Calibration of a Cooperative Radar Sensor System

Abstract

A collaborative radar sensor system having an arrangement of at least two radar sensors (10, 12) on a motor vehicle, wherein the radar sensor system is configured to transmit phase control signals between the radar sensors in order to control the high-frequency phase of the radar signals to be transmitted; in a method for calibrating the transmission of the phase control signals with corresponding phase delays (τk), the phase control signals are generated and transmitted between the radar sensors in two configurations, and radar signals are transmitted based on the generated or transmitted phase control signals, which are reflected on the same object (40) in a bistatic radar object measurement and received by another radar sensor. The phase delay (τk) of the transmission of the phase control signals is estimated based on the difference between the phase differences (ΔτM, ΔτS) determined for the two configurations between the received radar signals and the phase control signals present on the sensors.

Description

Field of the Invention

[0001] The present invention relates to a radar sensor system having an arrangement of at least two radar sensors on a motor vehicle. Background Art

[0002] DE 10 2018 101 913A1 describes a method for fusing sensor information in a vehicle including at least two environmental sensor devices. Sensor data received by the environmental sensor devices are fused into fusion data and provided to a driver assistance system. Calibration data are provided in a dynamic calibration step, which are used for the step of fusing the received sensor data.

[0003] DE 10 2014 104 273 A1 and WO 2015 / 144134 A2 describe a method in a radar system, in which a first non-coherent transceiver generates a first signal and transmits it through a path; a second non-coherent transceiver generates a first signal and transmits it through the same path; in the first transceiver, a comparison signal is formed from the first signal and the first signal received by the second transceiver through the path; in the second transceiver, a second comparison signal is formed from its first signal and the first signal received by the first transceiver through the path; and the second comparison signal is transmitted to the first transceiver through the second transceiver. The path is configured as an air interface. Comparison signal data regarding the clock state or phase state and frequency state of the second transceiver are analyzed by an analysis processing unit. The transmitted signals are frequency-modulated signals and are orthogonal to each other. In one example, the distance and relative speed between two non-coherent transceivers are determined.

[0004] Radar systems for measuring the distance, relative speed, and angle to objects such as vehicles and obstacles are increasingly used in motor vehicles for safety and comfort functions. During the functional expansion of driver assistance systems, multiple independently operating radar sensors are increasingly frequently used, which cover a large visual image. Summary of the Invention

[0005] For achieving a high angular resolution, it is desirable that the antenna has as large an aperture as possible in the relevant direction. In the case where a plurality of antenna elements are arranged as a grouped antenna, the aperture describes the overall extension scale of the arrangement of the antenna elements in the direction of the angle measurement with respect to the wavelength λ of the radar radiation. However, if the distance between adjacent antenna elements is too large, ambiguity in the angle measurement may occur because for run length differences that are integer multiples of the wavelength λ from each other, the same phase relationship is obtained between the received signals. For example, an unambiguous angle measurement can be achieved by means of a ULA (Uniform Linear Array) structure, in which the antenna elements are arranged at a spacing of λ / 2. However, in this case, as the aperture increases, the number of antenna elements also increases, and the number of required analysis and processing channels also increases, resulting in correspondingly high hardware costs.

[0006] The object of the present invention is to implement a novel cooperative radar sensor system having an arrangement of a plurality of radar sensors, which enables calibration of the cooperative, phase-coherent operation of the radar sensor system in a field, especially after a motor vehicle equipped with the radar sensor system is delivered to a customer. It is especially desirable to perform the calibration during continuous operation. It is especially desirable to perform the calibration autonomously.

[0007] This object is solved 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 configured to transmit a phase control signal between the radar sensors in order to control the high-frequency (HF) phase of the radar signal to be transmitted.

[0008] wherein the radar sensor system is further configured to perform a method for calibrating a respective phase delay of the transmission of the phase control signal between a respective first radar sensor and a respective second radar sensor among the radar sensors, in which method

[0009] a phase control signal is generated in a first configuration of the first radar sensor and transmitted into the second radar sensor, and the second radar sensor transmits a radar signal based on the transmitted phase control signal, and the radar signal is reflected on an object in a bistatic radar object measurement and received by the first radar sensor, and

[0010] a phase control signal is generated in a second configuration of one of the first and second radar sensors and transmitted into the other of the first and second radar sensors and a radar signal is transmitted, and the radar signal is reflected on the same object in a bistatic radar object measurement and received by the other radar sensor;

[0011] Among them, the phase difference between the radar signal received on one radar sensor for bistatic radar object measurement and the phase control signal existing in the radar sensor is determined for two configurations;

[0012] Among them, the phase delay of the phase control signal transmission between the first and second radar sensors is estimated according to the phase differences determined for the two configurations.

