CN113009431A

CN113009431A - Calibration of cooperative radar sensor systems

Info

Publication number: CN113009431A
Application number: CN202011506795.5A
Authority: CN
Inventors: D·申德勒; G·哈科拜恩; M·芬克
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-12-19
Filing date: 2020-12-18
Publication date: 2021-06-22
Also published as: DE102019220238A1

Abstract

A cooperative radar sensor system having an arrangement of at least two radar sensors (10, 12) on a motor vehicle, wherein the radar sensor system is provided for transmitting phase control signals between the radar sensors in order to control the high-frequency phase of a radar signal to be transmitted; in a method for calibrating the respective phase delay (τ k) of the transmission of the phase control signal, the phase control signal is generated and transmitted between radar sensors in two configurations, and a radar signal is emitted on the basis of the generated or transmitted phase control signal, which radar signal is reflected on the same object (40) in a bistatic radar object measurement and is received by the other radar sensor. The phase delay (τ k) of the transmission of the phase control signal is estimated from the difference of the phase differences (Δ τ M, Δ τ S) determined for the two configurations between the received radar signal and the phase control signal present on the sensor.

Description

Calibration of cooperative radar sensor systems

Technical Field

The invention relates to a radar sensor system having an arrangement of at least two radar sensors on a motor vehicle.

Background

DE 102018101913 a1 describes a method for merging sensor information in a vehicle comprising at least two ambient sensor devices. The sensor data received by the environment sensor device is combined into fused data and provided to the driver assistance system. Calibration data is provided in a dynamic calibration step for the step of combining the received sensor data.

DE 102014104273 a1 and WO 2015/144134 a2 describe a method in a radar system, in which a first incoherent transmit-receive unit generates a first signal and transmits it via a path; the second noncoherent transmitting and receiving unit generates a first signal and transmits the first signal through the same path; in the first transmitting and receiving unit, a comparison signal is formed by the first signal and the first signal received by the second transmitting and receiving unit through the path; in the second transmitting and receiving unit, a second comparison signal is formed by the first signal of the second transmitting and receiving unit and the first signal received by the first transmitting and receiving unit through the path; and transmitting the second comparison signal to the first transmit receive unit through the second transmit receive unit. The path is configured as an air interface. The comparison signal data about the clock state or the phase state and the frequency state of the second transmitting and receiving unit are analyzed and processed by the analysis processing unit. The transmitted signals are frequency modulated and are orthogonal to each other. In one example, the distance between two non-coherent transmit receive units and the relative velocity between them are determined.

Radar systems for measuring distances, relative speeds and angles to objects, such as vehicles and obstacles, are increasingly used in motor vehicles for safety and comfort functions. In the course of the functional expansion of driver assistance systems, it is increasingly frequent to use a plurality of radar sensors which operate independently of one another and which cover a large visual image.

Disclosure of Invention

In order to achieve a high angular resolution, it is desirable for the antenna to have as large an aperture as possible in the direction of interest. In the case of an arrangement of a plurality of antenna elements as a group antenna, the aperture describes the overall extension of the arrangement of the antenna elements in the angular measurement direction with respect to the wavelength λ of the radar radiation. However, if the distance between adjacent antenna elements is too large, an ambiguity in the angle measurement may occur because the same phase relationship is obtained between the received signals for run-length differences that differ from each other by integer multiples of the wavelength λ. For example, unambiguous angle measurement can be achieved by means of a ULA (Uniform Linear Array) structure, in which the antenna elements are arranged at a distance of λ/2. However, in this case, as the aperture increases, the number of antenna elements also increases, and the number of analysis processing channels required also increases, resulting in a correspondingly high hardware cost.

The object of the present invention is to provide a novel cooperative radar sensor system having an arrangement of a plurality of radar sensors, which makes it possible to calibrate the cooperative, phase-coherent operation of the radar sensor system in the field, in particular after the delivery of a motor vehicle equipped with the radar sensor system to a customer. It is desirable to perform the calibration especially in continuous operation. Autonomous execution of the calibration is particularly desirable.

This object is achieved according to the invention by a cooperative radar sensor system having an arrangement of at least two radar sensors on a motor vehicle, wherein the radar sensor system is provided for transmitting phase control signals between the radar sensors in order to control the High Frequency (HF) phase of the radar signal to be transmitted,

wherein the radar sensor system is further arranged for implementing a method for calibrating a respective phase delay of a phase control signal transmission between a respective first radar sensor and a respective second radar sensor of the radar sensors, in which method,

in a first configuration of the first radar sensor, a phase control signal is generated and transmitted into the second radar sensor, and the second radar sensor emits a radar signal based on the transmitted phase control signal, which radar signal is reflected on the object in the bistatic radar object measurement and received by the first radar sensor, and

generating and transmitting a phase control signal in a second configuration of one of the first and second radar sensors into the other of the first and second radar sensors and transmitting a radar signal, which is reflected on the same object in the bistatic radar object measurement and received by the other radar sensor;

wherein the phase difference value between the radar signal received at one radar sensor measured by the bistatic radar object and the phase control signal present at the radar sensor is determined for both configurations;

wherein the phase delay of the phase control signal transmission between the first and second radar sensors is estimated from the phase difference value determined for the two configurations.

