High-sensitivity rapid capturing method and system used in satellite-ground dynamic environment

Abstract

The invention discloses a high-sensitivity rapid acquisition method and system used in a satellite-ground dynamic environment, and the method comprises the steps: S1, transmitting a communication signal which accords with a target communication frequency through a transmitting end, and receiving the communication signal through a receiving end; s2, a plurality of local signals with different frequency points are generated in a frequency search interval through a local parallel digital control oscillator NCO group, and FFT-IFFT capture judgment is carried out on communication signals; s3, if it is judged that capturing fails, the frequency search interval is adjusted, and the step S2 is executed again; if it is judged that capture fails in the two adjacent frequency search intervals, performing sideband interval estimation on the two adjacent frequency search intervals, and performing FFT-IFFT capture judgment according to a sideband interval estimation result; and repeating the steps until the capture is determined to be successful. Under the conditions that the detection probability exceeds 99%, the minimum carrier-to-noise ratio is 34.66 dB and the minimum signal-to-noise ratio is 16 dB, the receiver sensitivity of-130 dBm can be achieved, the total Doppler frequency offset capture range can reach 140 kHz, and the capture time can be as low as 0.8 second.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-speed low-orbit micro-satellite satellite-to-ground communication, and relates to a high-sensitivity rapid capture method and system for use in a satellite-to-ground dynamic environment. Background Art

[0002] In recent years, aerospace technology has made significant progress, promoting the development of satellite constellations and formation technology. In particular, low-orbit small satellites have quickly become the focus of research at home and abroad because of their small size, short R&D cycle, low cost, and flexible launch. Through formation collaboration, they can achieve functions similar to traditional "large satellites". The orbital characteristics of low-orbit satellites give them efficient maneuverability and a short observation window. However, this high-speed movement will cause the state of the satellite-to-ground communication link to change rapidly, introducing Doppler frequency shifts of tens or even hundreds of kHz to the signal, increasing the difficulty of signal demodulation. Therefore, the capture capability of satellite-to-ground communication directly affects the performance of low-orbit satellites. Further, in the widely used pseudo-code spread spectrum telemetry and control transponder between satellites and the ground, capturing pseudo-code is the first step in establishing a communication link, and it is also a crucial step. The success or failure of the pseudo-code capture process is directly related to the stability and reliability of the communication link. Only after successfully capturing the pseudo-code and establishing a reliable satellite-to-ground communication link can the satellite receive remote control commands from the ground and transmit its data back to the ground, thereby successfully completing its scheduled work tasks.

[0003] Due to the fast movement speed of low-orbit satellites, the long distance between satellites and the ground, and the particularity of the work tasks, satellite-to-ground communication faces challenges such as large Doppler frequency shift, weak signal power at the receiving end, and burst signal reception. In view of these communication characteristics, an effective capture method with anti-frequency deviation capability, high sensitivity, and fast signal capture capability is needed. Traditional capture methods can be divided into serial capture and parallel capture. Serial capture is also called sliding correlation method. The principle of serial capture is simple, easy to implement, and consumes less resources, but the calculation is large and the capture time is long. It is only suitable for capturing signals with low dynamics and short pseudo code length. Parallel capture includes FFT capture method and matched filter method. The FFT capture method uses fast Fourier transform to replace the correlation operation in pseudo code capture, which is more efficient than serial capture. The matched filter method uses a matched filter to replace the integrator for correlation operation during the capture process, and has good capture efficiency, but this method consumes a lot of resources and has strict requirements on pseudo code rate and sampling frequency. In addition, the traditional FFT fast capture method has the defect of low frequency sweep efficiency, which directly affects the capture time of the receiver and limits the effective use of computing resources. Therefore, there is room for optimization in the traditional FFT capture method. In order to meet the needs of inter-satellite communication, the capture method needs to be improved and enhanced. Summary of the invention

[0004] To solve the above problems, the present invention provides a high-sensitivity fast capture method and system for use in a satellite-ground dynamic environment. The present invention takes the FFT fast capture method of sideband estimation as the core, and realizes high-dynamic, high-sensitivity fast capture of pseudo-code spread spectrum communication signals between the satellite and the ground. The scheme is feasible and has advantages over the traditional FFT capture method in terms of sensitivity, Doppler frequency offset resistance and capture time, and has good practicality.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A high-sensitivity rapid acquisition method for a satellite-ground dynamic environment comprises the following steps:

