CN118501866A - Unmanned aerial vehicle ADS-B response method and system based on FPGA - Google Patents

Abstract

The present invention discloses an ADS-B response method for unmanned aerial vehicles based on FPGA, comprising the following steps: collecting the inquiry signal sent by the inquiry end; performing pulse signal detection on the inquiry signal to obtain the pulse edge and pulse width information of the burst short pulse signal; detecting the frame header information of the inquiry signal to obtain a plurality of leading pulses; matching the timing of a plurality of leading pulses according to the pulse edge and pulse width information of the burst short pulse signal, screening out the signals that meet the preset error requirements and match, and obtaining a valid inquiry signal; performing demodulation and decoding processing on the valid inquiry signal; performing CRC check and error correction processing on the valid inquiry signal to obtain the error-corrected data; obtaining the inquiry information according to the error-corrected data, modulating the response information, and sending the response information to the inquiry end to realize the response. The present invention realizes the efficient response of the unmanned aerial vehicle to the inquiry end.

Description

A UAV-borne ADS-B response method and system based on FPGA

Technical Field

The present invention relates to the technical field of secondary surveillance radar, and in particular to an FPGA-based unmanned aerial vehicle ADS-B response method and system.

Background Art

Secondary surveillance radar is a radar system used for air traffic control. Currently, SSR systems are commonly used in Air Traffic Control Radar Beacon Systems (ATCRBS), Traffic Collision Avoidance Systems (TCAS), and in military electronic warfare (EW) as an Identification Friend or Foe (IFF) technology, in which aircraft are equipped with "transponders" (transponders) that transmit coded reply signals back to "interrogators" on the ground. This technology requires the use of secondary radar because of the coded high-frequency transmit and response signals. It responds to each interrogation signal by transmitting coded data such as identification code, aircraft altitude, and other information, depending on the selected mode. Common secondary surveillance methods are single pulse secondary surveillance radar (MSSR), Mode S, TCAS, and ADS-B.

ADS-B is the abbreviation of Automatic Dependent Surveillance-Broadcast. As the name implies, the system can automatically (once per second) obtain parameters from relevant airborne equipment to broadcast the aircraft's position, altitude, speed, heading, identification number and other information to other aircraft or ground stations without manual operation or inquiry, so that controllers can monitor the aircraft status. It is derived from ADS (Automatic Dependent Surveillance), which was originally a solution proposed for transoceanic aircraft that wanted to use satellites for monitoring when radar monitoring was not possible. ADS-B. The system broadcasts the aircraft's dynamic flight status, such as track, speed, longitude and latitude, in real time, and sends out the aircraft's unique identification information (ICAO code) to indicate the aircraft's identity.

Relative to the information transmission direction of aircraft, the application of ADS-B is divided into two categories: sending (OUT) and receiving (IN). OUT is the basic function of ADS-B, which is responsible for sending the signal from the aircraft sender to the ground receiving station or other aircraft through line-of-sight propagation. ADS-B IN means that the aircraft receives ADS-B OUT information sent by other aircraft or information sent by ground service equipment to provide operational support and situational awareness for the crew. At present, the function of ADS-B IN is less used, but it is the direction of future ADS-B application development.

With the rapid development of UAV technology, the research and development of airborne equipment and ground support equipment for UAVs has become more and more urgent. A secondary radar transponder system is installed on the UAV for ground identification. The system needs to be miniaturized and designed with low power consumption to carry the UAV system.

