14. Consideration of ULA structures and multiple modulation frequencies; processing of the velocity and angular spectrum

Abstract

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, in particular the evaluation of speed and angle. A radar system emits chirps in a frequency range with time delays via various transmitting antennas, which are simultaneously detected by receiving antennas. Additionally, another chirp is continuously emitted in a further frequency range, which is detected and evaluated by receiving antennas forming a uniform linear antenna array. The distance spectra of the receiving antennas of the uniform linear antenna array are coherently integrated, and the velocities are determined from this integration using Doppler analysis. Furthermore, the angles of the detected objects are estimated. Both of these values ​​are assigned to the objects detected by the entire antenna structure based on the determined distances.This can significantly accelerate further evaluation, e.g. by limiting the number of angle hypotheses to be considered for each recorded object.

Description

[0001] 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, in particular speed and angle evaluation.

[0002] Distributed radar antenna structures, also known in English as distributed, multi-static or bisatic or multiple-input-multiple-output (MIMO) antenna structures, are used in vehicle radar systems for environmental sensing.

[0003] 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.

[0004] When using MIMO functionality and spatial multiplexing, virtual antenna positions are spanned to form a virtual array. The virtual positions of the resulting receive channels can be separated by multiples or only fractions of wavelengths. This characteristic significantly increases the complexity of angle calculations and necessitates the use of extensive signal processing algorithms.

[0005] 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.

[0006] EP 3 712 654 A1 discloses a radar system, a device, an architecture and a method for generating a monostatic virtual array aperture using a radar control processing unit to construct a monostatic MIMO virtual array aperture from radar signals that are transmitted orthogonally from transmitting antennas and received at each receiving antenna, and for constructing a virtual monostatic MIMO forward difference array aperture by performing forward difference co-array processing on the virtual monostatic MIMO array aperture to fill gaps in the virtual monostatic MIMO array aperture, thereby mitigating or suppressing interference side lobes caused by gaps or holes in the virtual monostatic MIMO array aperture.

[0007] DE 10 2018 200 765 A1 describes an FMCW radar sensor with several antenna elements arranged at intervals in a row, each of which is associated with a mixer that generates an intermediate frequency signal by mixing a received signal with an oscillator signal, and an evaluation unit configured to record the intermediate frequency signal over a measurement period as a function of time and to convert the time signal thus obtained into a spectrum by Fourier transformation, as well as with an angle measuring device in which the spectra obtained from the various evaluation units are further evaluated in separate channels, characterized by: - ​​a beamforming device configured to perform beamforming for the signal received from a predetermined preferred direction by compensating for differences in the signal's propagation length to the various antenna elements,- a summing device for forming a summed spectrum by coherent addition of the spectra, and - a distance measuring device for determining distances between objects in the preferred direction based on the summed spectrum.

[0008] In the current state of the art, the compensation of such nonlinear phase terms for subsequent Doppler processing involves considerable computational effort and a massive utilization of a computing unit of the radar system.

[0009] Furthermore, the design of a complex implementation variant on a corresponding target hardware involves lengthy development times, specialized knowledge about the target hardware, and high development costs.

[0010] The invention is therefore based on the objective of improving a radar system, especially for vehicles, with a distributed antenna structure and its evaluation method, in particular reducing the computing power required for angle determination.

[0011] The invention is solved by a radar system having the features of claim 1 and a method having the features of claim 9; advantageous embodiments are set forth in the dependent claims.

[0012] The basic idea of ​​the invention is to transmit radar signals in the form of linearly monotonically varying signal segments, so-called chirps, in two different and disjoint frequency ranges. While the radar signals or chirps transmitted in one frequency range are alternately emitted with time delays from different transmitting antennas in that frequency range and received by receiving antennas, echo information is derived from the received radar echo signals in that frequency range by associated receiver modules, the subsequent chirps are continuously emitted as a further radar signal from 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 detected in a wider frequency range. At the central station, distance spectra are generated from this echo information, 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 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, and then 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 assigned to those objects detected using the echo information whose determined distances, within the assigned tolerance range, agree with the additional determined distances.

