Instrument landing navigation method

Abstract

The invention discloses an instrument landing navigation method which comprises the following steps: firstly, constructing an ILS instrument landing system comprising a course beacon LOC and a glide beacon station GS, and accurately calculating a DDM modulation degree difference by adopting a normalization method; then, the system receives an intermediate-frequency 70MHz signal transmitted by the VOR navigation station, and noise and interference components in the signal are effectively removed through digitization and low-pass filtering processing; then, amplitude modulation and frequency modulation demodulation are carried out on the filtered signal, and a key 30Hz navigation signal is successfully extracted; by using the DDM and the 30Hz signal, the system performs zero-cross detection and accurately calculates the phase difference; and finally, according to the calculated phase difference, the system determines the VOR azimuth angle deviation degree of the aircraft relative to the VOR navigation station, and the flight direction of the aircraft is calibrated according to the VOR azimuth angle deviation degree, so that the navigation accuracy and the flight safety are effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of navigation technology, and in particular to an instrument landing navigation method. Background Art

[0002] With the increasing growth of air traffic, the navigation requirements of aircraft in flight are becoming more and more complex. Traditional ground radar navigation, inertial navigation and other technologies are no longer able to meet the requirements of modern aviation due to limitations in weather conditions, equipment costs and accuracy. Therefore, it is particularly important to develop an aviation system that can work reliably under complex weather conditions and can be widely used on global routes. The Very High Frequency Omni-directional Range (VOR) navigation system is a short-range lateral guidance system operating in the very high frequency band. It has the advantages of all-weather, no terrain restrictions, and high accuracy. It is widely used for aircraft heading guidance. However, the existing VOR navigation system still has problems in some aspects, such as signal attenuation and insufficient error correction. A new VOR navigation technology is needed to improve its accuracy and stability. Summary of the Invention

[0003] This application provides an instrument landing navigation method, which improves the positioning accuracy, stability and anti-interference ability of the VOR navigation system by improving the signal processing algorithm, enhancing the signal propagation model and optimizing the receiving equipment.

[0004] The present application provides an instrument landing navigation method, comprising:

[0005] S1, constructing an ILS instrument landing system including a localizer LOC and a glide path beacon GS;

[0006] S2, in the ILS instrument landing system, the DDM modulation error is calculated using the normalization method;

[0007] S3 receives the 70MHz intermediate frequency signal transmitted by the VOR navigation station and performs digitization and low-pass filtering;

[0008] S4, performing AM and FM demodulation on the low-pass filtered signal to extract the 30 Hz navigation signal;

[0009] S5, using DDM and the extracted 30 Hz signal to perform zero-crossing detection and then calculate the phase difference;

[0010] S6 determines the degree of deviation of the aircraft's VOR azimuth relative to the VOR navigation station through the phase difference, and calibrates the aircraft's flight direction accordingly.

[0011] Preferably, the calculation of the DDM modulation error by using the normalization method specifically includes:

[0012] S21, receiving the audio frequency modulation signals transmitted by the localizer LOC and the glide path beacon GS, and demodulating the received signals to extract the 90 Hz and 150 Hz audio signals;

[0013] S22, set the modulation depth on the localizer and glide paths;

[0014] At S23, the 90 Hz and 150 Hz modulation signals are added to the carrier signal, respectively, to form a modulation signal containing two different frequency components;

[0015] S34, measure the amplitude of the 90Hz and 150Hz signals and calculate the DDM modulation difference between the two signals;

[0016] S35, normalized DDM modulation error.

[0017] Preferably, in said S35, the DDM modulation index deviation includes: a normalized DDM modulation index deviation calculation formula is:

[0018]

[0019] Where A and B are the amplitudes of the 90Hz and 150Hz signals, respectively; AB is the amplitude difference between the 90Hz and 150Hz signals; A+B is the sum of the modulation depths of the 90Hz and 150Hz signals; and DDM is the modulation depth difference calculation for the glide path and heading path of the ILS system.

