Photonic radar system with OFDR fibre length measurement for calibration

Abstract

The invention relates to a photonic radar system (100) and to a method for operating a photonic radar system (100) that includes monitoring transmission characteristics, wherein the photonic radar system (100) comprises a central station (200) and at least one radar head device (300, 300-n) which is designed as a transmitter and / or receiver module and which is connected to at least one individual optical transmission medium (400, 400-n), wherein signals exchanged for environmental sensing are modulated onto at least one optical carrier signal generated by the central station, wherein the method comprises the following steps: - generating a test signal having at least one frequency ramp that varies monotonically, preferably at a constant rate; - generating a reference signal that corresponds to the test signal; - coupling the test signal into the at least one transmission medium (400, 400-n); - out-coupling a returned portion of the test signal to a detection unit (630); and either - optically combining the returned test signal with the reference signal of the test signal in order to form an optical difference signal and detecting the difference signal, or alternatively, - detecting the returned test signal and electronically combining the detected returned test signal with the reference signal to produce the difference signal; - generating an OFDR spectrum (920) on the basis of the difference signal; and - determining parameters of at least the structures of the OFDR spectrum (920) that are correlated with the radar head devices (300, 300-n), and storing the parameters as calibration information in a memory (670) and / or outputting the calibration information.

Description

[0001] Description

[0002] Photonic radar system with OFDR fiber length measurement for calibration

[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 transmitter and receiver modules, is necessary.

[0007] The radar head units, functioning as transmitter and receiver 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] US Patent 10,686,523 B1 describes a photonic integrated circuit (PIC) with a common architecture for powering both optical and RF phased arrays to generate steerable, co-aligned optical and RF beams from a single chip. The PIC can be used for orientation, mobile data links, autonomous vehicles, and SG cellular communications. On the PIC, several switches are monolithically fabricated with the optical feed network to switch the optical power of the phased optical channel signals between the integrated optical antennas and the RF antennas, thus generating steerable optical and RF beams. The photodetectors and RF antennas can be discrete components or integrated into the optical feed network.To ensure that the optical and RF beams for the same steering commands are aligned together (within a specified angular tolerance), the PIC is positioned within the footprint of the RF antenna array.

[0010] US2005 / 203711A1 describes the use of a multiport link in combination with an inverse Fourier transform to determine the distance to a fault in an RF transmission line or waveguide without the use of heterodyne step-down conversion circuits. To provide an ultrawide bandwidth frequency-domain reflectometer, the output terminals of the multiport link are used to calculate the distance to the fault and the return loss. The inverse Fourier transform algorithm is modified to account for both the phase shift per unit length of the transmission line and the attenuation per unit length in the transmission line.The output of the modified inverse Fourier transform is applied to a module that removes the effect of previous faults by calculating the distances in advance, before the amplitudes are known, and by calculating the amplitude at each previous fault, starting with the first. The output of this module is then used with a threshold to remove the effects of noise, secondary reflections, and negligible spikes. The result is a time-domain waveform where the spike positions indicate the distance to actual faults, and where the return loss or percentage reflection is calculated for each fault.

[0011] In addition, internal calibration loads and special processing procedures are used to easily calibrate the reflectometer on site.

[0012] US Patent 2011 / 153543 A1 describes systems and methods for the unique identification or "fingerprinting" of optical fibers based on high-resolution measurements of backscattered light, such as those that can be performed with an optical frequency-domain reflectometer (OFDR). One embodiment of this application disclosure relates to a computer-readable storage medium containing a set of instructions executable by a processor.The command set is used to retrieve a profile for a designated fiber, wherein the profile contains unique measurement data of the designated fiber, to receive further measurement data of a connected fiber within a network from the OFDR, to compare the unique measurement data of the designated fiber with the further measurement data of the connected fiber and to confirm the identity of the connected fiber as the designated fiber if the unique measurement data matches the further measurement data, and to trigger a warning if the unique measurement data does not match the further measurement data.

