Photonic radar system, method for operating a photonic radar system, central unit and method for operating the central unit

Abstract

The invention relates to a photonic radar system (100) and a method for operating a photonic radar system (100). The invention further relates to a central unit (10) and a method for operating the central unit (10). The invention relates to reducing the computational effort required for Doppler processing in sparsely distributed antenna apertures by incorporating uniform linear array (ULA) structures (70).

Description

[0001] The invention relates to a photonic radar system and a method for operating a photonic radar system. Furthermore, the invention relates to a central processing unit and a method for operating the central processing unit.

[0002] Radar sensors have been established in the automotive sector for years, delivering reliable and fail-safe data in all weather conditions. To improve the signal-to-noise ratio, coherent summation across the dimensions of the receiving channels is usually performed. However, due to differing signal propagation times between the transmitting and receiving antennas and a potential target, varying measurement distances result in a non-linear phase term. This non-linear phase term prevents coherent integration across the dimensions of the receiving channels, which would otherwise improve the signal-to-noise ratio.

[0003] Document WO 2023 / 076 280 A2 relates to a method and device for imaging and object detection radars with subarray antenna groups arranged in a sparse array and MIMO configuration, which improves sensor performance.

[0004] Publication CN 107 436 429 A describes a method for the robust estimation of polarization dual-base MIMO radar parameters in an environment with impact noise by the joint implementation of a de-impact preprocessing and a sparse reconstruction mechanism with compressed sampling.

[0005] Document CN 103 885 048 A discloses a method for correcting amplitude and phase errors of dual-base MIMO radar transceiver arrays, which can achieve a more accurate estimation of the wave arrival angle and wave exit angle.

[0006] The invention is based on the objective of developing a distributed radar system and a method for operating a distributed radar system with reduced required computing effort.

[0007] The problem according to the invention is solved by a photonic radar system and a method for operating a photonic radar system, as well as a central processing unit and a method for operating the central processing unit, according to the independent claims. Preferred embodiments are the subject of the respective dependent claims.

[0008] A first aspect concerns a photonic radar system. The photonic radar system comprises a sparsely distributed antenna array, a central processing unit coupled to the sparsely distributed antenna array via at least one (optical) waveguide, and a data processing unit. Preferably, an optical fiber, for example, a glass fiber, is used as the waveguide. In other words, the photonic radar system is a sparsely distributed photonic radar system. A sparsely distributed (photonic) radar system is a radar system consisting of a limited number of radar sensors distributed over a large geographical area. In contrast to dense radar systems, which have many sensors close together, sparsely distributed systems take advantage of the greater distances between the sensors to achieve wider coverage while simultaneously reducing the costs and effort of installation and maintenance.In the simplest case, a sparsely distributed radar system can be achieved by a partially populated array of radar sensors.

[0009] The sparsely distributed antenna arrangement comprises at least one first radar receiver and a uniform linear array (ULA) structure. A ULA structure is an arrangement of radar sensors positioned at equal intervals along a straight line. The distance between adjacent radar sensors is preferably at most half a wavelength of the radar signal to be emitted. (d≤λ2). This prevents grating waves.

[0010] The ULA structure comprises at least one first radar transmitter and at least one second radar receiver. In other words, the first radar transmitter and the second radar receiver are spaced at a distance of at most half a wavelength of the emitted radar signal. The first radar receiver is sparsely distributed relative to the first radar transmitter. In other words, the distance between the first radar receiver and the radar transmitter (of the ULA structure) is at least such that a nonlinear phase term arises due to the differing measurement distances in the distributed antenna aperture. In other words, the radial distance between the first radar transmitter and a target object and the radial distance between the first radar receiver and the target object are different (d ≠ 2R0), so that coherent integration over the two radar receivers is no longer possible.Preferably, the distance between the first radar transmitter and the second radar receiver is at least one wavelength λ, for example, at least 2λ, at least 3λ, at least 4λ of the radar signal to be emitted, or greater. At a frequency of 77 gigahertz, this results, for example, in a wavelength of 0.389 mm. Preferably, the ULA structure comprises a plurality of radar transmitters and / or a plurality of (second) radar receivers arranged along a straight line at a constant distance of at most half a wavelength. Preferably, the photonic radar system comprises a plurality of (first) radar receivers arranged sparsely distributed relative to the first radar transmitter. The use of a ULA structure with a plurality of radar receivers advantageously enables the signal-to-noise ratio (SNR) and the response (gain) in a specific direction to be improved by coherent integration.The use of a ULA structure with a large number of radar transmitters advantageously allows angular information of the target object to be determined based on the ULA structure.

[0011] The central unit comprises a signal generator and an optical transmitter. The signal generator is configured to produce a ramp signal with a sequence of chirp signals. In other words, a chirp sequence with a plurality of repeating ramps of constant slope is created. The sequence preferably comprises at least one series of two, and preferably at least four, consecutive chirp signals. The optical transmitter is configured to provide an optical radar driver signal. The optical radar driver signal comprises an optical radar carrier signal and an optical ramp signal based on the ramp signal generated by the signal generator. In other words, the optical transmitter is configured to modulate the ramp signal generated by the signal generator onto the optical radar carrier signal as an optical ramp signal.The ramp signal causes the frequency of the radar carrier signal to be varied within a specific frequency range (frequency-modulated radar, FMCW). Consequently, the optical radar signal is preferably a superposition of the optical carrier signal and the optical ramp signal, which comprises a sequence of chirp signals. The frequency of the optical carrier signal is preferably in the THz range. The frequency of the ramp signal is preferably in the GHz range. The optical transmitter unit is further configured to couple the optical radar driver signal into the waveguide. In other words, the central unit provides an optical radar driver signal, containing a predefinable or predetermined ramp signal, which is transmitted via the waveguide to the sparsely distributed antenna array. The optical transmitter unit preferably comprises a laser diode and / or a modulator, in particular an optical modulator.The use of a modulator has the advantage that the laser diode itself does not need to be modulated, but only needs to provide the optical carrier signal in CW (Continuous Wave) mode. This allows the use of a cost-effective laser diode. The laser diode is preferably configured to emit light with a wavelength of at least 1000 nm to at most 1800 nm, preferably at least 1200 nm to at most 1600 nm, and particularly preferably 1310 nm and / or 1550 nm. The signal generator is preferably configured to generate the ramp signal as an electrical ramp signal and to supply this electrical ramp signal to the optical transmitter.

