals continuously collected over time to detect a stationary scene and construct an occupancy map of the stationary scene using confirmed detections determined from the acquired data. The confirmed detections are detections where the radar signal intensity exceeds a detection threshold and the velocity falls within the zero velocity bin, and detections where the radar signal intensity exceeds the detection threshold, the velocity is non-zero, and the overflow information is made to occur as a detection falling within the same bin as the zero velocity bin and being low enough.

[0035] Each further embodiment of this third aspect of the present invention, and the effects obtained through them, are very similar to those above descriptions for the first and second aspects of the present invention.

[0036] There is further provided a system including a stationary radar unit and a control unit according to the third aspect. This system provides advantages and features similar to any one of the embodiments described below.

[0037] Further features of the present invention, and the advantages thereby, will become apparent when considering the appended claims and the following description. Those skilled in the art will recognize that various features of the present invention may be combined to create other embodiments, each without departing from the scope of the present invention, other than those described below.

[0038] The various aspects of the present invention include their specific features and advantages and will be readily understood from the following forms for carrying out the invention and the accompanying drawings shown below. BRIEF DESCRIPTION OF THE DRAWINGS

[0039]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 1E

Figure 2

Figure 3

Figure 4A-4B

Figure 5

Figure 6

[0040] The present invention will be described in further detail below with reference to the accompanying drawings. Here, presently preferred embodiments of the present invention are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments shown below. Rather, these embodiments are provided for the sake of completeness and thoroughness and to fully convey the scope of the present invention to those skilled in the art. Similar reference numerals denote similar components throughout these drawings.

[0041] Looking at these drawings, particularly FIG. 1, a scene 1 is shown that includes a set of stationary objects 102a - d and a moving object 104. The stationary radar unit 100 is configured to map the scene 1 that includes the moving object 104 and the stationary objects 102a - d. For measuring velocity, the periodic transmission of signals is preferably used. Suitable transmission signals are pulsed signals that are periodically repeated, frequency - modulation sequences such as the linear frequency sweep used in FMCW, phase - modulation signals, or multi - carrier signals such as OFDM.

[0042] The radar unit 100 generally detects the strongest signal for each radius or range from the position of the radar unit 100. Thus, if the scene has not changed and is completely stationary, the same strongest object will be observed over time, and the observed stationary objects often become unclear over the azimuth angle for each range. However, when a small interference such as the moving object 104 is introduced into the scene 1, the scene changes, and thus the strongest detection may also change. This can result in the appearance of less - prominent features of the scene. For example, the moving object 104 first causes an occlusion in the area 106a of the object 102b and later causes an occlusion in the area 106b of the object 102c. Without the moving object 104, the smaller stationary object 102b may not be detected as the strongest detection due to the more prominent stationary object 102c. However, when the moving object 104 covers part of the stationary object 102c, the less - prominent object 102b may be detected and appear as more prominent.

[0043] During scene mapping, the radar unit 100 includes the detection of objects with zero speed, i.e., the detection of objects 102a to d. The detection of objects including the sampling of radar detections at individual times is also performed for individual speeds, herein called velocity bins. Processing the data in this way causes an overflow into neighboring bins due to spectral leakage. Similarly, the detection of the moving object 104 causes an overflow into neighboring bins due to spectral leakage. If the object is moving slowly enough, the detection will overflow into the same bin as the detection of a stationary object, and thus this velocity bin will include the sum of the overflows from the detection of stationary objects and the detection of low-speed objects. Therefore, by using an appropriate detection threshold such as the method proposed herein, the variations of these stationary objects in the detection of stationary objects will cause various objects and features of the scene to be observed over time due to this overflow information.

[0044] In addition to the above description, a stationary radar unit such as a frequency-modulated continuous-wave radar is used, and one object is detected for each individual range, i.e., each range bin, and for each individual velocity bin. Therefore, even if more than one object exists at the same range and the same speed, only one object is detected.

[0045] An object is detected when the radar signal exceeds a detection threshold, and for each detected object, an individual range, an individual radial velocity, an azimuth angle, and a signal strength may be measured. For each individual radius, in the occupancy map, all detections that fall within the zero-velocity bin and all detections that fall within the neighboring velocity bins of the zero-velocity bin are marked.

[0046] If the object 104 is moving slowly enough, each one or more of the combinations of (R0, zero velocity), (R0, +ΔV velocity), and (R0, -ΔV velocity) will include the sum of the detections of stationary objects and moving objects. Since only one detection is made for each combination, these combinations may not be the same as those where the moving object 104 does not exist. In other words, new information is added to the map.