[0013] Calibrating the lengths and monitoring the transmission paths, particularly during long-term operation of a photonic radar system with multiple radar head units, remains a challenge. The invention therefore aims to improve the calibration and diagnostic capabilities of a radar system.

[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 described in the dependent claims.

[0015] Basic idea of ​​the invention

[0016] The invention is based on the idea of ​​equipping the phonic radar system with a monitoring device. This device is designed to generate a test signal that is coupled into the transmission medium leading to the radar head units. Along the transmission medium, which is typically a fiber made of plastic or glass, intrinsic Rayleigh scattering occurs, causing a portion of the radiation to be backscattered within the transmission medium. Generally, much stronger backscattering and reflection occur at coupling points, splices, and points of damage. At other locations, such as sharp bends, loss of the guided radiation occurs. Characteristic locations such as splices, fiber ends, or coupling points, for example, between fibers and optical semiconductor elements, typically result in strong reflection.As a light pulse propagates in a fiber, backscattering and reflections of the propagating pulse occur at various positions along the fiber, arriving at the pulse's coupling point with a time delay. The time difference between the pulse's coupling point and the arrival of a pulse component backscattered, for example, at a splice, is a measure of the distance of the backscattering position (i.e., the splice) from the coupling point. This time difference corresponds to twice the travel time of the light or optical radiation in the transmission medium from the coupling point to the backscattering point. Such a method is called OTDR (time-domain reflectometry). However, a much better signal-to-noise ratio can be achieved by using a longer-term signal, such as a continuous wave signal, whose frequency is changed monotonically in sections, preferably at a constant monotonic level.The frequency of the optical radiation (light) coupled into the fiber thus has a different frequency at the time the reflected radiation arrives. With a constant monotonic frequency change of the incident test radiation, also called the test signal, the resulting frequency change between the coupled and reflected radiation depends on the time difference between the coupling time of the radiation and the arrival of the reflected radiation. When these two radiations / signals are superimposed, for example on a transducer, interference occurs, leading to a beat signal. This beat signal has a difference frequency that is linked to the signal's travel time to and from the reflection point. The frequency of the beat signal is therefore a measure of the distance to the reflection / scattering point where the reflected radiation causing this beat frequency was scattered or reflected.Since backscattering occurs along the entire length of a real transmission medium, and there are usually several locations with increased backscattering or losses (e.g., at points of strong curvature), the resulting interference signal contains many frequencies. To determine these frequencies, a Fourier transform is typically performed on the recorded time transient to obtain an OFDR spectrum. Within the OFDR spectrum, the individual frequency lines or structures can be assigned to locations along the transmission medium. This type of spectroscopy is called optical frequency domain reflectometry (OFDR).By performing such a measurement on the at least one transmission medium of the photonic radar system, to which at least one radar head is coupled, the precise distances of individual characteristic structures and associated elements along the transmission medium, as well as their parameters, can be determined. Repeated measurements allow for the monitoring of parameter changes over time. Assigning the characteristic structures and / or lines to the radar system components is generally straightforward based on prior knowledge of the radar system's design, as the approximate component distances are known from the manufacturing process.

[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 transmitter and / or receiver 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, so that signal transmission between the central station and the radar head units occurs using optical signals. This makes it possible to establish coherence between the radar radiation emitted by the individual transmitting antennas and also coherence at the central station for the radar echo information derived from radar echo radiation received by receiving antennas.

[0019] Radar signal information refers to signal information that characterizes radar radiation emitted by a radar head designed as a transmitter 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. The radar head, designed as transmitter modules, frequency-multiplies and amplifies the received radar signal information, separated from the optical carrier signal, before transmission.

[0020] 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.

[0021] A signal is considered to correspond to another signal if information contained in a temporal frequency change matches information contained in a temporal frequency change of the other signal. A signal modulated onto a carrier signal thus corresponds to the modulated carrier signal.