[0012] The sparsely distributed antenna array comprises an optical receiver and an optical modulator. The optical receiver of the sparsely distributed antenna array is configured to receive the optical radar driver signal coupled into the waveguide (by the optical transmitter of the central processing unit) and convert it into an electrical radar driver signal. The optical receiver is further configured to provide the (converted) electrical radar driver signal to the at least one radar transmitter of the ULA structure (for driving it). In other words, the at least first radar transmitter is enabled to be driven by the electrical radar driver signal to transmit a frequency signal containing the ramp signal (generated in the central processing unit) with the sequence of chirp signals. The optical receiver is preferably a photodiode.Photodiodes are well suited to converting the optical radar driver signal into an electrical radar driver signal. The optical modulation unit is configured to provide optical radar response signals, comprising radar echo signals received by the first and second radar receivers and the optical radar driver signal, and to couple these signals into the waveguide. In other words, the radar echo to the frequency signal transmitted by the first radar transmitter according to the ramp signal is received by the first and second radar receivers and each is provided to the optical modulation unit as an electrical radar echo signal. The optical modulation unit is configured to modulate the received radar echo signals onto the optical radar driver signal received by the central processing unit via the waveguide in order to generate the optical radar response signals, which are transmitted to the central processing unit via the waveguide.Preferably, the received (electrical) radar echo signals are mixed with the electrical radar driver signal in a mixer of the sparsely distributed antenna arrangement and then passed to the optical modulation unit.

[0013] The central unit further comprises a central optical receiver unit configured to receive the optical radar response signals coupled into the waveguide. The evaluation unit is configured to determine Doppler frequency information based on the radar echo signals received by the ULA structure, namely from at least one second radar receiver, and the sequence of chirp signals. In other words, according to the invention, Doppler processing is performed exclusively based on radar echo signals received by the ULA structure in order to prevent the occurrence of nonlinear phase terms during Doppler evaluation that would otherwise arise due to the differing measurement distances in the distributed antenna aperture. The evaluation unit is further configured to correct the radar echo signals received by the first radar receiver based on the determined Doppler frequency information.In other words, the phase terms contained in the radar echo signals received by the first radar receiver are subtracted based on the determined Doppler frequency information. This compensates for the nonlinear phase terms arising from the varying measurement distances in the distributed antenna aperture. Furthermore, the evaluation unit is configured to evaluate the corrected radar echo signals and the radar echo signals received by the ULA structure based on the sequence of chirp signals and to output radar information derived therefrom. The solution according to the invention therefore involves integrating at least one ULA structure into a sparsely designed large aperture of a distributed radar system to simplify its Doppler processing.This approach enables the evaluation of Doppler information using ULA receive signals and aims to eliminate nonlinear phase terms through geometric alignment of transmitters and receivers. The computational effort required for Doppler processing in sparsely distributed antenna apertures is advantageously reduced by incorporating ULA structures. This results in cost savings due to reduced reliance on high-performance computers.

[0014] Preferably, the evaluation unit is configured to perform a frequency analysis using a Fourier transform, thereby determining a (time-of-flight-based) distance coordinate of the target object(s). For example, the distance coordinate of the targets can be determined in the central unit's receive channel by cross-correlation of the respective radar response signal with the radar driver signal. In other words, distance spectra are derived from the received radar echo signals. Preferably, the radar information derived from the optical radar response signal is output to a driver assistance system and / or an automated driving system.

[0015] According to the invention, signal transmission between the central unit and the sparsely distributed antenna array is optical. This is achieved through the co-integration of optical and electrical components for generating and receiving a radar echo signal. The radar driver signal is generated centrally in the central unit and transmitted optically to the sparsely distributed antenna array. Optical transmission of the radar driver signal results in low signal attenuation compared to electrical transmission, making it possible to supply a large number of radar transmitters and receivers with a single radar driver signal. Furthermore, unlike electrical transmission, optical signal transmission achieves phase coherence of the radar driver signal, enabling a particularly simple implementation of a distributed radar system.Furthermore, only this phase-locked signal transmission makes it possible to reliably calculate the Doppler frequency information from the received radar echo signals and to correct the radar echo signals received by the first radar receiver accordingly. The generated ramp signals and the received radar response signals can be transmitted optically with exceptional efficiency, consistency, and immunity to interference due to the high speed of light. In contrast, with electrical signals, external interference, such as electromagnetic fields, threatens to "smear" the transmitted signals, particularly with regard to the phase terms, making reliable evaluation on the central processing unit impossible. In addition, optical waveguides are significantly lighter than comparable electrical conductors.The centralized optical generation of the radar driver signal in the central unit allows the radar transmitters and receivers to be manufactured and deployed in a compact design with small dimensions. This saves installation space and costs.

[0016] In distributed radar systems, if two or more radar receivers are spatially offset from one another, directional information of the incoming wave can also be determined by evaluating the time-of-flight differences. In other words, the evaluation unit is preferably also configured to determine directional information regarding the target object(s) by evaluating the time-of-flight differences. Furthermore, by distributing the radar transmitting and receiving units over a large area on the vehicle surface, for example in the form of EPIC chips, and by using coherent signal processing from the individual antennas, the resolution can be refined to the desired range of 0.1° (degrees). The maximum distance between the individual radar receivers (antennas) is crucial for the resolution of the radar system.For example, a resolution of 0.1° (degrees) can be achieved with a distance of 1 m to 1.5 m between two radar receivers, such as the first and second radar receivers, on the vehicle surface. For example, the minimum distance between at least two of the radar receivers is between 1 m and 1.5 m, preferably between 1.1 m and 1.4 m, and particularly preferably between 1.2 m and 1.3 m. If additional radar transmitters and receivers are arranged between the two radar receivers, this does not change the resolution of the radar system, but it does improve signal processing, as it allows the effects of other (undesired) effects contained in the radar echo signal to be filtered out.

[0017] In a preferred embodiment, the sparsely distributed antenna arrangement includes a second radar transmitter, which is sparsely distributed relative to the ULA structure. The optical receiver is preferably configured to provide the electrical radar driver signal to the first and second radar transmitters such that a first chirp signal from the sequence of chirp signals is assigned to the first radar transmitter and a second chirp signal from the sequence of chirp signals is assigned to the second radar transmitter. The use of the second radar transmitter allows for redundant determination of the Doppler frequency information, thus increasing the robustness of the photonic radar system. By using the generated radar driver signal to drive multiple radar transmitters, a particularly simple implementation of a distributed photonic radar system with multiple radar transmitters can be achieved.

