Photonic radar system with central down-mixing of the radar signals

Abstract

The invention relates to a central unit (Z) for a radar system which, in addition to the central unit (Z), comprises at least one radar transmitting unit (S-1, S-2, S-3, S-n) and at least one radar receiving unit (E-1, E-2, E-3, E-n). An optical carrier signal is provided by the central unit (Z), a radar driver signal is modulated onto the optical carrier signal, and the optical carrier signal modulated with the radar driver signal is transmitted to the at least one radar transmitting unit (S-1, S-2, S-3, S-n) and / or the at least one radar receiving unit (E-1, E-2, E-3, E-n). The central unit (Z) receives an optical signal from the at least one radar receiving unit (E-1, E-2, E-3, E-n) on which a radar echo signal is superimposed, and separates the superimposed radar echo signal from the received optical signal by means of an optical-electrical conversion. A down-conversion of the radar echo signal into a lower-frequency signal is carried out in the central unit (Z) by mixing the optical-to-electrical converted radar echo signal with a local oscillator signal.

Description

[0001] Description

[0002] Photonic radar system with central downmixing of radar signals

[0003] The present invention relates to a central unit for a radar system, which can, for example, be operated in a vehicle. The present invention further relates to a radar system with such a central unit. The invention also relates to a method for operating such a central unit and to a vehicle that has a radar system with such a central unit.

[0004] For driver assistance systems and safety systems in fully automated driving, the safest possible perception of the surroundings is essential. This is achieved by using sensors such as radar, lidar, and camera sensors integrated into the vehicle to detect the environment.

[0005] For example, an environmental model can be created based on the acquired sensor data using a suitable machine learning model. This can involve perception modules that can recognize learned objects in the environment and forward this information to a planning module. The planning module can then take the recognized objects into account for trajectory planning and safe vehicle control. Of particular importance here is a comprehensive 360° 3D capture, enabling complete 360-degree recording of all static and dynamic objects and the creation of the highest possible resolution 3D models of the environment.

[0006] 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 reliability.

[0007] 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 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 of 0.1° and below, with high insensitivity to interference from their surroundings. This cannot be achieved with conventional radar technology because the resolution of such systems is too low.

[0008] 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 frequency range. This allows for the co-integration of electronic and photonic components on a single semiconductor substrate, enabling extremely compact form factors for the individual radar sensors and, consequently, arrays with a large number of 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 gigahertz range, is converted into a lower intermediate frequency (INF) signal.intermediate frequency (IF), typically in the sub-gigahertz range, is converted.

[0009] German patent application DE 10 2017221 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.

[0010] In contrast to the prior art, one object of the invention is to provide a central unit for a radar system and a method for operating such a central unit, by means of which the requirements for implementing the radar system can be reduced. This object is achieved by the independent claims. Preferred embodiments of the invention are the subject of the dependent claims.

[0011] The invention is based on the finding that the electronics required in each individual sensor unit for downmixing the received radar echo signal into a lower frequency IF range can be avoided, thus reducing power consumption and the required chip area in the sensor units, if the mixing is performed in a central unit, hereinafter also referred to as the backend. The radar receiver units in the frontend can then be significantly simplified.

[0012] According to one aspect of the invention, a central unit for a radar system is provided, which, in addition to the central unit, comprises at least one radar transmitter and at least one radar receiver, wherein the central unit is configured to provide an optical carrier signal, to modulate a radar driver signal onto the optical carrier signal, and to send the optical carrier signal modulated with the radar driver signal to the at least one radar transmitter and / or the at least one radar receiver, to receive an optical signal from the at least one radar receiver to which a radar echo signal is superimposed, and to separate the superimposed radar echo signal from the received optical signal by means of an opto-electrical conversion.and to perform a downward conversion of the radar echo signal into a lower frequency signal by mixing the optically-to-electrically converted radar echo signal with a local oscillator signal.

[0013] Compared to known photonic radar systems, where the mixing is done in the individual radar receiver units of the photonic radar system, this reduces costs and installation space requirements.

[0014] Preferably, the central unit comprises an optical receiving and processing unit and at least one electrical mixer, wherein the optical receiving and processing unit is configured to receive the optical signal from the at least one radar receiving unit and to separate the superimposed radar echo signal, and wherein the optically-to-electrically converted radar echo signal is supplied to the at least one electrical mixer by the optical receiving and processing unit and the local oscillator signal is supplied by a local oscillator, and the radar echo signal is down-converted by mixing the radar echo signal with the local oscillator in the electrical mixer.

