Multiple-input-multiple-output-radar system for vehicles

Abstract

The invention relates to vehicle radar systems (100) having a distributed antenna structure (320) and to the evaluation of radar signals of a vehicle radar system (100) of this type for environment detection. In particular, it is proposed that the distributed antenna structure (320) comprises a further transmitting antenna and a plurality of further receiving antennas, wherein the plurality of further receiving antennas are arranged in a uniform linear array (330), and wherein the further transmitting antenna is provided to transmit a further radar signal with a continuous series of chirps in a further frequency range which differs from the one frequency range and in which the other transmitting antennas transmit temporally offset chirps as radar signals, the radar echo signals of which are received by the other receiving antennas. The further echo signals detected in the further frequency range are used to derive distances to objects and to determine the relative speeds thereof, which, on the basis of the echo signals detected in the one frequency band, are then assigned to objects for which an equal distance has been determined within a tolerance range. The invention also relates to the described evaluation method.

Description

[0001] Description

[0002] Consideration of ULA structures and multiple modulation frequencies in sparse array apertures for computationally efficient Doppler processing.

[0003] The invention relates to vehicle radar systems with distributed antenna structures and the evaluation of radar signals from such a vehicle radar system for environmental detection.

[0004] Distributed radar antenna structures, also known as distributed, multi-static or bi-static or multiple-input-multiple-output (MIMO) antenna structures, are used in vehicle radar systems for environmental detection.

[0005] Radar systems with distributed antenna structures observe potential targets from different angles to minimize fluctuation losses. However, calculating the target coordinates before coherently summing the individual signals is significantly more complex and computationally intensive compared to monostatic radar systems due to the varying signal propagation times.

[0006] The use of distributed transmit and receive antennas results in different signal propagation times between the transmit antenna, the receive antenna, or the receive antenna and a potential target, which in turn result in differing measurement distances. These differing measurement distances, in turn, result in a non-linear phase term, which prevents coherent integration over the dimension of the receive channels in favor of a better signal-to-noise ratio.

[0007] In the prior art, the compensation of such nonlinear phase terms for subsequent Doppler processing is associated with considerable computational effort and a massive utilization of a computing unit of the radar system. The invention is therefore based on the objective of improving a radar system, in particular for vehicles, with a distributed antenna structure, and its evaluation method, in particular reducing the required computing power.

[0008] The invention is solved by a radar system having the features of claim 1 and a method having the features of claim 11; advantageous embodiments are set forth in the dependent claims.

[0009] The basic idea of ​​the invention is to transmit radar signals in the form of linearly monotonically varying signal segments, called chirps, in two different and disjoint frequency ranges. While the radar signals or chirps transmitted in one frequency range are alternately transmitted with time delays via different transmitting antennas in that frequency range, and echo information is derived from the received radar echo signals in that frequency range by associated receiving antennas and associated receiving modules, the subsequent chirps are continuously transmitted as a further radar signal via one of the transmitting antennas in the other frequency range.The antenna structure comprises multiple receiving antennas forming a uniform linear array. Their associated receiving modules are designed to derive further echo information from radar echo signals acquired in a wider frequency range. At the central station, distance spectra are generated from this echo information, for example, using a Fourier transform, and distances to detected objects are determined. Each distance determined from the echo information is assigned a tolerance range, specifying the area within which the determined distance can vary for the different transmitting and receiving antenna pairs providing the echo information. Further distance spectra are then generated from this additional echo information, and further distances to detected objects are determined.The distance spectra generated from the additional echo information of all receiving antennas in the uniform linear array are coherently integrated. Subsequently, the relative velocities are determined by evaluating Doppler spectra based on the coherently integrated distance spectra. The objects detected using the additional echo information, and their relative velocities, are then assigned to those objects detected using the echo information whose determined distances, within the assigned tolerance range, agree with the further determined distances. Due to the structure of a linear uniform antenna array, it is possible to perform a coherent integration of the distance spectra of all receiving antennas in the uniform linear antenna array, thus significantly increasing the signal-to-noise ratio, even though only a limited number of antennas are evaluated.The calculation of relative velocities based on the evaluation of Doppler spectra using a discrete Fourier transform can thus be significantly simplified.

[0010] The entire further processing of the echo information can be significantly simplified and accelerated due to the assignment of the relative velocities to the detected objects over the further distances that correspond within the respective tolerance ranges of the determined distances.

[0011] In particular, a multiple-input multiple-output radar system of a vehicle is provided with a distributed antenna structure in which transmitting and receiving antennas are arranged, each of the transmitting antennas being assigned a transmitting module and each of the receiving antennas being assigned a receiving module, and a central station for generating radar signal information, which is converted by the transmitting modules into radar signals that are emitted by the transmitting antennas, and for evaluating radar echo information derived by the receiving modules from the radar echo signals received at the receiving antennas.

[0012] wherein the radar signal information and the echo information are modulated onto at least one optical carrier signal and transmitted between the central station and the transmitting and receiving modules, wherein the central station is configured to generate the radar signal information and transmit it to the transmitting modules and / or control it such that at least some of the transmitting modules, based on the transmitted radar signal information, emit signal segments (chirps) as radar signals via the assigned transmitting antennas, each with a time offset and monotonically linear frequency variation within a frequency range, and at least some of the receiving modules are configured to derive echo information from the radar echo signals simultaneously detected by assigned receiving antennas within the same frequency range and generated by objects in the environment, and to transmit this information to the central station, wherein

[0013] The central station is configured to generate the radar signal information and / or to control the transmitting and receiving modules in such a way that signal segments (further chirps) varying continuously and monotonically linearly with respect to frequency in a further frequency range are emitted as a further radar signal from a transmitting antenna assigned to one of the transmitting modules, wherein the further frequency range is disjoint from the one frequency range, and the antenna structure comprises a plurality of receiving antennas forming a uniform linear array, and whose assigned receiving modules are configured to derive further echo information from further radar echo signals in the further frequency range, which are generated by the objects in the environment, and to transmit this information to the central station.

[0014] wherein the central station is configured to generate distance spectra from the echo information and to determine distances to detected objects, wherein each distance determined from the echo information is assigned a tolerance range that specifies a range in which the determined distance can vary for the different transmitting and receiving antenna pairs providing the echo information, and to generate further distance spectra from the further echo information and to determine further distances to detected objects, and to coherently integrate the further distance spectra generated from the further echo information of all receiving antennas of the uniform linear array and subsequently to determine the relative velocities using Doppler spectra based on the coherently integrated further distance spectra, wherein the central station is further configured

[0015] to assign the objects detected using the additional echo information and their relative velocities to the objects detected using the echo information whose determined distance corresponds to the further determined distance within the assigned tolerance range.

