Radar system and method using virtual sensors

Abstract

The invention relates to a radar system comprising at least three radar sensors (1, 2, 3) that are phase-coherently connected to one another. A first radar sensor (1) and a second radar sensor (2) are arranged at a distance from one another. A virtual sensor (6) is formed by bistatic measurements of at least the first radar sensor (1) and the second radar sensor (2) using MIMO. At least one third radar sensor (3) is arranged offset with respect to the virtual sensor (6). The radar system is designed to detect the elevation angle of a target using the virtual sensor (6) and the at least one third radar sensor (3).

Description

[Technical Field]

[0001] The present invention relates to a radar system that uses a virtual sensor to detect the elevation angle of a target. Additionally, the present invention relates to a radar system that uses a virtual sensor to enable calibration and / or misalignment detection of a radar sensor of the radar system. Furthermore, the present invention relates to a method for detecting the elevation angle of a target using a virtual sensor and / or for performing calibration and / or misalignment detection. [Background technology]

[0002] Today, radar sensors are used to detect the range, velocity, and angle of a target relative to the sensor. The angle can be either the azimuth angle, which represents the angle relative to the target in the horizontal plane, or the elevation angle, which represents the angle relative to the target in the vertical plane, i.e., along the height. Each radar sensor transmits a signal, which is reflected by the target. In monostatic measurements, the reflected signal is received and evaluated by the same radar sensor. In bistatic measurements, the reflected signal is recorded by a second radar sensor, spatially separated from the first. Based on the known distance between the sensors, the target's range, velocity, or angle can then be determined.

[0003] In sensors, transmission may involve multiple transmit and receive antennas, a transmission scheme known as MIMO (Multiple-Input-Multiple-Output).

[0004] Radar systems using three radar sensors to detect both azimuth and elevation angles are known. However, in these radar systems, sensor data is processed separately by independent target evaluation at each sensor, and then the same targets determined at multiple sensors are merged in a central control device or an external computing device (also via cloud computing). Alternatively, sensor data is merged at the object or position level within the central control device. However, in this case, no additional target angle information is obtained from the sensor combination, and each sensor provides target angle information / data measured individually. Here, weighting of the reliability information of the individual sensors is often taken into account. Summary of the Invention [Means for solving the problem]

[0005] A radar system is disclosed that includes at least three radar sensors. The radar sensors are configured and arranged so that their field of view overlap. The radar sensors are phase-coherently coupled to each other to jointly evaluate the phase difference of the sensors' antenna arrays. The sensors are synchronized with each other using clock synchronization and / or high-frequency synchronization, such as via a common local oscillator, crystal clock, or bus clock. Thus, the at least three radar sensors form a phase-coherent cooperative sensor network.

[0006] The first radar sensor and the second radar sensor are spaced apart from each other. In this case, the radar sensors may be arranged in separate modules. Alternatively, the radar sensors may be spaced apart from each other within a common housing. For example, the first radar sensor and the second radar sensor are arranged at the same height on a common horizontal plane. In general, the first radar sensor and the second radar sensor may be arranged within each plane and at different angles relative to the horizontal plane. Only the installation angles and positions of the at least three radar sensors need to be known.

[0007] The first and second radar sensors form a virtual sensor using MIMO (multiple-input, multiple-output) through bistatic measurements. In this application, a "virtual sensor" refers to an imaginary sensor synthesized from a combination of two real sensors. MIMO is used between the two real sensors to generate a virtual sensor. In this case, both sensors transmit and receive signals from the other sensor, respectively. A virtual aperture is thereby spread across the two sensors, with the virtual sensor at the center. Additional radar sensors can also be involved in forming the virtual sensor. In some cases, the entire virtual aperture is sparse (a sparse matrix). Therefore, it may be intended to use only the measurement path combinations of the transmit and receive antennas belonging to the virtual sensor. These measurement path combinations are always bistatic measurements, i.e., one of the two sensors transmits and the other receives, or vice versa. Because individual radar sensors can have multiple transmit and receive antennas, multiple bistatic combinations belonging to the virtual sensor may also occur. The bistatic measurement paths belonging to the virtual sensor can then be evaluated in a known manner (as in conventional radar sensors), for example to determine the azimuth angle of a target.