[0013] Therefore, the first and second configurations are the configurations of the respective transmitting and receiving radar sensors and the transmission direction of the phase control signal between them.

[0014] The "high-frequency phase" of the radar signal should be understood as the oscillating phase of the radar frequency of the signal, especially the high-frequency oscillating phase. This can be the phase of the carrier frequency or the modulated carrier frequency.

[0015] The radar sensor system is set to transmit the phase control signal between the radar sensors to control the high-frequency phase of the radar signal to be transmitted. The phase-coherent cooperative operation of the radar sensors can be achieved in the following way: the first radar sensor in the radar sensors generates the phase control signal and transmits it to at least another radar sensor in the radar sensor system, and the at least another radar sensor controls the high-frequency phase of the radar signal to be transmitted by the transmitted phase control signal. The radar sensor system is preferably set for such an operation method. The radar sensor system can be set, for example, for the cooperative operation of the radar sensors, where the high-frequency phase of the radar signal to be transmitted by the at least another radar sensor is controlled based on the phase control signal generated by one of the radar sensors and transmitted to at least another of the radar sensors. Therefore, two or more radar sensors in the signal analysis processing can cooperate. In particular, the angular resolution of the radar system can be improved by arranging at least two radar sensors to enable cooperative radar measurement with a large aperture, where the aperture corresponds to the extension scale of the arrangement of the radar sensors in one direction. By analyzing and processing the monostatic and / or bistatic radar measurements of the cooperative radar sensor system, radar objects can be located and the angles of the located radar objects can be measured with high resolution.

[0016] Through the phase control signal, the transmitted signals of the radar sensors can be coupled to each other. Through the phase control signal, in particular, the phase position of the radar signal to be transmitted by one radar sensor can be controlled relative to the phase position of the radar signal to be transmitted by the following radar sensor: the radar sensor that generates the phase control signal and transmits it to at least another radar sensor.

[0017] The method for calibration is mainly based on: in the first configuration, the phase control signal is transmitted in the same direction as the transmitted radar signal on the measurement path passing through the object, that is, from the same first radar sensor to the same second radar sensor; in the second configuration, one of the two transmission directions is reversed, and the two signals are transmitted again, that is, the phase control signal and the radar signal for bistatic radar object measurement. In these two configurations, the measurement path of the bistatic radar object measurement (on which the transmitted radar signal is transmitted) is different from the phase control signal connection (through which the phase control signal is transmitted) between the radar sensors. Therefore, in the second configuration, a "cycle" of signals is generated by the sequential connection or addition of the propagation times of the phase control signal and the corresponding signal of the bistatic radar object measurement. Conversely, in the first configuration, the difference between the two corresponding propagation times can be determined at the radar sensor that receives the phase control signal and the radar signal for bistatic radar object measurement. Therefore, in particular, the difference between the propagation time differences obtained for the two configurations can be formed, which is equivalent to twice the estimated value of the phase delay of the phase control signal transmission between the radar sensors involved. Therefore, assuming that the measurement paths of the two configurations are basically unchanged, the propagation times of the bistatic radar object measurement cancel each other out.

[0018] Therefore, the estimation of the phase delay is preferably achieved under the assumption that the radar signal propagation times in the bistatic radar object measurement are similar or the same for the two configurations.

[0019] By estimating the phase delay of the transmission of the phase control signal, the cooperative radar sensor system can be calibrated with high precision and high efficiency, especially also during 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 the phase control signal line between the radar sensors, the length of the line and thus the length of the transmission path may change under temperature variations. For example, when starting a motor vehicle, large temperature changes may occur in the engine compartment during the first few minutes of the internal combustion engine operation. Therefore, the change in the transmission characteristics of the phase control signal connection, especially the phase control signal line, caused thereby can be compensated by performing this calibration method. It is also possible, for example, due to temperature, that the assembly device of the radar sensor is deformed, and this may lead to a change in the phase relationship (Phasenbezug) between the radar sensors of the radar sensor system. Unknown phase changes may cause estimation errors, for example, in the cooperative angle estimation of the radar sensors.

[0020] In the first configuration, for example, the second radar sensor can transmit a radar signal whose high-frequency phase is controlled based on the transmitted phase control signal.

[0021] In a second configuration, in particular a radar sensor can generate a phase control signal and transmit a radar signal having a fixed relationship with the generated phase control signal.