[0022] Preferred embodiments

[0023] Photonic radar system (100) comprising a central station (200) and at least one radar head assembly (300, 300-n) configured as a transmitter and / or receiver module, wherein the at least one radar head assembly (300, 300-n) is connected to at least one individual optical transmission medium (400, 400-n), wherein the central station and the at least one radar head assembly are configured to modulate signals transmitted from the central station to the at least one radar head assembly or signals transmitted back from the at least one radar head assembly to the central station onto at least one optical carrier signal generated by the central station for environmental detection, wherein a monitoring device is configured which includes a test signal generation device for generating an optical test signal with at least one preferably constant, monotonically changing frequency ramp,The instrument comprises means for generating a reference signal corresponding to the test signal, a detection unit, an evaluation unit, and a signal guidance means, wherein the signal guidance means are configured to couple at least one test signal component of the test signal into the at least one transmission medium and to couple out a test signal component transmitted back from the at least one transmission medium to the detection unit (630), where either the transmitted test signal component is optically superimposed with the reference signal in the detection unit so that a differential signal is detected by the detection unit, or the transmitted test signal component is detected in the detection unit and electronically superimposed with the reference signal to generate a differential signal, and wherein the evaluation unit is configured to generate an OFDR spectrum on the basis of the detected or generated differential signal and to evaluate at least reflection components.to identify the photonic components of at least one radar head device, to determine their parameters, and to store and / or output them as calibration information in a memory.

[0024] Furthermore, a method for operating a photonic radar system with monitoring of the transmission properties is described, wherein the photonic radar system comprises a central station and at least one radar head device designed as a transmitter and / or receiver module, which is connected to at least one individual optical transmission medium, wherein signals exchanged for environmental detection are modulated onto at least one carrier signal generated by the central station, wherein the method comprises the steps:

[0025] Generating a test signal with at least one monotonically changing frequency ramp, preferably constant,

[0026] Generating a reference signal corresponding to the test signal, coupling the test signal into the at least one transmission medium, extracting a back-transmitted test signal component to a detection unit (630), and either optically superimposing the back-transmitted test signal with the reference signal of the test signal to form an optical difference signal and detecting the difference signal, or alternatively detecting the back-transmitted test signal and electronically superimposing the detected back-transmitted test signal with the reference signal to generate the difference signal and generating an OFDR spectrum based on the difference signal, as well as determining parameters of at least the structures of the OFDR spectrum correlated with the radar head devices and storing the parameters as calibration information in a memory and / or outputting the calibration information.

[0027] One advantage is that the precise lengths of the individual transmission paths required for radar system calibration can be easily determined. The necessary information for assigning the structures observed in an OFDR spectrum to components of the radar system can be obtained from information stored in a calibration file, which is typically created during the radar system's manufacturing process. The necessary information is generated during the production and / or assembly of the transmission media for the radar system. Thus, the approximate lengths of the transmission media are known, and the precise lengths for each individual transmission media can then be determined using frequency-domain reflectometry (OFDR).

[0028] A radar system is particularly preferred in which a plurality of at least one radar head assembly is connected to the central unit, wherein each of the radar head assemblies is coupled to a transmission medium of the plurality of the at least one transmission medium, and wherein the central unit is configured to generate the signals transmitted by the plurality of the at least one radar head assembly for environmental detection and to jointly evaluate the signals transmitted back by this plurality. The evaluation unit can be used to measure and monitor the transmission media to this plurality of radar head assemblies.

[0029] Particularly preferred are embodiments in which the evaluation unit is designed to detect, in addition to the reflection components of the at least one radar head, other characteristic structures in the OFDR spectrum and to incorporate them into the calibration information. This makes it possible to react promptly to changes in transmission characteristics due to damage or changing environmental conditions. For example, if a splice changes due to aging or similar factors, and this results in increased signal transmission losses, this can be detected and taken into account during the evaluation.