Thus, the first and second configurations are configurations of the respective transmitting and receiving radar sensors and the transmission direction of the phase control signal therebetween.

The "high-frequency phase" of a radar signal is understood to mean the oscillation phase, in particular the high-frequency oscillation phase, of the radar frequency of the signal. This may be the carrier frequency or the phase of the modulated carrier frequency.

The radar sensor system is arranged for transmitting phase control signals between the radar sensors in order to control the high frequency phase of the radar signal to be transmitted. The phase-coherent cooperative operation of the radar sensor can be realized by: a first one of the radar sensors generates and transmits a phase control signal to at least one further radar sensor of the radar sensor system, and the at least one further radar sensor controls the high-frequency phase of its radar signal to be transmitted by means of the phase control signal transmitted thereto. The radar sensor system is preferably provided for such an operating method. The radar sensor system may be provided, for example, for the cooperative operation of radar sensors, wherein the high-frequency phase of the radar signal to be transmitted of at least one other of the radar sensors is controlled on the basis of a phase control signal generated by one of the radar sensors and transmitted to the at least one other radar sensor. Thus, two or more radar sensors in the signal analysis process may cooperate. In particular, the angular resolution of the radar system can be improved by the arrangement of at least two radar sensors enabling a cooperative radar measurement with a large aperture, wherein the aperture corresponds to the extension of the arrangement of radar sensors in one direction. By analytically processing monostatic and/or bistatic radar measurements of a cooperative radar sensor system, it is possible to locate radar objects and measure angles of the located radar objects with high resolution.

The transmission signals of the radar sensors can be coupled to one another by means of the phase control signal. By means of the phase control signal, the phase position of the radar signal to be transmitted of a radar sensor can be controlled, in particular, relative to the phase position of the radar signal to be transmitted of the following radar sensors: the radar sensor generates and transmits a phase control signal to at least one other radar sensor.

The method for calibration is mainly based on: in a first configuration, the phase control signal is transmitted in the same direction as the transmitted radar signal on the measurement path through the object, i.e. from the same first radar sensor to the same second radar sensor; in a second configuration, one of the two transmission directions is reversed, and the two signals, i.e. the phase control signal and the radar signal measured by the bistatic radar object, are transmitted again. In both configurations, the measurement path (over which the transmitted radar signal is transmitted) measured by the bistatic radar object is different from the phase control signal connection (through which the phase control signal is transmitted) between the radar sensor. Thus, in the second configuration, a "cycle" of signals is generated by the sequential connection or addition of the phase control signal and the corresponding signal propagation times measured by the bistatic radar object. Conversely, in a first configuration, the difference of the two respective propagation times may be determined at the radar sensor receiving the phase control signal and receiving the radar signal measured by the bistatic radar object. In particular, a difference in the propagation time differences determined for the two configurations can thus be formed, which corresponds to twice the estimated value of the phase delay of the phase control signal transmission between the radar sensors involved. Thus, the propagation times of the bistatic radar object measurements cancel each other out, assuming that the measurement paths of the two configurations are substantially unchanged.

Thus, the estimation of the phase delay is preferably achieved under the assumption that the radar signal propagation time in the bistatic radar object measurement is similar or identical for both configurations.

By estimating the phase delay of the transmission of the phase control signal, a highly accurate, highly efficient calibration of the cooperative radar sensor system may be performed, in particular also in continuous operation. This is particularly advantageous if the phase delay of the transmission of the phase control signal may change during continuous operation. For example, when the phase control signal is transmitted through a phase control signal line between the radar sensors, the length of the line and thus the length of the transmission path may change in the event of a temperature change. For example, when starting a motor vehicle, large temperature variations may occur within the engine compartment during the first few minutes of operation of the internal combustion engine. Thus, the resulting change in the transmission characteristics of the phase control signal connection, in particular of the phase control signal line, can be counteracted by carrying out the method for calibration. Deformation of the assembly apparatus of the radar sensor may also occur, for example, due to temperature, and may result in a change in the phase relationship (phasebezzug) between the radar sensors of the radar sensor system. Unknown phase variations may lead to estimation errors, for example, in the coordinated angle estimation of the radar sensor.

In a first configuration, for example, the second radar sensor may emit radar signals whose high frequency phase is controlled based on the transmitted phase control signal.

