CN113366339A - Sensor system for detecting objects in the surroundings of a vehicle - Google Patents
Sensor system for detecting objects in the surroundings of a vehicle Download PDFInfo
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- CN113366339A CN113366339A CN202080011884.4A CN202080011884A CN113366339A CN 113366339 A CN113366339 A CN 113366339A CN 202080011884 A CN202080011884 A CN 202080011884A CN 113366339 A CN113366339 A CN 113366339A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/003—Bistatic radar systems; Multistatic radar systems
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/42—Simultaneous measurement of distance and other co-ordinates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/87—Combinations of radar systems, e.g. primary radar and secondary radar
- G01S13/878—Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/93—Radar or analogous systems specially adapted for specific applications for anti-collision purposes
- G01S13/931—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of land vehicles
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4004—Means for monitoring or calibrating of parts of a radar system
- G01S7/4017—Means for monitoring or calibrating of parts of a radar system of HF systems
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
- G01S7/4082—Means for monitoring or calibrating by simulation of echoes using externally generated reference signals, e.g. via remote reflector or transponder
- G01S7/4091—Means for monitoring or calibrating by simulation of echoes using externally generated reference signals, e.g. via remote reflector or transponder during normal radar operation
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Abstract
The invention relates to a sensor system (10) for detecting an object (12) in a surroundings (14) of a vehicle (16), having: a first radar sensor node (S1) and a second radar sensor node (S2), the first radar sensor node and the second radar sensor node respectively including: at least two transmitting elements (Tx) for transmitting radar signals; at least two receiving elements (Rx) for receiving reflections of radar signals transmitted by the two radar sensor nodes; and a processor unit (22) for detecting objects in the surroundings of the vehicle based on the received reflections, and the first and second radar sensor nodes are arranged on the vehicle in a spaced-apart manner from each other, wherein the transmitting elements and the receiving elements of the first radar sensor node form an intra-node field of the aperture elements of the virtual receive aperture, and the transmitting elements of the first radar sensor node and the receiving elements of the second radar sensor node form a cross-node field of the aperture elements of the virtual receive aperture; and the distance between the two radar sensor nodes and the distance between the transmitting element and the receiving element within the first radar sensor node are selected such that: the position of the first aperture element of the intra-nodal field corresponds to the position of the second aperture element across the nodal field. The invention also relates to a vehicle and a calibration method for calibrating radar sensor nodes of a sensor system.
Description
The present invention relates to a sensor system for detecting objects in the surroundings of a vehicle and to a calibration method for calibrating radar sensor nodes of a sensor system.
Contemporary vehicles (automobiles, transport vehicles, trucks, motorcycles, etc.) include several sensors that provide information to the driver and semi-or fully automatically control the various functions of the vehicle. The important prerequisite here is that the surroundings of the vehicle itself are detected, identified and modeled. Sensor data with information about the surroundings are detected by means of surroundings sensors, such as radar sensors, lidar sensors, ultrasonic sensors and camera sensors. The objects in the surroundings of the vehicle can then be identified and classified as a function of the detected data and, if necessary, additionally considered data that are available in the vehicle. Based on the identified object, for example, the behavior of the autonomous or semi-autonomous vehicle may be adapted to the current situation or additional information may be provided to the driver.
A widely used sensor principle here is radar technology. Radar sensors for vehicles currently in use typically include multiple transmit elements and multiple receive elements and operate as multiple-input multiple-output radars (MIMO radars).
Radar sensors operate in part in coordination, where such a sensor network includes a plurality of individual sensors (also referred to as nodes). During the coordinated operation of a plurality of radar sensor nodes, additional information may be obtained when evaluating a multi-base signal (i.e., a signal sent by one radar sensor node and received by another radar sensor node). Therefore, on the one hand, the signals of the individual radar sensor nodes themselves are evaluated; on the other hand, the (multi-ground) signals transmitted from one radar sensor node to another are evaluated. Due to the increased physical extension (distance between the transmitting element and the receiving element), this evaluation of the multi-ground signal leads to a larger (virtual) aperture than would be the case if a single sensor were used. In making angle estimates in both azimuth and elevation, the aperture is a limiting amount of resolution. Furthermore, the additional coherent integrated power enables a larger range.
