Dual-slope LFM CW altimeter with one-way broadcast communications

Abstract

The present invention proposes a dual-slope linear frequency modulation continuous wave altimeter with a one-way broadcast communication function, including a microprocessor, a transmitting component and a receiving component; the microprocessor controls two microwave modules to generate linear frequency modulation continuous waves with two different slopes respectively, and transmits them after combining; after the altimeter receives the ground echo signal, it multiplies the transmitting signal with the echo signal to obtain a beat signal, analyzes the beat signal spectrum, searches for two spectrum targets based on two spectrum peaks, calculates two altitude measurement values ​​based on the frequency and slope, and obtains the output altitude value through data processing. The ground receiver obtains the ground beat signal based on the local signal and the received signal, analyzes the ground beat signal spectrum to search for two spectrum targets, and determines the amplitudes of the two spectrum targets to resolve the binary data modulated by the altimeter. The present invention improves the reliability and anti-interference ability of the altimeter, and realizes a low-cost broadcast communication function.

Description

Technical Field

[0001] The invention belongs to the field of radio ranging, and in particular relates to a dual-slope linear frequency modulation continuous wave altimeter with a unidirectional broadcast communication function. Background Art

[0002] The linear frequency modulation continuous wave altimeter is a widely used device for measuring the height of the ground in aircraft. However, in complex flight environments, due to interference, complex terrain and other factors, the accuracy and stability of the altimeter need to be further improved. In addition, with the development of radio technology, spectrum resources are becoming increasingly scarce. How to maximize the use of radio altimeter spectrum is an urgent problem to be solved. Summary of the invention

[0003] In order to solve the above problems existing in the prior art, the present invention provides a dual-slope linear frequency modulation continuous wave altimeter with a unidirectional broadcast communication function, comprising a microprocessor, a transmitting component and a receiving component; the transmitting component comprises a first microwave module, a second microwave module, a combiner and a transmitting antenna; the receiving component comprises a receiving module and a receiving antenna;

[0004] The microprocessor controls the first microwave module to slope Generate a first linear frequency modulation continuous wave signal, control the second microwave module with a slope generating a second linear frequency modulated continuous wave signal, and ; and according to the binary data to be sent , setting the amplitude relationship between the first linear frequency modulation continuous wave signal and the second linear frequency modulation continuous wave signal, the amplitude relationship is: and , or: and ;

[0005] The combiner combines the first linear frequency modulated continuous wave signal and the second linear frequency modulated continuous wave signal into a transmission signal, and transmits the transmission signal to the ground through the transmission antenna, and at the same time transmits the transmission signal to the receiving module of the receiving component;

[0006] After the receiving antenna obtains the echo signal reflected by the ground, it transmits it to the receiving module, and the receiving module multiplies the echo signal with the transmission signal to obtain a beat signal;

[0007] The receiving module transmits the beat signal to the microprocessor, and the microprocessor calculates the target frequencies of the two peak targets in the spectrum of the beat signal as follows: and , and determine the target frequency , With slope , The corresponding relationship is that when the target frequency With slope Corresponding, target frequency With slope Correspondingly, according to the formula

[0008]

[0009] Calculate two height measurements and , c is the propagation speed of electromagnetic waves;

[0010] The microprocessor calculates the two height measurements and After data processing, the final height H is obtained.

[0011] Furthermore, the expression of the transmission signal is:

[0012]

[0013] in To transmit the signal, For the moment, is the modulation period, is the carrier frequency of the first microwave module, is the carrier frequency of the second microwave module, and the corresponding slope of the first microwave module , the second microwave module corresponds to the slope , is the modulation bandwidth of the first microwave module, is the modulation bandwidth of the second microwave module.

[0014] Furthermore, the expression of the echo signal is:

[0015]

[0016] in is the echo signal, the peak amplitudes of the echo signal are C and D respectively, and the amplitude of the echo signal is related to the amplitude of the transmitted signal; is the round-trip delay from transmitting the signal to receiving the echo signal.