[0015] Likewise, the central unit preferably comprises a light source, an electro-optical modulator and a ramp generator, wherein the optical carrier signal generated by the light source is supplied to the electro-optical modulator, which modulates an electrical radar driver signal, consisting of a radar carrier signal and a radar ramp signal, onto the optical carrier signal, and wherein the radar ramp signal is generated by the ramp generator.

[0016] According to one embodiment of the invention, the local oscillator signal is supplied to the at least one electrical mixer from the ramp generator via an electrical connection.

[0017] According to a further embodiment of the invention, the local oscillator signal is regenerated via an optical-to-electrical conversion of the modulated optical carrier signal.

[0018] Advantageously, the optical carrier signal modulated by the electro-optical modulator can be fed to an optical beam splitter, and a partial beam generated by the optical beam splitter can be fed to an optical processing unit in which the local oscillator signal superimposed on the optical signal is separated by means of an opto-electrical conversion, wherein the local oscillator signal thus extracted from the optical signal is fed to the at least one electrical mixer.

[0019] In particular, the low-frequency radar echo signal generated in the central unit can be converted into a digital signal after downconversion.

[0020] According to another aspect of the invention, a radar system comprising a central unit according to the invention is provided.

[0021] In the radar system according to the invention, the radar transmitting units and the radar receiving units can each be integrated into a common unit.

[0022] According to a further aspect of the invention, a method for operating a central unit for a radar system, which in addition to a central unit comprises at least one radar transmitter and at least one radar receiver, is provided, wherein the central unit provides an optical carrier signal, a radar driver signal is modulated onto the optical carrier signal, and the optical carrier signal modulated with the radar driver signal is sent to the at least one radar transmitter and / or the at least one radar receiver, from which an optical signal is received to which a radar echo signal is superimposed, and the superimposed radar echo signal is separated from the received optical signal by means of an opto-electrical conversion.and by mixing the optically-to-electrically converted radar echo signal with a local oscillator signal, a downward conversion of the radar echo signal into a lower-frequency signal is carried out.

[0023] Finally, the invention also includes a vehicle that has a radar system with a central unit according to the invention.

[0024] Further features of the present invention will become apparent from the following description and the claims in conjunction with the figures. These show:

[0025] Fig. 1 shows a schematic representation of one embodiment of the radar system;

[0026] Fig. 2 shows a schematic representation of a first embodiment of a central unit of the radar system with integrated down-conversion of the received radar echo signal;

[0027] Fig. 3 shows a schematic representation of a second embodiment of a central unit of the radar system with integrated down-conversion of the received radar echo signal; and

[0028] Fig. 4 shows an exemplary integration of the radar system on the vehicle surface of a passenger car.

[0029] 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 departing from the scope of protection of the invention as defined in the claims.

[0030] In the following figures, electrical connections are represented by solid lines and optical connections by dashed lines for differentiation.

[0031] Figure 1 shows a schematic representation of a photonic radar system. For the sake of clarity, the downconversion of the radar echo signal in the central unit according to the invention is not shown in this figure, but is explained in detail in connection with the other figures.

[0032] The radar system 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 is referred to as the backend, and the radar transmitters and receivers as the frontend. Although the radar transmitters and receivers are depicted here as separate units, they can also be implemented using combined units that integrate both a transmitter and a receiver.

[0033] 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 can in particular be one or more optical fibers. In the case of an integrated unit on which circuits for transmitting and receiving are located, the signal only needs to be sent to this common unit.

[0034] 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.

[0035] At the central station, 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 radar driver 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.

[0036] 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.

[0037] 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 then coupled into the transmission medium G by means of further coupling units and sent back to the central unit.

[0038] The central unit Z then 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.

[0039] The radar transmitters and receivers 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.

[0040] 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.

[0041] Figure 2 schematically shows a first embodiment of a central unit of a photonic radar system according to the invention, in which components for downmixing high-frequency radar signals into a lower-frequency IF range are integrated.

[0042] 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.

[0043] The optical carrier signal generated by the light source 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 15. 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, e.g., using directly modulated light sources, are also possible.

