Distributed radar system with efficient doppler measurement

Abstract

The present invention relates to a central unit (Z) for a distributed radar system, which can be operated, for example, in a means of transport. The central unit (Z) is designed to provide a first transmission signal (S-C) in the form of a continuous sequence of chirp signals for a designated radar transmission unit, and to provide, in alternation, second transmission signals (S-I) in the form of an intermittent sequence of chirp signals for the rest of the radar transmission units. Multiple transmission frequencies, which differ from one another by a frequency swing, are used by the one designated radar transmission unit and the rest of the radar transmission units. The first radar echo signal (R-C) resulting from the first transmission signal (S-C) is evaluated for a Doppler measurement. The second radar echo signals (R-I) resulting from the second transmission signals (S-I) are used for detecting objects in the environment. The present invention also relates to a distributed radar system comprising such a central unit (Z). The invention also relates to a method and a computer program for operating such a central unit (Z) and to a means of transport which has a distributed radar system comprising such a central unit (Z).

Description

[0001] Description

[0002] Distributed radar system with efficient Doppler measurement

[0003] The present invention relates to a central unit for a distributed radar system, which can be operated, for example, in a means of transportation. The present invention further relates to a distributed radar system with such a central unit. The invention also relates to a method and a computer program for operating such a central unit, as well as a means of transportation comprising a distributed radar system with such a central unit.

[0004] For driver assistance systems and safety systems in fully automated driving, the safest possible environmental perception is essential. This is achieved by capturing the environment using sensors such as radar, lidar, and camera sensors integrated into the vehicle. Based on the captured sensor data, an environmental model can then be created using a suitable machine learning model. Perception modules can be used for this purpose, enabling the recognition of learned objects in the environment and forwarding this information to a planning module. The planning module can then take the recognized objects into account for trajectory planning and safe vehicle control. Particularly important here is a comprehensive 360° 3D capture, which allows for the complete 360-degree recording of all static and dynamic objects and the creation of the highest possible resolution 3D models of the environment. This also applies to objects below the vehicle, such as...may have gotten there during a prolonged period of standstill.

[0005] While lidar-based systems are capable of providing precise distance measurements and can also be used for classification, they are expensive and complex to build. Furthermore, lidar systems are susceptible to weather conditions such as rain, fog, or direct sunlight. Radar sensors, on the other hand, deliver reliable and fail-safe data in all weather conditions. Even poor visibility conditions such as rain, fog, snow, dust, and darkness hardly affect their accuracy.

[0006] However, the resolution is currently limited. For example, radar sensors currently used in series production in the automotive sector have a resolution of approximately 2°. This is insufficient, for instance, to meet the requirements for Levels 4 and 5 of automated driving with safe driving functions, as these require radar sensors to deliver three-dimensional images with a high resolution in the range of 0.1° and below, with high insensitivity to interference from their surroundings. This cannot be achieved with conventional radar technology, as the resolution of such systems is too low.

[0007] Currently under development are so-called photonic radar systems, in which driver signals in the GHz range can be distributed to a multitude of radar sensors using an optical carrier signal in the THz range. This allows for the co-integration of electronic and photonic components on a single semiconductor substrate, enabling extremely compact form factors for individual radar sensors and, consequently, arrays with numerous such radar sensors integrated into the vehicle. During the processing of the radar echo signals received by the radar sensors, the high-frequency radar signal information is downconverted in the individual sensor units. The received radio frequency (RF) signal, typically in the GHz range, is converted into a lower intermediate frequency (IF) signal, typically in the MHz range.

[0008] German patent application DE 102017221 257 A1 discloses a radar system in which signal transmission between a central unit and a radar transmitter or radar receiver is implemented optically. For this purpose, a radar driver signal is optically generated in the central unit and transmitted via at least one optical fiber to at least one radar receiver and / or at least one radar transmitter. In the radar transmitter, the radar driver signal is then converted into an electrical radar driver signal and used to drive a radar transmitter. A radar echo signal received by a radar receiver is mixed with the electrical radar driver signal in a mixer of the radar receiver. The mixed signal is then modulated onto the optical driver signal by means of a modulation unit, coupled into the optical fiber, and transmitted back to the central unit.The central unit receives the modulated optical signal and evaluates it using an evaluation unit. The result is then provided as radar information.

[0009] Distributed radar systems, so-called “distributed” or bistatic M1 MO systems (English:

[0010] Multiple Input Multiple Output (MIM) radar systems analyze potential targets from different angles to minimize fluctuation losses. However, calculating target coordinates before coherently summing the individual signals is significantly more complex and computationally intensive compared to monostatic radar systems due to the varying signal propagation times.

[0011] The use of distributed transmitting and receiving antennas results in different signal propagation times between the transmitting antenna, the receiving antenna, and a potential target, which in turn lead to differing measurement distances. These differing measurement distances, in turn, result in a non-linear phase term, which prevents coherent integration over the dimension of the receiving channels in favor of a better signal-to-noise ratio.

[0012] The compensation of such nonlinear phase terms for subsequent Doppler processing is associated with a considerable computational effort and a massive utilization of the corresponding computing unit.