[0017] Furthermore, the expression of the beat signal mix is:

[0018]

[0019] in and All are additional phases. is the reflection coefficient.

[0020] Furthermore, the process of the microprocessor acquiring the target frequencies of the two peak targets in the spectrum of the beat signal is as follows:

[0021] The microprocessor performs Fourier transform and Chirp-Z transform analysis on the beat signal in sequence: firstly, the beat signal is subjected to Fourier transform to find a rough target frequency range, and then Chip-Z transform is performed to obtain a refined spectrum of the beat signal; the target frequencies of the two peak targets obtained in the refined spectrum of the beat signal are respectively and .

[0022] Furthermore, the target frequency is determined , With slope , The corresponding process is:

[0023] According to the two target frequencies and The relationship between the size of the two carrier frequencies and The size relationship determines the target frequency , With carrier frequency , The corresponding relationship between , With slope , The corresponding relationship.

[0024] Furthermore, the microprocessor calculates the two height measurement values and The process of obtaining the final height H after data processing is:

[0025] Calculate the ratio of two target frequencies , and the corresponding ratio of the two slopes ;

[0026] like and If the error is less than the set threshold, the two target frequencies are considered correct and the two height measurement values ​​are taken. and The mean of is taken as the final height H;

[0027] Otherwise, it is considered that the target frequency search is wrong and the target frequency is searched again;

[0028] If multiple times in a row and If the errors of both exceed the set threshold, it is considered that the altimeter measurement is disturbed, and the difference between the two height measurement values ​​and the normal height of the historical measurement is calculated. If the difference between a certain height measurement value and the normal height of the historical measurement is less than the set threshold, the height measurement value is output as the final height H, otherwise the normal height of the historical measurement is output.

[0029] Furthermore, it also includes a ground receiver that realizes the one-way broadcast communication function; the ground receiver receives the transmission signal, multiplies it with the local signal to obtain a ground beat signal, analyzes the amplitude of two targets in the ground beat signal spectrum, and parses the data according to the target amplitude, and the parsing process is:

[0030] Perform Fourier transform on the ground beat signal and find two spectrum peaks and , and obtain the corresponding spectrum peak The signal amplitude and the corresponding spectrum peak The signal amplitude ;

[0031] According to the two spectrum peaks and The relationship between the size of the two carrier frequencies and The size relationship determines the spectrum peak , With carrier frequency , The corresponding relationship of and The corresponding relationship between the signal amplitude A and B; According to the relationship between the binary data set in the transmitted signal and the signal amplitude A and B, the signal amplitude is obtained and The corresponding binary data.

[0032] Beneficial effects:

[0033] The dual-slope linear frequency modulation continuous wave altimeter with a one-way broadcast communication function proposed in the present invention can obtain two altitude measurement values, which has many advantages over the traditional single-slope linear frequency modulation continuous wave altimeter. First, the altitude measurement value can be averaged to reduce the measurement error and improve the measurement accuracy; second, if the linear frequency modulation continuous wave frequency band of one slope is interfered and cannot provide the altitude measurement value, the linear frequency modulation continuous wave of the other slope can provide the measurement value, which improves the reliability and anti-interference ability of the system; third, since the beat signal frequency and the slope are in direct proportion, when analyzing the beat signal spectrum, the proportional relationship between the two slopes can be used to assist in finding the correct spectrum target, avoid searching for the wrong spectrum target, and further improve the stability and accuracy of the altimeter. Finally, the dual-slope linear frequency modulation continuous wave signal of the present invention represents different binary data through different transmission gains, and the ground receiver's data analysis process is also relatively simple. It only needs to judge the amplitude of the two spectrum targets to parse the modulated data, realizing a low-cost broadcast communication function. The present invention improves the accuracy and anti-interference capability of the linear frequency modulation continuous wave altimeter, can be used in scenarios such as automatic landing, automatic navigation, terrain matching, etc. of aircraft, and has good application effect.