[0016] Furthermore, a method for environmental sensing using a multiple-input, multiple-output radar system is created, comprising a central station for setting and controlling the radar signals emitted with time delay via different transmitting antennas and evaluating the echo information derived from simultaneously acquired radar echo signals in order to determine information about detected objects, comprising the steps of: time-delayed emission of radar signals via different transmitting antennas of an antenna structure, wherein the radar signals comprise signal segments, chirps, that vary monotonically linearly with respect to a frequency within a frequency range, and simultaneous acquisition of radar echo signals in that frequency range with receiving antennas of the antenna structure, derivation of echo information from the radar echo signals in that frequency range, and evaluation of the echo information to derive information for detected objects.which include at least a distance and a relative velocity, by generating distance spectra from the echo information and determining distances to the detected objects, wherein each distance determined from the echo information is assigned a tolerance range that specifies a range in which the determined distance can vary for the different receiving and transmitting antenna combinations providing the echo information, wherein,

[0017] Additionally, further signal segments, or chirps, which vary continuously and monotonically linearly with respect to a frequency, are emitted via a transmitting antenna of the antenna arrangement in a further frequency band that is disjoint from the first frequency band, and further radar echo signals in the further frequency range are received by a plurality of receiving antennas of the antenna arrangement, which form a uniform linear array, and further echo information is derived from these.wherein the central station generates further distance spectra based on the additional echo information and determines distance data for the detected objects, and the distance spectra generated from the additional echo information of all receiving antennas of the uniform linear array are coherently integrated, and subsequently the relative velocities are determined by evaluating Doppler spectra based on the coherently integrated distance spectra, and the relative velocities derived from the additional echo information are assigned to the objects detected using the echo information by means of a correspondence between the further distance data determined using the additional echo information and the distances determined using the echo information within the assigned tolerance ranges.

[0018] In a preferred further processing stage, the determined and assigned relative velocities are used for further processing of the echo information and the resulting data on the detected objects. Overall, this improves the processing of the echo information and reduces the speed required to calculate further data.

[0019] It is particularly advantageous, especially for the dual use of individual components in the generation of radar signal information, as well as for the synchronization of evaluation and / or the dual use of components of the central station in the processing of echo information and further echo information, and / or the dual use of evaluation algorithms, if the chirps and further chirps are identical with respect to a frequency change (a frequency deviation) and a temporal duration. It is particularly preferred that these chirps are also synchronized with respect to their temporal initiations in the central station, and particularly preferably that these temporal initiations are identical on an absolute timescale.Preferably, the radar signal information is generated and modulated onto an optical carrier signal in such a way that the resulting electrical signal, after conversion, can be emitted as a radar signal or as a further radar signal immediately after amplification or, if necessary, frequency multiplication. This allows for the design of simple transmitter modules. The corresponding receiver modules can also easily generate the signal required for the mixing process to derive the echo information or further echo information.

[0020] In the receiving modules, the radar echo signal or further radar echo signal supplied by the associated receiving antenna is amplified and mixed with an electrical signal derived from the radar signal information. This electrical signal corresponds to the radiated signal that was transmitted to generate the radar echo signal or further radar echo signal. This process transforms the signal into an intermediate frequency range. This signal, containing the echo information or further echo information, is then modulated onto an optical carrier signal for transmission back to the central station.

[0021] The use of optical carrier signals enables coherent evaluation, in which the phase relationship of the individual signals to each other is preserved during transmission and can be reconstructed.

[0022] Various configurations of the central station and the transmit and receive modules are possible. One embodiment involves generating a transmission signal in which chirps in one frequency range and further chirps in another frequency range are modulated onto an optical carrier signal. Filters in the transmit and receive modules then generate the electrical signals corresponding to the chirps or further chirps. The same transmission signal can, for example, be continuously transmitted to all receive modules and the transmit module for sending the further radar signal to emit the further chirps in the other frequency band, and alternately to the transmit modules for emitting the radar signals in one frequency range. The receive signals can be interconnected via a loop, thus saving on transmission media.Furthermore, a transmitting antenna can be used, at least in certain time intervals, to simultaneously transmit the radar signal in one frequency range and continuously, in one time interval and the remaining time intervals of a measurement sequence, the radar signal in the other frequency range. In another embodiment, the central station is configured to generate a transmission signal in which the chirps in one frequency range are modulated onto an optical carrier signal, and another transmission signal in which the further chirps in the other frequency range are modulated onto a further optical carrier signal.In this embodiment, the portion of the radar signal information associated with the emitted chirps in one frequency range and the derivation of the corresponding echo information can be selectively transmitted to the appropriate transmitting and receiving modules. These modules derive the echo information from the radar echo signals in that frequency range. The portion correlated with the emission of further chirps is transmitted to the transmitting module and receiving modules, which emit the further radar signal and receive the further radar echo signals in the other frequency range, deriving further echo information from them. The transmitting and receiving modules require fewer or no filters to separate the different frequency ranges.

[0023] In yet another embodiment, the central station generates the radar signal information with a sequence of signal segments, base chirps, that vary monotonically linearly with respect to frequency. The frequency deviation of these base chirps corresponds to the frequency bandwidth of one frequency band and another. The transmitting and receiving modules each have at least one frequency converter to convert a base chirp into a chirp in one frequency band or another chirp in the other frequency band. There is only one radar signal information consisting of base chirps, which are frequency-converted by the transmitting and receiving modules in such a way that a chirp in one frequency band or another chirp in the other frequency band is subsequently present. These chirps or further chirps, respectively, are then used to generate the radar signal.Signals exhibiting these chirps or further chirps can then be used to transmit the radar signal or further radar signal, or as a reference signal in a mixer when deriving the echo information or further echo information.

[0024] Particularly high resolution for a given number of transmitting and receiving antennas is achieved when the transmitting antennas, which radiate the radar signals in one frequency range, and the receiving antennas, which are assigned to receiver modules that derive echo information from the received radar echo signals in that frequency range, form a sparse antenna array. The total number of antennas required in the antenna structure can be reduced without loss of information by having at least one of the receiving antennas be part of both the sparse antenna array and the linear uniform antenna array.