[0030] The photonic radar system is preferably designed such that the radar head devices are at least partially connected to a detection device of the central station by means of a back-transmission medium in addition to the transmission medium, wherein a passive transparent bidirectional coupling exists between the transmission medium and the back-transmission medium, and the evaluation device is designed to identify backscatter pulses from the couplings of the back-transmission media with the central station in the derived OFDR spectrum and to store their parameters as calibration information.

[0031] One advantage is that not only the transmission media but also the return transmission media can be measured and monitored. This requires a transparent, bidirectional connection between the transmission medium carrying the test signal to the radar head and the return transmission medium, which is used for signal return. While the radar head may contain a modulation device to, for example, modulate radar echo information onto the at least one optical carrier signal transmitted by the central station, it does not actively generate an optical signal. Therefore, the connection between the transmission medium and the return transmission medium in the radar head is referred to as passive transparent coupling.It is also essential that the coupling is bidirectional, meaning that the transmitted test signal can also propagate through the radar head unit into the return transmission medium, and that components of the test signal scattered / reflected back from the return transmission medium or at its coupling point are coupled back into the transmission medium for the return transmission in the radar head unit.

[0032] One embodiment provides that, in addition, the parameters of structures are determined and stored and / or output as calibration information in the memory. These parameters correlate with reflections or backscatter at the central station, to which the test signal is transmitted via transparent return transmission media coupled to the transmission media in the radar head units. It is possible to perform the monitoring, preferably before commissioning and preferably also iteratively with a time delay relative to the signal transmissions for environmental sensing. The time intervals at which the individual transmission media are monitored can be freely defined.In such an embodiment, components of the central unit, which are intended for generating the at least one optical carrier signal and for modulating and optionally also generating radar signal information to be transmitted, can also be used for generating the frequency ramp and the optical test signal. In such an embodiment, the at least one optical carrier signal for the test signal has the same wavelength or frequency as the at least one optical carrier signal for transmitting signals for environmental sensing.

[0033] In some embodiments, the monitoring device and its components are thus entirely integrated into the central station. For example, the signal generation device (designed as a laser) and a modulator, which are used to generate the at least one optical carrier signal and to modulate at least one carrier signal of radar signal information onto this signal, can also be used to generate the test signal. At least individual components of a detection device and an evaluation device from the central station can also 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 transmitted test signal and the reference signal in the acquisition unit or electronically in the evaluation device to form the differential signal.

[0034] In another embodiment, the monitoring device is structurally separate from the central station and is optically coupled to the central station via a bidirectional optical coupling device. This coupling device transmits the test component of the test signal to the coupling device and receives the returned test signal. The coupling device connects the at least one transmission medium to the central station. Typically, the coupling device is a one-to-multiple distribution device, such as a one-to-multiple switch, through which the central station is connected to the individual transmission media of the radar head units. Generally, such a one-to-multiple switch provides a bidirectional connection between a single input and one of the multiple outputs.The switching state determines which of the multiple terminals or multiple outputs has a bidirectional connection.

[0035] One advantage of the physical separation 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 due to thermal effects during measurement can thus be eliminated or at least reduced. Furthermore, the system's ease of maintenance is improved. Additionally, diagnostics and monitoring of the radar system become 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 at least one carrier signal used for signal transmission between the central station and the radar head.

[0036] 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.

[0037] One embodiment of the photonic radar system therefore provides that the test signal is generated with a different optical frequency than the at least one carrier signal for signal transmission for environmental detection and that the acquisition and monitoring of the calibration information is carried out in wavelength or frequency multiplexing.

[0038] In a preferred photonic radar system, a central control unit at the central station is designed to perform calibration based on calibration information provided and / or updated by the monitoring unit. The evaluation of detected echo signals and the generation of radar signal information for transmission are performed using parameters contained in the calibration information. Since this information is preferably stored in a memory, for example, in a calibration file, an initial calibration can also be performed using this data, which may have been stored during manufacturing and, if necessary, determined using other measurement and transmission testing methods.It is particularly advantageous if the evaluation unit of the photonic radar system is designed to compare the previously stored calibration information with the currently determined calibration information and, if deviations are detected, to trigger an adjustment of the configuration and / or the calibration of the radar system.