[0013] One objective of the invention is to provide more efficient solutions for Doppler measurement using a distributed radar system.

[0014] This problem is solved by the independent claims. Preferred embodiments of the invention are the subject of the dependent claims.

[0015] According to a first aspect of the invention, a central unit for a distributed radar system, which in addition to the central unit comprises two or more radar transmitting units and two or more radar receiving units, is designed as follows:

[0016] - to provide a first transmission signal in the form of a continuous sequence of chirp signals for one of the two or more radar transmitting units, wherein one radar transmitting unit emits on a first frequency band;

[0017] - to provide second transmission signals alternately for the other two or more radar transmitting units, each in the form of an intermittent sequence of chirp signals, with the other radar transmitting units emitting on a second frequency band different from the first frequency band;

[0018] - to receive first radar echo signals from a first subset of the two or more radar receiving units, resulting from the first transmitted signal;

[0019] - to obtain second radar echo signals from a second subset of the two or more radar receiving units, resulting from the second transmitted signals; and - to evaluate the first radar echo signals obtained from the first subset for a Doppler measurement.

[0020] According to a further aspect of the invention, a method for operating a central unit for a distributed radar system, which in addition to the central unit comprises two or more radar transmitting units and two or more radar receiving units, is provided, wherein the central unit:

[0021] - a first transmission signal in the form of a continuous sequence of chirp signals is provided for one of the two or more radar transmitting units, with one radar transmitting unit emitting on a first frequency band;

[0022] - for the other two or more radar transmitting units, second transmission signals are provided alternately in the form of an intermittent sequence of chirp signals, with the other radar transmitting units emitting on a second frequency band different from the first frequency band;

[0023] - first radar echo signals are received from a first subset of the two or more radar receiving units, resulting from the first transmitted signal;

[0024] - second radar echo signals are received from a second subset of the two or more radar receiving units, resulting from the second transmitted signals; and - the first radar echo signals received from the first subset are evaluated for a Doppler measurement.

[0025] According to another aspect of the invention, a computer program contains instructions which, when executed by a processor, cause the processor to perform the steps for operating a central unit for a distributed radar system, which, in addition to the central unit, comprises two or more radar transmitters and two or more radar receivers:

[0026] - Providing a first transmission signal in the form of a continuous sequence of chirp signals to one of the two or more radar transmitting units, wherein one radar transmitting unit emits on a first frequency band;

[0027] - alternating provision of second transmission signals, each in the form of an intermittent sequence of chirp signals, to the other of the two or more radar transmitting units, wherein the other radar transmitting units emit on a second frequency band different from the first frequency band;

[0028] - Receiving first radar echo signals resulting from the first transmitted signal from a first subset of the two or more radar receiving units; - Receiving second radar echo signals resulting from the second transmitted signals from a second subset of the two or more radar receiving units; and

[0029] - Evaluating the first radar echo signals received from the first subset for a Doppler measurement.

[0030] The term "computer" is to be understood broadly. In particular, it also includes control units, embedded systems, and other processor-based data processing devices. Furthermore, the individual steps are not necessarily executed directly by the processor. It is equally possible that the processor controls or utilizes external components to perform individual steps.

[0031] The computer program can, for example, be made available for electronic retrieval or be stored on a computer-readable storage medium.

[0032] In the solution according to the invention, the distributed radar system includes a designated radar transmitter that emits a sequence of chirp signals. At least one designated radar receiver is also provided, which receives the time-delayed echo signal of this chirp sequence, which is used for Doppler measurement. Second transmission signals, each in the form of an intermittent sequence of chirp signals, are provided alternately to the other radar transmitters, so that the other radar transmitters emit chirp signals alternately. The designated radar transmitter and the other radar transmitters utilize multiple transmission frequencies that differ from each other by a frequency deviation. In other words, the chirp signals resulting from the first transmission signal and the second transmission signals are emitted on different frequency bands.

[0033] The use of a designated radar transmitting unit that emits the sequence of chirp signals in the assigned frequency band is particularly advantageous for smaller, sparse apertures, whose spatial extent is still so precise that nonlinearities prevent integration over all radar receiving units for Doppler processing.

[0034] The solution according to the invention allows the use of less powerful computing units, resulting in cost savings. Furthermore, it reduces algorithmic complexity, which helps prevent downstream implementation errors. Finally, the solution according to the invention contributes to meeting the ASIL-B requirements for safety-related sensor systems.

[0035] According to one aspect of the invention, the distributed radar system is designed as a photonic radar system. The co-integration of electronic and photonic components on a single semiconductor substrate in a photonic radar system enables extremely compact form factors for the individual radar sensors. This allows arrays with a large number of such radar sensors to be integrated into a vehicle.

[0036] According to one aspect of the invention, the first and second transmitted signals cover the same frequency band. In this embodiment of the invention, a transmitted signal is generated whose frequency modulation deviation extends over the entire frequency band. One output channel transmits a continuous sequence of chirp signals to a designated radar transmitter. The other output channels transmit the intermittent sequences of chirp signals to the other radar transmitters. In the other radar transmitters, the second transmitted signal is then processed, for example, by frequency filters or optical filters, so that the distributed radar system emits in the desired different frequency bands.