[0044] The optical carrier signal modulated by the electro-optical modulator 12 is first fed to an optional optical control unit 13, which can, for example, control or regulate the amplitude, phase, or polarization of the modulated optical carrier signal. Subsequently, the modulated optical carrier signal is fed to an optical 1:N switch or beam splitter 14, which ensures that the radar driver signal can be provided on multiple channels for the individual radar transmitters and / or radar receivers.

[0045] To receive and evaluate the signals received by the radar receivers, which are a distance-dependent, time-delayed copy of the signals emitted by the radar transmitters, the central unit Z initially comprises an optical receiver and processing unit 17. In the optical receiver and processing unit 17, the radar echo signal superimposed on the optical signal is separated by means of an opto-electrical conversion. For this purpose, a unit for separating the signals from the different radar receivers and, for each of the separated signals, a photodiode, each fast enough to detect even an unconverted radar echo signal, can be provided. Suitable photodiodes are known to those skilled in the art and are described, for example, in S. Lischke et al., “Ultra-fast germanium photodiode with 3-dB bandwidth of 265 GHz,” in Nature Photonics, 15, pp. 925–931, 2021.

[0046] The optically-to-electrically converted radar echo signal is then fed to at least one electrical mixer 18. A local oscillator signal, tapped from the electrical ramp generator 15, is fed to the second input of each mixer. Prior to this, the local oscillator signal can be processed in an optional electrical processing unit 16, for example, by amplification, phase shifting, or filtering. Mixing the radar echo signal with the local oscillator in the electrical mixer 18 then generates a low-frequency (IF) signal, typically in the sub-gigahertz range. Subsequently, the down-converted radar echo signal can also be amplified and further baseband processed by an optional additional electrical processing unit 19, for example, by phase shifting or filtering.The resulting signal is then first fed to a digital interface 20, where it is digitized by analog-to-digital converters. Optionally, further processing of the digitized signals can take place in a preprocessing unit 21, for example by means of an FFT to divide the signal into several frequency components.

[0047] The pre-processed signal is then fed to the evaluation unit 22, which derives radar information from the signal. This radar information can then be output and further processed, for example, for environmental detection.

[0048] Additionally, the electrical and optical components of the central unit Z can be controlled via one or more optional control interfaces and units 23, 24. 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 units 23, 24, and this communication can be carried out electrically, optically, or electrically and optically. For clarity, the control interfaces and units 23, 24 are divided into several blocks in the figure; however, in one implementation, they can also be realized in a single component.

[0049] Figure 3 schematically illustrates a second embodiment of a central unit of a photonic radar system according to the invention. The components of the central unit, in particular those for providing the modulated optical carrier signal, separating the radar echo signal from the optical signal received by the front end, and further processing the downmixed signal, partially correspond to those of the first embodiment; corresponding components are therefore designated with the same reference numerals and are not explained again. However, the generation of the local oscillator signal is not achieved here by purely electrical tapping at the ramp generator, but rather by an optical-to-electrical conversion of the modulated optical carrier signal.

[0050] For this purpose, the optical carrier signal modulated by the electro-optic modulator 12 is fed to an optical beam splitter or switch 25, which splits off a partial beam and feeds it to an optical processing unit 26. In the optical processing unit 26, the local oscillator signal superimposed on the optical signal is separated by means of an opto-electrical conversion. The local oscillator signal extracted from the optical signal in this way can first be processed in an optional electrical processing unit 27, for example by amplification, phase shifting, or filtering, before it is then fed to the at least one electrical mixer 18. The mixing of the radar echo signal with the local oscillator in the electrical mixer 18, as well as the processing of the downmixed signals, then takes place as in the first embodiment.

[0051] One advantage of this embodiment is that, ideally, the local oscillator experiences identical disturbances from optical-to-electrical and electrical-to-optical conversion as the radar echo signal, which in turn improves the quality of the IF signal.

[0052] 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, onto the vehicle surface of 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. 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. Similarly, the figure omits the representation of the transmission media between the central unit and the antenna chips.