Summary of the invention

In order to solve the technical problem that the prior art UAV lacks a secondary radar response system that is miniaturized, has good performance and low power consumption, the present invention provides an ADS-B response method and system for UAV based on FPGA. The technical solution adopted by the present invention is:

The first aspect of the present invention provides an FPGA-based unmanned aerial vehicle ADS-B response method, comprising the following steps:

Collect the ADS-B signal sent by the inquiry end;

Performing pulse signal detection on the ADS-B signal to obtain pulse edge and pulse width information of the burst short pulse signal;

Detecting frame header information of the ADS-B signal to obtain a number of leading pulses;

According to the pulse edge and pulse width information of the burst short pulse signal, the timing of the plurality of leading pulses is matched, and the matching signals that meet the preset error requirements are screened out to obtain a valid ADS-B signal;

Demodulating and decoding the valid ADS-B signal;

Perform CRC check and error correction on the effective ADS-B signal after demodulation and decoding to obtain error-corrected data;

The query information is obtained based on the error-corrected data, and after the response information is modulated into an ADS-B signal, the response information is sent to the query end to achieve a response.

As a preferred solution, the method of performing pulse signal detection on the ADS-B signal to obtain pulse edge and pulse width information of the burst short pulse signal includes:

After windowing the acquired time domain signal, a short-time Fourier transform is performed, and the formula is expressed as Where N is the short-time Fourier transform window width, so as to obtain the short-time Fourier spectrum of the ADS-B signal;

Each window of the short-time Fourier spectrum is subjected to frequency domain constant false alarm rate detection in the field, and the frequency domain constant false alarm rate gate limit of each window is calculated, and the formula is expressed as follows: Wherein is the expected false alarm probability P _FA , and the maximum value of the signal in each window is compared to determine whether there is a pulse signal in the window;

The MN method is used to detect the 0-1 sequence indicating the presence or absence of the signal in each window to obtain the starting and ending positions of the pulse signal in the time domain, and the precise edge and pulse width information of the burst short pulse signal is obtained through the coexistence of the signals in each window.

As a preferred solution, the method for demodulating and decoding the valid ADS-B signal includes:

The signal strength of the first half and the second half of each code element of the effective ADS-B signal is detected. If the signal strength of the first half is higher than that of the second half, the code element is judged as 1; if the signal strength of the first half is lower than that of the second half, the code element is judged as 0.

As a preferred solution, a method for performing CRC check and error correction processing on a valid ADS-B signal that has been demodulated and decoded to obtain error-corrected data includes:

A CRC check is performed on the data bits of the valid ADS-B signal through a preset protocol to obtain a CRC check code; if the result of the CRC check code proves that there is a transmission error in the data bit, the erroneous data position is found by combining the low confidence position obtained in the bit judgment with the CRC check code, and the erroneous data bit is inverted to obtain the error-corrected data.

As a preferred solution, the response information includes at least one of the following:

Aircraft information, flight altitude, speed and GPS location information.

The second aspect of the present invention provides an FPGA-based unmanned aerial vehicle ADS-B transponder system, comprising an FPGA, a signal acquisition module, a pulse signal detection module, a leading pulse detection module, a signal matching module, a PPM demodulation module, a data correction processing module and a PPM modulation module; the FPGA is respectively connected to the signal acquisition module, the pulse signal detection module, the leading pulse detection module, the signal matching module, the PPM demodulation module, the data correction processing module and the PPM modulation module;

The signal acquisition module is used to collect the ADS-B signal sent by the inquiry end;

The pulse signal detection module is used to perform pulse signal detection on the ADS-B signal to obtain pulse edge and pulse width information of the burst short pulse signal;

The leading pulse detection module is used to detect the frame header information of the ADS-B signal to obtain a plurality of leading pulses;

The signal matching module is used to match the timing of the plurality of leading pulses according to the pulse edge and pulse width information of the burst short pulse signal, screen out the matching signals that meet the preset error requirements, and obtain a valid ADS-B signal;

The PPM demodulation module is used to demodulate and decode the valid ADS-B signal;

The data correction processing module is used to perform CRC check and error correction processing on the effective ADS-B signal after demodulation and decoding processing to obtain error-corrected data;

The PPM modulation module is used to obtain inquiry information according to the error-corrected data, modulate the response information into an ADS-B signal, and then send the response information to the inquiry end to achieve a response.