[0037] According to one aspect of the invention, the second transmission signals are generated by switching between the individual chirp signals of the first transmission signal. Switching between the individual chirp signals of the first transmission signal represents a technically simple way to provide the required second transmission signals. The output channels for the second transmission signal can be switched arbitrarily. Furthermore, simultaneous transmission of the same transmission signal to a connected radar transmitter via different output channels is possible.

[0038] According to one aspect of the invention, the first transmit signal and the second transmit signals cover different frequency bands. In this embodiment of the invention, multiple transmit signals are generated that differ from each other by the desired frequency deviation even during generation. One output channel transmits a continuous sequence of chirp signals within a defined modulation band. All other output channels transmit intermittent sequences of chirp signals in any order, which deviate from the continuous sequence of chirp signals by the frequency deviation. Simultaneous transmission of transmit signals that differ by the frequency deviation to a front end is possible.

[0039] According to one aspect of the invention, the first transmission signal and the second transmission signals are shaped by two frequency modulators. In this way, the characteristics of both transmission signals can be individually controlled.

[0040] According to one aspect of the invention, the first subset of the two or more radar receiving units comprises exactly one radar receiving unit. For computationally efficient Doppler processing, it is advantageous if exactly one designated radar receiving unit evaluates the frequency range covered by the continuous sequence of chirp signals.

[0041] According to a further aspect of the invention, a radar transmitter unit for a distributed radar system is provided. The radar transmitter unit has a filter for the transmission of a predetermined frequency band. In this way, depending on the filter, the radar transmitter unit can emit in either the first or the second frequency band.

[0042] According to a further aspect of the invention, a radar receiver unit for a distributed radar system is provided. The radar receiver unit is configured to output radar echo signals on two different frequency bands. This allows a dedicated radar receiver unit for Doppler measurement to simultaneously be used as part of a virtual aperture. In addition to measuring speed, the dedicated radar receiver unit can thus also measure distance.

[0043] According to another aspect of the invention, a distributed radar system comprising a central unit according to the invention is provided.

[0044] In the distributed radar system according to the invention, the radar transmitting units and the radar receiving units can each be integrated into a common unit.

[0045] The distributed radar system according to the invention can, for example, be configured as a photonic radar system. The radar system, the central unit, and the method according to the invention can be used, in particular, in any means of transport, such as motor vehicles, ships, or aircraft, where radar-based environmental sensing is performed, for example, for driver assistance systems or for automatic or autonomous operation. The motor vehicles can be, in particular, passenger cars, commercial vehicles, trucks, or buses. However, application in radar-based environmental sensing in other technical fields is also possible.

[0046] Further features of the present invention will become apparent from the following description and the attached claims in conjunction with the figures.

[0047] Fig. 1 schematically shows a photonic radar system as an example of a distributed radar system;

[0048] Fig. 2 schematically shows a central unit for a distributed radar system;

[0049] Fig. 3 schematically shows a method for operating a central unit according to the invention for a distributed radar system;

[0050] Fig. 4 shows an exemplary integration of the radar system on the vehicle surface of a passenger car;

[0051] Fig. 5 shows a first embodiment of a backend for a distributed radar system;

[0052] Fig. 6 shows radar transmitter units of a front end for the back end from Fig. 5;

[0053] Fig. 7 shows radar receiver units of a front end for the back end from Fig. 5;

[0054] Fig. 8 shows a second embodiment of a backend for a distributed radar system;

[0055] Fig. 9 shows radar transmitter units of a front end for the back end from Fig. 8;

[0056] Fig. 10 shows a first embodiment of radar receiver units of a front end for the back end from Fig. 8; and Fig. 11 shows a second embodiment of radar receiver units of a front end for the back end from Fig. 8.

[0057] To better understand the principles of the present invention, embodiments of the invention are explained in more detail below with reference to the figures. It is understood that the invention is not limited to these embodiments and that the described features can also be combined or modified without leaving the scope of protection of the invention as defined in the appended claims.

[0058] Fig. 1 schematically shows a photonic radar system RS as an example of a distributed radar system. The radar system RS comprises a central unit Z, several radar transmitters S-1, S-2, S-3,..., Sn, and several radar receivers E-1, E-2, E-3,..., En. The central unit Z is referred to as the backend, and the radar transmitters and radar receivers E-1, E-2, E-3,..., En are referred to as the frontend. Although the radar transmitters S-1, S-2, S-3,..., Sn and the radar receivers E-1, E-2, E-3,..., En are shown here as separate units, they can also be implemented using combined units, each integrating both a transmitter and a receiver.

[0059] The central unit Z is connected via one or more transmission media G to the radar transmitting units S-1, S-2, S-3,..., Sn and the radar receiving units E-1, E-2, E-3,..., En, wherein the transmission media G can be, in particular, one or more optical fibers. In the case of an integrated unit containing circuits for transmitting and receiving, the signal only needs to be sent to this common unit.