[0008] A first solution according to the present invention provides for at least one third radar sensor being offset relative to the virtual sensor to detect the elevation angle. The radar sensor is positioned such that the third radar sensor and the virtual sensor have different antenna positions in the vertical direction, i.e., with respect to altitude. The antenna offset can be achieved by different sensor positioning, but also by simply offsetting the antennas within the sensor. In particular, the at least one third radar sensor can be positioned offset in height relative to the virtual sensor. Alternatively, the at least one third radar sensor can be rotated relative to the plane between the first and second radar sensors. In particular, in the case of the same radar sensor, the rotation causes the antennas of the sensors to be offset in height relative to each other. Particularly preferably, the at least one third radar sensor can be rotated 180° and positioned at the same height. The elevation angle of the target is detected using the virtual sensor and the at least one third sensor. In this case, data of the virtual sensor and data of at least one third radar sensor are jointly evaluated in a phase-coherent manner in order to determine the elevation angle of the target.

[0009] The joint evaluation can be based on the raw data of at least three radar sensors, for example time signals and spectra, etc. The evaluation of the raw data is carried out in a manner known per se, similar to the evaluation of the individual sensors, with the difference that all data of the radar system are evaluated jointly and in a phase-coherent manner as if they were one sensor.

[0010] Alternatively or additionally, the joint evaluation may be based at least in part on preprocessed data. When the complex amplitude values ​​of the radar sensor and the virtual sensor are available, multi-stage evaluation of the preprocessed data is possible. This allows the data to be calculated at various levels, for example, by 2D-FFT (two-dimensional fast Fourier transform), CFAR (constant false alarm rate), or angle evaluation. The calculation steps performed in each case are performed in a manner known per se, as in the evaluation of the individual sensors. In this case, previously performed calculation steps (e.g., 2D-FFT) can be omitted. An exception is a coherent calculation based on the already calculated target angle from the radar sensor. Here, each of the radar sensors (and therefore the virtual sensor) provides a complex amplitude value in addition to the angle after angle evaluation. The amplitudes of the sensors to be combined with each other, i.e., the virtual sensor and at least one third sensor, are calculated in phase coherence with each other via the complex amplitude value based on the relative positions, i.e., the offset of their antennas. This type of evaluation corresponds to a new angle calculation. For this reason, the approximate azimuth angle and / or approximate elevation angle can already be roughly calculated by the radar sensor, and the phase-coherent joint evaluation only needs to be performed in a narrow angle range around the already roughly calculated angle, respectively, so that the angle calculation can be performed with less computational effort.

[0011] As a result, the radar sensor and virtual sensor work together in a phase-coherent manner to detect elevation angles in addition to azimuth angles, allowing a radar sensor that only has a one-dimensional antenna arrangement and is therefore only able to detect target angles in one plane (usually azimuth angles) to detect both azimuth angles and elevation angles in a second plane.

[0012] If the radar sensor already has a two-dimensional antenna arrangement that can detect target angles in two planes (i.e., azimuth and elevation), the radar sensor and the virtual sensor operating in phase coherent cooperation can improve the angular resolution in the second plane, and therefore typically with respect to elevation.