[0053] The radar system, the central unit, and the method according to the invention can be used, in particular, in any road vehicles, such as passenger cars, commercial vehicles, trucks, or buses, in which radar-based environmental sensing is used, for example, for driver assistance systems or for automatic or autonomous driving functions, but is not limited to this. Application in radar-based environmental sensing in other technical fields is also possible. List of reference numerals

[0054] Central processing unit

[0055] S-1, S-2, S-3, Sn Radar transmitting units E-1, E-2, E-3, En Radar receiving units G Transmission medium 11 Light source 12 Electro-optical modulator 13 Optical control unit 14 Optical 1:N switch or divider 15 Ramp generator 16, 19, 21 Electrical processing unit 17 Optical receiving and processing unit 18 Electrical mixer 20 Analog-to-digital converter 22 Evaluation unit 23, 24 Electrical control interface and unit 25 Optical 1:N switch or divider 26 Optical processing unit 27 Electrical processing unit A Antenna chip

Claims

Patent claims 1. Central unit (Z) for a radar system, comprising, in addition to the central unit (Z), at least one radar transmitter (S-1, S-2, S-3, Sn) and at least one radar receiver (E-1, E-2, E-3, En), wherein the central unit (Z) is configured to provide an optical carrier signal, to modulate a radar driver signal onto the optical carrier signal, and to transmit the optical carrier signal modulated with the radar driver signal to the at least one radar transmitter (S-1, S-2, S-3, Sn) and / or the at least one radar receiver (E-1, E-2, E-3, En), to receive an optical signal from the at least one radar receiver (E-1, E-2, E-3, En) to which a radar echo signal is superimposed, and to separate the superimposed radar echo signal from the received optical signal by means of an opto-electrical conversion.and to perform a downward conversion of the radar echo signal into a lower frequency signal by mixing the optically-to-electrically converted radar echo signal with a local oscillator signal.

2. Central unit according to claim 1, wherein the central unit (Z) comprises an optical receiving and processing unit (17) and at least one electrical mixer (18), wherein the optical receiving and processing unit (17) is configured to receive the optical signal from the at least one radar receiving unit (E-1, E-2, E-3, En) and to separate the superimposed radar echo signal, and to which the optically-to-electrically converted radar echo signal and the local oscillator signal are supplied by the optical receiving and processing unit (17) to the at least one electrical mixer (18), and the radar echo signal is down-converted by mixing the radar echo signal with the local oscillator in the electrical mixer (18).

3. Central unit according to claim 2, wherein the central unit (Z) comprises a light source (11), an electro-optical modulator (12) and a ramp generator (15), wherein the optical carrier signal generated by the light source is supplied to the electro-optical modulator (12), which applies an electrical radar driver signal to the optical carrier signal. consisting of a radar carrier signal and a radar ramp signal, modulated, wherein the radar ramp signal is generated by the ramp generator (15).

4. Central unit according to claim 3, wherein the local oscillator signal is supplied to the at least one electrical mixer (18) from the ramp generator (15) via an electrical connection.

5. Central unit according to claim 3, wherein the local oscillator signal is regenerated via an optical-to-electrical conversion of the modulated optical carrier signal.

6. Central unit according to claim 5, wherein the optical carrier signal modulated by the electro-optic modulator (12) is supplied to an optical beam splitter (25) and a partial beam generated by the optical beam splitter is supplied to an optical processing unit (26) in which the local oscillator signal superimposed on the optical signal is separated by means of an opto-electrical conversion and wherein the local oscillator signal thus extracted from the optical signal is supplied to the at least one electrical mixer (18).

7. Central unit according to one of the preceding claims, wherein the low-frequency radar echo signal generated in the central unit is converted into a digital signal after down-conversion.

8. Radar system with a central unit (Z) according to any one of claims 1 to 7.

9. Radar system according to claim 8, wherein the radar transmitting units and the radar receiving units are each integrated into a common unit.

10. Method for operating a central unit (Z) for a radar system, which, in addition to a central unit (Z), comprises at least one radar transmitter (S-1, S-2, S-3, Sn) and at least one radar receiver (E-1, E-2, E-3, En), wherein the central unit (Z) provides an optical carrier signal, modulates a radar driver signal onto the optical carrier signal, and transmits the optical carrier signal modulated with the radar driver signal to the at least one radar transmitter (S-1, S-2, S-3, Sn) and / or the at least one radar receiver (E-1, E-2, E-3, En). - 15 - from which at least one radar receiving unit (E-1 , E-2, E-3, En) receives an optical signal to which a radar echo signal is superimposed, the superimposed radar echo signal is separated from the received optical signal by means of an opto-electrical conversion, and a downward conversion of the radar echo signal into a lower frequency signal is carried out by mixing the opto-to-electrical converted radar echo signal with a local oscillator signal.

11. Vehicle comprising a radar system with a central unit (Z) according to any one of claims 1 to 7.

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