[0034] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0036] Figure 1 A schematic diagram of a dual-slope linear frequency modulation continuous wave altimeter and a ground receiver with a one-way broadcast communication function provided by an embodiment of the present invention;

[0037] Figure 2 A schematic flow chart of a dual-slope linear frequency modulation continuous wave altimeter with a one-way broadcast communication function provided by an embodiment of the present invention;

[0038] Figure 3 This is a comparison chart between the beat signal FFT result and the CZT result;

[0039] Figure 4 The following is a comparison chart of the FFT results of the ground receiver's beat spectrum for different binary data. DETAILED DESCRIPTION

[0040] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0041] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0042] This embodiment proposes a dual-slope linear frequency modulation continuous wave altimeter with a one-way broadcast communication function, such as Figure 1 As shown, it includes a microprocessor, a transmitting component and a receiving component; the transmitting component includes a first microwave module, a second microwave module, a combiner and a transmitting antenna; the receiving component includes a receiving module and a receiving antenna.

[0043] According to the binary data to be sent, the microprocessor controls the first microwave module and the second microwave module to generate dual-slope linear frequency modulation continuous waves with different gains, which are then combined into a transmission signal through the combiner and transmitted to the ground by the transmitting antenna. At the same time, the transmission signal is also sent to the receiving module of the receiving component. The specific process is as follows:

[0044] The microprocessor controls the first microwave module and the second microwave module to respectively use different slopes. and Generate a linear frequency modulated continuous wave, and set the relationship between the transmit signal amplitude A of the first microwave module and the transmit signal amplitude B of the second microwave module according to the binary data data to be sent. The amplitude relationship is: and , or and ; For example, when data=1, A=2, B=1; when data=0, A=1, B=2; then the linear frequency modulation continuous wave generated by the two microwave modules is synthesized into a transmission signal through a combiner, that is, a dual-slope linear frequency modulation continuous wave, and its expression is:

[0045]

[0046] in, To transmit the signal, is the modulation period, which is 800ms in this embodiment. is the carrier frequency of the first microwave module, which is 4.3 GHz in this embodiment. is the carrier frequency of the second microwave module, which is 5.6 GHz in this embodiment, and the corresponding slope of the first microwave module is , the second microwave module corresponds to the slope , is the modulation bandwidth of the first microwave module, which is 150 MHz in this embodiment. is the modulation bandwidth of the second microwave module, which is 300 MHz in this embodiment.

[0047] After the receiving antenna obtains the echo signal reflected by the ground, it is transmitted to the receiving module, which multiplies the echo signal with the transmission signal to obtain a beat signal; the receiving module transmits the beat signal to the microprocessor, which performs Fourier transform and Chirp-Z transform analysis on the beat signal in turn to obtain the beat signal spectrum; according to the beat signal spectrum, two target frequencies are found, and two height measurement values ​​are calculated according to the corresponding slopes, and the final height is obtained after data processing of the two height measurement values. The specific process is:

[0048] In this embodiment, the actual value of the current altimeter from the ground is assumed to be h = 30 meters. Since the propagation speed of electromagnetic waves c is 3e8m / s, the double-slope linear frequency modulation continuous wave transmission signal undergoes a round-trip delay of The echo signal is obtained, and the expression of the echo signal is:

[0049]

[0050] in is the echo signal, the amplitude of the echo signal is C and D respectively, and the amplitude of the echo signal is related to the amplitude of the transmitted signal. The expression of the beat signal mix is ​​obtained by multiplying the transmitted signal and the echo signal:

[0051]

[0052] in and All are additional phases. is the reflection coefficient, differentiate the phase of the beat signal mix, and ignore the Doppler frequency shift, we can know that the instantaneous frequency expression of the beat signal is:

[0053]

[0054] Perform Fourier transform (FFT) and Chip-Z transform (CZT) on the beat signal to calculate the beat signal spectrum, and calculate the height based on the target frequency and slope. Since Chip-Z transform has higher frequency resolution than Fourier transform, Fourier transform is first performed on the beat signal to find the rough target frequency range, and then Chip-Z transform is performed to obtain the refined spectrum of the beat signal. Find two peak targets in the refined spectrum of the beat signal, and the target frequencies are and .