[0018] In a further preferred embodiment, the evaluation unit is configured to calculate an angular estimate for a target object based on the corrected radar echo signals, the radar echo signals received by the ULA structure, and the sequence of chirp signals, and to output the calculated angular estimate. For example, the calculated angular estimate corresponds to a portion of the derived radar information. In other words, it is possible to determine angular information regarding the target object. In particular, this advantageously allows the angular information to be determined preferably based on the ULA structure and independently of the other radar sensors of the sparsely distributed antenna array.

[0019] In a further preferred embodiment, the signal generator is configured to reduce the chirp sweep time and / or the frequency bandwidth of the chirp signals of the ramp signal such that the time interval between the first chirp signals of adjacent sequences of chirp signals of the ramp signal is below a predetermined maximum interval. A chirp sweep time corresponds to the duration of a ramp with a constant slope. A frequency bandwidth corresponds to the difference between the start and end frequencies of a ramp with a constant slope.When the chirp signals of a radar driver signal are distributed across multiple radar transmitters, for example, the first and second radar transmitters, the time interval, known as the pulse repetition interval, between the chirp signals of the same or adjacent sequences assigned to each radar transmitter can increase—for example, it can double if only every second chirp signal is assigned to the corresponding antenna—while the chirp sweep time remains constant. This extended pulse repetition interval leads to a lower maximum unique Doppler frequency (a requirement of the Nyquist theorem). The desired maximum unique Doppler frequency is advantageously achieved by shortening the chirp sweep time and / or reducing the frequency bandwidth. Furthermore, simultaneous fine-tuning of the chirp sequence from transmitters of the ULA structure within the chirp sequence of the entire distributed aperture is preferred.Preferably, the (unshortened) chirp sweep time is between 10 µs and 100 µs, more preferably between 20 µs and 75 µs, and most preferably between 30 µs and 50 µs. Such chirp sweep times are well suited for scanning the target object(s) and can be readily implemented using known hardware and software solutions.

[0020] In a further preferred embodiment, the ULA structure comprises a third radar receiver, and the antenna arrangement and / or the evaluation unit are configured to coherently integrate the radar echo signals simultaneously received by the ULA structure and to provide them as radar echo signals received by the ULA structure. This coherent integration across the receiving channels of the ULA structure advantageously improves the signal-to-noise ratio (SNR) and the response (gain) in a specific direction.

[0021] Another aspect of the invention relates to a method for operating a photonic radar system. The radar system is preferably the photonic radar system described above. The advantages achieved with the photonic radar system can be achieved analogously with the method. The disclosed combinations of features of the photonic radar system are transferable to the method by analogy. Therefore, a repetitive description of the features and advantages is omitted.

[0022] According to one step of the process, a ramp signal with a sequence of chirp signals is generated by a central processing unit, in particular the central processing unit mentioned above. In a further step of the process, an optical radar driver signal is provided by the central processing unit. The optical radar driver signal comprises an optical radar carrier signal and an optical ramp signal based on the generated ramp signal.

[0023] Furthermore, the optical radar driver signal is coupled into a waveguide through the central unit.

[0024] In a further process step, the optical radar driver signal coupled into the waveguide is received by a sparsely distributed antenna arrangement with a uniform linear array (ULA) structure and converted by this into an electrical radar driver signal.

[0025] In one step of the process, a radar transmitter of the ULA structure is driven by the electrical radar driver signal.

[0026] Furthermore, radar echo signals, in particular radar echo signals based on the signal emitted by the radar transmitter according to the electrical radar driver signal, are received by a first radar receiver and a second radar receiver. The first radar receiver is sparsely distributed relative to the radar transmitter, and the second radar receiver is enclosed by the ULA structure.

[0027] In a further process step, optical radar response signals, which include the radar echo signals received via the first and second radar receivers and the optical radar driver signal, are provided by the sparsely distributed antenna arrangement and coupled into the waveguide by it.

[0028] The optical radar response signals coupled into the waveguide are received by the central unit.

[0029] Doppler frequency information is determined based on the radar echo signals received by the ULA structure and the sequence of chirp signals.

[0030] The radar echo signals received by the first radar receiver are corrected based on the determined Doppler frequency information.

[0031] Furthermore, the corrected radar echo signals and the radar echo signals received by the ULA structure are evaluated based on the sequence of chirp signals, and radar information derived from this is output. The evaluation and output are preferably performed by the central processing unit.

[0032] Another aspect of the invention relates to a central unit for use in the photonic radar system described above. The central unit is preferably the one described above. The central unit comprises a central optical receiver configured to receive optical radar response signals coupled into the waveguide and an evaluation unit. The evaluation unit is configured to determine Doppler frequency information based on radar echo signals received by a uniform linear array (ULA) structure and a sequence of chirp signals, and to correct radar echo signals received by a first radar receiver arranged sparsely distributed relative to the ULA structure based on the determined Doppler frequency information.The evaluation unit is further configured to evaluate the corrected radar echo signals and the radar echo signals received by the ULA structure based on the sequence of chirp signals and to output radar information derived from this evaluation. The advantages achieved with the photonic radar system can be achieved analogously with the central processing unit. The feature combinations of the photonic radar system disclosed with respect to the central processing unit are analogously transferable to the central processing unit. Therefore, a repetitive description of the features and advantages is omitted.

[0033] In a preferred embodiment of the invention, the central unit further comprises a signal generator configured to generate a ramp signal with a sequence of chirp signals, and an optical transmitter unit configured to provide an optical radar driver signal comprising an optical radar carrier signal and an optical ramp signal based on the ramp signal generated by the signal generator, and to couple this signal into a waveguide.

[0034] Another aspect of the invention relates to a method for operating the central processing unit. The advantages achieved with the central processing unit can be achieved analogously with the method. The combinations of features disclosed with respect to the central processing unit are analogously transferable to the method. Therefore, a repetitive description of the features and advantages is omitted.

[0035] In this method, optical radar response signals coupled into the waveguide are received by the central unit.

[0036] Furthermore, Doppler frequency information is determined based on radar echo signals received by a uniform linear array (ULA) structure and a sequence of chirp signals.

[0037] Radar echo signals received by a first radar receiver sparsely distributed in relation to the ULA structure are corrected based on the determined Doppler frequency information.

[0038] The corrected radar echo signals and the radar echo signals received through the ULA structure are also evaluated based on the sequence of chirp signals, and radar information derived from this is output.

[0039] In a preferred embodiment, a ramp signal is generated using a sequence of chirp signals. Furthermore, an optical radar driver signal, comprising an optical radar carrier signal and an optical ramp signal based on the generated ramp signal, is provided and coupled into a waveguide.

