Photonic radar system comprising a simultaneous multipath monitoring unit

Abstract

The invention relates to a photonic radar system (100) with simultaneous multipath monitoring, comprising a central station (200) and a plurality of radar head devices (300-n) designed as transmitter and / or receiver modules, wherein individual optical transmission media (400-n) of the radar head devices (300-n) are each connected to a bidirectional optical one-to-multiple simultaneous distribution device (251), and a monitoring unit (600) comprises: a test signal generation unit (620) for generating a test signal having at least one modulated frequency ramp that varies monotonically at a constant rate; a detection unit (630); an evaluation unit (640); and a signal-guiding optical system which is designed to split the test signal generated by the test signal generation unit (620) into a test portion and a reference portion, to couple the test portion of the test signal into the bidirectional optical one-to-multiple simultaneous distribution device (251), and to out-couple the returned portion of the test signal to the detection unit (630) and to combine it, optically or electronically, with the reference portion of the test signal such that a difference signal is formed, wherein the evaluation unit (640) is designed to generate an OFDR spectrum (920) on the basis of the detected difference signal and to identify at least reflection components that can be associated with photonic components of the radar head devices (300-n), and to store and / or output their parameters as calibration information in a storage medium (670). The invention also relates to a method for operating such a radar system (100).

Description

[0001] Description

[0002] Photonic radar system with simultaneous multipath monitoring device

[0003] The invention relates to photonic radar systems, in particular multi-input multi-output (MIMO) systems, for environmental sensing, and especially for the environmental sensing of vehicles. Specifically, the invention relates to the diagnosis and calibration of such photonic radar systems.

[0004] Radar systems are defined as environmental detection systems that use electromagnetic radiation in the frequency range of 3 GHz to 300 GHz to determine the distance and speed of objects in the environment, and preferably also their angular orientation relative to the radar system, by emitting electromagnetic radiation in the frequency range of 3 GHz to 300 GHz and detecting the backscattered radiation. Radar systems, particularly historical ones, operating in lower frequency ranges are also known.

[0005] To achieve good angular resolution, the largest possible aperture is desirable. In a radar system, this can be increased by combining multiple transmitting and receiving antennas in an antenna array. The area covered by the antenna array determines the aperture size. It has proven advantageous to centralize signal generation and processing in a central station. Radar radiation is emitted via radar head units coupled to the antennas. These units simply amplify the radar signal information transmitted by the central station and, if necessary, multiply its frequency beforehand. The reflected or backscattered radar radiation is detected by the radar head units, and the corresponding echo signal information is transmitted back to the central station for processing.

[0006] If the transmission of radar signal information and echo signal information between the central station and the radar head units is optical, such a radar system is called a photonic radar system. The use of a central station to generate the radar signal information to be transmitted, and the use of optical transmission, further enables coherence between the radar signals emitted by the various transmitting antennas and the detected echo signal information transmitted back. For correct evaluation, among other things, precise knowledge of the travel time of the optical signals between the central station and the individual radar head units, which operate as transmit and receive modules, is necessary.

[0007] The radar head units, functioning as transmit and receive modules, are preferably implemented in an electronically-photonically cointegrated chip, a so-called EPIC. This enables the monolithic integration of photonic components, high-frequency electronics, and digital electronics on a single chip. The advantage lies in the fact that signal transmission can occur using optical signals in the terahertz (THz) range, onto which the radar signal information and echo signal information, preferably in the gigahertz (GHz) range, are modulated. In principle, designs with multiple microchips are also possible, in which photonic components and electronic components are implemented on separate chips.

[0008] Optical transmission links typically utilize fiber optics as their optical transmission medium. These fibers can change under adverse environmental conditions, such as temperature or humidity fluctuations, and / or be mechanically damaged or impaired. If such changes are ignored, they can interfere with and distort the data analysis.

[0009] US20220050187A describes devices and techniques for 3D LiDAR acquisition without beam scanning with moving parts, or for optical 2D imaging based on a combination of lens position-angle conversion and wavelength division multiplexing / demultiplexing (WDM) in the emitted test light of the LiDAR sensor. This 3D UDAR sensor technology can be implemented on stacked photonic integrated chips.

[0010] WO 2021 / 209604 A1 describes a fiber optic-based measurement system comprising a system for generating radiation with a monotonically tunable wavelength during the sweep periods, an optical path, and a detector connected to the radiation generation system via the optical path. The optical path includes the interferometer, which comprises the multiport element and the connected measurement optical fiber, sensitive to at least two environmental parameters. The mode excitation system is configured to excite at least the measurement mode with the first effective refractive index and the measurement mode with the second effective refractive index in the measurement optical fiber and exhibits different sensitivities to these two parameters.The measuring system includes the processing unit, to which the detector is connected via the analog-to-digital converter, and the processing unit is designed to generate the control signal for the radiation generation system.

[0011] US2017 / 0307473 A1 describes, among other things, methods and devices for the distributed measurement of at least one fiber bending or stress-related property along an optical path of a fiber under test. This involves the use of both a light input unit and a light output unit, which are connected to the fiber under test at a single end.

[0012] Calibration of lengths and monitoring of transmission media, especially during long-term operation of a photonic radar system with multiple radar head devices, remains unresolved.

[0013] The invention is therefore based on the objective of improving a radar system with regard to its calibration and diagnostic capabilities.

[0014] The invention is solved by a photonic radar system with the features of claim 1 and a method with the features of claim 8. Advantageous embodiments are set forth in the dependent claims.