In this respect, a motor vehicle having a plurality of radar sensors arranged at different installation locations and a method for operating a plurality of radar sensors arranged at different installation locations of a motor vehicle are described in DE 102016004305 a 1. Radar sensors are designed to detect the vicinity of a motor vehicle and can operate as transmitters and/or receivers. The at least one first radar sensor is designed to emit a transmission signal. At least one second radar sensor, which is different from the first radar sensor, is designed to receive a reflected signal of the transmitted signal.
A challenge in using radar sensors in a sensor network is calibration. Calibration is usually only possible at the point in time when the surroundings sensor has been installed in the vehicle. To perform the calibration process, the vehicle is typically driven into a suitable test chamber (absorption chamber) in order to perform the calibration. In most cases, a sensor target on the robot arm is moved to a predetermined measurement position and detected with a radar sensor. Depending on the scheme, joint coordination (abstimung) or calibration may be required for multiple radar sensor nodes in a sensor network. A particular challenge here is the phase and frequency drift and long-term aging effects of oscillators that have different effects on the radar sensor nodes.
In view of this, the object of the invention is to enable a plurality of independent radar sensor nodes to operate in coordination. In particular, an evaluation of the multi-ground signals should be carried out and the costs for the calibration should be kept low. Robustness against changes that occur over time, such as aging effects, should be achieved.
To achieve this object, the invention relates in a first aspect to a sensor system for detecting an object in the surroundings of a vehicle, having:
a first radar sensor node and a second radar sensor node, the first radar sensor node and the second radar sensor node respectively comprising: at least two transmitting elements for transmitting radar signals; at least two receiving elements for receiving reflections of radar signals transmitted by the two radar sensor nodes; and a processor unit for detecting objects in the surroundings of the vehicle based on the received reflections, and the first and second radar sensor nodes are arranged on the vehicle in a spaced-apart manner from each other, wherein,
the transmit elements and receive elements of the first radar sensor node form an intra-node field of an aperture element of a virtual receive aperture, and the transmit elements of the first radar sensor node and receive elements of the second radar sensor node form a cross-node field of the aperture element of the virtual receive aperture; and is
A distance between the two radar sensor nodes and a distance between a transmitting element and a receiving element within the first radar sensor node are selected such that: the position of the first aperture element of the intra-nodal field corresponds to the position of the second aperture element of the cross-nodal field.
The invention relates in a further aspect to a calibration method for calibrating a radar sensor node of the above sensor system, the calibration method having the steps of:
acquiring a phase difference of a transmitting element and a receiving element of the first radar sensor node, which is independent of the angle;
detecting objects in the surroundings of the vehicle in the far field of the radar sensor nodes; and is
Calculating a phase difference of the transmitting element of the second radar sensor node independent of the angle of the receiving element.
Other aspects of the invention relate to: a vehicle having the aforementioned sensor system; and a computer program product with a program code for performing the steps of the above calibration method when run on a computer; and a storage medium having stored thereon a computer program which, when run on a computer, causes the calibration method described herein to be carried out.
Preferred embodiments of the invention are described in the dependent claims. It goes without saying that the features mentioned and those still to be explained below can be used not only in the respectively given combination but also in other combinations or alone without departing from the scope of the invention. In particular, the sensor system, the calibration method, the vehicle and the computer program product are embodied in a manner corresponding to the design variants described for the sensor system and the calibration method in the dependent claims.
According to the invention, a sensor system or a sensor network is provided having at least two radar sensor nodes, wherein each individual radar sensor node has a plurality of transmitting elements and a plurality of receiving elements and can be operated as or as a MIMO radar. The processor unit of the radar sensor node is designed to: in addition to the reflection of the radar signal of the own radar sensor node, the reflection of a radar signal sent by another radar sensor node of the sensor system is also evaluated. Based on the evaluation of the reflection of the transmitted radar signal, objects in the surroundings of the vehicle can be detected. Higher angular resolution can be achieved if the signals of different radar sensor nodes are superimposed in a phase-correct manner.
For this purpose, the transmitting element and the receiving element of the first radar sensor node form an intra-node field of the aperture element of the virtual receive aperture. In this regard, the intra-node field corresponds to a virtual array of the MIMO radar. Furthermore, the transmit elements of one radar sensor node together with the receive elements of another radar sensor node form a cross-node field of the aperture elements of the virtual receive aperture. The cross-node field corresponds to a virtual array formed by elements of different radar sensor nodes.