[0040] The individual process steps of the methods according to the invention are preferably configured as one or more processes that run on one or more processors in one or more electronic computing devices and are generated during the execution of one or more computer programs. The computing devices are preferably configured to cooperate with other components in order to realize the functionalities described herein. Likewise, the radar system or individual components, in particular the central processing unit, are preferably configured as central (single-unit) or decentralized (multi-unit) components.

[0041] The individual components of the photonic radar system, in particular the evaluation unit of the central processing unit, are preferably configured, at least partially, as one or more processes running on one or more processors in one or more electronic computing devices and generated during the execution of one or more computer programs. The computing devices are preferably configured to cooperate with other components to implement the functionalities described herein. The instructions of the computer programs are also preferably stored in a memory, such as a RAM element. However, the computer programs can also be stored in a non-volatile storage medium, such as a CD-ROM, flash memory, or the like.

[0042] It is also apparent to those skilled in the art that the functionalities of several computers (data processing devices) can be combined or combined in a single device, or that the functionality of a particular data processing device can be distributed across a multitude of devices in order to carry out the steps of the methods according to the invention without deviating from the methods according to the invention.

[0043] Another aspect of the invention relates to a computer program comprising instructions which, when the program is executed by a computer, cause it to perform at least one of the methods according to the invention.

[0044] The central processing unit and the sparsely distributed antenna array preferably also include further electrical and / or optical components. Examples include transimpedance amplifiers and other amplifier devices used to amplify electrical signals, and / or electrical modulators that can be used in signal processing.

[0045] The present invention can be used, in particular, in a motor vehicle for environmental sensing. Exemplary applications include driver assistance systems such as parking assistants, adaptive cruise control, and the like, as well as automatic and / or autonomous driving and the like. In principle, however, the invention can also be used in all fields where radar systems are employed, such as aircraft radar systems, ship radar systems, container terminals, warehouse robot logistics, rail vehicles, military technology, and the like.

[0046] Further preferred embodiments of the invention result from the other features mentioned in the dependent claims.

[0047] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0048] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a photonic radar system according to one embodiment, Fig. 2 a schematic representation of a sparsely distributed antenna arrangement according to one embodiment, Fig. 3 a schematic representation of a sparsely distributed antenna arrangement according to a further embodiment, Fig. 4 a schematic representation of a sequence of chirp signals according to the sparsely distributed antenna arrangement from Fig. 3, Fig. 5 a schematic representation of the sequence from Fig. 4 with a shortened chirp-sweep time and Fig. 6 a schematic representation of a method for operating a photonic radar system according to one implementation form.

[0049] Detailed embodiments are now described, illustrated by way of example in the accompanying drawings. The effects and features of these embodiments are described with reference to the accompanying drawings. In the drawings, identical reference numerals denote identical elements, and redundant descriptions are avoided. The present disclosure can be implemented in various forms and is not to be understood as being limited only to the embodiments shown here. Rather, these embodiments are examples to ensure that this disclosure is thorough and complete and fully conveys the aspects and features of the present disclosure to the person skilled in the art.

[0050] Methods, elements, and techniques that are not necessary for a person skilled in the art to fully understand the aspects and features of this disclosure are therefore not described where applicable. In the drawings, the relative sizes of elements and areas may be exaggerated for clarity.

[0051] As used herein, the term “and / or” includes all combinations of one or more of the elements listed. Furthermore, the use of “may” in the description of embodiments of the present disclosure refers to “one or more embodiments of the present disclosure.” In the following description of embodiments, singular terms may also include the plural unless the context clearly indicates otherwise.

[0052] Although the terms "first" and "second" are used to describe different elements, these elements should not be restricted by these terms. These terms are used only to distinguish one element from another. For example, a first element may be called a second element, and likewise a second element may be called a first element, without this deviating from the scope of the present disclosure. Expressions such as "at least one of," when placed before a list of elements, modify the entire list and not just the individual elements of the list.

[0053] Fig. Figure 1 shows a schematic representation of a photonic radar system 100 according to one embodiment. For clarity, optical connections and photonic components are generally represented by dashed lines in the figures. The radar system 100 comprises a sparsely distributed antenna array 50, a central unit 10 coupled to the sparsely distributed antenna array 50 via at least one (optical) waveguide 12, 12', and an evaluation unit 14.

[0054] The central unit 10 comprises a signal generator 18, configured to generate a ramp signal with a sequence of chirp signals, and an optical transmitter 20a, configured to provide an optical radar driver signal. The optical radar driver signal comprises an optical radar carrier signal and an optical ramp signal based on the ramp signal generated by the signal generator 18. The optical transmitter 20a is further configured to couple the optical radar driver signal into the waveguide 12 in order to transmit it via the waveguide 12 to the sparsely distributed antenna array 50.

[0055] In the Fig. In the example shown, the evaluation unit 14 is arranged on the central unit 10. Preferably, the central unit 10 also includes a control interface 16, which is connected to the evaluation unit 14 and is configured to control the signal generator 18 such that the signal generator 18 generates the ramp signal. The signal generator 18 is preferably an analog signal generator and / or a digital signal generator. One advantage is that signal generators for generating ramp signals are very simple and therefore cost-effective to implement, for example, by simple circuits for generating ramp signals with sequences of chirp signals. The function and implementation of analog and / or digital signal generators or circuits are well known to those skilled in the art and are therefore not explained in detail here.The signal generator 18 is preferably configured to generate the ramp signal as an electrical ramp signal and to supply the electrical ramp signal to the optical transmitter 20a. Alternatively, an optical signal generator (not shown) is provided which is configured to generate the ramp signal optically and to supply it to the optical transmitter 20a as an optical ramp signal.

[0056] The optical transmitter unit 20a preferably comprises a light source, for example a laser diode 22 or an LED, and / or a modulator, in particular an optical modulator 20. The use of a modulator has the advantage that the laser diode 22 itself does not need to be modulated, but only needs to provide the optical carrier signal in CW mode. This allows the use of a cost-effective laser diode 22. The laser diode 22 is electrically connected to the control interface 16 for control purposes. Preferably, the optical modulator 20 is configured to change a material property of the waveguide 12 in order to modulate the optical wave. Preferably, the refractive index and / or the absorption properties of the waveguide 12 are changed.Preferably, the optical modulator 20 is configured to modify the material properties of the waveguide 12 by means of charge carriers (current), electric fields (voltage), temperature (heating electrodes), and / or mechanical modification, for example, by applying force to the waveguide 12. Preferably, the optical modulator 20 is designed according to its specific application, for example, with regard to bandwidth, rise / fall time, control, and so on.

