Radar system, method for operating a radar system, radar transmitting unit, radar receiving unit, central unit, and methods for operating same

Abstract

The invention relates to a radar system (100) and to a method for operating a radar system (100). The invention also relates to a radar transmitting unit (50), to a radar receiving unit (70), and to a central unit (10) of such a radar system (100). The invention also relates to a method for operating a radar transmitting unit (50), to a method for operating a radar receiving unit (70), and to a method for operating a central unit (10). According to the invention, the generated radar ramp signal comprises a plurality of frequency steps at each of which the frequency of the signal is kept constant for a predefined dwell time. Advantageously, the frequency steps can be precisely controlled and also recalibrated during operation of the radar system (100), thereby enabling interference-free continuous operation with high measurement quality.

Description

[0001] Description

[0002] Radar system, method for operating a radar system, radar transmitter, radar receiver, central unit and method for operating the same

[0003] The invention relates to a radar system and a method for operating a radar system. Furthermore, the invention relates to a radar transmitter, a radar receiver, and a central unit of such a radar system. In addition, the invention relates to a method for operating a radar transmitter, a method for operating a radar receiver, and a method for operating a central unit.

[0004] For automated driving, the safest possible environmental perception is essential. In modern vehicles, the vehicle's surroundings are captured using environmental sensors such as radar, LiDAR, and cameras. The primary goal is a comprehensive 360° 3D mapping of the environment, enabling the detection of as many static and dynamic objects as possible within the vehicle's vicinity. LiDAR technology, in particular, is well-suited for redundant, robust environmental perception, as this sensor type can be used precisely for environmental sensing, distance measurement, and object classification. However, these sensors are expensive and complex to design.In particular, 360° 3D environmental mapping with LiDAR technology is problematic, as it requires either numerous small individual sensors, which typically operate with many individual light sources and detector elements, or expensive large sensors to ensure such comprehensive environmental coverage. Furthermore, LiDAR systems are known to be susceptible to weather conditions such as rain, fog, or direct sunlight. This weather dependency, in particular, makes reliable environmental mapping with LiDAR systems difficult.

[0005] Radar sensors have been established in the automotive sector for years and deliver reliable and fail-safe data in all weather conditions. Even poor visibility, such as rain, fog, snow, dust, and darkness, hardly affects their detection reliability. However, their resolution—unlike LiDAR sensors—is more limited. Radar systems installed in modern vehicles typically achieve a resolution of up to approximately 5° (degrees). However, to meet the requirements for Level 4 and / or 5 automated driving with safe driving functions, radar sensors would need to deliver three-dimensional images with a fine resolution in the range of 0.1° (degrees) and even finer, with high insensitivity to interference from their surroundings. This cannot be achieved with conventional radar technology, as the resolution of existing systems is too low.

[0006] Current developments in photonic radar systems rely on the cointegration of electronic and photonic components in a single semiconductor. The generation of the FMCW signal, as well as all signal processing and evaluation, is performed by a central station. The transmit and receive modules consist of an electronically and photonically cointegrated chip (so-called "EPIC chip"). Silicon photonics technology is used for this cointegration. This enables the monolithic integration of photonic components, high-frequency electronics, and digital electronics together on a single chip ("electronic-photonic cointegration").

[0007] An example of a photonic radar system is disclosed in document DE 102017221 257 A1. In this system, GHz signals are transmitted using an optical carrier signal in the THz frequency range. The signal to be transmitted is modulated onto an optical carrier signal generated by the central station at, for example, 1 / 8 of the radar frequency and sent to the antenna chips via optical fiber. The antenna chips then perform an eightfold frequency amplification, allowing the radiation to be emitted from them in its original form. Signal detection occurs accordingly in reverse.

[0008] Conventional radars often use the principle of rapid chirp modulation, whereby the antennas emit modulated chirp signals (so-called upchirps or downchirps).

[0009] Here, a ramp signal with a continuously linear ramp modulation is generated to effect a continuous increase or decrease in the signal frequency over time, as exemplified in Figure 4, which depicts a rapid chirp modulation consisting of successive upchirs. Transmitted chirp signals can be detected in a highly noisy received signal using optimal filters (such as Fourier transforms). The invention is based on the objective of developing a radar system and a method for operating a radar system that can provide interference-free continuous operation with high measurement quality.

[0010] The problem according to the invention is solved by a radar system and a method for operating a radar system according to the independent claims. Preferred embodiments are the subject of the respective dependent claims.

[0011] A first aspect concerns a (photonic) radar system. The radar system comprises at least one radar transmitter, at least one radar receiver, and a central unit, which is coupled to the (at least one) radar transmitter and the (at least one) radar receiver via at least one (optical) waveguide. Preferably, the central unit is coupled to the radar transmitter via a first waveguide and to the radar receiver via a second waveguide. Additionally or alternatively, the radar transmitter and the radar receiver are coupled to the central unit via the same waveguide. Preferably, an optical fiber, for example, a glass fiber, is used as the waveguide.

[0012] The central unit comprises a signal generator configured to produce a radar ramp signal and an optical transmitter configured to provide an optical radar driver signal. The optical radar driver signal comprises an optical radar carrier signal and an optical radar ramp signal based on the radar ramp signal generated by the signal generator. In other words, the optical transmitter is configured to modulate the radar ramp signal generated by the signal generator onto the optical radar carrier signal as the optical radar ramp signal. The radar ramp signal causes the frequency of the radar carrier signal to be varied within a specific frequency range (frequency-modulated radar, FMCW). Consequently, the optical radar signal is preferably a superposition of the optical carrier signal and the optical radar ramp signal. The frequency of the optical carrier signal is preferably in the THz range.The frequency of the radar ramp signal is preferably in the GHz range. The optical transmitter unit is further configured to couple the optical radar driver signal into the waveguide. In other words, the central unit provides an optical radar driver signal, containing a predefinable or predetermined radar ramp signal, which is transmitted via the waveguide to the radar transmit and receive units. The optical transmitter unit preferably comprises a laser diode and / or a modulator, in particular an optical modulator. The use of a modulator has the advantage that the laser diode itself does not need to be modulated, but only needs to provide the optical carrier signal in CW (Continuous Wave) mode. This allows the use of a cost-effective laser diode.The laser diode is preferably configured to emit light with a wavelength of at least 1000 nm to at most 1800 nm, preferably at least 1200 nm to at most 1600 nm, and particularly preferably 1310 nm and / or 1550 nm. The signal generator is preferably configured to generate the radar ramp signal as an electrical radar ramp signal and to provide the electrical radar ramp signal to the optical transmitter unit.