[0022] Different from subsequently determining the phase deviation of two non-coherent radar sensors by means of respectively freely 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 signals 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 sensors can be ensured. Phase noise can, for example, cause a frequency change of the local oscillator, the characteristics of which are statistically distributed, and thus cannot be subsequently excluded or considered by calculation when analyzing bistatic radar measurements in the case of non-coherent radar sensors.

[0023] The phase delay can, for example, be estimated as one or more multiples of 360°.

[0024] The transmissions and measurements of the first configuration and the second configuration can be carried out in any order of the first configuration and the second configuration. The method for calibration can in particular include a first step corresponding to the first configuration and a second step corresponding to the second configuration, wherein the first and second steps can be carried out in any order.

[0025] Although the radar signal is reflected on the object in a bistatic radar object measurement, and the measurement path of the radar signal thus includes a distant object that is not part of the radar sensor system, the phase control signal is directly transmitted from the radar sensor generating the phase control signal into the respective other radar sensor, i.e., in particular without the intervention of an object that does not belong to the radar sensor system.

[0026] In the method for the cooperative operation of a radar sensor system, the radar signals preferably transmitted by the respective radar sensors are orthogonal to each other according to a multiplexing scheme. For example, the transmitting antenna elements of the respective radar sensors can be operated with mutually orthogonal transmission signals according to a multiplexing method, such as time-division multiplexing or frequency-division multiplexing or code-division multiplexing. Then, the changing relative positions of the transmitted and received radar sensors result in additional phase differences, thus resulting in a signal equivalent to the signal obtained by means of the configuration of a single transmitting radar sensor and an additional (virtual) receiving radar sensor. 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 a MIMO radar (Multiple-Input-Multiple-Output).

[0027] For example, the determination of the phase difference between the radar signal received on a radar sensor for bistatic radar object measurement and the phase control signal present on the radar sensor can be carried out in the control and analysis processing unit of the radar sensor involved, or can be carried out in the higher-level control and analysis processing 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 estimation value of the phase delay is determined based on the difference in the phase differences determined for the two arrangements) can be carried out in the control and analysis processing unit of a single radar sensor, or can be carried out in the higher-level 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.

[0028] Preferred configurations and extensions of the invention are specified in the dependent claims.

[0029] For example, the phase control signal can be transmitted via a phase control signal connection between the radar sensors involved. The phase control signal connection can be a phase control signal line, in particular a cable, in particular a coaxial cable. The phase control signal connection can also be a wireless connection, in particular a radio connection.

[0030] For example, corresponding phase control signal connections can be provided for two of the radar sensors involved in the radar sensor. The phase control signal connection can be a unidirectional connection or a bidirectional connection. More than one phase control signal connection can also be provided between two corresponding radar sensors, for example two phase control signal lines for different transmission directions. If the phase control signal connection is used in both directions according to the configuration, then the transmission characteristics of the phase control signal connection line, in particular the phase delay, should be as similar or identical as possible.

[0031] In one or more embodiments of the radar sensor system, the radar sensor system includes at least one phase control signal line for transmitting the phase control signal between the corresponding radar sensors of the radar sensor system. Thus, the phase control signal is transmitted via a phase control signal connection in the form of a phase control signal line.

[0032] 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 wirelessly between the radar sensors involved in the radar sensor system. Thus, the phase control signal is transmitted via a phase control signal connection in the form of a wireless connection.

[0033] 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 involved in the radar sensor system.

[0034] 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 may be considered to use a phase control signal in the form of a radar carrier frequency, in particular a frequency-modulated radar carrier frequency, to form the radar signal to be transmitted. For example, this can be done by frequency-modulating the phase control signal and transmitting it as the transmitted signal. For example, the radar signal to be transmitted can also be generated by a local oscillator, wherein the local oscillator is controlled by the phase control signal - for example by means of a phase-locked loop (PLL; Phase Locked Loop), by frequency division, or in other ways. Preferably, the phase of the radar signal to be transmitted of the radar sensor in question, i.e., the high-frequency phase, is adjusted in accordance with the phase control signal obtained at the radar sensor. This can be done not only when the frequencies of the high-frequency frequencies of the radar signals of the respective radar sensors are the same, but also when frequency division is performed in the respective radar sensors, which include the respective frequency dividers, or when frequency multiplication is performed in the respective radar sensors, which include a frequency multiplier that multiplies the frequency of the phase control signal in order to generate the carrier frequency. The radar sensor that generates the phase control signal can, for example, adjust the phase of the radar signal to be transmitted relative to the phase control signal. For example, the phase control signal can be generated from a carrier frequency signal - for example by frequency division, or the carrier frequency signal can be output as the phase control signal.