[0013] 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 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 therefore be considerably simplified.

[0014] Additionally, a rough angle estimation for the detected objects is planned. For this purpose, known methods, such as applying a Fourier transform for a rough angle estimation, will be used.

[0015] Due to the assignment of the objects detected using the additional echo information to the objects detected using the echo information derived from radar echo signals of one frequency range, it is possible to also use angle estimation in the evaluation of the echo information, especially for precise angle determination.

[0016] This involves compensating for the non-linear terms with respect to velocity influences. Additionally, the number of angle hypotheses evaluated for precise angle determination is limited. This limitation is applied to angular ranges compatible with the roughly estimated angles of the objects. That is, to the angular ranges around the initial estimates of the directions from which reflected radar echo signals are detected.

[0017] This can significantly reduce the computational effort.

[0018] 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.

[0019] 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. wherein the radar signal information and the echo information, modulated onto at least one optical carrier signal, are 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 to control them such that at least some of the transmitting modules can determine the location of the radar signal based on the transmitted radar signal information. The system emits signal segments (chirps) as radar signals, which vary monotonically linearly with respect to frequency within a frequency range, from assigned transmitting antennas at different times, and at least part of the receiving modules are designed to derive echo information from the radar echo signals simultaneously detected by assigned receiving antennas in the same frequency range and generated by objects in the environment, and to transmit this information to the central station, wherein 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. 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 which specifies a range in which the determined distance may vary for the different transmitting and receiving antenna pairs providing the echo information, and to generate further distance spectra and determine further distances to detected objects from the further echo information, and the distances generated from the further echo information to coherently integrate further distance spectra 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, 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, wherein the central station is designed to perform rough angle estimates for the detected objects using the additional echo information and to take the determined relative velocities and rough angle estimates into account in a precise angle estimate using the echo information.

[0020] 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, so-called chirps, that vary monotonically linearly with respect to a frequency within a frequency range; 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, in addition, further signal segments, further chirps, which vary monotonically linearly with respect to a frequency, are continuously radiated via a transmitting antenna of the antenna arrangement in a further frequency band that is disjoint from the one 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 correspond to the objects detected based on the echo information by means of a correspondence between the further distance data determined based on the additional echo information and the distances determined based on the echo information within the assigned tolerance ranges, and additionally based on the echo information or the additional echo information that is received by each receiving antenna.or, based on the additional echo information, rough angle estimates for the detected objects are performed, and the determined relative velocities and rough angle estimates are taken into account in a precise angle estimate based on the echo information.

[0021] A significantly simplified calculation is possible in embodiments where the central station is designed to use the relative velocities to compensate for velocity with respect to its velocity dependence.

[0022] Based on the roughly estimated angles for the detected objects, in one embodiment the central station is designed to use the rough angle estimates to limit a number of the angle hypotheses to be evaluated during a determination.

[0023] Particularly good angular resolution can be achieved with as few radar antennas as possible, using an antenna structure in which at least part of the receiving antennas forms a sparse antenna array.

[0024] A particularly compact design and the efficient use of many, preferably all, receiving antennas is achieved if one or more of the majority of receiving antennas of the linear uniform antenna array also belong to at least part of the receiving antennas whose associated receiving modules are designed to derive echo information from the radar echo signals received in one frequency range.

[0025] In order to ensure efficient communication via a photonic transmission medium, one embodiment provides that one or more of the plurality of receiving antennas of the linear uniform antenna array, which also belong to at least part of the receiving antennas, are configured in a mixer to convert the echo information and the further echo information into an intermediate frequency signal that represents the echo information and the further echo information in separate frequency ranges.

[0026] Another embodiment therefore provides that one or more of the plurality of receiving antennas of the linear uniform antenna array comprise a mixer that converts the echo information derived from the radar signals in one frequency range into an intermediate frequency signal, and a further mixer that converts the further echo information derived from the further radar echo signals in the further frequency range into a further intermediate frequency signal whose frequencies are different from those of the first intermediate frequency signal, wherein the echo information of the first intermediate frequency signal and the further echo information of the further intermediate frequency signal are modulated onto the same optical carrier signal in a modulation device using frequency division multiplexing, so that the echo information can be separated from the further echo information in the central station.