In order to ensure a phase-correct superposition, the (physical) distance between the radar sensor nodes or between the transmitting and receiving elements of these radar sensor nodes and the distance of the transmitting and receiving elements within the first radar sensor node are adjusted according to the invention. In particular, the adjustment is carried out in such a way that superimposed positions are generated within the two virtual arrays of radar sensor nodes. In other words, a virtual aperture in which the element positions are repeatedly present (doppelt vorkommen) is generated by appropriately selecting the positions of the transmission element and the reception element. The position of the aperture element of the intra-nodal field is the same as the position of the second aperture element across the nodal field.
Due to this selection of the distance, an automatic calibration of the sensor system may be performed. Based on the calibration that has been performed on one of the radar sensor nodes (first radar sensor node), the calibration may be passed to the second radar sensor node via the re-existing virtual element. In order to perform this transfer, it is only necessary to detect objects in the vehicle surroundings in the far field of the radar sensor nodes of the sensor system. Objects above a distance of 20m are generally sufficient for this purpose. Due to the selected distance, the same signal is then expected for both channels (receive element in the intra-nodal field and receive element in the cross-nodal field). The location of these objects need not be known. The calibration factor can be adapted or introduced when a deviation occurs.
The sensor system according to the invention offers a greatly simplified possible solution for calibration compared to current solutions for operating radar sensor networks and evaluating multi-base radar signals. In particular (in the case of using radar sensor nodes of the same type), a calibration of a single radar sensor node is sufficient, which can then be passed on to another radar sensor node via the repeatedly present elements. High-cost calibration of multiple radar sensor nodes is avoided. Thereby enabling cost reduction. It is possible in particular to carry out the coordination (calibration) of the two radar sensor nodes with respect to one another iteratively as a self-calibration. Aging effects and phase and frequency drifts can thereby be counteracted, so that an accurate detection of objects in the surroundings of the vehicle is ensured even after a long period of operation. A high resolution radar sensor system is provided.
In a preferred embodiment, the first aperture element is formed by a first transmitting element of the first radar sensor node and a first receiving element of the first radar sensor node. The second aperture element is formed by a second transmitting element of the first radar sensor node and a first receiving element of the second radar sensor node or by a second receiving element of the first radar sensor node and a first transmitting element of the second radar sensor node. The first aperture element is an aperture element of a virtual array (intra-nodal field) of the first radar sensor node. The second aperture element is an element of a virtual array (cross-node field) formed by two radar sensor nodes. For a cross-node field, the receive element of one of the two radar sensor nodes and the transmit element of the other of the two radar sensor nodes may be used, resulting in two possible solutions (directions). The repeated positions allow calibration of the second radar sensor node based on the calibration of the first radar sensor node. A more efficient calibration is achieved. Accurate assessment and detection of objects in the surroundings of the vehicle is ensured.
In a preferred embodiment, the sensor system comprises a further radar sensor node which is arranged on the vehicle at a distance from the first radar sensor node and the second radar sensor node. The transmitting and receiving elements of the further radar sensor node form a further nodal internal field of the aperture element of the virtual receive aperture. The transmitting or receiving elements of the further radar nodes form a further cross-node field of aperture elements of a virtual receive aperture with the transmitting or receiving elements of the first radar sensor node and/or the second radar sensor node. The distances of the further radar sensor nodes from the first and second radar sensor nodes and the distances of transmitting and receiving elements within the further radar sensor nodes are selected such that: the position of the further first aperture element of the further intra-nodal field corresponds to the position of the further second aperture element of the further cross-nodal field. Preferably more than two radar sensor nodes are present. All radar sensor nodes of the sensor system are spaced a distance with respect to each other, which distances do not have to be equal. However, all ranges are selected such that each radar sensor node and at least one further radar sensor node have a repeating element in the respective cross-node virtual receive aperture. It is thus possible to calibrate further radar sensor nodes in the sensor system based on the calibration of one radar sensor node. It is sufficient to measure a single radar sensor node. Costs can be avoided by having to perform only a calibration of a single radar sensor node. The calibration is simplified and costs are saved. In addition, the accuracy can be improved. Furthermore, calibration can be performed during continuous operation, which is resistant to aging effects and phase and frequency drift.
In a further advantageous embodiment, the radar sensor nodes are arranged at a distance of more than 20cm, preferably more than 50cm, from one another on the vehicle. The distance is at least 20 cm. Thereby enlarging the virtual aperture, which promotes an increase in the physical extension. Therefore, the resolution can be further improved when angle estimation is performed. An accurate detection of objects in the vehicle surroundings or a corresponding position assignment of these objects is achieved.