[0025] This means that at least one of the receiving antennas is assigned a receiving module that derives echo information based on the radar echo signals detected in one frequency range, as well as further echo information based on the radar echo signal detected in another frequency range. The antenna can also be assigned two separately designed receiving modules, one that evaluates the detected radar echo signals in one frequency range and the other radar echo signals in the other frequency range.

[0026] Likewise, one of the transmitting antennas of the sparse antenna array or a separate transmitting antenna can be used for the continuous transmission of the further radar signal in the wider frequency range.

[0027] The uniform linear antenna array is preferably designed such that the majority of the receiving antennas forming the uniform linear array have a distance to an adjacent receiving antenna that corresponds to half the mean wavelength of the further radar signal that is correlated with the emission of a further chirp.

[0028] A particularly advantageous configuration is one in which the uniform linear array is arranged along an axis of the antenna structure that coincides with a horizontal plane in a vehicle. This allows for particularly accurate determination of the relative speed in the plane where the radar system's horizontal axis lies. For road vehicles, this is the plane in which the relative speed is of particular importance.

[0029] The antenna structure preferably comprises two linear uniform receiving antenna arrays arranged along the two axes spanning the two-dimensional antenna array. It is understood that the evaluation is carried out such that the steps performed for one linear antenna array are executed analogously for the second linear antenna array.

[0030] One embodiment provides that a uniform linear array is formed along one axis of the antenna structure, and a further uniform linear array of receiving antennas is formed along another axis of the antenna structure. Preferably, the receiving modules associated with the receiving antennas of the further uniform linear array are configured for evaluating further echo information in the additional frequency range. The evaluation for the first uniform linear array of receiving antennas (350) and the evaluation for the further uniform linear array are performed separately.

[0031] The determined and assigned relative velocities are preferably used to compensate for echo information regarding relative velocity before further evaluation and / or to limit the echo information to be evaluated. This can significantly reduce the computational effort required for further processing.

[0032] The invention is explained in more detail below with reference to a drawing.

[0033] This shows:

[0034] Fig. 1 shows a schematic view of a photonic M1 MO radar system;

[0035] Fig. 2 shows a representation of a data structure of a measurement sequence and its processing according to the state of the art;

[0036] Fig. 3 shows a schematic representation of an Ml MO radar system according to a variant in which the central station modulates radar signal information onto a transmission signal;

[0037] Fig. 4 shows another schematic representation of a central station of a MIMO radar system according to a further variant in which two different optical transmission signals are generated as radar signal information, which are transmitted to the transmit and receive modules of the radar head devices via different optical transmission media;

[0038] Fig. 5 shows a schematic representation of a semiconductor structure for implementing transmit modules for a variant of the MIMO radar system, in which the transmission signal is generated with a sequence of base chirps; Fig. 6 shows a schematic representation of a semiconductor structure for implementing receive modules for a variant of the MIMO radar system, in which the transmission signal is generated with a sequence of base chirps;

[0039] Fig. 7 shows a schematic representation of a semiconductor structure for realizing transmitter modules for a variant of the MIMO radar system, in which an optical carrier signal onto which two sequences of chirps in different frequency ranges are modulated, or two different optical carrier signals are transmitted via one transmission medium, wherein a sequence of chirps in one frequency range is modulated onto one optical carrier signal and a further sequence of chirps in another frequency range is modulated onto the other optical carrier signal;

[0040] Fig. 8 shows a schematic representation of a semiconductor structure for realizing receiver modules for one variant of the MIMO radar system, in which an optical carrier signal onto which two sequences of chirps in different frequency ranges are modulated, or two different optical carrier signals are transmitted via the transmission medium, wherein a sequence of chirps in one frequency range is modulated onto one optical carrier signal and a further sequence of chirps in another frequency range is modulated onto the other optical carrier signal;

[0041] Fig. 9 shows a schematic representation of a semiconductor structure for realizing transmitter modules for a variant of the MIMO radar system, in which an optical carrier signal onto which two sequences of chirps in different frequency ranges are modulated, or two different optical carrier signals are transmitted via one transmission medium, wherein a sequence of chirps in one frequency range is modulated onto one optical carrier signal and a further sequence of chirps in another frequency range is modulated onto the other optical carrier signal, wherein only one transmitter module is realized on a semiconductor structure;

[0042] Fig. 10 shows a schematic representation of a semiconductor structure for realizing receiver modules for one variant of the MIMO radar system, in which an optical carrier signal onto which two sequences of chirps in different frequency ranges are modulated, or two different optical carrier signals are transmitted via the transmission medium, wherein a sequence of chirps in one frequency range is modulated onto one optical carrier signal and a further sequence of chirps in another frequency range is modulated onto the other optical carrier signal, wherein only one transmitter module is realized on a semiconductor structure;

[0043] Fig. 11 shows a schematic representation of a semiconductor structure for realizing transmitter modules for a variant of the M1 MO radar system, in which only an optical carrier signal is transmitted via the coupled transmission medium, onto which either the sequence of chirps in one frequency range or the other frequency range is transferred;

[0044] Fig. 12 shows a schematic representation of a semiconductor structure for realizing receiver modules for a variant of the M1 MO radar system, in which only an optical carrier signal is transmitted via the coupled transmission medium, onto which either the sequence of chirps in one frequency range or the other frequency range is transferred; and

[0045] Fig. 13 shows a schematic flow diagram and a schematic antenna structure to illustrate an evaluation of the radar signals and assignment of the measurement results, which are recorded on the basis of the radar echo signals and further radar echo signals in the different frequency ranges.

[0046] Figure 1 schematically depicts a photonic radar system 100. This system comprises a central station 200 and a plurality of radar head units 300, 300-n, configured as transmit and / or receive modules. The central station 200 and radar head units 300, 300-n are each individually coupled via two optical fibers 401, 401-n, 501, 501-n. The optical fibers 401, 401-n serve as transmission media 400 for transmitting optical signals from the central station to the radar head unit 300, 300-n. The optical fibers 501, 501-n serve as return transmission media 500. Additionally, the radar head units 300, 300-n are preferably connected to the central station 200 via an electronic control line 460 and an electronic return line 550. The electronic control line 460 and the electronic return line 560 can be configured as a bus system.Alternatively or additionally, the individual radar head units 300, 300-n can each be equipped with an individual control line and individual electronic return line.