[0035] In one or more embodiments of the radar sensor system, in a method for calibration, in two configurations of the radar sensor that receives the radar signal of the bistatic radar measurement, the (i) received radar signal of the bistatic radar measurement is mixed with the (ii) phase control signal present at the radar sensor or a signal generated based on the phase control signal present at the radar sensor. Preferably, the phase difference in question is determined from the obtained mixed signal. Since at the radar sensor that receives the radar signal of the bistatic radar measurement, either a phase control signal generated by the same radar sensor is present or a phase control signal transmitted by another radar sensor to this radar sensor is present, by mixing the above signals, a mixed signal, for example a fundamental frequency signal, can be directly generated, and then its phase position can be analyzed.

[0036] In one or more embodiments of a radar sensor system, in a method for calibration, half of the difference between the phase differences determined for two configurations is determined as an estimate of the phase delay of the transmission of a phase control signal between a first and a second radar sensor. Assuming that the propagation time of the radar signal in bistatic radar object measurement is the same for the two configurations and that the phase delay due to the transmission of the phase control signal is the same for the two configurations, the phase difference enters the phase differences determined for the two configurations with the same value, so that a two-fold value of the phase delay is obtained by difference formation.

[0037] The two configurations can be selected differently.

[0038] In a variant of the radar sensor system, in a method for calibration, in a second configuration, the radar signal transmission direction for bistatic radar object measurement is opposite to that in a first configuration, wherein the transmission direction of the phase control signal is the same in the two configurations. Thus, the phase control signal can be transmitted by a unidirectional phase control signal connection. Thus, the same phase control signal connection behavior can be adopted for the two configurations, and thus the phase delay is also the same.

[0039] For example, the first and second radar sensors can have antenna elements arranged such that a virtual superimposed measurement path is used for bistatic radar object measurement for the two configurations. For example, the first and second radar sensors can have the same antenna layout, which has the same distance between two antenna elements for transmission and for reception, for example a distance equivalent to half a wavelength, λ / 2.

[0040] In another 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 that in the first configuration, wherein the radar signal transmission direction for bistatic radar object measurement is the same in both configurations. Here, by using a bidirectional phase control signal connection, it is possible to achieve as high a similarity as possible in the transmission characteristics of the phase control signal connection. Advantageously, by using the same receiving antenna elements and transmitting antenna elements of the radar sensors involved, the similarity of the measurement paths of the bistatic radar object measurement passing through distant objects in both configurations can be increased. It is also possible to use, for example, sufficiently similar parallel phase control signal lines instead of the bidirectional phase control signal connection. Thus, in this variant, the radar sensors involved exchange the roles of the radar sensor generating the phase control signal (corresponding to the operation of the radar sensor as the host) and the radar sensor obtaining the phase control signal (corresponding to the operation of the radar sensor as the slave). Assuming that there are no substantial differences in the transmission characteristics of the phase control signal transmission in both directions, the corresponding phase delays occurring can be considered the same. Additionally advantageously, in this variant, the same radar sensor receives the radar signals for bistatic radar object measurement in both configurations. Therefore, this radar sensor can, for example, not only determine the phase difference between the received radar signal and the phase control signal present on the radar sensor for both configurations, but also estimate the phase delay of the phase control signal transmission from the difference between the phase differences determined for both configurations. Thus, there is no need to transmit data between the radar sensors.

[0041] In one or more embodiments of the radar sensor system, the arrangement of the radar sensors on a motor vehicle includes at least three radar sensors, and the at least three radar sensors are arranged at different positions along one direction, wherein the radar sensor system is configured to switch between the following modes:

[0042] An operating mode of the radar sensor system, in which a phase control signal is generated by one radar sensor, and the length of the phase control signal connection from this radar sensor to another radar sensor increases as the distance between the other radar sensor and this radar sensor in the said direction increases; and

[0043] An operating mode of the radar sensor system, in which a phase control signal is generated by one radar sensor and is transmitted into another radar sensor, and the other radar sensor surrounds this radar sensor in the said direction and in the opposite direction.

[0044] The radar sensor generating the phase control signal in the first-mentioned operating mode can be, for example, the radar sensor located at the end position of the arrangement of the radar sensors on the motor vehicle in the said direction.

[0045] For example, the method for calibration can be executed in separately activated operating modes.

[0046] For example, the operating method for the cooperative operation of a radar sensor can also be implemented in separately activated operating modes.

[0047] The difference between the operating modes of the radar sensor system lies in how the deviation of the phase delay occurring between the radar sensors affects during the time period after calibration and before a new calibration. For example, if the components of the radar sensor system change in temperature after calibration, it can be approximately considered that the change in distance between the radar sensors or the change in the length of the phase control signal line between the radar sensors is approximately proportional to the temperature.