As a preferred solution, the pulse signal detection module includes a short-time Fourier transform module, a frequency domain constant false alarm rate detection module and a sequence detection module;

The short-time Fourier transform module is used to perform short-time Fourier transform on the collected time domain signal after windowing. The formula is expressed as Where N is the short-time Fourier transform window width, so as to obtain the short-time Fourier spectrum of the ADS-B signal;

The frequency domain constant false alarm rate detection module is used to perform frequency domain constant false alarm rate detection on each window of the short-time Fourier spectrum, and calculate the frequency domain constant false alarm rate gate limit of each window, which is expressed as follows: Wherein is the expected false alarm probability P _FA , and the maximum value of the signal in each window is compared to determine whether there is a pulse signal in the window;

The sequence detection module is used to perform MN method detection on the 0-1 sequence indicating the presence or absence of the signal in each window, so as to obtain the starting and ending positions of the pulse signal in the time domain, and obtain the precise edge and pulse width information of the burst short pulse signal through the coexistence of the signals in each window.

As a preferred solution, the PPM demodulation module includes a signal strength detection module;

The signal strength detection module is used to detect the signal strength of the first half and the second half of each code element of the valid ADS-B signal. If the signal strength of the first half is higher than that of the second half, the code element is judged as 1; if the signal strength of the first half is lower than that of the second half, the code element is judged as 0.

As a preferred solution, the data correction processing module includes a CRC check module and an error correction module;

The CRC check module is used to perform CRC check on the data bits of the valid ADS-B signal through a preset protocol to obtain a CRC check code;

The error correction module is used to find the erroneous data position by combining the low confidence position obtained in the bit judgment with the CRC check code when the result of the CRC check code proves that there is a transmission error in the data bit, and invert the erroneous data bit to obtain the corrected data.

As a preferred solution, the response information includes at least one of the following:

Aircraft information, flight altitude, speed and GPS location information.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention uses a pulse detection algorithm based on short-time Fourier transform and frequency domain constant false alarm rate detection, which has better effects than traditional detection methods in low signal-to-noise ratio environments, has stronger robustness, and also has higher detection accuracy. The present invention adopts a secondary radar form, which can communicate with the radar in the radar deployment area to implement flight information sharing. At the same time, the inquiry and response signals adopt the ADS-B form, and can also communicate through the existing ADS-B ground receiver to share the aircraft's own information and improve the efficiency of information interaction. The present invention is carried on the drone end, providing the ground end with drone information and current flight status, including location, speed and other information, thereby improving the ability to supervise drones in the airspace.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of an FPGA-based unmanned aerial vehicle ADS-B response method provided in this embodiment;

FIG2 is a diagram of a standard ADS-B signal format provided by this embodiment;

FIG3 is a pulse signal detection flow chart provided in this embodiment;

FIG4 is a block diagram of an FPGA-based unmanned aerial vehicle ADS-B response system provided in this embodiment.

DETAILED DESCRIPTION

The accompanying drawings are only used for illustrative purposes and are not to be construed as limiting the present invention;

It should be clear that the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the embodiments of the present application.

The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present application. The singular forms of "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and/or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects, and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

In addition, in the description of this application, unless otherwise specified, "multiple" means two or more. "And/or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and/or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character "/" generally indicates that the previous and next associated objects are in an "or" relationship. The present invention is further described below in conjunction with the accompanying drawings and embodiments.

The present invention is further described below in conjunction with the accompanying drawings and embodiments.

Example 1

Referring to FIG. 1 to FIG. 3 , this embodiment provides an FPGA-based unmanned aerial vehicle ADS-B response method, comprising the following steps:

S1: Collect the ADS-B signal sent by the inquiry end;

It should be noted that the format of a standard ADS-B signal is shown in Figure 2. Each pulse consists of an 8μs characteristic preamble pulse and a 112μs message data block. The message block is composed of an 88-bit parameter information segment and a 24-bit CRC check code. In each code element, if the pulse is in the first half, it is represented as bit 1, and if the pulse is in the second half, it is represented as bit 0. The ADS-B message preamble header contains 4 pulses, which are fixed in position. The intervals between the second, third and fourth pulses and the first transmission pulse are 1.0μs, 3.5μs and 4.5μs respectively.