[0013] A second solution according to the present invention proposes that a third radar sensor be positioned at the location of the virtual sensor, i.e., centrally between the first and second radar sensors. The radar sensors are positioned such that the third radar sensor and the virtual sensor have antenna positions that overlap vertically, i.e., in terms of altitude. Phase synchronization is achieved by overlapping the antenna channels of the virtual sensor and at least one third radar sensor. For this purpose, received phase information of at least one of the overlapping antenna channels of the virtual sensor is compared with phase information of at least one of the overlapping antenna channels of the at least one third radar sensor. The phase information of the virtual sensor and the phase information of the at least one third radar sensor are jointly evaluated in a phase-coherent manner. Phase synchronization allows for calibration of each of the radar sensors. Ideally, the phase values ​​of the overlapping channels are identical during operation. If this is not the case, the phase can be readjusted by differential generation. Furthermore, even when multiple antenna channels are overlapped, misalignments can be detected and / or corrected depending on the number and position of the overlapping elements. Depending on the type of misalignment, a distinction can be made between phase offset and phase gradient. Phase offset is constant for all overlapping antenna channels and indicates an error in the assembly or placement of the sensor in the spatial direction. Phase gradient varies between overlapping antenna channels and indicates an error due to the tilt or rotation of the sensor in the azimuth or elevation direction. As already mentioned above, the joint evaluation can be based on raw sensor data or, alternatively or additionally, on preprocessed data.

[0014] Virtual sensors offer the advantage of reduced memory usage and computational effort, as unwanted measurement path combinations can be processed separately or discarded. The radar sensors may all have the same configuration. Alternatively, the radar sensors may have different configurations. In particular, the third radar sensor may be different from the first and second radar sensors. However, the first and second radar sensors may also be different.

[0015] The elevation angle can be determined depending on the distance to the target if one or more radar sensors are designed for this purpose (e.g., because the radar sensor has a two-dimensional antenna arrangement). The improved elevation angle resolution achieved by the combined evaluation is particularly advantageous at larger distances to the target, allowing for earlier detection of small obstacles. At closer ranges, a lower-resolution evaluation is sufficient. Therefore, the radar system does not need to simultaneously evaluate all data from all sensors, but can perform joint or separate evaluations, e.g., depending on the distance to the target.

[0016] The calculation of the elevation angle (and azimuth angle) using the virtual sensor in the radar system is preferably performed in the electronic control unit of the radar sensor of the radar system. In the case of so-called satellite sensors working in conjunction with a central control device, the calculation of the elevation angle (and azimuth angle) may also be performed in the central control device. Alternatively, the calculation can be performed in an external computing device. Cloud computing may also be contemplated here.

[0017] The computer program is specifically designed to execute the steps of the method when executed on the control device. This allows the method to be implemented in conventional electronic control devices without the need for structural modifications to the device. For this purpose, the computer program is stored on a machine-readable storage medium. Installing the computer program in a conventional electronic control device results in an electronic control device designed to detect the elevation angle of a target and / or perform calibration and / or position shift detection of a radar sensor. As mentioned above, this may be the electronic control device of the radar sensor, a central electronic control device, or an external computing device, particularly in the context of cloud computing.

[0018] The radar system is preferably used in a motor vehicle. The radar sensors are preferably located at the front and optionally at the rear of the vehicle. However, the radar system, and in particular the generation of the virtual sensors, is not associated with the axles or a specific orientation of the vehicle. The radar system can be applied to all visibility levels associated with the vehicle.

[0019] Exemplary embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. [Brief explanation of the drawings]

[0020] [Figure 1a] 1 is a schematic diagram of a radar system arrangement according to the present invention; [Figure 1b] 1 is a schematic diagram of a radar system arrangement according to the present invention; [Figure 1c] 1 is a schematic diagram of a radar system arrangement according to the present invention; [Figure 1d] 1 is a schematic diagram of a radar system arrangement according to the present invention; [Figure 1e] 1 is a schematic diagram of a radar system arrangement according to the present invention; [Figure 1f] 1 is a schematic diagram of a radar system arrangement according to the present invention; [Figure 2]1 is a schematic diagram of a first exemplary embodiment of a radar system according to the present invention; [Figure 3] FIG. 2 is a schematic diagram of a second exemplary embodiment of a radar system according to the present invention; [Figure 4] FIG. 4 is a schematic diagram of a third exemplary embodiment of a radar system according to the present invention. [Figure 5] 1 is a flow chart of an exemplary embodiment of a method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] 1a-1f show different arrangements of the first radar sensor 1, the second radar sensor 2, and the third radar sensor 3 when assembling a radar system according to the present invention. The radar sensors 1, 2, and 3 each have an antenna array 10-13, 20-23, or 30-33 capable of transmitting and receiving radar signals. The radar sensors 1, 2, and 3 can have the same or different configurations, as will be noted in the individual exemplary embodiments. All radar sensors 1, 2, and 3 are connected to each other using MIMO (multiple-input, multiple-output) technology, allowing them to receive and evaluate the radar signals of the other radar sensors 1, 2, and 3. The radar sensors 1, 2, and 3 are phase-coherently coupled to each other, allowing the phase difference between the antenna arrays 10-13, 20-23, and 30-33 of each radar sensor 1, 2, and 3 to be jointly evaluated. These couplings are indicated by arrows in FIGS. 1a-1f. The first radar sensor 1 and the second radar sensor 2 perform bistatic measurements using MIMO. In addition, the first radar sensor 1 and the second radar sensor 2 are synchronized with each other by clock synchronization and high frequency synchronization. This forms a virtual aperture 4 that includes the area of ​​the integrated radar sensors 1 and 2.

