Baseband signal digital processing method, device, equipment and instrument landing system

Abstract

The invention discloses a baseband signal digital processing method, a baseband signal digital processing device, baseband signal digital processing equipment and an instrument landing system, and relates to the technical field of signal processing, and the technical scheme is characterized in that AM demodulation is carried out on an ILS baseband signal to obtain an envelope signal; performing windowing processing on the envelope signal to obtain a windowed envelope signal; performing discrete Fourier transform on the windowed envelope signal to obtain a signal spectrum; carrying out statistics on DFT frequency points in a frequency spectrum main lobe corresponding to the direct current signal, the first frequency signal and the second frequency signal in the signal frequency spectrum so as to calculate the amplitude of the corresponding signal; and calculating a modulation depth difference according to the amplitudes of the DC signal, the first frequency signal and the second frequency signal. According to the method, the power of the two frequency components of the ILS baseband signal can be estimated more accurately, the tolerance to frequency deviation is improved, and the DFT frequency point does not need to accurately fall at 90Hz and 150Hz.

Description

Technical Field

[0001] The present invention relates to the field of signal processing technology, and more specifically, to a baseband signal digital processing method, device, equipment and an instrument landing system. Background Art

[0002] The Instrument Landing System (ILS), also known as the blind landing system, is the most widely used navigation system in the airport terminal area for guiding aircraft to conduct precision approaches and landings. Its principle is to construct a virtual path from the runway to the air by two horizontal and vertical radio signals emitted from the ground (i.e., the localizer LOC and the glide path beacon GS), thereby achieving three-dimensional guidance for the aircraft. The onboard ILS equipment on the aircraft measures the two radio signals to obtain the deviation between the aircraft and the virtual path, and then controls the aircraft to fly in the correct direction to the runway and smoothly descend in altitude, and finally land safely.

[0003] The airborne ILS equipment receives the LOC signal and the GS signal, and calculates the modulation depth difference (DDM) between the 150Hz and 90Hz modulation signals, and then outputs it to the automatic flight system to guide the aircraft. However, the current airborne ILS is mainly based on analog circuits. There are also some digital processing methods recorded in the prior art, such as: (1) Digital filtering method, which directly digitizes the analog circuit. The disadvantages are large processing delay (the signal needs to pass through a filter with a very long coefficient), large system resource consumption, and large calculation error; (2) DFT analysis method, which only considers the three DFT frequency points corresponding to DC, 90Hz and 150Hz in calculating DDM. The disadvantage is that the DFT frequency points must fall accurately at 90Hz and 150Hz, and there are requirements for the setting of sampling rate and DFT points, and the design is not flexible enough; when there is a frequency deviation between the 90Hz and 150Hz audio signals, the estimated DDM error is large.

[0004] Therefore, how to research and design a baseband signal digital processing method, device, equipment and navigation system that can overcome the above-mentioned defects is a problem that we urgently need to solve. Summary of the invention

[0005] To address the deficiencies in the prior art, the present invention aims to provide a baseband signal digital processing method, apparatus, equipment and instrument landing system, which can more accurately estimate the power of the two frequency components of the ILS baseband signal and improve the tolerance to frequency deviation. At the same time, there are no particularly strict requirements on the setting of the sampling rate and the number of DFT points, such as not requiring the DFT frequency points to fall exactly at 90 Hz and 150 Hz.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] In a first aspect, a baseband signal digital processing method is provided, comprising the following steps:

[0008] Perform AM demodulation on the ILS baseband signal to obtain an envelope signal;

[0009] Performing windowing processing on the envelope signal to obtain a windowed envelope signal;

[0010] Perform discrete Fourier transform on the windowed envelope signal to obtain the signal spectrum;

[0011] Performing statistics on DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal, and the second frequency signal in the signal spectrum to calculate the amplitude of the corresponding signal;

[0012] The modulation depth difference is calculated according to the amplitudes of the DC signal, the first frequency signal and the second frequency signal.

[0013] Furthermore, the ILS baseband signal includes two digital baseband signals, an in-phase component I and a quadrature component Q.

[0014] Furthermore, the envelope signal is windowed using a Hamming window or a Hamming window.

