FPGA-based instrument landing system signal processing method and system

Abstract

The invention relates to the technical field of air transportation, in particular to an instrument landing system signal processing method and system based on an FPGA, and the method comprises the steps: receiving a course channel signal and a glide channel signal of an instrument landing system, and carrying out the radio frequency processing of the signals, thereby obtaining an intermediate frequency signal; performing analog-to-digital conversion on the intermediate frequency signal to obtain a corresponding digital signal, and performing rectification processing, multi-stage decimation filtering processing, band-pass filtering processing, amplitude detection processing and modulation degree difference calculation on the digital signal in sequence to obtain a modulation degree difference; finally, according to the modulation degree difference value, the deviation state of the airplane relative to the runway center line and the lower slide way center line is judged. According to the invention, the measurement precision of the modulation degree difference value is improved, the circuit complexity is simplified, the navigation error of the aircraft in the approaching and landing stages is effectively reduced, and the flight safety is obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of aviation transportation technology, and in particular to a FPGA-based instrument landing system signal processing method and system. Background Art

[0002] With the vigorous development of civil aviation, air transport has become one of the main modes of transportation. However, among all the stages of an aircraft's flight, the flight safety issue during the approach and landing phase is particularly prominent.

[0003] The importance of the Instrument Landing System (ILS), a key aviation radio navigation system that ensures the safety of civil aviation during approach and landing, is self-evident. The ILS consists of a localizer (LOC) and a glide slope (GS), which provide horizontal and vertical guidance to the aircraft, respectively, ensuring a safe landing along the correct course and glide slope. Traditional ILS signal processing methods rely primarily on analog circuits, which have numerous drawbacks and shortcomings. For example, the complex structure of analog circuits not only increases the hardware cost and maintenance difficulty of the system, but also increases the probability of system failure. Furthermore, traditional analog methods have low accuracy when measuring the difference in modulation depth (DDM), making it difficult to meet the high-precision signal processing requirements of modern aviation navigation.

[0004] In the above scheme, the traditional instrument landing system (ILS) uses analog circuits to implement signal processing, which has the defects of high circuit complexity and low measurement accuracy of difference in modulation (DDM), resulting in insufficient navigation reliability during the aircraft approach and landing phases. Summary of the Invention

[0005] In view of this, the present invention provides an FPGA-based instrument landing system signal processing method and system to address the problem that traditional instrument landing systems use analog circuits to implement signal processing, which has the defects of high circuit complexity and low modulation error measurement accuracy, resulting in insufficient navigation reliability during the aircraft approach and landing phases.

[0006] In a first aspect, the present invention provides an instrument landing system signal processing method based on FPGA, the method comprising:

[0007] Receive the localizer signal and glide slope signal of the instrument landing system;

[0008] Performing radio frequency processing on the localizer signal and the glide path signal respectively to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal;

[0009] Performing analog-to-digital conversion on the first intermediate frequency signal and the second intermediate frequency signal, respectively, to obtain a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal;

[0010] performing rectification processing, multi-stage decimation filtering processing, bandpass filtering processing, amplitude detection processing, and modulation difference calculation on the first digital signal and the second digital signal, respectively, to obtain a first modulation difference corresponding to the localizer signal and a second modulation difference corresponding to the glide slope signal;

[0011] The deviation state of the aircraft relative to the runway centerline and the glide path centerline is determined based on the first modulation index difference and the second modulation index difference.

[0012] In an optional embodiment, receiving a localizer signal and a glide slope signal of an instrument landing system includes:

[0013] A localizer signal in a first frequency range sent by a localizer beacon and a glide path signal in a second frequency range sent by a glide path beacon are received.

[0014] In an optional embodiment, performing radio frequency processing on the localizer signal and the glide path signal respectively to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal includes:

[0015] Amplification, mixing, and filtering are performed on the localizer signal and the glide path signal, respectively, to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal; the center frequencies of the first intermediate frequency signal and the second intermediate frequency signal are equal.

[0016] In an optional embodiment, the rectification process includes:

[0017] The positive or negative value of the corresponding digital signal is determined according to the sign bit of the corresponding digital signal. If the corresponding digital signal is a positive number, the original value of the corresponding digital signal is retained; if the corresponding digital signal is a negative number, a complement conversion operation is performed on the corresponding digital signal; the corresponding digital signal includes the first digital signal and the second digital signal.

[0018] In an optional embodiment, the multi-stage decimation filtering process includes:

[0019] Performing a first-stage decimation filter on the corresponding digital signal after the rectification process, and reducing the signal sampling rate of the corresponding digital signal after the rectification process from a first sampling rate to a second sampling rate;

[0020] Performing a second-stage decimation filtering on the corresponding digital signal after the first-stage decimation filtering, and reducing the signal sampling rate of the corresponding digital signal after the first-stage decimation filtering from the second sampling rate to a third sampling rate;

[0021] A third-stage decimation filter is performed on the corresponding digital signal after the second-stage decimation filter, and the signal sampling rate of the corresponding digital signal after the second-stage decimation filter is reduced from the third sampling rate to the fourth sampling rate; each stage of decimation filtering adopts a CIC decimation filter, and the number of cascades of each CIC decimation filter is equal.

[0022] In an optional embodiment, the bandpass filtering process includes:

[0023] An FIR filter is used to extract the first frequency component of the first passband frequency range and the second frequency component of the second passband frequency range from the corresponding digital signal after the third-stage extraction filtering; the first passband frequency range is smaller than the second passband frequency range, and the frequency value of the first frequency component is smaller than the frequency value of the second frequency component.

[0024] In an optional implementation, the amplitude detection process includes:

[0025] Averaging calculation is performed on the first frequency component and the second frequency component of the corresponding digital signal after the bandpass filtering process to obtain a first amplitude average value corresponding to the first frequency component and a second amplitude average value corresponding to the second frequency component.

