Weak Doppler signal extraction method based on random modulation narrow pulse

Abstract

The invention belongs to the technical field of wind measurement radars, and relates to a weak Doppler signal extraction method based on random modulation narrow pulse, which comprises the following steps: generating a random signal by adopting a random sequence generator, generating a narrow pulse signal by adopting a sine wave generator, modulating the random signal on the narrow pulse signal to obtain a modulation signal, and transmitting the modulation signal; receiving an echo signal after the modulation signal is transmitted, carrying out frequency mixing and amplification filtering, and carrying out integral accumulation after random signal autocorrelation test to obtain a sampling sequence; doppler frequency shift is extracted according to the sampling sequence, wind speed calculation is carried out after preprocessing, decimation filtering and FFT filtering are carried out in sequence, and the wind speed and the wind direction are obtained. According to the invention, weak Doppler frequency shift signals can be extracted in a short near-space range.

Description

Technical Field

[0001] The present application relates to the technical field of wind measurement radars, and in particular to a method for extracting weak Doppler signals based on randomly modulated narrow pulses. Background Art

[0002] Wind radar is widely used in fields such as wind energy measurement and weather forecasting. In addition to random noise interference, ground echo interference is the main source of interference in wind radar applications. It will seriously affect the radar measurement precision and accuracy.

[0003] Ground object echo interference mainly comes from radar signals reflected from the surface of ground objects illuminated by the radar. These reflected signals include static interference reflected by distant mountains, vegetation, buildings, ground, sea surface, flying birds, etc., as well as dynamic interference such as multipath. These clutters are received and stored by the radar, which will cause the radar echo signal to attenuate, deform and blur, thereby reducing the radar measurement accuracy. Excessive ground object interference will also cause overload and damage to the radar system, thus affecting the normal operation of the radar system.

[0004] At present, the main methods to solve radar interference are:

[0005] 1) Hardware-based anti-interference methods: including the use of diversity radar, MIMO radar technology, polarization radar, multi-band radar technology, etc. to improve the coverage and resolution of radar signals, thereby reducing the impact of ground interference. The disadvantage of this type of algorithm is that the radar system structure is complex and the implementation cost is high.

[0006] 2) Filtering algorithm: mainly reduces noise and interference through various smoothing windows. The disadvantage is that it can usually only handle specific situations, has poor adaptability to complex and changeable ground interference environments, and has poor dynamic anti-interference performance.

[0007] 3) Anti-interference algorithms based on artificial intelligence: They often use technologies such as neural networks to learn the interference patterns of ground objects and classify and suppress them. The disadvantage of this type of algorithm is that it requires massive data sets for training, is relatively complex to implement, and requires high computing resources.

[0008] For near-air distance wind measurement radar, there are several difficulties in resisting interference from ground objects: first, the atmospheric scattering echo signal at near-air distance is very weak and can be easily drowned out by ground noise; second, the echo distance is short and the response time is short; third, a higher distance resolution is required while meeting the anti-interference requirement. Summary of the invention

[0009] Based on this, it is necessary to provide a weak Doppler signal extraction method based on randomly modulated narrow pulses to address the above technical problems, which can extract weak Doppler frequency shift signals within a shorter near-space range.

[0010] A method for extracting weak Doppler signals based on randomly modulated narrow pulses, comprising:

[0011] A random sequence generator is used to generate a random signal, a sine wave generator is used to generate a narrow pulse signal, the random signal is modulated on the narrow pulse signal to obtain a modulated signal, and the modulated signal is transmitted;

[0012] Receive the echo signal after the modulated signal is transmitted, perform mixing, amplification and filtering, and after the random signal autocorrelation test, perform integration and accumulation to obtain a sampling sequence;

[0013] The Doppler frequency shift is extracted according to the sampling sequence, and after preprocessing, decimation filtering and FFT filtering, the wind speed is solved to obtain the wind speed and wind direction.

[0014] In one embodiment, a random sequence generator is used to generate a random signal, a sine wave generator is used to generate a narrow pulse signal, and the random signal is modulated on the narrow pulse signal to obtain a modulated signal, including:

[0015]

[0016] In the formula, s(t) is the modulation signal, P(t) is the random signal, e is a natural constant, j is a complex number, is the frequency of the electromagnetic wave, t is the time, and φ0 is the phase.

[0017] In one embodiment, the random signal autocorrelation test includes:

[0018]

[0019] Where m = 2 n -1 is the maximum length and period of the M sequence, E is the autocorrelation function, P(t) is a random signal, τ = kT e (k=1,2,....L-1), T e is the symbol bandwidth of the M sequence, and L is the sequence length.

[0020] In one embodiment, performing integration and accumulation to obtain a sampling sequence includes:

[0021] To accumulate points:

[0022]

[0023] If the phase of the transmitter is continuous, then mixing is a phase subtraction process to obtain the intermediate frequency signal:

[0024]

[0025] In the formula, is the integral of the distance from R1 to R2, R1 is the closest point in the observation range, R2 is the farthest point in the observation range, R is the integral variable, v R is the particle velocity constant and c is the speed of light.

[0026] In one embodiment, after obtaining the intermediate frequency signal, the phase difference between two consecutive received signals is calculated and substituted into the intermediate frequency signal for idealization to obtain a sampling sequence:

[0027]

[0028] Where, T b is the sampling interval, δφ is the phase difference between two consecutive received signals, is the sampling sequence, φ c is the intermediate frequency signal phase.

[0029] In one embodiment, the Doppler frequency shift is extracted according to the sampling sequence, and after preprocessing, decimation filtering, and FFT filtering, the wind speed is solved to obtain the wind speed and wind direction, including:

[0030] The Doppler frequency shift is extracted according to the sampling sequence, and the preprocessing is completed after correlation discrimination, jitter filtering, data reorganization and distance selection. Then, the wind speed is solved after extraction filtering and FFT filtering in sequence to obtain the wind speed and wind direction.

[0031] In one embodiment, the relevant determination includes:

[0032] The random sequence signal transmitted locally is:

[0033]

[0034] The received random echo signal is:

[0035]

[0036] In the formula, is the echo signal amplitude, w is the transmitting signal frequency;

[0037] The result after random correlation is:

[0038]

[0039] In the formula, t1 is the starting time of a period, and t2 is the ending time of a period;

[0040] when When it is unrelated to P(t),

[0041] In one embodiment, the jitter filtering includes: filtering out interference caused by mechanical jitter of the device after correlation determination, and then performing data reorganization.