[0039] If, for example, a radar head for environmental sensing fails because the associated optical transmission medium is damaged, e.g., broken—which can be recognized, for instance, by the fact that only reflection and backscatter structures are visible in the corresponding OFDR spectrum, and these correlate with distances smaller than the at least roughly known distance of the radar head—then the underlying array radar head systems for evaluation can be adjusted accordingly. If meaningful environmental sensing is no longer possible, this can also be signaled to other control units of a vehicle, ensuring that only valid environmental information is provided.

[0040] In another embodiment, the monitoring device is structurally separate from the central station and includes the optical bidirectional one-to-multiple 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 at least one 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. This improves the modularity of the monitoring device, as individual components of the monitoring device can therefore be renewed and replaced separately from the components required for radar operation.

[0041] In this embodiment, the transmission media used for diagnostics and monitoring are each 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. The transmission media and secondary transmission media are then preferably laid parallel and close together, so that they are exposed to the same environmental influences.Preferably, the transmission media connected to the monitoring device are arranged externally within 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] In one embodiment, the means for generating the reference signal are part of the signal guidance means and are designed to generate the reference signal from the test signal that has not yet been transmitted by means of optical beam splitting.

[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 shows a schematic flowchart of a method for operating a photonic radar system with surveillance functionality;

[0052] Fig. 5 shows a schematic representation of a photonic M1 MO radar system in which the monitoring device is structurally separate from the central station;

[0053] 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.

[0054] 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 transmitter and / or receiver 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 560. 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.

[0055] 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.

[0056] Lowercase letters -n ... stand for natural numbers to indicate countability and distinguishability of the corresponding objects.

[0057] In the illustrated embodiment, the central station 200 is configured to generate radar signal information for transmission, wherein, 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 at least one 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 distribution device 251, which is, for example, configured as a 1:N switch. In the one-to-multiple distribution device 251, an optical bidirectional connection is established at any given time between the single input 252 and one of several multiple outputs 255, 255-n, preferably configured as fiber outputs. This transmits the at least one carrier signal coupled to the single input 252 to one of the radar head devices 300, 300-n via the corresponding transmission media 400, 400-n, which is connected to the switched multiple output 255, 255-n.The transmission media 400, 400-n are the optical waveguides 401, 401-n, i.e. preferably optical fibers 402, 402-n.

[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 at least one 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, so 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. It is understood that this feedback is omitted in transmitter modules that do not have a return transmission medium. The fiber 502, 502-n serving as the return transmission medium 500, 500-n 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 at least one 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 at least one 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 at least one 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 almost 360° environmental detection with high angular resolution.

[0063] In Fig. 2a, the vehicle 1000 is shown schematically from its front 1002 (Fig. 2a), in Fig. 2b from its left side 1004, and in Fig. 2c from its rear 1006. The right side of the vehicle is not shown here, but is preferably designed analogously to the left side 1004.

[0064] The figures show 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 of one another, essentially vertically spaced, along a lower edge 1012 of a windshield 1010 and along a left side edge 1014 of the windshield (viewed from the front). Additionally, radar head units 1100 are also arranged horizontally spaced along a front bumper 1020. On the left side 1004 of the vehicle 1000, shown in Fig. 2b, radar head units 1100 are arranged horizontally spaced along a rocker panel 1050, and radar head units 1100 are also arranged horizontally spaced along a roof edge 1030. Additionally, radar head units are arranged essentially vertically spaced 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 device 610 is integrated into the control unit 210. This controls the alternative, preferably alternating, operation in the environmental detection operating state and the monitoring operating state.

[0068] 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 operating mode, an optical test signal is generated and provided.