[0007] S1. The transmitting end obtains a communication signal that meets the target communication frequency after pulse code modulation, spread spectrum, and frequency modulation of the communication data, and transmits it, and the receiving end receives the communication signal;

[0008] S2. Generate several local signals with different frequencies in the frequency search interval through the local parallel digitally controlled oscillator NCO group, and perform FFT-IFFT capture and determination on the communication signal;

[0009] S3. If it is determined that the capture fails, adjust the frequency search interval and repeat step S2; if it is determined that the capture fails in two adjacent frequency search intervals, perform sideband interval estimation on the two adjacent frequency search intervals, and perform FFT-IFFT capture judgment based on the sideband interval estimation results; repeat this step until it is determined that the capture is successful.

[0010] Furthermore, the FFT-IFFT capture and determination comprises the following specific steps:

[0011] The communication signal received by the receiving end is down-converted by using a number of local signals with different frequencies to obtain a number of baseband spread spectrum signals;

[0012] Performing fast Fourier transform (FFT) processing on the obtained several baseband spread spectrum signals respectively to obtain the FFT result of each baseband spread spectrum signal;

[0013] At the same time, the receiving end generates a local pseudo code, performs fast Fourier transform (FFT) processing on the local pseudo code, and obtains the FFT result of the local pseudo code;

[0014] Take the conjugate of the FFT result of the local pseudo code, multiply it with the FFT result of each baseband spread spectrum signal bit by bit, perform inverse fast Fourier transform IFFT on the product result, and obtain the baseband signal corresponding to each baseband spread spectrum signal;

[0015] Performing non-coherent accumulation on the baseband signals respectively, and taking the root mean square value of the non-coherent accumulation result as the detection peak value of each baseband signal;

[0016] The maximum value among the detected peak values ​​of each baseband signal is taken. If the maximum value is greater than the preset detection threshold CT, it is determined that the capture is successful, otherwise it is determined that the capture fails.

[0017] Furthermore, the sideband interval is a frequency interval outside the capture range corresponding to a group of baseband signals corresponding to the last frequency point of the first frequency search interval of two adjacent frequency search intervals and a group of baseband signals corresponding to the first frequency point of the second frequency search interval.

[0018] Furthermore, the sideband interval estimation is specifically as follows: a preset normalized threshold T hz , the difference between the detection value of the baseband signal corresponding to the last frequency point of the first frequency search interval and the detection value of the baseband signal corresponding to the first frequency point of the second frequency search interval in two adjacent frequency search intervals is calculated; if the difference is greater than the normalization threshold T hz , then perform FFT-IFFT capture judgment within the estimation interval 1; if the difference is less than the negative value of the normalization threshold -T hz , then the FFT-IFFT capture decision is performed in the estimation interval three; otherwise, the FFT-IFFT capture decision is performed in the estimation interval two.

[0019] Furthermore, the method for determining the estimation interval is:

[0020] The baseband signal corresponding to the last frequency point of the first frequency search interval in two adjacent frequency search intervals is subtracted from the non-coherent accumulation result of the baseband signal corresponding to the first frequency point of the second frequency search interval to obtain a difference curve between the two, and the part of the difference curve between the two in the sideband interval is taken to obtain a monotonically decreasing curve; the monotonically decreasing curve exceeds the normalization threshold T hz The frequency interval corresponding to the part is the estimated interval 1, which is less than the negative value of the normalization threshold -T hz The frequency interval corresponding to the part is estimated interval three, and the frequency interval corresponding to the rest is estimated interval two.

[0021] Furthermore, by designing timing constraints, the FFT processing process of the baseband spread spectrum signal and the FFT processing process of the local pseudo code are performed simultaneously, and the FFT results of the two are output synchronously.

[0022] Furthermore, after the FFT-IFFT capture is determined to be successful, the coarse estimation results of the pseudo-code phase and carrier frequency of the communication signal are obtained, and then the pseudo-code phase fine tracking and carrier frequency fine tracking are turned on, the code element synchronization is performed on the tracked signal, and the code element decoding operation is performed.