[0042] In one embodiment, data reorganization includes:

[0043] The radar obtains a set of pulse echo signals through ADC oversampling, and the echo signals include Doppler frequency shift signals at different time points and different distances;

[0044] Extract the pulse echo signal within the concerned distance range, and segment the pulse echo signal according to different distance segments to obtain segmented data;

[0045] The segmented data are rearranged by distance, with the same distance segment signals in one column, forming a new matrix, in which the rows are distance information and the columns are different echo information.

[0046] In one embodiment, the distance selection includes: performing distance selection, caching echo signals within the desired near-space detection range, and filtering out all clutter signals outside the detection range.

[0047] The above-mentioned weak Doppler signal extraction method based on randomly modulated narrow pulses adopts a multiple narrow pulse signal system based on random modulation to realize the extraction of weak Doppler frequency shift signals under short-range echo conditions in a relatively short near-space range. This method can extract the Doppler characteristics of weak signals, has high range resolution, fast calculation time, requires little prior knowledge, has strong anti-interference performance, is suitable for various large-scale radars, and has high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a schematic diagram of a method for extracting weak Doppler signals based on randomly modulated narrow pulses in one embodiment;

[0049] Figure 2 It is a structural schematic diagram of an antenna millimeter wave radar system for measuring wind in a wind farm in one embodiment;

[0050] Figure 3 is a schematic diagram of a radio frequency module in one embodiment;

[0051] Figure 4 is a schematic diagram of an intermediate frequency signal processing module in one embodiment;

[0052] Figure 5 is a schematic diagram of a baseband signal processing module in one embodiment;

[0053] Figure 6 A schematic diagram of an antenna millimeter wave radar system module for measuring wind in a wind farm in one embodiment;

[0054] Figure 7 A schematic diagram of a randomly modulated periodic narrow pulse signal system in one embodiment;

[0055] Figure 8 is a signal processing flow chart of a baseband signal processing module in one embodiment;

[0056] Fig. 9 A schematic diagram of the data structure of an echo signal before data reorganization in an embodiment;

[0057] Fig.10 A schematic diagram of the data structure of an echo signal after data reorganization in an embodiment;

[0058] Fig.11 FIG. 4 is a diagram of a signal flow process in one embodiment. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0060] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0061] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "multiple groups" means at least two groups, such as two groups, three groups, etc., unless otherwise clearly and specifically defined.

[0062] In this application, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0063] In addition, the technical solutions between the various embodiments of the present application can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0064] The present application provides a method for extracting weak Doppler signals based on randomly modulated narrow pulses. Figure 1 As shown, the following steps are included.

[0065] Step S11: Use a random sequence generator to generate a random signal, use a sine wave generator to generate a narrow pulse signal, modulate the random signal on the narrow pulse signal to obtain a modulated signal, and transmit the modulated signal.

[0066] Specifically:

[0067]

[0068] In the formula, s(t) is the modulation signal, P(t) is the random signal, e is a natural constant, j is a complex number, is the frequency of the electromagnetic wave, t is the time, and φ0 is the phase.

[0069] In this step, the random signal is also a random sequence. The random sequence is a determined sequence with certain random characteristics, has statistical characteristics similar to white noise, has good randomness and correlation, and its correlation function has sharp characteristics. The power spectrum occupies a wide frequency band and is pre-determinable and repeatable. It is easy to separate from other signals or interferences and has good anti-interference characteristics. Common random sequences include Kasami sequence, M sequence, Gold sequence, chaotic sequence, truncated sequence, etc. Taking the M sequence as an example, the longer the code bit is, the closer the autocorrelation characteristic is to random noise.

[0070] Step S12: Receive the echo signal after the modulated signal is transmitted, perform mixing and amplification filtering, and after the random signal autocorrelation test, perform integration and accumulation to obtain a sampling sequence.

[0071] Specifically:

[0072] Random signal autocorrelation test, including:

[0073]

[0074] Where m = 2 n -1 is the maximum length and period of the M sequence, E is the autocorrelation function, P(t) is a random signal, τ = kT e (k=1,2,....L-1), T eis the symbol bandwidth of the M sequence, and L is the sequence length.

[0075] Perform integration and accumulation to obtain a sampling sequence, including:

[0076] To accumulate points:

[0077]

[0078] If the phase of the transmitter is continuous, then mixing is a phase subtraction process to obtain the intermediate frequency signal:

[0079]

[0080] In the formula, is the integral of the distance from R1 to R2, R1 is the closest point in the observation range, R2 is the farthest point in the observation range, R is the integral variable, v R is the particle velocity constant, c is the speed of light;

[0081] After obtaining the intermediate frequency signal, calculate the phase difference between two consecutive received signals and substitute it into the intermediate frequency signal to idealize it to obtain the sampling sequence:

[0082]

[0083] Where, T b is the sampling interval, δφ is the phase difference between two consecutive received signals, is the sampling sequence, φ c is the intermediate frequency signal phase.

[0084] Step S13: extract the Doppler frequency shift according to the sampling sequence, perform wind speed calculation after preprocessing, extraction filtering and FFT filtering in sequence, and obtain the wind speed and wind direction.

[0085] Specifically:

[0086] The Doppler frequency shift is extracted according to the sampling sequence, and the preprocessing is completed after correlation discrimination, jitter filtering, data reorganization and distance selection. Then, the wind speed is solved after extraction filtering and FFT filtering in sequence to obtain the wind speed and wind direction.