[0013] The radar transmitter unit comprises an optical receiver and a radar transmitter. The optical receiver of the radar transmitter unit is configured to receive the optical radar driver signal coupled into the waveguide (by the optical transmitter of the central processing unit) and convert it into an electrical radar driver signal. The optical receiver is further configured to provide the (converted) electrical radar driver signal to the radar transmitter (for driving the latter). In other words, the radar transmitter is enabled to be driven by the electrical radar driver signal to transmit a frequency signal containing the radar ramp signal (generated in the central processing unit). The optical receiver is preferably a photodiode.Photodiodes are well suited to converting the optical radar driver signal into an electrical radar driver signal, while still allowing the multiple frequency levels to be clearly distinguished from one another.

[0014] The radar receiving unit comprises a radar receiver and an optical modulation unit configured to provide an optical radar response signal, which includes a radar echo signal received by the radar receiver and the optical radar driver signal, and to couple this signal into the waveguide. In other words, the radar echo is received by the radar receiver on the frequency signal transmitted by the radar transmitter according to the radar ramp signal and provided to the optical modulation unit as an electrical radar echo signal. The optical modulation unit is configured to modulate the received radar echo signal onto the optical radar driver signal received by the central processing unit via the waveguide in order to generate the optical radar response signal, which is transmitted to the central processing unit via the waveguide.Preferably, the received (electrical) radar echo signal is mixed with the electrical radar driver signal in a mixer of the radar receiver unit and then passed to the optical modulation unit. The central unit further comprises a central optical receiver unit configured to receive the optical radar response signal coupled into the waveguide and an evaluation unit configured to evaluate the received optical radar response signal and output radar information derived therefrom. Preferably, the evaluation unit is configured to perform a frequency analysis by means of a Fourier transform and thereby determine both a (time-of-flight-based) distance coordinate of the target(s) and its / their Doppler frequency (relative velocity). Preferably, the radar information derived from the optical radar response signal is output to a driver assistance system and / or an automated driving system.

[0015] According to the invention, signal transmission between the central unit and a radar transmitter or radar receiver is optical. This is made possible by the co-integration of optical and electrical components for generating and receiving a radar echo signal. The radar driver signal is generated centrally in the central unit and transmitted optically to a radar transmitter or radar receiver. Unlike electrical transmission, optical transmission of the radar driver signal results in low signal attenuation, which makes it possible to supply a large number of radar transmitters and radar receivers with a single radar driver signal.Furthermore, in contrast to electrical lines, phase rigidity (coherence) of the radar driver signal is achieved through optical signal transmission, which enables a particularly simple realization of a distributed radar system with a large number of radar transmitting units and radar receiving units.

[0016] Furthermore, optical waveguides are significantly lighter than comparable electrical conductors and less susceptible to external interference, such as electromagnetic fields. The centralized optical generation of the radar driver signal in the central processing unit allows for the compact design and deployment of radar transmitters and receivers. This saves space and reduces costs. Additionally, the complexity of individual radar transmitters and receivers is reduced, making them simple and inexpensive to manufacture and quick and easy to replace in case of a defect.

[0017] According to the invention, the (electrical or optical) radar ramp signal further comprises a plurality of frequency levels, at each of which the signal frequency is held constant for a predetermined waiting period. In other words, each discrete frequency level of the plurality of frequency levels is held for a predetermined time interval and, after the predetermined waiting period / time interval has elapsed, switches to the next higher (or lower) frequency level. The predetermined time interval is selected such that the discrete frequency levels are distinguishable from one another. In other words, the frequency levels of the plurality of frequency levels are uniquely distinguishable from one another by the predetermined waiting period, so that the received radar echo signal allows conclusions to be drawn about the respective distinguishable frequency levels.A further advantage is that, due to the comparatively high frequency of light, the frequency levels can be transmitted with particularly high optical consistency, whereas with electrical signals, due to comparatively lower frequencies, a poorer "separation" of the frequency levels is achievable and / or the frequency levels are at risk of "smearing," especially over long transmission paths (long distances in the vehicle from the central unit to the radar transmitter or radar receiver). Thus, the frequency levels in the radar system according to the invention can be designed with smaller frequency differences.

[0018] Preferably, the radar ramp signal is modulated upwards or downwards. Instead of the otherwise conventional continuous-linear ramp modulation (rapid chirps), the radar ramp signal is modulated stepwise according to the invention. In other words, the radar ramp signal undergoes stepped-frequency modulation. This is achieved, for example, by a digital or analog circuit designed to generate a stepped-frequency signal (such as a DDS = Direct Digital Synthesizer). Because the radar ramp signal is modulated stepwise, the discrete frequency steps can be controlled very precisely and, for example, recalibrated even during operation of the radar system.In the exemplary case where the evaluation of the radar echo signal yields inconsistent results with respect to the last two frequency steps, it can be assumed that the transmitted radar driver signal may be (slightly) frequency-shifted relative to the originally desired radar driver signal (or subject to other undesirable effects), which can then be corrected or recalibrated by means of a simple correction of the radar ramp signal. Thus, the stepped radar ramp signal according to the invention enables interference-free continuous operation of the radar system with high measurement quality.

[0019] The waiting time specified according to the invention is particularly distinct from an intrinsic waiting time inherent in a component for generating a continuous chirp signal. In other words, the specified waiting time represents a (deliberate) additional waiting time alongside the intrinsic waiting time inherent in a component for generating a radar ramp signal between the individual frequency changes, resulting in the discrete frequency steps. Preferably, the duration of a frequency step is a multiple of the duration required for a transition from one frequency step to the next. Particularly preferably, this multiple is at least 1.1 times, more preferably at least 1.25 times, and more preferably at least 1.5 times or more, for example, at least twice as much.