[0047] Lowercase letters -n ... stand for natural numbers to indicate countability and distinguishability of the corresponding objects.

[0048] In the illustrated embodiment, the central station 200 is configured to generate radar signal information for transmission, whereby, in the illustrated example, this occurs at a frequency eight times lower than the transmission of a radar signal via an antenna 350, 350-n of one of the radar head units 300, 300-n configured as transmitter modules. For this purpose, the central station 200 comprises a control unit 210, which controls a coherent light source 220, preferably configured as a laser. In an environment detection operating state, radar signal information is modulated onto the optical carrier signal generated by the laser 220 via a modulation unit 230. For example, in a MIMO radar according to the prior art, the radar signal information is a frequency-modulated continuous wave (FMCW) signal intended for transmission, divided by a factor of eight.The modulation device is, for example, designed as a Mach-Zehnder modulator (MZM). The optical signal is forwarded via an optical control device 240 to a distribution device 250. The distribution device 250 preferably includes a switch that controls an optical signal fed into an input and switches it to one or more outputs. The distribution device 250 is also controlled by a control device 210 and selectively switches the optical signal to one or more fiber outputs. The optical signal is thus switched to one or more of the transmission media 400, 400-n and transmitted to one or more of the radar head devices 300, 300-n.

[0049] The fiber output is coupled to one of the optical waveguides 401, 401-n, i.e., one of the fibers 402, 402-n. The optical fibers 402, 402-n are connected at their other end to one of the radar head devices 300, 300-n.

[0050] The radar head units 300, 300-n each have a fiber input 305, 305-n, to which the fiber 402-n coming from the central station 200 is connected. The optical carrier signal with the modulated and transmitted radar signal information is coupled via a photoreceiver coupler 310 into an electronic photonic integrated circuit (EPIC) 315. The photonic components are preferably formed in a region where silicon is located on an insulator, whereas the electronic components are formed on so-called bulk silicon. Embodiments are also possible that are based on other materials or use separate photonic integrated circuits and electronic integrated circuits.In the radar head assembly 300, 300-n, the fiber input 305, 305-n is optically coupled to a fiber output 395, 395-n, such that at least part of the optical signal transmitted to the radar head assembly 300, 300-n via the fiber 402, 402-n serving as the transmission medium 400, 400-n is transmitted back to the central station 200 via the fiber 502, 502-n serving as the return transmission medium 500, 500-n. The fiber 502, 502-n serving as the return transmission medium 500 is connected to the corresponding fiber output 395, 395-n.

[0051] The transmitted optical signal can be converted into an electronic signal in the radar head unit 300, 300-n, whereby the radar signal information is separated from the carrier signal. The radar signal information is typically amplified in the radar head unit, which is designed as a transmitter module, and its frequency is often also multiplied and / or converted. It is then emitted as electromagnetic radiation from the corresponding antenna 350 of the radar head unit 300, 300-n as a radar signal.

[0052] The electromagnetic radiation reflected from an object in the vicinity is also received as a radar echo signal by an antenna 350, 350-n of one or more radar head units 300, 300-n. In a mixing process, radar echo signal information is typically derived from the radar echo signal and generated and processed as an intermediate frequency signal. This intermediate frequency signal is then optically modulated onto the carrier signal transmitted by the radar head unit and transmitted back to the central station 200 via the corresponding return transmission medium 500, 500-n. No carrier signal is actively generated in the radar head unit 300, 300-n, but it can be modified by modulation.

[0053] In the central station 200, a detection unit 260 separates the radar echo information from the optical carrier signal and converts it into an electrical signal during conversion into an electronic signal. The radar echo information received via the various transmission media is evaluated together in a processing unit 270 of the central station to determine the distance, relative velocity, and relative angular position of individual objects in the surrounding area. Upon transmission to the processing unit 270, electrical signals can be digitized in a digitizing unit 280 and pre-processed in a processing unit 290, for example, by undergoing a Fourier transform, which can be implemented in special modules.

[0054] The basic principle behind measuring the Doppler velocity of a dynamic object using an FMCW signal model is based on the sequential transmission of several so-called chirps (frequency-modulated radar signals). This generates a measurement sequence that significantly increases the observation period of an object compared to a single measurement. The radar signals acquired during a chirp transmission are sampled at equal time intervals. The time-based sampling is indexed with the lowercase letter n. If a measurement is performed simultaneously with a multitude of receiving antennas in an antenna array, a set of equally spaced time samples is obtained for each receiving antenna. The individual measurements of the measurement sequence are indexed with the lowercase letter m. A measurement sequence, or frame, thus yields a cube of data, as shown in Fig. 2.A phase term relevant for Doppler velocity measurement propagates with each newly emitted measurement signal within the measurement sequence and generates a signal waveform whose underlying frequency is proportional to the Doppler velocity. If an arbitrary temporal sampling step "n" of the measurement chirp is set constant over all chirps within the measurement sequence, the measurement signal can be described according to formula (1).

[0055]

[0056] In the case of a monostatic radar, or a bistatic radar where the spatial distance between transmitting and receiving antennas is negligible, d(p) = 2R0 applies. The outbound and return paths between the transmitting antenna, receiving antenna, and target are the same. With each additional measurement "m" within the measurement sequence, only the phase term "exp (j.^2vT" in formula (1) changes. PRIm', which describes the dependence on the Doppler velocity "v". A is the wavelength of the radar signal radiation and TPRI indicates the duration between two start times of successive measurements (period of chirp repetition). If the radar aperture includes additional receiving antennas for which the described property d(p) = 2R0 still applies, the individual measurement signals can be coherently added according to formula (1) to improve the signal-to-noise ratio. The final determination of the Doppler frequency is carried out, as is generally known, by frequency analysis in the form of discrete Fourier transforms. For bistatic radars in which transmitting and receiving antennas are spatially distributed, the previously made assumption d(p) = 2R0 is no longer valid. Instead, d(p) ≠ 2R0 applies, since the radial distance between the transmitting antenna position "p" Tx “and a target “p” and the receiving antenna position “p” Rx“and a target “p” differ from each other. For “d(p)”, therefore:

[0057]

[0058] This property of distributed radars has a significant influence on the calculation of the Doppler velocity, since "d(p)" within the phase terms "exp ( I2n — d(p)nT" s ]" and

[0059] X c o /

[0060] ( i— d(p) “ influencing the measurement signal non-linearly. A for the signal-to- Z /

[0061] A coherent integration across all receiving antennas, advantageous in terms of noise ratio, is no longer feasible. Instead, such an approach can, in the worst case, cause destructive interference and cancel out essential signal components. To counteract this problem, all nonlinear phase components in the measurement signal must be compensated according to formula (1) when using a distributed radar before processing the Doppler. Since the direction angle inherent in equation 2 is unknown during the Doppler measurement process, hypotheses about all targets within all angular and distance intervals within the radar's field of view must be formulated and applied to compensate for the nonlinear phase components.