[0015] Basic idea of ​​the invention

[0016] The invention is based on the idea of ​​equipping the phonic radar system, comprising a central station and a plurality of radar head units, with a monitoring device capable of determining at least the transmission times to the radar head units via the individual transmission media. For this purpose, it is proposed to implement optical frequency domain reflectometry (OFDR). To achieve rapid calibration, an optical test signal comprising at least one constant monotonous frequency ramp (i.e., onto which a constant monotonically increasing or constant monotonically decreasing frequency ramp is modulated) is transmitted simultaneously to the radar head units via all transmission media. An optical bidirectional one-to-multiple simultaneous distribution device is used for this purpose.This device is capable of simultaneously transmitting the test signal coupled to a single input to a plurality of transmission media connected to multiple outputs of the one-to-multiple simultaneous distribution unit. Each of these transmission media, preferably designed as fiber optics, is connected to a radar head unit configured as a transmit and / or receive module. Backscatter and / or reflections generated on the individual transmission media, including those caused at or within the radar head units, are transmitted back to the optical bidirectional one-to-multiple simultaneous distribution unit, combined into a common test signal, and then transmitted back to the single input.If this backscattered test signal is separated from the beam path and superimposed on the untransmitted current test signal, a difference signal is obtained. The frequencies of this difference signal are correlated, via the slope of the test signal's frequency ramp, with the travel times to the components or locations that caused the backscattering and / or reflections. This difference signal can be transformed into an OFDR spectrum. Within this specific OFDR spectrum, at least one structure, i.e., a frequency component, can be identified for each radar head, indicating the travel time of the optical signals to that particular radar head. These structures are identified, and their parameters are stored and used for calibration, configuration, and monitoring of the radar system.

[0017] Definitions

[0018] A photonic radar system is defined as a radar system comprising at least one, preferably several, radar head units connected to a central station. These units are configured as transmit and / or receive modules, and signal transmission between the central station and the radar head units is achieved via optical signals. Each radar head unit includes a radar antenna, which is referred to simply as an antenna. A group of several antennas arranged together in an antenna array is also called an antenna array. This array can also be considered a radar antenna with a large aperture, the size of which is determined by the dimensions of the antenna array.Signal generation and processing take place in a central station, which is connected to the radar head units via optical transmission media. Signal transmission between the central station and the radar head units is optical. This allows for coherence between the radar radiation emitted by the individual transmitting antennas and the radar echo information derived from the radar echo received by the receiving antennas at the central station. Radar signal information refers to signal information that characterizes radar radiation emitted by a radar head unit configured as a transmitting module. The radar signal information is often generated at a frequency two orders of magnitude lower than the actual transmission frequency and modulated onto an optical carrier signal for transmission to the radar head units.The radar head units, designed as transmitter modules, multiply the frequency and amplify the received radar signal information, which is separated from the optical carrier signal, before emission.

[0019] An optical bidirectional one-to-multiple simultaneous distribution device is an optical component that establishes, or can establish, a bidirectional optical connection simultaneously between a single optical port, referred to here as a single input, and multiple other ports, referred to here as multiple outputs. Such a one-to-multiple simultaneous distribution device can be implemented using a one-to-multiple beam splitter.

[0020] A one-to-multiple switch in which a bidirectional optical connection exists between only one input and one of the outputs at any given time is indeed an optical bidirectional one-to-multiple distribution device, but not a one-to-multiple simultaneous distribution device.

[0021] Passive bidirectional transparent coupling is defined as an optical coupling that does not include any components that actively generate optical signals. Furthermore, this coupling must allow the transmission of optical signals in both directions. A splice in an optical transmission medium, for example, represents such a passive bidirectional transparent coupling. A coupling in which the optical signal is first converted into an electronic signal and then back into an optical signal does not constitute passive bidirectional transparent coupling, even if bidirectional transmission of optical signals would be possible in this way.

[0022] Preferred embodiments

[0023] A photonic radar system with simultaneous multi-path monitoring is created, comprising: a central station and a plurality of radar head units configured as transmit and / or receive modules, each of the radar head units being connected to at least one individual optical transmission medium, the central station being configured to generate radar signal information and modulate it onto an optical carrier signal and transmit it to the radar head units via an optical distribution device, and to capture and jointly evaluate radar echo information modulated onto an optical carrier signal by means of a detection device, the radar head units being configuredto convert the radar signal information modulated onto the optical carrier signal into an electrical radar signal and to transmit it as radar radiation and / or to receive the radar echo radiation reflected from objects in the vicinity of the radar system and to extract radar echo information and modulate it onto the optical carrier signal for return transmission to the central station, characterized in that the individual optical transmission medium of the radar head devices are each connected to a bidirectional optical one-to-multiple simultaneous distribution device and a monitoring device is a,

[0024] A test signal generation device for generating a test signal onto which at least one constantly monotonically changing frequency ramp is modulated comprises a detection unit and an evaluation unit as well as a signal guidance optic, wherein the signal guidance optic is configured to split the test signal generated by the test signal generation device into a test component and a reference component, to couple the test component of the test signal into the bidirectional optical one-to-multiple simultaneous distribution device, and to couple the test signal component transmitted back to the detection unit and to optically superimpose it with the reference component of the test signal in the detection unit, so that a difference signal is detected by the detection unit, and wherein the evaluation unit is configured to generate an OFDR spectrum on the basis of the detected difference signal and to identify at least reflection components that can be attributed to photonic components of the radar head devices.to identify and determine their parameters and store and / or output them as calibration information in a storage medium.