In a second configuration, in particular one radar sensor may generate a phase control signal and emit a radar signal having a fixed relationship to the generated phase control signal.

In contrast to the subsequent determination of the phase offset of two incoherent radar sensors by means of respective free-running local oscillators, the high-frequency phase of the radar signal to be transmitted is controlled by transmitting a phase control signal between the radar sensors, so that the phase fidelity of the radar signal of the radar sensors is particularly high. Therefore, even in the case where phase noise occurs in the local oscillator in practice, the phase coherence of the radar sensor can be ensured. Phase noise can, for example, lead to a frequency change of the local oscillator, the characteristics of which are statistically distributed and therefore cannot be excluded or taken into account later by calculation in the evaluation of bistatic radar measurements in the case of incoherent radar sensors.

The phase delay can be estimated, for example, as one or more times divided by 360 °.

The transmission and measurement of the first configuration and the second configuration may be performed in any order of the first configuration and the second configuration. The method for calibration may in particular comprise a first step corresponding to the first configuration and a second step corresponding to the second configuration, wherein the first and second steps may be carried out in any order.

Although the radar signal is reflected on an object in bistatic radar object measurement and the measurement path of the radar signal therefore comprises distant objects which are not part of the radar sensor system, the phase control signal is transmitted directly from the radar sensor which generates the phase control signal into the respective other radar sensor, i.e. in particular without intervention of objects which do not belong to the radar sensor system.

In a method for the cooperative operation of a radar sensor system, the radar signals emitted by the respective radar sensors are preferably orthogonal to one another according to a multiplexing scheme. For example, the transmitting antenna elements of the respective radar sensors can be operated according to a multiplexing method with mutually orthogonal transmitting signals, for example with time division multiplexing or frequency division multiplexing or generation division multiplexing. The varying relative positions of the transmitted and received radar sensors then result in additional phase difference values, resulting in signals equivalent to those obtained with the configuration of a single transmitting radar sensor and additional (virtual) receiving radar sensors. In this way, the aperture of the cooperative radar sensor system is virtually increased and thus the angular resolution is improved, similar to the principle of MIMO radar (Multiple-Input-Multiple-Output).

For example, the phase difference value between the radar signal received at a radar sensor and the phase control signal present at the radar sensor, which is measured by the bistatic radar object, can be determined in the control and evaluation unit of the radar sensor concerned or in a higher-level control and evaluation device of the radar sensor system. Also, the estimation of the phase delay of the transmission of the phase control signal between the first and second radar sensors (i.e. the determination of the estimated value of the phase delay from the difference of the phase difference values determined for the two arrangements) may be performed in a control and analysis processing unit of a single radar sensor or may be performed in a superior control and analysis processing device of the radar sensor system. The radar sensors of the radar sensor system are arranged to transmit corresponding data via a data connection.

Preferred embodiments and embodiments of the invention are specified in the dependent claims.

The phase control signal may be transmitted, for example, via a phase control signal connection between the radar sensors concerned. The phase control signal connection may be a phase control signal line, in particular a cable, in particular a coaxial cable. The phase control signal connection may also be a wireless connection, in particular a radio connection.

For example, a respective phase control signal connection can be provided for two of the radar sensors involved. The phase control signal connection may be a unidirectional connection or a bidirectional connection. More than one phase control signal connection, for example two phase control signal lines for different transmission directions, can also be provided between two corresponding radar sensors. If the phase control signal connections are used in both directions according to the configuration, the transmission characteristics, in particular the phase delays, of the phase control signal connections should be as similar or identical as possible.

In one or more embodiments of the radar sensor system, the radar sensor system includes at least one phase control signal line for transmitting phase control signals between respective radar sensors of the radar sensor system. The phase control signal is thus transmitted via a phase control signal connection in the form of a phase control signal line.

In one or more embodiments of the radar sensor system, in the method for calibration, the phase control signal is transmitted wirelessly between the radar sensors of the radar sensor system in question in the first configuration and in the second configuration, respectively. The phase control signal is thus transmitted over the phase control signal connection in the form of a wireless connection.

In one or more embodiments of the radar sensor system, in the method for calibration, in the first configuration and in the second configuration, the phase control signal is transmitted directly between the radar sensors of the radar sensor system in question.