[0023] A high-sensitivity rapid acquisition system for use in a satellite-ground dynamic environment, used to implement the above method, comprising:

[0024] Signal transceiver module: used for the transmitter to obtain a communication signal that meets the target communication frequency after pulse code modulation, spread spectrum, and frequency modulation of the communication data, and transmit it, and the receiver receives the communication signal;

[0025] FFT-IFFT capture and judgment module: used to generate a number of local signals with different frequencies in the frequency search interval through the local parallel digital control oscillator NCO group, and perform FFT-IFFT capture and judgment on the communication signal;

[0026] Sideband interval estimation module: used to perform sideband interval estimation on two adjacent frequency search intervals, and perform FFT-IFFT capture judgment based on the sideband interval estimation results.

[0027] Furthermore, the signal transceiver module, the FFT-IFFT capture and determination module and the sideband interval estimation module are all implemented on an FPGA chip.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) In the present invention, a grouped parallel structure is adopted to further subdivide each frequency search interval, and a multi-channel local carrier frequency synthesizer with a fixed frequency difference is used to perform down-conversion modulation, pseudo-code spread spectrum demodulation and signal capture on the signal. The parallel structure makes full use of FPGA hardware resources and significantly improves the capture speed of Doppler frequency deviation.

[0030] 2) In the present invention, the sideband interval estimation method is adopted to optimize the spectrum analysis process, fully utilize the sideband information of the adjacent frequency search intervals captured twice in parallel, reduce the resource usage of the FFT-IFFT group, significantly shorten the data capture and processing time, and as the maximum Doppler frequency deviation range increases, the optimization effect will increase accordingly.

[0031] 3) In the present invention, the FFT processing of the signal and the pseudo code is realized by timing control, and the results are output synchronously. According to the order of FFT output, the result value of the signal Fourier transform is multiplied by the conjugate value of the pseudo code Fourier transform in real time. Compared with the traditional method of storing the pseudo code FFT results, this pipeline operation not only reduces the processing delay, but also reduces the hardware resources, and improves the flexibility and effectiveness of the method.

[0032] 4) Aiming at the communication needs between low-orbit micro-satellites and the ground, the present invention relies on a small satellite communication mission and performs the actual design of the hardware description language based on this method. After the present method is implemented, the functional test is carried out. The hardware test results show that the measurement and control transponder and high-sensitivity signal capture method of the present invention are functional and have good practicality, and can excellently complete the task of establishing a satellite-to-ground communication link. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is an overall hardware block diagram of the high-sensitivity satellite-to-ground spread spectrum measurement and control transponder in an embodiment of the present invention.

[0034] Figure 2 The figure is a simplified diagram of the hardware structure of the satellite-to-ground telemetry and control transponder in an embodiment of the present invention.

[0035] Figure 3 This is a functional block diagram of the FPGA chip in an embodiment of the present invention.

[0036] Figure 4 Schematic diagram of the function of the high-sensitivity rapid capture method in an embodiment of the present invention.

[0037] Figure 5 Schematic diagram of the capture method in an embodiment of the present invention.

[0038] Figure 6 It is a diagram illustrating the sideband interval structure of the capture method in an embodiment of the present invention.

[0039] Figure 7 It is a sideband interval difference curve in the embodiment of the present invention.

[0040] Figure 8 This is a measured diagram of the simulated satellite-to-earth communication hardware in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] A high-sensitivity rapid acquisition method for a satellite-ground dynamic environment comprises the following steps:

[0044] S1. The transmitting end obtains a communication signal that meets the target communication frequency after pulse code modulation, spread spectrum, and frequency modulation of the communication data, and transmits it, and the receiving end receives the communication signal;

[0045] S2. Generate several local signals with different frequencies in the frequency search interval through the local parallel digitally controlled oscillator NCO group, and perform FFT-IFFT capture and determination on the communication signal;

[0046] S3. If it is determined that the capture fails, adjust the frequency search interval and repeat step S2; if it is determined that the capture fails in two adjacent frequency search intervals, perform sideband interval estimation on the two adjacent frequency search intervals, and perform FFT-IFFT capture judgment based on the sideband interval estimation results; repeat this step until it is determined that the capture is successful.