[0057] The optical transmitter unit 20a preferably also comprises an optical control unit 24, an optical multiplexer 26, and / or a feedback loop unit 28. The optical control unit 24 is electrically connected to the laser diode 22 and is connected in the optical path between the optical modulator 20 and an optical output (not shown) of the optical transmitter unit 20a. The optical control unit 24 is configured to correlate the electrical control signal of the laser diode 22 with the optical radar driver signal output by the optical modulator 20 and to check for (undesired) differences or deviations. In other words, the optical control unit 24 ensures that the output optical radar driver signal is correct, as desired.The optical multiplexer 26 is preferably configured to apply a time-division multiplexing (TDM) and / or a wavelength-division multiplexing (WDM) method to the optical radar driver signal. Preferably, the optical multiplexer 26 is connected in the optical path between the optical modulator 20, particularly downstream of the optical control unit 24, and the optical output (not shown) of the optical transmitter unit 20a. Time-division multiplexing (TDM) is a method for transmitting and receiving independent signals over a common signal path using synchronized switches at each end of the transmission line, so that each signal appears on the line for only a fraction of the time according to predefined rules. It can be used, for example, when the bit rate of the transmission medium exceeds that of the signal to be transmitted.Wavelength division multiplexing allows multiple optical carrier signals to be multiplexed onto a single waveguide by using different wavelengths of light. This technique enables bidirectional communication over a single waveguide (also called wavelength duplexing) and a multiplication of the capacitance. The feedback loop unit 28 is electrically connected to the control interface 16 and is configured to tap the optical radar driver signal in the optical path between the optical modulator 20 and an optical output (not shown) of the optical transmitter unit 20a, specifically downstream of the optical control unit 24 and / or upstream of the optical multiplexer 26. The feedback loop unit 28 serves, in particular, to inform the control interface 16 whether and how the generated optical radar driver signal can be corrected and / or calibrated.Preferably, the feedback loop unit 28 is configured to perform a complex event processing (CEP) procedure.

[0058] With regard to Fig. 2 will be in Fig. 1. The sparsely distributed antenna arrangement shown in Figure 50 is explained in more detail. Fig. Figure 2 shows a schematic representation of a sparsely distributed antenna arrangement 50 according to one embodiment. In the case of a monostatic radar, or a bisstatic 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 identical. With each subsequent measurement within the measurement sequence, only a phase term changes, which describes the dependence on the Doppler velocity. If the aperture of the radar system includes additional receiving antennas for which the described property d(p) = 2R0 still applies, the individual measurement signals can be added coherently to improve the signal-to-noise ratio. The final determination of the Doppler frequency is preferably carried out by a frequency analysis in the form of a discrete Fourier transform.

[0059] The sparsely distributed antenna arrangement 50 comprises at least one first radar receiver 42, for example as part of a radar receiving unit 40, and a ULA structure 70. The ULA structure 70 comprises at least one first radar transmitter 60 and at least one second radar receiver 72. In other words, the first radar transmitter 60 and the second radar receiver 72 are arranged at a distance from each other that is at most half a wavelength of the radar signal to be emitted. The first radar receiver 42 is arranged sparsely with respect to the first radar transmitter 60. In other words, the distance between the first radar receiver 42 and the radar transmitter 60 of the ULA structure 70 is at least such that a nonlinear phase term arises due to the differing measurement distances in the distributed antenna aperture.In other words, the radial distance between the first radar transmitter 60 and a target object and the radial distance between the first radar receiver 42 and the target object are different from each other (d ≠ 2R0), so that a coherent integration over the two radar receivers 42, 72 is no longer possible.

[0060] To counteract this problem, all nonlinear phase components in the measurement signal must be compensated before Doppler processing when using a distributed radar system. However, since the direction angle is unknown during the Doppler measurement process, hypotheses about all targets within all angular and distance intervals within the radar system's field of view must be formulated and applied to compensate for the nonlinear phase components. The effort required to compensate for the nonlinear phase terms increases linearly with the granularity needed to distinguish between the individual hypotheses. With a conventional approach that simply subjects the transmit sequence of a receiving antenna in a receiving channel to a Fourier transform, there is a risk of no longer being able to distinguish target information from noise.In view of the extensive computational effort, the Doppler processing according to the invention is carried out exclusively on the basis of received radar echo signals of the ULA structure 70 in order to prevent the occurrence of the nonlinear phase terms that would otherwise arise due to the differing measurement distances in the distributed antenna aperture during the Doppler evaluation.

[0061] The ULA structure 70 comprises an optical receiver 52, which is configured to receive the optical radar driver signal coupled into the waveguide 12 (by the optical transmitter 20a of the central unit 10) and convert it into an electrical radar driver signal. This is preferably done by means of a photodiode. The optical receiver 52 is further configured to provide the (converted) electrical radar driver signal to the radar transmitter 60 (for driving the same). For this purpose, the optical receiver 52 is electrically connected to the radar transmitter 60. In other words, the radar transmitter 60 is enabled to be driven by the electrical radar driver signal in order to transmit a frequency signal with the ramp signal (generated in the central unit 10) containing the sequence of chirp signals.

[0062] The frequency signals emitted by the radar transmitter 60 are preferably in the frequency range of 24.05 GHz to 26.65 GHz (according to the radio approval standards for automotive radars ETSI EN 302 858 and ETSI EN 302 288) and / or from 76 GHz to 81 GHz (according to the radio approval standards for automotive radars ETSI EN 301 091 and ETSI EN 302 264).

[0063] The ULA structure 70 preferably further comprises a first amplifier 54, a frequency converter 56, and a second amplifier 58. The first amplifier 54 is preferably connected between the optical receiver 52 and the radar transmitter 60. The first frequency converter 56 is preferably connected between the optical receiver 52, particularly downstream of the first amplifier 54, and the radar transmitter 60. The second amplifier 58 is preferably connected between the optical receiver 52, particularly downstream of the frequency converter 56, and the radar transmitter 60. The first amplifier 54 serves to amplify the electrical signal generated by the optical receiver 52 (with respect to its amplitude). The second amplifier 58 serves to amplify the electrical signal passing through the frequency converter 56 (with respect to its amplitude).The frequency converter 56 is provided, for example, for the preferred embodiment described below. In this embodiment, the central optical transmitter unit 20a of the central unit 10 provides the optical radar driver signal at a frequency that corresponds to a fraction of the carrier frequency required for operating the radar transmitter 60. The frequency converter 56 of the ULA structure 70 is configured to multiply the optical radar driver signal from the required frequency to the necessary carrier frequency and provide it. This embodiment has the advantage that the optical radar driver signal does not need to be provided at the full required carrier frequency. For example, a fraction of 1 / 4 can be selected. With an exemplary required carrier frequency of 77 GHz, the optical carrier signal then only needs to have a frequency in the range of 19.25 GHz.In the ULA structure 70, the optical radar carrier signal is then electrically multiplied, in particular quadrupled, by means of the frequency converter 56, and thereby brought to the required frequency. A further advantage of this is that, due to the central provision of the radar driver signal, the individual ULA structure 70 requires significantly less energy, thus reducing problems with the dissipation of waste heat.

