Angle resolution radar system
By configuring frequency-spaced signals and performing mixed-frequency phase difference analysis in a cooperative radar system, the resolution and determinism problems of angle estimation in the prior art are solved, enabling target localization with large aperture and high resolution, and improving the accuracy and range of angle estimation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-12
- Publication Date
- 2026-04-14
AI Technical Summary
Existing cooperative radar systems struggle to achieve both high-resolution and precise target localization in angle estimation, especially due to the limited dynamic range caused by aperture constraints and sidelobe effects resulting from antenna spacing.
By configuring two radar sensors to send signals with a pre-given frequency interval, and comparing them with a reference signal after mixing, the angle is estimated using the phase difference of the signals. Combined with the high angle resolution capability of MIMO radar sensors, large aperture and high resolution angle estimation can be achieved.
It achieves clear and high-resolution target angle estimation over a wide angle range. By increasing the wavelength of the hypothetical radar wave, it overcomes the limitation of the Nyquist uniqueness criterion and improves the accuracy and resolution of angle estimation.
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Figure CN121866482A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to an angle-resolved radar system having two radar sensors arranged at a predetermined spacing, the radar sensors being configured to transmit coherent radar signals and being oriented such that a signal transmitted by one of the radar sensors and reflected on an object can be received by the other sensor. Background Technology
[0002] The radar systems described above are called cooperative radar systems and are increasingly being used in motor vehicles to detect traffic conditions.
[0003] The angle-resolving radar system based on existing technology is described, for example, in Schor's "Hochauflösende Winkelschätzung für automobile Radarsysteme (High-Resolution Angle Estimation of Automobile Radar Systems)," published by Dr. Hut, 2010.
[0004] In angle-resolved SIMO radar systems, the aperture size is limited by the fact that only a finite number of receive channels can be provided with reasonable overhead. In MIMO (Multiple-Input Multiple-Output) radar systems, attempts have been made to arrange the transmit and receive antennas in a way that allows for a large virtual aperture and thus high angle separation with a given number of transmit and receive channels, while minimizing sidelobes that are unavoidable due to the limited number of antennas and partly due to the large antenna spacing. However, achieving both precise and high-resolution angle estimation using these methods is difficult, for example, at the cost of reduced dynamic range. Summary of the Invention
[0005] The objective of this invention is to improve angle estimation in cooperative radar systems.
[0006] The present invention solves this problem by means of the following: signals transmitted by two radar sensors have frequencies f1 and f2 having a pre-given frequency interval f2-f1; at least one of the radar sensors is configured to mix a signal transmitted by the other sensor and reflected on an object with a signal transmitted by the other sensor; and an analysis and processing device is configured to compare the baseband signal generated by the mixing with a reference signal that is the same as the signal transmitted by the other sensor, and to determine the positioning angle (Ortungswinkel) of the object reflecting the signal based on the phase difference between these signals.
[0007] In cooperative radar systems, very large apertures are achieved through large spatial spacing between two or more radar sensors. However, since these spacings are much larger than the wavelength of the radar radiation, the Nyquist uniqueness criterion is severely violated. According to the present invention, the signals transmitted by the radar sensors, although rigidly coupled to each other in phase, have different frequencies. The frequency spacing between these signals allows for the generation of a baseband signal with significantly lower (beat) frequencies f2-f1, corresponding to a hypothetical radar wave with a correspondingly larger wavelength. The signal received from the radar target has an angle-dependent phase difference relative to the reference signal, which enables angle estimation. Because the wavelength of the simulated radar wave is very large, the angle estimation is well-defined at least over a wide angular range, and high resolution is still achieved due to the large aperture.
[0008] This invention is not limited to radar systems with exactly two radar sensors, but can also be applied to cooperative systems with more than two sensors. Similarly, the signal transmitted by each individual radar sensor can be a superposition of signals with multiple frequencies, as long as all frequency components in the two cooperative radar sensors have the same frequency spacing.
[0009] Advantageous configurations and extensions of the invention are given in the dependent claims.
[0010] The radar sensors participating in a cooperative system can themselves be angle-resolved, meaning they can achieve angle estimation based solely on signals transmitted and received by the same sensor. For example, one or more radar sensors in the system can be configured as MIMO radar sensors, which have high angle resolution due to their short wavelengths corresponding to frequencies f1 or f2, but only a very limited definite range due to their large aperture. For an object that can be located by both sensors, the ambiguity of the high-resolution angle estimation can be resolved using a definite angle estimate obtained based on the baseband signal at frequencies f2-f1. If the localization area of a single radar sensor overlaps with the localization areas of two adjacent sensors, that sensor can cooperate with each of the adjacent sensors that also locate the object.