[0047] Furthermore, the FFT-IFFT capture and determination comprises the following specific steps:

[0048] The communication signal received by the receiving end is down-converted by using a number of local signals with different frequencies to obtain a number of baseband spread spectrum signals;

[0049] Performing fast Fourier transform (FFT) processing on the obtained several baseband spread spectrum signals respectively to obtain the FFT result of each baseband spread spectrum signal;

[0050] At the same time, the receiving end generates a local pseudo code, performs fast Fourier transform (FFT) processing on the local pseudo code, and obtains the FFT result of the local pseudo code;

[0051] Take the conjugate of the FFT result of the local pseudo code, multiply it with the FFT result of each baseband spread spectrum signal bit by bit, perform inverse fast Fourier transform IFFT on the product result, and obtain the baseband signal corresponding to each baseband spread spectrum signal;

[0052] Performing non-coherent accumulation on the baseband signals respectively, and taking the root mean square value of the non-coherent accumulation result as the detection peak value of each baseband signal;

[0053] The maximum value among the detected peak values ​​of each baseband signal is taken. If the maximum value is greater than the preset detection threshold CT, it is determined that the capture is successful, otherwise it is determined that the capture fails.

[0054] Furthermore, the sideband interval is a frequency interval outside the capture range corresponding to a group of baseband signals corresponding to the last frequency point of the first frequency search interval of two adjacent frequency search intervals and a group of baseband signals corresponding to the first frequency point of the second frequency search interval.

[0055] Furthermore, the sideband interval estimation is specifically as follows: a preset normalized threshold T hz , the difference between the detection value of the baseband signal corresponding to the last frequency point of the first frequency search interval and the detection value of the baseband signal corresponding to the first frequency point of the second frequency search interval in two adjacent frequency search intervals is calculated; if the difference is greater than the normalization threshold T hz , then perform FFT-IFFT capture judgment within the estimation interval 1; if the difference is less than the negative value of the normalization threshold -T hz , then the FFT-IFFT capture decision is performed in the estimation interval three; otherwise, the FFT-IFFT capture decision is performed in the estimation interval two.

[0056] Furthermore, the method for determining the estimation interval is:

[0057] The baseband signal corresponding to the last frequency point of the first frequency search interval in two adjacent frequency search intervals is subtracted from the non-coherent accumulation result of the baseband signal corresponding to the first frequency point of the second frequency search interval to obtain a difference curve between the two, and the part of the difference curve between the two in the sideband interval is taken to obtain a monotonically decreasing curve; the monotonically decreasing curve exceeds the normalization threshold T hz The frequency interval corresponding to the part is the estimated interval 1, which is less than the negative value of the normalization threshold -T hz The frequency interval corresponding to the part is estimated interval three, and the frequency interval corresponding to the rest is estimated interval two.

[0058] Furthermore, by designing timing constraints, the FFT processing process of the baseband spread spectrum signal and the FFT processing process of the local pseudo code are performed simultaneously, and the FFT results of the two are output synchronously.

[0059] Furthermore, after the FFT-IFFT capture is determined to be successful, the coarse estimation results of the pseudo-code phase and carrier frequency of the communication signal are obtained, and then the pseudo-code phase fine tracking and carrier frequency fine tracking are turned on, the code element synchronization is performed on the tracked signal, and the code element decoding operation is performed.

[0060] Example 2

[0061] The high-sensitivity rapid acquisition method for a satellite-ground dynamic environment of the present invention has been applied to a large-scale low-orbit microsatellite constellation independently developed by a university.

[0062] like Figure 1 As shown, a high-dynamic and high-sensitivity satellite-to-ground spread spectrum measurement and control transponder includes hardware circuit design and digital signal processing module design, which is used to ensure the normal operation of the satellite-to-ground communication link in a complex electromagnetic environment. The spread spectrum signal capture hardware includes: FPGA chip, which is used to perform pulse code modulation, spread spectrum, frequency modulation and other processing on the data to be transmitted, and down-convert the received signal, realize spread spectrum capture of the down-converted baseband spread spectrum signal, and perform despreading, demodulation and other processing; the transmitting RF link is used to modulate the baseband spread spectrum signal generated by the FPGA to the transmitting frequency and transmit it through the transmitting antenna; the transmitting antenna is used to radiate the high-frequency spread spectrum signal after frequency modulation; the receiving antenna is used to receive the high-frequency spread spectrum signal; the receiver RF link is used to down-convert the received high-frequency spread spectrum signal to the baseband signal, and use a low-noise amplifier to amplify the signal. Among them, both the transmitting and receiving RF links adopt a zero intermediate frequency structure, and the signal frequency is converted to the target frequency band through one up-conversion or down-conversion.