[0055] Figure 3As can be seen, the FFT spectrum result of the beat signal has two obvious peak targets, but the spectrum resolution is low. The first target frequency is about 37.6KHz, and the second target frequency is about 74.95KHz. The frequency resolution of the CZT spectrum result of the beat signal is higher, and the first target frequency is obtained. , the second target frequency , Since the two target frequencies and The relationship between the size and the carrier frequency of the two microwave modules and The size relationship is consistent, and =4.3GHz, =5.6GHz, , so according to the size relationship, determine the target frequency With carrier frequency Corresponding, target frequency With carrier frequency Corresponding, then according to the carrier frequency The corresponding slope and carrier frequency The corresponding slope , according to the formula

[0056]

[0057] Two height measurements can be obtained .

[0058] In addition, theoretically, the height values ​​calculated by the two slope altimeters should be equal, that is, , then we can get the proportional relationship between the two target frequencies and the slopes , due to the slope and is a known quantity. In this embodiment , then theoretically According to this proportional relationship, the correctness of the two searched target frequencies can be verified. In this embodiment, , if the error between the ratio of the two target frequencies and the corresponding slope ratio is less than the set threshold, it is considered that the two target frequencies searched for this measurement are correct, and the final altitude value can be further calculated. On the contrary, if during this measurement, the difference between the ratio of the two target frequencies and the slope ratio is large (for example, the error is greater than 10%), it can be considered that the target frequency search is wrong and the target frequency needs to be searched again. If the difference between the target frequency ratio and the slope ratio exceeds the set threshold for multiple consecutive times, it is considered that the altimeter measurement is interfered with, and the availability of the two altitude measurement values ​​needs to be evaluated. For example, assuming that the altimeter 4.3G band is interfered with and the 5.6G band is not interfered with, then The 4.3G altimeter is not available under slope and the correct target frequency cannot be searched ,and The 5.6G altimeter is available at a slope. , and the calculated height value and The difference between them is large. Therefore, the method used to evaluate the availability of the two height measurement values ​​is to use the previously obtained historical measurement normal height data to calculate the difference between the two height measurement values ​​and the historical measurement normal height. Due to interference at this time, at least one height measurement value must be very different from the historical measurement normal height. If the difference between a certain height measurement value and the historical measurement height is less than the set threshold at this time, it is considered that there is no interference in the frequency band corresponding to the height measurement value, and the height measurement value is output as the final height H; if the difference between the two height measurement values ​​and the historical measurement normal height is large, the historical measurement normal height is output, and an indication of interference is given. The historical measurement normal height here refers to the most recent normal height measured during the measurement process. In this embodiment, the normal height data of the historical measurement is used to determine whether the height measurement value has interference in the corresponding frequency band, and the normal .... The measurement data is abnormally unavailable. The measured data is available, and the output final height is It can be seen that the dual-slope altimeter proposed by the present invention has improved anti-interference capability compared with the traditional single-slope altimeter.

[0059] In this embodiment, under normal circumstances, the two height measurement values ​​are averaged and the final height value H is output, which is expressed as follows: The actual height h = 30m, so the measurement error is 0.13m.

[0060] In addition, the altimeter proposed in this embodiment also has a one-way broadcast communication function. The ground receiver receives the transmitted signal, multiplies it with the local signal to obtain a ground beat signal, analyzes the amplitude of the two targets in the ground beat signal spectrum, and parses the data according to the target amplitude. The specific process is as follows:

[0061] The dual slope linear frequency modulation continuous wave transmission signal undergoes a one-way propagation delay , the received signal e(t) reaching the ground receiver is expressed as:

[0062]

[0063] in, is the attenuation coefficient, which is set to 0.95 in this embodiment. The amplitude of the ground receiving signal is directly related to the amplitude of the altimeter transmitting signal. Assume that the local signal expression of the ground receiver is:

[0064]

[0065] The ground receiver multiplies the local signal with the received signal to obtain the ground beat signal The expression is:

[0066]

[0067] in, and It is the additional phase of the system. Using a random value has no effect on the frequency result. Differentiating the phase of the ground beat signal and ignoring the Doppler shift, the instantaneous frequency of the ground beat signal can be obtained. The expression is:

[0068]

[0069] Perform Fourier transform on the ground beat signal and find two spectrum peaks and , and obtain the signal amplitude corresponding to the two spectrum peaks and , and parse out the binary data by judging the amplitude.