[0020] Preferably, the S3 specifically includes:

[0021] S31, receives the 70MHz intermediate frequency signal transmitted from the VOR navigation station;

[0022] S32, the received VOR navigation station signal is sampled by an A / D converter, and the continuous analog signal is converted into a discrete digital signal;

[0023] S33, the sampled digital signal is processed by a low-pass filter to filter out high-frequency components and retain useful information at 9960 Hz.

[0024] Preferably, the step S4 specifically includes: performing demodulation processing on the low-pass filtered signal to extract a variable phase signal with a 30 Hz envelope and a 30 Hz reference phase signal respectively.

[0025] Preferably, the variable phase signal for extracting the 30Hz envelope is as follows: the filtered signal is amplitude-limited, the signal amplitude is controlled within a predetermined range by a limiter, and then filtered by a low-pass filter with a cut-off frequency higher than 30Hz but much lower than other high-frequency components to obtain a 30Hz envelope signal; the reference phase signal for extracting 30Hz is as follows: the signal after discriminator frequency processing is low-pass filtered to filter out high-frequency noise, and the cut-off frequency is higher than 30Hz.

[0026] Preferably, in the step S5, when zero-crossing detection is performed on the 30Hz signal, it further includes: performing zero-crossing detection on the variable phase signal of the extracted 30Hz envelope and the 30Hz reference phase signal, combining the DDM value, and accurately calculating the phase difference according to the position of the zero-crossing point and the DDM indication.

[0027] Preferably, the specific calculation of the phase difference is as follows:

[0028] S51, set the variable Xi (i = 1, 2, 3...) as the phase error value for each measurement and perform adjustment processing; the adjustment formula is expressed as:

[0029]

[0030] If 0° ≤ Xi ≤ 180°, then adjust Xi to Xi + 360°; if 180° < Xi ≤ 360°, then Xi remains unchanged.

[0031] S52, perform multiple averaging processes on the adjusted phase difference to determine the final phase difference; the confirmation formula is expressed as:

[0032]

[0033] Add up all the adjusted phase differences Xi to obtain a total value; calculate the average value Y of the sum as the preliminary estimated value of the phase difference; determine whether the average value Y is greater than 360°. If Y is greater than 360°, it indicates that an overflow may have occurred during the adjustment process. At this time, the final phase difference Z = Y - 360°; if Y is less than or equal to 360°, then the final phase difference Z = Y.

[0034] One or more technical solutions provided in this application have at least the following technical effects or advantages:

[0035] By calculating the DDM modulation degree difference through the normalization method, combining the reception and processing of the signals transmitted by the VOR navigation station, extracting the key 30Hz signal, and using the DDM and this signal to perform zero-crossing detection to calculate the phase difference, the deviation degree of the aircraft's VOR azimuth relative to the VOR navigation station can be accurately determined, providing reliable technical support for calibrating the flight direction of the aircraft, and effectively improving the navigation accuracy and flight safety.

[0036] The calculation accuracy of the phase difference is improved through multiple measurements and smoothing processing, and the calculation error problem caused by the phase difference swinging near 0° is effectively solved. The entire processing flow is rigorous and reliable, which can avoid the calculation errors caused by various factors, improve the stability and reliability of the phase difference calculation, and is simple and convenient to implement. It is suitable for various occasions that require accurate calculation of the phase difference and has broad application value and prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The figure is a flow chart of an instrument landing navigation method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, the present application will be described more comprehensively below with reference to the relevant drawings; the drawings show preferred embodiments of the present invention, but the present invention can be implemented in many different forms and is not limited to the embodiments described herein; on the contrary, the purpose of providing these embodiments is to enable a more thorough and comprehensive understanding of the disclosed content of the present invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains; the terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0040] Example 1: Figure 1 The figure is a flow chart of an instrument landing navigation method according to an embodiment of the present invention.