[0020] In a preferred embodiment, the specified waiting time per frequency step of the plurality of frequency steps is at least 5 nanoseconds (ns), at least 10 ns, or at least 15 ns, and / or at most one microsecond. For example, the specified waiting time per frequency step of the plurality of frequency steps may also be at least 20 ns, at least 30 ns, at least 50 ns, or at least 100 ns, and / or at most 500 ns, at most 750 ns, or at most several microseconds, for example, at most 2 microseconds, at most three microseconds, or at most 5 microseconds. The numerical values ​​given are merely examples, and it is understood that the specific design of the specified waiting time may depend on the specific implementation.The specified waiting times were chosen primarily in relation to the typical durations of a rapid chirp signal, which are emitted for a few microseconds each, for example, 8.5 microseconds. With a short predefined waiting time in the lower nanosecond range, a radar ramp signal can be generated with a comparatively large number of frequency steps, for example, dozens, hundreds, or more, per given time unit. Conversely, with a correspondingly long predefined waiting time in the upper nanosecond or even microsecond range, a radar ramp signal can be generated with fewer frequency steps per given time unit, making the individual frequency steps easier to detect in the radar echo signal.

[0021] In a further preferred embodiment, the signal generator includes a Direct Digital Synthesizer (DDS) component for generating the radar ramp signal. A DDS component is an electronic component for digital signal processing used to generate periodic, band-limited signals with (practically arbitrarily) fine frequency resolution. The underlying direct digital synthesis is based on a digital adder with a register and feedback, which serves as a phase memory. The DDS can be implemented (without an analog converter) in an FPGA, DSP, or ASIC. The hardware generation of the radar ramp signals is thus preferably performed by the DDS component, which, through suitable digital control, realizes the intended ramp profile.Through appropriate functional extensions of the DDS, further (additional) modulations are also possible, for example angle modulation (phase noise) or amplitude modulation of the output signal.

[0022] In a further preferred embodiment, the radar system comprises at least one additional radar transmitter unit, particularly of essentially identical construction, and at least one additional radar receiver unit, particularly of essentially identical construction, each coupled to the central unit via the at least one and / or one additional waveguide. Thus, the radar system preferably comprises a plurality of radar transmitter units, particularly of essentially identical construction, and a plurality of radar receiver units, particularly of essentially identical construction. In other words, the radar system is preferably designed as a distributed radar system. If two or more radar receivers are arranged spatially offset from one another, directional information of the incoming wave can also be determined by evaluating the time-of-flight differences.In other words, the evaluation unit is preferably also configured to determine directional information regarding the target(s) by evaluating the time-of-flight differences. Furthermore, by distributing the radar transmitting and receiving units over a large area on the vehicle surface, for example in the form of EPIC chips, and by using coherent signal processing from the individual antennas, the resolution can be refined to the desired range of 0.1° (degrees). The maximum distance between the individual radar receivers (antennas) is crucial for the resolution of the radar system. For example, a resolution of 0.1° (degrees) can be achieved with a distance of 1 m to 1.5 m between two radar receivers on the vehicle surface.If additional radar transmitters and receivers are arranged between the two radar receivers, this does not change the resolution of the radar system, but it does improve signal processing, since this allows the influence of other (undesired) effects contained in the radar echo signal to be factored out. Preferably, the additional radar transmitters and receivers are arranged at a predetermined minimum distance from the radar transmitters and receivers. Preferably, the minimum distance between the antennas is chosen such that a resolution of at least 0.1 degrees is achieved. For example, the minimum distance between at least two of the radar receivers is between 1 m and 1.5 m, preferably between 1.1 m and 1.4 m, and particularly preferably between 1.2 m and 1.3 m.In a further preferred embodiment, the radar system also includes at least one line designed for transmitting electrical signals, which is coupled via the central unit to the radar transmitter and / or the radar receiver. The combination of optical lines and additional electrical lines between the central unit and the radar transmitter and / or the radar receiver enables signal transmission using two different transmission technologies, allowing the advantages of both technologies to be exploited, for example, to mitigate the disadvantages of the other. Furthermore, this provides redundant signal transmission. Overall, this increases the reliability of the radar system. Consequently, a more fail-safe radar system is achieved, which is particularly advantageous for autonomous driving.

[0023] Another aspect of the invention relates to a method for operating a radar system. The radar system is preferably the radar system described above. The advantages achieved with the radar system can be achieved analogously with the method. The disclosed combinations of features of the radar system are transferable to the method by analogy. Therefore, a repetitive description of the features and advantages is omitted.

[0024] According to one process step, a radar ramp signal is generated by a central unit, in particular the central unit mentioned above. The radar ramp signal comprises a multitude of frequency levels, at each of which the frequency of the signal is kept constant for a predetermined waiting period.

[0025] In a further step of the process, an optical radar driver signal is provided by the central processing unit. The optical radar driver signal comprises an optical radar carrier signal and an optical radar ramp signal based on the generated radar ramp signal.

[0026] Furthermore, the optical radar driver signal is coupled into a waveguide through the central unit.

[0027] In a further process step, the optical radar driver signal coupled into the waveguide is received by a radar transmitter and converted into an electrical radar driver signal. In one step of the process, a radar transmitter of the radar transmitter is driven by the electrical radar driver signal.

[0028] Furthermore, a radar echo signal, in particular the radar echo signal of the signal emitted by the radar transmitter according to the electrical radar driver signal, is received by a radar receiver of a radar receiving unit.

[0029] In a further process step, an optical radar response signal, which includes the received radar echo signal and the optical radar driver signal, is provided by the radar receiver unit and coupled into the waveguide by it.

[0030] The optical radar response signal coupled into the waveguide is received and evaluated by the central unit.

[0031] Furthermore, the central unit outputs radar information derived from the radar response signal.

[0032] Another aspect of the invention relates to a radar transmitter unit for use in the radar system described above. The radar transmitter unit is preferably the one described above. The radar transmitter unit comprises a radar transmitter and an optical receiver unit configured to receive the optical radar driver signal coupled into a waveguide, convert it into an electrical radar driver signal, and supply the electrical radar driver signal to the radar transmitter. The advantages achieved with the radar system can be achieved analogously with the radar transmitter unit. The combinations of features of the radar system disclosed with respect to the radar transmitter unit are analogously transferable to the radar transmitter unit. Therefore, a repetitive description of the features and advantages is omitted.

[0033] Another aspect of the invention relates to a radar receiving unit for use in the radar system described above. The radar receiving unit is preferably the radar receiving unit described above. The radar receiving unit comprises a radar receiver and an optical modulation unit configured to provide an optical radar response signal, which includes a radar echo signal received via the radar receiver and the optical radar driver signal, and to couple this signal into a waveguide. The advantages achieved with the radar system can be achieved analogously with the radar receiving unit. The combinations of features of the radar system disclosed with respect to the radar receiving unit are analogously transferable to the radar receiving unit. Therefore, a repetitive description of the features and advantages is omitted.