[0026] In an optional implementation manner, the modulation difference value of the first digital signal after amplitude detection is calculated using the following formula:

[0027] DDM1=(m190-m1150) / (m190+m1150)*0.4;

[0028] The modulation index difference of the second digital signal after amplitude detection is calculated using the following formula:

[0029] DDM2=(m290-m2150) / (m290+m2150)*0.8;

[0030] Among them, DDM1 represents the first modulation index difference, DDM2 represents the second modulation index difference, m190 represents the first amplitude average value corresponding to the first digital signal after amplitude detection processing, m1150 represents the second amplitude average value corresponding to the first digital signal after amplitude detection processing, m290 represents the first amplitude average value corresponding to the second digital signal after amplitude detection processing, and m2150 represents the second amplitude average value corresponding to the second digital signal after amplitude detection processing.

[0031] In an optional embodiment, determining the deviation state of the aircraft relative to the runway centerline and the glide path centerline based on the first modulation index difference and the second modulation index difference includes:

[0032] If the first modulation index difference is within a preset first threshold range and the second modulation index difference is within a preset second threshold range, it is determined that the aircraft is located on the runway centerline and the glide path centerline;

[0033] If the first modulation difference is greater than the maximum value of the first threshold range, it is determined that the aircraft has deviated to the left of the runway centerline; if the second modulation difference is greater than the maximum value of the second threshold range, it is determined that the aircraft has deviated above the glide path centerline;

[0034] If the first modulation index difference is less than the minimum value of the first threshold range, it is determined that the aircraft deviates to the right of the runway centerline; if the second modulation index difference is less than the minimum value of the second threshold range, it is determined that the aircraft deviates below the glide path centerline.

[0035] In a second aspect, the present invention provides an instrument landing system signal processing system based on FPGA, the system comprising an antenna, a radio frequency module, an ADC sampling module, an FPGA signal processing module, and a general control module;

[0036] The antenna is used to receive the localizer signal and the glide slope signal of the instrument landing system;

[0037] The radio frequency module is used to perform radio frequency processing on the localizer signal and the glide path signal respectively to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal;

[0038] The ADC sampling module is configured to perform analog-to-digital conversion on the first intermediate frequency signal and the second intermediate frequency signal, respectively, to obtain a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal;

[0039] The FPGA signal processing module is configured to sequentially perform rectification processing, multi-stage decimation filtering processing, bandpass filtering processing, amplitude detection processing, and modulation difference calculation on the first digital signal and the second digital signal, respectively, to obtain a first modulation difference corresponding to the localizer signal and a second modulation difference corresponding to the glide slope signal;

[0040] The master control module is configured to control signal transmission between modules in the system and determine the deviation state of the aircraft relative to the runway centerline and the glide path centerline based on the first modulation index difference and the second modulation index difference.

[0041] In a third aspect, the present invention provides a computer device comprising: a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the computer instructions to thereby perform an FPGA-based instrument landing system signal processing method according to the first aspect or any corresponding embodiment thereof.

[0042] In a fourth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute an FPGA-based instrument landing system signal processing method according to the first aspect or any corresponding embodiment thereof.

[0043] In a fifth aspect, the present invention provides a computer program product comprising computer instructions, the computer instructions being used to enable a computer to execute an FPGA-based instrument landing system signal processing method according to the first aspect or any corresponding embodiment thereof.

[0044] The technical solution provided by the present invention can have the following beneficial effects:

[0045] The present invention adopts multi-stage extraction filtering and band-pass filtering, combined with amplitude mean calculation, to improve the calculation accuracy of the modulation index difference to ±0.001, effectively reducing the navigation error of the aircraft during the approach and landing phases, and significantly improving flight safety. In addition, based on the parallel processing capability of the FPGA signal processing module, the present invention adopts a multi-stage extraction filtering processing method to greatly shorten the signal processing link delay. The output frequency of the modulation index difference can be flexibly configured to meet the real-time requirements of dynamic flight attitude adjustment. Secondly, the present invention achieves a high degree of unification of the processing of the course signal and the glide path signal, simplifies the system architecture, reduces the difficulty and cost of development and maintenance, and improves the reliability and scalability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0047] Figure 1 is a schematic diagram of a heading radiation pattern according to an embodiment of the present invention;

[0048] Figure 2 is a schematic diagram of a glide path radiation pattern according to an embodiment of the present invention;

[0049] Figure 31 is a schematic structural diagram of an instrument landing system signal processing system based on FPGA according to an embodiment of the present invention;

[0050] Figure 4 is a flow chart of a signal processing method for an instrument landing system based on FPGA according to an embodiment of the present invention;

[0051] Figure 5 is a flow chart of another FPGA-based instrument landing system signal processing method according to an embodiment of the present invention;

[0052] Figure 6 is a schematic diagram of an algorithm flow of an FPGA signal processing module according to an embodiment of the present invention;

[0053] Figure 7 Schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0055] It's important to note that the Instrument Landing System (ILS) consists of a localizer (LOC) and a glide slope (GS) beacon. The aircraft is guided to landing using signals from the airport. These two signals correspond to two subsystems: one provides lateral guidance (i.e., heading) and the other provides vertical guidance (i.e., glide slope). The ILS receiver conducts in-depth analysis of the two signals from the airport, adjusting the aircraft's landing attitude and speed through the autopilot system. This provides flight path deviation guidance to the instrument and flight control systems during approach and landing. The lateral guidance signal is provided by the localizer, mounted at the far end of the runway. The localizer transmits two signals, 90Hz and 150Hz, to the aircraft. The beams of these two signals are positioned slightly to the left and right of the runway centerline, respectively. The difference in the intensity of the two signal beams is used to determine whether the aircraft is on the extended runway centerline. In the cockpit, the flight instruments also display the aircraft's position relative to the runway centerline.

[0056] The localizer transmitter is installed on the extended center line of the runway in the landing direction. It transmits two beams of the same shape with one side overlapping each other along the runway center line. Figure 1The following figure shows a schematic diagram of the heading radiation pattern. The carrier frequency of the beam to the left of the runway centerline is modulated with a 90Hz tone, while the carrier frequency of the beam to the right is modulated with a 150Hz tone, with both modulations at 20%. The difference in amplitude modulation (DDM) between the two tones varies according to the relative field strength of the two beams. On the runway centerline, the modulation difference is zero, and increases with increasing deviation from the centerline. To the left of the runway centerline, the 90Hz tone component is greater than the 150Hz tone component, while the opposite is true to the right. Within the range of ±4° to ±6° from the runway centerline, the difference varies linearly with angle.