[0087] The above-mentioned weak Doppler signal extraction method based on randomly modulated narrow pulses is a Doppler frequency shift detection method based on a random modulated multiple narrow pulse signal system suitable for wind measuring radar. In view of the characteristics of very weak echo signals, susceptibility to ground noise interference, short echo time, and low signal-to-noise ratio in the application background of wind measuring radar, it solves the problems of anti-ground interference and high precision and high distance resolution. Specifically: a multiple narrow pulse signal system based on random modulation is adopted to extract weak Doppler frequency shift signals in a shorter near-air range, and it can extract accurate signals from weak echo signals under short-range echo conditions. The Doppler frequency shift characteristics of weak signals in the range resolution enable the receiving channel to only receive echo signals within the range of interest. Interference echoes greater than or less than this distance range, such as ground clutter, sea level clutter, mountain clutter, and leaf reflection clutter, can be filtered out. It has the advantages of high range resolution, fast calculation time, less prior knowledge required, strong anti-interference performance, and adaptability to various large-scale radars. It is suitable for application scenarios with high real-time requirements, higher computing efficiency, and less processing time and computing resource consumption, such as embedded processors such as DSP, ARM, and FPGA, which are suitable for large-scale radars.

[0088] This application is not only suitable for strong echo signal processing, but also for weaker or even faint signals, and still applicable to situations with large low-frequency noise and high-frequency ground interference. It has better robustness and robustness to general thermal noise, hardware circuit noise, a certain degree of clock phase noise, sea surface, ground, environmental clutter reflection and other interference. The reduction of signal quality requirements makes the system more adaptable and reliable. Through random modulation, correlation discrimination, distance selection, data reorganization, extraction filtering, etc., the structure of sampled data is changed, the signal-to-noise ratio of sampled data is further enhanced, and various interferences on the system link are reduced (not only low-frequency thermal noise and power supply noise can be filtered out, but also high suppression capabilities are provided for high-frequency ground scattered clutter, sea surface scattered clutter, mountain clutter, environmental electromagnetic interference, etc.), and the reliability and efficiency of signal feature detection are improved.

[0089] The present application also provides an antenna millimeter wave radar system for measuring wind in a wind farm, such as Figures 2 to 6 As shown, it includes: an antenna module, a radio frequency module, an intermediate frequency signal processing module, a baseband signal processing module, a peripheral module and a power module.

[0090] The connection relationship between the modules is: the antenna module, the RF module, the intermediate frequency signal processing module, the baseband signal processing module and the peripheral module are connected in sequence, the antenna module, the RF module, the intermediate frequency signal processing module, the baseband signal processing module and the peripheral module are all connected to the power module, the antenna module is also connected to the baseband signal processing module, and the RF module is also connected to the baseband signal processing module.

[0091] 1) Antenna module is the front end of signal reception and transmission, used to receive and transmit the RF signal of the antenna. The antenna module includes: lens antenna, multiple microstrip feed sources distributed in an array, and phase shift control circuit. The lens antenna is set on the scanning path of all microstrip feed sources, and each microstrip feed source is connected to the phase shift control circuit.

[0092] In the antenna module: each microstrip feed emits electromagnetic waves, and the phase shift control circuit controls the time and direction so that each microstrip feed scans in turn. After being converged and enhanced by the lens antenna, it is emitted to achieve a sharp antenna pattern, thereby meeting the sensitivity requirements and achieving high gain. It is a single antenna with low side lobes and integrated transmission and reception. For example: the antenna module includes: a lens antenna, three microstrip feeds distributed in a linear array, and a phase shift control circuit, which can switch beams in three different directions, scan different directions of atmospheric scattered echoes, and receive and transmit 24Ghz millimeter wave beams in time. This application combines the transmit and receive antennas into one, designs a unique single antenna system, and uses a single antenna to detect near-air wind conditions.

[0093] 2) RF module, which is a component of the signal path, is used to convert the received RF signal into an intermediate frequency signal and send it to the intermediate frequency signal processing module, and to convert the intermediate frequency signal of the intermediate frequency module and send it to the RF module. The RF module includes: an RF receiving channel, an RF transmitting channel and a first local oscillator signal source. The RF receiving channel includes a single-channel RF switch 11, a first-stage amplifier 12, a down converter (specifically a first down converter 13), a first-stage bandpass filter (specifically a first receiving filter 14) and a second-stage amplifier (specifically a first receiving amplifier 15) connected in sequence. The RF transmitting channel includes a first-stage bandpass filter (specifically a first transmitting filter 25), a first-stage amplifier (specifically a first transmitting amplifier 24), an up converter (specifically a first up converter 23), a second-stage amplifier 22 and a single-channel RF switch 21 connected in sequence. The single-channel RF switch 11 of the RF receiving channel and the single-channel RF switch 21 of the RF transmitting channel are connected to the antenna module through the same RF switch (i.e., they share a common RF switch). The two ends of the first local oscillator signal source are respectively connected to the down converter and the up converter. The RF receiving channel converts the 24Ghz RF signal received by the antenna into an intermediate frequency signal below 8Ghz that can be processed by the intermediate frequency signal processing module. When the receiving channel is closed, the signal begins to be received. The RF signal is first amplified by a low-noise amplifier, and then converted into an intermediate frequency signal through a first-stage down-conversion. The signal is filtered through a bandpass filter, amplified again, and output to the intermediate frequency signal processing module. The RF transmitting channel converts the intermediate frequency signal below 8Ghz into a 24Ghz millimeter wave signal. When the transmitting channel is closed, the intermediate frequency signal below 8Ghz is amplified and filtered in the first stage, and then up-converted into a 24Ghz RF signal, which is sent to the antenna through a power amplifier and a two-stage switch.

[0094] In the RF module, a multi-stage RF switch is set to increase the isolation of the transceiver link, and a multi-stage amplification is set to suppress the power of noise and increase the power of the signal. The first local oscillator signal source is a clock circuit with a PLL phase-locked loop (i.e., the first clock source PLL1, the specific circuit is the existing technology), and a homologous local oscillator mechanism is used (the same clock that provides the phase-locked loop provides clock signals for the up-converter and the down-converter at the same time, and the homologous coherence of the receiving and transmitting signal clock local oscillators is used to offset the error introduced by the clock local oscillator phase noise) to provide homologous local clock signals for the RF receiving channel and the RF transmitting channel of the RF module. The homologous phase cancellation fundamentally reduces the requirements for the VCO phase noise. Ordinary clocks can meet the requirements, and expensive high-precision clocks are not required, which greatly reduces the cost.