In a further advantageous embodiment, the radar sensor nodes are designed for transmitting and receiving radar signals in the frequency range of 76GHz to 81GHz, preferably 77 GHz. The use of such radar frequencies is now common in the industrial and automotive fields. The measurement can be performed with high resolution, wherein at the same time a sufficient range is ensured.
In a further advantageous embodiment, the sensor system comprises a frequency generator for generating a clock frequency common to the radar sensor nodes, preferably in the range of 20GHz, wherein the frequency generator is connected to the radar sensor nodes. Improved coordination may be achieved by using a unified frequency generator. It is possible in particular to perform a coordinated calibration. The accuracy of detecting the position of an object in the surroundings of the vehicle can be further improved.
In a preferred embodiment, the radar sensor nodes each have the same number of transmitting and receiving elements and the same topology. In this respect, topology is to be understood as the arrangement of the transmitting elements and the receiving elements. In particular, the same radar sensor may be used as radar sensor node. Calibration is further simplified by using the same sensor, since the coordinated behavior of different radar sensor nodes can be preset.
In a preferred embodiment of the calibration method, the steps of detecting and calculating are carried out repeatedly, preferably at regular time intervals, during the operation of the vehicle. By repeatedly carrying out the steps of detecting and calculating, a regular calibration of the sensor system in the sense of a self-calibration can be performed. An accurate detection of objects in the surroundings of the vehicle can be ensured even in the case of sensor systems operating over a relatively long period of time.
In an advantageous embodiment of the calibration method, the step of calculating comprises: a range-doppler matrix of signal paths of the first and second aperture elements is acquired and a correlation between the acquired range-doppler matrices is calculated. A simple process can be performed by using the range-doppler matrix. The calibration may be based on the location of the repeated presence of the virtual aperture element.
The radar sensor transmits a radar signal and receives a reflection of the radar signal on an object within a visible range of the radar sensor. The visible range here represents an area within which an object can be detected. The vehicle surroundings include, inter alia, the area in the vicinity of the vehicle that is visible from a radar sensor mounted on the vehicle. The sensor system according to the invention may also be referred to as a radar sensor network. In particular, a plurality of radar sensor nodes can be used, which for example enable a 360 ° omnidirectional field of view and thus can represent a complete image of the vehicle surroundings. The sensor data of the radar sensor nodes comprise inter alia the range, elevation and azimuth for various detections of the radar sensor nodes. In this respect, a scanning point is to be understood as a single point or a single detection of an object or object. A large number of scanning points are typically generated during the measurement period of the radar sensor node. A measurement cycle is understood here to mean a transient passing through the field of view. The field of aperture elements may be referred to as a virtual array. The distance may be understood as a euclidean distance, in particular.
The invention will be described and explained in detail hereinafter with the aid of selected embodiments in conjunction with the accompanying drawings. In the drawings:
fig. 1 schematically shows a view of a vehicle according to the invention with a system for detecting objects in the surroundings of the vehicle;
FIG. 2 schematically illustrates a radar sensor node;
figure 3 schematically shows the field of aperture elements of a virtual receive aperture;
FIG. 4 schematically illustrates the configuration of two radar sensor nodes and the field formed by the aperture elements; and is
Fig. 5 schematically shows a method according to the invention.
Fig. 1 schematically shows a vehicle 16 according to the invention having a sensor system 10 for detecting an object 12 in the surroundings 14 of the vehicle 16. The sensor system 10 includes a first radar sensor node S1 and a second radar sensor node S2. The radar sensor nodes S1, S2 are arranged on the vehicle in a spaced-apart manner from each other. The two radar sensor nodes S1, S2 may be located, for example, in the range of the left and right headlights of a passenger motor vehicle. The distance between the radar sensor nodes is in most cases at least 20 cm. Since the radar signals of the two radar sensor nodes can also be received by the respective other radar sensor nodes (multi-base), an enlarged virtual aperture and an increased received power compared to a single sensor can be achieved. The resolution of the angle estimation in azimuth and elevation can thereby be improved.