[0041] like Figure 1 As shown, an instrument landing navigation method includes the following steps:

[0042] S1, construct an ILS instrument landing system including a localizer LOC and a glide path beacon GS.

[0043] Specifically, the ILS system category (Category I, II, or III) and the required navigation accuracy and reliability must be determined based on the airport's specific conditions and aircraft landing requirements. Next, localizer (LOC) and glide path beacon (GS) equipment that meet International Civil Aviation Organization (ICAO) standards must be selected. The installation locations of the localizer and glide path beacons are carefully designed based on the runway's direction, length, and surrounding environment to ensure that the signal coverage and accuracy meet the required standards.

[0044] A localizer antenna is installed approximately 200 to 900 meters from the runway end, extending from the runway centerline. Connect the localizer transmitter to the antenna to ensure proper signal transmission. The localizer (LOC) provides azimuth guidance, specifically the aircraft's horizontal position relative to the runway centerline. It emits a 90Hz left-side AM beam and a 150Hz right-side AM beam.

[0045] A glide path beacon antenna is installed on one side of the runway, 120 to 200 meters from the runway centerline and approximately 300 to 450 meters from the runway threshold. A glide path beacon transmitter is connected to the antenna to ensure proper signal transmission. The glide path beacon (GS) provides downline guidance, or the aircraft's vertical position relative to the desired glide path. It transmits a 90Hz upper audio AM beam and a 150Hz lower audio AM beam. The modulation difference between the two audio beams varies depending on the field strength of the upper and lower beams.

[0046] When a helicopter approaches an airport, it first intercepts the beam signal emitted by the ILS localizer. Based on the localizer's LOC (Local Observation Code) information about the helicopter's deviation from the runway center, the combined receiving equipment transmits this information to the flight control system, controlling the helicopter to steer toward the runway centerline.

[0047] Specifically, when the helicopter is to the left of the runway centerline, the heading deviation indicator needle will deviate to the right; otherwise, it will deviate to the left. When the helicopter is above the glide path, the glide path deviation indicator needle will deviate downward; otherwise, it will deviate upward. When the helicopter is simultaneously on the runway centerline (localizer) and the glide path, both the glide path deviation indicator and the heading deviation indicator will return to zero.

[0048] In addition, when the signal is unreliable or the equipment fails, the corresponding glide and heading warning indicators will display a warning; otherwise, no warning indication will appear. The pilot can control the helicopter according to the display of the indicator to safely approach and land along the optimal route.

[0049] S2, in the ILS instrument landing system, the DDM modulation error is calculated using the normalization method.

[0050] The DDM modulation error is the ratio of the amplitude difference between the 90Hz and 150Hz signals to the sum of the modulation indices. The sum of the modulation indices is a known value determined by system design and represents the percentage of the sum of the 90Hz and 150Hz signal amplitudes relative to a certain reference.

[0051] Specifically, the normalization method is used to calculate the DDM modulation error, including:

[0052] S21, receiving and demodulating signals: receiving audio frequency modulation signals transmitted by the localizer LOC and the glide path beacon GS, and demodulating the received signals to extract 90 Hz and 150 Hz audio signals.

[0053] S22, setting modulation: On the heading channel and the glide path, the system will set a specific modulation (eg, the heading channel may be 40%, the glide path may be 80%, the specific value is determined by the system).

[0054] S23, extracting amplitude information: 90Hz and 150Hz modulation signals are added to the carrier signal, forming modulated signals containing two different frequency components. The receiver extracts the amplitude information of these modulated signals through demodulation. Since the amplitude is proportional to the modulation index, the modulation index can be inferred by measuring the amplitude.

[0055] S24, calculate the DDM modulation difference: In an ILS system, the modulation sum is fixed for a specific channel (such as heading or glideslope). Measure the amplitudes of the 90Hz and 150Hz signals and calculate the DDM modulation difference between the two signals.