[0095] 3) The intermediate frequency signal processing module is a component of the signal path, which is used to convert the received intermediate frequency signal into a low frequency signal and send it to the baseband signal processing module, and to convert the low frequency signal of the baseband signal processing module into an intermediate frequency signal. The intermediate frequency signal processing module includes: an intermediate frequency receiving channel, an intermediate frequency transmitting channel and a second local oscillator signal source. The intermediate frequency receiving channel includes a first-level bandpass filter (specifically a second receiving filter 16), a first-level low noise amplifier (specifically a second receiving amplifier 17), a down converter (specifically a second down converter 18), a second-level bandpass filter 19 and a second-level low noise amplifier 20 connected in sequence. The intermediate frequency transmitting channel includes a first-level low noise amplifier 26, a first-level bandpass filter 27, an up converter (specifically a second up converter 28), a second-level low noise amplifier (specifically a second transmitting amplifier 29) and a second-level bandpass filter (specifically a second transmitting filter 30) connected in sequence. The first-level bandpass filter of the intermediate frequency receiving channel is connected to the RF receiving channel of the RF module, the second-level bandpass filter of the intermediate frequency transmitting channel is connected to the RF transmitting channel of the RF module, and the second-level low noise amplifier 20 of the intermediate frequency receiving channel and the first-level low noise amplifier 26 of the intermediate frequency transmitting channel are both connected to the baseband signal processing module. The intermediate frequency signal below 8GHz processed by the RF module enters the intermediate frequency signal processing module, and after a first-level filtering and amplification, it is down-converted to a low-frequency signal below 1Mhz, and then a second-level filtering and amplification are performed to further improve the signal quality before being sent to the baseband signal processing module. The low-frequency transmission signal generated by the baseband signal processing module enters the intermediate frequency signal processing module, and after a first-level amplification and filtering, it is up-converted to an intermediate frequency signal below 8Ghz, and after a second-level amplification and filtering, it is transmitted to the intermediate frequency signal processing module.

[0096] In the intermediate frequency signal processing module, multi-stage amplification is set to suppress the power of noise, increase the power of the signal, and thus improve the signal quality. The second local oscillator signal source includes two different PLL phase-locked clock sources (i.e., the second clock source PLL2 and the third clock source PLL3) and a switch. The second clock source is connected to the down converter, and the up converter is connected to the third clock source and the second clock source through a switch (single-pole double-throw switch). When transmitting a signal, the switch switches to the second clock source, and the second clock source is connected to the second down converter 18 and the second up converter 28 at the same time, and provides a clock signal at the same time; when receiving a signal, the switch switches to the third clock source, and the third clock source is connected to the second up converter 28 to achieve isolation. That is to say, when preparing to transmit a signal, the switch switches to PLL2 to work. At this time, the local oscillator source that provides a first-level frequency conversion for the transmission link is PLL2, that is, during the effective transmission period, the transmission frequency is f2. When preparing to receive the signal, the switch switches to PLL3. At this time, the local oscillator source that provides the first-level frequency conversion for the transmission link is PLL3, that is, during the effective transmission period, the transmission frequency is f3. At the same time, PLL2 provides the first-level frequency conversion local oscillator PLL2 for the receiving link. In this way, during the period of effective signal reception, the transmitted signal at the same time is not in the same frequency band, which greatly increases the isolation between the transmitter and the receiver, and avoids the pollution of the received signal by the transmission channel. For the received effective signal, its transmission clock and receiving clock are the same source local oscillator clocks, and both use a shared local oscillator, that is, PLL2, as the first-level local oscillator clock source. This ensures that the phase noise cancels each other, greatly compressing the frequency error caused by the transmission local oscillator phase noise. The local oscillator clock source of the intermediate frequency signal processing module can be switched by controlling the switch, so that the local oscillator clock source of the received signal in the intermediate frequency band is different from the local oscillator clock source of the transmitted signal in the same period (different sources, different frequencies). For the same transmitted signal in different time periods, the clock local oscillator is guaranteed to be of the same source and frequency during the secondary frequency conversion of the intermediate frequency and high frequency, so that different local oscillator clock sources are used for transmission and reception in the same period of reception and transmission. In this way, when receiving the signal, the receiving local oscillator clock source deviates from the local oscillator clock source of the transmitting signal. Through deviation modulation, the signal transmission and receiving links work in different intermediate frequency bands during the period when they work at the same time. This mechanism can achieve that the local oscillator clock of the transmitting channel is different from that of the receiving end while receiving the signal, thereby increasing the isolation of the transmitting and receiving channels by more than 55dB, reducing the leakage of the transmitted signal, and avoiding the submersion and pollution of the weak detection signal by the transmitted signal, so that the transceiver link can have a higher sensitivity to weak signals in a low signal-to-noise ratio environment. The intermediate frequency signal processing module uses switch control to achieve the same source of the local oscillator clock of the transmitted signal and the local oscillator clock of the receiving channel when receiving the signal echo. By utilizing the coherence of the local oscillator of the receiving and transmitting signal clocks, the error introduced by the phase noise of the clock local oscillator is offset.The same source phase cancellation fundamentally reduces the requirements for VCO phase noise. Ordinary clocks can meet the requirements, and expensive high-precision clocks are not needed, which greatly reduces costs. If the dynamic range of the transceiver link is not large enough, the radar receiver may be overloaded or even damaged when receiving a strong signal; and when receiving a weak signal, the radar receiver may not be able to detect it. Deviation modulation can also increase the dynamic range of the transceiver link, and the attenuation of different frequencies by the filter can enable the radar to adapt to a wider range of input signal strength changes. This deviation modulation technology has the advantages of high sensitivity, high isolation, high dynamic range, and low cost.

[0097] It should be noted that the RF receiving channel of the RF module and the IF receiving channel of the IF signal processing module constitute a receiver channel, and the RF transmitting channel of the RF module and the IF transmitting channel of the IF signal processing module constitute a transmitter channel.

