Radar target simulation method and device based on DRFM

Abstract

The present invention discloses a radar target simulation method and device based on DRFM, which is different from the prior art in that the instantaneous frequency of the signal is obtained by the frequency measurement technology in the signal processing, the phase compensation factor is constructed by using the instantaneous frequency value, and the phase compensation factor is multiplied with the signal to complete the modulation of the target distance and speed. The method of the present invention makes the closest distance of the simulated target not limited by the inherent delay of the system, and the closest distance can be simulated to zero meters, and high-precision distance simulation and speed simulation are obtained at the same time.

Description

Technical Field

[0001] The invention relates to a radar target simulation method and equipment based on DRFM, belonging to the field of radar testing. Background Art

[0002] With the rapid development of assisted driving and autonomous driving, the demand for vehicle-mounted millimeter-wave radar is increasing day by day. Target simulators are needed for radar research and development and mass production testing. Radar target simulators based on digital radio frequency memory (DRFM) technology, which are widely used in the military field, have a relatively large inherent delay of about tens of meters due to analog-to-digital conversion (ADC), digital-to-analog conversion (DAC) and field programmable gate array (FPGA) digital signal processing. As a result, these DRFM-based target simulators can simulate targets at a limited distance. Therefore, many simulator manufacturers choose optical fiber or other dielectric analog delay lines for close-range simulation. The disadvantages of these simulation methods are that the control is not flexible and one channel can only simulate one target. In addition, integrating two systems in the simulator system makes the system complex and increases costs.

[0003] For example, the early radar target simulator of National Instrument in the United States was divided into two parts. The closest target using FPGA technology could only be simulated up to 90 meters, and the target within 90 meters used fiber delay line technology, which was later changed to fiber. The original ARTS9510C automotive radar simulator of Rohde & Schwarz used DRFM technology and could only simulate up to 8 meters. The E8708A radar target simulator of Keysight Technologies in the United States uses fiber delay technology and can simulate up to 3 meters. The ME7220E series radar target simulator of Keycom in Japan uses DRFM technology and can only simulate up to 12 meters.

[0004] In addition to automotive radar, many fields such as traffic radar, smart home radar, lighting radar sensors, military radar fuses, radio altimeters, etc., all face difficulties in close-range simulation.

[0005] The technical advantage of DRFM is that a single channel can simulate multiple targets at the same time, which is impossible with analog delay lines such as optical fiber and dielectrics. However, the problem of not being able to simulate close distances currently limits the application of DRFM technology in simulators. There are also several patents that complete close-range simulation, but they are difficult to adapt to all radar waveforms and have poor usability. Summary of the invention

[0006] According to the present invention, the DRFM technology is still used, and the following beneficial effects can be achieved only through digital signal processing:

[0007] 1. Compensation for the inherent delay of the system makes the closest distance of the simulated target not limited by the inherent delay. The closest distance can be simulated to zero meters without adding any cost.

[0008] 2. There is no need to know the radar waveform information. It can naturally adapt to the vast majority of existing automotive radar waveforms, whether it is a combination of CW or stepped frequency, FMCW signals with multiple frequency modulation slopes, or a DDMA waveform used for MIMO. As long as it is a waveform that uses phase or frequency for ranging, it can adapt.

[0009] 3. The simulation of moving targets can be achieved by changing the compensation distance, without the need to use the traditional FIFO solution to achieve distance delay, which simplifies the system and does not increase any cost.

[0010] 4. Since the compensation distance is expressed using fixed-point data and the decimal point position is defined by oneself, high precision can be achieved very easily, making the distance stepping amount much lower than the centimeter level of conventional digital FIFO, and easily achieving millimeter or even micron level distance stepping without increasing any cost.

[0011] 5. Since the step size of the compensation distance can be very small, far less than 1 / 10 of the wavelength of the electromagnetic wave, highly realistic Doppler simulation can be achieved directly without the need for additional velocity modulation, thus simplifying the system and not increasing any cost.

[0012] The present invention proposes a radar target simulation method based on digital radio frequency memory, wherein the method comprises: obtaining a frequency measurement value f[n] of an input signal x[n], and calculating a phase compensation factor y[n] in real time according to the frequency measurement value f[n], the formula is as follows

[0013]

[0014] Where j is an imaginary number, k is 1 or -1, π is the ratio of pi, and ΔR is the distance R corresponding to the target distance R to be simulated minus the distance value R corresponding to the inherent delay of the system in the simulation scenario. g , R g It includes the distance between the radar and the target simulator, as well as the inherent delay within the target simulator system. c is the speed of light, n is the discrete time sequence number, and f[n] is the frequency measurement value of the signal. Multiplying y[n] with the input signal x[n] completes the modulation of the target distance and speed.