[0060] The central processing unit Z generates a frequency-modulated continuous wave (FMCW) signal and processes and evaluates the signals generated by the radar receiver units E-1, E-2, E-3, ..., En. Instead of a frequency-modulated continuous wave signal, a signal with a different waveform can also be generated. This centralized processing and evaluation of the signals allows the individual radar sensors to be designed as small and cost-effectively as possible.

[0061] In the central unit Z, a radar driver signal is generated, which consists of a radar carrier signal with frequency fcarrier and a radar ramp signal with frequency fr. ra m PThe signal is modulated onto an optical carrier signal. The frequency of the radar driver signal is preferably only a fraction of the carrier frequency required to drive the individual radar transmitters. For example, the signal to be transmitted can be modulated with 1 / 8 of the radar frequency. With a carrier frequency of 77 GHz currently common for road vehicles, this results in a frequency of 9.625 GHz. The optical carrier signal modulated with the radar driver signal is then coupled into the transmission medium G.

[0062] The optical carrier signal modulated by the radar driver signal is coupled out of the transmission medium G by each of the individual radar transmitter units S-1, S-2, S-3,..., Sn by means of a coupling unit (not shown), and the radar driver signal is separated in each case. If this radar driver signal is only a fraction of the radar frequency used, for example, 1 / 8 of the radar frequency, it is first amplified eightfold in each of the individual radar transmitter units S-1, S-2, S-3,..., Sn. The resulting signal then drives the respective radar transmitters in the radar transmitter units S-1, S-2, S-3,..., Sn. The individual radar transmitters include, in particular, radar antennas, each of which then transmits a radar signal.

[0063] Additionally, the optical carrier signal is also transmitted to the individual radar receivers E-1, E-2, E-3,..., En and likewise coupled out of the transmission medium G by means of a coupling unit. Radar echo signals are received by the individual radar receivers E-1, E-2, E-3,..., En and modulated onto the optical carrier signal. The resulting signal is coupled into the transmission medium G by means of further coupling units and sent back to the central unit Z.

[0064] The central unit Z receives the signals from the radar receivers E-1, E-2, E-3,..., En, evaluates them, and provides derived radar information. This radar information can then be further processed, for example, to create or update an environmental model.

[0065] The radar transmitting units S-1, S-2, S-3,..., Sn and radar receiving units E-1, E-2, E-3,..., En can each be designed as separate electronically and photonically cointegrated chips (so-called "EPIC chips") or implemented on a single electronically or photonically integrated chip. Silicon photonics technology can be used for the cointegration of the electronic and photonic components, enabling the monolithic integration of photonic components, high-frequency electronics, and digital electronics on a single chip. A hybrid implementation using separate electronic (EIC) and photonic (PIC) chips is also possible.

[0066] The integration of optical components into the chip can be achieved, for example, using so-called silicon-on-insulator (SOI) regions, while the integration of electronic components can be accomplished using bulk silicon regions. In SOI regions, a thin silicon layer is separated from the silicon substrate by an insulating layer, such as silicon dioxide. Since silicon is transparent at the near-infrared wavelengths common in optical communication technology, and the refractive indices of silicon and silicon dioxide differ significantly in this wavelength range, various optical components can be implemented using SOI structures. This allows for high signal quality with low parasitic interference, particularly at high data rates.The integration of the RF circuits for the radar antennas, including the frequency multiplier, with the photonic circuit can be implemented in a monolithic design without additional wire or flip-chip bonding. Furthermore, chips can be optically and electrically tested directly at the wafer level. Additionally, the scalability to large volumes in the highly integrated manufacturing of electronically and photonically integrated circuits enables a significant reduction in assembly costs and a more efficient cost structure.

[0067] The basic principle behind measuring the Doppler velocity of a dynamic object using an FMCW signal model is based on the sequential transmission of several so-called chirps, i.e., frequency-modulated radar signals. This generates a measurement sequence that significantly increases the observation period of an object compared to a single measurement. A phase term relevant for Doppler velocity measurement propagates with each newly emitted measurement signal within the sequence, creating a signal waveform whose underlying frequency is proportional to the Doppler velocity. If an arbitrary sampling step "n" of the measurement chirp is set constant across all chirps within the sequence, the measurement signal s can be determined. n describe a measurement m according to formula (1):

[0068] s n (m) = Aexp

[0069]

[0070] Here, the amplitude of the mixed received signal, v, denoted the velocity of an arbitrary object that was measured during the measurement period, T. RPI the time interval between two successive chirps, a the ratio between the bandwidth and the modulation time of a chirp, d(p) the bi-static distance between the target and the transmitting antenna and receiving antenna pair, T s the sampling interval for collecting the sample samples, c0 the speed of light and R o any default distance to describe a radial distance.

[0071] In the case of a monostatic radar, or a bisstatic radar where the spatial distance between transmitting and receiving antennas is negligible, d(p) = 2R0 applies. The outbound and return paths between the transmitting antenna, receiving antenna, and target are the same. With each additional measurement m within the measurement sequence, only the phase term exp i — 2vT in formula (1) changes. PRI m, which describes the dependence on the Doppler velocity v. If the radar aperture includes additional receiving antennas for which the described property d(p) = 2R0 still applies, the individual measurement signals can be coherently added according to formula (1) to improve the signal-to-noise ratio. The final determination of the Doppler frequency is carried out by frequency analysis in the form of a discrete Fourier transform.