[0069] The test signal is generated as an optical carrier signal with at least one, preferably superimposed, monotonically varying frequency ramp, preferably constant, and particularly preferably with several successive ramps. Alternatively to modulation, the optical frequency of the carrier signal can be directly varied to create one or more frequency ramps that are preferably at least partially monotonous. 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 400-n at the central station 200 can propagate through the radar head assembly 300-n and via the return transmission medium 500-n 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 (400 n) and the longest return transmission medium (500 n). Additionally, time buffers are taken into account for propagation delays in the central station (200 n) and / or the monitoring unit (600 n), as well as in the radar head (300 n).

[0070] An insertion 800 schematically represents an exemplary frequency ramp signal 810. Graphically, the frequency 811 is plotted against the time 812.

[0071] The test signal propagates in the transmission media 400, 400-n connected to the switched multiple output 255-n of the distribution device 251 and is at least partially reflected or backscattered at the radar head devices 300, 300-n. The reflected and / or backscattered test signal components are output at the single input 252 of the one-to-multiple distribution device 251. In an optical control device 240, for example a circulator, the back-transmitted test signal is extracted and optically superimposed in the detection unit 630 with a reference signal, for example separated at the modulator, which is an extracted component of the currently generated test signal.

[0072] Alternatively, in some embodiments, the reference signal can be an electronic signal that is, or corresponds to, the frequency ramp signal that controls the modulation of the frequency ramp onto the at least one optical carrier signal, the laser light. In this case, the reflected and / or backscattered test signal components are first converted into an electrical signal in the detection unit and then electronically superimposed with the reference signal. This preferably occurs in an analog circuit.

[0073] These superpositions are shown schematically in the frequency diagram inset 820. 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 by means of reflection, together with the reference signal 840 (solid line). A frequency 811 is plotted against time 812.

[0074] The inset 860 shows the difference signal 870 resulting from the optical / electronic superposition in a time-domain image. The amplitude 861 is plotted against the time 812. It is understood that in a real case, the difference signal contains many different frequency components.

[0075] The optical difference 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. If electronic mixing takes place, the reflected and / or backscattered test signal component is converted into the electronic signal in this way before mixing.

[0076] The difference 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. The resulting spectrum is called an OFDR spectrum.

[0077] Figure 3 schematically depicts an OFDR spectrum together with a highly simplified fiber optic network of a radar system, schematically indicated above it and connected to the switched multiple output of the one-to-multiple distribution device. 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 optic network.

[0078] At a first connector 965 of the OFDR measuring device 960, a first significant coupling loss occurs, manifested as a distinct amplitude drop 915. A further coupling loss, accompanied by another amplitude drop 920, correlates with a splice 970 in the fiber network. At another connector 975, a reflection occurs, recognizable as a distinct amplitude peak 925 in the OFDR spectrum. At a bend 980 with a small bending radius, the light transmission is disrupted, resulting in a further insertion loss, recognizable in the OFDR spectrum as an amplitude drop 930. A mechanical splice 985 causes a reflection and can be identified by an amplitude peak 935. In the illustrated embodiment, the fiber of the transmission medium terminates at a radar head device 990. This generates a further reflection pulse 940.Based on the position of the individual structures 915 to 940 in the OFDR spectrum, the propagation times can be deduced from the corresponding difference frequencies. A slightly different spectrum results for each transmission medium, depending on the length of the transmission medium to the corresponding radar head unit 990. These are, for example, distributed along the vehicle body (see Figs. 2a to 2c). The propagation speed in the transmission media correlates the propagation time with the distance of the component causing the structure from the OFDR measuring device 960. In the evaluation unit 640, which is implemented, for example, in the processing 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 990 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.

[0079] Preferably, measurements are carried out successively on the various radar head devices 300, 300-n in order to be able to calibrate all transmission media.