A single radar sensor node S is schematically shown in fig. 2. The radar sensor node S comprises two transmitting elements Tx1, Tx2, which are designed for transmitting radar signals. The radar sensor node S further comprises two receiving elements Rx1, Rx2, which are designed to receive reflections of the transmitted radar signals on objects in the vehicle surroundings. In this regard, the radar sensor node S corresponds to a MIMO radar having a plurality of transmitting elements and a plurality of receiving elements. It is to be understood that the radar sensor node S may also comprise further transmitting elements and/or receiving elements. Furthermore, the radar sensor node S comprises a processor unit 22, which is designed to detect objects in the vehicle surroundings on the basis of the received reflections. The functionality of the processor unit 22 may be partly or completely implemented in software and/or hardware. In this respect, the processor unit 22 may be designed as a processor, a processor module, or also as software for a processor.
In fig. 3, a basic configuration of a MIMO radar sensor node having ten receiving elements Rx (first row in fig. 3) and two transmitting elements Tx (second row) is shown. As each receive element Rx receives reflections of the signals from the two transmit elements Tx, a field of aperture elements of a virtual receive aperture is generated, which has a total of 20 aperture elements (third row, also referred to as antenna position or virtual array). As shown, the virtual receive aperture here has a larger extension than the receive aperture of the receive element Rx. In the example shown, the middle element m of the virtual receive aperture is repeated.
For angle estimation of the target, different aperture elements in the virtual receive apertureThe phase difference of the radar signals is observed at the element. In the illustrated example, consider the case where all receive elements Rx and transmit elements Tx are along the x-axis of the coordinate space for simplicity. In a three-dimensional coordinate system, xTx,iIndicates the position of the transmitting element and xRx,iIndicating the position of the receiving element. The signals between these elements and the position x are thenRx,j、xTx,jThe phase difference of the signals between the elements at (1) is:
where λ is the wavelength and
is the angle of incidence of the signal. The phase difference is generated directly at the antenna position (aperture element). The following additional, angle-independent phase differences are added to this phase difference: and tracing back the transmission time difference of the signal in the radar sensor node according to the additional phase difference. This angle-independent phase difference must be compensated by a corresponding calibration factor.
In fig. 4, a sensor system 10 according to the invention with two radar sensor nodes S1, S2 is schematically shown. The two radar sensor nodes S1, S2 have two transmitting elements Tx1, Tx2 and three receiving elements Rx1, Rx2, Rx3, respectively. Furthermore, the two radar sensor nodes S1, S2 each have a processor unit 22.
In fig. 4, additional, angle-independent phase differences (added phase differences) are shown by way of example for two transmitting elements and two receiving elements. Typically, these phase differences within a single sensor are measured during a calibration process and compensated for in the signal processing. Such a phase difference also arises between the transmitting and receiving elements of different radar sensor nodes if a sensor network with a plurality of radar sensor nodes is operated and a multi-base evaluation is performed. In order to jointly evaluate the multiple ground signals, the phase difference must be known.
According to the invention, it is proposed to generate the following virtual apertures in a cross-node manner by appropriately selecting the positions of the transmitting and receiving elements within the radar sensor node: at least one virtual element location is repeated in the virtual aperture. Creating a repeating aperture element. The element is composed of a transmitting element and two receiving elements of one radar sensor node and a transmitting element of another radar sensor node. Alternatively, it is also possible to use two transmitting elements and one receiving element of one radar sensor node and one receiving element of another radar sensor node.
The phase difference φ is exemplarily shown in FIG. 4 for the two radar sensor nodes S1, S20To phi3. These phase differences are taken into account in the presence of the following two transmissions: a transmission at the transmit element Tx2 from the second radar sensor node S2 to the receive element Rx3 of the first radar sensor node S1, and a transmission at the transmit element Tx1 from the first radar sensor node S1 to the receive element Rx1 of the first radar sensor node S1. To ensure that the aperture elements or receiving elements of the virtual aperture are equivalent, the following equation must be satisfied (for simplicity, the aperture elements are arranged along the x-axis):
XTr2(S2)+XRr2(S1)＝XTr1(S1)+XRr1(S1)
the radar sensor nodes S1, S2 are arranged or spaced apart from one another in the following manner and the transmitting and receiving elements of the radar sensor nodes are designed: such that this condition is fulfilled for each radar sensor node and at least one further radar sensor node.