[0072] For bistatic radars, where transmitting and receiving antennas are spatially distributed, the previously made assumption d(p) = 2R0 is no longer valid. Instead, d(p) = 2R0, since the radial distance between the transmitting antenna position p is different. Tx and a target p from the radial distance of the receiving antenna position p Rx and differs from the goal p. Therefore, for d(p):

[0073]

[0074] This property of distributed radars has a significant influence on the calculation of the Doppler velocity, since d(p) within the phase terms exp ( I2n — d(p)nT s ] and

[0075] X c o /

[0076] (i— Z d(p) J the measurement signal is affected nonlinearly. A coherent integration over all receiving antennas, which is advantageous for the signal-to-noise ratio, is no longer feasible. Instead, such an approach can, in the worst case, cause destructive interference and cancel out essential signal components. To counteract this problem, all nonlinear phase components in the measurement signal must be compensated according to formula (1) when using a distributed radar before processing the Doppler. Since the direction angles inherent in formula (2) are unknown in the Doppler measurement process step, hypotheses about all targets within all angular and distance intervals within the radar's field of view must be formulated and applied to compensate for the nonlinear phase components.Starting with the input dataset, it is multiplied by a hypothesis dataset, accumulated over the dimension of the receiving antennas, and finally Fourier-transformed over the dimension of the received sequence. Each hypothesis dataset assumes a target in the direction of an assumed solid angle, which occurs within each distance gate. The effort required to compensate for the nonlinear phase terms increases linearly according to the granularity with which the individual hypotheses differ from one another. With a conventional approach that only subjects the transmit sequence of a receiving antenna of a receiving channel to a Fourier transform, there is a risk of no longer being able to distinguish target information from noise.

[0077] Figure 2 schematically illustrates an embodiment of a central unit according to the invention for a distributed radar system. The distributed radar system is again, by way of example, a photonic radar system. The thin lines in Figure 2 represent electrical connections, and the thick lines represent connections via optical waveguides.

[0078] To provide the optical carrier signal, the central unit Z comprises a light source 11. This can be, in particular, a laser diode that emits continuous laser light in the near-infrared range. Preferably, the wavelength of the laser diode is in a range where optical losses and dispersion are as low as possible, for example, 850 nm, 1310 nm, or 1550 nm. However, an ASE (Amplified Spontaneous Emission) light source can also be used, which emits light generated by spontaneous emission and subsequently optically amplified by stimulated emission.

[0079] The optical carrier signal generated by the light source 11 is fed to an electro-optic modulator 12, which modulates the electrical radar driver signal, consisting of the radar carrier signal and the radar ramp signal, onto the optical carrier signal. The radar ramp signal is generated by a ramp generator 13. For example, the electro-optic modulator 12 can be a Mach-Zehnder modulator, in which the optical carrier signal is first split into two waveguides where phase modulation is performed and then recombined. Depending on their relative phase, the partial signals superimpose to form the modulated output signal. Alternative modulation principles, such as those using directly modulated light sources, are also possible.

[0080] The optical carrier signal modulated by the electro-optic modulator 12 is then fed to an optical processing unit 14, which ensures that a first transmission signal SC is provided for one of the radar transmitting units in the form of a continuous sequence of chirp signals, wherein the one radar transmitting unit emits on a first frequency band, and that second transmission signals Sl are provided alternately for the other radar transmitting units, each in the form of an intermittent sequence of chirp signals, wherein the other radar transmitting units emit on a second frequency band different from the first frequency band.

[0081] To receive and evaluate the signals received by the radar receivers, which are distance-dependent, time-delayed copies of the signals emitted by the radar transmitters, the central unit Z comprises an optical receiver 15 and an evaluation unit 16. First radar echo signals RC, resulting from the first transmitted signal SC, are received from a first subset of the radar receivers, and second radar echo signals Rl, resulting from the second transmitted signals Sl, are received from a second subset. The optical receiver 15 comprises, for each modulated signal RC, Rl of an associated radar receiver to be evaluated, a photodiode 17, a transimpedance amplifier 18, and an IQ mixer 19. The optical receiver 15 may also include filter units for selecting individual wavelength ranges, etc.Each of the modulated signals RC, Rl is converted into an output current by the photodiode 17. The output current is then converted into a proportional voltage signal in the transimpedance amplifier 18 and subsequently demodulated in the IQ mixer 19. The demodulated signal is fed to the evaluation unit 16, which derives radar information from the signal. This radar information can then be output and further processed, for example, for environmental detection.

[0082] Additionally, the electrical and optical components of the central unit Z can be controlled via one or more optional control interfaces and control units 20. In particular, this includes switching the electrical and optical components on and off, parameterizing them, diagnosing them, etc. Furthermore, communication with the radar transmitters and receivers can also be established via the control interfaces and control units 20, and this communication can be carried out electrically, optically, or electrically and optically. For clarity, the control interfaces and control units 20 are shown in a single component in Fig. 2; however, in a given implementation, they can also be divided into several blocks.