[0047] When the moving target 104 moves at a given radius R0 and azimuth angle, as seen by the radar unit 100 at various times or frames, it will cover the object with a shadow, that is, 102b and 102c will come behind the object 104. Therefore, if the moving object is in front of stationary objects such as 102b and 102c, the reflections from these objects will weaken while other reflections from the same range remain the same. Therefore, even in this case, each of the combinations of (R0, zero velocity), (R0, +ΔV velocity), and (R0, -ΔV velocity) can contain new information to be added to the map.

[0048] More specifically, looking at Figure 1B, a conceptual range-Doppler plot 200 is shown. The Doppler velocity is shown on the x-axis, where the radar signal measurement values indicate the center peak Pv and the side lobes Sv. Further, the center peak Pr and the side lobes Sr are shown on the y-axis. The corresponding power graphs are shown, which indicate the main lobes Pr and Pv in the Fourier transform of the collected detections. When the detection exceeds the detection threshold, that is, when the peak has an amplitude exceeding the detection threshold 220, the detection is considered to be confirmed.

[0049] Referring to FIG. 1C, another range-Doppler plot 201 is shown, where two targets 210 and 212 occur. These targets have zero velocity and are thus considered stationary. In other words, in the corresponding power-versus-velocity plot, similar to that shown in FIG. 1B, the peaks both occur at zero velocity. In the power-versus-range plot 202 shown in FIG. 1C, the difference in range, i.e., the relative displacement along the y-axis along the zero velocity line 203 in the range-Doppler diagram, is reflected by the displacement of the corresponding peaks 212a and 210a in plot 202. Peak 212a is lower than peak 210a, and since only the highest peak is selected for a given range, object 212 is considered "invisible", i.e., not detected by the radar. However, the overlap between lobes 212a and 210a and their side lobes indicate spectral leakage between two non-zero detections that can cause a confirmed detection. Each lobe may be considered to represent a bin.

[0050] Referring to FIG. 1D here, a moving object 214 is introduced here. In the range-Doppler diagram 205, an entity 214 representing the moving object is shifted to the right in FIG. 205 away from the zero velocity axis 203. Further, the power versus Doppler velocity plot 204 shows the main lobes 210b, 212b, and 214a, as well as their relative displacements with respect to each other. Again, the overlap between the lobes indicates an overflow region. In particular, the side lobe 212c belonging to the detection of the stationary object 212 that was not detectable as described in relation to FIG. 1C and the side lobe 214b belonging to the detection of the moving object 214 overlap at 215, and the sum of these signals (not shown to avoid cluttering the drawing), that is, the sum of the overlaps of the lobes 212c, 214c, may exceed the detection threshold 220. Thus, as described in FIG. 1B, not only the detection of objects with non-zero velocity performed in a given range but also the detection of the combined lobes 212c and 214b fall within the non-zero velocity bins, thereby generating a confirmed detection for the previous "invisible" stationary object 212. The velocity of the object 214 is low enough to cause an overflow into the same bin, that is, into the lobe 212c belonging to the non-zero detection of the object 212. Still further, the velocity of the object 214 is low enough such that the combined signal of the lobes 212c and 214b exceeds the detection threshold 220.

[0051] As shown in the power versus velocity diagram 206 of FIG. 1E, since the velocity of the object 214 was substantially higher, spectral leakage may occur, and the sum of the overlapping lobes such as the lobes 212c and 214c as described above does not cause a confirmed detection, that is, a combined signal exceeding the threshold 220. Thus, the velocity of the object 214 is excessively high, causing spectral leakage, which may cause a confirmed detection of non-zero velocity.

[0052] The above realization is such that detection is thresholded, including detections where the radar signal intensity exceeds the detection threshold and the speed falls within the zero-speed bin, and detections where the radar signal intensity exceeds the detection threshold, the speed is non-zero, and the overflow information is caused to occur as a detection that falls within the same bin and the zero-speed bin, at a sufficiently low level so that detections where the speed is non-zero, i.e., detections in bins where the speed is non-zero, are performed.

[0053] Figure 2 is a flowchart of method steps according to respective embodiments of the present invention.

[0054] In step 102, a set of receiver antennas of a stationary radar unit is used to continuously collect radar signals over time to detect a stationary scene. The stationary radar unit 100 is operative to transmit a radar signal towards scene 1 and includes a set of receiver antennas configured to detect radar signals from any direction. As a result, the stationary radar unit 100 does not utilize beamforming. The stationary radar unit 100 is configured to measure the target speed in individual speed bins, i.e., the speed of the detected target is measured in individual steps.