The intra-node field F1 of the aperture elements of which the transmitting elements and the receiving elements form a virtual receiving aperture of the first radar sensor node S1 is schematically shown in fig. 4. The transmitting and receiving elements of the second radar sensor node S2 form the intra-node field F2 of the aperture element of the virtual receive aperture. The transmit element of the first radar sensor node and the receive element of the second radar sensor node form a cross-node field Fx of the aperture element of the virtual receive aperture. In the example shown, a repeating element 26 is obtained, which is present both in the intra-node field F2 and in the cross-node field Fx of the second radar sensor node S2. In other words, the position of the first aperture element of the intra-nodal field corresponds to the position of the second aperture element across the nodal field. At this repetitive aperture element 26, the phase must be the same due to the distance of the radar sensor nodes from each other or the arrangement of the transmitting and receiving elements of the radar sensor nodes. Calibration can be performed when deviations occur.
The sensor system can be calibrated completely automatically if measurements are performed during operation of the radar sensor node. For this purpose, it is necessary for an object in the far field of the sensor system to be measured. This precondition is usually given because objects at a distance of about at least 20m are sufficient for this purpose. The location of the object need not be known.
The measurement data is evaluated in terms of distance and relative velocity (doppler). This usually results in a range-doppler matrix. The matrices in the calibrated system must be the same for the signal path considered for calibration (i.e. for the re-existing aperture elements 26), since these matrices map the same measurement. However, in practice there may be phase differences here.
Δφ＝φ0+φ3-(φ1+φ2) The phase difference is determined by calculating the correlation between the two range-doppler matrices. The correlation shifts the distance (in the common definition replaced by time t). In addition to the phase difference Δ Φ, the correlation results in a possible transmission time offset. The phase phi is known due to the calibration of the first radar sensor node S1 that has been performed1To phi3The interrelationship between them. Now the sum phi can be determined by solving the last equationoThe deletion relationship of (1). If all radar sensor nodes are calibrated independently, cross-node calibration can be performed by the presence of overlapping aperture elements.
It is possible here for the self-calibrating sensor system to comprise further radar sensor nodes. If the calibration of one radar sensor node is known and another radar isThe sensor nodes have the same arrangement type of transmitting and receiving elements, then phi can be obtained as described aboveo. For the signal phase φ of Tx2(S2) relative to Rx1(S1)12And φ of Tx2(S1) relative to Rx1(S2)21Then the following applies:
φ12-φ21＝φ0+φ2-(φTx2(S1)+φRx1(S2))，
since these signals must also be identical. Phase difference phi12-φ21Again by calculating the correlation. Since all variables (phi) of the equation are known in this caseRx1(S2) excluded), so the value can be determined. All further phases are then determined according to this principle. For each further radar sensor node in the sensor system, there must also be a repetitive aperture element in order to be able to perform the calibration. Thereby eliminating the need to calibrate all radar sensor nodes in the sensor system. It is sufficient to measure only one radar sensor node and to automatically perform a calibration of the further radar sensor nodes.
In the diagram of fig. 4, it is shown that the radar sensor nodes have an (optional) common frequency generator 24. The frequency generator 24 is connected to the radar sensor nodes S1, S2 and generates a common clock frequency. Drift is (additionally) prevented by the common clock frequency.
The calibration method according to the invention for calibrating radar sensor nodes of a sensor system is schematically illustrated in fig. 5. The method comprises the following steps: acquiring S10 angle-independent phase differences, detecting S12 objects and calculating S14 angle-independent phase differences of the second radar sensor node. The calibration method according to the invention can be implemented, for example, as software for a vehicle controller or a portable computer or also as software for a processor unit of a radar sensor node.
The invention is generally described and illustrated by the figures and specification. The description and illustrations should be regarded as illustrative instead of limiting. The present invention is not limited to the disclosed embodiments. Other embodiments or variations will occur to those skilled in the art upon a reading of the specification and a study of the drawings, the disclosure and the appended patent claims.
In the patent claims, the words "comprising" and "having" do not exclude the presence of other elements or steps. The indefinite article "a" or "an" does not exclude the presence of a plurality. A single element or a single unit may perform the functions of several units mentioned in the patent claims. The elements, units, interfaces, devices and systems may be partly or completely implemented in hardware and/or software. The mere fact that certain measures are recited in mutually different dependent patent claims does not indicate that a combination of these measures cannot be used to advantage. The computer program may be stored/run on a non-volatile data carrier, for example on an optical memory or a semiconductor drive (SSD). The computer program may be run together with hardware and/or as part of software, for example by means of the internet or by means of a wired or wireless communication system. Reference signs in the patent claims shall not be construed as limiting.