[0083] Fig. 3 schematically shows a method for operating a central unit according to the invention for a distributed radar system, which, in addition to the central unit, comprises two or more radar transmitters and two or more radar receivers. In this method, the central unit provides a first transmission signal in the form of a continuous sequence of chirp signals S1 to one of the two or more radar transmitters. This one radar transmitter emits on a first frequency band. Second transmission signals, each in the form of an intermittent sequence of chirp signals S2, are provided alternately to the other two or more radar transmitters. These other radar transmitters emit on a second frequency band different from the first. First radar echo signals S3, resulting from the first transmission signal, are received by a first subset of the two or more radar receivers.Second radar echo signals S4 are received from a second subset of the two or more radar receiving units, resulting from the second transmitted signals. The first radar echo signals received from the first subset are then evaluated for a Doppler measurement S5.

[0084] Figure 4 schematically shows an exemplary large-area integration of a multitude of antenna chips A, each of which can comprise the described radar transmitting units and / or radar receiving units, on the vehicle surface of a means of transport F, here a passenger car. For example, the windshield, rear window, and bumper can be used for integration into the front and rear, and the vehicle floor, roof, and B-pillar for integration along the sides of the vehicle. The central unit of the photonic radar system is not shown in this illustration and can, for example, be implemented as a radar control unit located in the vehicle's interior or engine compartment. Likewise, the figure omits the representation of the transmission media between the central unit and the antenna chips.

[0085] Preferred embodiments of the invention will now be explained with reference to Figures 5 to 11. In these embodiments, the distributed radar system is a photonic radar system. Figure 5 shows a first embodiment of a backend or central processing unit Z for a distributed radar system. Figure 5a) shows the central processing unit Z and Figure 5b) shows the provided chirp sequences SC and Sl. In this embodiment of the central processing unit Z, the entire frequency band from f0 to f0 + 2Af is used for frequency modulation. The thin lines represent electrical connections, and the thick lines represent connections via optical waveguides.

[0086] Starting with an electrically frequency-modulated transmission signal, this is modulated onto an optical carrier signal from a light source 11 by means of an electro-optical modulator 12. Different transmission sequences of the output signals SC, Sl are provided via an optical control unit 23 and an optical switch 22. One of the output channels SC provides a continuous chirp sequence, while the remaining output channels Sl switch between the individual chirps of the sequence. All output channels SC, Sl cover the same frequency band. For distribution across different frequency bands, the front end must configure the passband of a filter for the corresponding frequency band. Optionally, an arrayed waveguide grating 24 can be provided to divide the optical carrier signal from the light source 11 into different carrier signals based on their wavelength.In addition, a feedback loop 21 may be provided, for example for the control of the carrier-envelope offset (CEO) or the carrier-envelope phase (CEP).

[0087] To receive and evaluate the signals RC, Rl received by the radar receivers, the central unit Z comprises one photodiode 17 for each modulated signal RC, Rl of an associated radar receiver. First radar echo signals RC, resulting from the first transmitted signal SC, are received from a first subset of the radar receivers, and second radar echo signals Rl, resulting from the second transmitted signals Sl, are received from a second subset. The output signals of the photodiodes 17 are digitized via a digital interface 25, e.g., an analog-to-digital converter, and fed to an evaluation unit 16, e.g., a PC or a graphics processing unit. Optionally, a signal processing unit 26 can be connected upstream, e.g., for a fast Fourier transform (FFT). An electrical output channel E oand an electrical input channel Ej allows communication between the central unit Z and the radar transmitting units and radar receiving units.

[0088] Fig. 6 shows radar transmitter units S-1, S-2, S-3, Sn of a front end for the back end from Fig. 5. The radar transmitter units S-1, S-2, S-3, Sn are shown as a semiconductor structure.

[0089] According to the preferred frequency band on which the virtual array is based, the continuously switching output channels are connected via optical couplers 30 to the inputs of the transmitting antennas Txi to Tx n -i is set. A downstream optical filter 31 allows the transmission of the preferred frequency band. The output of the backend that generates a continuous signal sequence is connected via an optical coupler 30 to the input for the designated transmitting antenna Tx. nlaid out. Here too, a downstream filter 31 ensures the passage of the corresponding frequency band for Doppler processing. The signals for driving the transmitting antennas Txi to Tx n Each signal is amplified by an amplifier 32.