[0015] Preferably, the signal may be an intermediate frequency signal, the method may include analog-to-digital conversion, and the frequency measurement value f[n] may be obtained by continuously and real-time instantaneous frequency measurement processing of the intermediate frequency signal after the analog-to-digital conversion, or may be given by the radar through an external voltage signal.

[0016] Preferably, the signal may be a radio frequency signal, the method may include analog-to-digital conversion, and the frequency measurement value f[n] may be obtained by continuously and real-timely performing instantaneous frequency measurement processing on the intermediate frequency signal after the analog-to-digital conversion and adding a fixed frequency deviation.

[0017] Preferably, the instantaneous frequency measurement process can be performed by a phase difference method.

[0018] Preferably, the method may further include: before obtaining the frequency measurement value f[n] of the signal, improving the signal-to-noise ratio of the signal by using channelization or other filtering techniques.

[0019] Preferably, the method may further include: performing image frequency suppression filtering when performing analog-to-digital conversion on a single-channel real signal.

[0020] Preferably, the method may further include: the method of the present invention may be used in combination with the FIFO delay technology of a traditional FPGA, the method of the present invention is used for short distances, and the FIFO delay technology of a traditional FPGA is used for long distances.

[0021] The present invention also proposes a radar target simulation device based on a digital radio frequency memory, wherein the device implements the radar target simulation method as described above.

[0022] According to the present invention, without knowing the radar emission waveform, the DRFM method can be used to complete the simulation of close-range, high-precision distance targets and complete Doppler modulation at the same time, and the closest distance can be zero meters. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a principle block diagram of the prior art;

[0024] Figure 2 It is a principle block diagram of the method of the present invention;

[0025] Figure 3 Block diagram of the 77GHz band radar target simulator system. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0027] The embodiment of the method of the present invention is as follows:

[0028] According to the present invention, a DRFM radar target simulation method is proposed, which can selectively retain the hardware and software framework of the existing DRFM simulator. Figure 1 Shown is a functional block diagram of the prior art DRFM simulator. Figure 2 FIG. 1 is a block diagram of the principle of the method of the present invention. Figure 2 The difference from the existing technical features is mainly reflected in the fact that its signal processing steps include a process for compensating for the system's inherent delay. The processing steps are as follows: first, the instantaneous frequency is measured continuously in real time, and a phase compensation factor y[n] is constructed based on the frequency measurement result f[n], and then the phase compensation factor y[n] is used to compensate for the system's inherent delay.

[0029] The multi-target simulation process of the prior art is as follows: the receiving antenna obtains the radar transmission signal, and the intermediate frequency signal (which can be a real signal or a complex signal) is obtained through the down-conversion module, and then enters the FPGA after being collected by the ADC. If it is a real signal, it is necessary to obtain the IQ complex signal x[n] after image frequency suppression filtering. If two ADCs are used to implement IQ sampling, the complex signal x[n] is directly obtained. The complex signal is then divided into multiple modulation branches, each of which modulates the distance and Doppler information of a target respectively. Finally, the parallel modulation branches of all targets are superimposed together, output to the up-conversion module through the DAC, and then radiated to the radar by the transmitting antenna to complete the multi-target simulation.

[0030] According to the present invention, the ADC data is collected in two paths, one of which is subjected to image frequency suppression filtering to obtain x[n]. If it is a complex signal, image frequency suppression filtering is not required, and x[n] is directly obtained; before x[n] is divided into multiple branches for target information modulation, a multiplication operation of inherent delay compensation is first performed, that is, a complex multiplication operation of x[n] and a phase compensation factor y[n] is performed. The calculation formula of the phase compensation factor y[n] is as follows:

[0031]

[0032] Wherein, j is an imaginary number, k is 1 or -1, ΔR is the distance value corresponding to the inherent delay, c is the speed of light, n is the discrete time sequence number corresponding to the number of FPGA operation clocks, and f[n] is the frequency value of the RF signal measured in real time by the instantaneous frequency measurement module after the ADC.

[0033] The applicable conditions of the embodiment of the method of the present invention are described below.

[0034] Since the method of the present invention measures the frequency of the signal in real time, calculates the phase compensation factor in real time, and realizes the compensation of the fixed delay of the system in real time, it is effective for radar signal waveforms that use frequency and phase to measure distance, including the following waveforms: frequency modulated continuous wave (FMCW), frequency shift keying FSK, point frequency continuous wave, fast scan sawtooth wave, multiple frequency shift keying (MFSK), double group sawtooth wave, and any combination of various waveforms in time, and is adaptable to the parameters of the above various waveforms. For example, the method of the present invention is applicable to FMCW signals with various variable periods and variable frequency modulation slopes, FSK signals with variable frequencies f1 and f2, and MFSK signals with various parameters, etc.