[0080] It is important to note, although not shown here, that in the OFDR spectrum, if a return transmission medium 500, 500-n is transparently coupled to the transmission medium in the radar head unit 300, 300-n, backscatter and reflections occurring in the return transmission medium 500, 500-n, in particular a reflection at the coupling point with the central station, are also transmitted back via the return transmission medium, the transparent coupling in the radar head unit 300, 300-n, and the transmission medium 400, 400-n to the single input 252 of the one-to-multiple distribution unit 251. Thus, the parameters of the return transmission media can also be acquired and monitored.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] Next, a calibration file 2200 is loaded, which contains information about the radar system and previously performed diagnostic steps, in particular monitoring parameters for the individual radar head devices of the radar system as calibration information.

[0085] OFDR measurements are then performed successively on all radar head devices of the radar system, the corresponding transmission parameters are determined, and the calibration information is derived from them 2300.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] If the calibration is not up-to-date, a calibration of the radar system is initiated (2700), the calibration file is adjusted accordingly, and the procedure continues with the loading of the calibration file (2200). If, however, it is determined in procedure 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.

[0090] 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 device 620, which preferably comprises a laser and a modulation device for generating the frequency ramps. Alternatively, the carrier frequency of the laser light can be varied. The test signal is routed via an optical control device 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 distribution device 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.

[0091] This embodiment is suitable for generating the test signal with a different optical frequency than the at least one 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. In this case, it is only necessary to acquire a signal from the central unit, from which the switched multiple output 255, 255-n can be determined in order to assign the measurement results to the corresponding transmission medium 400, 400-n and the corresponding radar head unit 300, 300-n, and optionally to the corresponding return transmission medium 500, 500-n.

[0092] If the monitoring device is operated in the monitoring operating state alternating with the monitoring operating state, switching of the one-to-multiple distributor is preferably effected by the control unit 620 via the control unit 210 of the central station.

[0093] Figure 6 shows a further 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.

[0094] In this embodiment, the testing device 600 itself comprises an optical distribution device 660 designed as a one-to-multiple distribution device, which can be a switch, in order to distribute the test signal to the transmission media 400, 400-n.

[0095] In this embodiment, the necessary calibration information is preferably 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 an environmental sensing mode is possible, eliminating the need for multiplexing. 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 further return transmission media 550-n, can be measured and taken into account during the assembly of the respective fibers. This information is stored in the calibration file. It is 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.

[0096] Reference symbol list for photonic radar system

[0097] Central station

[0098] Control unit

[0099] Light source (laser)

[0100] Modulation device optical control device

[0101] Distribution system

[0102] One-to-multiple distribution device

[0103] Single input, 255-n multiple output

[0104] Detection device

[0105] Unit of calculation

[0106] Digitization facility

[0107] Processing unit, 300-n radar head unit, 305-n fiber input electronic-photonic integrated circuit (EPIC), 350-n antenna, 395-n fiber output, 400n 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 07 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 Difference signal 11 Amplitude 12 Time 20 OFDR spectrum 25 Amplitude drop 30 Further amplitude drop

[0108] 935 Peak amplitude

[0109] 940 reflection pulse

[0110] 945, 945-n amplitude peaks

[0111] 960 OFDR measuring device

[0112] 965 first connector

[0113] 980° curvature

[0114] 985 mechanical splice

[0115] 990 radar head assembly

[0116] 1000 motor vehicles

[0117] 1002 Front

[0118] 1004 Left side

[0119] 1006 reverse

[0120] 1100 Antenna symbol 1010 Windscreen

[0121] 1012 bottom edge

[0122] 1014 left side edge

[0123] 1020 front bumper

[0124] 1030 Roof edge

[0125] 1040 B-pillar

[0126] 1050 sills

[0127] 1060 Rear window

[0128] 1064 lower side edge

[0129] 1070 rear bumper

[0130] 1100 Antenna symbol

[0131] 2000 Flowchart

[0132] 2100 Switch to monitoring operating mode

[0133] 2200 Loading calibration file

[0134] 2300 OFDR measurement

[0135] 2400 Functionality test

[0136] 2500 Radar system adjustment

[0137] 2600 Is calibration up to date?