Specifically, the ADRV9009 chip is used to collect the ADS-B signal sent by the inquiry end;

S2: Perform pulse signal detection on the ADS-B signal to obtain pulse edge and pulse width information of the burst short pulse signal;

In a specific embodiment, referring to FIG. 3 , a method for performing pulse signal detection on the ADS-B signal to obtain pulse edge and pulse width information of a burst short pulse signal includes:

After windowing the acquired time domain signal, a short-time Fourier transform is performed, and the formula is expressed as Where N is the short-time Fourier transform window width, so as to obtain the short-time Fourier spectrum of the ADS-B signal;

Each window of the short-time Fourier spectrum is subjected to frequency domain constant false alarm rate detection in the field, and the frequency domain constant false alarm rate gate limit of each window is calculated, and the formula is expressed as follows: Wherein is the expected false alarm probability P _FA , and the maximum value of the signal in each window is compared to determine whether there is a pulse signal in the window;

The MN method is used to detect the 0-1 sequence indicating the presence or absence of the signal in each window to obtain the starting and ending positions of the pulse signal in the time domain, and the precise edge and pulse width information of the burst short pulse signal is obtained through the coexistence of the signals in each window.

S3: Detecting frame header information of the ADS-B signal to obtain a number of leading pulses;

S4: Matching the timing of the plurality of leading pulses according to the pulse edge and pulse width information of the burst short pulse signal, screening out the matching signals that meet the preset error requirements, and obtaining a valid ADS-B signal;

S5: Demodulate and decode the valid ADS-B signal;

In a specific embodiment, the method for demodulating and decoding the valid ADS-B signal includes:

The signal strength of the first half and the second half of each code element of the effective ADS-B signal is detected. If the signal strength of the first half is higher than that of the second half, the code element is judged as 1; if the signal strength of the first half is lower than that of the second half, the code element is judged as 0.

S6: Perform CRC check and error correction on the effective ADS-B signal after demodulation and decoding to obtain error-corrected data;

It should be noted that the ADS-B signal has a total of 112 bits of data, using cyclic redundancy coding (CRC), including 88 bits of aircraft information and 24 bits of checksum. The CRC checksum has a certain error correction capability, correcting low-confidence data within a certain range to ensure the stability of the system.

In a specific embodiment, a method for performing CRC check and error correction processing on a valid ADS-B signal that has been demodulated and decoded to obtain error-corrected data includes:

A CRC check is performed on the data bits of the valid ADS-B signal through a preset protocol to obtain a CRC check code; if the result of the CRC check code proves that there is a transmission error in the data bit, the erroneous data position is found by combining the low confidence position obtained in the bit judgment with the CRC check code, and the erroneous data bit is inverted to obtain the error-corrected data.

S7: Obtain inquiry information based on the error-corrected data, modulate the response information into an ADS-B signal, and then send the response information to the inquiry end to achieve a response.

In a specific embodiment, the response information includes at least one of the following:

Aircraft information, flight altitude, speed and GPS location information;

Specifically, using the DDS IP core, the generated 112-bit data code is added with an 88-bit check bit and then PPM modulation is performed. Each code element generates a corresponding data pulse, and a preamble pulse is added to generate a frame of ADS-B signal. The modulated digital baseband signal is sent to the ADRV9009 chip for transmission to achieve response.