[0025] Furthermore, a method for operating a photonic radar system with simultaneous multipath monitoring is proposed, wherein the photonic radar system comprises a central station and a plurality of radar head devices configured as transmit and / or receive modules, each of the radar head devices being connected to at least one individual optical transmission medium, wherein the method comprises the steps of: generating a test signal onto which at least one constantly monotonically changing frequency ramp is modulated,

[0026] Splitting the test signal into a test component and a reference component, coupling the test component of the test signal into an optical bidirectional one-to-multiple simultaneous distribution device in order to transmit the test signal simultaneously to the majority of the radar head units via the transmission media connected to them, combining the test signal components transmitted back to the bidirectional optical one-to-multiple simultaneous distribution device into a transmitted test signal and optically superimposing the transmitted test signal with the reference component of the test signal to form an optical difference signal, acquiring the difference signal and generating an OFDR spectrum as well as determining parameters of the structures of the OFDR spectrum correlated with the radar head units and transmission media and storing the parameters as calibration information in a memory and / or outputting the calibration information.

[0027] The advantage of the proposed solutions is that a single measurement simultaneously captures all relevant parameters relating to signal propagation times on the transmission media to the radar head units, which are necessary for the calibration of the radar system. It is understood by those skilled in the art that a single measurement here does not necessarily refer to the measurement results acquired during the transmission of a single frequency ramp of the test signal. Rather, an averaging over a longer period or multiple frequency ramps in the test signal can be performed.

[0028] The evaluation can use algorithms that are known from the evaluation of frequency modulated continuous wave radar signals (FMCW).

[0029] Not only defects in the radar head devices, but also changes in the optical network are evaluated and recorded.

[0030] It should be noted that not all radar head units need to be directly connected to the one-to-multiple simultaneous distribution unit. Indirect bidirectional optical connections are also possible, i.e., further distribution units in the optical network. However, it is essential that a bidirectional optical connection exists simultaneously to all monitored components. In a preferred embodiment of the photonic radar system, the lengths of the transmission media are coordinated so that the propagation times to the various radar head units are different in pairs and do not coincide with propagation times to other points in the OFDR spectrum that trigger a characteristic feedback structure in the OFDR spectrum of one of the other transmission media.This ensures that for each radar head, at least one characteristic structure appears in the common OFDR spectrum, which correlates with the travel time of optical signals to the respective radar head. This makes it possible to reliably attribute changes to individual transmission media and to quickly and unambiguously detect the failure of individual radar heads by simply assigning the relevant structures in the OFDR spectrum to the radar heads.

[0031] If the lengths are not matched, it can happen that two or more radar head units develop their characteristic structure at the same frequency of the OFDR spectrum. While the transit time to these radar head units can be determined, changes in the attenuation behavior for individual radar head units, changes in transit time to individual radar head units, or even a fiber break may not be detected and / or cannot be reliably attributed to the correct radar head unit.

[0032] In addition to the propagation times and frequencies that can be derived from the OFDR spectrum, the associated backscatter amplitudes can also be evaluated for the individual structures. Parameters derived from this can also be saved as calibration information. Changes in the backscatter amplitudes indicate a change in the attenuation of the signal transmission to the associated radar head.

[0033] In a preferred embodiment, the radar head devices are at least partially connected to the detection device of the central station via a back-transmission medium, in addition to the transmission medium. A passive, transparent, bidirectional coupling exists between the transmission medium and the back-transmission medium. The evaluation device is configured to identify backscattered pulses from the couplings of the back-transmission media with the detection device of the central station in the derived OFDR spectrum and to store and / or output their parameters as calibration information. It is understood by those skilled in the art that the calibration information can include information from any component of the optical network and is, of course, used not only for calibrating the radar system but also for monitoring it.Radar head units, at least those configured as receiver modules, are connected to the central station via a return transmission medium for the transmission of radar echo information. For this purpose, the radar echo information is modulated onto the carrier signal provided by the central station. Within the radar head unit, a bidirectional, transparent passive connection exists between the transmission medium and the return transmission medium, allowing the return transmission media to be monitored simultaneously with the transmission media at a suitably selected test signal intensity. This eliminates the need for separate diagnostic and / or calibration measurements for the return transmission media, which are also preferably designed as optical fibers.

[0034] A further development of the procedure therefore provides that the parameters of structures are additionally determined and stored and / or output as calibration information in the memory, which are correlated with reflections or backscattering at the detection device of the central station, to which the test signal is transmitted via back transmission media coupled transparently with the transmission media in the radar head devices.

[0035] In some embodiments, the optical distribution device of the central station comprises a bidirectional optical one-to-multiple simultaneous distribution device, preferably designed as a one-to-multiple beam splitter. This distribution device is also used to transmit the carrier signal and, optionally, information modulated thereon to the radar head units. This allows for a particularly compact design of the radar system.

[0036] In some embodiments, the monitoring device and its components are entirely integrated into the central station. For example, the laser-type signal generation device and a modulator used to generate the optical carrier signal and to modulate radar signal information onto this carrier signal can also be used to generate the test signal. Similarly, at least some components of a detection device and an evaluation device from the central station can be used for the acquisition unit and the evaluation device. If necessary, slight modifications to the beam guidance optics for the test signal are required to optically superimpose the returned test signal and the currently transmitted test signal in the acquisition unit or electronically in the evaluation device to form the difference signal.