[0027] Furthermore, it is thus provided that at least one of the receiving antennas is used to receive both radar echo signals in one frequency range and further radar echo signals in the other frequency range, and that radar echo information is derived from the radar echo signal and further echo information from the other radar echo signal using one or more associated receiving modules and transmitted to the central station for evaluation.

[0028] In further evaluation, the relative velocities are preferably taken into account by compensating the velocity-dependent terms with respect to the determined relative velocities.

[0029] Accordingly, the rough angle estimates are preferably taken into account by limiting the number of evaluated angle hypotheses to those that are compatible with the rough angle estimates.

[0030] The invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 a schematic view of a photonic MIMO radar system; Fig. 2. A representation of a data structure of a measurement sequence and its processing according to the state of the art, which for graphical reasons is in Fig. 2A and Fig. 2B is divided, which are to be joined together at the dash-dot line to form the entire Fig. to result in 2; Fig. Figure 3 shows a schematic representation of a MIMO radar system according to a variant in which the central station modulates radar signal information onto a transmission signal; Fig. 4 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 via different optical transmission media to the transmit and receive modules of the radar head devices; Fig. 5 a schematic representation of a semiconductor structure for realizing transmitter modules for a variant of the MIMO radar system in which the transmission signal is generated with a sequence of basic chirps; Fig. 6 a schematic representation of a semiconductor structure for realizing receiver modules for one variant of the MIMO radar system, in which the transmission signal is generated with a sequence of basic chirps; Fig. 7 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; Fig. 8 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 one transmission medium, wherein one optical carrier signal is modulated with a sequence of chirps in one frequency range and the other optical carrier signal is modulated with another sequence of chirps in another frequency range, which for graphical reasons are shown in Fig. 8A and Fig. 8B is divided, which are to be joined together at the dash-dot line to form the entire Fig. to result in 8; Fig. 9 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; Fig. 10 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 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 which, for graphical reasons, is shown in Fig. 10A and Fig. 10B is divided, which are to be joined together at the dash-dot line to form the entire Fig. to result in 10; Fig. 11 a schematic representation of a semiconductor structure for realizing transmitter modules for a variant of the MIMO 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 further frequency range is transferred; Fig. 12 A schematic representation of a semiconductor structure for realizing receiver modules for a variant of the MIMO 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, which for graphical reasons are in Fig. 12A and Fig. 12B is divided, which are to be joined together at the dash-dot line to form the entire Fig. to yield 12; Fig. 13 a schematic representation of a semiconductor structure for realizing receiver modules for a variant of the MIMO radar system, in which the sequence of chirps in one frequency range as well as in the other frequency range is transmitted via the coupled transmission medium and echo information is derived from and further echo information is derived; and Fig. 14 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.

[0031] In Fig. 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.

[0032] Lowercase letters -n ... stand for natural numbers to indicate countability and distinguishability of the corresponding objects.

[0033] 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.

[0034] One of the optical waveguides 401, 401-n, i.e., one of the fibers 402, 402-n, is coupled to the fiber output. The optical fibers 402, 402-n are connected at their other end to one of the radar head devices 300, 300-n.

[0035] 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.

[0036] 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 often its frequency is also multiplied and / or converted, and then emitted as electromagnetic radiation from the corresponding antenna 350 of the radar head unit 300, 300-n as a radar signal.

[0037] 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.

[0038] 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 digitization unit 280 and pre-processed in a processing unit 290, for example, by undergoing a Fourier transform, which can be implemented in special modules.