Example 2

Please refer to FIG4 . This embodiment provides an FPGA-based unmanned aerial vehicle ADS-B transponder system, including an FPGA, a signal acquisition module, a pulse signal detection module, a leading pulse detection module, a signal matching module, a PPM demodulation module, a data correction processing module, and a PPM modulation module; the FPGA is respectively connected to the signal acquisition module, the pulse signal detection module, the leading pulse detection module, the signal matching module, the PPM demodulation module, the data correction processing module, and the PPM modulation module;

The signal acquisition module is used to collect the ADS-B signal sent by the inquiry end;

Specifically, the signal acquisition module uses the ADRV9009 chip to collect the ADS-B signal sent by the inquiry end;

The pulse signal detection module is used to perform pulse signal detection on the ADS-B signal to obtain pulse edge and pulse width information of the burst short pulse signal;

In a specific embodiment, the pulse signal detection module includes a short-time Fourier transform module, a frequency domain constant false alarm rate detection module and a sequence detection module;

The short-time Fourier transform module is used to perform short-time Fourier transform on the collected time domain signal after windowing. The formula is expressed as Where N is the short-time Fourier transform window width, so as to obtain the short-time Fourier spectrum of the ADS-B signal;

The frequency domain constant false alarm rate detection module is used to perform frequency domain constant false alarm rate detection on each window of the short-time Fourier spectrum, and calculate the frequency domain constant false alarm rate gate limit of each window, which is expressed as follows: Wherein is the expected false alarm probability P _FA , and the maximum value of the signal in each window is compared to determine whether there is a pulse signal in the window;

The sequence detection module is used to perform MN method detection on the 0-1 sequence indicating the presence or absence of the signal in each window, so as to obtain the starting and ending positions of the pulse signal in the time domain, and obtain the precise edge and pulse width information of the burst short pulse signal through the coexistence of the signals in each window.

The leading pulse detection module is used to detect the frame header information of the ADS-B signal to obtain a plurality of leading pulses;

The signal matching module is used to match the timing of the plurality of leading pulses according to the pulse edge and pulse width information of the burst short pulse signal, screen out the matching signals that meet the preset error requirements, and obtain a valid ADS-B signal;

The PPM demodulation module is used to demodulate and decode the valid ADS-B signal;

In a specific embodiment, the PPM demodulation module includes a signal strength detection module;

The signal strength detection module is used to detect the signal strength of the first half and the second half of each code element of the valid ADS-B signal. If the signal strength of the first half is higher than that of the second half, the code element is judged as 1; if the signal strength of the first half is lower than that of the second half, the code element is judged as 0.

The data correction processing module is used to perform CRC check and error correction processing on the effective ADS-B signal after demodulation and decoding processing to obtain error-corrected data;

In a specific embodiment, the data correction processing module includes a CRC check module and an error correction module;

The CRC check module is used to perform CRC check on the data bits of the valid ADS-B signal through a preset protocol to obtain a CRC check code;

The error correction module is used to find the erroneous data position by combining the low confidence position obtained in the bit judgment with the CRC check code when the result of the CRC check code proves that there is a transmission error in the data bit, and invert the erroneous data bit to obtain the corrected data.

The PPM modulation module is used to obtain inquiry information according to the error-corrected data, modulate the response information into an ADS-B signal, and then send the response information to the inquiry end to achieve a response;

Specifically, the PPM modulation module includes a radio frequency end, and the radio frequency end adopts an ADRV9009 chip. The radio frequency end is used to send the response information to the inquiry end to achieve a response.

In a specific embodiment, the response information includes at least one of the following:

Aircraft information, flight altitude, speed and GPS location information.

Specifically, the system of the present invention adopts an SDR (Software Defined Radio) platform based on ADRV9009 and Zynq7100. The RF end selects the ultra-wideband, high-performance integrated transceiver chip ADRV9009 of ADI. The ADRV9009 chip adopts a zero intermediate frequency architecture, integrates two independent ADCs and receiving channels, has a tunable input and output range of 75MHZ to 6GHz, and the data interface adopts the industry's mainstream high-speed serial JESD204B interface to convert the RF analog signal between ADRV9009 and FPGA and the I and Q baseband digital signals.