[0048] In the operating mode where the length of the phase control signal connection from the radar sensor generating the phase control signal to another radar sensor increases as the distance of the other radar sensor from this radar sensor in the said direction increases, it can be approximately considered that there is the following relationship: Regarding the deviation of the value of the phase delay determined during calibration, it can be considered that as the distance of the radar sensor from the radar sensor generating the phase control signal in the said direction increases, the occurring deviation also increases. In the case of angle determination by a cooperative radar sensor system (whose aperture corresponds to the extension scale of the arrangement of the radar sensors in the said direction), this deviation increasing with the position in the said direction corresponds to the change in the object angle of the radar object located, which is "seen", i.e., estimated, by the radar sensor system. Therefore, in this operating mode, although there is a systematic deviation in the determined angle of the object, the positioning and angle determination of the radar object can be achieved with good functionality. Thus, for example, when the expected deviation of the phase delay is large due to the large length of the phase control signal line, such an operating mode is advantageous for the radar sensor arrangement. Because although there is a large phase deviation in this case, for example, the angle determination can still fully function, even if the determined angle may contain a systematic deviation.

[0049] In contrast, if the expected deviation of the phase delay remains generally small, the following operating mode is advantageous: in this operating mode, the phase control signal is generated by one radar sensor and transmitted to other radar sensors that surround this radar sensor in that direction and in the opposite direction. This can be the case, for example, with short phase control signal lines. Because in this operating mode, the radar sensors surrounding the radar sensor that generates the phase control signal in that direction and in the opposite direction may have similar phase delay deviations from each other. For example, the radar sensors may have an increased phase delay on both sides of the radar sensor that generates the phase control signal, or a reduced phase delay on both sides of this radar sensor. Therefore, the influence of the phase delay deviation on the angle determination by the radar sensor system can be reduced.

[0050] If a prefabricated radar sensor system is to be installed on a vehicle with different arrangements of radar sensors depending on the vehicle, then the switchability of the operating mode is particularly advantageous. For the corresponding arrangement of the radar sensors selected on the vehicle, it is possible to simply switch to the desired operating mode. However, if, for example, according to the activated driver assistance system, the corresponding operating mode is particularly suitable for the distribution of the phase control signal, then it is also possible to perform the switch dynamically during the continuous operation of the radar sensor system. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Embodiments of the present invention will be further described hereinafter with reference to the drawings.

[0052] The drawings show:

[0053] Figure 1 A schematic block diagram of a radar sensor system according to the present invention;

[0054] Figure 2 A schematic diagram showing two configurations of a radar sensor system for calibrating phase delay;

[0055] Figure 3 A schematic diagram showing two configurations of a radar sensor system for calibrating phase delay according to another embodiment;

[0056] Figure 4 A schematic diagram showing a part of the block diagram of a radar sensor;

[0057] Figure 5 A schematic diagram showing a radar sensor system with three radar sensors;

[0058] Figure 6 A schematic diagram showing another example of a radar sensor system with three radar sensors; and

[0059] Figure 7Schematic diagram showing a portion of a block diagram of a radar sensor system. DETAILED DESCRIPTION

[0060] exist Figure 1 The radar sensor system shown in FIG. 1 includes a plurality of radar sensors 10, 12 (in Figure 1 10 , 12 ) and a common control and analysis device 14, which includes a control and analysis unit 16 respectively assigned to the radar sensors 10, 12 and a common superordinate control and analysis unit 18. Radar sensors 10, 12 can be arranged on a motor vehicle, for example, at different transverse positions at the front of the vehicle.

[0061] Each radar sensor 10, 12 includes at least one transmitting antenna Tx and a plurality of receiving antennas Rx, one of which is shown as an example. Radar sensors 10, 12 are installed and arranged in the motor vehicle in such a way that radar sensors 10, 12 are arranged at different positions spaced apart from each other along direction A, so that the superordinate arrangement of radar sensors 10, 12 has a superordinate aperture of the radar sensor arrangement along direction A.

[0062] The radar sensors 10 and 12 are connected to each other via a phase control signal line 20, through which a phase control signal of the first radar sensor 10 operating in the master mode is transmitted to the other radar sensor 12 operating in the slave mode. The first radar sensor 10 includes a phase control signal unit 22, which controls the generation of a radar signal to be transmitted by a radar signal generating unit 24. The radar signal generating unit 24 includes a local oscillator 26 and a modulation unit 28 for modulating a phase frequency (high frequency 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 can be configured, for example, to periodically modulate the frequency of the transmission signal provided by the local oscillator 26 in the form of an increasing frequency ramp and / or a decreasing frequency ramp (Chirps, linear frequency modulation) sequence.

