Unmanned aerial vehicle image transmission signal frequency and bandwidth estimation method and device

Abstract

The invention discloses an unmanned aerial vehicle image transmission signal frequency and bandwidth estimation method and device, and the method comprises the steps: carrying out the segmentation interception of a received signal, and obtaining a signal segmentation sequence; performing preliminary screening on the signal segments by using the frequency spectrum conjugate symmetry of the ZC sequence; carrying out delay correlation processing on the primarily screened signal segments to obtain a delay correlation result sequence, taking an index value corresponding to the maximum modulus value of the delay correlation result sequence as an initial index, and obtaining a signal segment containing a ZC sequence; zC sequences under different bandwidths stored locally are obtained, conjugate multiplication is carried out on the ZC sequences and signal fragments containing the ZC sequences, whether the signals are image transmission signals of the unmanned aerial vehicle or not is determined according to frequency spectrum module value peaks of conjugate multiplication results, and meanwhile the center frequency and the bandwidth of the image transmission signals are obtained. According to the invention, the signals are intercepted in a segmented manner, and the peak-to-average ratio is used for rapid preliminary screening, so that the real-time performance is significantly improved; robustness and accuracy are greatly enhanced through a double-confirmation mechanism, calculation is efficient, and the method has good application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of image transmission signal transmission, and particularly relates to a method and device for estimating the frequency and bandwidth of an unmanned aerial vehicle (UAV) image transmission signal. BACKGROUND

[0002] With the development of science and technology, unmanned aerial vehicles (UAVs) play an increasingly important role in low-altitude environments in production and life, and are widely used in fields such as agricultural irrigation, remote sensing surveying and mapping, and emergency rescue. At the same time, behaviors such as “black flight” and “random flight” of UAVs also pose a great security risk to public affairs and personal information. In order to protect the safety of the public and personal privacy, it is necessary to obtain the frequency and bandwidth characteristics of the UAV image transmission signal, and then use these characteristics to complete the interference and expulsion of abnormal flying UAVs.

[0003] The commonly used method for estimating the frequency and bandwidth of the UAV image transmission signal constructs a spectrum waterfall diagram for the IQ data, and then uses image morphological methods to process the spectrum waterfall diagram to obtain the frequency and bandwidth of the image transmission signal. However, this method has the problems of long data collection time and poor real-time performance. In addition, when the signal-to-noise ratio is low, the signal block characteristics in the spectrum waterfall diagram are not strong, and the detection accuracy of this method is difficult to guarantee.

[0004] Some signals in the UAV image transmission signal contain pilot sequences for synchronization, which are often composed of ZC (Zadoff-Chu) sequences, and the root index is constant. ZC sequences have ideal periodic autocorrelation characteristics and good cross-correlation characteristics. In addition, the construction of the ZC synchronization sequence in the UAV image transmission signal is often related to its bandwidth (for example, a 9MHz bandwidth image transmission signal is a ZC sequence with a length of 601 and a root index of 600; an 18MHz bandwidth image transmission signal is a ZC sequence with a length of 1201 and a root index of 1200), and the periodicity appears when transmitting image signals (for example, a synchronization ZC sequence is sent every 20ms). If these characteristics are utilized, the frequency and bandwidth estimation of the UAV image transmission signal can be completed when the synchronization pilot sequence appears. SUMMARY

[0005] In order to effectively solve the above problems in the prior art, the application provides a method and device for estimating the frequency and bandwidth of a UAV image transmission signal, which does not need to construct a spectrum waterfall diagram, ensuring real-time performance, and because ZC sequences have good cross-correlation characteristics, they still have good detection accuracy at low signal-to-noise ratios, ensuring estimation performance.