The FPGA part uses Xilinx's Zynq7100 chip for baseband signal processing. This series of chips has low power consumption, stable performance, and fast processing speed, which can meet the system design requirements. The Zynq7100 chip includes PL and PS ends. Users configure the required parameters through the host computer software and transmit them to the PS end through the UART serial port, which can realize fast initialization and configuration of the ADRV9009 chip; at the same time, it is transmitted to the PL end through the AXI-LITE interface to realize demodulation and modulation of the received baseband signal.

More specifically, the workflow of the system of the present invention also includes:

When the system is powered on, the PS end completes the startup and initialization of the ADRV9009 chip, the PL end is in reset state, and the host computer displays the current system status;

The user selects the required parameters on the PC host system for configuration, including the working center frequency, bias, low noise amplifier gain factor of the RF end, the short-time Fourier transform window width, false alarm rate, frequency domain constant false alarm rate reference window width and other detection parameters of the detection module, as well as the response information parameters, and clicks configuration to send it to the system PS end;

The PL receives the parameters sent by the PS, cancels the reset and starts working, and detects the pulse signal of the received signal;

If a valid ADS-B signal is detected, it is demodulated and the information is read;

If the demodulated information is the agreed inquiry information, the response module is started, the response information is modulated and sent to the RF end for transmission, and the response is completed.

Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims (10)

1. An unmanned aerial vehicle ADS-B response method based on FPGA is characterized by comprising the following steps:

Collecting ADS-B signals sent by an inquiry terminal;

Pulse signal detection is carried out on the ADS-B signal, and the pulse edge and the pulse width information of the burst short pulse signal are obtained;

Detecting frame header information of the ADS-B signal to obtain a plurality of leading pulses;

according to the pulse edge and the pulse width information of the burst short pulse signals, matching the time sequences of the plurality of leading pulses, screening out matched signals meeting the preset error requirement, and obtaining effective ADS-B signals;

carrying out demodulation and decoding processing on the effective ADS-B signal;

Performing CRC and error correction on the effective ADS-B signal subjected to demodulation and decoding to obtain error corrected data;

and obtaining inquiry information according to the error-corrected data, modulating response information into an ADS-B signal, and sending the response information to an inquiry terminal to realize response.

2. The unmanned aerial vehicle ADS-B response method based on the FPGA of claim 1, wherein the method for detecting the pulse signal of the ADS-B signal to obtain the pulse edge and the pulse width information of the burst short pulse signal comprises the following steps:

after windowing the acquired time domain signals, carrying out short-time Fourier transform, and expressing as follows N is the width of a short-time Fourier transform window, so that a short-time Fourier spectrum of the ADS-B signal is obtained;

detecting the frequency domain constant false alarm rate in the field of each window of the short-time Fourier spectrum, and calculating the frequency domain constant false alarm rate gate limit of each window, wherein the formula is as follows: Comparing the maximum value of the signals in each window for judging whether the pulse signals exist in the window or not for the expected false alarm probability P _FA;

and detecting the 0-1 sequence representing the existence of the signals in each window by an mn method so as to obtain the starting and ending positions of the pulse signals in the time domain, and obtaining the accurate edge and pulse width information of the burst short pulse signals through the coexistence of the signals in each window.

3. The method for performing demodulation and decoding processing on the valid ADS-B signal according to claim 1, wherein the method comprises:

Detecting the signal intensity of the first half part and the second half part of each code element of the effective ADS-B signal, and judging the code element to be 1 if the signal intensity of the first half part is higher than that of the second half part; if the first half signal strength is lower than the second half, the symbol decision is 0.

4. The unmanned aerial vehicle-mounted ADS-B response method based on the FPGA of claim 1, wherein the method for performing CRC check and error correction processing on the valid ADS-B signal subjected to demodulation and decoding processing to obtain the error corrected data includes:

Performing CRC (cyclic redundancy check) on the data bits of the effective ADS-B signal through a preset protocol to obtain a CRC code; if the result of the CRC check code proves that the data bit has transmission errors, searching the error data position by combining the low confidence position obtained in the bit judgment with the CRC check code, and inverting the error data bit to obtain error corrected data.