[0055] In step 104, an occupancy map of the stationary scene is constructed using the confirmed detections determined from the collected radar signals. The confirmed detections are detections that satisfy a radar signal intensity exceeding the detection threshold and where the speed falls within the zero-speed bin. Further, the confirmed detections also include detections where the radar signal intensity exceeds the detection threshold, the speed is non-zero, and the overflow information is caused to occur as a detection that falls within the same bin and the zero-speed bin, at a sufficiently low level. As described above, this type of thresholding provides additional information for mapping the stationary scene as compared to detecting only fully stationary objects.

[0056] FIG. 3 conceptually shows the construction of the occupancy map of Scene 1 by considering probability values in the occupancy grid 300. The occupancy grid includes a grid of cells 302, where only one of the cells 302 is marked in FIG. 3.

[0057] When the detections made by the radar unit 100 are confirmed by the algorithm, the probability value in the corresponding cell of the grid is increased. For example, the cells marked from groups 302a to d are cells in the region where confirmed detections have been made, corresponding to stationary objects 102a to d respectively. Therefore, as further detections are made over time for the same stationary object, the probability further increases in the corresponding cell, thereby increasing the likelihood of the stationary object existing in the corresponding region. Note that since the occupancy map 300 is under construction, regions 302a to d are smaller than stationary objects 102a to d.

[0058] Furthermore, to increase the contrast of the occupancy map, the probability is decreased in cells that fall within the region between the confirmed detections and the position of the radar unit 100. This further serves to reduce the influence of moving objects that appear in the occupancy map 300. For example, at a first time, the moving object 104 covers the stationary object 102b. At this time, the probability in region 304a will increase, and since the stationary object 102b is blocked by the moving object 104, the probability in the region of object 302b does not change. However, the probability in the region between region 304a and the radar unit 100 is decreased. Subsequently, the moving object 104 moves to a position where it partially covers the object 102c, such that the object 102b becomes detectable by the radar unit 100 here. Therefore, the probability value in the corresponding region 302b of the occupancy map 300 is increased, and the probability in the region between region 302b and the radar unit 100 is decreased. The detections made in region 304a fade out over time. As a result, the detections of stationary objects 102a to d will appear in the occupancy map 300.

[0059] Furthermore, the reduced occupied map area preferably intersects a straight line 306 between a first area such as the detected area 302b in the occupancy map 300 and the position of the radar 100.

[0060] Furthermore, the occupancy probability value is increased in an area adjacent to the first area. Although it is repetitive, taking the area 302b as the first area in the current frame, when detection is performed in the area 302b, the occupancy probability value may also be increased in the area 303b adjacent to the area 302b.

[0061] The occupancy map 300 is constructed by collecting detections over a period of time. In other words, the occupancy map 300 is filled with matching detections, where only detections immediately made on moving objects will be averaged.

[0062] Figures 4A to 4B show examples of the constructed occupancy map 400 at two separate times. Figure 4A shows the occupancy map 400 at time t1, and Figure 4B shows the occupancy map 400 at time t2, which is about 1 minute apart. During that time, for example, the person exemplified by the object 104 in Figures 1A and 3 is moving within the scene. In Figure 4A, only a small part of the stationary objects in the scene is detected and marked in black. As time progresses, using the method described with reference to Figure 3, for the mechanism described with reference to Figure 1A, the occupancy map 400 is formed, and much of the scene can be gradually detected, that is, more black areas appear, which may correspond to the walls of the building, and more white areas appear, which may correspond to open areas such as lawns or empty parking spaces.

[0063] The radar unit 100 operates by performing detections at individual radii and individual velocities. During operation, one radar detection for each combination of an individual radius from the position of the radar and a detection associated with a velocity bin near the zero velocity bin is included in the occupancy map 300. Looking at FIG. 3 again, radius 308 conceptually shows one individual radius 308, where in the current frame, it blocks regions 302a and 304a. Here, the detection in region 302a corresponds to a confirmed detection of an object with a velocity of zero, i.e., an object that falls within the zero velocity bin, and the detection in region 304a corresponds to a detection associated with a velocity bin near the zero velocity bin.

[0064] Preferably, for each of a set of individual radii from the position of the radar, all of the confirmed detections are included in the occupancy map.