Preferably, the phase control signal is at least one of a radar carrier frequency, a frequency modulated radar carrier frequency, a trigger signal or a phase reference signal. For example, it is conceivable to use a phase control signal in the form of a radar carrier frequency, in particular a frequency-modulated radar carrier frequency, to form a radar signal to be transmitted, for example by frequency-modulating the phase control signal and transmitting it as a transmission signal. The radar signal to be transmitted can also be generated, for example, by a local oscillator, which is controlled by a Phase control signal, for example by means of a Phase Locked Loop (PLL), by means of frequency division or by other means. The phase of the radar signal to be transmitted of the radar sensor concerned, i.e. the high-frequency phase, is preferably adjusted (ausrichten) in accordance with a phase control signal obtained at the radar sensor. This can be done both with the same frequency of the high-frequency of the radar signal of the respective radar sensor and with a frequency division in the respective radar sensor, which then comprises a respective frequency divider, or with a frequency multiplication in the respective radar sensor, which then comprises a frequency multiplier, which multiplies the frequency of the phase control signal in order to generate the carrier frequency. The radar sensor generating the phase control signal may, for example, adjust the phase of the radar signal to be transmitted and the phase control signal relative to each other. For example, the phase control signal may be generated from the carrier frequency signal, e.g., by frequency division, or the carrier frequency signal may be output as the phase control signal.

In one or more embodiments of the radar sensor system, in the method for calibration, in both configurations of the radar sensor receiving radar signals of the bistatic radar measurements, (i) the received radar signals of the bistatic radar measurements are mixed with (ii) a phase control signal present on the radar sensor or a signal generated based on the phase control signal present on the radar sensor. The phase difference values involved are preferably determined from the obtained mixed signal. Since at the radar sensor receiving the radar signal measured by the bistatic radar either a phase control signal generated by the same radar sensor or a phase control signal transmitted into the radar sensor by another radar sensor is present, a mixed signal, for example a base frequency signal, can be generated directly by mixing the above signals, and its phase position can then be evaluated.

In one or more embodiments of the radar sensor system, in the method for calibrating, half of the difference in the phase difference values determined for the two configurations is determined as an estimate of the phase delay of the transmission of the phase control signal between the first and second radar sensors. Assuming that the propagation time of the radar signal in the bistatic radar object measurement is the same for both configurations and the phase delay due to the transmission of the phase control signal is the same for both configurations, the phase difference value enters the phase difference value determined for both configurations with the same value, so that a double value of the phase delay is obtained by difference formation.

The two configurations may be chosen differently.

In one variant of the radar sensor system, in the method for calibration, in the second configuration the radar signal transmission direction measured by the bistatic radar object is opposite to the first configuration, wherein the transmission direction of the phase control signal is the same in both configurations. Thus, the phase control signal may be transmitted over a unidirectional phase control signal connection. Thus, the same phase control signal connection behavior can be assumed for both configurations, and thus the phase delay is also the same.

For example, the first and second radar sensors may have antenna elements which are arranged such that a virtually superimposed measurement path is used for the bistatic radar object measurement of the two configurations. For example, the first and second radar sensors may have the same antenna layout with the same distance between the two antenna elements for transmitting and for receiving, e.g. a distance λ/2 corresponding to half a wavelength.

In a further variant of the radar sensor system, in the method for calibration, in the second configuration the transmission direction of the phase control signal is opposite to the first configuration, wherein the radar signal transmission direction measured by the bistatic radar object is the same in both configurations. In this case, by using a bidirectional phase control signal connection, the highest possible similarity of the transmission characteristics of the phase control signal connections can be achieved. Advantageously, by using the same receive and transmit antenna elements of the radar sensor involved, the similarity of the measurement paths through distant objects measured by the two configured bistatic radar objects can be improved. Instead of a bidirectional phase control signal connection, for example, sufficiently similar parallel phase control signal lines can also be used. In this variant, the radar sensor concerned therefore exchanges the roles of a radar sensor which generates a phase control signal (corresponding to the operation of the radar sensor as master) and a radar sensor which obtains a phase control signal (corresponding to the operation of the radar sensor as slave). Assuming that the transmission characteristics of the phase control signal transmission do not differ substantially in both directions, the respective phase delays that occur can be considered to be the same. Furthermore, advantageously, in this variant, the same radar sensor receives the radar signals measured by the bistatic radar object in both configurations, so that the radar sensor can determine, for example, not only the phase difference between the received radar signals and the phase control signal present at the radar sensor for both configurations, but also the phase delay of the transmission of the phase control signal from the difference in the phase difference determined for both configurations. There is no need to transmit data between the radar sensors.

In one or more embodiments of the radar sensor system, the arrangement of radar sensors on the motor vehicle comprises at least three radar sensors arranged in different positions in one direction, wherein the radar sensor system is arranged to switch between:

an operating mode of the radar sensor system, wherein a phase control signal is generated by a radar sensor, wherein the length of the phase control signal connection from the radar sensor to a further radar sensor increases with increasing distance of said further radar sensor from the radar sensor in said direction; and

an operating mode of the radar sensor system, wherein a phase control signal is generated by one radar sensor and is transmitted to a further radar sensor, which surrounds the radar sensor in the direction and in the opposite direction.