5. An FPGA-based unmanned aerial vehicle ADS-B reply method according to claim 1, wherein the reply information includes at least one of:

Aircraft information, altitude, speed, and GPS location information.

6. An unmanned aerial vehicle ADS-B response system based on an FPGA is characterized by comprising the FPGA, a signal acquisition module, a pulse signal detection module, a preamble pulse detection module, a signal matching module, a PPM demodulation module, a data correction processing module and a PPM modulation module; the FPGA is respectively in communication connection with the signal acquisition module, the pulse signal detection module, the preamble pulse detection module, the signal matching module, the PPM demodulation module, the data correction processing module and the PPM modulation module;

the signal acquisition module is used for acquiring an ADS-B signal sent by the query end;

The pulse signal detection module is used for detecting the pulse signal of the ADS-B signal to obtain the pulse edge and the pulse width information of the burst short pulse signal;

the preamble pulse detection module is used for detecting frame header information of the ADS-B signal to obtain a plurality of preamble pulses;

The signal matching module is used for matching the time sequences of the plurality of leading pulses according to the pulse edges and the pulse width information of the burst short pulse signals, screening out matched signals meeting the preset error requirement and obtaining effective ADS-B signals;

The PPM demodulation module is used for carrying out demodulation and decoding processing on the effective ADS-B signal;

the data correction processing module is used for performing CRC (cyclic redundancy check) and error correction processing on the effective ADS-B signal subjected to demodulation and decoding processing to obtain error corrected data;

The PPM modulation module is used for obtaining inquiry information according to the error-corrected data, modulating response information into ADS-B signals, and sending the response information to an inquiry end to realize response.

7. The unmanned aerial vehicle ADS-B response system based on the FPGA of claim 6, wherein the pulse signal detection module comprises a short-time Fourier transform module, a frequency domain constant false alarm rate detection module and a sequence detection module;

The short-time Fourier transform module is used for carrying out short-time Fourier transform after windowing the acquired time domain signals, and the formula is expressed as N is the width of a short-time Fourier transform window, so that a short-time Fourier spectrum of the ADS-B signal is obtained;

The frequency domain constant false alarm rate detection module is used for detecting the frequency domain constant false alarm rate in the field of each window of the short-time Fourier spectrum, and calculating the frequency domain constant false alarm rate gate limit of each window, wherein the formula is expressed as follows: Comparing the maximum value of the signals in each window for judging whether the pulse signals exist in the window or not for the expected false alarm probability P _FA;

the sequence detection module is used for detecting the 0-1 sequence representing whether the signals in each window exist or not by an mn method, so that the starting position and the ending position of the pulse signals in the time domain are obtained, and the accurate edge and the pulse width information of the burst short pulse signals are obtained through the coexistence of the signals in each window.

8. The unmanned aerial vehicle ADS-B response system based on the FPGA of claim 6, wherein the PPM demodulator module includes a signal strength detection module;

The signal strength detection module is used for detecting the signal strength of the first half part and the second half part of each code element of the effective ADS-B signal, and if the signal strength of the first half part is higher than that of the second half part, the code element is judged to be 1; if the first half signal strength is lower than the second half, the symbol decision is 0.

9. The unmanned aerial vehicle ADS-B response system based on the FPGA of claim 6, wherein the data correction processing module includes a CRC check module and an error correction module;

The CRC module is used for carrying out CRC on the data bits of the effective ADS-B signal through a preset protocol to obtain a CRC code;

and the error correction module is used for searching for the wrong data position by combining the low confidence position obtained in the bit judgment with the CRC check code when the result of the CRC check code proves that the data bit has transmission errors, and inverting the wrong data bit to obtain error corrected data.

10. An FPGA-based unmanned aerial vehicle ADS-B reply system according to claim 6, wherein the reply information includes at least one of:

Aircraft information, altitude, speed, and GPS location information.