[0006] The application provides a method for estimating the frequency and bandwidth of a UAV image transmission signal, which comprises the following steps: Step 110: segmenting and intercepting the received UAV image transmission signal to obtain a plurality of signal segments; Step 120, using the spectral conjugate symmetry of the ZC sequence, the multiple signal segments are individually pre-screened to obtain the signal segments passing the pre-screening; Step 130, delay correlation processing is performed on each signal segment passing the pre-screening to obtain a corresponding delay correlation result sequence; Step 140, the index value corresponding to the maximum modulus value in the delay correlation result sequence is taken as the starting index of the ZC sequence to intercept the signal segment containing the ZC sequence; Step 150, reference ZC sequences under different bandwidths are obtained; Step 160, the signal segment containing the ZC sequence is conjugate multiplied with the reference ZC sequences under different bandwidths and then subjected to fast Fourier transform processing to obtain the spectrum of the conjugate multiplication result; according to the peak-to-average ratio of the spectrum modulus value of the conjugate multiplication result, it is determined whether the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal; if it is determined that the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal, the image transmission signal bandwidth is obtained according to the type of the reference ZC sequence, and the image transmission signal center frequency is obtained according to the peak position of the spectrum modulus value of the conjugate multiplication result; if it is determined that the signal segment containing the ZC sequence is not the synchronization ZC sequence of the UAV, then jump back to step 120 to re-screen the signal segment until the signal segment passing the pre-screening is obtained.

[0007] The application also provides a UAV image transmission signal frequency and bandwidth estimation device, which is used to implement the steps of the foregoing method, and comprises: A first module is configured to segment and intercept the received UAV image transmission signal to obtain multiple signal segments; A second module is configured to use the spectral conjugate symmetry of the ZC sequence to pre-screen the multiple signal segments one by one to obtain the signal segments passing the pre-screening; A third module is configured to perform delay correlation processing on each signal segment passing the pre-screening to obtain a corresponding delay correlation result sequence; A fourth module is configured to take the index value corresponding to the maximum modulus value in the delay correlation result sequence as the starting index of the ZC sequence to intercept the signal segment containing the ZC sequence; A fifth module is configured to obtain reference ZC sequences under different bandwidths; The sixth module is used for conjugate multiplication of the signal segment containing the ZC sequence and a reference ZC sequence under different bandwidths, and then fast Fourier transform processing is performed on the conjugate multiplication result to obtain a frequency spectrum of the conjugate multiplication result; whether the signal segment containing the ZC sequence is a synchronization ZC sequence of the UAV image transmission signal is determined according to a peak-to-average ratio of the frequency spectrum modulus value of the conjugate multiplication result; if it is determined that the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal, the image transmission signal bandwidth is obtained according to the type of the reference ZC sequence, and the image transmission signal center frequency is obtained according to the peak position of the frequency spectrum modulus value of the conjugate multiplication result; if it is determined that the signal segment containing the ZC sequence is not the synchronization ZC sequence of the UAV, the step of the second module is returned to, and the signal segmentation is re-performed for initial screening until the signal segment of the synchronization ZC sequence of the UAV image transmission signal is obtained.

[0008] Compared with the prior art, the UAV image transmission signal frequency and bandwidth estimation method and device provided by the application has the following beneficial effects: (1) The application performs segmentation and interception on the image transmission signal, and performs fast initial screening by using the peak-to-average ratio, so that the calculation amount is small, parallel or streaming processing of short data blocks is allowed, and real-time performance is significantly improved.

[0009] (2) The application fully utilizes the correlation characteristics of the ZC sequence, and greatly enhances the robustness and accuracy in a low signal-to-noise ratio environment (depending on the strong correlation characteristics of the ZC sequence) through a double confirmation mechanism (combination of initial screening in step 120 and conditional judgment in step 160), which is computationally efficient and provides fast and reliable bandwidth information for a UAV detection and countermeasure system, and has a good application prospect in the field of UAV image transmission signal analysis and detection. BRIEF DESCRIPTION OF DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments or examples of the application.

[0011] Figure 1 The step flow chart of the UAV image transmission signal frequency and bandwidth estimation method in one embodiment of the application; Figure 2 The waterfall chart of the synchronization ZC sequence of the DJI Lingling 4PV2.0 image transmission signal in the experiment of the application; Figure 3 The modulus value sequence in the experiment of the application schematic diagram; Figure 4 The modulus value schematic diagram of the delay correlation result sequence in the experiment of the application; Figure 5The sequence used in the experiment of the present application is shown in the following. The modulus diagram of the sequence. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0013] The present application will be further described in detail below in combination with the drawings and specific examples of the specification.

