DME interference detection and identification method and system based on ZYNQ

Abstract

The invention belongs to the technical field of interference detection and identification, and discloses a DME interference detection and identification method and system based on ZYNQ. The method comprises the following steps: a radio frequency transceiver performs a series of processing on a received radio frequency signal to obtain IQ two-path signals, and a front end receives the IQ two-path signals and sends the IQ two-path signals to an FPGA for signal processing; carrying out downsampling, filtering and envelope detection demodulation processing on IQ signals received by the front end to obtain baseband signals, and carrying out amplitude detection and legal signal identification to obtain existence intervals of legal DME signals and interference signals; carrying out identification code calculation, pulse pair number statistics and power calculation on the legal DME signal; and performing power calculation and interference length calculation on the interference signal, and judging the interference type by calculating the derivative of the phase difference and the time domain envelope fluctuation. According to the invention, DME signal receiving and interference detection and identification are integrated, the integration level is improved, and the design difficulty is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of interference detection and identification, and in particular relates to a ZYNQ-based DME interference detection and identification method and system. Background Art

[0002] In the field of aircraft navigation, distance measurement plays an important role in engineering. A distance measuring instrument (DME), also known as a pulse short-range navigation system, is a high-precision, non-autonomous, time-based short-range navigation system used to provide straight-line distance information between the aircraft and a ground station. This device can be installed and coordinated with a VHF omni-directional (VOR) to provide high-precision navigation services for aircraft.

[0003] The above analysis reveals the following problems and shortcomings of existing technologies: With the advancement of urbanization in my country and the resulting regional shortage of aviation frequency band resources, DME systems face threats from a variety of interference sources. They are susceptible to AM interference, FM interference, and linear frequency modulation signals from air traffic control L-band primary surveillance radars. This reduces DME ranging accuracy and can even threaten aircraft safety. Regarding signal processing, existing technologies lack integration between the RF front-end and signal baseband components, resulting in significant design complexity and limited flexibility in practical applications. Summary of the Invention

[0004] To overcome the problems in related technologies, the present invention discloses a method and system for detecting and identifying DME interference based on Zynq (Zynq-7000 All Programmable SoC, i.e., FPGA+ARM).

[0005] The technical solution is as follows: a ZYNQ-based DME interference detection and identification method, comprising the following steps:

[0006] In step S1, the RF transceiver scans the DME system channels in sequence, obtains the channels with signals, and receives the signals in these channels. The RF transceiver processes the received RF signals to obtain IQ signals. The front end receives the IQ signals and sends them to the FPGA for signal processing.

[0007] S2 downsamples, filters, and performs envelope detection and demodulation on the IQ signals received by the front end to obtain baseband signals. Then, through amplitude detection and legitimate signal identification, the existence intervals of legitimate DME signals and interference signals are obtained.

[0008] S3: Perform identification code analysis, pulse pair count, and power calculation on the legitimate DME signal; perform power calculation and interference length calculation on the interference signal, and determine the interference type by calculating the derivative of the phase difference and the time domain envelope fluctuation.

[0009] In step S1, the front end receives two IQ signals and sends them to the FPGA for signal processing, including: ARM configures the AD9361 in the front end receiving unit, and the receiving channel, receiving frequency and receiving gain default initial values ​​are adjusted through the serial port and network port;

[0010] The DME system adjusts the receiving frequency of the RF transceiver AD9361 and switches sequentially within the DME channel. The average power of the signal within the channel is calculated once per second. Each channel outputs two powers. The formula for calculating the average power is:

[0011]

[0012] Where P is the average power, n is the length of the signal, and x i is the amplitude of each sampling point of the signal;

[0013] When all channels are scanned, the channel with the highest average power that is greater than the threshold value is found as the channel currently used by the DME system, and the RF transceiver is adjusted to the frequency of the channel and the result is output.

[0014] In step S2, the IQ signals received by the front end are downsampled, filtered, and subjected to envelope detection and demodulation to obtain baseband signals, including:

[0015] First, for downsampling processing, the obtained IQ two-way signals are downsampled;

[0016] Secondly, the downsampled signal is filtered through an FIR filter;

[0017] Finally, the received signal is demodulated using the envelope detection method, and the square sum of the in-phase and quadrature branches is calculated, and then the square root is obtained.