[0034] Another aspect of the invention relates to a central unit for use in the radar system described above. The central unit is preferably the one mentioned above. The central unit comprises a signal generator configured to generate a radar ramp signal, wherein the radar ramp signal comprises a plurality of frequency levels at which the frequency of the signal is held constant for a predetermined waiting period, and an optical transmitter unit configured to provide the optical radar driver signal, which comprises an optical radar carrier signal and an optical radar ramp signal based on the radar ramp signal generated by the signal generator, and to couple this signal into a waveguide. The advantages achieved with the radar system can be achieved analogously with the central unit. The combinations of features of the radar system disclosed with respect to the central unit are analogously transferable to the central unit.Therefore, a repetitive description of the features and advantages is omitted.

[0035] In a preferred embodiment of the invention, the central unit further comprises a central optical receiving unit configured to receive the optical radar response signal coupled into the waveguide and an evaluation unit configured to evaluate the received optical radar response signal and to output radar information derived therefrom.

[0036] Another aspect of the invention relates to a method for operating the radar transmitter unit. The advantages achieved with the radar transmitter unit can be achieved analogously with the method. The combinations of features disclosed with respect to the radar transmitter unit are transferable to the method by analogy. Therefore, a repetitive description of the features and advantages is omitted.

[0037] According to this method, the optical radar driver signal coupled into a waveguide is received and converted into an electrical radar driver signal. Furthermore, the radar transmitter is driven by the electrical radar driver signal. Another aspect of the invention relates to a method for operating the radar receiver unit. The advantages achieved with the radar receiver unit can be achieved analogously with this method. The combinations of features disclosed with respect to the radar receiver unit are analogously transferable to the method. Therefore, a repetitive description of the features and advantages is omitted.

[0038] According to this method, a radar echo signal is received by the radar receiver and an optical radar response signal, comprising the received radar echo signal and the optical radar driver signal, is provided. Furthermore, the optical radar response signal is coupled into a waveguide.

[0039] Another aspect of the invention relates to a method for operating the central processing unit. The advantages achieved with the central processing unit can be achieved analogously with the method. The combinations of features disclosed with respect to the central processing unit are analogously transferable to the method. Therefore, a repetitive description of the features and advantages is omitted.

[0040] In this method, a radar ramp signal is generated, comprising a multitude of frequency levels, at each of which the signal frequency is held constant for a predetermined waiting period. Furthermore, an optical radar driver signal, comprising an optical radar carrier signal and an optical radar ramp signal based on the generated radar ramp signal, is provided and coupled into a waveguide.

[0041] In a preferred embodiment of the invention, in a further process step, the optical radar response signal coupled into the waveguide is received and evaluated by the central unit. Finally, radar information derived from the radar response signal is output by the central unit.

[0042] The individual process steps of the methods according to the invention are preferably configured as one or more processes that run on one or more processors in one or more electronic computing devices and are generated during the execution of one or more computer programs. The computing devices are preferably configured to cooperate with other components in order to realize the functionalities described herein. Likewise, the radar system or individual components, in particular the central processing unit, are preferably configured as central (single-unit) or decentralized (multi-unit) components.The individual components of the radar system, in particular the evaluation unit of the central processing unit, are preferably configured, at least partially, as one or more processes running on one or more processors in one or more electronic computing devices and generated by the execution of one or more computer programs. The computing devices are preferably configured to cooperate with other components to implement the functionalities described herein. The instructions of the computer programs are also preferably stored in a memory, such as a RAM element. However, the computer programs can also be stored in a non-volatile storage medium, such as a CD-ROM, flash memory, or the like.

[0043] It is also apparent to those skilled in the art that the functionalities of several computers (data processing devices) can be combined or combined in a single device, or that the functionality of a particular data processing device can be distributed across a multitude of devices in order to carry out the steps of the methods according to the invention without deviating from the methods according to the invention.

[0044] Another aspect of the invention relates to a computer program comprising instructions which, when the program is executed by a computer, cause it to perform at least one of the methods according to the invention.

[0045] The central unit, the radar transmitter unit, and / or the radar receiver unit preferably also includes further electrical and / or optical components. Examples include transimpedance amplifiers and other amplifier devices used to amplify electrical signals, and / or electrical modulators that can be used in signal processing.

[0046] The present invention can be used, in particular, in a motor vehicle for environmental sensing. Exemplary applications include driver assistance systems such as parking assistants, adaptive cruise control, and the like, as well as automatic and / or autonomous driving and the like. In principle, however, the invention can also be used in all fields where radar systems are employed, such as aircraft radar systems, ship radar systems, container terminals, warehouse robot logistics, rail vehicles, military technology, and the like. Further preferred embodiments of the invention are described in the remaining features specified in the dependent claims.

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

[0048] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show:

[0049] Fig. 1 is a schematic representation of a radar system according to a

[0050] embodiment,

[0051] Fig. 2 is a schematic representation of a radar transmitter unit according to a

[0052] embodiment,

[0053] Fig. 3 shows a schematic representation of a radar receiver unit according to a

[0054] embodiment,

[0055] Fig. 4 shows a schematic representation of a known rapid chirp modulation consisting of successive upchirps,

[0056] Fig. 5 shows a schematic representation of a rapid chirp modulation according to a

[0057] embodiment and

[0058] Fig. 6 shows a schematic representation of a method for operating a

[0059] Radar system according to an implementation form.

[0060] Detailed embodiments are now described, illustrated by way of example in the accompanying drawings. The effects and features of these embodiments are described with reference to the accompanying drawings. In the drawings, identical reference numerals denote identical elements, and redundant descriptions are omitted. The present disclosure can be implemented in various forms and is not to be understood as being limited only to the embodiments shown here. Rather, these embodiments are examples to ensure that this disclosure is thorough and complete and fully conveys the aspects and features of the present disclosure to the person skilled in the art. Methods, elements, and techniques that are not necessary for the person skilled in the art to fully understand the aspects and features of the present disclosure are therefore not described where applicable.In the drawings, the relative sizes of elements, layers, and areas may be exaggerated for clarity.