[0022] In the exemplary embodiment of FIGS. 1a-1e, the third radar sensor 3 functions as a master and transmits a radar signal using a clock. The clock may be generated, for example, by a local oscillator, a crystal clock, or a bus clock. The radar signal from the third radar sensor 3 is received by the two radar sensors 1 and 2. The radar sensors 1 and 2 function as slaves and output radar signals that are phase-coherent with the radar signal from the third radar sensor 3.

[0023] In the exemplary arrangement of the exemplary embodiment according to FIG. 1a, the third radar sensor 3 is positioned higher than the other two radar sensors 1 and 2. Therefore, the antenna array 30 of the third sensor 3 is positioned vertically above the antenna array 10 of the first radar sensor 1 and the antenna array 20 of the second radar sensor 2, as well as the virtual aperture 4. However, a lower positioning of the third radar sensor 3 is also contemplated. In FIG. 1a, all radar sensors 1, 2, and 3 and all their antenna arrays 10, 20, and 30 are identically configured. The exemplary embodiment according to FIG. 1b differs from the exemplary embodiment according to FIG. 1b in that the radar sensors 1, 2, and 3 are different, i.e., the first radar sensor 1 has a first antenna array 11, the second radar sensor 2 has a second antenna array 11, and the third radar sensor 3 has a third antenna array 30, each of which is different from one another. The first radar sensor 1 and / or the second radar sensor 2 may be, for example, a repeater. In a further exemplary embodiment, two of the radar sensors 1, 2, 3 may be identical, or only one may be different.

[0024] In a further exemplary arrangement of the exemplary embodiment according to Fig. 1c, all radar sensors 1, 2, and 3 are at the same height and are identically configured. The third radar sensor 3, located in the middle of the other two radar sensors 1 and 2, is rotated by 180°. Again, the antenna array 30 of the third sensor is thus positioned at a different height than the antenna arrays 10 and 20 of the other two radar sensors 1 and 2.

[0025] 1d shows an arrangement in which the first radar sensor 1 and the third radar sensor 3 are arranged at the same height and are identically configured. The second radar sensor 2 is arranged above the other two radar sensors 1 and 3 and is structurally different from the other two radar sensors 1 and 3, particularly in that the antenna array 22 is different therefrom. The third radar sensor 3 is thus arranged at an edge position. Furthermore, a virtual aperture 4 is formed by the first radar sensor 1 and the second radar sensor 2.

[0026] In the exemplary embodiment of FIG. 1e, all radar sensors 1, 2, and 3 are located at different heights and configured differently with various antenna arrays 11, 22, and 30. The third radar sensor 3 is located in the center of the other two radar sensors 1 and 2. Furthermore, a virtual aperture 4 is formed by the first radar sensor 1 and the second radar sensor 2. This arrangement provides particularly good altitude resolution when determining elevation angles when all sensor signals are jointly evaluated. See FIG. 5 and the associated description. The third sensor has an antenna position that overlaps with a virtual sensor (not shown). Therefore, this arrangement can be used for phase calibration and misalignment detection. The virtual sensor creates redundancy for the third radar sensor 3.