The radar sensor which generates the phase control signal in the first-mentioned operating mode may be, for example, a radar sensor which is located in the direction at an end position of a radar sensor arrangement on the motor vehicle.

The method for calibration can be carried out, for example, in a respectively switched-on operating mode.

For example, the operating method for the coordinated operation of the radar sensors can also be carried out in the respectively switched-on operating mode.

The operating modes of the radar sensor system differ in the way in which deviations in the phase delay occurring between the radar sensors during the time period after a calibration and before a new calibration has been carried out have an effect. For example, if a component of the radar sensor system undergoes a temperature change after calibration, it can be approximately considered that a distance change of a distance between the radar sensors or a length change of a phase control signal line between the radar sensors is generated approximately in proportion to the temperature.

In an operating mode in which the length of the phase control signal connection from the radar sensor generating the phase control signal to the further radar sensor increases with increasing distance of the further radar sensor from the radar sensor in said direction, the following relationship can be approximately assumed: it can be considered that the deviation occurring as the distance of the radar sensor from the radar sensor generating the phase control signal in the direction increases, the deviation with respect to the value of the phase delay determined at the time of calibration also increases. In the case of an angle determination by means of a cooperative radar sensor system, the aperture of which corresponds to the extension of the radar sensor arrangement in the direction, this deviation, which increases with the position in the direction, corresponds to a change in the object angle of the radar object "seen", i.e. estimated, by the radar sensor system. In this operating mode, therefore, the positioning and angle determination of the radar object can be carried out with good functionality, although the determined angle of the object deviates systematically. Such a mode of operation is therefore advantageous for a radar sensor arrangement, for example when the expected deviation of the phase delay is large due to the large length of the phase control signal line. Since, despite the large phase deviations in this case, for example, the angle determination can still function fully, even if the determined angle may contain systematic deviations.

In contrast, if the expected deviation of the phase delay is kept small overall, the following operating modes are advantageous: in this operating mode, the phase control signal is generated by one radar sensor and transmitted to the other radar sensor, which surrounds it in the direction and in the opposite direction. This may be the case, for example, with short phase control signal lines. Since in this operating mode the radar sensors surrounding the radar sensor generating the phase control signal in said direction and in the opposite direction may have phase delay deviations similar to each other. For example, the radar sensor may have an increased phase delay on both sides of the radar sensor generating the phase control signal or a decreased phase delay on both sides of the radar sensor. Thus, the influence of the phase delay deviation on the angle determination by the radar sensor system can be reduced.

This switchability of the operating mode is particularly advantageous if a prefabricated radar sensor system is to be mounted on a vehicle in different arrangements of radar sensors, depending on the vehicle. For the respective arrangement of the radar sensor selected on the vehicle, it is possible to simply switch to the desired operating mode. However, a dynamic switching during continuous operation of the radar sensor system is also possible if, for example, depending on the activated driver assistance system, the respective operating mode is particularly suitable for the assignment of the phase control signal.

Drawings

Embodiments of the invention are further elucidated below with reference to the drawings.

The figures show:

FIG. 1 shows a schematic block diagram of a radar sensor system according to the present invention;

FIG. 2 shows schematic diagrams of two configurations of a radar sensor system for calibrating phase delay;

FIG. 3 shows schematic diagrams of two configurations of a radar sensor system for calibrating phase delay according to another embodiment;

FIG. 4 shows a schematic diagram of a portion of a block diagram of a radar sensor;

FIG. 5 shows a schematic diagram of a radar sensor system having three radar sensors;

FIG. 6 shows a schematic diagram of another example of a radar sensor system having three radar sensors; and

fig. 7 shows a schematic view of a part of a block diagram of a radar sensor system.

Detailed Description

The radar sensor system shown in fig. 1 comprises a plurality of radar sensors 10, 12 (two of which are shown by way of example in fig. 1) and a common control and evaluation unit 14, which comprises a control and evaluation unit 16 and a common superordinate control and evaluation unit 18, which are assigned to the

radar sensors

10, 12, respectively. The

radar sensors

10, 12 can be arranged, for example, on the motor vehicle at different lateral positions in front of the vehicle.

Each

radar sensor

10, 12 comprises at least one transmitting antenna Tx and a plurality of receiving antennas Rx, of which one is exemplarily shown. The

radar sensors

10, 12 are mounted and arranged in the motor vehicle in such a way that the

radar sensors

10, 12 are arranged at different positions at a distance from one another in the direction a, so that the superordinate arrangement of the

radar sensors

10, 12 has a superordinate aperture of the radar sensor arrangement in the direction a.