[0014] In one embodiment, as shown in Figure 1 The present application provides a UAV image transmission signal frequency and bandwidth estimation method, comprising: Step 110, segmenting and intercepting the received UAV image transmission signal to obtain a plurality of signal segments; Step 120, using the spectral conjugate symmetry of the ZC sequence, performing preliminary screening on each of the plurality of signal segments to obtain a signal segment that passes the preliminary screening; Step 130, performing delay correlation processing on each signal segment that passes the preliminary screening to obtain a corresponding delay correlation result sequence; Step 140, taking the index value corresponding to the maximum modulus value in the delay correlation result sequence as the starting index of the ZC sequence, and intercepting a signal segment containing the ZC sequence; Step 150, obtaining reference ZC sequences under different bandwidths; Step 160, performing conjugate multiplication on the signal segment containing the ZC sequence and the reference ZC sequences under different bandwidths, and then performing fast Fourier transform processing to obtain the spectrum of the conjugate multiplication result; determining whether the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal according to the peak-to-average ratio of the spectrum modulus of the conjugate multiplication result; if it is determined that the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal, then obtaining the image transmission signal bandwidth according to the type of the reference ZC sequence and obtaining the center frequency of the image transmission signal according to the peak position of the spectrum modulus of the conjugate multiplication result; if it is determined that the signal segment containing the ZC sequence is not the synchronization ZC sequence of the UAV, then jumping back to step 120 to re-screen the signal segment until a signal segment that is determined to be the synchronization ZC sequence of the UAV image transmission signal is obtained.

[0015] The UAV image transmission signal frequency and bandwidth estimation method provided by the present application is based on the full use of the characteristics of the ZC (Zadoff-Chu) sequence. The ZC sequence is a constant amplitude zero autocorrelation (CAZAC) sequence widely used in communication systems, which has spectral conjugate symmetry, ideal periodic autocorrelation and good cross-correlation. If the time domain representation of the ZC sequence is: ( ), its spectrum conjugate symmetry refers to the even symmetry of the corresponding spectrum amplitude and the odd symmetry of the phase. When it is an odd number, the fast Fourier transform of the ZC sequence (using represents the operation of FFT transformation) satisfies: ; in, express The conjugate frequency domain signal of (the complex signal is conjugated).

[0016] The spectrum conjugate symmetry of the ZC sequence is beneficial to reducing the complexity of the OFDM system equalizer.

[0017] Specifically, in step 110, the drone image transmission signal is received , ; The received drone image transmission signal is a complex signal (IQ data), which consists of an in-phase component (I) and a quadrature component (Q), and can be expressed as ,in Is an imaginary unit.

[0018] For all image transmission signals Perform segmented interception to obtain multiple signal segments , forming a signal segment sequence ,in, , is the data length of the signal segment (including the number of sampling points), so we define is the half-length parameter of the signal segment; represents the total number of signal segments, and , Express Rounding; Indicates that the image transmission signal is being continuously captured. ~ All sampled signals.

[0019] Further, step 120 includes: Step 121, using the spectrum conjugate symmetry of the ZC sequence, each signal is segmented Perform delayed autocorrelation operation to obtain the autocorrelation result: ; in, express The conjugate signal (complex signal conjugate) segmented, " represents element-by-element multiplication (Hadamard product), Indicates interception of signal segments The first half of the sampling points (from 1 to sampling points), Indicates the sampling point of the second half of the conjugate signal segment (the to sampling points), Is the length of The complex vector of .

[0020] Step 122, the autocorrelation result Perform fast Fourier transform (FFT transform) and get: ; Is the length of The complex frequency domain sequence of The modulus value of each component (complex modulus operation) gives a modulus sequence: ; Calculate the modulus sequence Peak-to-average ratio: ; in, is the maximum value function, is the averaging function; Set the half-length parameter of the signal segment For example, typically, the sampling rate When it is 15.36MHz, ; Sampling rate When it is 61.44MHz, .