[0018] Furthermore, the obtained IQ signals are downsampled, including: reducing the sampling rate from 40 MHz to 10 MHz;

[0019] The downsampled signal is filtered through an FIR filter, including filtering the downsampled signal through a 64-order low-pass filter with an FIR sampling frequency of 10 MHz and a passband frequency of 1 MHz. The FIR filter equation is:

[0020]

[0021] Where y(n) is the filter output, N is the filter order, k is the number of delay cycles, h(k) is the filter coefficient, and (nk) is x(n) delayed by k cycles.

[0022] The transfer function H(z) of the system is:

[0023]

[0024] Where z i is the delayed sampling period, h(i) is the filter coefficient;

[0025] Calculate the sum of the squares of the in-phase and quadrature branches, and then find the square root. The calculation formula is as follows:

[0026] x 11 (n)=x(n)cos(ωn) (4)

[0027] x 21 (n)=x(n)sin(ωn) (5)

[0028]

[0029] Where x 11 (n),x 21 (n) are IQ signals, m(n) is the baseband signal, x(n) is the received signal, n is the sampling point number, and ω is the carrier frequency;

[0030] The baseband signal passes through a 64th-order FIR low-pass filter with a sampling frequency of 10 MHz and a passband frequency of 0.005 MHz.

[0031] In step S2, the existence intervals of the legitimate DME signal and the interference signal are obtained through amplitude detection and legitimate signal identification, including:

[0032] The threshold value is calculated based on the amplitude of the baseband signal as a criterion for whether there is an interference signal or a legitimate DME signal. The amplitude of the baseband signal is detected and judged, and the baseband signal amplitude is compared with the threshold value. The judgment formula is:

[0033]

[0034] Where r1 is the judgment result, m(n) is the baseband signal, T is the threshold value, 01 indicates no interference or legal signal, and 11 indicates interference or legal signal;

[0035] When the baseband signal amplitude is greater than the threshold, it is determined to be an interference signal or a legal DME signal; when the baseband signal amplitude is less than the threshold, it is determined to be no interference signal or a legal DME signal; then the interference signal or legal DME signal is identified as a legal signal, and the rising edge distance is determined. If it meets the legal DME signal standard, that is, for the X channel, the interval between the two pulses of the interrogation pulse pair is 12±0.5μs, and the time interval of the response pulse pair is 12±0.25μs; for the Y channel, the time interval of the interrogation pulse pair is 36±0.5μs, and the time interval of the response pulse pair is 30±0.25μs; then it is determined to be a legal DME signal, otherwise it is determined to be an interference signal;

[0036] The formula for determining the legal DME signal identification using the X-channel interrogation pulse is:

[0037]

[0038] Where r2 is the recognition result, 02 represents the interference signal, 12 represents the legitimate signal, and t is the time.

[0039] In step S3, the identification code of the legal DME signal is solved, including: integrating the obtained legal DME signal, taking only the first pulse of a pulse pair and setting the second pulse to zero to obtain the integrated signal; judging the pulse interval of the integrated signal, and the pulse that meets the standard requirements is the identification code pulse; the judgment formula is:

[0040]

[0041] Where r3 is the judgment result, 03 represents the non-identification code position, and 13 represents the identification code position;

[0042] The baseband signal of the Morse code is demodulated and down-sampled before being transmitted to the ARM side, where the identification code is obtained by Morse code decoding.

[0043] In step S3, pulse pair statistics are performed on the legal DME signal, including:

[0044] The obtained legal DME signal is counted and two high levels are considered as a pair of DME pulses. The number of pulse pairs in the previous second is output per second and the counter is reset to zero.

[0045] Power calculation for legal DME signals includes:

[0046] Calculate the peak power of the legal DME signal obtained and output the peak power per second. The calculation formula for the peak power is:

[0047]

[0048] Where x iis the peak value of the legal DME signal pulse, P pk is the peak power.

[0049] In step S3, the power of the interference signal is calculated, including:

[0050] Calculate the average power of the interference signal obtained and output the average power of the previous second per second;

[0051] Interference length calculation includes: calculating the length of the interference signal and outputting the interference signal length in the previous second in seconds.