[0070] Specifically, due to the two microwave module carrier frequencies in the transmitted signal and The magnitude relationship between the two spectrum peaks and The magnitude relationship between them is consistent, so we can get the amplitudes A and B of the two microwave modules transmitting signals in the transmitting signal and the signal amplitude and In this embodiment, , , so the carrier frequency is The signal amplitude A and the spectrum peak The signal amplitude Correspondingly, the carrier frequency is The signal amplitude B and the spectrum peak The signal amplitude Corresponding. Since in the transmitted signal, and , so if , binary data is 1, if , the binary data is 0. Figure 4 The first target FFT magnitude can be seen in The second target FFT amplitude is 0.092. is 0.177, the corresponding data is 0; the first target FFT amplitude The second target FFT amplitude is 0.177. is 0.092, and the corresponding data is 1. It can be seen that the process of ground receiver parsing data is simple and easy to implement.

[0071] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A dual-slope linear frequency modulation continuous wave altimeter with one-way broadcast communication function, characterized in that: It includes a microprocessor, a transmitting component and a receiving component; the transmitting component includes a first microwave module, a second microwave module, a combiner and a transmitting antenna; the receiving component includes a receiving module and a receiving antenna; The microprocessor controls the first microwave module to generate a first linear frequency modulation continuous wave signal with a slope k1, and controls the second microwave module to generate a second linear frequency modulation continuous wave signal with a slope k2, and k1≠k2; and according to the binary data data to be sent, sets the amplitude relationship between the first linear frequency modulation continuous wave signal and the second linear frequency modulation continuous wave signal, and the amplitude relationship is: data=1, A>B and data=0, A<B, or: data=1, A<B and data=0, A>B; A is the transmission signal amplitude of the first microwave module, and B is the transmission signal amplitude of the second microwave module; The combiner combines the first linear frequency modulated continuous wave signal and the second linear frequency modulated continuous wave signal into a transmission signal, and transmits the transmission signal to the ground through the transmission antenna, and at the same time transmits the transmission signal to the receiving module of the receiving component; After the receiving antenna obtains the echo signal reflected by the ground, it transmits it to the receiving module, and the receiving module multiplies the echo signal with the transmission signal to obtain a beat signal; The receiving module transmits the beat signal to the microprocessor, and the microprocessor obtains the target frequencies of two peak targets in the spectrum of the beat signal, respectively: b1 and f b2 , and determine the target frequency f b1 、f b2 The corresponding relationship with the slopes k1 and k2 is as follows: b1 Corresponding to the slope k1, the target frequency f b2 When corresponding to the slope k2, according to the formula Calculate the two height measurements H1 and H2, where c is the propagation speed of electromagnetic waves; The microprocessor performs data processing on the two calculated height measurement values ​​H1 and H2 to obtain a final height H.

2. A dual-slope linear frequency modulation continuous wave altimeter with one-way broadcast communication function according to claim 1, characterized in that: The expression of the transmission signal is: s(t)=Asin(2πf1t+πk1t 2 )+Bsin(2πf2t+πk2t 2 ),0<t<T m Where s(t) is the transmitted signal, t is the time, T m is the modulation period, f1 is the carrier frequency of the first microwave module, f2 is the carrier frequency of the second microwave module, and the corresponding slope of the first microwave module is The second microwave module corresponds to the slope B1 is the modulation bandwidth of the first microwave module, and B2 is the modulation bandwidth of the second microwave module.