[0021] Step 123, using the peak-to-average ratio to determine the signal segment Whether it passes the initial screening: If the peak-to-average ratio Greater than or equal to the set threshold , it means that the signal is segmented It may contain ZC sequence to determine the signal segmentation After the initial screening, proceed to the subsequent step 130; if the peak-to-average ratio Less than the set threshold , then the signal is considered to be segmented Does not contain ZC sequence, determine signal segmentation If the signal fails to pass the initial screening, steps 121 to 123 are continued to be executed on the next signal segment.

[0022] Preferably, the threshold Can be set to 10.

[0023] Specifically, in step 130, the signal that passes the initial screening is segmented delay correlation processing is performed to obtain a delay correlation result sequence: , ; wherein, is a sliding window range for performing the delay correlation processing; is a length of an OFDM symbol (excluding a cyclic prefix), the OFDM symbol including a cyclic prefix and a valid data part in a time domain, wherein the valid data part is generated by inverse fast Fourier transform of modulation symbols on frequency domain subcarriers; is a cyclic prefix length of the OFDM symbol.

[0024] In general, a sampling rate is 15.36 MHz, is set to 72, is set to 1024; a sampling rate is 61.44 MHz, is set to 288, is set to 4096.

[0025] Further, in step 140, since the tail data of the OFDM symbol is the same as the cyclic prefix thereof, the index value corresponding to the maximum modulus value in the delay correlation result sequence is taken as the starting index of the ZC sequence, that is, the following is taken: ; wherein, is a function of finding a maximum value point; then is the starting index of the ZC sequence.

[0026] The signal segment containing the ZC sequence in the IQ data is intercepted: ; The signal segment containing the ZC sequence is used in subsequent steps to calculate correlation coefficients with reference ZC sequences of different bandwidths stored locally to determine whether the signal segment is a synchronization ZC sequence of the UAV image transmission signal.

[0027] Specifically, in step 150, reference ZC sequences of different bandwidths stored locally are obtained for different sampling rates, including: The frequency domain representation of the reference ZC sequence corresponding to the local storage for different sampling rates is: .

[0028] wherein, is a root index of the ZC sequence, is the total number of sampling points of the signal. If the bandwidth of the video transmission signal is 9MHz, , root index ; if the bandwidth of the video transmission signal is 18MHz, , root index .

[0029] Preferably, when the bandwidth of the video transmission signal is 9MHz, the sampling rate is 15.36MHz, a zero vector with a length of 1024 is constructed , the value of is placed in the position with an index value of 213:813 in , inverse fast Fourier spectrum shift (ifftshift) operation is performed on , and inverse fast Fourier transform (ifft) operation is completed, so that the ZC sequence in the time domain is obtained. The ifftshift operation restores the frequency domain data to the original position, ensuring the correctness of the subsequent inverse Fourier transform.

[0030] Through similar operations, when the bandwidth of the video transmission signal is 18MHz, the sampling rate is 61.44MHz, the ZC sequence in the time domain can be obtained.

[0031] The ZC sequence in the time domain and are taken as the reference ZC sequence stored locally.

[0032] Further, in step 160, the signal segment containing the ZC sequence , and the reference ZC sequence stored locally and are used to determine whether the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV video transmission signal through correlation coefficient calculation, comprising: Step 161, the conjugate multiplication of and is performed to obtain the conjugate multiplication result ; Fast Fourier transform operation is performed on , and the fast Fourier spectrum shift (fftshift) operation of left-right exchange is performed to obtain the spectrum of ; The modulus value of the spectrum of is taken to obtain the sequence of the spectrum modulus value ; The maximum value max of the sequence and the corresponding maximum value index are calculated; that is The peak position of the spectrum modulus value; make Middle index value to Set the value to zero and then use the maximum value function to obtain The second largest value second_val , and mean ; calculate Peak-to-average ratio: ; Step 162, when The peak-to-average ratio satisfies the condition: ,and When the signal segment As the synchronous ZC sequence of the UAV image transmission signal bandwidth of 9MHz, according to The peak position of ) The center frequency of the image transmission signal is: ; in, is the sampling rate when the bandwidth of the drone image transmission signal is 9MHz, The number of sampling points of the fast Fourier transform when the bandwidth of the drone image transmission signal is 9MHz; When the conditions are met: ,or When , go to step 163.