[0035] The feasibility of the method of the present invention is analyzed below.

[0036] The radars to which the present invention is applicable all use the method of converting the echo time delay into phase or frequency to measure the distance. For example, the FSK signal uses the phase to measure the distance, and the FMCW uses the beat frequency to measure the distance. MFSK is a combination of FSK and FMCW signals, and the double sawtooth wave is also a combination of FSK and FMCW signals.

[0037] First, let's look at the FSK signal. The FSK signal transmits two frequency signals of f1 and f2 in a time-sharing manner, and uses the phase difference between the two frequency echoes to measure the distance. The specific formula for the phase difference is as follows:

[0038]

[0039] Where Δf = f1-f2 is the frequency difference, R is the target distance corresponding to the simulator delay modulation, that is, it corresponds to the target distance set by the user, R g is the distance value corresponding to the inherent delay of the system in the simulation scenario composed of radar and target simulator, R g It includes the distance between the radar and the target simulator, as well as the inherent delay within the target simulator system. g Even if the user sets R to zero, the distance measured by the radar is R g , which is the minimum distance that the traditional DRFM simulator can simulate the target. After the compensation of the present invention, the phase difference is

[0040]

[0041] The distance R set by the user can be accurately measured through phase-to-distance conversion.

[0042] Secondly, let's verify FMCW. For one cycle of the FMCW signal, the frequency of the transmitted signal can be expressed as f=f0+kt, where k is the frequency modulation slope and t is time. The time domain expression of the difference frequency signal of the stationary target echo is

[0043]

[0044] The FFT frequency measurement is converted into distance, and the measured distance result is R+R g R is the target distance corresponding to the simulator delay modulation, that is, it corresponds to the target distance set by the user. g is the distance value caused by the inherent delay. g Even if the user sets R to zero, the distance measured by the radar is R g , which is the minimum distance that the traditional DRFM simulator can simulate the target. After the compensation of the present invention, the time domain expression of the difference frequency signal of the stationary target echo is:

[0045]

[0046] The distance R set by the user can be accurately measured by converting the frequency measurement into distance through FFT.

[0047] For MFSK or double sawtooth wave signals, they are a combination of FSK and FMCW signals, that is, they use phase and frequency to measure distance, so the method of the present invention is still effective. The reason why the present invention is feasible is that the phase term of the target echo is It only depends on the distance to the target and the frequency of the transmitted signal. Therefore, as long as the frequency is tracked in real time, the compensation phase can be constructed to complete the compensation through multiplication.

[0048] Since the system inherent delay is compensated by digital signal processing, the distance value ΔR corresponding to any system inherent delay can be fully compensated, so the simulator can simulate a zero-meter target.

[0049] Device embodiment 1 of the present invention: 24 GHz frequency band radar target simulator.

[0050] The block diagram of the 24GHz frequency band radar target simulator system is as follows: Figure 3As shown. The device of the present invention includes: an antenna subsystem, a microwave subsystem and a signal processing subsystem. The antenna subsystem includes a receiving antenna and a transmitting antenna. The microwave subsystem includes a signal receiving module, a signal transmitting module and a frequency synthesis module. The signal processing subsystem can be one or more signal processing boards, and the devices included are mainly: high-speed ADC, FPGA, high-speed DAC. The FPGA in the signal processing subsystem completes all the steps of the method of the present invention, including an image frequency suppression filter module, an instantaneous frequency measurement module, a system inherent delay compensation module, as well as distance modulation, Doppler modulation, modulation information calculation module, display and control module, etc. The display and control module mainly completes the communication with the user interface. The working process of the 24GHz frequency band radar target simulator device is as follows.