[0098] 4) Baseband signal processing module, which is the algorithm processing backend, is used to complete digital signal processing by FPGA processor. The baseband signal processing module includes: a cache unit, a preprocessing unit 31, an extraction filter unit 32 (greatly reducing the computing resource requirements), an FFT filter unit 33, a wind speed calculation unit 34, an internal control unit 35, a transceiver timing control unit 36 ​​and a signal generating unit 37, which are connected in sequence. The cache unit is also connected to the intermediate frequency receiving channel of the intermediate frequency signal processing module, the transceiver timing control unit 36 ​​is also connected to the FFT filter unit 33, the signal generating unit 37 is also connected to the extraction filter unit 32 and the preprocessing unit 31, and the baseband processing module is also connected to the antenna module to provide a control signal. The preprocessing unit 31 includes interference preprocessing, data reorganization, and distance selection, and mainly performs preprocessing and anti-interference processing on the echo signal to eliminate some useless clutter interference; the extraction filter unit 32 greatly reduces the requirements for signal processing resources by designing multiple groups of extraction filters; the FFT filter unit 33 mainly filters and extracts the reorganized echo data; the transceiver timing control unit 36 ​​mainly includes communication data control, system timing control, and antenna control; the signal generating unit 37 includes a sine wave generator and a random sequence generator, which are mainly used for random modulation and RF signal generation.

[0099] In the baseband signal processing module, the signal generating unit adopts a randomly modulated periodic narrow pulse signal system (i.e., a weak Doppler signal extraction method based on randomly modulated narrow pulses). A random generator generates a string of random coding sequences, which are modulated on the transmitting pulse signal. By controlling the RF switch, the periodic transmission of hundreds of nanoseconds (e.g., 200ns) of randomly modulated narrow pulses is achieved, and then the transmission is turned off for 2us, repeating the cycle.

[0100] The random modulation period narrow pulse signal system includes steps S11 to S13:

[0101] Step S11: Use a random sequence generator to generate a random signal, use a sine wave generator to generate a narrow pulse signal, modulate the random signal on the narrow pulse signal to obtain a modulated signal, and transmit the modulated signal.

[0102] Step S12: Receive the echo signal after the modulated signal is transmitted, perform mixing and amplification filtering, and after the random signal autocorrelation test, perform integration and accumulation to obtain a sampling sequence.

[0103] Step S13: extract the Doppler frequency shift according to the sampling sequence, perform wind speed calculation after preprocessing, extraction filtering and FFT filtering in sequence, and obtain the wind speed and wind direction.

[0104] like Figure 7 As shown in the figure, this special signal system ensures that the radar system does not transmit when receiving and does not receive when transmitting, which greatly increases the isolation of the transmit and receive channels; the design of periodic transmission of hundreds of nanoseconds (for example, 200ns) and reception of 2us is conducive to distance selection for back-end data processing; random modulation solves the problem of ground interference. The entire signal system solves the problems of the atmospheric scattering echo signal of the near-air wind measurement radar being very weak and easily submerged by ground noise, the echo distance being short, the response time being short, and the need for high distance resolution while meeting anti-interference requirements. It is combined with the corresponding random code autocorrelation anti-interference algorithm to cleverly filter out environmental clutter such as ground clutter, mountain clutter, ocean clutter, and trees.

[0105] like Figure 8 As shown in the figure, in the baseband signal processing module, the signal processing flow is as follows: the sine wave generator in the baseband signal processing module generates a low-frequency sine wave signal, and the local random sequence generator generates a random sequence. After modulation, a baseband transmission signal is generated and sent out. When the antenna receives the echo signal, after ADC oversampling, the distance selection is performed first, the echo signal within the required near-space detection range is cached, and all clutter signals outside the detection range are filtered out. After caching 1S of data, the data sequence is sent to the random correlation discrimination module to filter out non-correlated clutter. Then, the interference caused by the mechanical jitter of the equipment is filtered out through the jitter filter module, and then the data is reorganized according to the distance information to form a new pulse matrix (the row is the distance information and the column is the echo information). This matrix is ​​sent to the extraction filter for extraction, and finally through the FFT filter, the Doppler frequency shift extraction module completes the extraction of the Doppler frequency shift through the filtering algorithm.

[0106] In the baseband signal processing module, the signal processing of the preprocessing unit includes the following steps: correlation discrimination, jitter filtering, data reorganization and distance selection. Among them, the correlation discrimination determines whether the received echo signal is the echo signal of the transmitted signal, rather than other interference clutter, by using a coherent algorithm to compare the echo signal and the local random sequence signal. A random modulation narrow pulse signal system is adopted, and a random generator generates a string of random coding sequences, which are modulated on the transmitted pulse signal. The random sequence signal has a property similar to white noise. The received echo signal passes through the correlator, which can filter out the irrelevant clutter signals and distinguish the effective signal from the clutter signal.

[0107] Specifically, the relevant determination includes steps S21 to S23:

[0108] Step S21: The signal modulated by the random sequence transmitted locally is:

[0109]

[0110] Step S22: The received random echo signal is:

[0111]

[0112] In the formula, is the echo signal amplitude, and w is the transmitting signal frequency.

[0113] Step S23: The result after random correlation is:

[0114]

[0115] In the formula, t1 is the starting time of a period, and t2 is the ending time of a period.

[0116] when When it is unrelated to P(t),

[0117] The interference of wind radar includes meteorological interference, electromagnetic interference, ground interference, equipment interference, etc. Among them, the impact of ground interference is quite large, mainly reflected in the following aspects: First, the detection performance is reduced. Ground interference can cause the detection performance of the radar to decline, making it difficult to accurately detect the target. For example, in an environment with a lot of vegetation and water, the detection ability of the radar may be seriously affected. Second, signal distortion. Ground interference can cause radar signal distortion, making it impossible for the radar to accurately judge information such as distance, wind speed and wind direction. Third, signal quality is reduced. Ground interference will reduce the quality of wind radar signals, thereby increasing the difficulty of data processing, because interference will cause a lot of noise and inaccurate information in the data, which requires more time and resources to process.

[0118] In the wind measurement application environment, radar interference signals are mainly divided into white noise and clutter interference. White noise mainly comes from thermal noise and power noise, which are low-frequency noise; clutter interference mainly comes from the backscattered noise of the ground, sea, mountains, trees, and birds, as well as the noise of the receiver itself, which are high-frequency noise. Low-frequency noise can be filtered out by high-pass filters or band-pass filters, but clutter interference is usually in the same bandwidth as the echo signal and is difficult to filter out. When the signal-to-noise ratio is too low, the probability of Doppler shift detection will be much lower than the confidence rate.

[0119] It can be seen that the correlation discrimination method has a greater ability to suppress ground clutter, mountain clutter, vegetation clutter and other ground interference.