[0064] The first radar receiver 42 of the radar receiving unit 40 and the second radar receiver 72 of the ULA structure 70 are described analogously below due to their identical mode of operation. The radar receiving unit 40 and the ULA structure 70 each comprise an optical modulation unit 49, 80, which is configured to provide an optical radar response signal. This signal comprises a radar echo signal received via the first radar receiver 42 or the second radar receiver 72, respectively, and the optical radar driver signal, and is coupled into the waveguide 12. In other words, the radar echo to the frequency signal transmitted by the radar transmitter 60 according to the ramp signal with the sequence of chirp signals is received by the first radar receiver 42 and the second radar receiver 72 and each is provided as an electrical radar echo signal to the optical modulation unit 49, 80.The radar receiver 40 and the ULA structure 70 each preferably comprise a photodiode 48, 78, which receives the optical radar driver signal and converts it into an electrical radar driver signal. The electrical radar driver signal is then preferably transmitted to the optical modulation unit 49, 80. The optical modulation units 49, 80 are each configured to modulate the received radar echo signal onto the optical radar driver signal received by the central unit 10 via the waveguide 12 in order to generate the optical radar response signal, which is transmitted to the central unit 10 via the waveguide 12. Preferably, the received (electrical) radar echo signal is mixed with the electrical radar driver signal in a mixer 46, 76.Preferably, the radar receiver 40 and the ULA structure 70 each further comprise an amplifier 74, which amplifies the received electrical radar echo signal (with respect to its amplitude). Furthermore, a low-pass filter (LPF) (not shown) is preferably provided on the radar receiver 40 and the ULA structure 70, for example between the mixer 46, 76 and the optical modulation unit 49, 80 or between the amplifier 44, 74 and the mixer 46, 76.

[0065] As further in Fig. As shown in Figure 1, the central unit 10 further comprises a central optical receiver 30 configured to receive optical radar response signals coupled into the waveguide 12. The evaluation unit 14 is configured to determine Doppler frequency information based on the radar echo signals received by the ULA structure 70, namely from the at least one second radar receiver 72, and the sequence of chirp signals. In other words, according to the invention, Doppler processing is performed exclusively based on received radar echo signals from the ULA structure 70 in order to prevent the occurrence of nonlinear phase terms during Doppler evaluation that would otherwise arise due to the differing measurement distances in the distributed antenna aperture. The evaluation unit 14 is further configured to correct the radar echo signals received by the first radar receiver 42 based on the determined Doppler frequency information.In other words, the phase terms contained in the radar echo signals received by the first radar receiver 42 are subtracted based on the determined Doppler frequency information. This compensates for the nonlinear phase terms arising from the varying measurement distances in the distributed antenna aperture. Furthermore, the evaluation unit 14 is configured to evaluate the corrected radar echo signals and the radar echo signals received by the ULA structure 70 based on the sequence of chirp signals and to output radar information derived therefrom. For this purpose, the evaluation unit 14 is electrically connected to the central optical receiver unit 30. Preferably, the radar information derived from the optical radar response signal is output to a driver assistance system and / or an automated driving system.The solution according to the invention therefore involves integrating at least one ULA structure 70 into a sparsely designed large aperture of a distributed radar system 100 to simplify its Doppler processing. This approach enables the evaluation of Doppler information using ULA receive signals and aims to eliminate nonlinear phase terms through geometric alignment of transmitters and receivers. Advantageously, the computational effort required for Doppler processing in sparsely distributed antenna apertures is reduced by incorporating ULA structures 70. This results in cost savings due to reduced dependence on high-performance computers.

[0066] In preferred embodiments, the central optical receiver 30 is connected to the optical modulator 20 to modulate the received optical radar response signal onto the optical radar driver signal (unless this has already been done by the sparsely distributed antenna array 50). The central unit 10 further preferably comprises a mixer 32, an analog-to-digital converter (ADC), and / or a preprocessing unit 36. The mixer 32 is preferably interposed between the optical receiver 30 and the evaluation unit 14. The ADC 34 is preferably interposed between the optical receiver 30, particularly downstream of the mixer 32, and the evaluation unit 14. The preprocessing unit 36 ​​is preferably interposed between the optical receiver 30, particularly downstream of the ADC 34, and the evaluation unit 14.The preprocessing unit 36 ​​is preferably configured to perform a fast Fourier transform (FFT - Fast Fourier Transform).

[0067] According to the invention, the radar driver signal is generated optically and centrally in the central unit 10. Signal transmission between the central unit 10 and the sparsely distributed antenna arrangement 50 is optical. This is made possible by the co-integration of optical and electrical components for generating and receiving a radar echo signal. In contrast to electrical transmission, optical transmission of the radar driver signal results in low signal attenuation, which makes it possible to supply a large number of radar transmitters and receivers with a single radar driver signal. Furthermore, unlike electrical transmission, optical signal transmission achieves phase rigidity (coherence) of the radar driver signal, which enables a particularly simple implementation of a distributed radar system 100.Furthermore, only this phase-locked signal transmission makes it possible to reliably calculate the Doppler frequency information from the received radar echo signals and to correct the radar echo signals received by the first radar receiver accordingly. The generated ramp signals and the received radar response signals can be transmitted optically with exceptional efficiency, consistency, and immunity to interference due to the high speed of light. In contrast, with electrical signals, external interference, such as electromagnetic fields, threatens to "smear" the transmitted signals, particularly with regard to the phase terms, making reliable evaluation on the central processing unit impossible.