[0027] In the exemplary embodiment of FIG. 1f, a central control device 5 is provided, each connected to radar sensors 1, 2, and 3. Here, radar sensors 1, 2, and 3 are called satellite sensors and function as quasi-slaves. The central control device generates a common phase / frequency reference signal using a local oscillator (or alternatively using a crystal clock or bus clock) as a clock for coherent processing. The radar sensors 1, 2, and 3 are phase-coherently synchronized via the common phase / frequency reference signal. Here, the arrangement of radar sensors 1, 2, and 3 is similar to, but not limited to, that of the exemplary embodiment of FIG. 1c.

[0028] Further exemplary embodiments may also reflect the arrangement of radar sensors 1, 2, 3 according to Figures 1a to 1f. The detection of the target elevation angle will now be described with reference to FIGS. 2 to 4. In FIGS. 2 to 4, the radar sensors 1, 2, and 3 are shown, as described with reference to FIG. 1, along with the virtual aperture 4 formed by the first and second radar sensors 1 and 2. Here, the radar sensors 1, 2, and 3 are arranged according to the exemplary embodiment of FIG. 1a, i.e., the third radar sensor 3 is arranged in the center of the other two radar sensors 1 and 2, at a higher level than them. However, elevation angle detection is not limited to this arrangement. Other arrangements of the radar sensors 1, 2, and 3 can also be used, particularly those shown in FIGS. 1b to 1f, including an edge-positioned arrangement of the third radar sensor 3. The signals evaluated depend on the arrangement of the radar sensors 1, 2, and 3. The clock can be predetermined by one of the radar sensors 1, 2, and 3, particularly by the third radar sensor 3 acting as a master, or by a central control device 5, as described in the exemplary embodiment of FIG. 1f.

[0029] 2 to 4 also show a virtual sensor 6 formed using MIMO by bistatic measurements of the first actual radar sensor 1 and the second actual radar sensor 2. The virtual sensor 6 is formed in the center of the virtual aperture 4 of the two radar sensors 1 and 2. Correspondingly, the virtual sensor 6 has a virtual antenna array 60 or 63.

[0030] To determine the elevation angle, data from the virtual sensor 6 formed from the bistatic measurements are combined with data from a real third radar sensor 3 performing monostatic measurements. The third radar sensor 3 is displaced in height relative to the virtual sensor 6. In this example, the third radar sensor 3 is located above the virtual sensor 6, while in another example (not shown) it is located below. Furthermore, the virtual sensor 6 and the third radar sensor 3 form a virtual aperture 7.

[0031] In the first exemplary embodiment according to Fig. 2, the radar sensors 1, 2, and 3 have one-dimensional antenna arrays 10, 20, and 30, respectively. The virtual aperture 7 extends in the elevation direction and includes the sensor planes of the one-dimensional antenna array 30 of the third radar sensor 3 and the virtual antenna array 60 of the virtual sensor 6. The elevation angle detection is achieved by a joint evaluation of bistatic measurements via the virtual sensor 6 and monostatic measurements via the real third radar sensor 3.

[0032] In the second and third exemplary embodiments from Figures 3 and 4, the radar sensors 1, 2, and 3 have two-dimensional antenna arrays 13, 23, and 33, respectively. An improved resolution is achieved when detecting the elevation angle by joint evaluation of bistatic measurements via the virtual sensor 6 and monostatic measurements via the real third radar sensor 3. In the second exemplary embodiment according to Figure 3, the antenna array 33 of the real third radar sensor 3 and the virtual antenna array 63 of the virtual sensor 6 do not overlap. Therefore, the highest possible resolution is achieved when detecting the elevation angle.