[0015] Furthermore, the process of performing statistics on the DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal, and the second frequency signal in the signal spectrum to calculate the amplitude of the corresponding signal is specifically as follows:

[0016] The energy of the corresponding signal in a frame of signal is calculated based on the sum of the DFT frequency point energies in the main lobe of the spectrum corresponding to a single signal;

[0017] The amplitude of the corresponding signal is determined according to the ratio of the energy of the corresponding signal in a frame signal to the frame length, and the amplitude of the corresponding signal is positively correlated with the corresponding ratio.

[0018] Furthermore, if the single signal is a DC signal, the energy of the DC signal in one frame of signal is calculated according to the Parsval theorem;

[0019] If the single signal is a first frequency signal or a second frequency signal, the energy of the first frequency signal and the second frequency signal in one frame of the signal is calculated according to the conjugate symmetry characteristic of the real signal spectrum.

[0020] Furthermore, the calculation process of the modulation depth difference is specifically as follows:

[0021] determining an amplitude difference between the second frequency signal and the first frequency signal;

[0022] The modulation depth difference is determined as the ratio of the amplitude difference to the amplitude of the DC signal.

[0023] Furthermore, the method also includes:

[0024] High-pass filter the envelope signal and output Morse code audio.

[0025] In a second aspect, a baseband signal digital processing device is provided, comprising:

[0026] A signal demodulation unit, used for performing AM demodulation on the ILS baseband signal to obtain an envelope signal;

[0027] A windowing processing unit, used for performing windowing processing on the envelope signal to obtain a windowed envelope signal;

[0028] A signal conversion unit, used for performing discrete Fourier transform on the windowed envelope signal to obtain a signal spectrum;

[0029] An amplitude calculation unit, used for performing statistics on DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal and the second frequency signal in the signal spectrum, so as to calculate the amplitude of the corresponding signal;

[0030] The modulation calculation unit is used to calculate the modulation depth difference according to the amplitudes of the DC signal, the first frequency signal and the second frequency signal.

[0031] In a third aspect, an airborne ILS device is provided, comprising:

[0032] The pre-processing module is used to perform frequency selection, amplification, orthogonal down-conversion, filtering and digital sampling on the received LOC signal and GS signal to obtain the ILS baseband signal;

[0033] A digital processing module, used to execute a baseband signal digital processing method as described in any one of the first aspects.

[0034] In a fourth aspect, an instrument landing system is provided, comprising:

[0035] Localizer ground transmitter, used to transmit LOC signal;

[0036] Glide beacon ground transmitter, used to transmit GS signal;

[0037] The airborne ILS device is used to obtain an ILS baseband signal after frequency selection, amplification, orthogonal down-conversion, filtering and digital sampling of the received LOC signal and GS signal, and execute a baseband signal digital processing method as described in any one of the first aspects.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. A baseband signal digital processing method provided by the present invention can estimate the power of two frequency components of the ILS baseband signal more accurately, improve the tolerance to frequency deviation, and at the same time, there is no particularly strict requirement for the setting of the sampling rate and the number of DFT points, such as not requiring the DFT frequency points to fall exactly at 90 Hz and 150 Hz;

[0040] 2. The present invention adopts the Hamming window to reduce the leakage of signal energy by the rectangular window side lobes, while the widened main lobe can utilize more DFT frequency points for energy estimation, thereby improving the calculation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0042] Figure 1 is a flow chart of Embodiment 1 of the present invention;

[0043] Figure 2 is a schematic diagram of an envelope signal in Embodiment 1 of the present invention;

[0044] Figure 3 is the spectrum of the windowed envelope signal in Embodiment 1 of the present invention;

[0045] Figure 4 is a block diagram of a device in Embodiment 2 of the present invention;

[0046] Figure 5 is a working principle diagram of an airborne ILS device in Embodiment 2 of the present invention;

[0047] Figure 6 It is a system block diagram of the navigation system in Example 2 of the present invention. DETAILED DESCRIPTION

[0048] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0049] The localizer ground transmitter emits two beams of VHF amplitude modulated waves with strong directivity, with a frequency range of 108.00-111.95MHz and a channel spacing of 50kHz. For example, the beam on the left side of the runway centerline is a 90Hz single-frequency signal amplitude modulated wave, and the beam on the right side is a 150Hz single-frequency signal amplitude modulated wave. When the aircraft is on the left side of the runway centerline, the 90Hz modulated signal is dominant in the received signal; when the aircraft is on the right side of the runway centerline, the 150Hz modulated signal is dominant in the received signal.