[0037] In another embodiment, the monitoring device is structurally separate from the central station and is optically coupled bidirectionally to the optical bidirectional one-to-multiple simultaneous distribution device in the central station. This allows the device to transmit the test signal to the one-to-multiple simultaneous distribution device and to receive the returned test signal. An advantage of this configuration is that the components required for diagnostics are protected, in particular, from the thermal load generated in the central station due to the high computing power required by the processor(s) used there. Adverse effects caused by thermal effects during measurement can thus be eliminated or at least reduced. Furthermore, the system's ease of maintenance is improved.Furthermore, diagnostics and monitoring of the radar system are possible in parallel with its use for environmental sensing by employing frequency or wavelength division multiplexing. In frequency division multiplexing, the test signal is generated at a different frequency than the carrier signal used for signal transmission between the central station and the radar head.

[0038] Frequency or wavelength division multiplexing for the purpose of simultaneous monitoring / diagnosis can also be used in embodiments that are fully integrated into the central unit if an additional source for generating an optical signal is provided in the central unit.

[0039] In another embodiment, the monitoring device is structurally separate from the central station and comprises the optical bidirectional one-to-multiple simultaneous distribution device to which the transmission media of the radar head units are connected. The radar head units are additionally connected to the central station via further optical transmission media for transmitting the carrier signal. This allows the optical verification to be almost completely separated from the function of the photonic radar system during environmental sensing and thus performed simultaneously with environmental sensing. A link is still maintained via calibration. This improves the modularity of the monitoring device, allowing individual components of the monitoring device to be renewed and replaced separately from the components required for radar operation.

[0040] In this embodiment, each transmission medium used for diagnostics and monitoring is paired with a further transmission medium used for environmental sensing. This allows length changes in individual transmission media to be transmitted to their respective secondary transmission media. Systematic differences, such as slightly varying lengths between the transmission media and their secondary transmission media, can be calibrated during the radar system's manufacturing process and stored as calibration information in the calibration file.

[0041] The transmission media and other transmission media are then preferably laid parallel and close together, so that they are exposed to the same environmental influences. Particularly preferably, the transmission media connected to the monitoring device are arranged externally in a fiber strand, so that external damage occurs during operation of the monitoring device before it affects environmental monitoring. With these systems, there are no time gaps in environmental monitoring that would otherwise occur with intermittent monitoring and diagnostics.

[0042] In this embodiment, at least in some wheel head units, the transmission media can be coupled with return transmission media used for diagnostics. These are arranged in parallel to additional associated return transmission media used for transmission back to the central station during environmental sensing. This allows all relevant transmission durations to be reliably determined and monitored.

[0043] Preferably, the evaluation unit is designed to compare previously stored calibration information with the currently determined calibration information and, if deviations are detected, to trigger an adjustment of the radar system's calibration. Depending on the type of deviation, a reconfiguration or complete re-configuration of the radar system may also be necessary, for example, in the event of a radar head failure. If changes occur in the signal propagation times, the signal generation and signal processing can be adjusted accordingly. The same applies if changes in the attenuation of the transmitted signals occur based on the determined backscatter signal strengths.If the failure of one or more radar head units is detected, for example, because the structures associated with the radar head unit(s) no longer appear in the OFDR spectrum or because new, strong backscatter structures indicating a fiber break are present, this can be signaled to the central station and, if applicable, other vehicle systems that use the information provided by the radar system. This signals that the provided information and data are no longer valid. This increases redundancy in fault detection, which is particularly important for autonomous driving.

[0044] It is therefore preferably provided that the previously determined calibration information is read from the memory and compared with the currently determined calibration information, and if a change is detected, an adjustment of the configuration of the radar system and / or a calibration is carried out.

[0045] In principle, diagnostics and monitoring significantly improve fault detection and enhance road safety. In particular, simultaneous or intermittent diagnostics and environmental monitoring can also improve the reliability of other vehicle systems, firstly through better and more accurate environmental monitoring and secondly through the early detection of invalid data. This increases the road safety of the vehicle, which utilizes the data and information gathered during environmental monitoring.

[0046] The invention is explained in more detail below with reference to a drawing. The drawing shows:

[0047] Fig. 1 shows a schematic view of a photonic M1 MO radar system with a

[0048] Monitoring device;

[0049] Fig. 2a - 2c shows a schematic front, side and rear view of a motor vehicle with the positions of radar antennas shown;

[0050] Fig. 3 shows a schematic representation of an OFDR spectrum and an associated highly simplified fiber network of a photonic radar system;

[0051] Fig. 4 a schematic flowchart of a method for operating a photonic radar system with monitoring functionality; Fig. 5 a schematic representation of a photonic M1 MO radar system in which the monitoring device is structurally separate from the central station;

[0052] Fig. 6 shows a schematic representation of a photonic M1 MO radar system in which the monitoring device is completely structurally separate from the central station.

[0053] 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 units 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 460 and individual electronic return line 560.

[0054] For the sake of simplicity, in the embodiment described here, it is assumed that all radar head units 300, 300-n are coupled to a transmission medium 400, 400-n and a return transmission medium 500. However, radar head units designed solely as transmitter modules are generally not coupled to a return transmission medium. This simplification also applies to the other embodiments described here. Radar head units can therefore also have only an optical connection without this affecting the described solution.

[0055] Lowercase letters -n ... stand for natural numbers to indicate countability and distinguishability of the corresponding objects.