[0057] When the aircraft approaches the airport, the onboard equipment receives the signal transmitted by the localizer ground station, detects the 90Hz and 150Hz signal components and compares them, and outputs a digital signal proportional to the modulation difference (that is, proportional to the angle of deviation from the runway center) to the deviation and warning indicator and other instruments.

[0058] The glide path launcher is installed on the side near the runway entrance. It launches two beams of the same shape with one side overlapping each other at a certain elevation angle. Figure 2 The diagram below shows a schematic diagram of the glide path radiation pattern. The beams are arranged vertically. The carrier of the upper beam is modulated with a 90Hz tone, while the carrier of the lower beam is modulated with a 150Hz tone, with both amplitudes modulated by 40%. The difference between the two tone amplitudes (DDM) varies according to the field strength of the upper and lower beams. At the center of the glide path, this difference is zero. Within a certain range of angles above and below the glide path, the difference increases as the angle of departure from the glide path increases. The glide path is a straight line located in a plane perpendicular to the extended runway centerline, with a horizontal elevation angle of approximately 2° to 4°.

[0059] When the aircraft approaches, the onboard equipment receives the signal transmitted by the glide path, detects the 90Hz and 150Hz audio components, compares them, and outputs a digital or analog signal proportional to the difference in the amplitude of the two audio frequencies (that is, proportional to the angle of deviation from the glide path) to the glide path deviation and warning indicator and other instruments.

[0060] When the aircraft is on the left side of the runway centerline, the heading deviation indicator pointer deviates to the right, otherwise it deviates to the left; when the aircraft is above the glide path centerline, the glide path deviation indicator pointer deviates downward, otherwise it deviates upward. When the aircraft is on the runway centerline (localizer) and on the glide path centerline, the heading deviation pointer and the glide path deviation pointer return to zero at the same time. When the equipment fails or the signal is unreliable, the corresponding heading and glide path warnings will appear, otherwise no warning indication will appear. The pilot can operate the aircraft according to the instructions of the indicator and safely approach and land according to the optimal route.

[0061] In this embodiment, an instrument landing system signal processing system based on FPGA is provided. Figure 3 FIG. 1 is a schematic diagram of the structure of an instrument landing system signal processing system based on FPGA according to an embodiment of the present invention. Figure 3 As shown, the system includes an antenna, a radio frequency module, an ADC sampling module, an FPGA signal processing module and a general control module;

[0062] The antenna is used to receive the localizer signal and glide slope signal of the instrument landing system;

[0063] The radio frequency module is used to perform radio frequency processing on the localizer signal and the glide path signal respectively to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal;

[0064] The ADC sampling module is used to perform analog-to-digital conversion on the first intermediate frequency signal and the second intermediate frequency signal respectively to obtain a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal;

[0065] The FPGA signal processing module is configured to sequentially perform rectification processing, multi-stage decimation filtering processing, bandpass filtering processing, amplitude detection processing, and modulation difference calculation on the first digital signal and the second digital signal, respectively, to obtain a first modulation difference corresponding to the localizer signal and a second modulation difference corresponding to the glide slope signal;

[0066] The overall control module is used to control signal transmission between modules in the system and determine the deviation state of the aircraft relative to the runway centerline and the glide path centerline based on the first modulation index difference and the second modulation index difference.

[0067] Furthermore, the antenna is used to receive the localizer signal (LOC) and the glide slope signal (GS) of the instrument landing system.

[0068] The RF module is used to perform RF processing on the LOC signal and the GS signal, including amplification, mixing, and filtering, and convert the signals into a first intermediate frequency signal (corresponding to the LOC signal) and a second intermediate frequency signal (corresponding to the GS signal) with a center frequency of 21.4 MHz.

[0069] The ADC sampling module performs analog-to-digital conversion on the first and second IF signals. Using a 65MHz sampling rate ADC chip module, the 21.4MHz IF signal is sampled to produce a first digital signal (21.4MHz@65Msps) corresponding to the localizer signal and a second digital signal (21.4MHz@65Msps) corresponding to the glide path signal.

[0070] The FPGA signal processing module is used to perform the following processing on the first digital signal and the second digital signal respectively:

[0071] Rectification processing: judge the positive or negative according to the sign bit of the data. Positive numbers retain the original value, and negative numbers take the complement.

[0072] Multi-stage decimation filtering: CIC decimation filter is used for multi-stage decimation filtering, gradually reducing the signal sampling rate to 1KHz.

[0073] Bandpass filtering: Use FIR bandpass filters to extract 90Hz and 150Hz signals respectively.

[0074] Amplitude detection processing: Calculate the amplitude average of the 90Hz and 150Hz signals.

[0075] Modulation difference calculation: Calculate the first modulation difference (DDM1) of the localizer signal and the second modulation difference (DDM2) of the glide path signal according to the formula.

[0076] Main control module: controls the signal transmission and timing control between modules in the entire system, and determines the deviation status of the aircraft relative to the runway centerline and glide path centerline based on DDM1 and DDM2.

[0077] The system realizes the whole process from signal reception to aircraft deviation status judgment through the division of labor and cooperation among various modules, ensuring the precise operation of the instrument landing system.

[0078] In summary, this embodiment adopts multi-stage extraction filtering and band-pass filtering, combined with amplitude mean calculation, to improve the calculation accuracy of the modulation index difference to ±0.001, effectively reducing the navigation error of the aircraft during the approach and landing phases, and significantly improving flight safety. In addition, this embodiment adopts a multi-stage extraction filtering processing method based on the parallel processing capability of the FPGA signal processing module, which greatly shortens the signal processing link delay. The output frequency of the modulation index difference can be flexibly configured to meet the real-time requirements of dynamic flight attitude adjustment. Secondly, this embodiment achieves a high degree of unification of the processing of the localizer signal and the glide path signal, simplifies the system architecture, reduces the difficulty and cost of development and maintenance, and improves the reliability and scalability of the system.