The

radar sensors

10, 12 are connected to one another via a phase control signal line 20, and the phase control signal of the first radar sensor 10 operating in the master mode is transmitted via the phase control signal line 20 to the further radar sensor 12 operating in the slave mode. The first radar sensor 10 includes a phase control signal unit 22 that controls the generation of a radar signal to be transmitted by a radar signal generation unit 24. The radar signal generation unit 24 includes a local oscillator 26 and a modulation unit 28 for modulating a phase frequency (high-frequency) generated by the local oscillator. The signal provided by the phase control signal unit 22 to the radar signal generating unit 24 controls the phase of the generated radar signal. The modulation unit 28 may, for example, be arranged to periodically modulate the frequency of the transmit signal provided by the local oscillator 26 in the form of an up-ramp and/or down-ramp (chirp) sequence.

The further radar sensor 12, which is operated in the slave mode, is constructed in a similar manner, wherein corresponding components are denoted by the same reference numerals. However, the phase control signal unit 22 of the radar sensor 12 operating in the slave mode is arranged to obtain a phase control signal via the phase control signal line 20 and to control the radar signal generating unit 24 on the basis of said phase control signal.

The

radar sensors

10, 12 further comprise a multiplexing modulation unit 30 which is arranged to modulate the respective transmission signals according to a multiplexing method, so that the received signals originating from the

respective radar sensors

10, 12 can be processed analytically separately by demodulation in the control and analysis processing unit 18.

The signal received by the antenna element Rx is input to a mixer 32 where it is mixed with the signal provided by the local oscillator 26. The obtained signal is input to an analog/digital converter 36 through a filter 34. In order to calibrate the phase delay of the phase control signal line 20, the digital signals thus obtained are evaluated by a phase evaluation unit 38 in order to determine the phase difference between the radar signals received at the antenna elements Rx of the

radar sensors

10, 12 and the phase control signals present at the

radar sensors

10, 12.

The phase difference Δ τ M is determined by a phase evaluation unit 38 of the radar sensor 12, which evaluates the signals emitted by the radar sensor 10 operating in the master mode. A phase evaluation unit 38 of the radar sensor 10, which evaluates the signals emitted by the radar sensor 12 operating in the slave mode, determines the phase difference Δ τ S. For this purpose, the phase analysis processing unit 38 analyzes and processes the complex amplitude of the peak corresponding to the radar object in the two-dimensional range-velocity radar image. The phase difference values Δ τ M and Δ τ S are output to the upper-level control and evaluation unit 18.

The radar sensor system may be calibrated in particular according to the method described below with reference to fig. 2 or 3.

Fig. 2 shows a first configuration of a radar sensor system on the left, with a first radar sensor 10 operating in a master mode and a second radar sensor 12 operating in a slave mode. The

radar sensors

10, 12 are connected to each other by a phase control signal line 20. The radar sensor system may correspond to the structure according to fig. 1, for example.

In the first configuration, the first radar sensor 10 generates and transmits a phase control signal to the radar sensor 12 via the phase control signal line 20. Meanwhile, the first radar sensor 10 transmits a radar signal generated under the control of its own phase control signal 20 through its transmitting antenna Tx. The transmitted radar signal is reflected by a distant external object 40, for example an object 40 in the traffic environment of the own motor vehicle (for example another vehicle), and is received by the second radar sensor 12 via its receiving antenna Rx and evaluated. For the transmission of the phase control signal via the phase control signal line 20, the phase delay τ k is derived. The signal propagation time on the

measurement path

42, 44 including the object 40 results in a delay τ z1+ τ z 2. By evaluating the phase of the signal mixed at the mixer 32, the phase evaluation unit 38 determines the difference Δ τ M between the delay of the radar channel (measurement path) and the coupling delay of the phase control signal transmission, wherein: Δ τ M ═ (τ z1+ τ z2) - τ k.

In the second configuration shown on the right in fig. 2, the phase control signal is generated again by the first radar sensor 10 operating as a master, with the position of the object 40 almost unchanged, and is transmitted via the phase control signal line 20 into the second radar sensor 12. However, in this configuration, the radar signal generated by the second radar sensor 12 is controlled in phase by the phase control signal, and the second radar sensor transmits the radar signal through its transmitting antenna Tx. The radar signal reflected by the object 40 is received by the first radar sensor 10 and mixed with the own signal of the local oscillator 26 generated based on the own phase control signal, and is analyzed and processed by the phase analysis processing unit 38. The determined phase delay Δ τ S corresponds to the sum of the delay of the

measurement paths

44, 42 and the coupling delay on the phase control signal line 20: Δ τ S ═ τ z1+ τ z2) + τ k.

The upper control and evaluation unit 18 calculates the difference between the phase difference Δ τ M and Δ τ S, for which approximately:

ΔτM-ΔτS＝[(τz1+τz2)-τk]-[(τz1+τz2)+τk]＝-2τk

thus, an estimated value of the phase delay τ k of the transmission of the phase control signal on the phase control signal line 20 is determined from the obtained value. The difference in phase difference values may be calculated, for example, as follows: the complex amplitudes of the mixed signals obtained in the respective radar sensors are multiplied by each other in a complex conjugate manner.