[0090] Fig. 7 shows radar receiver units E-1, E-2, E-3, En of a front end for the back end from Fig. 5. The radar receiver units E-1, E-2, E-3, En are shown as a semiconductor structure. According to the preferred frequency band on which the virtual array is based, the continuously switching output channels are connected via optical couplers 30 to the inputs of the receiving antennas Rxi to Rx. n-i is set. A downstream optical filter 31 allows the transmission of the preferred frequency band. The output of the backend that generates a continuous signal sequence is connected via an optical coupler 30 to the input for the designated receiving antenna Rx. n laid out. Here too, a downstream filter 31 ensures the passage of the corresponding frequency band for Doppler processing. The receiving antennas Rxi to Rx nThe received signals are each amplified by an amplifier 32. Depending on the underlying frequency band, the received signal is mixed with the reference signal, i.e., the transmitted signal, by means of a mixer 33. The intermediate signal thus generated is passed on to an optical modulator 34, electro-optically converted, and transmitted to the backend via an optical coupler 30 and an optical fiber. A second mixer 33 in the illustrated radar receiver En ensures that the designated receiving antenna Rx n It can also be used as part of a virtual aperture. Fig. 8 shows a second embodiment of a backend or central unit Z for a distributed radar system. Fig. 8a) shows the central unit Z and Fig. 8b) shows the provided chirp sequences SC and Sl. The thin lines again represent electrical connections, the thick lines connections via optical waveguides.

[0091] The backend largely corresponds to that shown in Fig. 5; however, in this embodiment, the output signals SC and Sl utilize different portions of the frequency band. The starting point consists of two frequency modulators that generate an electrically frequency-modulated output signal within the specified frequency bands. These output signals are then modulated onto an optical carrier signal from a light source 11 by means of two electro-optical modulators 12. While one output signal is passed on to an optical switch 22 and generates an alternating sequence of transmissions for the output signals Sl, the other output signal is fed directly to the output channel SC and provides a continuous transmission sequence. The output channels for the output signals Sl and SC emit at different transmission frequencies.

[0092] Fig. 9 shows radar transmitter units S-1, S-2, S-3, Sn of a front end for the back end from Fig. 8. The radar transmitter units S-1, S-2, S-3, Sn are shown as a semiconductor structure.

[0093] According to the preferred frequency band on which the virtual array is based, the continuously switching output channels are connected via optical couplers 30 to the inputs of the transmitting antennas Txi to Tx n -i. The output of the backend that generates a continuous signal sequence is connected via an optical coupler 30 to the input for the designated transmitting antenna Tx. n laid. The signals for driving the transmitting antennas Txi to Tx n Each signal is amplified by an amplifier 32.

[0094] Fig. 10 shows a first embodiment of radar receiver units E-1, E-2, E-3, En of a front end for the back end from Fig. 8. The radar receiver units E-1, E-2, E-3, En are shown as a semiconductor structure. According to the preferred frequency band on which the virtual array is based, the continuously switching output channels are connected to the inputs of the receiving antennas Rxi to Rxn-i via optical couplers 30. The output of the back end that generates a continuous signal sequence is connected via an optical coupler 30 to the input for the designated receiving antenna Rx. n laid. The receiving antennas Rxi to Rx nThe received signals are each amplified by an amplifier 32. Depending on the underlying frequency band, the received signal is mixed with the reference signal, i.e., the transmitted signal, by means of a mixer 33. The intermediate signal thus generated is passed on to an optical modulator 34, electro-optically converted, and transmitted to the backend via an optical coupler 30 and an optical fiber.

[0095] Fig. 11 shows a second embodiment of radar receiver units E-1, E-2, E-3, En of a front end for the back end from Fig. 8. The radar receiver units E-1, E-2, E-3, En are shown as a semiconductor structure. According to the preferred frequency band on which the virtual array is based, the continuously switching output channels are connected via optical couplers 30 to the inputs of the receiving antennas Rxi to Rx. n-i. The output of the backend that generates a continuous signal sequence is connected via an optical coupler 30 to the input for the designated receiving antenna Rx. n laid. The receiving antennas Rxi to Rx n The received signals are each amplified by an amplifier 32. Depending on the underlying frequency band, the received signal is mixed with the reference signal, i.e., the transmitted signal, by means of a mixer 33. The intermediate signal thus generated is passed on to an optical modulator 34, electro-optically converted, and transmitted to the backend via an optical coupler 30 and an optical fiber. A second mixer 33 in the illustrated radar receiver En ensures that the designated receiving antenna Rx n It can also be used as part of a virtual aperture. Reference sign list