[0056] S25, apply DDM value: the normalized DDM modulation deviation calculation formula is:

[0057]

[0058] Where A and B are the amplitudes of the 90Hz and 150Hz signals, respectively; AB is the amplitude difference between the 90Hz and 150Hz signals; and A+B is the sum of the modulation intensities of the 90Hz and 150Hz signals. The calculated DDM value is used to calculate the modulation intensities of the glide path and heading path of the ILS system to provide navigation information.

[0059] S3 receives the intermediate frequency 70MHz signal transmitted by the VOR navigation station and performs digitization and low-pass filtering.

[0060] Specifically, S3 includes:

[0061] S31, receive VOR navigation station signal: receive the intermediate frequency 70MHz signal transmitted from the VOR navigation station. The signal transmitted by the VOR navigation station is used to determine the aircraft's position relative to the navigation station.

[0062] S32, Analog Signal Sampling: The received VOR navigation station signal is sampled by an A / D converter, converting the continuous analog signal into a discrete digital signal. The sampling rate must meet the Nyquist sampling theorem. In practical applications, the sampling rate is typically set significantly higher than twice the highest signal frequency to ensure anti-aliasing filtering and subsequent processing. For a 70MHz signal, the sampling rate is typically set significantly higher than 140MHz.

[0063] S33, Digital Signal Low-Pass Filtering: The sampled digital signal is processed through a low-pass filter. This filter removes high-frequency components while retaining useful information at frequencies such as 9960 Hz. It attenuates approximately 50 dB at 70 MHz to suppress high-frequency noise, and no more than 1 dB at 9960 Hz to ensure signal quality. The filter can be designed using either an FIR or IIR algorithm, with coefficients determined based on the frequency response requirements.

[0064] S4, performing amplitude modulation and frequency modulation demodulation on the low-pass filtered signal to extract the 30 Hz navigation signal.

[0065] Specifically, the low-pass filtered signal is demodulated to extract a variable phase signal with a 30 Hz envelope and a 30 Hz reference phase signal.

[0066] Among them, the variable phase signal of the 30Hz envelope is extracted as follows: the amplitude of the filtered signal is limited, the signal amplitude is controlled within a predetermined range by a limiter, and then filtered by a low-pass filter with a cutoff frequency higher than 30Hz but much lower than other high-frequency components to obtain a 30Hz envelope signal. The prior art can be referred to and will not be described in detail in this article.

[0067] The 30Hz reference phase signal is extracted by low-pass filtering the signal after frequency discrimination processing to remove high-frequency noise, with a cutoff frequency slightly higher than 30Hz to ensure the quality of the reference phase signal. This article will not elaborate on this topic and can refer to the existing technology.

[0068] S5, using DDM and the extracted 30 Hz signal to perform zero-crossing detection, and then calculate the phase difference.

[0069] Specifically, the extracted 30Hz envelope variable phase signal and the 30Hz reference phase signal are subjected to zero-crossing detection. Combined with the DDM value, the phase difference is accurately calculated based on the zero-crossing location and DDM indication. The DDM value serves as a reference or weight for adjusting or calibrating the phase difference calculation.

[0070] Zero-crossing detection refers to detecting the moment when the signal crosses zero, either from positive to negative or from negative to positive. If the 30Hz signal doesn't cross zero again within the specified time, the system returns to resample the signal. If the 30Hz signal crosses zero again, the system stops counting and records the timing result. Specifically, the timer starts when a zero crossing is detected, and the time interval between the two zero crossings is recorded. The phase difference reflects the degree of deviation of the aircraft's bearing relative to the VOR navigation station.

[0071] S6 determines the degree of deviation of the aircraft's VOR azimuth relative to the VOR navigation station through the phase difference, and calibrates the aircraft's flight direction accordingly.

[0072] Specifically, the calculated phase difference is used in combination with the DDM value to determine the azimuth deviation degree of the aircraft relative to the VOR navigation station. According to the deviation degree, the flight direction of the aircraft is calibrated to ensure that the aircraft flies along a predetermined path.