[0062] In the prior art evaluation method, where all measurements are performed with chirps in the same frequency range, the following procedure is used to compensate for nonlinear phase terms for coherent integration over all receiving antennas for Doppler processing: Starting with the input data set, it is multiplied by a hypothesis data set, accumulated over the dimension of the receiving antennas, and finally Fourier-transformed over the dimension of the received sequence. Each hypothesis data set assumes a target in the direction of an assumed solid angle, which occurs within each distance gate. Mathematically, this procedure can be formulated as follows:

[0063]

[0064] T sis the sampling period, Co is the speed of light, where a is a ratio between bandwidth and modulation time of a frequency ramp, i.e., a ratio of the frequency deviation to the ramp duration.

[0065] For a hypothesis to be correct, integration in the direction of the receiving antenna dimension causes constructive interference, so that target information stands out against noise in the range-Doppler spectrum.

[0066] The computational effort required to compensate for nonlinear phase terms increases linearly with the degree of granularity by which individual hypotheses differ (see Fig. 2). A conventional approach, which merely subjects the transmit sequence of a receiving antenna in a receiving channel to a Fourier transform, risks failing to distinguish target information from noise. Given the extensive computational effort involved, a proposal is presented here concerning the design of the sparse aperture of a distributed radar.

[0067] In the proposed embodiment of an M1 MO radar system, 350 radar signals are transmitted and received by the antennas in two disjoint frequency ranges. In both frequency ranges, a frequency-modulated continuous wave signal, consisting of so-called chips, is transmitted. While the radar signal in one frequency range is transmitted alternately from different transmitting antennas with time delays, so that one of the chirps is always transmitted by one of the transmitting antennas as the radar signal, and the different antennas are used alternately for this purpose, in the other frequency range, chirps of the frequency-modulated continuous wave signal (FMCW) are continuously transmitted by the same transmitting antenna as another radar signal.

[0068] The antenna arrangement of the 350 antennas comprises, firstly, antennas coupled to receiving modules designed to evaluate received radar echo signals in one frequency range. These antennas, together with the transmitting antennas that radiate the radar signals in this frequency range, form a sparse antenna array. The antenna arrangement of the 350 antennas also includes receiving antennas coupled to receiving modules designed to evaluate additional radar echo signals received in a wider frequency range. It is essential that these receiving antennas, referred to here as additional receiving antennas for clarity, form a uniform linear antenna array.The chirps that determine the frequency response of one radar signal and the other radar signal are preferably identical with respect to their frequency deviation and duration, but offset from each other by at least the frequency of the deviation. This ensures that the radar echo signal can be unambiguously assigned to one frequency range or the other. This also makes it possible to unambiguously establish a correlation with the corresponding transmitting antenna at any given time.

[0069] The starting time of the chirps and subsequent chirps are synchronized with each other and preferably coincide at the central station.

[0070] It is possible to implement this in such a way that, at least at one time interval, both the continuously transmitted radar signal and the radar signal generated in one frequency range are emitted via the same antenna for the duration of a chirp. It is also possible that one or more of the additional receiving antennas, coupled to a receiving module that evaluates radar echo signals in the additional frequency range, are also antennas of the sparse antenna array, and that the receiving modules coupled to them are also capable of processing radar echo signals in the one frequency range.

[0071] There are fundamentally different ways to configure the central station and the individual radar head units, i.e., the transmitting and receiving modules. The central station can be configured to generate only one radar signal, consisting of a sequence of chirps. This signal is modulated onto an optical carrier, which is then simultaneously transmitted to at least one of the transmitting modules, which radiates the radar signal in the first frequency range, and simultaneously to the second transmitting module, which continuously radiates the second radar signal. The transmitting modules that radiate the first radar signal and the second transmitting module, which radiates the second radar signal, differ in that one of the transmitting modules, or the second transmitting module, or both of them, have a frequency matching device.This allows the radar signal information to be transmitted in different frequency ranges, even though it consists only of a sequence of chirps. The receiving modules and other receiving modules are designed accordingly, generating a corresponding electronic signal from the radar signal information in one frequency range or the other. This signal corresponds to the transmitted radar signal or the other radar signal and is used to mix it with the radar echo signal or the other radar echo signal. This process derives the echo information associated with one frequency range and the echo information associated with the other frequency range, converting it into an intermediate frequency band. This intermediate frequency is then modulated onto an optical carrier signal and transmitted back to the central station for evaluation.

[0072] Figure 3 schematically shows an embodiment of the central unit that generates radar signal information in the form of a sequence of chirps on an optical carrier signal. On the right, the radar signal information for four signals is plotted in the frequency domain against time, modulated onto the optical carrier signal. It can be seen that one signal with a fundamental frequency fo comprises a continuous sequence of chirps with a frequency deviation 2Af and a ramp duration At, each representing a linearly decreasing ramp. The other three signals shown also have the fundamental frequency fo and each comprise individual, time-spaced chirps that are identical to the chirps of the first signal in terms of frequency deviation 2Af and ramp duration At.

[0073] In order to transmit radar signals and other radar signals that differ in their frequency bands so that they do not overlap, it is necessary for the transmitting and receiving modules to each have frequency converters to convert the radar signal information into corresponding different frequency ranges.