Fig. 3 shows a diagram corresponding to fig. 2, a further example of two configurations for calibrating the phase delay of the phase control signal transmission.

The first configuration corresponds to the first configuration of the example of fig. 2. The second configuration on the right side of fig. 3 differs from the first configuration in that the transmission direction of the phase control signal on the phase control signal line 20 is reversed. In this configuration, the second radar sensor 12 operates in a master mode and generates a phase control signal that is transmitted by the phase control signal unit 22 to the first radar sensor 10 via the phase control signal line 20. At the same time, the first radar sensor 12 generates a radar transmission signal controlled by the obtained phase control signal.

The radar signal emitted by the first radar sensor 10 and received by the second radar sensor 12 by reflection on the object 40 is mixed with the high-frequency signal generated by the radar sensor under the control of its phase control signal, and is subjected to analysis processing by the phase analysis processing unit 38. In this example, the second radar sensor 12 determines not only the phase difference Δ τ M in the first configuration but also the phase difference Δ τ S in the second configuration and transmits both values into the superordinate control and evaluation unit 18. Thus, in this example, the phase control signal line 20 is bi-directional in operation.

Fig. 4 schematically shows a part of a

radar sensor

10, 12 according to a variant of the radar sensor system of fig. 1. The

radar sensors

10, 12 differ from the

radar sensors

10, 12 shown in fig. 1 in that a common antenna element 46 is provided for transmitting and receiving radar signals. The antenna element 46 is connected to the local oscillator 26 via a circulator 48. The circulator is designed to transmit the radar signals generated by the local oscillator 26, optionally modulated by the multiplexing unit 30, into the antenna 46 and to transmit the radar signals received by the antenna into the mixer 32, to which the filter 34, the analog/digital converter and the phase evaluation unit 38 are connected. The method for calibrating the phase delay may be performed as described above.

Instead of transmitting the phase control signal of the phase control signal unit 22 via the phase control signal line 20 as described in the above example, it is also possible, for example, to transmit the high-frequency signal generated by the local oscillator 26 of the

radar sensor

10 or 12 operating as a master as a phase control signal via the phase control signal line 20' shown by a dashed line in fig. 1 to the

radar sensor

12 or 10 operating in slave mode and to transmit it there as a radar signal or to mix the received radar signal at the mixer 32. Alternatively, a lower-frequency signal derived from the high-frequency signal of the

radar sensor

10 or 12 operating as master can also be transmitted as a phase reference signal via a phase control signal line 20 ″ shown by a dashed line in fig. 1 to the

radar sensor

12 or 10 operating in slave mode and converted there into a high-frequency signal. For this purpose, for example, the radar signal generating unit 24 of a radar sensor operating as a master may include a frequency divider, while the radar signal generating unit 24 of a radar sensor operating as a slave may include a frequency multiplier. For example, a phase reference signal (phase control signal) of a frequency of 10GHz obtained through the phase control signal line 20 ″ can be converted into a radar signal of 80GHz by frequency multiplication by 8 times.

Fig. 5 and 6 each show schematically in the upper part the distribution of a phase control signal which is generated by the radar sensor 10 operating in the master mode and is transmitted to a further radar sensor 12, 12' operating in the slave mode. The two illustrated radar sensor systems of fig. 5 and 6 can be different operating modes of the same radar sensor system, wherein the radar sensor system is arranged to be switched between the operating mode according to fig. 5 and the operating mode according to fig. 6 by switching the respective phase control signal line 20. The operating mode according to fig. 5 corresponds to a star-shaped distribution of the phase control signals, whereas the operating mode according to fig. 6 corresponds to a sequential distribution of the phase control signals.

In the lower part of fig. 5 and 6, the expected phase deviations of the individual radar sensors 10, 12' in the direction a at the location of the radar sensor concerned, which may occur in the operating interval between two phase delay calibrations in the case of temperature changes or deformation of the radar sensor arrangement, are shown in each case. It is assumed here that as the length of the phase control signal line 20 increases, an increasing phase deviation occurs. In fig. 5, the phase deviations in the same direction (positive in fig. 5) are detected on the left and right of the first radar sensor 10 operating in the master mode. In fig. 6, the phase deviation of each radar sensor 10, 12' increases from left to right in the direction a.