[0033] Step 163, let and Perform conjugate multiplication to obtain the conjugate multiplication result ; right Perform fast Fourier transform operation and obtain the value by fftshift operation with left and right swapping. spectrum; Pick The modulus of the spectrum, to obtain the sequence of spectrum modulus values ; Calculation sequence The maximum value , and the corresponding maximum value index ; that is The peak position of the spectrum modulus value; make Middle index value to Set the value to zero and then use the maximum value function to obtain The second largest value , and the mean ; calculate Peak-to-average ratio: ; Step 164, when The peak-to-average ratio satisfies the condition: ,and When the signal segment As the synchronous ZC sequence of the UAV image transmission signal bandwidth of 18MHz, and based on The peak position of ) The center frequency of the image transmission signal is: ； in, The sampling rate of the UAV image transmission signal when its bandwidth is 18MHz. The number of sampling points of the fast Fourier transform when the bandwidth of the drone image transmission signal is 18MHz; Step 165: When the above conditions are not met, it indicates that the signal segment Does not contain ZC sequence, also known as signal fragment If it is not the synchronous ZC sequence of the UAV image transmission signal, go back to step 120 and segment the signal. Perform the initial screening again and re-execute steps 120 to 160 until a signal segment containing a ZC sequence that is determined to be a synchronized ZC sequence of the UAV image transmission signal is obtained.

[0034] In view of the above embodiments, the present invention has conducted corresponding experiments to verify the effectiveness of the method for estimating the frequency and bandwidth of the image transmission signal of the drone proposed in the present invention. This experiment was conducted on a DJI Phantom 4 PV2.0 to identify the image transmission signal frequency and bandwidth. Figure 2 The waterfall diagram of the synchronized ZC sequence of the DJI Phantom 4 PV2.0 image transmission signal is given, as shown in the figure below: Figure 2 As shown, there is a synchronous ZC sequence at time 25μs to 90μs. The modulus sequence in step 120 ,like Figure 3 As shown, it can be seen that the sequence The peak-to-average ratio is relatively large. In step 130, the delayed correlation result sequence The modulus value is Figure 4 As shown. In step 160, Figure 5 As shown, the sequence The maximum value index of the modulus is 1980, and the calculated signal center frequency is -1.035MHz, which is the same as Figure 2 The above process fully demonstrates the effectiveness of this method.

[0035] The unmanned aerial vehicle image transmission signal frequency and bandwidth estimation method provided by the application, through segmenting and intercepting the received signal, the peak-to-average ratio is used for fast preliminary screening of potential signal segments. Delay correlation processing is performed on the preliminary screening segment, and the starting point of the ZC sequence is located and the segment is intercepted by using the ideal autocorrelation characteristics of the ZC sequence. The correlation coefficient of the segment and the local reference ZC sequence is calculated for accurate matching confirmation. Once the confirmation is successful, the bandwidth is directly determined according to the detected ZC sequence length (such as 601 corresponding to 9MHz, 1201 corresponding to 18MHz). The scheme discards the time-consuming spectrum diagram construction and image processing, and through segmenting and intercepting the signal and using the spectral conjugate symmetry of the ZC sequence for fast preliminary screening, the calculation amount is small and the system allows parallel or streaming processing of short data blocks, which significantly improves the real-time performance. Make full use of the correlation characteristics of the ZC sequence itself, through the double confirmation mechanism (combination of preliminary screening in step 120 and conditional judgment in step 160), the robustness and accuracy in low signal-to-noise ratio environment are greatly enhanced (depending on the strong correlation characteristics of the ZC sequence), the calculation is efficient, and the unmanned aerial vehicle detection and countermeasure system provides fast and reliable bandwidth information, which has good application prospect in the field of unmanned aerial vehicle image transmission signal analysis and detection.