[0074] Figure 4 shows another embodiment of a central station 200, which differs in that it generates two optical carrier signals onto which identical sequences of chirps are modulated at different frequencies, but which lie in one frequency range and the other frequency range, respectively. For this purpose, the central station has an additional laser 225 and an additional modulator 235, which modulates a sequence of chirps in a different frequency range onto the optical carrier signal than the first modulator 230. The carrier signal is routed to a further optical control device 245. As in the embodiment according to Figure 3, one optical carrier signal, which continuously displays chirps in the wider frequency range in temporal sequence, is transmitted via an optical transmission medium 400-1, and the optical carrier signal is transmitted with a time delay via the other transmission media 400-2 to 400-N.One advantage of this embodiment is that the transmitting and receiving modules can be designed more simply. In the illustrated embodiment, the two frequency ramp signals, the sequences of chirps, are modulated separately onto an optical carrier signal. This results in two different signals, each modulated onto a sequence of chirps at different frequencies. In another embodiment, the two frequency ramps in the different frequency ranges are modulated onto the same carrier signal using frequency-division multiplexing. This creates a carrier that encompasses both frequency ramp signals at different frequencies. In this embodiment, the two sequences of chirps in the different frequency ranges must be selected accordingly in the transmitting and receiving modules. This is preferably done using optical filters.In principle, it would also be possible to first perform an optoelectronic conversion and then filter the electrical signal.

[0075] It is generally preferred that the two frequency ranges are disjoint but closely adjacent. Preferably, they are adjacent to each other. That is, one frequency range extends from a fundamental frequency f0 to the sum of the fundamental frequency plus the frequency deviation fAf of the chirps, i.e., from f0 to f0 + fAf. The wider frequency range adjoins this and extends from the fundamental frequency plus the frequency deviation fAf to the frequency given by the fundamental frequency plus twice the frequency deviation 2Af, i.e., from f0 + fAf to f0 + 2Af. A small additional offset may preferably exist to improve the separation of the frequency ranges. The frequencies of the first and second frequency ranges may also be interchanged.

[0076] Figure 5 schematically depicts a transmitter module 600 that is compatible with a central station 200 according to Figure 3. A transmission medium 400 is connected to the transmitter module 600. This medium is connected to an optical coupler 610. The optical carrier signal is coupled into the transmitter module 600 through this coupler. At a converter device 620, which is designed, for example, as a photodiode 630, the optical signal is converted into an electronic signal. In this process, the radar signal information modulated onto the optical carrier signal is separated from the optical carrier signal and remains as an electronic signal. The electronic signal 640 is then routed via a preamplifier 650 to a frequency converter 660 and a further frequency converter 670. The frequency converter 660 converts the radar signal information of the electronic signal 640 into an electronic transmission signal 680 in a specific frequency range.The electronic transmission signal 680 is forwarded via transmitting amplifiers 700 to each of the transmitting antennas 350 and radiated via these antennas as a radar signal in one frequency range. To ensure that the frequency ramps / chips contained in the radar signal information are radiated as a radar signal with a time delay via the different transmitting antennas 350, the corresponding transmitting amplifiers 700 can be individually controlled with a time delay via an electronic control line (not shown) that is connected to the control line 460 according to Fig. 1. The further frequency converter 670 converts the radar signal information into the next frequency band, so that another electronic transmission signal 690 is radiated as a further radar signal in the next frequency range via another transmitting amplifier 710 and another of the transmitting antennas 350. This signal comprises continuously successive chirps / frequency ramps.In this embodiment, all electronic components can be formed on a single semiconductor.

[0077] In alternative embodiments, the semiconductor component of the transmitter module contains only one transmit amplifier for one frequency range and another transmit amplifier for the second frequency range, along with their associated frequency converters. Such a module can accommodate a transmit antenna for the sparse antenna array and the transmit antenna for the uniform linear antenna array consisting of receiving antennas for the second frequency range. The first amplified transmit radar signal and the second amplified transmit radar signal are then fed to the same transmit antenna.

[0078] In other embodiments not explicitly shown, the transmitter module comprises only a frequency converter and a transmitter amplifier, or only a further frequency converter and a further transmitter amplifier, each with a coupled transmitting antenna. These transmitter modules can emit either a radar signal in one frequency range or another radar signal in a different frequency range.

[0079] Figure 6 schematically depicts a receiver module 800, which corresponds to the central station shown in Figure 3. Identical technical features in the receiver module are designated in the same way as in the transmitter module. In this embodiment, the electronic signal 640 is fed, without prior amplification (which could optionally be provided), to a frequency converter 660 and a further frequency converter 670. The frequency-converted electronic signals 740 and 750 generated in this process correspond to the transmit signal 680 and the further transmit signal 690, respectively. These are fed to a mixer 760 and a further mixer 770, respectively. A receiver amplifier 780 is connected to one of the antennas 350 of the sparse antenna array and amplifies the radar echo signals 800 received in one frequency range. The amplification can also be non-frequency-selective. However, at mixer 760 only radar echo information is translated into an intermediate frequency signal 870.This radar echo information is modulated onto the optical signal 605 via an optical modulator 900, and the modulated optical signal 910 is coupled out via another optical coupler 920 onto the return transmission medium 500, so that it is transmitted back to the central station. Similarly, from another of the receiving antennas 350, which together form a uniform linear antenna array, the received radar echo signal 810 is routed via further receiving amplifiers 790 to the further mixer 770, which generates another intermediate frequency signal 880 representing the further radar echo information and is modulated accordingly onto the optical carrier signal 605 for transmission back to the central station via the optical modulator 900.

[0080] The same semiconductor substrate can house further analog optical and electronic components to process the received signals from other receiving antennas of the sparse antenna array, as well as from other receiving antennas of the uniform linear antenna array, for the return transmission of the corresponding echo information or further echo information. When deriving the echo information signals and modulating them onto an optical carrier signal for the return transmission, the echo information signals must be generated in different frequency ranges or converted into different frequency ranges using frequency division multiplexing in order to separate them from each other at the central station.

[0081] Figures 7 and 8 schematically depict corresponding transmitting and receiving modules, in which the central station 200 modulates two frequency chirps at different frequencies onto the optical carrier signal, which are transmitted via the same transmission medium 400. Before conversion into an electronic signal, the optical signal is routed via an optical splitter 950 to an optical filter 960 and a further optical filter 970. The optical filter 950 selects the radar signal information associated with one frequency band, and the further optical filter 960 selects the radar signal information associated with the other frequency band. In the illustrated embodiment, the electronic signals after conversion already have the frequency at which, after amplification, the radar signal or further radar signal is emitted via the appropriately connected antennas.

[0082] Compared to the embodiment shown in Figures 5 and 6, the frequency converters and the optional preamplifier 650 are therefore omitted. Otherwise, the operation of the transmit and receive modules shown in Figures 7 and 8 is identical to that shown in Figures 5 and 6.