[0096] A antenna chip

[0097] E-1, E-2, E-3, En radar receiver unit

[0098] Egg Electrical input channel

[0099] Eo Electrical output channel

[0100] F Means of transport

[0101] G transmission medium

[0102] OM-1, OM-2 frequency modulator

[0103] RC First radar echo signal

[0104] Rl Second radar echo signal

[0105] RS Distributed Radar System

[0106] RXj receiving antenna

[0107] S-1, S-2, S-3, Sn radar transmitter unit

[0108] SC First transmission signal

[0109] Second transmission signal

[0110] Txi transmitting antenna

[0111] Central processing unit

[0112] 11 Light source

[0113] 12 Electro-optical modulator

[0114] 13 Ramp generator

[0115] 14 Optical Processing Unit

[0116] 15 Optical receiving unit

[0117] 16 evaluation units

[0118] 17 Photodiode

[0119] 18 T transimpedance amplifiers

[0120] 19 IQ mixers

[0121] 20 Control interface and control unit 21 Feedback loop

[0122] 22 Optical Switch

[0123] 23 Optical control unit

[0124] 24 Arrayed Waveguide Grating

[0125] 25 Digital interface Signal processing unit

[0126] Optical coupler

[0127] Optical filter

[0128] amplifier

[0129] mixer

[0130] Optical modulator

[0131] Providing an initial transmission signal

[0132] Providing second transmission signals

[0133] Received first radar echo signals

[0134] Receiving second radar echo signals

[0135] Evaluating the first radar echo signals for Doppler measurement

Claims

- 22 - Patent claims 1. Central unit (Z) for a distributed radar system (RS), which, in addition to the central unit (Z), comprises two or more radar transmitting units (S-1, S-2, S-3, Sn) and two or more radar receiving units (E-1, E-2, E-3, En), wherein the central unit (Z) is configured as follows: - to provide a first transmit signal (SC) in the form of a continuous sequence of chirp signals (S1) for one of the two or more radar transmitting units (S-1, S-2, S-3, Sn), wherein the one radar transmitting unit (S-1, S-2, S-3, Sn) emits on a first frequency band; - to provide second transmission signals (S1) alternately for the other two or more radar transmitting units (S-1, S-2, S-3, Sn) in the form of an intermittent sequence of chirp signals (S2), wherein the other radar transmitting units (S-1, S-2, S-3, Sn) emit on a second frequency band different from the first frequency band; - to receive first radar echo signals (RC) (S3) from a first subset of the two or more radar receiving units (E-1 , E-2, E-3, En) resulting from the first transmitted signal (S- C); - to receive second radar echo signals (Rl) from a second subset of the two or more radar receiving units (E-1 , E-2, E-3, En) (S4) resulting from the second transmitted signals (Sl); and - to evaluate the first radar echo signals (RC) received from the first subset for a Doppler measurement (S5).

2. Central unit (Z) according to claim 1, wherein the distributed radar system (RS) is configured as a photonic radar system.

3. Central unit (Z) according to claim 1 or 2, wherein the first transmit signal (SC) and the second transmit signals (Sl) cover the same frequency band.

4. Central processing unit (Z) according to claim 3, wherein the second transmission signals (Sl) are generated by switching between the individual chirp signals of the first transmission signal (SC).

5. Central processing unit (Z) according to claim 1 or 2, wherein the first transmission signal (SC) and the second transmission signals (Sl) cover different frequency bands.

6. Central unit (Z) according to claim 5, wherein the first transmit signal (SC) and the second transmit signals (Sl) are shaped by two frequency modulators (OM-1, OM-2).

7. Central unit (Z) according to one of the preceding claims, wherein the first subset of the two or more radar receiving units (E-1, E-2, E-3, En) comprises exactly one radar receiving unit (E-1, E-2, E-3, En).

8. Method for operating a central unit (Z) for a distributed radar system (RS), which, in addition to the central unit (Z), comprises two or more radar transmitting units (S-1, S-2, S-3, Sn) and two or more radar receiving units (E-1, E-2, E-3, En), wherein the central unit (Z): - for one of the two or more radar transmitting units (S-1, S-2, S-3, Sn) a first transmit signal (SC) in the form of a continuous sequence of chirp signals is provided (S1), wherein one radar transmitting unit (S-1, S-2, S-3, Sn) emits on a first frequency band; - for the other two or more radar transmitting units (S-1, S-2, S-3, Sn) second transmitting signals (S1) are provided alternately in the form of an intermittent sequence of chirp signals (S2), wherein the other radar transmitting units (S-1, S-2, S-3, Sn) emit on a second frequency band different from the first frequency band; - first radar echo signals (RC) are received from a first subset of the two or more radar receiving units (E-1 , E-2, E-3, En) (S3), resulting from the first transmitted signal (SC); - second radar echo signals (Rl) are received from a second subset of the two or more radar receiving units (E-1, E-2, E-3, En) (S4), resulting from the second transmitted signals (Sl); and - the first radar echo signals (RC) received from the first subset are evaluated for a Doppler measurement (S5).

9. Computer program with instructions which, when executed by a processor, cause the processor to execute the steps of the method according to claim 8.

10. Radar transmitting unit (S-1, S-2, S-3, Sn) for a distributed radar system (RS), wherein the radar transmitting unit (S-1, S-2, S-3, Sn) has a filter (31) for passing a predetermined frequency band.

11. Radar receiving unit (E-1, E-2, E-3, En) for a distributed radar system (RS), wherein the radar receiving unit (E-1, E-2, E-3, En) is configured to output radar echo signals (RC, Rl) on two different frequency bands.

12. Distributed radar system (RS) with a central unit (Z) according to any one of claims 1 to 8.

13. Distributed radar system (RS) according to claim 12, wherein the radar transmitting units (S-1, S-2, S-3, Sn) and the radar receiving units (E-1, E-2, E-3, En) are each integrated into a common unit.

14. Distributed radar system (RS) according to claim 12 or 13, wherein the distributed radar system (RS) is configured as a photonic radar system.

15. Means of transport (F) with a distributed radar system (RS) according to any one of claims 12 to 14.

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