[0036] In addition, in another embodiment, the application provides an unmanned aerial vehicle image transmission signal frequency and bandwidth estimation device, which is used to realize the steps of the method described in the foregoing embodiments, and the device comprises: The first module is used for segmenting and intercepting the received unmanned aerial vehicle image transmission signal to obtain a plurality of signal segments. The second module is used for using the spectral conjugate symmetry of the ZC sequence to preliminarily screen the plurality of signal segments one by one to obtain signal segments that pass the preliminary screening. The third module is used for performing delay correlation processing on each signal segment that passes the preliminary screening to obtain a corresponding delay correlation result sequence. The fourth module is used for taking the index value corresponding to the maximum value of the modulus in the delay correlation result sequence as the starting index of the ZC sequence to intercept the signal segment containing the ZC sequence. The fifth module is used for acquiring reference ZC sequences under different bandwidths. The sixth module is used for performing conjugate multiplication on the signal segment containing the ZC sequence and a reference ZC sequence under different bandwidths, and then performing fast Fourier transform processing to obtain a spectrum of the conjugate multiplication result; determining whether the signal segment containing the ZC sequence is a synchronization ZC sequence of the UAV image transmission signal according to a peak-to-average ratio of the spectrum modulus value of the conjugate multiplication result; if it is determined that the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal, obtaining the image transmission signal bandwidth according to the type of the reference ZC sequence and obtaining the center frequency of the image transmission signal according to the peak position of the spectrum modulus value of the conjugate multiplication result; and if it is determined that the signal segment containing the ZC sequence is not the synchronization ZC sequence of the UAV, jumping back to the step of the second module to re-perform preliminary screening on the signal segment until a signal segment of the synchronization ZC sequence of the UAV image transmission signal is obtained.

[0037] In an embodiment, the present application provides a computer device, which can be a server, comprising a processor, a memory, a network interface and a database connected through a system bus. The processor of the device is used to provide computing and control capabilities. The memory of the device comprises a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operating system and the computer program in the non-volatile storage medium. The database of the device is used to store the UAV image transmission signal frequency and bandwidth estimation data. The network interface of the device is used to communicate with an external terminal through a network connection. The computer program is executed by the processor to implement the UAV image transmission signal frequency and bandwidth estimation method.

[0038] Those skilled in the art can understand that the description of the technical features of the device in the above embodiments does not constitute a limitation on all devices to which the scheme of the present application is applied. A specific device can include more or fewer components, or combine certain components, or have a different arrangement of components.

[0039] In another embodiment, the present application provides a computer readable storage medium having a computer program stored thereon, wherein the computer program is executed by a processor to implement the steps of the UAV image transmission signal frequency and bandwidth estimation method provided in any of the above embodiments.

[0040] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when the computer program is executed, the processes of the above-mentioned embodiment methods can be included. Any reference to memory, storage, database or other medium used in the embodiments provided in the present application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration but not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0041] The details of the present application are known.

[0042] The technical features of the above embodiments can be combined in any way. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, but as long as the combination of the technical features does not exist, it should be considered as the scope of the present application.

[0043] The above embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application.