[0039] 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 the transmission of a chirp are sampled at equal time intervals. The time-based sampling is indexed with the lowercase letter n. If an acquisition is performed simultaneously with a large number of receiving antennas in an antenna array, a set of equally spaced 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 provides a cube of data, which is then divided into... Fig. Figure 2 illustrates this. A phase term relevant for Doppler velocity measurement propagates with each newly emitted measurement signal within the measurement sequence, generating 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 across all chirps within the measurement sequence, the measurement signal can be described according to formula (1): sn(m)=Aexp(i2πλ2vTPRIm)exp(i2παc0d(p)nTs)exp(i2πλd(p))

[0040] 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 in formula (1) changes. “exp(i2πλ2vTPRIm)”, which describes the dependence on the Doppler velocity "v". λ is the wavelength of the radar signal radiation and T PRI This indicates the duration between two starting 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.

[0041] For bistatic radars where transmitting and receiving antennas are spatially distributed, the previously made assumption d(p) = 2R0 is no longer valid. Instead, d(p) ≠ 2R0, 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. Therefore, for “d(p)”: d(p)=‖pTx−p‖2+‖pRx−p‖2

[0042] This property of distributed radars has a significant influence on the calculation of the Doppler velocity, since “d(p)” within the phase terms “exp(i2παc0d(p)nTs)” and “exp(i2πλd(p))” The measurement signal is affected nonlinearly. A coherent integration over all receiving antennas, which is advantageous for the signal-to-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 in the Doppler measurement process step, 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.

[0043] 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: sn(m)=Aexp(i2πλ2vTPRIm)exp(i2παc0d(p)nTs)exp(i2πλd(p))×exp(−i2πλd(p)) T sc0 is the sampling period, c0 is the speed of light, where α is a ratio between bandwidth and modulation time of a frequency ramp, i.e., a ratio of the frequency deviation to the ramp duration.

[0044] For a hypothesis to be correct, integration in the direction of the receiving antenna dimension causes constructive interference, so that target information stands out from noise in the range Doppler spectrum.

[0045] The effort required to compensate for the nonlinear phase terms increases linearly according to the granularity by which individual hypotheses differ from one another (see Fig. 2) A conventional approach, which merely subjects the transmission sequence of a receiving antenna of 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.

[0046] In the proposed embodiment of a MIMO 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.

[0047] 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.

[0048] 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 radar echo signals can be unambiguously assigned to one frequency range or the other. It also makes it possible to unambiguously establish a correlation with the corresponding transmitting antenna at any given time.

[0049] The starting time of the chirps and subsequent chirps are synchronized with each other and preferably coincide at the central station.

[0050] Distance spectra, generated from additional echo information derived from further radar echo signals received by the antennas of the uniform linear antenna array, can be coherently integrated. For distance gates where objects are detected, Doppler spectra can be evaluated from the distance spectra coherently integrated across all receiving antennas of the uniform linear antenna array to determine the corresponding relative velocities.

[0051] After successful detection of the Doppler velocity of a potential object, this velocity information can be used to compensate for the phase term in the measurement signal that is influenced by the Doppler velocity. This preprocessing step is crucial for the subsequent processing of the direction angle, since without this compensation, which affects the spatial aperture signal, no hypothesis from the hypothesis space for estimating the direction angle would be valid. Measurement equation (1) is reduced, after successful compensation, to all phase components required for the angle evaluation. sn(m)=A exp(i2παc0d(p)nTs)exp(i2πλd(p))

[0052] In light of the angle evaluation, a formulation of equation (3) as a function of a virtual antenna parameter is appropriate. It follows that: sn(v)=A exp(i2παc0d(p)nTs)exp(i2πλdv(p))

[0053] Subsequent angle estimation using sparsely populated large apertures is not readily possible with conventional methods such as a Fourier transform. Instead, various derivatives of a matched filter are used in combination with compressive sensing techniques. This approach is based on the specific configuration of the physical antenna positions using MIMO functionality and spatial multiplexing to construct a virtual antenna array. This virtual antenna array represents a kind of template or signature that defines a spatial aperture signal depending on the target distance and solid angle. This aperture signal can be formally described according to Formula 4.