[0079] According to an embodiment of the present invention, an embodiment of a signal processing method for an instrument landing system based on an FPGA is provided. It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system, such as a set of computer-executable instructions. Moreover, although a logical sequence is shown in the flowcharts, in some cases, the steps shown or described may be executed in an order different from that shown.

[0080] This embodiment provides an instrument landing system signal processing method based on FPGA, which can be applied to Figure 3 An FPGA-based instrument landing system signal processing system is shown. Figure 4 FIG. 1 is a flow chart of a signal processing method for an instrument landing system based on FPGA according to an embodiment of the present invention. Figure 4 As shown, the process includes the following steps:

[0081] Step S401: receiving a localizer signal and a glide slope signal from an instrument landing system.

[0082] Furthermore, this embodiment utilizes an antenna to receive the localizer (LOC) and glide slope (GS) signals from the instrument landing system (ILS). The antenna serves as the interface between the system and external signal sources, capturing radio waves propagating in space and converting them into electrical signals for subsequent processing.

[0083] Step S402: Perform radio frequency processing on the localizer signal and the glide path signal to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal.

[0084] Furthermore, this embodiment performs radio frequency processing on the captured localizer and glide slope signals. Radio frequency processing converts received high-frequency signals into intermediate frequency (IF) signals suitable for subsequent processing. This includes amplifying the signals to increase their power level for further processing; converting the signal frequency to a 21.4 MHz IF through mixing for more efficient signal processing; and filtering to remove unwanted noise and interference to ensure signal purity. After processing, a first IF signal corresponding to the localizer signal and a second IF signal corresponding to the glide slope signal are obtained.

[0085] Step S403: performing analog-to-digital conversion on the first intermediate frequency signal and the second intermediate frequency signal to obtain a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal.

[0086] Furthermore, this embodiment performs analog-to-digital conversion on the first and second intermediate frequency signals. The ADC sampling module converts the analog signals into digital signals, generating a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal, enabling digital signal processing in the FPGA signal processing module.

[0087] In step S404, rectification, multi-stage decimation filtering, bandpass filtering, amplitude detection, and modulation difference calculation are sequentially performed on the first digital signal and the second digital signal to obtain a first modulation difference corresponding to the localizer signal and a second modulation difference corresponding to the glide path signal.

[0088] Furthermore, this embodiment sequentially performs multiple processing steps on the first digital signal and the second digital signal, including:

[0089] Rectification: Convert the negative half of the digital signal into the positive half, making the signal a unipolar signal for subsequent processing.

[0090] Multi-stage decimation filtering: Use CIC decimation filter to perform multi-stage decimation filtering on the signal, gradually reducing the sampling rate of the signal and the amount of data while retaining the key information of the signal.

[0091] Bandpass filtering: An FIR bandpass filter is used to extract the 90 Hz and 150 Hz frequency components from the signal. The signal at this specific frequency carries key information about the aircraft's position relative to the runway.

[0092] Amplitude detection processing: Calculate the amplitude averages of the 90 Hz frequency component and the 150 Hz frequency component to obtain a first amplitude average and a second amplitude average, which reflect the relative strengths of the two frequency components.

[0093] Modulation difference calculation: Calculate the first modulation difference (DDM1) of the localizer signal and the second modulation difference (DDM2) of the glide path signal according to the formula.

[0094] Step S405 : Determine the deviation state of the aircraft relative to the runway centerline and the glide path centerline based on the first modulation index difference and the second modulation index difference.

[0095] Furthermore, this embodiment determines the aircraft's deviation from the runway centerline and the glide path centerline based on the calculated first modulation difference (DDM1) of the localizer signal and the second modulation difference (DDM2) of the glide path signal. If the first modulation difference (DDM1) is within a first threshold range, the aircraft is located on the runway centerline; if the first modulation difference (DDM1) is greater than the maximum value of the first threshold range, the aircraft is to the left of the runway centerline; if the first modulation difference (DDM1) is less than the minimum value of the first threshold range, the aircraft is to the right of the runway centerline; if the second modulation difference (DDM2) is within a second threshold range, the aircraft is located on the glide path centerline; if the second modulation difference (DDM2) is greater than the maximum value of the second threshold range, the aircraft is above the glide path centerline; and if the second modulation difference (DDM2) is less than the minimum value of the second threshold range, the aircraft is below the glide path centerline.

[0096] In summary, this embodiment adopts multi-stage extraction filtering and band-pass filtering, combined with amplitude mean calculation, to improve the calculation accuracy of the modulation index difference to ±0.001, effectively reducing the navigation error of the aircraft during the approach and landing phases, and significantly improving flight safety. In addition, this embodiment adopts a multi-stage extraction filtering processing method based on the parallel processing capability of the FPGA signal processing module, which greatly shortens the signal processing link delay. The output frequency of the modulation index difference can be flexibly configured to meet the real-time requirements of dynamic flight attitude adjustment. Secondly, this embodiment achieves a high degree of unification of the processing of the localizer signal and the glide path signal, simplifies the system architecture, reduces the difficulty and cost of development and maintenance, and improves the reliability and scalability of the system.

[0097] This embodiment provides an instrument landing system signal processing method based on FPGA, which can be applied to Figure 3 An FPGA-based instrument landing system signal processing system is shown. Figure 5 FIG. 1 is a flow chart of another FPGA-based instrument landing system signal processing method according to an embodiment of the present invention. Figure 5 As shown, the process includes the following steps:

[0098] Step S501: receiving a localizer signal in a first frequency range from a localizer and a glide path signal in a second frequency range from a glide path beacon; the number of channel points of the localizer signal is equal to the number of channel points of the glide path signal, and the channels are allocated in pairs.