[0052] In step S3, the interference type is determined by calculating the derivative of the phase difference and the time domain envelope fluctuation, including:

[0053] Calculate the time domain envelope fluctuation of the interference signal and the derivative of the phase difference of the interference signal interval in the downsampled signal. The calculation formula of the time domain envelope fluctuation is:

[0054]

[0055] Where R is the time domain envelope fluctuation, σ 2 is the variance of the interference signal after envelope detection, μ is the mean of the interference signal after envelope detection;

[0056] The derivative of the phase difference is calculated as:

[0057]

[0058] Where F is the derivative of the phase difference, f is the sampling rate, and T is the sampling interval;

[0059] When the derivative of the phase difference of the interference signal is greater than the threshold value, it is judged to be a linear frequency modulation signal of the air traffic control L-band primary surveillance radar; when the derivative of the phase difference of the interference signal is less than the threshold value and the time domain envelope fluctuation is greater than the threshold value, it is judged to be amplitude modulation interference; when the derivative of the phase difference of the interference signal is less than the threshold value and the time domain envelope fluctuation is less than the threshold value, it is judged to be frequency modulation interference.

[0060] Another object of the present invention is to provide a ZYNQ-based DME interference detection and identification system, which implements the ZYNQ-based DME interference detection and identification method, and includes:

[0061] The RF transceiver is used to scan the DME system channels in sequence, obtain the channels with signals, and receive the signals in the channels; the RF transceiver performs a series of processing on the received RF signals to obtain IQ two-way signals. The front end receives the IQ two-way signals and sends them to the FPGA for signal processing;

[0062] The legitimate signal and interference signal acquisition module is used to downsample, filter, and envelope detect and demodulate the IQ signals received by the front end to obtain baseband signals, and then obtain the existence range of legitimate DME signals and interference signals through amplitude detection and legitimate signal identification;

[0063] The interference type judgment module is used to solve the identification code of the legal DME signal, count the number of pulse pairs and calculate the power; calculate the power and interference length of the interference signal, and judge the interference type by calculating the derivative of the phase difference and the time domain envelope fluctuation.

[0064] In combination with all the above technical solutions, the beneficial effects of the present invention are as follows:

[0065] First, the present invention uses the AD9361 RF transceiver to sequentially scan the DME system channels, identifying channels with signals and receiving signals within those channels. The RF transceiver performs a series of processing on the received RF signals to generate I / Q signals, which are then sent to the FPGA for signal processing by the front-end. The received signals are then downsampled, filtered, and envelope-detected and demodulated to obtain baseband signals. The amplitude detection and legitimate signal identification process are then used to determine the ranges where DME and interference signals exist. The DME signal undergoes identification code analysis, pulse pair counting, and power calculation. The interference signal undergoes power and interference length calculations, and the interference type is determined by calculating the derivative of the phase difference and the time-domain envelope fluctuation.

[0066] Second, this invention integrates DME signal reception with interference detection and identification, improving integration and reducing design complexity. This invention utilizes an FPGA + ARM processor to implement DME signal interference detection and identification. This outstanding advantage in interference detection and identification allows for excellent reception and analysis of DME signals, as well as identification of interference presence and type. Furthermore, the integration of the AD9361 RF front-end and signal baseband processing significantly reduces the complexity of design and signal processing.

[0067] Third, the present invention takes ZYNQ as the core and completes the design of the front-end RF transceiver module, envelope detection module, amplitude detection module, legal signal identification module, identification code solution module, power calculation module and interference identification module according to the signal characteristics of DME signal, AM interference, FM interference and air traffic control L-band primary surveillance radar linear FM signal. It has the advantages of high integration in application and good flexibility.

[0068] Fourth, the present invention uses ARM to complete the output functions of the serial port and the network port, which can realize the modification and adjustment of multiple functions such as channel selection, receiving frequency selection, gain control, threshold value setting, etc.; at the same time, it can realize the output of various information such as navigation information, channel status, interference type, signal data, etc., and has the advantages of flexible use, low cost, small size and easy operation by technicians. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure;

[0070] Figure 1 This is a schematic diagram of a ZYNQ-based DME interference detection and identification method provided by an embodiment of the present invention;

[0071] Figure 2 This is a flow chart of a ZYNQ-based DME interference detection and identification method provided by an embodiment of the present invention;

[0072] Figure 3 The embodiment of the present invention provides a method for identifying three interference patterns, namely, amplitude modulation, frequency modulation, and linear frequency modulation, by using the derivative of the time domain envelope fluctuation and phase difference;

[0073] Figure 4 4 is a relationship diagram between the interference detection and recognition accuracy and the interference-to-signal ratio provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0074] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0075] The innovation of the present invention lies in: the DME interference detection and identification method based on ZYNQ (Zynq-7000 All Programmable SoC, i.e. FPGA+ARM) provided by the present invention adopts FPGA+ARM to realize DME interference detection and identification, which has outstanding advantages in signal detection and identification, and can well realize DME signal reception, DME signal analysis, and interference presence detection and interference type identification.