[0056] 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. The radar signal information is, for example, a frequency-modulated continuous wave (FMCW) signal intended for transmission, divided by a factor of eight.The modulation device is, for example, configured as a Mach-Zehnder modulator (MZM). The optical signal is forwarded via an optical control device 240 to a distribution device 250. In the illustrated embodiment, the distribution device 250 comprises a one-to-multiple simultaneous distribution device 251, which is, for example, configured as a 1:N beam splitter. In the one-to-multiple simultaneous distribution device 251, simultaneous, i.e., concurrent, optical bidirectional connections are formed between the single input 252 and all multiple outputs 255, 255-n, preferably configured as fiber outputs. This allows the carrier signal coupled into the single input 252 to be transmitted simultaneously to all radar head devices 300, 300-n via the transmission media 400, 400-n, which are connected to the multiple outputs 255, 255-n. The transmission media 400, 400-n are the optical waveguides 401, 401-n, i.e.preferably optical fibers 402, 402-n.

[0057] Which of the radar head units 300, 300-n converts and emits the transmitted radar signal information into radar radiation can be controlled, for example, via the electronic control line 460.

[0058] 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 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 and the detection device 260 of the central station 200.

[0059] 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 and often its frequency is also multiplied in the radar head unit 300, 300-n, and then emitted as electromagnetic radiation from the corresponding antenna 350, 350-n of the radar head unit 300, 300-n as a radar signal.

[0060] 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 of the radar head units 300, 300-n or by several antennas 350, 350-n of several radar head units 300, 300-n. In a mixing process, radar echo information is usually derived from the radar echo signal and generated and processed as an intermediate frequency signal, and then optically modulated onto the carrier signal transmitted by the radar head unit 300, 300-n and transmitted back to the central station 200 via the corresponding return transmission medium 500, 500-n.

[0061] In the central station 200, the radar echo information is separated from the optical carrier signal and converted into an electrical signal in a detection unit 260 during conversion into an electronic signal. The radar echo information received via the various return transmission media 500, 500-n is evaluated together in a processing unit 270 of the central station 200 to determine the distance, relative velocity, and relative angular position of individual objects in the environment. Upon transmission to the processing unit 270, electrical signals can be digitized in a digitizing unit 280 and pre-processed in a processing unit 290, for example, by undergoing a Fourier transform, which can be implemented in special modules.

[0062] Figures 2a to 2c schematically illustrate a possible distribution of the radar head units with their antennas on a motor vehicle 1000. This enables nearly 360° surround detection with high angular resolution. Figure 2a schematically shows the front of the vehicle 1000 1002 (Figure 2a), Figure 2b shows its left side 1004, and Figure 2c shows its rear 1006. The right side of the vehicle is not shown here but is preferably designed analogously to the left side 1004.

[0063] The diagram shows schematic small antenna symbols 1100, which indicate the positions of radar head units. On the front 1002 of the vehicle 1000, these are arranged, for example, at intervals between them, on a lower edge 1012 of a windshield 1010 and on a left side edge 1014 of the windshield (viewed from the front), essentially vertically spaced apart. Additionally, radar head units 1100 are also arranged horizontally spaced apart along a front bumper 1020.

[0064] On the left side 1004 of the vehicle 1000, shown in Fig. 2b, radar head units 1100 are arranged horizontally spaced apart from one another along a sill 1050, and radar head units 1100 are also arranged horizontally spaced apart from one another along a roof edge 1030. Additionally, radar head units are arranged substantially vertically spaced apart from one another along a B-pillar 1040.

[0065] On the rear side 1006, shown in Fig. 2c, the antenna symbols 1100, representing the radar head devices, are arranged horizontally spaced apart from each other along the rear bumper 1070 and horizontally and vertically spaced apart from each other along a lower side edge 1064 of the rear window 1060 along the left side edge 1066 of the rear window 1060 as seen from the rear.

[0066] The operating state of the environmental detection system is only simplified and briefly presented here and is known to those skilled in the art for a photonic radar system with a plurality of radar head devices designed as transmitting and / or receiving modules.

[0067] The embodiment shown in Fig. 1 also includes a monitoring device 600, which is distributed across various components of the central station 200. A monitoring control unit 610 is integrated into the control unit 210. This unit controls the alternative, preferably alternating, operation in the environmental detection operating state and the monitoring operating state. In a monitoring operating state, the monitoring control unit 610, integrated into the control unit 210, ensures that a test signal generation unit 620 is formed by means of the laser 220 and the modulation unit 230. In monitoring mode, an optical test signal is generated and provided.

[0068] The test signal is generated as an optical carrier signal with at least one superimposed, constantly monotonically changing frequency ramp, preferably with several successive ramps. The duration of a single frequency ramp is greater than twice the maximum transmission duration of an optical pulse that can occur in the photonic radar system 100 (without reflections). A pulse that is coupled, for example, into a transmission medium 400n at the central station 200 can propagate through the radar head assembly 300n and via the return transmission medium 500n back to the central station 200. The duration of a frequency ramp must therefore be greater than twice the sum of the transmission durations over the longest transmission medium 400n and the longest return transmission medium 500n.Additionally, time buffers are taken into account for the operating times in the central station 200 and / or the monitoring facility 600 as well as in the radar head unit 300.

[0069] An insertion 800 schematically represents an exemplary frequency ramp signal 810. Graphically, the frequency 811 is plotted against the time 812.

[0070] The test signal propagates simultaneously in the transmission media 400, 400-n and is partially reflected or backscattered at least at the radar head units 300, 300-n. The reflected and / or backscattered test signal components are combined in the one-to-multiple simultaneous distribution unit to form a back-transmitted test signal and output at the single input 252. In an optical control unit 240, for example a circulator, the back-transmitted test signal is extracted and optically superimposed in the detection unit 630 with a reference component of the currently generated test signal, for example separated at the modulator.