[0068] Fig. Figure 3 shows a schematic representation of a sparsely distributed antenna arrangement 50 according to a further embodiment. The sparsely distributed antenna arrangement 50 according to the further embodiment differs from the one shown in Figure 3 in that... Fig. 2. In the embodiment shown, a plurality of transmitting antennas T x1 are x4 and a large number of receiving antennas R x1 to R x9 are shown. However, this number shown is merely exemplary and the revelation is not limited to it. The transmitting antennas T x1 and T x4 as well as the receiving antennas R x1 to R x3 and R x8 and R x9 are sparsely distributed along the x-axis (left and right sparse arrays). The ULA structure 70 with the transmitting antennas T is located between the two sparse arrays. x2 and T x3 (as radar transmitter 60) and the receiving antennas R x4 to R x7(as a second radar receiver 72). The transmit and receive antennas of the ULA structure 70 are each arranged at a constant distance from each other, with a maximum separation of half a wavelength. The transmit and receive antennas of the sparse arrays are arranged at an arbitrary distance relative to the ULA structure 70.

[0069] Fig. Figure 4 shows a schematic representation of a sequence of chirp signals according to the sparsely distributed antenna arrangement. Fig. 3. The sequence comprises four consecutive identical chirp signals, representing a repeating MIMO cycle. Each of the four chirp signals is associated with one of the four transmitting antennas T. x1 and T x4 assigned. In such a division of the chirp signals of the radar driver signal across several radar transmitters, for example the four transmitting antennas T x1 and T x4, a time interval, the so-called pulse repetition interval T, can develop - with a constant chirp sweep time. PRI , between the chirp signals of the same sequence or adjacent sequences assigned to the respective radar transmitter. As in Fig. Figure 4 shows the pulse repetition interval T increasing. PRI , ULA between the transmitting antennas T x2 and T x3 the ULA structure 70 to a multiple, for example a doubling between the transmitting antennas T x2 and T x3 and a quadrupling between a respective transmitting antenna T x2 or T x3 The resulting extended pulse repetition interval T PRI , ULA This leads to a smaller maximum unique Doppler frequency (requirement of the Nyquist theorem).

[0070] To avoid a loss of uniqueness of the Doppler frequency, the signal generator 18 is configured to reduce the chirp sweep time and / or the frequency bandwidth of the chirp signals of the ramp signal such that the time interval between the first chirp signals of adjacent sequences of chirp signals of the ramp signal is below a predetermined maximum interval, as is the case, for example, in Fig. 5, which is a schematic representation of the sequence from Fig. Figure 4 shows a shortened chirp sweep time. Advantageously, the desired maximum unambiguous Doppler frequency is achieved by shortening the chirp sweep time and / or reducing the frequency bandwidth. Preferably, the (unshortened) chirp sweep time of a chirp signal in Fig. 4. Example: 40 µs. The chirp sweep time of the shortened chirp signal according to Fig. For example, chirp sweep time 5 is 20 µs. Such chirp sweep times are well-suited for scanning the target object(s) and can be readily implemented using established hardware and software solutions. The time of a MIMO cycle is also correspondingly reduced.

[0071] Fig. Figure 6 shows a schematic representation of a method for operating a photonic radar system 100, in particular the above, according to one implementation form.

[0072] In a first process step 102, a ramp signal with a sequence of chirp signals is generated by a central processing unit 10. For example, the one in the Fig. 4 or Fig.A ramp signal shown in Figure 5 is generated. According to a second process step 104, an optical radar driver signal is provided by the central unit 10. This optical radar driver signal comprises an optical radar carrier signal and an optical ramp signal based on the generated ramp signal. Furthermore, the optical radar driver signal is coupled into a waveguide 12 by the central unit 10 (third process step 106). In a fourth process step 108, the optical radar driver signal coupled into the waveguide 12 is received by a sparsely distributed antenna array 50 with a ULA structure 70 and converted into an electrical radar driver signal. According to a fifth process step 110, a radar transmitter 60 of the sparsely distributed antenna array 50 is driven by the electrical radar driver signal.Furthermore, radar echo signals are received by a first radar receiver 42 and a second radar receiver 72 (sixth process step 112). The first radar receiver 42 is sparsely distributed relative to the radar transmitter 60, and the second radar receiver 72 is enclosed by the ULA structure 70. In a seventh process step 114, optical radar response signals, comprising the radar echo signals received by the first and second radar receivers 42 and 72 and the optical radar driver signal, are provided by the sparsely distributed antenna array 50 and coupled into the waveguide 12. According to an eighth process step 116, the optical radar response signals coupled into the waveguide 12 are received by the central unit 10. Furthermore, Doppler frequency information is determined based on the radar echo signals received by the ULA structure 70 and the sequence of chirp signals (ninth process step 118).In a tenth process step 120, the radar echo signals received by the first radar receiver 42 are corrected based on the determined Doppler frequency information. Finally, the corrected radar echo signals and the radar echo signals received by the ULA structure 70 are evaluated based on the sequence of chirp signals, and radar information derived from this is output (eleventh process step 122). Reference symbol list 10 Central processing unit 12, 12' waveguide 14 evaluation units 16 Control interface 18 Signal generator 20a optical transmitter unit 20 optical modulators 22 Laser diode 24 optical control unit 26 optical multiplexers 28 Feedback loop unit 30 central optical receiving units 32 mixers 34 ADC converters 36 Pre-processing unit 40 radar receiver unit 42 first radar receiver 44 amplifiers 46 mixers 48 Photodiode 49 optical modulation unit 50 sparsely distributed antenna array 52 optical receiving unit 54 first amplifier 56 frequency converters 58 second amplifier 60 first radar transmitter 70 ULA structure 72 second radar receiver 74 amplifiers 76 mixers 78 Photodiode 80 optical modulation units 100 radar systems 102 First process step - Generating ramp signal 104 Second procedure step - Providing optical radar driver signal 106 Third process step - Coupling optical radar driver signal 108 Fourth process step - Receiving and converting radar driver signal 110 fifth process step - driving radar transmitter 112 sixth procedure step - Receiving radar echo signals 114 Seventh procedure step - Providing and coupling the radar response signals 116 Eighth procedure step - Receiving the optical radar response signals 118 Ninth procedure step - Determining Doppler frequency information 120 Tenth procedure step - Correcting the radar echo signals 122 Eleventh procedure step - Evaluating and outputting the radar information T xn Transmitting antennas R xn Receiving antennas