[0063] The digital signal processing module mainly realizes the signal capture processing at the transmitter and the receiver. The signal processing at the transmitter includes: a coding module, which performs pulse code modulation on the communication data to obtain coding gain; a narrowband transmission module, which performs BPSK modulation on the coded data; a spread spectrum transmission module, which performs BPSK modulation on the coded data and performs pseudo code spread spectrum modulation on the modulated data; and an up-conversion module, which up-converts the modulated signal to the communication frequency band.

[0064] The signal capture processing at the receiving end includes: a down-conversion module, which down-converts the received high-frequency spread spectrum signal to baseband; a conventional serial scanning module, which realizes correlation operations through parallel FFT transformation and performs non-correlated accumulation; a sideband interval scanning module, which estimates the sideband interval of two adjacent frequency search intervals and performs FFT-IFFT capture judgment based on the sideband interval estimation results; a capture judgment module, which combines the results of the above modules, obtains the Doppler frequency deviation estimation value, and makes a capture judgment; a despreading module, which despreads the baseband spread spectrum signal; a demodulation module, which performs BPSK demodulation on the despread signal; a codeword synchronization module, which makes codeword judgment based on the demodulated signal; and a decoding module, which decodes the synchronized codewords.

[0065] like Figure 2 As shown, the design of the satellite-to-ground telemetry transponder involved in this example mainly includes the RF front-end and the digital signal processing part. The RF front-end part is divided into the transmitting link and the receiving link, and the digital signal processing part is based on the FPGA chip. The transmitting and receiving links can be integrated on the PCB board of the same transponder. By default, the transponder is in receiving mode. When other protocol layers send data that needs to be communicated, the transponder can automatically switch to transmitting mode. In addition, the transponder can also turn on and off the transmitting and receiving functions through ground remote control commands, which makes it possible to achieve transmission and reception through one transponder.

[0066] Specifically: When the transponder is in the transmitting mode, after the data is processed by the FPGA, the FPGA performs operations such as modulation and spread spectrum on the communication data, and converts it into a baseband analog signal through a D / A converter. The baseband analog signal is modulated to the target communication frequency band after an up-conversion, and then the signal passes through the intermediate frequency amplifier and the band selection filter to remove the out-of-band noise, and is transmitted to the channel through the power amplifier. When the transponder is in the receiving mode, the received communication signal first passes through a low-noise amplifier and a band selection filter, and then performs a down-conversion operation to mix the signal to the intermediate frequency range. After the intermediate frequency signal passes through the intermediate frequency amplifier and filter to remove the out-of-band noise, it is converted into an intermediate frequency digital signal through an A / D converter and sent to the FPGA chip for subsequent processing. The transponder uses Figure 2 The structure can realize frequency shifting through one up-conversion or down-conversion, thereby simplifying the transponder structure.

[0067] like Figure 3 As shown, in the measurement and control transponder of the present invention, the FPGA chip is mainly responsible for the signal processing of the transmitting and receiving functions. In the transmitting mode, the transponder receives the communication data signal from other protocol layers. First, the data is pulse-coded modulated. Secondly, the encoded communication data is bit-wise multiplied with the local pseudo-code to achieve spread spectrum modulation. Finally, the spread spectrum direct spread spectrum signal is sent to the D / A converter after BPSK modulation. In the receiving mode, the FPGA receives the digital communication signal from the A / D converter and captures the signal through the high-sensitivity fast capture method of the present invention for the satellite-ground dynamic environment. After successfully capturing the spread spectrum signal, the transponder performs despreading and demodulation operations on it. The demodulated signal is processed by symbol synchronization, and the synchronized symbol is decoded. Finally, the decoded communication data frame will be sent to other protocol layers for further processing.

[0068] like Figure 4 As shown in FIG. 1 , it is a flow chart of a high-sensitivity fast acquisition method for satellite-ground dynamic environment in the present invention. The method is implemented by FPGA. The core technology is to use a parallel FFT pseudo-code phase acquisition method combined with an interval estimation module, thereby significantly improving the acquisition speed, capture sensitivity and Doppler frequency deviation capture range, and enhancing the overall reliability of the acquisition method. The steps are as follows: Figure 5 As shown, the details are as follows:

[0069] S1. The transmitting end performs pulse code modulation on the communication data, further performs BPSK modulation and direct spread spectrum modulation on the local pseudo code, up-converts the modulated signal to the target communication frequency and transmits it, and the receiving end receives the communication signal;

[0070] S2. Generate several local signals with different frequencies in the frequency search interval through a local parallel digitally controlled oscillator (NCO) group, and perform FFT-IFFT capture and determination on the communication signal;

[0071] S3. If it is determined that the capture fails, adjust the frequency search interval and repeat step S2; if it is determined that the capture fails in two adjacent frequency search intervals, perform sideband interval estimation on the two adjacent frequency search intervals, and perform FFT-IFFT capture judgment based on the sideband interval estimation results; repeat this step until it is determined that the capture is successful.