[0050] The ground transmitter of the glide path beacon emits two beams of UHF amplitude modulated waves with strong directivity, with a frequency range of 329.15 to 335.00 MHz and a channel spacing of 150 kHz. For example, the beam above the glide path is a 90 Hz single-frequency signal amplitude modulated wave, and the beam below is a 150 Hz single-frequency signal amplitude modulated wave. When the aircraft is at the top of the glide path, the 90 Hz modulation signal is dominant in the received signal; when the aircraft is at the bottom of the glide path, the 150 Hz modulation signal is dominant in the received signal.

[0051] Embodiment 1: A method for digitally processing a baseband signal, such as Figure 1 As shown, the following steps are included:

[0052] S1: AM demodulate the ILS baseband signal to obtain the envelope signal;

[0053] S2: Perform windowing processing on the envelope signal to obtain a windowed envelope signal;

[0054] S3: Perform discrete Fourier transform on the windowed envelope signal to obtain a signal spectrum;

[0055] S4: performing statistics on DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal and the second frequency signal in the signal spectrum to calculate the amplitude of the corresponding signal;

[0056] S5: Calculate the modulation depth difference according to the amplitudes of the DC signal, the first frequency signal and the second frequency signal.

[0057] In step S1, the ILS baseband signal includes two digital baseband signals, an in-phase component I and a quadrature component Q.

[0058] For example, the input ILS baseband signal sampling rate R s , divided into the in-phase component s I [n] and the orthogonal component s Q [n] two channels. AM demodulation is performed to obtain the envelope signal s[n]. AM demodulation can be expressed as;

[0059]

[0060] like Figure 2 As shown in the figure, an example of envelope signal is given. Taking the first frequency signal of 90Hz and the second frequency signal of 150Hz as an example, the time domain s(t) expression is

[0061]

[0062] Among them, f 90 (θ), f 150(θ) are the amplitudes of the antenna radiation field of the 90Hz and 150Hz signals at an angle θ away from the runway centerline, Ω 90 ,Ω 150 are 90Hz and 150Hz angular frequencies respectively, m is the AM modulation index, U m For receiving gain.

[0063] In step S2, the envelope signal may be windowed using a Hamming window or may be windowed using a Hamming window.

[0064] For example, windowing an envelope signal with a frame length of N gives:

[0065] x[n]=s[n]×w[n], n=0,1,…,N;

[0066] In this embodiment, the Hamming window is used, and its expression is:

[0067]

[0068] The use of the Hamming window can reduce the leakage of signal energy from the rectangular window side lobes, while the widened main lobe can utilize more DFT frequency points for energy estimation, thereby improving the calculation accuracy.

[0069] In step S3, a discrete Fourier transform (DFT) is performed on the windowed frame signal to obtain its spectrum:

[0070]

[0071] Among them, the frequency corresponding to the kth DFT frequency point is (k <N / 2)。

[0072] make ( represents the rounding down of x), then the 90Hz frequency is located at the kth 90Hz and kth 90Hz +1 DFT frequency point, 150Hz frequency is located at the kth 150Hz and kth 150Hz +1 DFT frequency point. The characteristic of the Hamming window function spectrum is that the main lobe width between the two zero points is Therefore, there are at most 4 DFT frequency points in the main lobe of the spectrum of the windowed sinusoidal signal. DFT can be implemented by a fast Fourier transform algorithm (FFT).

[0073] It should be noted that the aliasing of the 90Hz and 150Hz spectrum main lobes should be avoided, so it is necessary to maintain That is, the length of each frame N ≥ R s / 15Hz.

[0074] In step S4, statistics are performed on the DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal and the second frequency signal in the signal spectrum to calculate the amplitude of the corresponding signal. The specific process is: the energy of the corresponding signal in a frame signal is calculated based on the sum of the DFT frequency point energies in the main lobe of the spectrum corresponding to a single signal; the amplitude of the corresponding signal is determined based on the ratio of the energy of the corresponding signal in a frame signal to the frame length, and the amplitude of the corresponding signal is positively correlated with the corresponding ratio.