Claims

1. A method for estimating frequency and bandwidth of a UAV image transmission signal, characterized in that, The method comprises the following steps: Step 110: segmentally intercepting the received UAV image transmission signal to obtain a plurality of signal segments; Step 120: using the spectral conjugate symmetry of the ZC sequence to individually perform preliminary screening on the plurality of signal segments to obtain signal segments that pass the preliminary screening; Step 130: performing delay correlation processing on each signal segment that passes the preliminary screening to obtain a corresponding delay correlation result sequence; Step 140: using the index value corresponding to the maximum modulus value in the delay correlation result sequence as the starting index of the ZC sequence to intercept a signal segment containing the ZC sequence; Step 150: obtaining reference ZC sequences under different bandwidths; Step 160: performing fast Fourier transform processing on the signal segment containing the ZC sequence after conjugate multiplication with the reference ZC sequences under different bandwidths to obtain the spectrum of the conjugate multiplication result; and determining whether the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal according to the peak-to-average ratio of the spectral modulus of the conjugate multiplication result; If it is determined that the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal, then obtaining the bandwidth of the image transmission signal according to the type of the reference ZC sequence and obtaining the center frequency of the image transmission signal according to the peak position of the spectral modulus of the conjugate multiplication result; if it is determined that the signal segment containing the ZC sequence is not the synchronization ZC sequence of the UAV, then returning to step 120 to re-perform preliminary screening on the signal segments until a signal segment that is determined to be the synchronization ZC sequence of the UAV image transmission signal is obtained. 2.The UAV image transmission signal frequency and bandwidth estimation method of claim 1, wherein, The ZC sequence refers to a Zadoff-Chu sequence in a constant-amplitude zero-autocorrelation sequence; the spectral conjugate symmetry of the ZC sequence refers to even symmetry of the corresponding spectral amplitude and odd symmetry of the phase. 3.The UAV image transmission signal frequency and bandwidth estimation method of claim 2, wherein, The step 110 comprises the following steps: Receiving a drone image transmission signal , ; is the total number of sampling points of the signal; the is IQ data in complex form, composed of in-phase component I and quadrature component Q; all the image transmission signals segmented and obtained a plurality of signal segments wherein, , is a half-length parameter of the signal segment, is a data length of the signal segment; is a total number of the signal segments, represents rounding off ; represents continuously intercepting all the sampling signals of ~ in the image transmission signals.

4. The method of claim 3, wherein, The step 120 comprises the following steps: Step 121, using the spectral conjugate symmetry of the ZC sequence, the signal segment of each signal delayed autocorrelation operation is performed to obtain autocorrelation results ; Step 122, a fast Fourier transform is performed on the autocorrelation result to obtain a complex frequency domain sequence of length ​ ； Take The modulus of each component, resulting in a modulus sequence: ; Computing a sequence of modulus values peak-to-average ratio: ； wherein is a max function, is an average function; Setting a half-length parameter of signal segmentation ; Step 123, segmenting the signal using peak-to-average ratio Passes initial screening: If peak-to-average ratio is greater than or equal to a set threshold , then determine signal segment may contain a ZC sequence, determine signal segment By preliminary screening, perform subsequent step 130; If the peak-to-average ratio is less than a set threshold value , then the signal segment is determined to not contain a ZC sequence, and the signal segment fails the preliminary screening, and the next signal segment is subjected to steps 121-123.

5. The UAV image transmission signal frequency and bandwidth estimation method of claim 4, wherein, The step 130 comprises segmenting the signals passing the preliminary screening delay correlation processing to obtain a sequence of delay correlation results , ; wherein is a sliding window range for performing delay dependent processing; is a length of an OFDM symbol comprising a cyclic prefix and a valid data portion in time domain, wherein the valid data portion is generated by an inverse fast Fourier transform of modulation symbols on frequency domain subcarriers; is a cyclic prefix length of an OFDM symbol.

6. The UAV image transmission signal frequency and bandwidth estimation method of claim 5, wherein, The step 140 comprises the following steps: delayed correlation result sequence the index value corresponding to the maximum value of the modulus value as the starting index of the ZC sequence ； wherein is a function that seeks the maximum value point; then is the starting index of the ZC sequence; intercepting a signal segment containing the ZC sequence in the IQ data; 。 7. The UAV image transmission signal frequency and bandwidth estimation method of claim 6, wherein, The step 150 comprises the following steps: Obtain the frequency domain representation of the locally stored reference ZC sequence at different bandwidths : ； wherein is a root index of a ZC sequence, is a total number of sampling points of a signal, is an imaginary unit; When the bandwidth of the UAV image transmission signal is 9MHz, , , by using and inverse fast Fourier transform, the ZC sequence in the time domain under 9MHz bandwidth is obtained: ; When the bandwidth of the UAV image transmission signal is 18MHz, , , the ZC sequence in the time domain under the condition of 18MHz bandwidth is obtained by using and inverse fast Fourier transform: ; The ZC sequence of the time domain is And As a locally stored reference ZC sequence.