[0072] The present invention adopts a multi-channel parallel mode, that is, a local NCO is used to generate multiple carrier frequencies with fixed frequency differences and down-convert the received signals respectively, and then the multiple down-converted baseband signals are subsequently processed to improve the signal carrier frequency search efficiency.

[0073] The FFT-IFFT capture and determination specifically comprises the following steps:

[0074] The communication signal received by the receiving end is down-converted into several baseband spread spectrum signals through several local signals with different frequencies, and the signal is amplified by a low noise amplifier (LNA);

[0075] Fast Fourier Transform (FFT) processing is performed on a plurality of baseband spread spectrum signals respectively to obtain the FFT result of each baseband spread spectrum signal; at the same time, a local pseudo code is generated at the receiving end, and Fast Fourier Transform (FFT) processing is performed on the local pseudo code to obtain the FFT result of the local pseudo code; by designing timing constraints, the FFT processing process of the plurality of baseband spread spectrum signals and the FFT processing process of the local pseudo code are performed simultaneously, and the FFT results of the two are output synchronously.

[0076] Take the conjugate of the FFT result of the local pseudo code, multiply it bit by bit with the FFT result of each baseband spread spectrum signal, perform inverse fast Fourier transform (IFFT) on the product result, and obtain the baseband signal corresponding to each baseband spread spectrum signal;

[0077] In order to improve the receiver capture sensitivity, the IFFT results of the baseband signal are non-coherently accumulated, and the RMS value of the non-coherent accumulation result is used as the detection value of each baseband signal;

[0078] The maximum value among the detection values ​​of each baseband spread spectrum signal is taken. If the maximum value is greater than the preset detection threshold CT, it is determined that the capture is successful, otherwise it is determined that the capture fails.

[0079] like Figure 6 As shown, it is a diagram illustrating the sideband interval structure of the capture method in an embodiment of the present invention, and the figure shows two adjacent frequency search intervals, which correspond to parallel NCO groups of center frequency point 1 and center frequency point 2 respectively. Each peak corresponds to the NCO frequency search range. When the detected peak value exceeds the set threshold value CT, the system will perform signal capture at the corresponding NCO frequency. If the capture fails in both adjacent frequency search intervals, the frequency interval outside the capture range corresponding to a group of baseband signals corresponding to the last frequency point of the first frequency search interval of the two adjacent frequency search intervals and a group of baseband signals corresponding to the first frequency point of the second frequency search interval is used as the sideband interval. The detailed interval range is given by Figure 7 Definition.

[0080] like Figure 7As shown, the incoherent accumulation result of the baseband signal corresponding to the last frequency point of the first frequency search interval in two adjacent frequency search intervals (curve a) and the incoherent accumulation result of the baseband signal corresponding to the first frequency point of the second frequency search interval (curve b) are subtracted to obtain a difference curve (curve c). The difference curves of the two are taken in the sideband interval ( Figure 7 In the part of ④), a monotonically decreasing curve is obtained; the monotonically decreasing curve exceeds the normalized threshold T hz The frequency interval corresponding to the part is the estimated interval ( Figure 7 ①), the negative value less than the normalization threshold -T hz The frequency interval corresponding to the part is the estimated interval three ( Figure 7 ③), the frequency interval corresponding to the rest is the estimated interval 2 ( Figure 7 (2)

[0081] The sideband interval estimation is specifically as follows: preset a normalized threshold T hz , normalized threshold T hz According to the performance test setting, the detection peak value of the baseband signal corresponding to the last frequency point of the first frequency search interval in two adjacent frequency search intervals is subtracted from the detection value of the baseband signal corresponding to the first frequency point of the second frequency search interval; if the difference is greater than the normalization threshold T hz , then perform FFT-IFFT capture judgment within the estimation interval 1; if the difference is less than the negative value of the normalization threshold -T hz , then the FFT-IFFT capture decision is performed in the estimation interval three; otherwise, the FFT-IFFT capture decision is performed in the estimation interval two.