3. A dual-slope linear frequency modulation continuous wave altimeter with a one-way broadcast communication function according to claim 2, characterized in that: The expression of the echo signal is: r(t)=Csin(2πf1(t-τ h )+πk1(t-τ h ) 2 )+Dsin(2πf2(t-τ h )+πk2(t-τ h ) 2 ),t h <t<T m +t h Where r(t) is the echo signal, the amplitudes of the echo signals are C and D respectively, and the amplitude of the echo signal is related to the amplitude of the transmitted signal; τ h is the round-trip delay from transmitting the signal to receiving the echo signal.

4. A dual-slope linear frequency modulation continuous wave altimeter with one-way broadcast communication function according to claim 3, characterized in that: The expression of the beat signal mix is: mix(t)=αACsin(2πf1τ h +2πk1τ h t+β1)+αBDsin(2πf2τ h +2πk2τ h t+β2) Where β1 and β2 are both additional phases, and α is the reflection coefficient.

5. The dual-slope linear frequency modulation continuous wave altimeter with one-way broadcast communication function according to claim 1, characterized in that: The process of the microprocessor acquiring the target frequencies of the two peak targets in the spectrum of the beat signal is as follows: The microprocessor performs Fourier transform and Chirp-Z transform analysis on the beat signal in sequence: firstly, the beat signal is subjected to Fourier transform to find a rough target frequency range, and then Chip-Z transform is performed to obtain a refined spectrum of the beat signal; the target frequencies of the two peak targets obtained in the refined spectrum of the beat signal are f respectively. b1 and f b2 .

6. A dual-slope linear frequency modulation continuous wave altimeter with a one-way broadcast communication function according to claim 2, Features: Determine the target frequency f b1 、f b2 The corresponding process with slopes k1 and k2 is: According to the two target frequencies f b1 and f b2 The size relationship between the two carrier frequencies f1 and f2 determines the target frequency f b1 、f b2 The corresponding relationship with the carrier frequencies f1 and f2, and then determine the target frequency f b1 、f b2 The corresponding relationship with the slopes k1 and k2.

7. A dual-slope linear frequency modulation continuous wave altimeter with one-way broadcast communication function according to claim 1, characterized in that: The process of the microprocessor performing data processing on the two calculated height measurement values ​​H1 and H2 to obtain the final height H is as follows: Calculate the ratio f of two target frequencies b2 / f b1 , and the corresponding ratio of the two slopes k2 / k1; If f b2 / f b1 If the error with k2 / k1 is less than the set threshold, the two target frequencies are considered correct, and the average of the two height measurement values ​​H1 and H2 is taken as the final height H; otherwise, it is considered that the target frequency search is wrong, and the target frequency is searched again; If multiple times f b2 / f b1 If the errors with k2 / k1 exceed the set threshold, it is considered that the altimeter measurement is disturbed, and the difference between the two altitude measurement values ​​and the normal altitude of historical measurement is calculated. If the difference between a certain altitude measurement value and the normal altitude of historical measurement is less than the set threshold, the altitude measurement value is output as the final altitude H, otherwise the normal altitude of historical measurement is output.

8. The dual-slope linear frequency modulation continuous wave altimeter with one-way broadcast communication function according to claim 1, characterized in that: It also includes a ground receiver that realizes the one-way broadcast communication function; the ground receiver receives the transmission signal, multiplies it with the local signal to obtain a ground beat signal, analyzes the amplitude of two targets in the spectrum of the ground beat signal, and parses the data according to the target amplitude. The parsing process is: Perform Fourier transform on the ground beat signal and find two spectrum peaks f c1 and f c2 , and obtain the corresponding spectrum peak f c1 The signal amplitude A1 and the corresponding spectrum peak f c2 The signal amplitude A2; According to the two spectrum peaks f c1 and f c2 The magnitude relationship between the two carrier frequencies f1 and f2 determines the spectrum peak f c1 、f c2 The corresponding relationship between the signal amplitudes A1 and A2 and the signal amplitudes A and B is determined according to the corresponding relationship with the carrier frequencies f1 and f2; and the binary data corresponding to the signal amplitudes A1 and A2 is obtained according to the relationship between the binary data set in the transmitted signal and the signal amplitudes A and B.

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