[0063] Another radar sensor 12 operated in 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 operated in slave mode is configured to receive a phase control signal via the phase control signal line 20 and to control the radar signal generating unit 24 based on the phase control signal.

[0064] The radar sensors 10, 12 further include a multiplexing modulation unit 30, which is configured to modulate the corresponding transmitted signals according to a multiplexing method, such that the received signals from the corresponding radar sensors 10, 12 can be separately analyzed and processed by demodulation in the control and analysis processing unit 18.

[0065] The signal received by the antenna element Rx is input to a mixer 32, where the signal 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 signal thus obtained is analyzed and processed by a phase analysis processing unit 38 to determine the phase difference between the radar signal received at the antenna element Rx of the radar sensors 10, 12 and the phase control signal present on the radar sensors 10, 12.

[0066] The phase analysis processing unit 38 of the radar sensor 12 determines the phase difference ΔτM, which analyzes and processes the signal transmitted by the radar sensor 10 operating in the master mode. The phase analysis processing unit 38 of the radar sensor 10 determines the phase difference ΔτS, which analyzes and processes the signal transmitted by the radar sensor 12 operating in the slave mode. To this end, 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 differences ΔτM and ΔτS are output to the upper-level control and analysis processing unit 18.

[0067] In particular, the radar sensor system can be calibrated according to the method described in Figure 2 or 3 below.

[0068] Figure 2 A first configuration of the radar sensor system is shown on the left, which has a first radar sensor 10 operating in the master mode and a second radar sensor 12 operating in the slave mode. The radar sensors 10, 12 are interconnected through a phase control signal line 20. The radar sensor system can, for example, correspond to the structure according to Figure 1 as described.

[0069] In a first configuration, a first radar sensor 10 generates a phase control signal and transmits it via a phase control signal line 20 to a radar sensor 12. At the same time, the first radar sensor 10 emits a radar signal generated under the control of its own phase control signal 20 via its transmitting antenna Tx. The emitted radar signal is reflected by a distant external object 40, such as an object 40 (e.g., another vehicle) in the traffic environment of the present motor vehicle, and is received and analyzed by the second radar sensor 12 via its receiving antenna Rx. For the transmission of the phase control signal via the phase control signal line 20, a phase delay τk is obtained. The signal propagation time on the measurement paths 42, 44 including the object 40 results in a delay τz1 + τz2. By analyzing the phase of the signals mixed at the mixer 32, a phase analysis processing unit 38 determines the difference ΔτM between the delay of the radar channel (measurement path) and the coupling delay of the phase control signal transmission, where: ΔτM = (τz1 + τz2) - τk applies.

[0070] In Figure 2 In the second configuration shown on the right, with the position of the object 40 remaining almost unchanged, the phase control signal is again generated by the first radar sensor 10 operating as a master and is transmitted via the phase control signal line 20 to the second radar sensor 12. However, in this configuration, the radar signal generated by the second radar sensor 12 has its phase controlled by the phase control signal, and the second radar sensor emits this radar signal via its transmitting antenna Tx. The radar signal reflected by the object 40 is received by the first radar sensor 10 and mixed with the self-signal of the local oscillator 26 generated based on its own phase control signal, and is analyzed by the phase analysis processing unit 38. The obtained phase delay ΔτS corresponds to the sum of the delays of the measurement paths 44, 42 and the coupling delay on the phase control signal line 20: ΔτS = (τz1 + τz2) + τk.

[0071] The higher-level control and analysis processing unit 18 calculates the difference between the phase differences ΔτM and ΔτS, for which approximately:

[0072] ΔτM - ΔτS = [(τz1 + τz2) - τk] - [(τz1 + τz2) + τk] = -2τk

[0073] Therefore, an estimated value of the phase delay τk of the transmission of the phase control signal on the phase control signal line 20 is determined based on the obtained value. For example, the difference between the phase differences can be calculated by multiplying the complex amplitudes of the mixed signals obtained in the respective radar sensors in a conjugate complex manner.

[0074] Figure 3 Corresponding to Figure 2The illustrated figure shows another example of two configurations for calibrating the phase delay of phase control signal transmission.