[0061] As used herein, the term "and / or" includes all combinations of one or more of the elements listed. Furthermore, the use of "may" in the description of embodiments of the present disclosure refers to "one or more embodiments of the present disclosure." In the following description of embodiments, singular terms may also include the plural unless the context clearly indicates otherwise.

[0062] Although the terms "first" and "second" are used to describe different elements, these elements should not be restricted by these terms. These terms are used only to distinguish one element from another. For example, a first element may be called a second element, and likewise a second element may be called a first element, without this deviating from the scope of the present disclosure. Expressions such as "at least one of," when placed before a list of elements, modify the entire list and not just the individual elements of the list.

[0063] Terms such as "essentially", "approximately", and similar are used as approximations, not as degrees, and are intended to account for the inherent variations in measured or calculated values ​​that are recognized by those skilled in the art. When the term "essentially" is used in conjunction with a characteristic that can be expressed by a numerical value, the term "essentially" refers to a range of at least + / - 5% of the value centered on that value.

[0064] Figure 1 shows a schematic representation of a radar system 100 according to one embodiment. For clarity, optical connections and photonic components are generally represented by dashed lines in the figures. The radar system 100 comprises at least one radar transmitter 50, at least one radar receiver 70, a central unit 10, and at least one waveguide 12, which couples the central unit 10 to the radar transmitter 50 and the radar receiver 70. In preferred

[0065] In various configurations, the radar system 100 comprises a plurality of radar transmitters 50, 50', a plurality of radar receivers 70, 70', and a plurality of waveguides 12, 12', as indicated in Figure 1. In this case, a distributed radar system 100 is present, in which preferably all radar transmitters 50, 50' are centrally driven by a driver signal provided by the central unit 10. Because the signal transmission is optical via the waveguides 12, 12', it is phase-locked, meaning that no unwanted phase-shifted driver signals reach the radar transmitters 50, 50' and the radar receivers 70, 70'.

[0066] The central unit 10 comprises a signal generator 18 configured to generate a radar ramp signal and an optical transmitter unit 20a configured to provide an optical radar driver signal. The optical radar driver signal comprises an optical radar carrier signal and an optical radar ramp signal based on the radar ramp signal generated by the signal generator 18. The radar ramp signal causes the frequency of the radar carrier signal to be varied within a specific frequency range according to the radar ramp signal. The optical transmitter unit 20a is further configured to couple the optical radar driver signal into the waveguide 12 in order to transmit it via the waveguide 12 to the radar transmit and radar receive units 50 and 70.

[0067] The central unit 10 further comprises an evaluation unit 14 and preferably a control interface 16, which is connected to the evaluation unit 14 and is configured to control the signal generator 18 such that the signal generator 18 generates a desired radar ramp signal. The signal generator 18 is preferably an analog signal generator and / or a digital signal generator. The function and implementation of analog signal generators are well known to those skilled in the art and are therefore not explained in detail here. A digital signal generator can, for example, be implemented using a DDS module. The signal generator 18 is preferably configured to generate the radar ramp signal as an electrical radar ramp signal and to provide the electrical radar ramp signal to the optical transmitter unit 20a.

[0068] The optical transmitter unit 20a preferably comprises a light source, for example a laser diode 22, and / or a modulator, in particular an optical modulator 20. The use of a modulator has the advantage that the laser diode 22 itself does not need to be modulated, but only needs to provide the optical carrier signal in CW mode. This allows the use of a cost-effective laser diode 22. The laser diode 22 is electrically connected to the control interface 16 for control purposes. Preferably, the optical modulator 20 is configured to change a material property of the waveguide 12 to modulate the optical wave. Preferably, the refractive index and / or the absorption properties of the waveguide 12 are changed.Preferably, the optical modulator 20 is configured to modify the material properties of the waveguide 12 by means of charge carriers (current), electric fields (voltage), temperature (heating electrodes), and / or mechanical modification, for example, by applying force to the waveguide 12. Preferably, the optical modulator 20 is designed according to its specific application, for example, with regard to bandwidth, rise / fall time, control, and so on.

[0069] The optical transmitter unit 20a preferably also comprises an optical control unit 24, an optical multiplexer 26, and / or a feedback loop unit 28. The optical control unit 24 is electrically connected to the laser diode 22 and is connected in the optical path between the optical modulator 20 and an optical output (not shown) of the optical transmitter unit 20a. The optical control unit 24 is configured to correlate the electrical control signal of the laser diode 22 with the optical radar driver signal output by the optical modulator 20 and to check for (undesired) differences or deviations. In other words, the optical control unit 24 ensures that the output optical radar driver signal is correct, as desired.The optical multiplexer 26 is preferably configured to apply a time-division multiplexing (TDM) and / or a wavelength-division multiplexing (WDM) method to the optical radar driver signal. Preferably, the optical multiplexer 26 is connected in the optical path between the optical modulator 20, particularly downstream of the optical control unit 24, and the optical output (not shown) of the optical transmitter unit 20a. Time-division multiplexing (TDM) is a method for transmitting and receiving independent signals over a common signal path using synchronized switches at each end of the transmission line, so that each signal appears on the line for only a fraction of the time according to predefined rules. It can be used, for example, when the bit rate of the transmission medium exceeds that of the signal to be transmitted.Wavelength division multiplexing allows multiple optical carrier signals to be multiplexed onto a single waveguide by using different wavelengths of light. This technique enables bidirectional communication over a single waveguide (also called wavelength duplexing) and a multiplication of the capacitance. The feedback loop unit 28 is electrically connected to the control interface 16 and is configured to tap the optical radar driver signal in the optical path between the optical modulator 20 and an optical output (not shown) of the optical transmitter unit 20a, specifically downstream of the optical control unit 24 and / or upstream of the optical multiplexer 26. The feedback loop unit 28 serves, in particular, to inform the control interface 16 whether and how the generated optical radar driver signal can be corrected and / or calibrated.Preferably, the feedback loop unit 28 is configured to perform a procedure for processing complex events (CEP - Complex Event Processing).

[0070] The central unit 10 further comprises a central optical receiver 30 configured to receive an optical radar response signal coupled into the waveguide 12. The evaluation unit 14 is configured to evaluate the received optical radar response signal and output radar information derived therefrom (not shown). For this purpose, the evaluation unit 14 is electrically connected to the central optical receiver 30. Preferably, the evaluation unit 14 is configured to perform a frequency analysis by means of a Fourier transform, to determine a (time-of-flight-based) distance coordinate of the target(s) and / or its / their Doppler frequency (relative velocity). Preferably, the radar information derived from the optical radar response signal is output to a driver assistance system and / or an automated driving system.