[0120] Jitter filtering includes:

[0121] After the relevant judgment, the interference caused by the mechanical jitter of the equipment is filtered out, and then the data is reorganized.

[0122] Data reorganization includes:

[0123] The radar obtains a set of pulse echo signals through ADC oversampling, and the echo signals include Doppler frequency shift signals at different time points and different distances;

[0124] Extract the pulse echo signal within the concerned distance range, and segment the pulse echo signal according to different distance segments to obtain segmented data;

[0125] The segmented data are rearranged by distance, with the same distance segment signals in one column, forming a new matrix, in which the rows are distance information and the columns are different echo information.

[0126] Through data reorganization, subsequent filters can further filter out clutter in both time and space dimensions. In order to improve the signal-to-noise ratio, the radar system sampling frequency is much higher than the data bandwidth, resulting in a relatively large amount of data. In order to save computing resources and adapt to embedded system applications, a set of extraction filters are designed to extract the echo matrix after data reorganization, thereby reducing the requirements for computing resources without losing the signal-to-noise ratio, making the method less restricted and more widely used. This application has a moderate amount of calculation, does not require large-capacity storage, is friendly to embedded processors, and is suitable for large-scale radar systems.

[0127] like Fig. 9 The echo signal structure before the data reconstruction shown in FIG. Fig.10 The echo signal structure after data reorganization is shown.

[0128] The distance selection includes: performing distance selection, caching the echo signals within the required near-space detection range, and filtering out all clutter signals outside the detection range.

[0129] In the baseband signal processing module, the FFT filtering unit adopts an FFT filtering algorithm based on data reorganization, including steps S31 to S33.

[0130] Step S31: The radar obtains a set of pulse echo signals through ADC oversampling. This set of echo signals includes Doppler frequency shift signals at different time points and different distances.

[0131] Step S32: first extract the pulse echo signal within the concerned distance range, and then segment the pulse echo signal according to different distance segments to obtain segmented data.

[0132] Step S33: rearrange the segmented data by distance, with the same distance segment signals as one column, to form a new matrix, in which the rows are distance information and the columns are different echo information.

[0133] In the baseband signal processing module, data within 1S is reorganized according to distance segments through data reorganization, and then the classic FFT filtering algorithm is performed, which can further filter out clutter in both time and space dimensions, thereby improving the signal-to-noise ratio.

[0134] Note: Before doing FFT, the discrete sampling value spectrum of the noise is evenly dispersed in N frequency units. After doing N-point FFT correlation accumulation, only the passband of the narrowband filter with the center frequency equal to the characteristic signal is selected by the noise sampling value, and the noise power is reduced to 1 / N of the original. The noise power of the selected noise sampling value increases by N 2 Therefore, after N-point FFT, the total noise power increases by (1 / N)*N. 2 times, the signal-to-noise ratio increases N times.

[0135] 5) Peripheral module, used for jitter sensing and data communication. The communication modes of the peripheral module include: 3G, 4G and WiFi.

[0136] 6) The power module is the energy supply end, which is used to power the antenna module, RF module, intermediate frequency signal processing module, baseband signal processing module and peripheral modules. The power module includes: 12V power supply or 24V power supply.

[0137] like Fig.11As shown, in this application, the signal flow process is: after the system is initialized, it enters the transmission mode. In the transmission mode, the baseband signal processing module is responsible for generating a local random sequence and modulating it with the baseband sinusoidal signal. After filtering, the modulated signal is sent to the intermediate frequency signal processing module. In this module, the DAC digital-to-analog conversion, filtering, amplification and first-level mixing of the transmission signal are completed, and the modulated low-frequency signal is up-converted to an intermediate frequency signal below 8GHz, and then sent to the transmission link of the RF module through amplification and filtering. In the RF module, it is further amplified, filtered and completed in the second level of up-conversion, and the intermediate frequency signal below 8GHz is up-converted to a 24Ghz signal. The baseband controls the RF switch, opens the transmission channel, and transmits the 24GHz millimeter wave signal into the atmosphere through a single antenna module. After tens of nanoseconds, the RF switch is turned off to enter the signal receiving mode.

[0138] In the receiving mode, the antenna receives the 24GHz atmospheric echo signal, performs a first-stage down-conversion after the low-noise amplifier, and reduces the 24Ghz signal to an intermediate frequency signal below 8Ghz through mixing, and then filters and amplifies it before sending it to the intermediate frequency signal processing module. In the intermediate frequency signal processing module, the secondary frequency conversion is completed, and the intermediate frequency signal below 8Ghz is converted into a baseband signal through secondary frequency conversion, which is then filtered and amplified again before being sent to the ADC for analog-to-digital conversion and sampling. After the receiving mode lasts for hundreds of nanoseconds, the RF switch is switched to enter the signal transmission mode. The sampled digital signal is first subjected to anti-interference preprocessing and correlation discrimination in the baseband signal processing module, and the effective data is cached after filtering out the clutter signal.

[0139] The baseband signal processing module repeats the transmission and reception process by controlling the RF switch. The sampled data is selected by distance, and then the effective data fragments cached for 1 second (S) are coherently judged and sent to the data reorganization module after removing the ground clutter. The data is reorganized by distance segment and then sent to the extraction filter for group extraction. The extracted matrix is ​​sent to the FFT filter to extract the Doppler frequency shift information of each distance segment. Finally, the Doppler frequency shift information is sent to the wind speed solution module for wind speed analysis to obtain the wind speed and wind direction information of different distance segments, which are output through the device interface.

[0140] It should be noted that the effective signal transmission frequency band and the effective reception frequency band are the same frequency band, but when receiving, the transmission frequency band is switched to another frequency band; that is, at the transmission time (for the transmission signal), PLL2 is used, and the intermediate frequency local oscillator signal sources of the transmitter channel and the receiver channel operate in the same frequency band, and at the reception time (for the reception signal), PLL3 is used, and the intermediate frequency local oscillator signal sources of the transmitter channel and the receiver channel are in different frequency bands.