[0033] In the third exemplary embodiment according to FIG. 4 , an overlap 8 occurs between the antenna array 33 of the real third radar sensor 3 and the virtual antenna array 63 of the virtual sensor 6. In this exemplary embodiment, an additional phase calibration between the third radar sensor 3 and the virtual sensor 6 (and thus indirectly between the two real radar sensors 1 and 2) can be performed. Since the measurement results of the overlapping antenna channels, i.e., in this case the lower channel of the antenna array 33 of the third radar sensor 3 and the upper channel of the antenna array 63 of the virtual sensor 3, must be identical, a phase correction value can be determined by comparing the measurement results of these overlapping measurement channels. This correction value can also be applied to the non-overlapping antenna channels of the respective sensors 3 and 6. Furthermore, if the measurement results of the overlapping antenna channels are not identical, a comparison with a static target can also be used to determine assembly or alignment errors of the radar sensors 1, 2, and 3.

[0034] During the evaluation, raw data from the third radar sensor 3 and the virtual sensor 6, such as time signals and spectra, can be evaluated. Alternatively, preprocessed data is evaluated, as shown in FIG. 5 . The radar sensors 1, 2, and 3 perform measurements 100. Each radar sensor 1, 2, and 3 records multiple detection results, such as the target's range, relative velocity, azimuth angle, area, and possibly also elevation angle. In FIG. 5 , the detections of the first radar sensor 1 are designated by reference numeral 101, the detections of the second radar sensor 2 by reference numeral 102, and the detections of the third radar sensor 3 by reference numeral 103. The bistatic measurements of the first radar sensor 1 and the second radar sensor 2 form the virtual sensor 6 using MIMO (104). The detections 101 and 102 of the first radar sensor 1 and the second radar sensor 2, linked via the virtual sensor 6, are compared with the detection 103 of the third radar sensor 3 (105). The individual detections can then be calculated relative to one another, which reduces the required data rate between the sensors 3, 6. The spatial positions of the detections 101, 102, 103 relative to the sensors 3, 6 and the associated areas of the detections 101, 102, 103 are compared with one another. If the detections 101, 102, 103 do not match, the misalignment is detected and / or corrected (106). If there is sufficient match, a common processing 107 is performed by calculating the complex amplitudes of the detections 101, 102, 103 relative to one another.

Claims

1. A radar system comprising at least three radar sensors (1, 2, 3) connected to each other in a phase-coherent manner, wherein a first radar sensor (1) and a second radar sensor (2) are arranged spaced apart from each other, a virtual sensor (6) is formed by bistatic measurements of at least the first radar sensor (1) and the second radar sensor (2) using MIMO, and at least one third radar sensor (3) is arranged offset from the position where the virtual sensor (6) is formed, and the radar system is designed to detect an elevation angle of a target using the virtual sensor (6) and the at least one third radar sensor (3). the at least one third radar sensor (3) is arranged at a height offset with respect to a plane between the first radar sensor (1) and the second radar sensor (2); a portion of the at least one third radar sensor (3) and a portion of the virtual sensor (6) overlap (8); A radar system characterized by:

2. 1. A method for detecting an elevation angle using a radar system comprising at least three radar sensors (1, 2, 3) connected to each other in a phase-coherent manner, wherein a virtual sensor (6) is formed (105) by bistatic measurements of the first radar sensor (1) and the second radar sensor (2) using MIMO, and data of the virtual sensor (6) and data of the at least one third radar sensor (3) are jointly evaluated in a phase-coherent manner to detect (107) the elevation angle of a target and / or to perform phase calibration and / or position shift detection (106) of the radar sensors (1, 2, 3), the at least one third radar sensor (3) is arranged at a height offset with respect to a plane between the first radar sensor (1) and the second radar sensor (2); a portion of the at least one third radar sensor (3) and a portion of the virtual sensor (6) overlap (8); A method characterized by:

3. 3. The method according to claim 2, characterized in that raw and / or pre-processed data of the sensors are used during the joint evaluation.

4. A computer program designed to carry out the steps of the method according to claim 2 or 3.

5. A machine-readable storage medium on which the computer program according to claim 4 is stored.

6. An electronic control device (5) designed to detect the elevation angle and / or to perform phase calibration and / or position deviation detection of a radar sensor (1, 2, 3) using the method according to claim 2 or 3.

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