[0054] The second phase date in equation (4) “exp(i2παc0d(p)nTs)” A spectral value at a specific distance is specified as part of a preceding Fourier transformation. During angle estimation, all hypotheses relating to the radar's field of view and its resolution are considered based on Equation 4. Therefore, for the position of a target according to Equation (2): p=(xyz)=r(cosθcosϕcosθsinϕsinθ)

[0055] According to equation (3), the angle “θ” describes the elevation angle and “ϕ” the azimuth angle. For example, assuming a resolution of “Δθ = Δφ = 0.1°” and a field of view (FoV) of 120° in azimuth and 30° in elevation, then, for a known target distance “r”, the following would apply: N=120°∗30°0.1°=360,000 Hypotheses are constructed to correlate with the spatial aperture signal according to formula (1). Such a hypothesis is constructed according to formula 4: s(v)=Aexp(i2πλdv(p))

[0056] Based on a rough angle estimate, the number of angle hypotheses to be considered can be significantly reduced.

[0057] The rough angle estimation is performed using known methods, either based on the additional echo information by means of a Fourier transform.

[0058] Alternatively, the rough angle estimation can be performed using a Fourier transform based on a received signal that is either captured (derived) in one frequency range or in the other frequency range.

[0059] 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 additionally designed to process radar echo signals in the one frequency range.

[0060] 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 radiating the first radar signal and the second transmitting module, which radiates the second radar signal, differ in that either the first or the second transmitting module, or both, possess a frequency matching capability.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 another. This signal corresponds to the transmitted radar signal or other radar signal and is mixed with the radar echo signal or other radar echo signal to derive the echo information associated with one frequency range and the other echo information associated with the other frequency range. This mixture is then converted into an intermediate frequency band. This intermediate frequency is modulated onto an optical carrier signal and transmitted back to the central station for evaluation.

[0061] In Fig. 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 modulated onto the optical carrier signal is plotted in the frequency domain against time for four signals. It can be seen that a signal with a fundamental frequency f0 comprises a continuous sequence of chirps with a frequency deviation 2Δf and a ramp duration Δt, each representing a linearly decreasing ramp. The other three signals shown also have the fundamental frequency f0 and each comprise individual, time-spaced chirps that are identical to the chirps of the first signal in terms of frequency deviation 2Δf and ramp duration Δt.

[0062] 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 in order to convert the radar signal information into corresponding different frequency ranges.

[0063] In Fig. Figure 4 shows a further 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 a further laser 225 and a further 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 Fig. 3. One optical carrier signal, which continuously exhibits chirps in a temporal sequence across a wider frequency range, 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. An advantage of such an 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.

[0064] 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. Alternatively, optoelectronic conversion followed by filtering of the electrical signal would also be possible.

[0065] It is generally preferred that the two frequency ranges are disjoint but closely adjacent. Preferably, they are contiguous. That is, one frequency range extends from a base frequency f0 to the sum of the base frequency plus the frequency deviation Δf of the chirps, i.e., from f0 to f0+Δf. The second frequency range is adjacent and extends from the base frequency plus the frequency deviation Δf to the frequency given by the base frequency plus twice the frequency deviation 2Δf, i.e., from f0+Δf to f0+2Δf. A small additional offset may preferably be present to improve the separation of the frequency ranges. The frequencies of the first and second frequency ranges may also be interchanged.

[0066] In Fig. Figure 5 is a schematic representation of a 600-unit transmitter module, which is connected to a 200-unit central station. Fig. 3 is compatible. A transmission medium 400 is connected to the transmitter module 600. This is connected to an optical coupler 610. This couples the optical carrier signal into the transmitter module 600. At a converter device 620, which is designed, for example, as a photodiode 630, the optical signal is converted into an electronic signal, whereby 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 one frequency range.The electronic transmission signal 680 is forwarded via transmitting amplifiers 700 to each of the transmitting antennas 350 and radiated via these as a radar signal in one frequency range. In order to ensure that the frequency ramps / chirps 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), which is connected to the control line 460. Fig. 1 is connected. The further frequency converter 670 converts the radar signal information into the further frequency band, so that a further electronic transmit signal 690 is emitted as a further radar signal in the further frequency range via a further transmit amplifier 710 and another of the transmit antennas 350. This comprises continuously successive chirps / frequency ramps. In this embodiment, all electronic components can be formed on a semiconductor.