[0076] Example 1, as Figure 1 As shown, the present invention provides a method and principle for detecting and identifying DME interference based on ZYNQ. Figure 2As shown, the present invention provides a ZYNQ-based DME interference detection and identification method comprising:

[0077] In step S1, the RF transceiver scans the DME system channels in sequence, obtains the channels with signals, and receives the signals in these channels. The RF transceiver processes the received RF signals to obtain IQ signals. The front end receives the IQ signals and sends them to the FPGA for signal processing.

[0078] S2 downsamples, filters, and performs envelope detection and demodulation on the IQ signals received by the front end to obtain baseband signals. Then, through amplitude detection and legitimate signal identification, the existence intervals of legitimate DME signals and interference signals are obtained.

[0079] S3: Perform identification code analysis, pulse pair count, and power calculation on the legitimate DME signal; perform power calculation and interference length calculation on the interference signal, and determine the interference type by calculating the derivative of the phase difference and the time domain envelope fluctuation.

[0080] Exemplarily, in step S1, the RF transceiver AD9361 scans the DME system channels in sequence to obtain channels with signals and receives the signals in the channels; the RF transceiver performs a series of processing on the received RF signals to obtain IQ two-way signals, and the front end receives the IQ two-way signals and sends them to the FPGA for signal processing, specifically including: ARM configures the AD9361 in the front-end receiving unit, and the default initial values ​​such as the receiving channel, receiving frequency and receiving gain can be adjusted through the serial port and network port.

[0081] When the system is powered on, it automatically adjusts the receiving frequency of the RF transceiver AD9361 and switches in sequence within the DME channel, staying in each channel for 2 seconds. The average power of the signal in the channel is calculated once per second. Each channel outputs two powers. The calculation formula for the average power is:

[0082]

[0083] Where P is the average power, n is the length of the signal, and x i is the amplitude of each sampling point of the signal;

[0084] When all channels are scanned, the channel with the highest average power greater than the threshold value is found as the channel currently used by the DME system, and the RF transceiver AD9361 is adjusted to the frequency of the channel, and the result is output to indicate the current channel.

[0085] The RF transceiver AD9361 performs analog-to-digital conversion on the received RF signal, digitizes the RF signal to obtain IQ signals, and then sends them to the FPGA for processing.

[0086] Exemplarily, in step S2, the signal received by the front end is downsampled, filtered, and subjected to envelope detection and demodulation to obtain a baseband signal. This includes: first, for downsampling, the sampling rate of the IQ signals obtained in step S1 is reduced from 40 MHz to 10 MHz. That is, through sampling, one point is selected every 15 sampling points as the downsampled signal.

[0087] Secondly, for filtering, the downsampled signal is passed through a 64-order FIR low-pass filter with a sampling frequency of 10 MHz and a passband frequency of 1 MHz. The FIR filter equation is:

[0088]

[0089] Where y(n) is the filter output, N is the filter order, k is the number of delay cycles, h(k) is the filter coefficient, and (nk) is x(n) delayed by k cycles.

[0090] The transfer function H(z) of the system is:

[0091]

[0092] Where z i is the number of delayed cycles, h(i) is the filter coefficient;

[0093] Finally, the received signal is demodulated using the envelope detection method. The sum of the squares of the in-phase and quadrature branches is calculated, and then the square root is calculated. The calculation formula is as follows:

[0094] x 11 (n)=x(n)cos(ωn) (4)

[0095] x 21 (n)=x(n)sin(ωn) (5)

[0096]

[0097] Where x 11 (n),x 21 (n) are IQ signals, m(n) is the baseband signal, x(n) is the received signal, n is the sampling point number, and ω is the carrier frequency;

[0098] The baseband signal then passes through a 64th-order FIR low-pass filter with a sampling frequency of 10 MHz and a passband frequency of 0.005 MHz.