8. The UAV image transmission signal frequency and bandwidth estimation method of claim 7, wherein, The step 160 comprises the following steps: Step 161, multiply with to get a conjugate multiplication result ; right Perform fast Fourier transform operation and obtain the fast Fourier spectrum shift operation by swapping left and right. spectrum; Take the modulus of the spectrum, obtaining a sequence of spectral modulus ; The maximum value of the sequence The maximum value of the sequence and the corresponding maximum value index ; the peak position of ;​ Let the index value be zeroed, and the second largest value of is obtained by using the max function ; ; Computing the peak-to-average ratio: ; Step 162, when the peak-to-average ratio satisfies the condition: , and , then the signal segment is taken as the synchronization ZC sequence of the UAV image transmission signal with a bandwidth of 9 MHz, according to the peak position of the peak value , the center frequency of the image transmission signal is obtained as: ； wherein, is a sampling rate for a bandwidth of 9 MHz for a UAV video signal, is a number of sampling points for a fast Fourier transform for a bandwidth of 9 MHz for a UAV video signal. When the condition is met: or then execute: Step 163, the result of the conjugate multiplication is obtained by performing a conjugate multiplication on the result of the multiplication in step 162 and the result of the multiplication in step 161 with each other, to obtain a conjugate multiplication result ; the spectrum of the left and right exchanged spectrum of the fast Fourier transform​​ Take the modulus of the spectrum, obtaining a sequence of spectral modulus ; The maximum value max of the sequence and the corresponding maximum index ; the peak position is ​ Let the index value be zeroed, and the second largest value of is obtained by using the max function ; ; Computing the peak-to-average ratio: ; Step 164, when the peak-to-average ratio satisfies the condition: , and , then the signal segment is taken as the synchronization ZC sequence of the UAV image transmission signal with a bandwidth of 18 MHz, and the center frequency of the image transmission signal is obtained according to the peak position of the ZC sequence . ； wherein, is a sampling rate for a bandwidth of 18 MHz for a UAV image transmission signal, is a number of sampling points for a fast Fourier transform for a bandwidth of 18 MHz for a UAV image transmission signal. Step 165, when none of the above conditions are met, determine the signal segment is not a synchronization ZC sequence of the UAV image transmission signal, return to step 120 to segment the signal re-perform the preliminary screening, and re-perform steps 120-160 until a signal segment containing a ZC sequence that is determined to be a synchronization ZC sequence of the UAV image transmission signal is obtained.

9. An unmanned aerial vehicle image transmission signal frequency and bandwidth estimation device, characterized in that, The device is used to implement the steps of the method according to any one of claims 1-8, and the device comprises the following modules: A first module is used to segmentally intercept the received UAV image transmission signal to obtain a plurality of signal segments; A second module is used to use the spectral conjugate symmetry of the ZC sequence to individually perform preliminary screening on the plurality of signal segments to obtain signal segments that pass the preliminary screening; A third module is used to perform delay correlation processing on each signal segment that passes the preliminary screening to obtain a corresponding delay correlation result sequence; A fourth module is used to use the index value corresponding to the maximum modulus value in the delay correlation result sequence as the starting index of the ZC sequence to intercept a signal segment containing the ZC sequence; A fifth module is used to obtain reference ZC sequences under different bandwidths; A sixth module is used to perform fast Fourier transform processing on the signal segment containing the ZC sequence after conjugate multiplication with the reference ZC sequences under different bandwidths to obtain the spectrum of the conjugate multiplication result; and determine whether the signal segment containing the ZC sequence is the synchronization ZC sequence of the UAV image transmission signal according to the peak-to-average ratio of the spectral modulus of the conjugate multiplication result. If the signal segment containing the ZC sequence is determined to be the synchronization ZC sequence of the UAV image transmission signal, the bandwidth of the image transmission signal is obtained according to the type of the reference ZC sequence, and the center frequency of the image transmission signal is obtained according to the peak position of the spectral modulus of the conjugate multiplication result; if the signal segment containing the ZC sequence is determined to be not the synchronization ZC sequence of the UAV, the step of the second module is jumped back to, and the signal segmentation is re-performed for the initial screening until the signal segment determined to be the synchronization ZC sequence of the UAV image transmission signal is obtained.

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