[0051] The receiving antenna of the 24GHz band radar target simulator device receives the RF signal of the 24GHz band, and after down-conversion, the signal is converted to the intermediate frequency range of 100-450MHz, with an instantaneous bandwidth of 350MHz. The ADC module converts the intermediate frequency analog signal into a digital signal after sampling at 1GSPS. The digital signal is divided into two paths. One path is converted into 4 parallel orthogonal signals after image suppression filtering, each with a data rate of 250MSPS, and the four paths together are x[n]; the other path is subjected to instantaneous frequency measurement to obtain the instantaneous frequency measurement value f[n] of the signal. Instantaneous frequency measurement can use the low-latency phase difference method to measure the frequency, and then filter it to improve the frequency measurement accuracy. It can also use channelization technology to first improve the signal-to-noise ratio, then use the phase difference method to measure the frequency, and finally perform smoothing filtering to improve the frequency measurement accuracy. Before x[n] is divided into multiple branches for target information modulation, the inherent delay of the system is compensated, that is, x[n] is multiplied by a phase compensation factor y[n], and the calculation formula of the phase compensation factor y[n] is as follows:

[0052]

[0053] Among them, j is an imaginary number, π is the circumference of a circle, ΔR is the distance value corresponding to the inherent delay of the DRFM simulator system, in meters, c is the speed of light, in meters per second, and n is the discrete time sequence number, corresponding to the number of FPGA operation clocks. The inherent delay of the system of this device is 200 nanoseconds (ns), and the corresponding distance is the inherent delay of the system multiplied by the speed of light. After calculation, ΔR = 60 meters is obtained. Finally, the phase compensation factor y[n] is multiplied by x[n] to complete the compensation of the inherent delay of the system. The processing delays of the instantaneous frequency measurement branch and the image frequency suppression filter branch are inconsistent, and the delay can be controlled by FPGA to make its influence negligible. The compensated signal is divided into multiple channels for multi-target modulation, and each channel is modulated by target distance and Doppler, generating a digital modulation signal. The multi-channel modulation signals are superimposed and sent to the DAC to convert into an intermediate frequency analog signal, and finally radiated by the transmitting antenna after up-conversion.

[0054] Device embodiment 2 of the present invention: 77 GHz frequency band 1 GHz instantaneous bandwidth radar target simulator.

[0055] The receiving antenna of the device receives the RF signal in the 77GHz band, and after down-conversion, it converts the signal to the intermediate frequency range of 100-1100MHz, with an instantaneous bandwidth of 1GHz. The up-down and down-conversion local oscillator can be set arbitrarily in the range of 76GHz-81GHz to achieve full frequency coverage of 76GHz-81GHz. The intermediate frequency analog signal is converted into a digital signal through 2.5GSPS sampling by the ADC module. The digital signal is divided into two paths. One path is converted into 10 parallel orthogonal signals x[n] after image suppression filtering, with a data rate of 250MSPS for each path; the other path is subjected to instantaneous frequency measurement to obtain the instantaneous frequency measurement value f[n] of the signal. Subsequent processing is similar to that of the 77GHz radar target simulator.

[0056] Device Example 3 of the Invention: 77 GHz Frequency Band 4 GHz Instantaneous Bandwidth Radar Target Simulator

[0057] The receiving antenna of the device receives the RF signal in the 77GHz frequency band, and after orthogonal down-conversion, the signal is converted to an IQ complex signal in the intermediate frequency range of -2GHz to 2GHz, with an instantaneous bandwidth of 4GHz. The up-down and down-conversion local oscillator can be set arbitrarily in the range of 76GHz to 81GHz to achieve full frequency band coverage of 76GHz to 81GHz. After two-channel IQ ADC sampling, with a sampling rate of 5GSPS per channel, the orthogonal intermediate frequency analog signal is converted into an orthogonal digital signal. The orthogonal digital signal is then divided into two paths, one of which is converted into 20 parallel orthogonal signals x[n] through serial-to-parallel conversion, with a data rate of 250MSPS for each path; the other path is subjected to instantaneous frequency measurement to obtain the instantaneous frequency measurement value f[n] of the signal. Subsequent processing is similar to that of the 77GHz radar target simulator.

[0058] In summary, the present invention provides a radar target simulation method and device based on DRFM. The above are only some embodiments of the present invention and are not intended to limit the protection scope of the present invention. In fact, the present invention has no restrictions on the frequency band and bandwidth of the radar. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A radar target simulation method based on digital radio frequency memory, characterized in that: The method comprises: obtaining a frequency measurement value f[n] of an input signal x[n], and calculating a phase compensation factor y[n] in real time according to the frequency measurement value f[n], as follows: Where j is an imaginary number, k is 1 or -1, π is the ratio of pi, and ΔR is the distance R corresponding to the target distance R to be simulated minus the distance value R corresponding to the inherent delay of the system in the simulation scenario. g , R g It includes the distance between the radar and the target simulator, as well as the inherent delay within the target simulator system. c is the speed of light, n is the discrete time sequence number, and f[n] is the frequency measurement value of the signal. Multiplying y[n] with the input signal x[n] completes the modulation of the target distance and speed.

2. A radar target simulation device based on digital radio frequency memory, characterized in that: The device implements the radar target simulation method according to claim 1.

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