List of reference numerals
10 sensor system
12 objects
14 surroundings
16 vehicle
S1 first radar sensor node
S2 second radar sensor node
22 processor unit
24 frequency generator
26 repeated aperture elements
Claims (12)
1. A sensor system (10) for detecting an object (12) in a surroundings (14) of a vehicle (16), having:
a first radar sensor node (S1) and a second radar sensor node (S2), the first and second radar sensor nodes respectively comprising: at least two transmitting elements (Tx) for transmitting radar signals; at least two receiving elements (Rx) for receiving reflections of radar signals transmitted by the two radar sensor nodes; and a processor unit (22) for detecting objects in the surroundings of the vehicle based on the received reflections, and the first and second radar sensor nodes are arranged on the vehicle in a spaced-apart manner from each other, wherein,
the transmit elements and receive elements of the first radar sensor node form an intra-node field of an aperture element of a virtual receive aperture, and the transmit elements of the first radar sensor node and receive elements of the second radar sensor node form a cross-node field of the aperture element of the virtual receive aperture; and is
A distance between the two radar sensor nodes and a distance between a transmitting element and a receiving element within the first radar sensor node are selected such that: the position of the first aperture element of the intra-nodal field corresponds to the position of the second aperture element of the cross-nodal field.
2. The sensor system (10) of claim 1,
the first aperture element is formed by a first transmitting element (Tx) of the first radar sensor node (S1) and a first receiving element (Rx) of the first radar sensor node (S1); and is
The second aperture element is formed by a second transmitting element of the first radar sensor node and a first receiving element of the second radar sensor node or by a second receiving element of the first radar sensor node and a first transmitting element of the second radar sensor node.
3. The sensor system (10) of one of the preceding claims, having a further radar sensor node arranged on the vehicle (16) spaced apart from the first radar sensor node (S1) and the second radar sensor node (S2), wherein,
the transmit element (Tx) and the receive element (Rx) of the further radar sensor node form a further intra-node field of the aperture element of the virtual receive aperture and the transmit element or the receive element of the further radar sensor node and the transmit element or the receive element of the first radar sensor node and/or the second radar sensor node form a further cross-node field of the aperture element of the virtual receive aperture; and is
The distances of the further radar sensor nodes from the first and second radar sensor nodes and the distances of transmitting and receiving elements within the further radar sensor nodes are selected such that: the position of the further first aperture element of the further intra-nodal field corresponds to the position of the further second aperture element of the further cross-nodal field.
4. Sensor system (10) according to one of the preceding claims, wherein the radar sensor nodes (S1, S2) are arranged at a distance of more than 20cm, preferably more than 50cm, from each other on the vehicle (16).
5. Sensor system (10) according to one of the preceding claims, wherein the radar sensor nodes (S1, S2) are designed for transmitting and receiving radar signals in the frequency range of 76GHz to 81GHz, preferably 77 GHz.
6. Sensor system (10) according to one of the preceding claims, having a frequency generator (24) for generating a clock frequency common to the radar sensor nodes (S1, S2), preferably in the range of 20GHz, wherein the frequency generator is connected to the radar sensor nodes.
7. The sensor system (10) according to one of the preceding claims, wherein the radar sensor nodes (S1, S2) have the same number of transmit elements (Tx) and receive elements (Rx), respectively, and have the same topology.
8. A vehicle having a sensor system (10) according to one of the preceding claims.
9. Calibration method for calibrating a radar sensor node (S1, S2) of a sensor system (10) according to one of claims 1 to 7, the calibration method having the steps of:
acquiring (S10) a phase difference of a transmitting element of the first radar sensor node independent of an angle of a receiving element;
detecting (S12) an object (12) in a surroundings (14) of the vehicle (16) in a far field of the radar sensor node; and is
-calculating (S14) a phase difference of the transmitting element of the second radar sensor node independent of the angle of the receiving element.
10. The calibration method according to claim 9, wherein the steps of detecting (S12) and calculating (S14) are carried out repeatedly, preferably at regular time intervals, during operation of the vehicle (16).
11. Calibration method according to one of claims 9 to 10, wherein the step of calculating (S14) comprises: a range-doppler matrix of signal paths of the first and second aperture elements is acquired and a correlation between the acquired range-doppler matrices is calculated.
12. Computer program product with a program code for performing the steps of the calibration method according to one of claims 9 to 11 when the program code runs on a computer.
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