[0065] As an example, when occupancy map 300 or 400 is constructed, the azimuth angle of the confirmed detection is determined. The azimuth angle α is the angle along the individual radius 308 where the confirmed detection was made. During the processing of the radar detection, a Fourier transform, preferably a discrete Fourier transform, of the phase difference between the radar signals is calculated. This generally results in a spectrum of various angle - to - power, which includes a global peak 502, i.e., the peak with the most energy content, and a set of side lobes 504, as conceptually shown in FIG. 5. Determining the azimuth angle α may be done by calculating the discrete Fourier transform of the phase difference between the radar signals collected by various receiver antennas divided along a first axis 310 parallel to the plane of the azimuth angle, and selecting the frequency with the most energy content, i.e., the azimuth angle, in that discrete Fourier transform. It may also be possible to simply select the frequency higher than the one with the most energy content, however, in a preferred embodiment, the frequency with the most energy content, i.e., the azimuth angle, is selected. This is because it may be difficult to accurately determine whether the peak is the actual target or just a side lobe. Similar selections may be made for range detection and velocity detection. See also the description related to FIGS. 1A - 1E.

[0066] Similarly, even when the elevation angle is considered, to provide a radar image along the elevation angle, constructing the occupancy map involves determining the elevation angle of the confirmed detection by selecting the frequency with the most energy content of the Fourier transform of the phase difference between the radar signals collected by various receiver antennas divided along a second axis perpendicular to the plane of the azimuth angle.

[0067] This is done in a manner similar to that described in relation to the azimuth angle.

[0068] FIG. 6 is a block diagram of a radar system 600 including a stationary radar and a control unit 602. The number of receiver antennas 604a to 604h of the stationary radar unit does not exceed 16, preferably does not exceed 10, and more preferably does not exceed 8. Here, eight receiver antennas are shown, which represents a relatively simple and low-cost radar unit 100. The stationary radar unit 100 may operate to transmit radar signals in all directions. Preferably, the radar unit 100 operates without utilizing beamforming.

[0069] The channels, i.e., antennas 604a to 604h, may be physical antennas or virtual antennas. Antennas 604a to 604h may be implemented as virtual antennas of a multiple-input multiple-output (MIMO) radar. The receiver circuit 606 is adapted to receive radar signals from antennas 604a to 604h and convert them into signals that may be acquired by the control unit 602. Such a receiver circuit may include, for example, mixers, filters, analog-to-digital converters, etc. Such a receiver circuit 606 may have various components and configurations depending on the specific implementation targeted.

[0070] The control unit 602 is configured to acquire data indicative of radar signals continuously collected over time and detect a stationary scene. The radar signals are detected by antennas 604a to 604h.

[0071] Furthermore, the control unit 602 is configured to construct an occupancy map of the stationary scene using confirmed detections determined from the acquired data. As described above, the confirmed detections are detections where the radar signal intensity exceeds the detection threshold and the speed falls within the zero-speed bin, and detections where the radar signal intensity exceeds the detection threshold, the speed is non-zero, and the overflow information is made to occur as a detection within the same bin and within the zero-speed bin, and the detection is low enough.

[0072] The control unit includes a microprocessor, a microcontroller, a programmable digital signal processor, or another programmable device. The control unit also includes, or alternatively, an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. The control unit includes a programmable device such as the microprocessor, microcontroller, or programmable digital signal processor described above. The processor may further include code executable by a computer that controls the operation of the programmable device.

[0073] The control functions of the present disclosure may be implemented using an existing computer processor, or by a dedicated computer processor incorporated for this or another purpose for a suitable system, or by a hardwired system. Embodiments within the scope of the present disclosure include a program product that includes machine-executable instructions, or a machine-readable medium for executing or having data structures stored thereon or having these. Such a machine-readable medium can be any available medium that can be accessed by a general-purpose or dedicated computer or other machine having a processor. By way of example, such a machine-readable medium can be RAM, ROM, EPROM, EEPROM, CD-ROM, or other optical disk storage, magnetic disk storage, or other magnetic storage devices, or any other medium that can be used to execute or store the desired program code in the form of machine-executable instructions or data structures and that can be accessed by a general-purpose or dedicated computer or other machine having a processor. When information is transferred or provided to a machine via a network or another communication connection (either hardwired, wireless, or a combination of hardwired or wireless), that machine correctly views that connection as a machine-readable medium. Accordingly, any such connection is properly termed a machine-readable medium. The above combinations are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data that cause a general-purpose computer, a dedicated computer, or a dedicated processing machine to perform a particular function or a group of functions.

[0074] The drawings may show a sequence, but the order of steps may be different from that depicted. Also, two or more steps may be performed simultaneously, or may be partially simultaneous. Such variations will depend on the software and hardware systems selected, as well as the designer's choices. All such variations are within the scope of the present disclosure. Similarly, software implementations can be achieved using standard programming techniques involving rule-based logic and other logic for accomplishing various connection steps, processing steps, comparison steps, and decision steps. Additionally, although the present invention has been described with reference to its specifically illustrated embodiments, many various changes and modifications, etc., will be apparent to those skilled in the art.