[0073] The technical solutions in the embodiments of the present application at least have the following technical effects or advantages:

[0074] By calculating the DDM modulation difference through the normalization method, combining with receiving and processing the signals transmitted by the VOR navigation station, extracting the key 30Hz signal, and using the DDM and this signal for zero-crossing detection to calculate the phase difference, the deviation degree of the aircraft's VOR azimuth relative to the VOR navigation station is accurately determined, providing reliable technical support for calibrating the flight direction of the aircraft, and effectively improving the accuracy of navigation and flight safety.

[0075] Embodiment 2: Calculate the DDM modulation difference through the normalization method, combine with VOR navigation signal processing to extract the 30Hz signal, use zero-crossing detection to calculate the phase difference, accurately determine the azimuth deviation degree of the aircraft, provide reliable support for flight direction calibration, and improve the accuracy of navigation and flight safety. Due to crystal oscillator drift, interference noise, and system errors brought during the processing, the detection of the standard zero-crossing point is not uniquely determined, and the above-mentioned interference will cause delay jitter to the entire waveform. Therefore, the calculation of the phase difference cannot be obtained through a single solution, but needs to be subjected to multiple averaging and smoothing processes. However, the problem caused by multiple averaging is that when the two phases coincide or are close to coinciding, the phase difference swings around 0°, and thus the angle will jump between a very small value greater than 0° and a very large value close to 360°. If directly adding them and averaging, the obtained result will be a wrong phase difference.

[0076] In some embodiments, when calculating the phase difference, step S5 further includes:

[0077] S51, set the variable Xi (i = 1, 2, 3...) as the phase error value measured each time, and perform adjustment processing.

[0078] Specifically, the following adjustment processing is performed on each measured phase error Xi:

[0079] If 0° ≤ Xi ≤ 180°, then adjust Xi to Xi + 360° (to ensure that all phase error values are within a unified range in subsequent processing and avoid the influence of jumps near 0°); if 180° < Xi ≤ 360°, then Xi remains unchanged to ensure that all phase error values are within a unified range.

[0080] The adjustment formula is expressed as: [[ID=2x]]

[0081] [[ID=2x]] [[ID=2x]]

[0082] It should be noted that during the multiple averaging processes, special attention should be paid to the problem of the phase difference swinging around 0° when the two phases coincide or are close to coincide, and the possible jump of the angle value between a small value greater than 0° and a large value close to 360°.

[0083] S52: Perform multiple averaging processes on the adjusted phase difference to determine a final phase difference.

[0084] Specifically, all adjusted phase differences Xi are summed to obtain a total value, and then the average value Y of the sum is calculated as a preliminary estimate of the phase difference; then, it is determined whether the average value Y is greater than 360°, as expressed by the formula:

[0085]

[0086] If Y is greater than 360°, it indicates that overflow may have occurred during the adjustment process. In this case, the final phase difference Z = Y-360°. If Y is less than or equal to 360°, the final phase difference Z = Y to ensure that the final phase difference is between 0° and 360°.

[0087] The technical solutions in the above embodiments of the present application have at least the following technical effects or advantages:

[0088] The calculation accuracy of the phase difference is improved through multiple measurements and smoothing processing, and the calculation error problem caused by the phase difference swinging near 0° is effectively solved. The entire processing flow is rigorous and reliable, which can avoid the calculation errors caused by various factors, improve the stability and reliability of the phase difference calculation, and is simple and convenient to implement. It is suitable for various occasions that require accurate calculation of the phase difference and has broad application value and prospects.