[0071] In preferred embodiments, the central optical receiver 30 is connected to the optical modulator 20 to modulate the received optical radar response signal onto the optical radar driver signal (unless this has already been done by the radar receiver 50). The central unit 10 further preferably comprises a mixer 32, an analog-to-digital converter (ADC), and / or a preprocessing unit 36. The mixer 32 is preferably interposed between the optical receiver 30 and the evaluation unit 14. The ADC 34 is preferably interposed between the optical receiver 30, particularly downstream of the mixer 32, and the evaluation unit 14. The preprocessing unit 36 ​​is preferably interposed between the optical receiver 30, particularly downstream of the ADC 34, and the evaluation unit 14.The preprocessing unit 36 ​​is preferably configured to perform a fast Fourier transform (FFT - Fast Fourier Transform).

[0072] Figure 1 further shows that the central unit 10 preferably has a first electrical line 36 connected to the radar transmitter 50 and a second electrical line 38 connected to the radar receiver 70. In other words, preferred embodiments provide a redundant second channel between the central unit 10 and the radar transmitter 50 and the radar receiver 70, thereby further increasing the reliability of the radar system 100.

[0073] With reference to Figure 2, the radar transmitter 50 shown in Figure 1 is explained in more detail. Figure 2 shows a schematic representation of a radar transmitter 50 according to one embodiment.

[0074] The radar transmitter 50 comprises an optical receiver 52 and a radar transmitter 60. The optical receiver 52 of the radar transmitter 50 is configured to receive the optical radar driver signal coupled into the waveguide 12 (by the optical transmitter 20a of the central unit 10) and convert it into an electrical radar driver signal. This is preferably done by means of a photodiode. The optical receiver 52 is further configured to provide the (converted) electrical radar driver signal to the radar transmitter 60 (for driving it). For this purpose, the optical receiver 52 is electrically connected to the radar transmitter 60. In other words, the radar transmitter 60 is enabled to be driven by the electrical radar driver signal in order to transmit a frequency signal with the radar ramp signal (generated in the central unit 10).

[0075] The frequency signals emitted by the radar transmitter 60 are preferably in the frequency range of 24.05 GHz to 26.65 GHz (according to the radio approval standards for automotive radars ETSI EN 302 858 and ETSI EN 302 288) and / or from 76 GHz to 81 GHz (according to the radio approval standards for automotive radars ETSI EN 301 091 and ETSI EN 302 264).

[0076] The radar transmitter 50 preferably further comprises a first amplifier 54, a frequency converter 56, and a second amplifier 60. The first amplifier 54 is preferably connected between the optical receiver 52 and the radar transmitter 60. The first frequency converter 56 is preferably connected between the optical receiver 52, particularly downstream of the first amplifier 54, and the radar transmitter 60. The second amplifier 58 is preferably connected between the optical receiver 52, particularly downstream of the frequency converter 56, and the radar transmitter 60. The first amplifier 54 serves to amplify the electrical signal generated by the optical receiver 52 (with respect to its amplitude). The second amplifier 58 serves to amplify the electrical signal passing through the frequency converter 56 (with respect to its amplitude).The frequency converter 56 is provided, for example, for the preferred embodiment described below. In this embodiment, the central optical transmitter unit 20a of the central unit 10 provides the optical radar driver signal at a frequency that corresponds to a fraction of the carrier frequency required for operating the radar transmitter 60. The frequency converter 56 of the radar transmitter unit 50 is configured to multiply the optical radar driver signal from the required frequency to the necessary carrier frequency and provide it. This embodiment has the advantage that the optical radar driver signal does not need to be provided at the full required carrier frequency. For example, a fraction of 1 / 4 can be selected. With an exemplary required carrier frequency of 77 GHz, the optical carrier signal then only needs to have a frequency in the range of 19.25 GHz.In the radar transmitter unit 50, the optical radar carrier signal is then electrically multiplied, in particular quadrupled, by means of the frequency converter, and thereby brought to the required frequency. A further advantage of this is that, due to the central provision of the radar driver signal, the individual radar transmitter unit 50 requires significantly less energy, thus reducing problems with the dissipation of the waste heat generated.

[0077] With reference to Figure 3, the radar receiver unit 70 shown in Figure 1 is explained in more detail. Figure 3 shows a schematic representation of a radar receiver unit 70 according to one embodiment.

[0078] The radar receiving unit 70 comprises a radar receiver 72 and an optical modulation unit 80, which is configured to provide an optical radar response signal comprising a radar echo signal received via the radar receiver 72 and the optical radar driver signal, and to couple this signal into the waveguide 12. In other words, the radar echo to the frequency signal transmitted by the radar transmitter 60 according to the radar ramp signal is received by the radar receiver 72 and provided to the optical modulation unit 80 as an electrical radar echo signal. The radar receiving unit 70 preferably includes a photodiode 78, which receives the optical radar driver signal and converts it into an electrical radar driver signal. The electrical radar driver signal is then preferably transmitted to the optical modulation unit 80.The optical modulation unit 80 is configured to modulate the received radar echo signal onto the optical radar driver signal received by the central unit 10 via the waveguide 12, in order to generate the optical radar response signal, which is transmitted to the central unit 10 via the waveguide 12. Preferably, the received (electrical) radar echo signal is mixed with the electrical radar driver signal in a mixer 76 of the radar receiver 70. Also preferably, the radar receiver 70 further comprises an amplifier 74, which amplifies the received electrical radar echo signal (with respect to its amplitude).

[0079] According to the invention, the radar driver signal is generated optically and centrally in the central unit 10. Signal transmission between the central unit 10 and the radar transmitter 50, and between the central unit 10 and the radar receiver 70, is also optical. This is made possible by the co-integration of optical and electrical components for generating and receiving a radar echo signal. In contrast to electrical transmission, optical transmission of the radar driver signal results in low signal attenuation, which makes it possible to supply a large number of radar transmitters 50, 50' and radar receivers 70, 70' with a single radar driver signal.Furthermore, in contrast to electrical lines, phase rigidity of the radar driver signal is achieved through optical signal transmission, which enables a particularly simple realization of a distributed radar system 100 with a large number of radar transmitting units 50, 50' and radar receiving units 70, 70'.