[0075] Furthermore, variations to the disclosed embodiments can be understood and achieved by the named person skilled in the art in the practice of the invention for which patent rights are claimed, by consideration of this drawing, this disclosure, and the appended claims of this patent. Further, in the claims, the term "comprising" does not exclude other elements or steps. The indefinite article "a" or "an" does not exclude a plurality.

Claims

A method for mapping stationary objects in a stationary scene (1) using a stationary radar unit (100) adapted to detect signals from all directions without using beamforming or scanning, wherein the stationary radar unit is not moving relative to the stationary scene and is operative to transmit radar signals towards the stationary scene, the stationary radar unit comprising a set of receiver antennas (102a to h) configured to detect radar signals from any direction, the stationary radar unit being configured to measure target velocity in individual velocity bins, the method comprising: continuously collecting radar signals over time using the set of receiver antennas of the stationary radar unit to detect stationary and moving objects in the stationary scene (S102); constructing an occupancy map (300, 400) of stationary objects in the stationary scene using confirmed detections determined from the collected radar signals (S104); comprising: wherein the confirmed detections are detections where the radar signal strength exceeds a detection threshold and the velocity falls within a zero velocity bin, and detections where the radar signal strength exceeds the detection threshold and the non-zero velocity is low enough to cause overflow information in the same bin as the zero velocity bin; method. **Claim 2** The method according to claim 1, wherein the number of the receiver antennas does not exceed 16. **Claim 3** Constructing the occupancy map comprises, over time, including in the occupancy map, for each of a set of individual radii from the position of the radar, all detections where the radar signal strength exceeds the detection threshold and there is no velocity, and all detections where the radar signal strength exceeds the detection threshold and there is a non-zero velocity (S106). The method according to claim 1. **Claim 4** Constructing the occupancy map comprises, for each of the confirmed detections, increasing an occupancy probability value in a corresponding first region (302b) of the occupancy map and decreasing the probability value in a region between the first region and the position of the radar in the occupancy map. The method according to claim 1. **Claim 5** The method according to claim 4, wherein the region between the first region in the occupancy map and the position of the radar intersects a straight line (306) between the first region in the occupancy map and the position of the radar.

6. The method according to claim 4, including increasing the occupancy probability value in a region (303b) adjacent to the first region.

7. The method according to claim 4, wherein the occupancy map is constructed by collecting the probability values over time.

8. The method according to claim 1, including including in the occupancy map one radar detection for each combination of an individual radius from the position of the radar and a detection related to a velocity bin adjacent to the zero velocity bin.

9. Constructing the occupancy map includes determining the azimuth angle of the confirmed detection using selecting the frequency with the most energy content in the Fourier transform of the phase difference between radar signals collected by various receiver antennas divided along a first axis. The method according to claim 1.

10. Constructing the occupancy map includes determining the elevation angle of the confirmed detection using selecting the frequency with the most energy content in the Fourier transform of the phase difference between radar signals collected by various receiver antennas divided along a second axis. The method according to claim 1.

11. The method according to claim 1, wherein the stationary radar unit operates to transmit radar signals in all directions.

12. A non-transitory computer-readable recording medium including a computer program which, when executed by a computer, includes instructions for causing the computer to execute the method according to any one of claims 1 to 11. A control unit (602) for mapping stationary objects in a stationary scene (1), using radar signals collected by a stationary radar unit (100) adapted to detect signals from all directions without using beamforming or scanning, wherein the stationary radar unit is not moving relative to the stationary scene, transmits radar signals towards the stationary scene, and is operative to detect radar signals from any direction using a set of receiver antennas (102a to h), the stationary radar unit being configured to measure target velocity in individual velocity bins, the control unit obtains data indicative of radar signals continuously collected over time by the stationary radar unit to detect stationary and moving objects in the stationary scene, is configured to construct an occupancy map of stationary objects in the stationary scene using confirmed detections determined from the obtained data, wherein the confirmed detections are detections where the radar signal intensity exceeds a detection threshold and the velocity falls within the zero velocity bin, and detections where the radar signal intensity exceeds the detection threshold and the non-zero velocity is low enough to cause overflow information in the same bin as the detections in the zero velocity bin, control unit.

14. A radar system (600) comprising a stationary radar and the control unit according to claim 13.

15. The radar system according to claim 14, wherein the number of receiver antennas of the stationary radar unit does not exceed 16.

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