[0141] The physical principle is: by emitting 24GHZ millimeter waves to the near-air area in front of the wind turbine blades, when the beam encounters the air medium or suspended particles such as cloud droplets and raindrops, the incident wave will be scattered from these media or particles. After a part of the scattered wave returns to the radar and is received, the Doppler frequency shift information carried by the scattered echo is extracted to detect wind speed and direction.

[0142] Assuming that the energy flux density emitted by the antenna is normally distributed with the off-axis angle, considering that the millimeter wave is weakened in the propagation medium and the scattering volume is not filled with precipitation, under the condition of Rayleigh scattering, the millimeter wave meteorological radar equation is as follows:

[0143]

[0144] Among them, P r is the radar echo power, P t is the radar transmission power, G t is the antenna gain, θ is the angular width of the antenna beam cross section in the horizontal direction, φ is the angular width of the beam cross section in the vertical direction, h is the radar transmit pulse length, λ is the radar wavelength, ψ is the beam filling factor, Z is a constant reflecting the size of the particles in the air, R is the distance from the radar to the target, and k = 4.343k L , the dimension of k is decibel / length, k L The dimension of is 1 / length, they are all attenuation coefficients, and r is the distance.

[0145] The above parameters need to be carefully selected so that the echo signal can be detected under clear weather conditions. In clear weather, Z is approximately -28dBz. If the antenna gain is not enough, the reflected signal is very weak and the echo signal cannot be detected.

[0146] The principle of Doppler wind measurement is: The principle of Doppler radar wind measurement is based on the Doppler effect. When an object approaches the radar, the frequency of the electromagnetic waves it emits becomes higher. When an object moves away from the radar, the frequency of the electromagnetic waves it emits becomes lower. This change is called Doppler shift. The size of the Doppler shift is proportional to the speed of the target. The wind measuring radar emits a beam of electromagnetic waves from the transmitter, which is scattered by atmospheric particles and the echo is received by the antenna. By analyzing the received signal and measuring the size of the Doppler shift, the wind speed and direction information can be calculated.

[0147] The above-mentioned antenna millimeter wave radar system for wind farm wind measurement and the weak Doppler signal extraction method based on randomly modulated narrow pulses have the following advantages:

[0148] 1) Strong anti-interference ability: A unique random pulse signal system is designed, with a time delay of 200ns and a frequency of 0.45M for transmitting pulse signals. It can cooperate with the algorithm to achieve high-frequency clutter suppression and improve the signal-to-noise ratio of the echo signal. Through random coherence technology, anti-interference preprocessing is performed before Doppler frequency shift information detection to filter out invalid clutter signals in the echo, ensuring that the echo signal of the effective transmission signal is received, rather than other irrelevant scattered signals. At the same time, a narrow-band pulse of the corresponding period is designed to filter out clutter signals outside the detection range. And improved the conventional FFT algorithm, adopting a random modulation anti-interference algorithm, filtering out clutter through random sequence technology, and then reorganizing the data, and then performing multiple groups of FFT filtering, processing clutter in both time and space dimensions, pre-reorganizing and screening the data, and through 1s pulse matrix coherent accumulation, after random code anti-interference filtering, the pulse echo signals within the 1s time delay are reorganized according to the distance segment to form a sampling matrix at different time points and different distances, and the FFT coherent accumulation is performed on this matrix, and the noise is further filtered out, which greatly improves the system's anti-interference ability; this anti-interference algorithm does not require too much prior It does not require too much computing resources, nor does it require complex hardware support. It can also greatly suppress ground clutter, equipment scattered clutter, distant mountain clutter, invalid meteorological clutter, and environmental clutter. By expanding the big data observation time window, historical data information is utilized through data reorganization and FFT coherent accumulation to improve the detection confidence rate. The structure of the receive and transmit RF link and the multi-stage switch are also designed. The deviation modulation effectively improves the isolation of the transmit and receive link, avoids the interference of the transmit channel on the receiving end, ensures the high gain and low noise of the link, and adopts the same source local oscillator mechanism to avoid further contamination of the echo signal by the clock phase noise.

[0149] 2) Accurate distance resolution: It is difficult for millimeter wave wind measurement radar with FMCW signal system to have good distance resolution. This system has designed a unique pulse signal system and adopted an improved FFT algorithm to have accurate distance resolution in the near-air range, thus improving the accuracy of the data.

[0150] 3) High sensitivity: High sensitivity is achieved through the random modulation of multiple narrowband pulse signal system, RF multi-stage switch, RF multi-stage amplification and filtering, RF co-origin local oscillator mechanism, and intermediate frequency deviation modulation. The sensitivity is further improved by using the structure of lens antenna and 3 microstrip line array feed sources. It can detect weak echo signals with power below -163dBm, which is more than 10dB higher than the sensitivity of existing wind measurement millimeter wave radar. Among them, intermediate frequency deviation modulation means that when the radar transceiver link is strongly coupled, the transmitted signal may leak into the receiving link, which will not only drown out the weak target echo and reduce the receiver sensitivity, but also may cause the receiver to saturate and fail, thereby having a negative impact on anti-interference. Through deviation modulation, the present application increases the isolation between receiving and transmitting by 60dB, reduces the leakage of the transmitted signal, avoids the submersion and pollution of the weak detection signal by the transmitted signal, and enables the transceiver link to have a high sensitivity to weak signals in a low signal-to-noise ratio environment.

[0151] 4) It can realize near-air wind condition detection: This application is suitable for near-air radar measurement, with high distance resolution. The signal return distance and time of near-air radar measurement are short, which is not suitable for transmitting longer pulse signals, which will cause confusion and interference; it can obtain better distance resolution with narrow pulse signals, and at the same time has good anti-interference performance to meet the needs of near-air measurement; pulse compression technology is used to compress wide pulses into narrow pulses using matching filters to improve the distance resolution at the receiving end. A homologous local oscillator mechanism is designed to ensure that weak echo signals are not polluted by local clock phase noise, and multi-stage filtering, amplification, and mixing are carefully designed. A unique signal process that adapts to a single antenna system is designed. Through this signal processing process, it can adapt to the application environment of millimeter-wave radar wind speed measurement within a few hundred meters (for example, 300 meters) in the near-air range, solve the problems of weak echo signals, low signal-to-noise ratio, short echo time, and complex ground interference in this application, and can detect near-air wind speed and direction of about hundreds of meters, thereby obtaining advance margin for wind turbine control, giving enough reaction time for wind turbine execution equipment, and realizing precise control of wind turbine attitude. At a lower cost and power consumption, by measuring the near-air wind conditions within a few hundred meters in front of the wind turbine blades, it provides all-weather, advanced, real-time and accurate reference data for the wind turbine's pitch and yaw system control, thereby solving the problem of control lag and greatly improving the data availability of wind measuring equipment in low visibility environments such as rain, snow, fog and haze. Compared with the laser wind measurement system, it can provide data in low visibility environments such as rain, snow, fog and haze, with enhanced all-weather performance and increased usable time throughout the year.