[0083] Figures 9 and 10 show corresponding embodiments in which only the elements for a transmitting antenna and a receiving antenna, respectively, are formed on a semiconductor structure. Otherwise, these embodiments are technically identical to those of Figures 7 and 8. Figures 11 and 12 show corresponding embodiments for transmitting and receiving modules. In these embodiments, the optical filters can be omitted compared to the embodiments of Figures 9 and 10, since only the radar signal information belonging to one frequency range, in the form of frequency ramps in that frequency range, or alternatively the frequency ramps / chirps in the other frequency range, are modulated onto the carrier signal. Thus, after electronic conversion, the signals are already present in the corresponding frequency ranges as required for transmitting and radiating the radar signal and the other radar signal.are needed for mixing with the received radar echo signals or other radar echo signals.

[0084] Again, embodiments are possible in which the structures for a large number of antennas are formed on the same semiconductor material, or embodiments are possible in which the transmitting and / or receiving module structures are formed on a semiconductor material for only one transmitting and / or receiving antenna.

[0085] Figure 13 illustrates once again the exemplary evaluation of the radar echo information recorded in one frequency range, which is referred to here for short as echo information, and the further radar echo information associated with the other frequency range, which is also referred to for short as further echo information.

[0086] It is expressly emphasized here that one frequency range can contain higher frequencies than the other frequency range. In another embodiment, the other frequency range can contain the higher frequencies and the first frequency range the lower frequencies. The crucial point is that the two frequency ranges are disjoint. Preferably, the two frequency ranges are adjacent to each other, so that the entire occupied frequency band has a bandwidth that corresponds to twice the bandwidth of either the first or the second frequency range.

[0087] Distance spectra are generated in the usual way from both the echo information 1100 and the additional echo information 1200 (1110, 1210), and from these, the distances and further distances to objects in the vicinity are determined. Thus, distances to the objects, also called object distances, are obtained from the echo information, and further object distances, referred to simply as further distances, are obtained from the additional distance spectra of the further echo information. Because the additional echo information was acquired with a uniform linear antenna array, it is possible to coherently integrate the distance spectra of all receiving antennas of the uniform linear antenna array (1220) and then evaluate the corresponding Doppler spectra (1230) to determine the relative velocities of the objects.Each distance determined from the echo information is assigned a tolerance range, defined by the fact that an object located at a specific radial distance is perceived by different transmitting-receiving antenna pairs at varying distances, with these different distances defining the tolerance range. The tolerance range is dictated by migration due to the varying possible distances to the individual antennas of the sparse antenna array. The tolerance range is determined by the area within which the distance measurements of the distributed receiving antennas migrate. The determined object distances and any further determined object distances can then be correlated within the tolerance ranges around the object distances., within this tolerance of this tolerance range, the determined object distance can be correlated with a further object distance and thereby the relative velocity determined on the basis of the further echo information can be assigned to the target detected on the basis of the echo information 1240 and used for further evaluation in particular determination of the elevation and azimuth angle of the corresponding object 1300.

[0088] In the lower right of Fig. 13, an antenna array 320 is indicated, comprising a uniform linear antenna array 330. The remaining antennas 350 form a sparse antenna array 340. The determined object distance 1000 is indicated, derived from the echo information acquired by the antennas 350 of the sparse antenna array 340 in one frequency range. A corresponding tolerance range 1010 is indicated by a wide hatching. A distance gate 1020 (narrow hatching) is also shown, which correlates with the further object distance 1030. A relative velocity has been determined for this gate. A correlation with the distance determined from the echo information is achieved by comparing the object distance with the further object distance.If the further object distance 1030 corresponds to the object distance 1000 within the tolerance range 1010, the corresponding relative velocity is assigned to the object at that distance. It is understood by those skilled in the art that only exemplary embodiments are described here. Reference numerals list.

[0089] photonic radar system

[0090] Central station

[0091] Control unit

[0092] Laser

[0093] further laser

[0094] Modulation device

[0095] further modulation device

[0096] optical control device

[0097] optical control device

[0098] Distribution system

[0099] Detection device

[0100] Unit of calculation

[0101] Digitization facility

[0102] Processing facility

[0103] , 300-n radar head assembly

[0104] , 305-n fiber input

[0105] Photoreceiver coupler

[0106] electronic-photonic integrated circuit (EPIC) antenna structure

[0107] uniform linear array

[0108] antenna

[0109] , 395-n fiber output

[0110] , 400n transmission medium

[0111] , 401 n optical fiber

[0112] , 402-n fiber

[0113] , 450-n further transmission medium

[0114] electronic control line

[0115] , 500-n return transmission medium

[0116] , 501 -n optical fiber

[0117] , 502-n fiber

[0118] , 550-n further return transmission medium 560 electronic return line

[0119] 600 transmitter module

[0120] 605 optical signal

[0121] 610 optical coupler

[0122] 620 converter unit

[0123] 630 photodiode

[0124] 640 electronic signal

[0125] 650 preamplifiers

[0126] 660 frequency converters

[0127] 670 frequency converters

[0128] 680 electronic transmission signal

[0129] 690 further electronic transmission signal

[0130] 700 transmitter amplifiers

[0131] 710 additional transmitter amplifiers

[0132] 740 frequency-converted electronic signal

[0133] 750 frequency-converted electronic signal

[0134] 760 mixers

[0135] 770 more mixers

[0136] 800 receiver module

[0137] 870 Intermediate frequency signal

[0138] 880 additional intermediate frequency signal

[0139] 900 Modulator

[0140] 910 modulated optical signal

[0141] 920 additional optical couplers

[0142] 950 optical splitter

[0143] 960 additional optical filters

[0144] 1000 object distance

[0145] 1010 Tolerance range

[0146] 1020 Distance Gate

[0147] 1030 more object distance

[0148] 1100 echo information

[0149] 1110 Generate distance spectrum

[0150] 1200 more echo information

[0151] 1210 Generating a further distance spectrum

[0152] 1220 Coherent integration of all ULA distance spectra 1230 Evaluation of Doppler spectra / Determination of relative velocity 1240 Correction of the detected objects

[0153] 1300 precise angle determination azimuth / elevation etc.