[0011] Radar signals transmitted by different sensors can be rigidly derived from the phase of the fundamental frequency f0 of the synchronization signal, for example by multiplying f0 and modulating (aufmodulieren) multi-tone baseband signals, especially OFDM (Orthogonal Frequency Division Multiplexing) signals. Attached Figure Description
[0012] The embodiments are described in more detail below with the aid of the accompanying drawings. The drawings show: Figure 1 A block diagram of a radar system according to the present invention is shown; Figure 2A schematic diagram illustrating the principle of an angle estimation method implemented in a radar system is shown; and Figure 3 A top view of a motor vehicle equipped with a radar system according to the present invention is shown. Detailed Implementation
[0013] exist Figure 1 The diagram shows two cooperative radar sensors 10 and 12, which are installed, for example, in a motor vehicle (not shown), such that their positioning areas overlap, so that an object 14 existing in the overlapping area can be located by both sensors.
[0014] The two radar sensors 10 and 12 are configured as MIMO radar sensors and each has a high-frequency section 16 or 18 and a digital analysis and processing unit 20 or 22.
[0015] The high-frequency section 18 has a MIMO antenna array 24 with transmitting antennas 26 and receiving antennas 28. For clarity, only two transmitting antennas and three receiving antennas are shown here. The radar signal to be transmitted by the transmitting antenna 26 is generated by a local oscillator 30. Each receiving antenna 28 is assigned a mixer 32, which mixes the received signal with the signal generated by the local oscillator 30 (the corresponding signal lines are not shown), thereby generating a low-frequency intermediate frequency (IF) signal. The IF signals generated in different receiving channels are digitized and then further analyzed and processed in the analysis and processing unit 22. In a known manner, a set of ambiguous angle estimates is generated in the angle estimator 34. i_12, each angle estimate gives a candidate value for the azimuth angle of object 14. This ambiguity is resolved in another analysis processing stage 36, which will be further elaborated below. The high-frequency section 16 of sensor 10 has a MIMO antenna array 38, which may have the same structure as array 24 of another sensor, but is shown in a mirror image here for clarity. The transmit antenna 40 of array 38 is fed by modulator 42, which receives a synchronization signal 44 from the local oscillator 30 of the other sensor 12 and generates a transmit signal that is rigidly coupled to the transmit signal of sensor 12 in phase. For example, the local oscillator 30 generates a signal with a frequency f1 of 76.5 GHz, and the modulator 42 rigidly converts this signal in phase to a signal with a frequency f2 of 76.7 GHz, with a fixed frequency interval f2-f1 = 200 MHz.
[0016] Each receiving antenna 46 of the MIMO array 38 is equipped with a mixer 48, which mixes the received signal with the signal generated by the modulator 42. The intermediate frequency signal thus obtained in each receiving channel is digitized and further processed in the analysis and processing unit 20. The angle estimator 50 generates a set of ambiguous angle estimates. i_10, and then transmit it to another analysis and processing stage 52.
[0017] A portion of the signal transmitted by the transmitting antenna 40 of sensor 10 can be reflected onto object 14, such that the reflected signal is received by the receiving antenna 28 of sensor 12. At least one of these receiving antennas is capable of transmitting the received signal not only to its associated mixer 32 but also to another mixer 54. According to embodiments, the signal from this antenna can be split and fed to two mixers 32, 54, or alternately switched between the two mixers. The high-frequency portion 18 of sensor 12 includes a modulator 56 that functions identically to the modulator 42 in sensor 10, thus generating a signal with a frequency of f2. In mixer 54, this signal is mixed with the signal received by the antenna. This produces a baseband signal B whose frequency is approximately equal to the frequency interval f2-f1, but depends on the propagation time of the signal from the transmitting antenna 46 through object 14 to the receiving antenna 28, and therefore depends on the positioning angle of the object. In the analysis and processing apparatus 22, the baseband signal B is compared with a reference signal R in a bistatic angle estimator 58. The reference signal is generated by mixer 60, which mixes the output signal of local oscillator 30 with the output signal of modulator 56. Therefore, the reference signal R has exactly the frequency f2-f1. (The following text uses...) Figure 2 As will be explained in detail, a specific value of the azimuth angle of object 14 can be determined from the phase difference between the baseband signal B and the reference signal R. _12. This value is transmitted to analysis processing level 36, where it is processed from a high-resolution but ambiguous estimate. Select from i_12 and The one that best matches _12 indicates the true angle from which object 14 is seen from sensor 12. *_12.