[0067] 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 one amplified transmit radar signal and the other amplified transmit radar signal are then fed to the same transmit antenna.

[0068] 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.

[0069] In Fig. Figure 6 shows a schematic representation of a receiver module 800, which is connected to the central station. Fig. 3 corresponds. 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 to a frequency converter 660 and a further frequency converter 670 without prior amplification, which could optionally be provided. The frequency-converted electronic signals 740, 750 generated in this way 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, which amplifies the radar echo signals 800 received in one frequency range. The amplification can also be non-frequency-selective. However, only radar echo information is translated into an intermediate frequency signal 870 at the mixer 760.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.

[0070] 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.

[0071] In Fig. 7 and Fig. Figure 8 schematically depicts corresponding transmitting and receiving modules, in which the central station 200 modulates two frequency chirs 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 beam splitter (splitter 950) to an optical filter 960 and another optical filter 970. The optical filter 960 selects the radar signal information associated with one frequency band, and the other optical filter 970 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.

[0072] Compared to the embodiment according Fig. 5 and Fig. 6. Therefore, the frequency converters and the optional 650 preamplifier are omitted. Otherwise, the operation of the transmit and receive modules remains the same. Fig. 7 and Fig. 8 identical to those of the Fig. 5 and Fig. 6.

[0073] In Fig. 9 and Fig. Figure 10 shows corresponding embodiments in which only the elements for a transmitting antenna or a receiving antenna are formed on a semiconductor structure. Otherwise, the embodiments are technically identical to those of Fig. 7 and Fig. 8.

[0074] In Fig. 11 and Fig. Figure 12 shows corresponding embodiments for transmitting and receiving modules. In these embodiments, the optical filters can be modified accordingly compared to the embodiments according to Fig. 9 and Fig. 10 are omitted, since the carrier signal only contains either the radar signal information belonging to one frequency range in the form of frequency ramps in that one frequency range or alternatively the frequency ramps / chirps lying in the other frequency range, so that after an electronic conversion the signals are already available in the corresponding frequency ranges as they are needed for transmitting and radiating the radar signals and other radar signals or for mixing with the received radar echo signals or other radar echo signals.

[0075] 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.

[0076] In Fig. Figure 13 shows receiving modules 800 for receiving antennas, which are part of the uniform linear antenna array and the sparsely populated antenna array. The received echo signal is connected after the receiving amplifier to two mixers 760 and 770, which are connected to the corresponding electronic signals 740 and 750, representing the transmit signal and the subsequent transmit signal in the different frequency ranges. The carrier signal transmitted on the transmission medium 400 is split at a beam splitter 950 and then routed to the filters 960 and 970 for the two frequency ranges.

[0077] The echo information is derived by mixer 760 and the further echo information by mixer 770, and each is converted into an intermediate frequency signal for the return transmission. These are generated at different frequencies and both are modulated together onto the carrier signal.

[0078] Based on Fig. Section 14 presents once again the exemplary evaluation of the radar echo information recorded in one frequency range in 2010, which is referred to here as echo information for short, and the further radar echo information associated with the other frequency range in 2020, which is also referred to here as further echo information for short.

[0079] 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.

[0080] Based on both the echo information from 2010 and the additional echo information from 2020, distance spectra for 2030 and further distance spectra for 2040 are generated in the usual manner, and from these, the distances to objects in the vicinity for 2050 and further distances for 2060, respectively, are determined. Thus, the distances to objects for 2050, also called object distances, are obtained from the echo information from 2010, and further object distances, referred to as further distances for 2060, are obtained from the additional distance spectra for 2040 derived from the additional echo information from 2020.Due to the fact that the further echo information in 2020 was acquired with a uniform linear antenna array, it is possible to coherently integrate the further distance spectra of all receiving antennas of the uniform linear antenna array in 2080 and then evaluate the corresponding Doppler spectra in 2100 to determine the relative velocities of the objects in 2120.