Claims

[1] Photonic radar system (100), comprising: - a sparsely distributed antenna arrangement (50) with at least one first radar receiver (42) and a uniform linear array (ULA) structure (70) with at least one first radar transmitter (60) and at least one second radar receiver (72), wherein at least the first radar receiver (42) is sparsely distributed relative to the first radar transmitter (60), - a central unit (10) coupled via at least one waveguide (12) to the sparsely distributed antenna arrangement (50) with a signal generator (18) and an optical transmitter unit (20a), wherein the signal generator (18) is configured to generate a ramp signal with a sequence of chirp signals, and the optical transmitter unit (20a) is configured to provide an optical radar driver signal comprising an optical radar carrier signal and an optical ramp signal based on the ramp signal generated by the signal generator (18), and to couple this signal into the waveguide (12), wherein the sparsely distributed antenna arrangement (50) comprises an optical receiving unit (52) and an optical modulation unit (80, 49), wherein the optical receiving unit (52) is configured to receive the optical radar driver signal coupled into the waveguide (12) and to convert it into an electrical radar driver signal and to provide the electrical radar driver signal to the first radar transmitter (60), and the optical modulation unit (80, 49) is configured to provide optical radar response signals, which comprise radar echo signals received via the first and second radar receivers (42, 72) and the optical radar driver signal, and to couple these into the waveguide (12), wherein the central unit (10) further comprises a central optical receiving unit (30) designed to receive the optical radar response signals coupled into the waveguide (12), and - an evaluation unit (14) which is set up for this purpose: - to determine Doppler frequency information based on the radar echo signals received by the ULA structure (70) and the sequence of chirp signals, - to correct the radar echo signals received by the first radar receiver (42) based on the determined Doppler frequency information and - to evaluate the corrected radar echo signals and the radar echo signals received by the ULA structure (70) based on the sequence of chirp signals and to output radar information derived from this. [2] Radar system (100) according to claim 1, wherein the sparsely distributed antenna arrangement (50) comprises a second radar transmitter which is sparsely distributed with respect to the ULA structure (70), wherein the optical receiving unit (52) is configured to provide the electrical radar driver signal to the first radar transmitter (60) and the second radar transmitter such that a first chirp signal of the sequence of chirp signals is assigned to the first radar transmitter (60) and a second chirp signal of the sequence of chirp signals is assigned to the second radar transmitter. [3] Radar system (100) according to claim 2, wherein the evaluation unit (14) is configured to calculate an angle estimate to a target object based on the corrected radar echo signals received by the ULA structure (70) and on the sequence of chirp signals and to output the calculated angle estimate. [4] Radar system (100) according to one of claims 2 or 3, wherein the signal generator (18) is configured to reduce a chirp sweep time and / or a frequency bandwidth of the chirp signals of the ramp signal such that a time interval between the first chirp signals of adjacent sequences of chirp signals of the ramp signal is less than a predetermined maximum interval. [5] Radar system (100) according to one of the preceding claims, wherein the ULA structure (70) comprises a third radar receiver and the antenna arrangement (50) and / or the evaluation unit (14) is / are configured to coherently integrate the radar echo signals received simultaneously by the ULA structure (70) and to provide them as radar echo signals received by the ULA structure (70). [6] Method for operating a photonic radar system (100) comprising the steps: - Generating (102) a ramp signal with a sequence of chirp signals by a central processing unit (10), - Providing (104) an optical radar driver signal by the central unit (10), wherein the optical radar driver signal comprises an optical radar carrier signal and an optical ramp signal based on the generated ramp signal, - Coupling (106) of the optical radar driver signal into a waveguide (12) by the central unit (10), - Receiving and converting (108) the optical radar driver signal coupled into the waveguide (12) into an electrical radar driver signal by a sparsely distributed antenna arrangement (50) with a uniform linear array (ULA) structure (70), - Driving (110) a radar transmitter (60) of the ULA structure (70) with the electrical radar driver signal, - Receiving (112) radar echo signals with a first radar receiver (42) and a second radar receiver (72), wherein the first radar receiver (42) is sparsely distributed in relation to the radar transmitter (60) and the second radar receiver (72) is encompassed by the ULA structure (70), - Providing and coupling (114) optical radar response signals, comprising the radar echo signals received via the first and second radar receivers (42, 72) and the optical radar driver signal, into the waveguide (12) through the sparsely distributed antenna arrangement (50), - Receiving (116) the optical radar response signals coupled into the waveguide (12) by the central unit (10), - Determining (118) Doppler frequency information based on the radar echo signals received by the ULA structure (70) and the sequence of chirp signals, - Correcting (120) the radar echo signals received by the first radar receiver (42) based on the determined Doppler frequency information and - Evaluating (122) the corrected radar echo signals and the radar echo signals received by the ULA structure (70) based on the sequence of chirp signals and outputting radar information derived therefrom. [7] Central unit (10) for use in a photonic radar system (100) according to any one of claims 1 to 5, comprising: - a central optical receiving unit (30) designed to receive optical radar response signals coupled into the waveguide (12) and - an evaluation unit (14) which is set up for this purpose: - to determine Doppler frequency information based on radar echo signals received by a uniform linear array (ULA) structure (70) and a sequence of chirp signals, - to correct radar echo signals received by a first radar receiver (42) sparsely distributed in relation to the ULA structure (70) based on the determined Doppler frequency information and - to evaluate the corrected radar echo signals and the radar echo signals received by the ULA structure (70) based on the sequence of chirp signals and to output radar information derived from this. [8] Central processing unit (10) according to claim 7, further comprising: - a signal generator (18) configured to generate a ramp signal with a sequence of chirp signals and - an optical transmitting unit (20a) configured to provide an optical radar driver signal comprising an optical radar carrier signal and an optical ramp signal based on the ramp signal generated by the signal generator (18), and to couple this signal into a waveguide (12) that can be coupled to the central unit (10). [9] Method for operating a central processing unit (10) according to claim 7 or 8, comprising the steps: - Receiving (116) optical radar response signals coupled into the waveguide (12) by the central unit (10), - Determining Doppler frequency information based on radar echo signals received by a uniform linear array (ULA) structure (70) and a sequence of chirp signals, - Correction of radar echo signals received by a first radar receiver (42) sparsely distributed in relation to the ULA structure (70) based on the determined Doppler frequency information and - Evaluating the corrected radar echo signals and the radar echo signals received by the ULA structure (70) based on the sequence of chirp signals and outputting radar information derived therefrom. [10] The method of claim 9, further comprising the steps of: - Generating (102) a ramp signal with a sequence of chirp signals, - Providing (104) an optical radar driver signal comprising an optical radar carrier signal and an optical ramp signal based on the generated ramp signal, and - Coupling (106) of the optical radar driver signal into the waveguide (12).

Images