[0075] The spectrum of the windowed envelope signal is as follows: Figure 3 As shown in the figure, the dotted line is the continuous spectrum of the envelope signal, and the circle is the DFT discrete spectrum of the envelope signal. Thanks to the extremely low sidelobe energy leakage of the Hamming window function, it can be approximately considered that the energy spectrum of the signal is almost entirely concentrated in the main lobe, and the contribution of the sidelobe energy to the total signal energy can be ignored.

[0076] Therefore, according to the Pasval theorem, the DC signal energy E in a frame signal DC for:

[0077] E DC =|X[0]| 2 +|X[1]| 2 +|X[N-1]| 2 ;

[0078] Wherein, X[N-1] represents the N-1th component of the spectrum.

[0079] The energy of a 90Hz (or 150Hz) sinusoidal signal can be roughly considered to be concentrated in the four DFT frequency points near 90Hz (or 150Hz), namely, k 90Hz -1, k 90Hz , k 90Hz +1 and k 90Hz +2(or k 150Hz -1, k 150Hz , k 150Hz +1 and k 150Hz +2).

[0080] According to the conjugate symmetry characteristics of the real signal spectrum, the energies of the 90Hz and 150Hz sinusoidal signals are:

[0081]

[0082] Then calculate the DC signal amplitude A DC for: And calculate the amplitude A of the 90Hz and 150Hz sinusoidal signals 90H z、A 150H z are: and

[0083] In step S5, the calculation process of the modulation depth difference is specifically as follows: determining the amplitude difference between the second frequency signal and the first frequency signal; and determining the modulation depth difference by the ratio of the amplitude difference to the amplitude of the DC signal.

[0084] Specifically, the calculation formula of the modulation depth difference (DDM) is as follows:

[0085]

[0086] In addition, there is also 1020Hz Morse code recognition audio in the LOC and GS baseband signals, which needs to be separated and output to the airborne audio system. To this end, the present invention also performs high-pass filtering on the envelope signal to output the Morse code audio.

[0087] Embodiment 2: A baseband signal digital processing device, the device is used to implement a baseband signal digital processing method as described in Embodiment 1, such as Figure 4 As shown, it includes a signal demodulation unit, a windowing processing unit, a signal conversion unit, an amplitude calculation unit and a modulation calculation unit.

[0088] Among them, the signal demodulation unit is used to perform AM demodulation on the ILS baseband signal to obtain an envelope signal; the windowing processing unit is used to perform windowing processing on the envelope signal to obtain a windowed envelope signal; the signal conversion unit is used to perform discrete Fourier transform on the windowed envelope signal to obtain a signal spectrum; the amplitude calculation unit is used to count the DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal and the second frequency signal in the signal spectrum to calculate the amplitude of the corresponding signal; the modulation calculation unit is used to calculate the modulation depth difference according to the amplitude of the DC signal, the first frequency signal and the second frequency signal.

[0089] The present invention also describes an airborne ILS device, comprising a preprocessing module and a digital processing module. The preprocessing module is used to select, amplify, orthogonally down-convert, filter and digitally sample the received LOC signal and GS signal to obtain an ILS baseband signal; the digital processing module is used to execute a baseband signal digital processing method as described in any one of the first aspects.

[0090] like Figure 5 As shown in the figure, the airborne ILS equipment performs frequency selection, amplification, orthogonal down-conversion, filtering and digital sampling on the received LOC and GS signals to obtain two digital baseband signals, the in-phase component (I) and the quadrature component (Q), which are processed and output as DDM. The difference between the LOC and GS channels mainly lies in the RF analog and digital front-end, including frequency selection, amplification, orthogonal down-conversion and filtering. If the data rate of the output I / Q baseband signals is the same, the functions of the digital baseband processing part are also the same and can be reused.

[0091] The present invention also records an instrument landing system, such as Figure 6 As shown, it includes a localizer ground transmitter, a glide path beacon ground transmitter and airborne ILS equipment.

[0092] Among them, the localizer ground transmitter is used to transmit the LOC signal; the glide path beacon ground transmitter is used to transmit the GS signal; the airborne ILS equipment is used to select the frequency, amplify, orthogonally down-convert, filter and digitally sample the received LOC signal and GS signal to obtain the ILS baseband signal, and execute a baseband signal digital processing method as described in Example 1.