Claims

- 28 - Patent claims 1. A multiple-input, multiple-output radar system (100) of a vehicle with a distributed antenna structure (320) in which transmitting and receiving antennas (350) are arranged, wherein each transmitting antenna is connected to a transmitting module and each of the receiving antennas (350) is connected to a receiving module, and a central station for generating the radar signal information, which is converted by the transmitting modules into radar signals that are emitted by the transmitting antennas (350), and for evaluating radar echo information derived by the receiving modules from the radar echo signals received at the receiving antennas (350), wherein the radar signal information and the echo information are modulated onto optical carrier signals and transmitted between the central station and the transmitting and receiving modules, characterized in that The central station is configured to generate the radar signal information and transmit it to the transmitting modules and / or control them, wherein at least a part of the transmitting modules is configured to emit signal segments, which vary monotonically linearly with respect to frequency in a frequency range and are called chirps, as radar signals via the associated transmitting antennas (350) based on the transmitted radar signal information, and at least a part of the receiving modules is configured to derive echo information from the radar echo signals simultaneously detected by associated receiving antennas (350) in the same frequency range and generated by objects in the environment, and to transmit this information to the central station. characterized by the fact that one of the transmitting modules is configured to continuously radiate, via an associated transmitting antenna, monotonically linear signal segments varying in frequency in a further frequency range, which are called further chirps, based on the radar signal information generated by the central station, wherein the further frequency range is disjoint from the one frequency range, and the antenna structure (320) comprises a plurality of receiving antennas (350) forming a uniform linear array, and whose associated receiving modules are configured to derive further echo information from further radar echo signals in the further frequency range generated by objects in the surrounding area and to transmit it to the to transmit to the central station wherein the central station is configured to generate distance spectra based on the additional echo information and to determine distances to detected objects, and to coherently integrate the distance spectra generated from the additional echo information of all receiving antennas (350) of the uniform linear array, and subsequently to determine the relative velocities based on Doppler spectra derived from the coherently integrated distance spectra, wherein the central station is further configured to also determine distances to the detected objects based on the echo information, wherein each distance determined based on the echo information is assigned a tolerance range which specifies a range in which the distance for the individual receiving antennas (350) providing the echo information can vary, and the central station is configuredThe objects detected using the additional echo information and the derived relative velocities correspond to the objects detected using the echo information with the distance determined using the echo information within the assigned tolerance range.

2. Multiple-input multiple-output radar system (100) according to claim 1, characterized in that the determined and assigned relative velocities are used for further processing of the echo information and information derived therefrom about the detected objects.

3. Multiple-input multiple-output radar system (100) according to claim 1 or 2, characterized in that the central station is configured to generate a transmission signal in which the chirps in one frequency range and the further chirps in the further frequency range are modulated onto an optical carrier signal.

4. Multiple-input multiple-output radar system (100) according to one of the preceding claims, characterized in that the central station is configured to generate a transmission signal in which the chirps in one frequency range are modulated onto an optical carrier signal, and a further transmission signal in which the further chirps in the further frequency range are modulated onto a further optical carrier signal.

5. Multiple-input multiple-output radar system (100) according to one of the preceding claims, characterized in that the transmitting antennas (350) which radiate the radar signals in one frequency range and the receiving antennas (350) which are assigned to receiving modules which derive echo information from the received radar echo signals in one frequency range, form a sparse antenna array.

6. Multiple-input multiple-output radar system (100) according to one of the preceding claims, characterized in that at least one of the receiving antennas (350) is both a component of the sparse antenna array and of the linear uniform antenna array.

7. Multiple-input multiple-output radar system (100) according to claim 6, characterized in that at least one of the antennas (350) is assigned a receiver module that derives both echo information based on the radar echo signals detected in one frequency range and further echo information based on the radar echo signal detected in the further frequency range.

8. Multiple-input multiple-output radar system (100) according to one of the preceding claims, characterized in that the plurality of receiving antennas (350) forming the uniform linear array have a distance from each other which corresponds to half of the maximum wavelength of the further radar signals during the emission of a further chirp or is less than this half.

9. Multiple-input multiple-output radar system (100) according to one of the preceding claims, characterized in that the uniform linear array is formed along one axis of the antenna structure and a further uniform linear antenna array of receiving antennas (350) is formed along another axis of the antenna structure (320).

10. Multiple-input multiple-output radar system (100) according to one of the preceding claims, characterized in that the central station generates the radar signal information with a sequence of signal segments, base chirps, which vary monotonically linearly with respect to frequency and whose frequency deviation corresponds to a frequency bandwidth of one frequency band and the other frequency band, and the transmitting modules and the receiving modules each have at least one They have frequency converters to convert a basic chirp into a chirp in one frequency band or another chirp in another frequency band.

11. A method for environmental detection using a multiple-input multiple-output radar system, comprising a central station for setting and controlling the time-delayed transmission of radar signals via different transmitting antennas (350) and evaluating the echo information derived from simultaneously acquired radar echo signals in order to obtain information about detected objects, comprising the steps of: time-delayed transmission of radar signals via different transmitting antennas (350) of an antenna structure (320), wherein the radar signals comprise monotonically linearly varying signal segments, called chirps, in a frequency range, and simultaneous acquisition of radar echo signals in the one frequency range with receiving antennas (350) of the antenna structure (320) and derivation of echo information from the radar echo signals in the one frequency range, and evaluation of the echo information to derive information for detected objects.which comprise at least one distance and one relative velocity, characterized in that, In addition, further signal segments, which vary continuously with respect to a frequency monotonically linearly and are referred to as further chirps, are emitted via a transmitting antenna of the antenna arrangement in a further frequency band that is disjoint from the one frequency band and are received by a plurality of receiving antennas (350) of the antenna structure (320), which form a uniform linear array, further radar echo signals in the further frequency range and further echo information is derived from these,wherein the central station generates distance spectra based on the additional echo information and determines distances to detected objects, and the distance spectra generated from the additional echo information of all receiving antennas (350) of the uniform linear array are coherently integrated, and subsequently the relative velocities are determined by evaluating Doppler spectra based on the coherently integrated distance spectra, wherein the central station also determines further distances to the detected objects based on the echo information, wherein each further distance determined based on the echo information is assigned a tolerance range that specifies a range in which the determined further distance can vary for the different receiving and transmitting antenna combinations providing the echo information, and, the objects detected based on the further echo information and, - 32 - The derived relative velocities of the objects detected using the echo information correspond to the distance information determined using the further echo information with the further distances determined using the echo information within the assigned tolerance ranges.

12. Method according to claim 7, characterized in that the determined and assigned relative velocities are used to compensate for the echo information regarding the relative velocity prior to further evaluation.

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