[0071] This is shown schematically in inset 820 in the frequency diagram. The diagram schematically shows the test signal 830 (dashed line), generated by reflection from a point in the optical network, for example at a radar head, and transmitted back, together with the reference component of the test signal 840 (solid line). A frequency 811 is plotted against time 812. Inset 860 shows the difference signal 870 resulting from the optical superposition in the time diagram. The amplitude 861 is plotted against time 812. It is understood that in a real-world scenario, the difference signal contains many different frequency components.

[0072] The differential signal is converted into an electrical signal in the detection unit. A converter, such as a photodiode, which is otherwise used to convert radar echo information, can be used for this purpose.

[0073] The signal is then preferably digitized in the digitizing unit 280 and transformed into the frequency domain in a processing unit 290, for example by means of a Fourier transform. For this purpose, time transients from several frequency ramps can be added or averaged.

[0074] It is also possible to implement embodiments in which no optical superposition takes place and the transmitted test signal is captured and electronically superimposed with the current test signal, for example the separately captured signal of the reference component, in the evaluation unit 640 or in the acquisition unit 630 to generate the difference signal.

[0075] Figure 3 schematically depicts an OFDR spectrum 920 together with a highly simplified fiber network 950 of a radar system 100, schematically indicated above it. An amplitude 911, which can be associated with an intensity of the backscattered test signal, is plotted against time 912. The structures observed in the OFDR spectrum can be assigned to components of the fiber network 950.

[0076] At the first connector 965 of the OFDR measuring device 960, a first significant coupling loss occurs, manifested as a distinct amplitude drop 925. A further coupling loss, accompanied by another amplitude drop 930, correlates with a splice 970 in the fiber network 950. At another connector 975, a reflection occurs, recognizable as a distinct amplitude peak 935 in the OFDR spectrum. At the bidirectional one-to-multiple simultaneous distribution device, configured as a beam splitter 980, a reflection and a further insertion loss occur, recognizable in the OFDR spectrum as an amplitude peak 940 followed by an amplitude drop. The individual radar head units 985, 985-n can be identified by their amplitude peaks 945, 945-n.The individual fiber lengths between the beam splitter 980 and the radar head units 985 are all selected to be of different lengths, so that for each radar head unit 485-n, an amplitude peak 495-n can also be detected in the OFDR spectrum. The propagation speed in the transmission media correlates the propagation time with the distance of the component causing the structure from the OFDR measuring unit 960. In the evaluation unit 640, which is implemented, for example, in the computing unit 270 of the central station 200, the individual parameters such as signal propagation times, occurring attenuation losses, etc., are determined and stored as calibration information in a calibration file.The information required to assign the individual structures in the OFDR spectrum to radar head devices 985, 985-n and other components of the resulting fiber network 950 is preferably stored in the calibration file during manufacturing, which is then updated and supplemented by the monitoring device 600 during further OFDR measurements.

[0077] Fig. 4 shows a highly simplified schematic representation of the operating procedure of a photonic radar system with a monitoring device as a flowchart 2000.

[0078] The radar system can be operated in an environmental detection state, corresponding to radar operation, and in a monitoring state. In some embodiments that use frequency division multiplexing or have a structurally separate design of the monitoring unit from the central station, both operating states can be assumed simultaneously. Here, an embodiment is described in which the operating states are assumed alternatively, optionally interleaved in time.

[0079] When the photonic radar system is activated, it first switches to the monitoring operating state 2100. Other embodiments may begin with the environment sensing operating state.

[0080] Next, a calibration file is loaded (2200), containing information about the radar system and previously performed diagnostic steps, in particular monitoring parameters for the individual radar head units of the radar system, as calibration information. An OFDR measurement is then performed simultaneously on all radar head units of the radar system, the corresponding transmission parameters are determined, and the calibration information is derived from these (2300).

[0081] Then the derived transmission parameters and calibration information are evaluated for anomalies and / or deviations from the known information in the calibration file and checked to see if the radar system is functioning correctly.

[0082] If this is not the case, the processing unit and / or the control unit of the central station is notified, so that an adjustment of the radar system is made, which is also referred to as reconfiguration or reconfiguration. This results, for example, in changes to the radar signal information generation, modifications in signal processing, etc. 2500. Furthermore, the calibration file is adjusted accordingly and the procedure continues with the loading of the calibration file. 2200.

[0083] If, however, it is determined in process step 2400 that no anomalies or deviations are present, then in step 2600 it is checked whether the calibration of the radar system is up to date.

[0084] If the calibration is not up-to-date, a calibration of the radar system is initiated (2700) and the calibration file is adjusted accordingly, and the procedure continues with the loading of the calibration file (2200).

[0085] If, however, it is determined in process step 2600 that the calibration is up to date, the system switches to the environmental sensing operating state 2800. The radar system's control unit then preferably re-initiates the monitoring operating state at intervals.