[0093] Working principle: The present invention can estimate the power of the two frequency components of the ILS baseband signal more accurately, improve the tolerance to frequency deviation, and at the same time, there are no particularly strict requirements for the setting of the sampling rate and the number of DFT points, such as not requiring the DFT frequency points to fall accurately at 90Hz and 150Hz; in addition, the present invention uses a Hamming window to reduce the leakage of signal energy by the side lobes of the rectangular window, and at the same time, the widened main lobe can use more DFT frequency points for energy estimation, thereby improving the calculation accuracy.

[0094] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0095] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0096] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0097] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0098] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A baseband signal digital processing method, characterized in that: The following steps are involved: Perform AM demodulation on the ILS baseband signal to obtain an envelope signal; Performing windowing processing on the envelope signal to obtain a windowed envelope signal; Perform discrete Fourier transform on the windowed envelope signal to obtain the signal spectrum; Performing statistics on DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal, and the second frequency signal in the signal spectrum to calculate the amplitude of the corresponding signal; The modulation depth difference is calculated according to the amplitudes of the DC signal, the first frequency signal and the second frequency signal.

2. A baseband signal digital processing method according to claim 1, characterized in that: The ILS baseband signal includes two digital baseband signals: an in-phase component I and a quadrature component Q.

3. The method for digitally processing a baseband signal according to claim 1, wherein: The envelope signal is windowed using a Hamming window or a Hamming window.

4. The method for digitally processing a baseband signal according to claim 1, wherein: The process of performing statistics on the DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal and the second frequency signal in the signal spectrum to calculate the amplitude of the corresponding signal is specifically as follows: The energy of the corresponding signal in a frame of signal is calculated based on the sum of the DFT frequency point energies in the main lobe of the spectrum corresponding to a single signal; The amplitude of the corresponding signal is determined according to the ratio of the energy of the corresponding signal in a frame signal to the frame length, and the amplitude of the corresponding signal is positively correlated with the corresponding ratio.

5. A baseband signal digital processing method according to claim 4, characterized in that: If the single signal is a DC signal, the energy of the DC signal in one frame of signal is calculated according to the Pasval theorem; If the single signal is a first frequency signal or a second frequency signal, the energy of the first frequency signal and the second frequency signal in one frame of the signal is calculated according to the conjugate symmetry characteristic of the real signal spectrum.

6. The method for digitally processing a baseband signal according to claim 1, characterized in that: The calculation process of the modulation depth difference is specifically as follows: determining an amplitude difference between the second frequency signal and the first frequency signal; The modulation depth difference is determined as the ratio of the amplitude difference to the amplitude of the DC signal.

7. The method for digitally processing a baseband signal according to claim 1, wherein: The method further includes: High-pass filter the envelope signal and output Morse code audio.

8. A baseband signal digital processing device, characterized in that: include: A signal demodulation unit, used for performing AM demodulation on the ILS baseband signal to obtain an envelope signal; A windowing processing unit, used for performing windowing processing on the envelope signal to obtain a windowed envelope signal; A signal conversion unit, used for performing discrete Fourier transform on the windowed envelope signal to obtain a signal spectrum; An amplitude calculation unit, used for performing statistics on DFT frequency points in the main lobe of the spectrum corresponding to the DC signal, the first frequency signal and the second frequency signal in the signal spectrum, so as to calculate the amplitude of the corresponding signal; The modulation calculation unit is used to calculate the modulation depth difference according to the amplitudes of the DC signal, the first frequency signal and the second frequency signal.

9. An airborne ILS device, characterized in that: include: The pre-processing module is used to perform frequency selection, amplification, orthogonal down-conversion, filtering and digital sampling on the received LOC signal and GS signal to obtain the ILS baseband signal; A digital processing module, used to execute a baseband signal digital processing method as described in any one of claims 1-7.

10. An instrument landing system, characterized in that: include: Localizer ground transmitter, used to transmit LOC signal; Glide beacon ground transmitter, used to transmit GS signal; The airborne ILS device is used to obtain an ILS baseband signal after frequency selection, amplification, orthogonal down-conversion, filtering and digital sampling of the received LOC signal and GS signal, and execute a baseband signal digital processing method as described in any one of claims 1 to 7.

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