[0075] The first configuration corresponds to the first configuration of the example of Figure 2 The second configuration on the right differs from the first configuration in that the transmission direction of the phase control signal on the phase control signal line 20 is opposite. In this configuration, the second radar sensor 12 operates in the host mode and generates a phase control signal, which is transmitted by the phase control signal unit 22 through the phase control signal line 20 into the first radar sensor 10. At the same time, the first radar sensor 12 generates a radar transmission signal controlled by the obtained phase control signal. Figure 3 The radar signal transmitted by the first radar sensor 10 and received by the second radar sensor 12 after reflection on the object 40 is mixed with the high-frequency signal generated by this radar sensor under the control of its phase control signal, and is analyzed and processed by the phase analysis processing unit 38. In this example, the second radar sensor 12 determines not only the phase difference ΔτM in the first configuration but also the phase difference ΔτS in the second configuration, and transmits the two values to the upper-level control and analysis processing unit 18. Therefore, in this example, the phase control signal line 20 operates bidirectionally.

[0076]

[0077] Figure 4 Figure 1 Schematically shows a part of the radar sensors 10, 12 of a variant of the radar sensor system according to Figure 1 The radar sensors 10, 12 differ from the radar sensors 10, 12 shown in in that there is a common antenna element 46 for transmitting and receiving radar signals. The antenna element 46 is connected to the local oscillator 26 through a circulator 48. The circulator is arranged to transmit the radar signal generated by the local oscillator 26, modulated by the multiplexing modulation unit 30 if necessary, into the antenna 46 and to transmit the radar signal received by the antenna into the mixer 32, to which the filter 34, the analog / digital converter and the phase analysis processing unit 38 are connected. The method for calibrating the phase delay can be performed as described above.

[0078] Figure 1 Instead of transmitting the phase control signal of the phase control signal unit 22 through the phase control signal line 20 as described in the above example, for example, the high-frequency signal generated by the local oscillator 26 of the radar sensor 10 or 12 operating as the host can also be used as the phase control signal through Figure 1The phase control signal line 20' shown by the dashed line in the middle is transmitted to the radar sensors 12 or 10 operating in slave mode, where it is either transmitted as a radar signal or used for mixing the received radar signals at the mixer 32. Alternatively, a lower frequency signal derived from the high frequency signal of the radar sensor 10 or 12 operating as the master can also be used as a phase reference signal and transmitted through the phase control signal line 20” shown by the dashed line in the middle to the radar sensors 12 or 10 operating in slave mode, where it is converted into a high frequency signal. For this purpose, for example, the radar signal generation unit 24 of the radar sensor operating as the master can include a frequency divider, while the radar signal generation unit 24 of the radar sensor operating as the slave can include a frequency multiplier. For example, a phase reference signal (phase control signal) with a frequency of 10 GHz obtained through the phase control signal line 20” can be converted into a radar signal of 80 GHz by frequency multiplication by 8 times. Figure 1 The phase control signal line 20” shown by the dashed line in the middle is transmitted to the radar sensors 12 or 10 operating in slave mode, where it is converted into a high frequency signal. For this purpose, for example, the radar signal generation unit 24 of the radar sensor operating as the master can include a frequency divider, while the radar signal generation unit 24 of the radar sensor operating as the slave can include a frequency multiplier. For example, a phase reference signal (phase control signal) with a frequency of 10 GHz obtained through the phase control signal line 20” can be converted into a radar signal of 80 GHz by frequency multiplication by 8 times.

[0079] Figure 5 and 6 The distribution of the phase control signal generated by the radar sensor 10 operating in master mode and transmitted to the other radar sensors 12, 12' operating in slave mode is schematically shown in the upper part respectively. Figure 5 and 6 The two shown radar sensor systems can be different operating modes of the same radar sensor system, where the radar sensor system is set to switch between the operating mode according to Figure 5 and the operating mode according to Figure 6 by switching the corresponding phase control signal line 20. The operating mode according to Figure 5 corresponds to the star distribution of the phase control signal, while the operating mode according to Figure 6 corresponds to the sequential distribution of the phase control signal.

[0080] In Figure 5 and 6 In the lower part, the expected phase deviations of the respective radar sensors 10, 12, 12' along the direction A at the positions of the radar sensors involved are shown respectively. Such phase deviations may occur in the operating interval between two phase delay calibrations in case of temperature changes or deformation of the radar sensor arrangement. Here, it is assumed that with the increase in the length of the phase control signal line 20, an increasing phase deviation occurs. In Figure 5 Positive phase deviations in the same direction are obtained on the left and right sides of the first radar sensor 10 operating in master mode ( Figure 5 is positive in Figure 6 ). In

[0081] Figure 7 A radar sensor arrangement is schematically shown, in which a first radar sensor 10 and a second radar sensor 12 have antenna elements which are arranged such that for a configuration according to Figure 2 a virtual superposition of radar channels (bistatic measurement paths) is used. The arrangement of the radar sensors 10, 12 with the respective antenna elements Tx, Rx corresponds to a virtual bistatic MIMO antenna array with a virtual superposition of radar channels. Between the transmit and receive antenna pairs Tx, Rx of the first radar sensor, the distance a is equal to the distance a between the transmit and receive antenna pairs 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. Thereby, the coordination of the signal propagation times τz1 + τz2 of the bistatic radar object measurement in both configurations can be improved. The radar sensor system can otherwise correspond to the above example.