[0086] Figure 5 schematically illustrates another embodiment of a radar system with a monitoring device 600. Identical technical features are designated with the same reference numerals in all figures. In the embodiment according to Figure 5, the individual components of the monitoring device 600 are designed separately from the central station 200 and its components. The monitoring device 600 includes a test signal generation unit 620, which preferably comprises a laser and a modulation unit for generating the frequency ramps. The test signal is routed via an optical control unit 650 to an output 605 of the monitoring device 600. This output is connected via a fiber optic cable 607 to the one-to-multiple simultaneous distribution unit 251 of the central station 200.The optical control unit 650 in the monitoring unit 600 is configured to extract the back-transmitted test signal from the beam path and optically superimpose it with the currently generated test signal on a converter in the acquisition unit 630, where the resulting differential signal is acquired. As described above, the electrical differential signal is digitized and transformed into an OFDR spectrum and evaluated accordingly by the evaluation unit 640. Alternatively, the back-transmitted test signal can also be acquired and electronically superimposed with the test signal to generate the differential signal. The calibration information is stored in a memory 670, which the central station 200 can access. Alternatively or additionally, a copy can be transmitted to the central station.If a deviation occurs that requires a new configuration or calibration of the radar system, this is signaled to the central unit with the required calibration information, and a new configuration and / or calibration of the radar system is initiated and carried out.

[0087] This embodiment is suitable for generating the test signal with a different optical frequency than the carrier signal in the central station. The OFDR measurement can thus be performed simultaneously with the environmental sensing in frequency-division multiplexing mode. Optionally, filter elements can be provided in the converter components of the radar head units and the detection unit to prevent the test signal from interfering with the radar operation, i.e., the environmental sensing.

[0088] Figure 6 shows another embodiment in which the monitoring device 600" is completely separate from the central station 200. In addition to transmission media 400, 400-n and, optionally, optically coupled return transmission media 500, 500-n in the radar head devices, via which the test signals are transmitted, at least further transmission media 450, 450-n and further return transmission media 550, 550-n are provided between the central station 200 and the radar head devices 300, 300-n, via which the radar signal information and the radar echo signal information are transmitted and returned.

[0089] To distribute the test signal to the transmission media 400, 400-n, the monitoring device 600 itself comprises an optical distribution device 660 designed as a one-to-multiple simultaneous distribution device, which can be a multi-splitter. In this embodiment, the necessary calibration information is transmitted directly from the monitoring device 600 to the processing unit 270 of the central station 200. The advantage of this embodiment is that parallel operation in a monitoring mode and in an environmental sensing mode is possible, and multiplexing solutions are not required. Deviations between the transmission media 400-n and corresponding further transmission media 450-n, as well as between the return transmission media 500-n and the further return transmission media 550-n, can be measured and taken into account during the assembly of the corresponding fibers.This information is stored in the calibration file.

[0090] It will be understood by those skilled in the art that only exemplary embodiments are described here. The features shown in the different embodiments can be used in any combination to implement the invention.

[0091] Reference symbol list for photonic radar system

[0092] Central station

[0093] Control unit

[0094] Light source (laser)

[0095] Modulation device optical control device

[0096] Distribution system

[0097] One-to-multiple simultaneous distribution device

[0098] Single input, 255-n multiple output

[0099] Detection device

[0100] Unit of calculation

[0101] Digitization facility

[0102] Processing unit, 300-n radar head unit, 305-n fiber input electronic-photonic integrated circuit (EPIC), 350-n antenna, 395-n fiber output, 400-n transmission medium, 401-n optical fiber, 402-n fiber, 450-n further transmission medium electronic control line, 500-n return transmission medium, 501-n optical fiber, 502-n fiber, 550-n further return transmission medium electronic return line monitoring unit output

[0103] Connecting fiber 10 Monitoring control unit 20 Test signal generation unit 30 Acquisition unit 40 Evaluation unit 50 Optical control unit 60 Optical distribution unit 70 Memory 00 Insertion 10 Frequency ramp signal 11 Frequency 12 Time 20 Insertion 30 Backtransmitted test signal 40 Reference component of the test signal 60 Insertion 61 Amplitude 70 Differential signal 11 Amplitude 12 Time 20 OFDR spectrum 25 Amplitude drop

[0104] 930 further amplitude drop

[0105] 935 Peak amplitude

[0106] 945, 945-n amplitude peaks

[0107] 950 fiber network

[0108] 960 OFDR measuring device

[0109] 965 first connector

[0110] 980 beam splitters

[0111] 985, 985-n radar head units

[0112] 1000 motor vehicles

[0113] 1002 Front

[0114] 1004 Toad Page

[0115] 1006 reverse

[0116] 1100 Antenna symbol

[0117] 1010 Windscreen

[0118] 1012 bottom edge 1014 left side edge

[0119] 1020 front bumper

[0120] 1030 Roof edge

[0121] 1040 B-pillar

[0122] 1050 sills

[0123] 1060 Rear window

[0124] 1064 lower side edge

[0125] 1070 rear bumper

[0126] 1100 Antenna symbol

[0127] 2000 Flowchart

[0128] 2100 Switch to monitoring operating mode

[0129] 2200 Loading calibration file

[0130] 2300 OFDR measurement

[0131] 2400 Functionality test

[0132] 2500 Radar system adjustment

[0133] 2600 Is calibration up to date?