[0099] Furthermore, this embodiment receives the localizer signal (in a specific first frequency range) from the localizer beacon and the glide path signal (in a specific second frequency range) from the glide path beacon through the antenna. Among them, the localizer signal is used to indicate the lateral position of the aircraft, and the glide path signal is used to indicate the vertical position. In particular, the number of channel points of the two is equal and allocated in pairs, which ensures the correspondence and coordination of the signals, provides a basis for subsequent precise processing, and enables the system to accurately match and analyze the navigation information carried by the two signals. The first frequency range is 108.1~111.95MHz, with a total of 40 channels, which is used for horizontal guidance; the second frequency range is 329.15~335.10MHz, with a total of 40 channels, which is used for vertical guidance. The channels of the two are allocated in pairs, as shown in the table below:

[0100] Table 1

[0101]

[0102]

[0103] In step S502, amplification, mixing, and filtering are performed on the localizer signal and the glide path signal, respectively, to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal; the center frequencies of the first intermediate frequency signal and the second intermediate frequency signal are equal.

[0104] Furthermore, this embodiment sequentially performs amplification, mixing, and filtering on the received localizer and glide slope signals. Amplification enhances signal strength for subsequent stable processing; mixing converts the signal frequency to a unified center frequency (the center frequencies of the first and second intermediate frequency signals are equal) to facilitate standardized processing; filtering removes clutter and interference from the signals, making the output first intermediate frequency signal (corresponding to the localizer) and second intermediate frequency signal (corresponding to the glide slope) purer and more stable, laying a good foundation for subsequent analog-to-digital conversion and digital processing. The center frequency of the first and second intermediate frequency signals is 21.4 MHz.

[0105] Step S503: performing analog-to-digital conversion on the first intermediate frequency signal and the second intermediate frequency signal to obtain a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal.

[0106] Furthermore, this embodiment utilizes an ADC sampling module to convert the analog first and second IF signals into digital signals. The 21.4 MHz IF signal is sampled at a 65 MHz sampling rate to generate a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal. This converts the analog signals into a digital format suitable for processing by a digital processing module such as an FPGA.

[0107] In step S504, rectification, multi-stage decimation filtering, bandpass filtering, amplitude detection, and modulation difference calculation are sequentially performed on the first digital signal and the second digital signal to obtain a first modulation difference corresponding to the localizer signal and a second modulation difference corresponding to the glide slope signal.

[0108] In an optional embodiment, the rectification process includes:

[0109] The sign of the corresponding digital signal is determined based on the sign bit of the corresponding digital signal. If the corresponding digital signal is a positive number, the original value of the corresponding digital signal is retained; if the corresponding digital signal is a negative number, a complement conversion operation is performed on the corresponding digital signal; the corresponding digital signal includes the first digital signal and the second digital signal.

[0110] Furthermore, this embodiment uses an FPGA signal processing module to extract and filter the 21.4MHz intermediate frequency signal, calculating and outputting the modulation difference between the localizer and glideslope. This embodiment performs rectification on the first and second digital signals, determining their sign based on the sign bit. If the sign is positive, the original value is retained; if the sign is negative, a two's complement conversion operation is performed (the corresponding digital signal is bitwise inverted and then 1 is added), unifying the first and second digital signals to positive values. This eliminates the impact of signal polarity on subsequent processing and facilitates analysis of signal amplitude characteristics.

[0111] In an optional embodiment, the multi-stage decimation filtering process includes:

[0112] performing a first-stage decimation filter with a 65-fold decimation on the corresponding digital signal after the rectification process, and reducing the signal sampling rate of the corresponding digital signal after the rectification process from the first sampling rate to the second sampling rate;

[0113] performing a second-stage decimation filter with a 100-fold decimation on the corresponding digital signal after the first-stage decimation filter, and reducing the signal sampling rate of the corresponding digital signal after the first-stage decimation filter from the second sampling rate to a third sampling rate;

[0114] A third-stage decimation filter is performed on the corresponding digital signal after the second-stage decimation filter with 10 times decimation, and the signal sampling rate of the corresponding digital signal after the second-stage decimation filter is reduced from the third sampling rate to the fourth sampling rate; each stage of decimation filtering adopts a CIC decimation filter, and the number of cascades (5 stages) of each CIC decimation filter is equal.

[0115] Furthermore, this embodiment uses a five-stage CIC decimation filter to reduce the sampling rate in three stages. The first stage of decimation filtering (65x decimation) reduces the sampling rate of the rectified signal from the first sampling rate (65MHz) to the second sampling rate (1MHz). The second stage (100x decimation) further reduces it to the third sampling rate (10kHz). The third stage (10x decimation) further reduces it to the fourth sampling rate (1kHz). Each stage of the filter has an equal number of cascades, which reduces the amount of data while retaining key frequency components, improving processing efficiency and reducing computational complexity.

[0116] In an optional embodiment, the bandpass filtering process includes:

[0117] An FIR filter is used to extract the first frequency component of the first passband frequency range and the second frequency component of the second passband frequency range from the corresponding digital signal after the third-stage extraction filtering; the first passband frequency range is smaller than the second passband frequency range, and the frequency value of the first frequency component is smaller than the frequency value of the second frequency component.

[0118] Furthermore, this embodiment uses a 64-tap FIR filter to process the signal after the third-stage decimation filter, extracting a first frequency component (90 Hz) within a first passband frequency range (0.12π to 0.24π) and a second frequency component (150 Hz) within a second passband frequency range (0.24π to 0.36π). The first passband frequency range is smaller than the second passband frequency range, and the first frequency component has a lower frequency value. Both of these factors are key indicators for determining aircraft deviation.

[0119] In an optional embodiment, the amplitude detection process includes:

[0120] The first frequency component and the second frequency component of the corresponding digital signal after the bandpass filtering process are averaged to obtain a first amplitude average value corresponding to the first frequency component and a second amplitude average value corresponding to the second frequency component.

[0121] Furthermore, this embodiment performs an averaging calculation on 1024 data points of the first and second frequency components after bandpass filtering to obtain the corresponding first amplitude averages (e.g., m190 and m290) and second amplitude averages (e.g., m1150 and m2150). By averaging and smoothing signal fluctuations, the amplitude characteristics of each frequency component are accurately reflected, providing reliable data for modulation calculation.