[0080] Furthermore, waveguides 12 are significantly lighter than comparable electrical conductors and less susceptible to external interference, such as electromagnetic fields. The centralized optical generation of the radar driver signal in the central unit 10 allows the radar transmitter units 50, 50' and the radar receiver units 70, 70' to be manufactured and provided in a compact design with small dimensions. This saves installation space and costs. Moreover, the complexity of the individual radar transmitter units 50, 50' and individual radar receiver units 70, 70' is reduced, making them easy and inexpensive to manufacture and quick and easy to replace in case of a defect.

[0081] Figure 4 shows a schematic representation of a known rapid chirp modulation consisting of successive upchirps. Conventional radars use the principle of rapid chirp modulation, whereby the antennas emit modulated chirp signals (so-called upchirps or downchirps). A ramp signal with a continuously linear ramp modulation is generated to effect a continuous increase or decrease in the signal frequency over time, as illustrated by Figure 4, which depicts a rapid chirp modulation consisting of successive upchirps. Figure 5 shows a schematic representation of a rapid chirp modulation according to one embodiment. According to the invention, the radar ramp signal comprises a plurality of frequency steps, at each of which the signal frequency is held constant for a predetermined waiting period.In other words, each discrete frequency level of the plurality of frequency levels is held for a predetermined time interval and, after this interval has elapsed, switched to the next higher (or lower) frequency level. The predetermined time interval is chosen such that the discrete frequency levels are distinguishable from one another. In other words, the frequency levels of the plurality of frequency levels are uniquely distinguishable from one another by the predetermined waiting time, so that the received radar echo signal allows conclusions to be drawn about the respective distinguishable frequency levels. Preferably, the radar ramp signal is upward or downward modulated. Instead of the otherwise usual continuous linear ramp modulation (rapid chirps, see Figure 4), the radar ramp signal is modulated stepwise according to the invention (see Figure 5). In other words, the radar ramp signal undergoes stepped-frequency modulation.This is achieved, for example, by a signal generator 18 comprising a digital or analog circuit configured to generate a stepped-frequency signal. By modulating the radar ramp signal in steps, the discrete frequency steps can be controlled very precisely and, for example, recalibrated even during operation of the radar system 100. In the case where the evaluation of the radar echo signal yields inconsistent results with respect to the last two frequency steps, it can be assumed that the transmitted radar driver signal may be (slightly) frequency-shifted relative to the originally desired radar driver signal (or subject to other undesirable effects), which can then be corrected or recalibrated by means of a simple correction of the radar ramp signal.Thus, the stepped radar ramp signal according to the invention enables interference-free continuous operation of the radar system 100 with high measurement quality.

[0082] The time signal s shown in Figure 5 can be analyzed. TX (t) of a single frequency ramp can be described as follows: where N represents the number of discrete frequency levels per chirp and n is the corresponding tracking index with 0 < n < N - 1. The complete transmitted signal s shown as an example in Figure 5. TX (t) consisting of a sequence of M graded chirp signals, where m is the corresponding running index with 0 < m < M - 1, can be expressed mathematically as follows:

[0083] Although the steps shown in Figure 5 are all depicted as being of equal size, the present disclosure is not limited to such a structure. Rather, a multitude of differently pronounced steps can be contained in the chirp signals, thereby individualizing the respective steps and consequently allowing them to be better assigned within the radar echo signal. This simplifies the correction and / or calibration of the radar ramp signal (for example, using the feedback loop unit 28). In other words, two or more different waiting times can be specified for each of the multiple frequency steps.

[0084] Figure 6 shows a schematic representation of a method for operating a radar system 100, in particular the one above, according to an implementation form.

[0085] In a first process step 102, a radar ramp signal is generated by a central unit 10, wherein the radar ramp signal comprises a plurality of frequency levels, on which the frequency of the signal is kept constant for a predetermined waiting time.

[0086] According to a second process step 104, an optical radar driver signal is provided by the central unit 10. The optical radar driver signal comprises an optical radar carrier signal and an optical radar ramp signal based on the generated radar ramp signal.

[0087] Furthermore, the optical radar driver signal is coupled into a waveguide 12 by the central unit 10 (third process step 106).

[0088] In a fourth process step 108, the optical radar driver signal coupled into the waveguide 12 is received by a radar transmitter unit 50 and converted by this unit into an electrical radar driver signal.

[0089] According to a fifth process step 110, a radar transmitter 60 of the radar transmitting unit 50 is driven by the electrical radar driver signal. Furthermore, a radar echo signal is received by a radar receiver 72 of a radar receiving unit 70 (sixth process step 112).

[0090] In a seventh process step 114, an optical radar response signal, which includes the received radar echo signal and the optical radar driver signal, is provided by the radar receiving unit 70 and coupled into the waveguide 12 by it.

[0091] According to an eighth process step 116, the optical radar response signal coupled into the waveguide 12 is received by the central unit 10 and evaluated by it.

[0092] Finally, radar information derived from the radar response signal is output by the central unit 10 (ninth process step 118).

[0093] Among other advantages, the following arise: simple hardware-based signal generation with low noise and low phase noise; a large range of accuracy for distance measurement, thus avoiding over-range; unambiguous recognition of the transmitted signal at the receiver through coding; the possibility of simultaneously transmitting multiple measurement signals from multiple transmitting antennas and unambiguous recovery at the receiver; reduced computational effort in signal processing; energy savings for signal processing; and / or the possibility of use in photonic, photonic, and electronic semiconductor circuits for use in photonic radar systems. The methods described herein can be applied to LiDAR, camera, and satellite communication systems in both civilian and military applications.