[0152] 5) Small size, light weight, and low power consumption: The single antenna mode with integrated transmission and reception greatly reduces the mechanical complexity of the antenna module, and the size of the equipment can be reduced to nearly half of the dual antenna mode; accordingly, the weight of the equipment is also reduced, which is more suitable for outdoor, high-altitude, and weight-restricted installation conditions of wind farms. In addition, a low-power design is adopted: the system ensures that the transmission time is very short and the reception time is relatively longer, thereby reducing part of the power consumption; at the same time, unlike the meteorological radar that detects at the kilometer level, this radar system is not a wind profile radar that detects at the kilometer level, and does not detect scattered echoes from boundary layers and stratospheric clouds. It is a low-power radar with very low transmission power and a detection area within a few hundred meters of the near-air range. Compared with the wind profile meteorological radar, it has low cost, small size, low power consumption, and less applicability restrictions; the system is implemented using low-power devices. The above means achieve overall low power consumption, about 5W.

[0153] In summary, the present application adopts a single antenna design and a unique RF and baseband signal processing system, which has a higher clutter suppression capability. The isolation between the receiving and transmitting channels of the millimeter-wave wind measurement radar is increased by random pseudo-code modulation of multiple narrow pulse signal systems, multi-level switching of RF channels, and intermediate frequency deviation modulation. The signal-to-noise ratio of the detection signal is greatly improved through single antenna design, multi-level amplification and filtering design, intermediate frequency deviation modulation, random pseudo-code modulation of multiple narrow pulse signal systems, pseudo-code modulation anti-interference algorithm, and data reconstruction FFT algorithm, so that the radar system has the characteristics of high sensitivity, high anti-interference, small size, low cost, low power consumption, and all-weather, and has higher clutter suppression capability, more accurate distance resolution capability and better near-air wind condition detection performance.

[0154] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0155] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for extracting weak Doppler signals based on randomly modulated narrow pulses, characterized in that: include: A random sequence generator is used to generate a random signal, a sine wave generator is used to generate a narrow pulse signal, the random signal is modulated on the narrow pulse signal to obtain a modulated signal, and the modulated signal is transmitted; Receive the echo signal after the modulated signal is transmitted, perform mixing, amplification and filtering, and after the random signal autocorrelation test, perform integration and accumulation to obtain a sampling sequence; The Doppler frequency shift is extracted according to the sampling sequence, and after preprocessing, decimation filtering and FFT filtering, the wind speed is solved to obtain the wind speed and wind direction.

2. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to claim 1, characterized in that: A random sequence generator is used to generate a random signal, a sine wave generator is used to generate a narrow pulse signal, and the random signal is modulated on the narrow pulse signal to obtain a modulated signal, including: In the formula, s(t) is the modulation signal, P(t) is the random signal, e is a natural constant, j is a complex number, is the frequency of the electromagnetic wave, t is the time, and φ0 is the phase.

3. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to claim 2, characterized in that: Random signal autocorrelation test, including: Where m = 2 n -1 is the maximum length and period of the M sequence, E is the autocorrelation function, P(t) is a random signal, τ = kT e (k=1,2,....L-1), T e is the symbol bandwidth of the M sequence, and L is the sequence length.

4. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to claim 3, characterized in that: Perform integration and accumulation to obtain the sampling sequence including: To accumulate points: If the phase of the transmitter is continuous, then mixing is a phase subtraction process to obtain the intermediate frequency signal: In the formula, is the integral of the distance from R1 to R2, R1 is the closest point in the observation range, R2 is the farthest point in the observation range, R is the integral variable, v R is the particle velocity constant and c is the speed of light.

5. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to claim 4, characterized in that: After obtaining the intermediate frequency signal, calculate the phase difference between two consecutive received signals and substitute it into the intermediate frequency signal to idealize it to obtain the sampling sequence: Where, T b is the sampling interval, δφ is the phase difference between two consecutive received signals, is the sampling sequence, φ c is the intermediate frequency signal phase.

6. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to any one of claims 1 to 5, characterized in that: The Doppler frequency shift is extracted according to the sampling sequence, and after preprocessing, extraction filtering, and FFT filtering, the wind speed is solved to obtain the wind speed and wind direction, including: The Doppler frequency shift is extracted according to the sampling sequence, and the preprocessing is completed after correlation discrimination, jitter filtering, data reorganization and distance selection. Then, the wind speed is solved after extraction filtering and FFT filtering in sequence to obtain the wind speed and wind direction.

7. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to claim 6, characterized in that: Relevant judgments include: The random sequence signal transmitted locally is: The received random echo signal is: In the formula, is the echo signal amplitude, w is the transmitting signal frequency; The result after random correlation is: In the formula, t1 is the starting time of a period, and t2 is the ending time of a period; when When it is unrelated to P(t), 8. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to claim 7, characterized in that: Jitter filtering includes: filtering out the interference caused by mechanical jitter of the device after relevant judgment, and then reorganizing the data.

9. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to claim 8, characterized in that: Data reorganization includes: The radar obtains a set of pulse echo signals through ADC oversampling, and the echo signals include Doppler frequency shift signals at different time points and different distances; Extract the pulse echo signal within the concerned distance range, and segment the pulse echo signal according to different distance segments to obtain segmented data; The segmented data are rearranged by distance, with the same distance segment signals in one column, forming a new matrix, in which the rows are distance information and the columns are different echo information.

10. The method for extracting weak Doppler signals based on randomly modulated narrow pulses according to claim 9, characterized in that: The distance selection includes: performing distance selection, caching the echo signals within the required near-space detection range, and filtering out all clutter signals outside the detection range.

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