[0122] In an optional implementation, the modulation difference value of the first digital signal after the amplitude detection processing is calculated using the following formula:

[0123] DDM1=(m190-m1150) / (m190+m1150)*0.4;

[0124] The modulation index difference of the second digital signal after amplitude detection is calculated using the following formula:

[0125] DDM2=(m290-m2150) / (m290+m2150)*0.8;

[0126] Among them, DDM1 represents the first modulation index difference, DDM2 represents the second modulation index difference, m190 represents the first amplitude average value corresponding to the first digital signal after amplitude detection processing, m1150 represents the second amplitude average value corresponding to the first digital signal after amplitude detection processing, m290 represents the first amplitude average value corresponding to the second digital signal after amplitude detection processing, and m2150 represents the second amplitude average value corresponding to the second digital signal after amplitude detection processing.

[0127] Step S505: If the first modulation index difference is within a preset first threshold range and the second modulation index difference is within a preset second threshold range, it is determined that the aircraft is located on the runway centerline and the glide path centerline.

[0128] Furthermore, if the first modulation difference (DDM1) is within a preset first threshold range (the first threshold range is 0±0.004), and the second modulation difference (DDM2) is within a preset second threshold range (the second threshold range is 0±0.004), the modulation difference between the 90Hz first frequency component and the 150Hz second frequency component is within an ideal range, indicating that the aircraft is in an ideal position both laterally (runway) and vertically (glide path), i.e., on the runway centerline and on the glide path centerline, and the flight path is accurate. The first and second threshold ranges may be equal.

[0129] Step S506: If the first modulation difference is greater than the maximum value of the first threshold range, it is determined that the aircraft has deviated to the left of the runway centerline; if the second modulation difference is greater than the maximum value of the second threshold range, it is determined that the aircraft has deviated above the glide path centerline.

[0130] Furthermore, when the first modulation difference (DDM1) is greater than the maximum value of the first threshold range (i.e., 0.004), it indicates that the modulation difference between the 90Hz first frequency component and the 150Hz second frequency component in the localizer signal exceeds the positive standard, and the aircraft is judged to have deviated to the left of the runway centerline. If the second modulation difference (DDM2) is greater than the maximum value of the second threshold range (i.e., 0.004), it indicates that the corresponding modulation difference in the glide path signal exceeds the positive standard, and the aircraft is judged to have deviated above the glide path centerline, prompting the pilot to adjust the lateral or vertical flight path.

[0131] Step S507: If the first modulation difference is less than the minimum value of the first threshold range, it is determined that the aircraft has deviated to the right of the runway centerline; if the second modulation difference is less than the minimum value of the second threshold range, it is determined that the aircraft has deviated below the glide path centerline.

[0132] Furthermore, if the first modulation difference (DDM1) is less than the minimum value of the first threshold range (i.e., -0.004), it indicates that the localizer signal modulation difference exceeds the negative standard, and the aircraft is judged to have deviated to the right of the runway centerline. When the second modulation difference (DDM2) is less than the minimum value of the second threshold range (i.e., -0.004), it indicates that the glide path signal modulation difference exceeds the negative standard, and the aircraft is judged to have deviated below the glide path centerline. The pilot is promptly alerted to make reverse adjustments to ensure that the aircraft returns to the correct landing path.

[0133] For further information, see Figure 6The algorithm flow diagram of the FPGA signal processing module is shown. First, the localizer signal processing flow based on the FPGA signal processing module includes:

[0134] (1) Rectify the 21.4 MHz first intermediate frequency signal after sampling by the ADC sampling module. The method is to judge the sign bit of the first digital signal. If it is a positive number, the rectified data is the first digital signal itself; if it is a negative number, the rectified signal is the complement of the first digital signal.

[0135] (2) The rectified signal is filtered by 65 times (first-stage decimation filtering). The decimation filter uses a CIC decimation filter, a five-stage cascade, and 65 times decimation. Since the main signals are 90 Hz and 150 Hz, flatness compensation is not required. After 65 times decimation, the signal sampling rate is 1 MHz (i.e., the second sampling rate).

[0136] (3) The 1MHz sampling rate signal is subjected to a 100x decimation filter (second-stage decimation filter). The decimation filter uses a CIC decimation filter, a 5-stage cascade, and 100x decimation. Since the main signals are 90Hz and 150Hz, flatness compensation is not required. After 100x decimation, the signal sampling rate is 10KHz (i.e., the third sampling rate).

[0137] (4) Perform a 10x decimation filter (third-stage decimation filter) on the 10KHz sampling rate signal. The decimation filter uses a CIC decimation filter, a 5-stage cascade, and 10x decimation. Since the main signals are 90Hz and 150Hz, flatness compensation is not required. After 10x decimation, the signal sampling rate is 1KHz (i.e., the fourth sampling rate).

[0138] (5) Perform 90Hz and 150Hz bandpass filtering on the 1kHz sampling rate signal to obtain 90Hz and 150Hz signals. See (6) and (7) for the specific method.

[0139] (6) Perform a 90Hz bandpass filter on the 1kHz sampling rate signal. Use an FIR bandpass filter with a filter order of 64 and a passband of 0.12π to 0.24π (i.e., the first passband frequency range). The output of the bandpass filter is a 90Hz signal of the localizer (i.e., the first frequency component).

[0140] (7) Perform a 150Hz bandpass filter on the 1kHz sampling rate signal. Use an FIR bandpass filter with a filter order of 64 and a passband of 0.24π to 0.36π (i.e., the second passband frequency range). The output of the bandpass filter is a 150Hz signal of the heading channel (i.e., the second frequency component).

[0141] (8) Perform amplitude detection on the 90Hz and 150Hz signals respectively. The detection method is to average the 1024 data points and obtain the amplitude average values ​​m190 and m1150 of the 90Hz and 150Hz signals respectively.

[0142] (9) Calculate the DDM1 value and output it.

[0143] The calculation formula of DDM1 value is: DDM1 = (m190-m1150) / (m190+m1150)*0.4;

[0144] If the DDM1 value is 0±0.004 (i.e., the first threshold range), it indicates that the aircraft is on the centerline of the localizer. If the DDM1 value is greater than 0.004, it indicates that the aircraft is deviating to the left of the centerline of the localizer, and the larger the value, the greater the deviation. If the DDM1 value is less than -0.004, it indicates that the aircraft is deviating to the right of the centerline of the localizer, and the smaller the value, the greater the deviation.