[0089] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An instrument landing navigation method, characterized in that: include: S1, constructing an ILS instrument landing system including a localizer LOC and a glide path beacon GS; S2, in the ILS instrument landing system, the DDM modulation error is calculated using the normalization method; S3 receives the 70MHz intermediate frequency signal transmitted by the VOR navigation station and performs digitization and low-pass filtering; S4, performing AM and FM demodulation on the low-pass filtered signal to extract the 30 Hz navigation signal; S5, using DDM and the extracted 30 Hz signal to perform zero-crossing detection and then calculate the phase difference; S6 determines the degree of deviation of the aircraft's VOR azimuth relative to the VOR navigation station through the phase difference, and calibrates the aircraft's flight direction accordingly.

2. The instrument landing navigation method according to claim 1, wherein: The calculation of the DDM modulation error using the normalization method specifically includes: S21, receiving the audio frequency modulation signals transmitted by the localizer LOC and the glide path beacon GS, and demodulating the received signals to extract the 90 Hz and 150 Hz audio signals; S22, set the modulation depth on the localizer and glide paths; At S23, the 90 Hz and 150 Hz modulation signals are added to the carrier signal, respectively, to form a modulation signal containing two different frequency components; S34, measure the amplitude of the 90Hz and 150Hz signals and calculate the DDM modulation difference between the two signals; S35, normalized DDM modulation error.

3. The instrument landing navigation method according to claim 2, wherein: In S35, the DDM modulation index deviation includes: the normalized DDM modulation index deviation calculation formula is: Where A and B are the amplitudes of the 90Hz and 150Hz signals, respectively; AB is the amplitude difference between the 90Hz and 150Hz signals; A+B is the sum of the modulation depths of the 90Hz and 150Hz signals; and DDM is the modulation depth difference calculation for the glide path and heading path of the ILS system.

4. The instrument landing navigation method according to claim 1, wherein: The S3 specifically includes: S31, receives the 70MHz intermediate frequency signal transmitted from the VOR navigation station; S32, the received VOR navigation station signal is sampled by an A / D converter, and the continuous analog signal is converted into a discrete digital signal; S33, the sampled digital signal is processed by a low-pass filter to filter out high-frequency components and retain useful information at 9960 Hz.

5. The instrument landing navigation method according to claim 1, wherein: The S4 specifically includes: performing demodulation processing on the low-pass filtered signal to extract a variable phase signal with a 30 Hz envelope and a 30 Hz reference phase signal.

6. The instrument landing navigation method according to claim 5, characterized in that: include: The variable phase signal with a 30Hz envelope is extracted by limiting the amplitude of the filtered signal, controlling the signal amplitude within a predetermined range through a limiter, and then filtering it through a low-pass filter with a cutoff frequency higher than 30Hz to obtain a 30Hz envelope signal. The 30Hz reference phase signal is extracted by low-pass filtering the signal after frequency discrimination processing to filter out high-frequency noise, with a cutoff frequency higher than 30Hz.

7. The instrument landing navigation method according to claim 1, wherein: In the S5, the 30 Hz signal is subjected to zero-crossing detection, which also includes: performing zero-crossing detection on the variable phase signal of the extracted 30 Hz envelope and the 30 Hz reference phase signal, combining the DDM value, and accurately calculating the phase difference according to the position of the zero-crossing point and the DDM indication.

8. The instrument landing navigation method according to claim 7, wherein: The phase difference is calculated as follows: S51. Set the variable Xi (i = 1, 2, 3...) as the phase error value of each measurement and perform adjustment processing. The adjustment formula is expressed as: If 0° ≤ Xi ≤ 180°, then adjust Xi to Xi + 360°; if 180° < Xi ≤ 360°, then Xi remains unchanged; S52. Perform multiple averaging processes on the adjusted phase difference to determine the final phase difference; The confirmation formula is expressed as: Add up all the adjusted phase differences Xi to obtain the total value; calculate the average value Y after summation as the preliminary estimated value of the phase difference; determine whether the average value Y is greater than 360°. If Y is greater than 360°, it means that an overflow may have occurred during the adjustment process. At this time, the final phase difference Z = Y - 360°; if Y is less than or equal to 360°, then the final phase difference Z = Y.

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