[0018] Furthermore, this specific value _12 is also transmitted to the analysis and processing stage 52 in sensor 10 and used to extract the high-resolution but ambiguous estimate. Select from i_10 and The one that best matches _12, thus giving the true angle of object 14 as seen from sensor 10. *_10.
[0019] Analysis and processing devices 20 and 22 include Figure 1Other analysis and processing stages, not shown, are used to determine the spacing and relative velocity of object 14. Advantageously, for the angle estimation method presented here, the signals transmitted by transmitting antennas 26 and 40 have fixed frequencies, or consist of a superposition of signals with fixed frequencies, as is the case, for example, in OFDM radar. In this type of radar, the transmitted signal is a superposition of orthogonal subcarrier frequencies that do not change over time. The waveform of the transmitted signal is digitally modulated and forms a series of code symbols, which are digitally demodulated at the receiving end. Therefore, unlike, for example, FMCW radar, the spacing and angle information are obtained not through the time variation of frequency, but through the time variation of code symbols.
[0020] exist Figure 2 The diagram schematically shows two sensors 10 and 12, which are separated from each other by a known distance d, for example, 75 cm. The distance to the object 14 is much greater than the distance d, so the lines of sight S10 and S12 from sensors 10 and 12 to the object 14 are almost parallel. The line of sight S10 forms an angle with the optical axis A of sensor 10. This angle corresponds to the azimuth angle of object 14. The line of sight S12 forms approximately the same angle with the optical axis of sensor 12 (not shown here).
[0021] exist Figure 2 The diagram depicts two imaginary wavefronts, W1 and W2, propagating at the speed of light c with a frequency of f2-f1, and therefore a wavelength of λ = c / (f2-f1). Wavefront W1 arrives at sensor 12 at a positioning angle dependent on object 14. The time delay Δt reaches sensor 10, and this time delay is equal to the path length difference cΔt = d sin( The phase difference δ between the baseband signal B and the reference signal R is proportional to 2π. The ratio of the phase difference δ to 2π is equal to the ratio of the path length difference cΔt to the wavelength λ. Therefore, the positioning angle can be determined based on the measured phase difference. As long as the spacing d = max{cΔt} is less than c / (2(f2-f1)), the estimated positioning angle obtained in this way is clear.
[0022] exist Figure 3The diagram shows a top view of a motor vehicle 60 equipped with a cooperative radar system. This radar system comprises a total of six radar sensors 10, 12, and 62 to 68, schematically represented here by stylized radar beam symbols. These radar sensors are, for example, OFDM radars, transmitting a series of code symbols with fixed subcarrier frequencies during each measurement cycle. The transmitted signal sequence is interrupted by a transmission pause, during which electronic analysis of the received radar echoes is performed. The measurement cycles of all six radar sensors are synchronized. Each pair of adjacent sensors can cooperate with each other. For example, sensor 12 can cooperate with sensor 10 or sensor 62. As long as two sensors locate the same object, they can cooperate and perform accurate angle estimation in the manner described. If a single object is located within the location area of three or more radar sensors, the angle estimation method can be further improved by analyzing the phase difference and spacing of these multiple sensors.
Claims
1. An angle-resolved radar system having two radar sensors (10, 12) arranged at a predetermined spacing (d), the radar sensors being configured to transmit coherent radar signals, the radar sensors being oriented such that a signal transmitted by one of the radar sensors and reflected on an object (14) can be received by the other sensor, characterized in that, The signals transmitted by the two radar sensors (10, 12) have frequencies f1 and f2 with a pre-given frequency interval f2-f1. At least one of the radar sensors (12) is configured to mix a signal transmitted by the other sensor (10) and reflected on the object (14) with a signal transmitted by the other sensor (10). An analysis processing device (22) is configured to compare a baseband signal (B) generated by the mixing with a reference signal (R) that is identical to the signal transmitted by the other sensor (10), and to determine the positioning angle of the object (14) reflecting the signal based on the phase difference between these signals. ).
2. The radar system according to claim 1, having at least three radar sensors (10, 12, 62...68), wherein the at least three radar sensors cooperate with each other when locating the same object (14).
3. The radar system according to claim 1 or 2, wherein, At least one of the radar sensors (10, 12) is angle-resolved.
4. The radar system according to claim 3, wherein, The at least one angle-resolved radar sensor (10, 12) is a MIMO radar.
5. The radar system according to claim 3 or 4, wherein, The at least one angle-resolved radar sensor (10, 12) is configured for high-resolution but ambiguous angle estimation, and the positioning angle obtained through the cooperation of the radar sensor ( () is used to distinguish ambiguity.
6. The radar system according to any one of the preceding claims, wherein, At least one of the radar sensors is an OFDM radar.