[0134] 2700 Bump Calibration

[0135] 2800 Change to environmental sensing operating state

Claims

Patent claims 1. Photonic radar system (100) with simultaneous multipath monitoring device comprising a central station (200) and a plurality of radar head units (300, 300-n) configured as transmit and / or receive modules, wherein each of the radar head units (300, 300-n) is connected to at least one individual optical transmission medium (400, 400-n), wherein the central station (200) is configured to generate radar signal information and modulate it onto an optical carrier signal and transmit it via an optical distribution device (250) to the radar head units (300, 300-n) and to detect and jointly evaluate radar echo information modulated onto an optical carrier signal by means of a detection device (260), wherein the radar head units (300, 300-n) are configuredto convert the radar signal information modulated onto the optical carrier signal into an electrical radar signal and to emit it as radar radiation and / or to receive the radar echo radiation reflected from objects in the vicinity of the radar system (100) and to extract radar echo information and to modulate it onto the optical carrier signal for return transmission to the central station (200), characterized in that the individual optical transmission media (400, 400-n) of the radar head devices (300, 300-n) are each connected to a bidirectional optical one-to-multiple simultaneous distribution device (251) and a monitoring device is a, The test signal generation device (620) for generating a test signal onto which at least one constantly monotonically changing frequency ramp is modulated, and a corresponding reference signal, comprises a detection unit (630) and an evaluation device (640) as well as a signal guidance optic (650), wherein the signal guidance optic is configured to divide the test signal generated by the test signal generation device (620) into a test component and a reference component, and to divide the test component of the test signal into the bidirectional optical to couple to the one-to-multiple simultaneous distribution device (251), and to couple the test signal component transmitted back from the bidirectional optical one-to-multiple simultaneous distribution device (251) to the detection unit (630), wherein either the transmitted test signal component is optically superimposed with the reference component of the test signal in the detection unit (630) so that a differential signal is detected by the detection unit (630), or the transmitted test signal component is detected in the detection unit (630) and electronically superimposed with the reference component of the test signal to generate a differential signal, wherein the evaluation device is configured to generate an OFDR spectrum (920) on the basis of the detected or generated differential signal and to identify at least reflection components that can be attributed to photonic components of the radar head devices (300, 300-n).to identify and determine their parameters and store and / or output them as calibration information in a memory (670).

2. Photonic radar system (100) according to claim 1, characterized in that the lengths of the transmission media are matched to each other, so that the transit times to the different radar head devices (300, 300-n) are each pairwise different and do not coincide with transit times to other points of one of the other transmission media (400, 400-n) that trigger a characteristic back transmission structure in the OFDR spectrum (920).

3. Photonic radar system (100) according to claim 1 or 2, characterized in that the radar head devices (300, 300-n) are at least partially connected to the detection device of the central station (200) by means of a back transmission medium in addition to the transmission medium (400, 400-n), wherein a passive transparent bidirectional coupling exists between the transmission medium (400, 400-n) and the back transmission medium, and the evaluation device (640) is configured to also identify backscatter pulses from the couplings of the back transmission media (500, 500-n) with the central station (200) in the derived OFDR spectrum (920) and to store their parameters as calibration information.

4. Photonic radar system (100) according to one of the preceding claims, characterized in that the optical distribution device of the central station (200) comprises the bidirectional optical one-to-multiple distribution device (251).

5. Photonic radar system (100) according to claim 4, characterized in that the monitoring device (600) is structurally separate from the central station (200) and is bidirectionally optically coupled to the central station (200) in order to transmit the test component of the test signal to the central station (200) and to receive the test signal transmitted back.

6. Photonic radar system (100) according to one of claims 1 to 3, characterized in that the monitoring device (600) is structurally separate from the central station (200) and the monitoring device (600) comprises the optical bidirectional one-to-multiple simultaneous distribution device (251) with which the transmission media (400, 400-n) of the radar head devices (300, 300-n) are connected, wherein the radar head devices (300, 300-n) are additionally connected to the central station (200) via further optical transmission media (400, 400-n) for transmitting the carrier signal.

7. Photonic radar system (100) according to one of the preceding claims, characterized in that the evaluation device (640) is configured to compare the previously stored calibration information with the currently determined calibration information and, in the event of a detection of deviations, to trigger an adjustment of the configuration and / or the calibration of the radar system (100).

8. Method for operating a photonic radar system (100) with simultaneous multipath monitoring, wherein the photonic radar system (100) comprises a central station (200) and a plurality of radar head devices (300, 300-n) configured as transmit and / or receive modules, wherein each of the radar head devices (300, 300-n) is connected to at least one individual optical transmission medium (400, 400-n), wherein the method comprises the steps: Generating a test signal onto which at least one constantly monotonically changing frequency ramp is modulated, Splitting the test signal into a test component and a reference component, coupling the test component of the test signal into an optical bidirectional one-to-multiple simultaneous distribution device (251) in order to transmit the test signal simultaneously to the majority of the radar head devices (300, 300-n) via the transmission media (400, 400-n) connected to them, combining the signals to the bidirectional optical one-to-multiple simultaneous distribution device (251) backtransmitted test signal components to a backtransmitted test signal and either optical superposition of the backtransmitted test signal with the reference component of the test signal to form an optical difference signal, detection of the difference signal or detection of the backtransmitted test signal and electronic superposition of the detected backtransmitted test signal with an electronic electrical signal representing the reference component of the test signal to generate the difference signal and generate an OFDR spectrum (920) as well as determining parameters of the structures of the OFDR spectrum (920) correlated with the radar head devices (300, 300-n) and storing the parameters as calibration information in a memory and / or outputting calibration information.

9. Method according to claim 8, characterized in that the parameters of structures are additionally determined and stored and / or output as calibration information in the memory (670), which are correlated with reflections or backscattering at the central station (200), to which the test signal is transmitted via back transmission media (500, 500-n) coupled transparently with the transmission media in the radar head devices (300, 300-n).

10. Method according to claim 8 or 9, characterized in that the previously determined calibration information is read from the memory (670) and compared with the currently determined calibration information and, if a change is detected, an adjustment of the configuration and / or calibration of the radar system (100) is made.

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