[0145] Secondly, the glide slope signal processing process based on the FPGA signal processing module includes:

[0146] (1) Rectify the 21.4MHz second intermediate frequency signal after sampling by the ADC sampling module. The method is to judge the sign bit of the second digital signal. If it is a positive number, the rectified data is the second digital signal itself; if it is a negative number, the rectified signal is the complement of the second digital signal.

[0147] (2) The rectified signal is filtered by 65 times (first-stage decimation filtering). The decimation filter uses a CIC decimation filter, a five-stage cascade, and 65 times decimation. Since the main signals are 90 Hz and 150 Hz, flatness compensation is not required. After 65 times decimation, the signal sampling rate is 1 MHz (i.e., the second sampling rate).

[0148] (3) The 1MHz sampling rate signal is subjected to a 100x decimation filter (second-stage decimation filter). The decimation filter uses a CIC decimation filter, a 5-stage cascade, and 100x decimation. Since the main signals are 90Hz and 150Hz, flatness compensation is not required. After 100x decimation, the signal sampling rate is 10KHz (i.e., the third sampling rate).

[0149] (4) Perform a 10x decimation filter (third-stage decimation filter) on the 10KHz sampling rate signal. The decimation filter uses a CIC decimation filter, a 5-stage cascade, and 10x decimation. Since the main signals are 90Hz and 150Hz, flatness compensation is not required. After 10x decimation, the signal sampling rate is 1KHz (i.e., the fourth sampling rate).

[0150] (5) Perform 90Hz and 150Hz bandpass filtering on the 1kHz sampling rate signal to obtain 90Hz and 150Hz signals. See (6) and (7) for the specific method.

[0151] (6) Perform a 90Hz bandpass filter on the 1kHz sampling rate signal. Use an FIR bandpass filter with a filter order of 64 and a passband of 0.12π to 0.24π (i.e., the first passband frequency range). The output of the bandpass filter is a 90Hz signal of the localizer (i.e., the first frequency component).

[0152] (7) Perform a 150Hz bandpass filter on the 1kHz sampling rate signal. Use an FIR bandpass filter with a filter order of 64 and a passband of 0.24π to 0.36π (i.e., the second passband frequency range). The output of the bandpass filter is a 150Hz signal of the heading channel (i.e., the second frequency component).

[0153] (8) Perform amplitude detection on the 90Hz and 150Hz signals respectively. The detection method is to average the 1024 data points and obtain the amplitude average values ​​m190 and m1150 of the 90Hz and 150Hz signals respectively.

[0154] (9) Calculate the DDM2 value and output it.

[0155] The calculation formula of DDM2 value is: DDM2 = (m290-m2150) / (m290+m2150)*0.8;

[0156] If the DDM2 value is 0±0.004 (i.e., the second threshold range), the aircraft is on the glide path centerline. If the DDM2 value is greater than 0.004, the aircraft is above the glide path centerline, with larger values ​​indicating greater deviation. If the DDM1 value is less than -0.004, the aircraft is below the localizer centerline, with smaller values ​​indicating greater deviation. This demonstrates that this embodiment achieves a unified architecture and flexible methods. The localizer data processing method and the glide path data processing method are essentially the same, simplifying signal processing.

[0157] In summary, this embodiment adopts multi-stage extraction filtering and band-pass filtering, combined with amplitude mean calculation, to improve the calculation accuracy of the modulation index difference to ±0.001, effectively reducing the navigation error of the aircraft during the approach and landing phases, and significantly improving flight safety. In addition, this embodiment adopts a multi-stage extraction filtering processing method based on the parallel processing capability of the FPGA signal processing module, which greatly shortens the signal processing link delay. The output frequency of the modulation index difference can be flexibly configured to meet the real-time requirements of dynamic flight attitude adjustment. Secondly, this embodiment achieves a high degree of unification of the processing of the localizer signal and the glide path signal, simplifies the system architecture, reduces the difficulty and cost of development and maintenance, and improves the reliability and scalability of the system.

[0158] See also Figure 7 , Figure 7 is a structural diagram of a computer device provided by an optional embodiment of the present invention, such as Figure 7 As shown, the computer device includes: one or more processors 10, memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components utilize different buses to communicate with each other and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in the memory or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Equally, multiple computer devices can be connected, and each device provides part of the necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 7 A processor 10 is taken as an example.

[0159] The processor 10 may be a central processing unit, a network processor, or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit, a programmable logic device, or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic, or any combination thereof.

[0160] The memory 20 stores instructions that can be executed by at least one processor 10, so as to enable at least one processor 10 to execute the method shown in the above embodiment.

[0161] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system and application programs required for at least one function; the data storage area may store data created based on the use of the computer device, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0162] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0163] The computer device further includes a communication interface 30 for the computer device to communicate with other devices or a communication network.

[0164] The embodiment of the present invention also provides a computer-readable storage medium. The above-mentioned method according to the embodiment of the present invention can be implemented in hardware, firmware, or implemented as a computer code that can be recorded in a storage medium, or implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and downloaded through a network and will be stored in a local storage medium, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state drive, etc.; further, the storage medium can also include a combination of the above-mentioned types of memory. It can be understood that a computer, a processor, a microprocessor controller or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor or hardware, the method shown in the above embodiment is implemented.

[0165] A portion of the present invention may be applied as a computer program product, such as a computer program instruction, which, when executed by a computer, can call or provide the method and / or technical solution according to the present invention through the operation of the computer. Those skilled in the art should understand that the form in which the computer program instruction exists in a computer-readable medium includes, but is not limited to, a source file, an executable file, an installation package file, etc. Accordingly, the way in which the computer program instruction is executed by the computer includes, but is not limited to: the computer directly executes the instruction, or the computer compiles the instruction and then executes the corresponding compiled program, or the computer reads and executes the instruction, or the computer reads and installs the instruction and then executes the corresponding installed program. Here, the computer-readable medium may be any available computer-readable storage medium or communication medium that can be accessed by the computer.