[0099] Exemplarily, in step S2, obtaining the existence interval of the legitimate DME signal and the interference signal through amplitude detection and legitimate signal identification specifically includes:

[0100] The present invention innovatively calculates a threshold value by the amplitude of the baseband signal as a criterion for determining whether there is an interference signal or a legitimate DME signal; the amplitude of the baseband signal is detected and judged, that is, the baseband signal amplitude is compared with the threshold value, and the judgment formula is:

[0101]

[0102] Where r1 is the judgment result, m(n) is the baseband signal, T is the threshold value, 01 indicates no interference or legal signal, and 11 indicates interference or legal signal;

[0103] When the baseband signal amplitude is greater than the threshold, it is determined to be an interference signal or a legal DME signal; when the baseband signal amplitude is less than the threshold, it is determined to be no interference signal or a legal DME signal; then the interference signal or legal DME signal is identified as a legal signal, and the rising edge distance is determined. If it meets the legal DME signal standard, that is, for the X channel, the interval between the two pulses of the interrogation pulse pair is 12±0.5μs, and the time interval of the response pulse pair is 12±0.25μs; for the Y channel, the time interval of the interrogation pulse pair is 36±0.5μs, and the time interval of the response pulse pair is 30±0.25μs; then it is determined to be a legal DME signal, otherwise it is determined to be an interference signal;

[0104] The formula for determining the legal DME signal identification using the X-channel interrogation pulse is:

[0105]

[0106] Where r2 is the recognition result, 02 represents the interference signal, 12 represents the legitimate signal, and t is the time.

[0107] Exemplarily, in step S3, performing identification code calculation on the legal DME signal specifically includes: integrating the legal DME signal obtained in step S2, that is, taking only the first pulse of a pulse pair and setting the second pulse to zero to obtain an integrated signal; performing pulse interval judgment on the integrated signal, and the pulse that meets the standard requirements is the identification code pulse; the judgment formula is:

[0108]

[0109] Where r3 is the judgment result, 03 represents the non-identification code position, and 13 represents the identification code position;

[0110] The baseband signal of the Morse code is demodulated, downsampled, and transmitted to the ARM. When two identification code pulses are detected, the baseband signal of the Morse code is high. If no identification code pulses appear after 780 μs, the baseband signal of the Morse code is set to low. The baseband signal of the Morse code is then downsampled to 400 Hz through sampling. The identification code is then obtained by Morse code decoding on the ARM.

[0111] In another exemplary embodiment, the DME signal obtained in step S2 is integrated, i.e., only the first pulse of a pulse pair is taken, and the second pulse is set to zero to obtain the integrated signal. The pulse interval of the integrated signal is determined, and the 1350Hz pulse that meets the standard requirements is the identification code. The identification code pulse is demodulated to obtain the Morse code baseband signal, which is downsampled and transmitted to the ARM terminal. The identification code is obtained by Morse code decoding on the ARM terminal. The "dot" or "dash" is determined by determining the duration of the high and low levels of the Morse code baseband signal. The high level duration of the "dot" is 0.1 seconds, and the high level duration of the "dash" is 0.3 seconds. The interval between the high levels is then used to determine whether a letter has ended. The interval between the same letter is 0.1 seconds, and the interval between different letters is 0.3 seconds.

[0112] Exemplarily, in step S3, counting the number of pulse pairs of the legal DME signal includes:

[0113] The legal DME signal obtained in step S2 is counted, and two high levels are a pair of DME pulses. The number of pulse pairs in the previous second is output per second, and the counter is reset to zero.

[0114] Exemplarily, in step S3, calculating the power of the legal DME signal includes:

[0115] The peak power of the legal DME signal obtained in step S2 is calculated and output per second. The peak power calculation formula is:

[0116]

[0117] Where x i is the peak value of the legal DME signal pulse, P pk is the peak power.

[0118] Exemplarily, in step S3, calculating the power of the interference signal includes:

[0119] Calculate the average power of the interference signal obtained in step S2, and output the average power of the previous second per second. The calculation formula of the average power is:

[0120]

[0121] Where xi is the amplitude of each sampling point of the signal, and n is the length of the signal;

[0122] Exemplarily, in step S3, the interference length calculation includes:

[0123] The length of the interference signal obtained in step S2 is calculated, and the length of the interference signal in the previous second is output in seconds.