Claims

1. A collaborative radar sensor system having an arrangement of at least two radar sensors (10, 12) on a motor vehicle, wherein, The radar sensor system is arranged to transmit phase control signals between the radar sensors in order to control the high-frequency phase of the radar signals to be transmitted. Wherein, the radar sensor system is also arranged to implement a method for calibrating a respective phase delay (τk) of the transmission of the phase control signal between a respective first radar sensor and a respective second radar sensor in the radar sensors (10, 12), in which method a phase control signal is generated in a first configuration of the first radar sensor (10) and transmitted to the second radar sensor (12), and the second radar sensor transmits a radar signal based on the transmitted phase control signal, the radar signal being reflected on an object (40) in a bistatic radar object measurement and received by the first radar sensor (10), and a phase control signal is generated in a second configuration of one of the first and second radar sensors (10, 12) and transmitted to the other of the first and second radar sensors (12, 10) and a radar signal is transmitted, the radar signal being reflected on the same object (40) in a bistatic radar object measurement and received by the other radar sensor (12, 10), wherein, for both configurations, a phase difference (ΔτM, ΔτS) between the radar signal received on one radar sensor (10, 12) of the bistatic radar object measurement and the phase control signal present on this radar sensor is determined, wherein, based on the phase differences determined for both configurations, a phase delay (τk) of the transmission of the phase control signal between the first and second radar sensors (10, 12) is estimated.

2. The radar sensor system according to claim 1, having at least one phase control signal line (20) for transmitting phase control signals between the 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, in the first configuration and in the second configuration, the phase control signals are transmitted wirelessly, respectively, between the radar sensors (10, 12) involved in the radar sensor system.

4. The radar sensor system according to one of claims 1 to 3, wherein, In the method for calibration, in the first configuration and in the second configuration, the phase control signals are transmitted directly, respectively, between the radar sensors (10, 12) involved in the radar sensor system.

5. The radar sensor system according to one of claims 1 to 3, 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. The radar sensor system according to one of claims 1 to 3, wherein, In the method for calibration, in both configurations of the radar sensor that receives the radar signal of the bistatic radar measurement, the received radar signal of the bistatic radar measurement is mixed with the phase control signal present on this radar sensor or a signal generated based on the phase control signal present on this radar sensor, wherein, based on the obtained mixed signal, the respective phase difference (ΔτM; ΔτS) is determined.

7. The radar sensor system according to one of claims 1 to 3, wherein, In the method for calibration, half of the difference between the phase difference values determined for two configurations is determined as the estimated value of the phase delay (τk) of the transmission of the phase control signal between the first and second radar sensors (10, 12).

8. The radar sensor system according to one of claims 1 to 3, wherein, In the method for calibration, in the second configuration, the radar signal transmission direction of the bistatic radar object measurement is opposite to that in 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) each have antenna elements (Rx, Tx), and the antenna elements are arranged such that a virtual superimposed measurement path is used for the bistatic radar object measurement in both configurations.

10. The radar sensor system according to one of claims 1 to 3, wherein, In the method for calibration, in the second configuration, the transmission direction of the phase control signal is opposite to that in the first configuration, wherein the radar signal transmission direction of the bistatic radar object measurement is the same in both configurations.

11. The radar sensor system according to one of claims 1 to 3, wherein, The arrangement of the radar sensors on a motor vehicle includes at least three radar sensors (10, 12, 12'), which are arranged at different positions along one direction (A), wherein the radar sensor system is set to switch between the following modes: An operating mode of the radar sensor system, in which a phase control signal is generated by one radar sensor (10), and wherein the length of the phase control signal connection (20) from the one radar sensor (10) to the other radar sensors (12, 12') increases as the distance of the other radar sensors from the one radar sensor in the direction (A) increases; and An operating mode of the radar sensor system, in which a phase control signal is generated by one radar sensor (10), and the phase control signal is transmitted to the other radar sensors (12, 12'), and the other radar sensors surround the one radar sensor in the direction and in the opposite direction.

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