[0166] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the defined scope.

Claims

1. A signal processing method for an instrument landing system based on FPGA, characterized in that: The method comprises: Receive the localizer signal and glide slope signal of the instrument landing system; Performing radio frequency processing on the localizer signal and the glide path signal respectively to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal; Performing analog-to-digital conversion on the first intermediate frequency signal and the second intermediate frequency signal, respectively, to obtain a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal; performing rectification processing, multi-stage decimation filtering processing, bandpass filtering processing, amplitude detection processing, and modulation difference calculation on the first digital signal and the second digital signal, respectively, to obtain a first modulation difference corresponding to the localizer signal and a second modulation difference corresponding to the glide slope signal; The deviation state of the aircraft relative to the runway centerline and the glide path centerline is determined based on the first modulation index difference and the second modulation index difference.

2. The method according to claim 1, characterized in that The receiving of the localizer signal and the glide slope signal of the instrument landing system comprises: A localizer signal in a first frequency range sent by a localizer beacon and a glide path signal in a second frequency range sent by a glide path beacon are received.

3. The method according to claim 1, characterized in that The performing radio frequency processing on the localizer signal and the glide path signal respectively to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal includes: Amplification, mixing, and filtering are performed on the localizer signal and the glide path signal, respectively, to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal; the center frequencies of the first intermediate frequency signal and the second intermediate frequency signal are equal.

4. The method according to claim 1, wherein The rectification process includes: The positive or negative value of the corresponding digital signal is determined according to the sign bit of the corresponding digital signal. If the corresponding digital signal is a positive number, the original value of the corresponding digital signal is retained; if the corresponding digital signal is a negative number, a complement conversion operation is performed on the corresponding digital signal; the corresponding digital signal includes the first digital signal and the second digital signal.

5. The method according to claim 4, characterized in that The multi-stage decimation filtering process includes: Performing a first-stage decimation filter on the corresponding digital signal after the rectification process, and reducing the signal sampling rate of the corresponding digital signal after the rectification process from a first sampling rate to a second sampling rate; Performing a second-stage decimation filtering on the corresponding digital signal after the first-stage decimation filtering, and reducing the signal sampling rate of the corresponding digital signal after the first-stage decimation filtering from the second sampling rate to a third sampling rate; A third-stage decimation filter is performed on the corresponding digital signal after the second-stage decimation filter, and the signal sampling rate of the corresponding digital signal after the second-stage decimation filter is reduced from the third sampling rate to the fourth sampling rate; each stage of decimation filtering adopts a CIC decimation filter, and the number of cascades of each CIC decimation filter is equal.

6. The method according to claim 5, characterized in that The bandpass filtering process includes: An FIR filter is used to extract the first frequency component of the first passband frequency range and the second frequency component of the second passband frequency range from the corresponding digital signal after the third-stage extraction filtering; the first passband frequency range is smaller than the second passband frequency range, and the frequency value of the first frequency component is smaller than the frequency value of the second frequency component.

7. The method according to claim 6, characterized in that The amplitude detection process includes: Averaging calculation is performed on the first frequency component and the second frequency component of the corresponding digital signal after the bandpass filtering process to obtain a first amplitude average value corresponding to the first frequency component and a second amplitude average value corresponding to the second frequency component.

8. The method according to claim 7, characterized in that The modulation difference of the first digital signal after amplitude detection is calculated using the following formula: DDM1=(m190-m1150) / (m190+m1150)*0.4; The modulation index difference of the second digital signal after amplitude detection is calculated using the following formula: DDM2=(m290-m2150) / (m290+m2150)*0.8; Among them, DDM1 represents the first modulation index difference, DDM2 represents the second modulation index difference, m190 represents the first amplitude average value corresponding to the first digital signal after amplitude detection processing, m1150 represents the second amplitude average value corresponding to the first digital signal after amplitude detection processing, m290 represents the first amplitude average value corresponding to the second digital signal after amplitude detection processing, and m2150 represents the second amplitude average value corresponding to the second digital signal after amplitude detection processing.

9. The method according to any one of claims 1 to 8, characterized in that The determining, based on the first modulation index difference and the second modulation index difference, a deviation state of the aircraft relative to a runway centerline and a glide path centerline includes: If the first modulation index difference is within a preset first threshold range and the second modulation index difference is within a preset second threshold range, it is determined that the aircraft is located on the runway centerline and the glide path centerline; If the first modulation difference is greater than the maximum value of the first threshold range, it is determined that the aircraft has deviated to the left of the runway centerline; if the second modulation difference is greater than the maximum value of the second threshold range, it is determined that the aircraft has deviated above the glide path centerline; If the first modulation index difference is less than the minimum value of the first threshold range, it is determined that the aircraft deviates to the right of the runway centerline; if the second modulation index difference is less than the minimum value of the second threshold range, it is determined that the aircraft deviates below the glide path centerline.

10. An instrument landing system signal processing system based on FPGA, characterized in that: The system includes an antenna, a radio frequency module, an ADC sampling module, an FPGA signal processing module and a general control module; The antenna is used to receive the localizer signal and the glide slope signal of the instrument landing system; The radio frequency module is used to perform radio frequency processing on the localizer signal and the glide path signal respectively to obtain a first intermediate frequency signal corresponding to the localizer signal and a second intermediate frequency signal corresponding to the glide path signal; The ADC sampling module is configured to perform analog-to-digital conversion on the first intermediate frequency signal and the second intermediate frequency signal, respectively, to obtain a first digital signal corresponding to the localizer signal and a second digital signal corresponding to the glide slope signal; The FPGA signal processing module is configured to sequentially perform rectification processing, multi-stage decimation filtering processing, bandpass filtering processing, amplitude detection processing, and modulation difference calculation on the first digital signal and the second digital signal, respectively, to obtain a first modulation difference corresponding to the localizer signal and a second modulation difference corresponding to the glide slope signal; The master control module is configured to control signal transmission between modules in the system and determine the deviation state of the aircraft relative to the runway centerline and the glide path centerline based on the first modulation index difference and the second modulation index difference.

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