[0124] Exemplarily, in step S3, determining the interference type by calculating the derivative of the phase difference and the time domain envelope fluctuation includes:

[0125] The time domain envelope fluctuation of the interference signal in step S2 and the derivative of the phase difference of the interference signal interval in the downsampled signal are calculated. The calculation formula of the time domain envelope fluctuation is:

[0126]

[0127] Where R is the time domain envelope fluctuation, σ 2 is the variance of the interference signal after envelope detection, μ is the mean of the interference signal after envelope detection;

[0128] The derivative of the phase difference is calculated as:

[0129]

[0130] Where F is the derivative of the phase difference, f is the sampling rate, and T is the sampling interval;

[0131] like Figure 3 As shown in the figure, the blue line is the signal after envelope detection, the red line is the time-domain envelope fluctuation value, the green line is the derivative of the phase difference (derivative of the instantaneous frequency), and the black line marks the location of AM interference, FM interference, and LFM interference. It can be seen that the derivative of the phase difference (green line) is larger at the LFM interference location; at the AM interference location, the time-domain envelope fluctuation value (red line) is greater than that of the FM interference. The time-domain envelope fluctuation and the derivative of the phase difference can be used to better distinguish between AM, FM, and LFM interference.

[0132] When the derivative of the interference signal phase difference is greater than the threshold value, it indicates that the frequency of the interference signal has a continuous growth trend, and it is judged to be a linear frequency modulation signal of the air traffic control L-band primary surveillance radar; when the derivative of the interference signal phase difference is less than the threshold value and the time domain envelope fluctuation is greater than the threshold value, it indicates that the frequency of the interference signal has no continuous growth trend, and the fluctuation degree of the signal time domain is large, and it is judged to be amplitude modulation interference; when the derivative of the interference signal phase difference is less than the threshold value and the time domain envelope fluctuation is less than the threshold value, it indicates that the frequency of the interference signal has no continuous growth trend, and the fluctuation degree of the signal time domain is small, and it is judged to be frequency modulation interference. Figure 4As shown in the figure, the phase difference derivative threshold is set to 10, and the envelope fluctuation threshold is set to 65. 100 interference signals are randomly generated at each interference ratio. A graph showing the relationship between the interference detection and recognition accuracy and the interference-to-signal ratio is obtained when the signal-to-noise ratio is 10dB. It can be seen that when the interference-to-signal ratio is greater than 0dB, the interference detection and recognition accuracy exceeds 90%.

[0133] It can be understood that the present invention uses the above formula to distinguish between three types of interference: amplitude modulation interference, frequency modulation interference, and linear frequency modulation interference.

[0134] The present invention uses the derivative of the time domain envelope fluctuation and the phase difference to distinguish the three interferences of FM, AM and LFM. The existing technology rarely involves distinguishing the three interferences of FM, AM and LFM in the DME system.

[0135] It can be seen from the above embodiments that the present invention can be designed as a convenient signal receiving device and a DME interference detection and identification instrument; it can meet the requirements of experimental researchers and has important significance in the field of interference detection and identification.

[0136] There are currently no published patents involving a DME interference detection and identification system designed using a ZYNQ chip using the derivative of time domain envelope fluctuations and phase difference.

[0137] The present invention adopts a design scheme based on FPGA+ARM, which can reduce the complexity of hardware circuits and effectively solve the problem of complex design.

[0138] This invention proposes a simple and effective method for implementing a DME interference detection and identification system, which can achieve the desired function using FPGA + ARM. This is a technical solution that is not easily conceived by those skilled in the art and breaks through technical prejudice.

[0139] In embodiment 2, the present invention provides a ZYNQ-based DME interference detection and identification system comprising:

[0140] The RF transceiver is used to scan the DME system channels in sequence, obtain the channels with signals, and receive the signals in the channels; the RF transceiver performs a series of processing on the received RF signals to obtain IQ two-way signals. The front end receives the IQ two-way signals and sends them to the FPGA for signal processing;

[0141] The legitimate signal and interference signal acquisition module is used to downsample, filter, and envelope detect and demodulate the IQ signals received by the front end to obtain baseband signals, and then obtain the existence range of legitimate DME signals and interference signals through amplitude detection and legitimate signal identification;

[0142] The interference type judgment module is used to solve the identification code of the legal DME signal, count the number of pulse pairs and calculate the power; calculate the power and interference length of the interference signal, and judge the interference type by calculating the derivative of the phase difference and the time domain envelope fluctuation.