[0138] 2700 Bump Calibration

[0139] 2800 Change to environmental sensing operating state

Claims

Patent claims 1. Photonic radar system (100) comprising a central station (200) and at least one radar head assembly (300, 300-n) configured as a transmitter and / or receiver module, wherein the at least one radar head assembly (300, 300-n) is connected to at least one individual optical transmission medium (400, 400-n), wherein the central station and the at least one radar head assembly (300, 300-n) are configured to modulate signals transmitted from the central station to the at least one radar head assembly (300, 300-n) or signals transmitted back from the at least one radar head assembly (300, 300-n) to the central station (200) onto at least one optical carrier signal generated by the central station for environmental detection, characterized in that a monitoring device (600) is configured which includes a test signal generation device (620) for generating an optical test signal with at least one variable, preferably constant,monotonically changing frequency ramp, The instrument comprises means for generating a reference signal corresponding to the test signal, a detection unit (630), an evaluation unit (640), and a signal guidance means (650), wherein the signal guidance means (650) are configured to couple at least one test signal component of the test signal into the at least one transmission medium (400, 400-n) and to couple out a test signal component transmitted back from the at least one transmission medium (400, 400-n) to the detection unit (630), where either the transmitted test signal component is optically superimposed with the reference 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 signal to generate a differential signal, and wherein the evaluation unit is configuredto generate an OFDR spectrum (920) based on the detected or generated difference signal and at least reflection components, the photonic components of the at least one radar head device (300, 300-n), to identify and determine the parameters of the data that can be assigned and to store and / or output them as calibration information in a memory (670).

2. Photonic radar system (100) according to claim 1, characterized in that a plurality of the at least one radar head assembly (300, 300-n) are connected to the central unit, each of which is coupled to a plurality of the at least one transmission medium (400, 400-n), wherein the central unit is configured to generate the signals transmitted by the plurality of the at least one radar head assembly (300, 300-n) for environmental detection and to jointly evaluate the signals transmitted back by this plurality.

3. Photonic radar system (100) according to claim 1 or 2, characterized in that the evaluation device is configured to detect other characteristic structures in the OFDR spectrum in addition to the reflection components of the at least one radar head device (300, 300-n) and to include them in the calibration information.

4. Photonic radar system (100) according to claim 3, characterized in that the radar head devices (300, 300-n) are at least partially connected to a 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.

5. Photonic radar system (100) according to one of the preceding claims, characterized in that a central control unit of the central station is configured to perform a calibration based on the calibration information provided and / or updated by the monitoring unit.

6. 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 calibration of the radar system (100).

7. Photonic radar system (100) according to one of the preceding claims, characterized in that the test signal is generated with a different optical frequency than the at least one carrier signal for signal transmission for environmental detection and the acquisition and monitoring of the calibration information is carried out in wavelength or frequency multiplexing.

8. Method for operating a photonic radar system (100) with monitoring of the transmission characteristics, wherein the photonic radar system (100) comprises a central station (200) and at least one radar head device (300, 300-n) configured as a transmitter and / or receiver module, which is connected to at least one individual optical transmission medium (400, 400-n), wherein signals exchanged for environmental detection are modulated onto at least one optical carrier signal generated by the central station, wherein the method comprises the steps: Generating a test signal with at least one monotonically changing frequency ramp, preferably constant, Generating a reference signal corresponding to the test signal, coupling the test signal into the at least one transmission medium (400, 400-n), extracting a back-transmitted test signal component to a detection unit, and either optically superimposing the back-transmitted test signal with the reference signal of the test signal to form an optical difference signal and detecting the difference signal, or alternatively detecting the back-transmitted test signal and electronically superimposing the detected back-transmitted test signal with the reference signal to generate the difference signal and generating an OFDR spectrum (920) based on the difference signal, as well as determining parameters of at least 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 the 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 associated with reflections or backscattering at the The central station (200) is correlated, to which the test signal is transmitted via return 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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