[0081] In the illustrated embodiment, the solid angle 2140 for the detected objects is also roughly determined using conventional methods based on the additional echo information.

[0082] 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 at different distances by the various transmitting and receiving antenna pairs. These different distances define 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 measurement of the distributed receiving antennas can migrate. The determined object distances and any further object distances can then be correlated within the tolerance ranges around the object distances.This means that, within this tolerance range, the determined object distances can be correlated with another object distance, and the relative velocity 2120 and roughly determined angles 2140 determined on the basis of the further echo information can be assigned to the target detected on the basis of the echo information 2200, and used for further evaluation, in particular for determining 2300 the solid angle of the corresponding object.

[0083] For this purpose, a compensation of the velocity dependencies is first performed based on the assigned relative velocities 2310. Furthermore, angle hypotheses are calculated 2320, which, however, are restricted to an angular range that is compatible with the roughly determined angles. Only angle hypotheses that fall within the uncertainty range of the roughly determined angle are calculated. For precise angle determination, these restricted angle hypotheses are correlated with the acquired echo information 2330 to determine the best-fitting angle hypothesis, which then defines the precise angle. This can be further processed by other assistance systems.

[0084] It will be understood by those skilled in the art that only exemplary embodiments are described here. Reference symbol list 100 photonic radar systems 200 Central Station 210 Control unit 220 lasers 225 more lasers 230 Modulation unit 235 additional modulation devices 240 optical control unit 245 additional optical control devices 250 distribution equipment 260 Detection device 270 calculation unit 280 Digitization facility 290 Processing unit 300, 300-n radar head assembly 305, 305-n fiber input 310 Photoreceiving coupler 315 electronic photonic integrated circuit (EPIC) 320 antenna structure 330 uniform linear array 350 antenna 395, 395-n fiber output 400, 400n transmission medium 401, 401n optical fibers 402, 402-n fiber 450, 450-n further transmission medium 460 electronic control line 500, 500-n return transmission medium 501, 501-n optical fibers 502, 502-n fiber 550, 550-n further return transmission medium 560 electronic return line 600 transmitter module 605 optical signal 610 optical coupler 620 converter unit 630 photodiode 640 electronic signal 650 preamplifiers 660 frequency converters 670 frequency converters 680 electronic transmission signal 690 further electronic transmission signal 700 transmitter amplifiers 710 additional transmitter amplifiers 740 frequency-converted electronic signal 750 frequency-converted electronic signal 760 mixers 770 more mixers 800 receiver module 850 beam splitters 870 Intermediate frequency signal 880 additional intermediate frequency signal 900 Modulator 910 modulated optical signal 920 additional optical couplers 950 optical splitter 960 additional optical filters 2010 Echo information 2020 Echo Information 2030 distance spectra 2040 further distance spectra 2050 distances 2060 more distances 2080 coherent integration of the further distance spectra 2100 evaluate the Doppler spectra 2120 relative speeds 2140 Rough determination of solid angles 2200 Assigning the recorded objects based on distances or further distances 2300 precise determination of the solid angle 2310 Compensation of the velocity-dependent terms 2320 Calculating the angle hypotheses restricted to angle ranges around the roughly determined angles 2330 correlate the calculated angle hypotheses with the acquired echo information for precise angle determination.