[0094] Reference symbol list

[0095] Central unit, 12' waveguide evaluation unit control interface signal generator a optical transmitter unit optical modulator laser diode optical control unit optical multiplexer feedback loop unit central optical receiver unit mixer

[0096] ADC converter

[0097] Preprocessing unit, first electrical line, second electrical line, radar transmitter unit, further radar transmitter unit, optical receiver unit, first amplifier, frequency converter, second amplifier, radar transmitter

[0098] Radar receiving unit, 70' further radar receiving unit radar receiver amplifier

[0099] Mixer Photodiode Optical Modulation Unit Radar System First Process Step - Generating Radar Ramp Signal Second Process Step - Providing Optical Radar Driver Signal Third Process Step - Coupling Optical Radar Driver Signal Fourth Process Step - Receiving and Converting Radar Driver Signal Fifth Process Step - Driving Radar Transmitter Sixth Process Step - Receiving Radar Echo Signal Seventh Process Step - Providing and Coupling Radar Response Signal Eighth Process Step - Receiving and Evaluating Ninth Process Step - Outputting Radar Information

Claims

- 27 - Patent claims 1. Radar system (100) comprising: at least one radar transmitter unit (50) with an optical receiver unit (52) and a radar transmitter (60), at least one radar receiver unit (70) with a radar receiver (72) and an optical modulation unit (80), a central unit (10) coupled to the radar transmitter unit (50) and the radar receiver unit (70) via at least one waveguide (12), wherein the central unit (10) comprises a signal generator (18) configured to generate a radar ramp signal and an optical transmitter unit (20a) configured to provide an optical radar driver signal comprising an optical radar carrier signal and an optical radar ramp signal based on the radar ramp signal generated by the signal generator (18), and to couple this signal into the waveguide (12), wherein the optical receiver unit (52) of the radar transmitter unit (50) is configured toto receive the optical radar driver signal coupled into the waveguide (12) and convert it into an electrical radar driver signal and to provide the electrical radar driver signal to the radar transmitter (60), wherein the optical modulation unit (80) of the radar receiving unit (70) is configured to provide an optical radar response signal comprising a radar echo signal received via the radar receiver (72) and the optical radar driver signal, and to couple this signal into the waveguide (12), wherein the central unit (10) further comprises a central optical receiving unit (30) configured to receive the optical radar response signal coupled into the waveguide (12) and an evaluation unit (14) configured to evaluate the received optical radar response signal and to output radar information derived therefrom, and wherein the optical radar ramp signal comprises a plurality of frequency levels,on which the frequency of the signal is kept constant for a predetermined waiting period.

2. Radar system (100) according to claim 1, wherein the predetermined waiting time per frequency step of the plurality of frequency steps is at least five nanoseconds, at least ten nanoseconds or at least 15 nanoseconds and / or at most one microsecond.

3. Radar system (100) according to one of the preceding claims, wherein the signal generator (18) comprises a Direct Digital Synthesizer (DDS) module for generating the radar ramp signal.

4. Radar system (100) according to one of the preceding claims, further comprising: at least one further radar transmitting unit (50') and at least one further radar receiving unit (70'), each coupled to the central unit (10) via the at least one and / or one further waveguide (12').

5. Radar system (100) according to one of the preceding claims, further comprising at least one line (36, 38) designed to transmit electrical signals, which is coupled via the central unit (10) to the radar transmitting unit (50) and / or the radar receiving unit (70).

6. Method for operating a radar system (100), comprising the steps: Generating (102) a radar ramp signal by a central unit (10), wherein the radar ramp signal comprises a plurality of frequency levels at which the frequency of the signal is kept constant for a predetermined waiting time; providing (104) an optical radar driver signal by the central unit (10), wherein the optical radar driver signal comprises an optical radar carrier signal and an optical radar ramp signal based on the generated radar ramp signal. Coupling (106) of the optical radar driver signal into a waveguide (12) by the central unit (10), Receiving and converting (108) the optical radar driver signal coupled into the waveguide (12) into an electrical radar driver signal by a radar transmitting unit (50), Driving (110) a radar transmitter (60) of the radar transmitting unit (50) with the electrical radar driver signal, Receiving (112) a radar echo signal with a radar receiver (72) of a radar receiving unit (70), Providing and coupling (114) an optical radar response signal comprising the received radar echo signal and the optical radar driver signal into the waveguide (12) by the radar receiving unit (70), Receiving and evaluating (116) the optical radar response signal coupled into the waveguide (12) by the central unit (10) and Output (118) of radar information derived from the radar response signal by the central unit (10).

7. Radar transmitting unit (50) for use in a radar system (100) according to any one of claims 1 to 5, comprising: a radar transmitter (60) and an optical receiving unit (52) which is configured to receive the optical radar driver signal coupled into a waveguide (12) and to convert it into an electrical radar driver signal and to provide the electrical radar driver signal to the radar transmitter (60).

8. Radar receiving unit (70) for use in a radar system (100) according to any one of claims 1 to 5, comprising: a radar receiver (72) and an optical modulation unit (80) configured to provide an optical radar response signal comprising a radar echo signal received via the radar receiver (72) and the optical radar driver signal, and coupling this signal into a waveguide (12).

9. Central unit (10) for use in a radar system (100) according to any one of claims 1 to 5, comprising: a signal generator (18) configured to generate a radar ramp signal, wherein the radar ramp signal comprises a plurality of frequency levels at which the frequency of the signal is kept constant for a predetermined waiting time, and an optical transmitter unit (20a) configured to provide the optical radar driver signal, which comprises an optical radar carrier signal and an optical radar ramp signal based on the signal generated by the signal generator (18). comprised of the generated radar ramp signal, and coupling this into a waveguide (12).

10. Central unit (10) according to claim 9, further comprising: a central optical receiving unit (30) configured to receive the optical radar response signal coupled into the waveguide (12) and an evaluation unit (14) configured to evaluate the received optical radar response signal and to output radar information derived therefrom.

11. Method for operating a radar transmitting unit (50) according to claim 7, comprising the steps: Receiving and converting (108) the optical radar driver signal coupled into a waveguide (12) into an electrical radar driver signal and Driving (110) the radar transmitter (60) with the electrical radar driver signal.

12. Method for operating a radar receiving unit (70) according to claim 8, comprising the steps: Receiving (112) a radar echo signal with the radar receiving unit (70) and Providing and coupling (114) an optical radar response signal comprising the received radar echo signal and the optical radar driver signal into a waveguide (12).

13. Method for operating a central processing unit (10) according to claim 9 or 10, comprising the steps: Generating (102) a radar ramp signal comprising a plurality of frequency levels, at each of which the frequency of the signal is kept constant for a predetermined waiting time, Providing (104) an optical radar driver signal comprising an optical radar carrier signal and an optical radar ramp signal based on the generated radar ramp signal, and Coupling (106) of the optical radar driver signal into a waveguide (12).

14. The method of claim 13, further comprising the steps of: - 31 - Receiving and evaluating (116) the optical radar response signal coupled into the waveguide (12) and Output (118) radar information derived from the radar response signal.

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