[0143] The above description is only a preferred specific implementation method of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A ZYNQ-based DME interference detection and identification method, characterized in that: The method comprises the following steps: In step S1, the RF transceiver scans the DME system channels in sequence, obtains the channels with signals, and receives the signals in these channels. The RF transceiver processes the received RF signals to obtain IQ signals. The front end receives the IQ signals and sends them to the FPGA for signal processing. S2 downsamples, filters, and performs envelope detection and demodulation on the IQ signals received by the front end to obtain baseband signals. Then, through amplitude detection and legitimate signal identification, the existence intervals of legitimate DME signals and interference signals are obtained. S3: Perform identification code analysis, pulse pair count, and power calculation on the legitimate DME signal; perform power calculation and interference length calculation on the interference signal, and determine the interference type by calculating the derivative of the phase difference and the time domain envelope fluctuation.

2. The ZYNQ-based DME interference detection and identification method according to claim 1, characterized in that: In step S1, the front end receives two IQ signals and sends them to the FPGA for signal processing, including: ARM configures the AD9361 in the front end receiving unit, and the receiving channel, receiving frequency and receiving gain default initial values ​​are adjusted through the serial port and network port; The DME system adjusts the receiving frequency of the RF transceiver AD9361 and switches sequentially within the DME channel. The average power of the signal within the channel is calculated once per second. Each channel outputs two powers. The formula for calculating the average power is: Where P is the average power, n is the length of the signal, and x i is the amplitude of each sampling point of the signal; When all channels are scanned, the channel with the highest average power that is greater than the threshold value is found as the channel currently used by the DME system, and the RF transceiver is adjusted to the frequency of the channel and the result is output.

3. The ZYNQ-based DME interference detection and identification method according to claim 1, characterized in that: In step S2, the IQ signals received by the front end are downsampled, filtered, and subjected to envelope detection and demodulation to obtain baseband signals, including: First, for downsampling processing, the obtained IQ two-way signals are downsampled; Secondly, the downsampled signal is filtered through an FIR filter; Finally, the received signal is demodulated using the envelope detection method, and the square sum of the in-phase and quadrature branches is calculated, and then the square root is obtained.

4. The ZYNQ-based DME interference detection and identification method according to claim 3, characterized in that: The obtained IQ two-way signals are downsampled, including: reducing the sampling rate from 40MHz to 10MHz; The downsampled signal is filtered through an FIR filter, including filtering the downsampled signal through a 64-order low-pass filter with an FIR sampling frequency of 10 MHz and a passband frequency of 1 MHz. The FIR filter equation is: Where y(n) is the filter output, N is the filter order, k is the number of delay cycles, h(k) is the filter coefficient, and x(nk) is x(n) delayed by k cycles. The transfer function H(z) of the system is: Where z i is the delayed sampling period, h(i) is the filter coefficient; Calculate the sum of the squares of the in-phase and quadrature branches, and then find the square root. The calculation formula is as follows: x 11 (n)=x(n)cos(ωn)(4) x 21 (n)=x(n)sin(ωn)(5) Where x 11 (n),x 21 (n) are IQ signals, m(n) is the baseband signal, x(n) is the received signal, n is the sampling point number, and ω is the carrier frequency; The baseband signal passes through a 64th-order FIR low-pass filter with a sampling frequency of 10 MHz and a passband frequency of 0.005 MHz.