Claims

[1] 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 linked to a transmitting module and each of the receiving antennas (350) is linked 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, wherein the central station is configured to generate the radar signal information and transmit it to the transmitting modules and / or to control them in such a way that at least part of the transmitting modules are configured to emit chirps, which are signal segments varying monotonically and linearly with respect to frequency in a frequency range, as radar signals via the assigned transmitting antennas (350) at a time offset, and at least part of the receiving antennas are assigned receiving modules which are configured to derive echo information and transmit it to the central station based on the radar echo signals generated by objects in the environment, which are simultaneously detected by at least part of the receiving antennas (350) in the same frequency range. characterized by , that one of the transmitting modules is configured to continuously radiate further chirps, which are monotonically linear signal segments varying with respect to frequency, in a further frequency range via an associated transmitting antenna, based on the radar signal information generated by the central station, wherein the further frequency range is disjoint from the first 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 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 configuredto assign the objects detected using the additional echo information and the derived relative velocities to the objects detected using the echo information based on a correlation between the further distance information determined using the additional echo information and the distance determined using the echo information within the assigned tolerance range, and additionally to perform rough angle estimates for the detected objects based on the echo information or the additional echo information received by a receiving antenna, or based on the additional echo information, and to take the determined relative velocities and rough angle estimates into account in a precise angle estimate based on the echo information. [2] Multiple-input multiple-output radar system (100) according to claim 1, characterized by, that the central station is designed to use the relative velocities to compensate for the velocity-dependent terms in the precise angle estimation with respect to their velocity dependence. [3] Multiple-input multiple-output radar system (100) according to claim 1 or 2, characterized by , that the central station is trained to use the rough angle estimates to narrow down a number of the angle hypotheses to be evaluated when determining precise angle estimates. [4] Multiple-input multiple-output radar system (100) according to any one of the preceding claims, characterized by , that at least some of the receiving antennas (350) form a sparse antenna array. [5] Multiple-input multiple-output radar system (100) according to any one of the preceding claims, characterized by, that one or more of the majority of receiving antennas (350) of the linear uniform antenna array also belong to at least a part of the receiving antennas whose associated transmitting modules are designed to derive echo information from the radar echo signals received in one frequency range. [6] Multiple-input multiple-output radar system (100) according to claim 5, characterized by , that at least part of the receiving antennas, whose associated transmitting modules are designed to derive echo information from the radar echo signals received in one frequency range, form a sparse antenna array. [7] Multiple-input multiple-output radar system (100) according to claim 5 or 6, characterized by, that one or more of the plurality of receiving antennas (350) of the linear uniform antenna array, which also belong to at least part of the receiving antennas, are configured in a mixer to convert the echo information and the further echo information into an intermediate frequency signal that represents the echo information and the further echo information in separate frequency ranges. [8] Multiple-input multiple-output radar system (100) according to claim 5, characterized by, that one or more of the plurality of receiving antennas (350) of the linear uniform antenna array comprise a mixer that converts the echo information derived from the radar signals in one frequency range into an intermediate frequency signal, and a further mixer that converts the further echo information derived from the further radar echo signals in the further frequency range into another intermediate frequency signal, the frequencies of which are different from those of the one intermediate frequency signal, wherein the echo information of the one intermediate frequency signal and the further echo information of the further intermediate frequency signal are modulated onto the same optical carrier signal by utilizing frequency division multiplexing in a modulation device, so that the echo information can be separated from the further echo information in the central station. [9] A method for environmental sensing 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 for 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 include at least a distance and a relative velocity, , characterized by , 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 first 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 the relative velocities are then determined by evaluating Doppler spectra based on the coherently integrated distance spectra, wherein the central station also determines distances to the detected objects based on the echo information, wherein each 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 using the additional echo information and the derived relative velocities are assigned to the objects detected using the echo information based on a correlation between the distance information determined using the additional echo information and the distances determined using the echo information within the assigned tolerance ranges, and additionally, rough angle estimates for the detected objects are carried out using the echo information or the additional echo information received by a receiving antenna, or using the additional echo information, and the determined relative velocities and rough angle estimates are taken into account in a precise angle estimate based on the echo information. [10] Method according to claim 9, characterized by, that the relative velocities are taken into account by compensating the velocity-dependent terms in the precise angle estimation with respect to the determined relative velocities. [11] Method according to claim 9 or 10, characterized by , that the rough angle estimates are taken into account by restricting a number of evaluated angle hypotheses in the precise angle estimates to those that are compatible with the rough angle estimates. [12] Method according to any one of claims 9 to 11, characterized by, that with at least one of the receiving antennas both radar echo signals in one frequency range and further radar echo signals in the further frequency range are received, and with one or more associated receiving modules radar echo information is derived from the radar echo signal and further echo information from the further radar echo signal and transmitted to the central station for evaluation.

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