Fig. 7 schematically shows a radar sensor arrangement, wherein the first radar sensor 10 and the second radar sensor 12 have antenna elements which are arranged such that virtually superimposed radar channels (bistatic measurement paths) are used for the configuration according to fig. 2. The arrangement of the

radar sensors

10, 12 with the individual antenna elements Tx, Rx corresponds to a virtual bistatic MIMO antenna array with virtually superimposed radar channels. Between the transmitting and receiving antenna pair Tx, Rx of the first radar sensor, the distance a is equal to the distance a between the transmitting and receiving antenna pair Tx, Rx of the second radar sensor. Thus, for the transmit and receive antenna pairs Tx, Rx involved, the measurement path in the first configuration is as long as the measurement path in the second configuration in both configurations. The coordination of the bistatic radar object measurements of the signal propagation times τ z1+ τ z2 in both configurations can thereby be improved. The radar sensor system may otherwise be comparable to the above example.

Claims

1. A cooperative radar sensor system having an arrangement of at least two radar sensors (10, 12) on a motor vehicle, wherein the radar sensor system is provided for transmitting phase control signals between the radar sensors in order to control the high-frequency phase of a radar signal to be transmitted,

wherein the radar sensor system is further arranged for implementing a method for calibrating a respective phase delay (τ k) of a phase control signal transmission between a respective first and a respective second one of the radar sensors (10, 12), in which method,

in a first configuration of the first radar sensor (10), a phase control signal is generated and transmitted to the second radar sensor (12), and the second radar sensor emits a radar signal based on the transmitted phase control signal, which radar signal is reflected on an object (40) and received by the first radar sensor (10) in bistatic radar object measurement, and

generating and transmitting a phase control signal in a second configuration of one of the first and second radar sensors (10, 12) onto the other of the first and second radar sensors (12, 10) and transmitting a radar signal which is reflected on the same object (40) in the bistatic radar object measurement and received by the other radar sensor (12, 10),

wherein the phase difference value (DeltaTM, DeltaTS) between a radar signal received at a radar sensor (10, 12) measured by a bistatic radar object and a phase control signal present at the radar sensor is determined for both configurations,

wherein the phase delay (τ k) of the phase control signal transmission between the first and second radar sensors (10, 12) is estimated from the phase difference values determined for both configurations.

2. The radar sensor system according to claim 1, having at least one phase control signal line (20) for transmitting phase control signals between respective radar sensors (10, 12) of the radar sensor system.

3. The radar sensor system according to claim 1, wherein in the method for calibration, phase control signals are wirelessly transmitted between the radar sensors (10, 12) of interest of the radar sensor system in the first configuration and in the second configuration, respectively.

4. The radar sensor system according to one of the preceding claims, wherein in the method for calibration, phase control signals are transmitted directly between the radar sensors (10, 12) concerned of the radar sensor system in the first configuration and in the second configuration, respectively.

5. The radar sensor system of any one of the preceding claims, wherein the phase control signal is at least one of a radar carrier frequency, a frequency modulated radar carrier frequency, a trigger signal, or a phase reference signal.

6. Radar sensor system according to one of the preceding claims, wherein in the method for calibration, in both configurations of a radar sensor receiving radar signals measured by bistatic radar, the received radar signals measured by bistatic radar are mixed with a phase control signal present on the radar sensor or a signal generated on the basis of a phase control signal present on the radar sensor, wherein the phase difference value (Δ τ M; Δ τ S) concerned is determined from the obtained mixed signal.

7. Radar sensor system according to one of the preceding claims, wherein in the method for calibration half the difference of the phase difference values determined for the two configurations is determined as an estimate of the phase delay (τ k) of the transmission of the phase control signal between the first and second radar sensors (10, 12).

8. Radar sensor system according to one of claims 1 to 7, wherein in the method for calibration, in the second configuration, the bistatic radar object measures a radar signal transmission direction which is opposite to the first configuration, wherein the transmission direction of the phase control signal is the same in both configurations.

9. The radar sensor system according to claim 8, wherein the first and second radar sensors (10, 12) have antenna elements (Rx, Tx) arranged such that virtually superimposed measurement paths are used for bistatic radar object measurements in both configurations.

10. Radar sensor system according to one of claims 1 to 7, wherein in the method for calibration, in the second configuration the transmission direction of the phase control signal is opposite to the first configuration, wherein the radar signal transmission direction measured by a bistatic radar object is the same in both configurations.

11. The radar sensor system of one of the preceding claims, wherein the arrangement of the radar sensors on the motor vehicle comprises at least three radar sensors (10, 12, 12') arranged in different positions along one direction (a), wherein the radar sensor system is arranged for switching between:

-a mode of operation of the radar sensor system, in which phase control signals are generated by one radar sensor (10), wherein the length of the phase control signal connection (20) from the one radar sensor (10) to the other radar sensor (12, 12') increases with increasing distance of the other radar sensor from the one radar sensor in the direction (a); and

an operating mode of the radar sensor system, in which a phase control signal is generated by one radar sensor (10) and is transmitted to a further radar sensor (12, 12'), which surrounds the one radar sensor in the direction and in the opposite direction.