5. The ZYNQ-based DME interference detection and identification method according to claim 1, characterized in that: In step S2, the existence intervals of the legitimate DME signal and the interference signal are obtained through amplitude detection and legitimate signal identification, including: The threshold value is calculated based on the amplitude of the baseband signal as a criterion for whether there is an interference signal or a legitimate DME signal. The amplitude of the baseband signal is detected and judged, and the baseband signal amplitude is compared with the threshold value. The judgment formula is: Where r1 is the judgment result, m(n) is the baseband signal, T is the threshold value, 01 indicates no interference or legal signal, and 11 indicates interference or legal signal; When the baseband signal amplitude is greater than the threshold, it is determined to be an interference signal or a legal DME signal; when the baseband signal amplitude is less than the threshold, it is determined to be no interference signal or a legal DME signal; then the interference signal or legal DME signal is identified as a legal signal, and the rising edge distance is determined. If it meets the legal DME signal standard, that is, for the X channel, the interval between the two pulses of the interrogation pulse pair is 12±0.5μs, and the time interval of the response pulse pair is 12±0.25μs; for the Y channel, the time interval of the interrogation pulse pair is 36±0.5μs, and the time interval of the response pulse pair is 30±0.25μs; then it is determined to be a legal DME signal, otherwise it is determined to be an interference signal; The formula for determining the legal DME signal identification using the X-channel interrogation pulse is: Where r2 is the recognition result, 02 represents the interference signal, 12 represents the legitimate signal, and t is the time.

6. The ZYNQ-based DME interference detection and identification method according to claim 5, characterized in that: In step S3, the identification code of the legal DME signal is solved, including: integrating the obtained legal DME signal, taking only the first pulse of a pulse pair and setting the second pulse to zero to obtain the integrated signal; judging the pulse interval of the integrated signal, and the pulse that meets the standard requirements is the identification code pulse; the judgment formula is: Where r3 is the judgment result, 03 represents the non-identification code position, and 13 represents the identification code position; The baseband signal of the Morse code is demodulated and down-sampled before being transmitted to the ARM side, where the identification code is obtained by Morse code decoding.

7. The ZYNQ-based DME interference detection and identification method according to claim 1, characterized in that: In step S3, pulse pair statistics are performed on the legal DME signal, including: The obtained legal DME signal is counted and two high levels are considered as a pair of DME pulses. The number of pulse pairs in the previous second is output per second and the counter is reset to zero. Power calculation for legal DME signals includes: Calculate the peak power of the legal DME signal obtained and output the peak power per second. The calculation formula for the peak power is: Where x i is the peak value of the legal DME signal pulse, P pk is the peak power.

8. The ZYNQ-based DME interference detection and identification method according to claim 1, characterized in that: In step S3, the power of the interference signal is calculated, including: Calculate the average power of the interference signal obtained and output the average power of the previous second per second; Interference length calculation includes: calculating the length of the interference signal and outputting the interference signal length in the previous second in seconds.

9. The ZYNQ-based DME interference detection and identification method according to claim 4, characterized in that: In step S3, the interference type is determined by calculating the derivative of the phase difference and the time domain envelope fluctuation, including: Calculate the time domain envelope fluctuation of the interference signal and the derivative of the phase difference of the interference signal interval in the downsampled signal. The calculation formula of the time domain envelope fluctuation is: Where R is the time domain envelope fluctuation, σ 2 is the variance of the interference signal after envelope detection, μ is the mean of the interference signal after envelope detection; The derivative of the phase difference is calculated as: Where F is the derivative of the phase difference, f is the sampling rate, and T is the sampling interval; When the derivative of the phase difference of the interference signal is greater than the threshold value, it is judged to be a linear frequency modulation signal of the air traffic control L-band primary surveillance radar; when the derivative of the phase difference of the interference signal is less than the threshold value and the time domain envelope fluctuation is greater than the threshold value, it is judged to be amplitude modulation interference; when the derivative of the phase difference of the interference signal is less than the threshold value and the time domain envelope fluctuation is less than the threshold value, it is judged to be frequency modulation interference.

10. A ZYNQ-based DME interference detection and identification system, characterized in that: The system implements the ZYNQ-based DME interference detection and identification method according to any one of claims 1 to 9, and the system includes: The RF transceiver is used to scan the DME system channels in sequence, obtain the channels with signals, and receive the signals in the channels; the RF transceiver performs a series of processing on the received RF signals to obtain IQ two-way signals. The front end receives the IQ two-way signals and sends them to the FPGA for signal processing; The legitimate signal and interference signal acquisition module is used to downsample, filter, and envelope detect and demodulate the IQ signals received by the front end to obtain baseband signals, and then obtain the existence range of legitimate DME signals and interference signals through amplitude detection and legitimate signal identification; The interference type judgment module is used to solve the identification code of the legal DME signal, count the number of pulse pairs and calculate the power; calculate the power and interference length of the interference signal, and judge the interference type by calculating the derivative of the phase difference and the time domain envelope fluctuation.

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