[0082] After the FFT-IFFT capture is successful, the pseudo code phase and carrier frequency rough estimation results of the communication signal are obtained, the Doppler frequency shift is determined according to the non-correlated accumulated value, and the local pseudo code is moved according to the maximum value of the IFFT detection peak, so as to realize the despreading of the received signal, and then the pseudo code phase fine tracking and carrier frequency fine tracking are turned on to further accurately estimate the carrier frequency and pseudo code phase difference. The tracked signal is synchronized with the code element, and the code element is decoded.

[0083] In the above method, the improved parallel FFT fast acquisition method adds sideband interval estimation. Compared with the traditional FFT fast acquisition method, the main improvements of this method are:

[0084] 1) A grouped parallel structure is adopted to further subdivide each frequency search interval, and a multi-channel local carrier frequency synthesizer with a fixed frequency difference is used to perform down-conversion modulation, pseudo code spread spectrum demodulation and signal capture. The parallel structure makes full use of FPGA hardware resources and significantly improves the capture speed of Doppler frequency deviation.

[0085] 2) The sideband interval estimation method is used to optimize the spectrum analysis process, fully utilize the sideband information of the adjacent scanning intervals captured twice in parallel, reduce the resource utilization rate of the FFT-IFFT group, and significantly shorten the data capture and processing time. As the maximum Doppler frequency deviation range increases, the optimization effect will increase accordingly.

[0086] 3) In the software implementation, the FFT processing of the signal and the pseudocode is realized through timing control, and the results are output synchronously. According to the order of FFT output, the result value of the signal Fourier transform is multiplied by the conjugate value of the pseudocode Fourier transform in real time. Compared with the traditional method of storing the pseudocode FFT results, this pipeline operation not only reduces the processing delay, but also reduces the hardware resources, and improves the flexibility and effectiveness of the method.

[0087] like Figure 8 As shown in the figure, the hardware measured diagram of the satellite-to-ground telemetry transponder of the present invention shows the composition of the telemetry transponder, including the power supply system, the transmitter transponder, the receiver transponder and the adjustable attenuator. The improved FFT fast capture method is implemented by the hardware description language VHDL and burned into the chip used by the ISE software of Xilinx. The hardware verification results show that the receiver limit sensitivity of the present invention can reach -130dBm, the total Doppler frequency deviation capture range can reach 140kHz, and the capture time is as low as 0.8 seconds, which fully meets the actual application requirements.

[0088] The above specific implementation modes are used to explain the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A high-sensitivity rapid capture method for satellite-ground dynamic environment, characterized in that: The following steps are involved: S1. The transmitting end obtains a communication signal that meets the target communication frequency after pulse code modulation, spread spectrum, and frequency modulation of the communication data, and transmits it, and the receiving end receives the communication signal; S2. Generate several local signals with different frequencies in the frequency search interval through the local parallel digitally controlled oscillator NCO group, and perform FFT-IFFT capture and determination on the communication signal; S3. If it is determined that the capture fails, adjust the frequency search interval and repeat step S2; if it is determined that the capture fails in two adjacent frequency search intervals, perform sideband interval estimation on the two adjacent frequency search intervals, and perform FFT-IFFT capture judgment based on the sideband interval estimation results; repeat this step until it is determined that the capture is successful.

2. The high-sensitivity rapid capture method for satellite-ground dynamic environment according to claim 1, characterized in that: The FFT-IFFT capture and determination specifically comprises the following steps: The communication signal received by the receiving end is down-converted by using a number of local signals with different frequencies to obtain a number of baseband spread spectrum signals; Performing fast Fourier transform (FFT) processing on the obtained several baseband spread spectrum signals respectively to obtain the FFT result of each baseband spread spectrum signal; At the same time, the receiving end generates a local pseudo code, performs fast Fourier transform (FFT) processing on the local pseudo code, and obtains the FFT result of the local pseudo code; Take the conjugate of the FFT result of the local pseudo code, multiply it with the FFT result of each baseband spread spectrum signal bit by bit, perform inverse fast Fourier transform IFFT on the product result, and obtain the baseband signal corresponding to each baseband spread spectrum signal; Performing non-coherent accumulation on the baseband signals respectively, and taking the root mean square value of the non-coherent accumulation result as the detection peak value of each baseband signal; The maximum value among the detected peak values ​​of each baseband signal is taken. If the maximum value is greater than the preset detection threshold CT, it is determined that the capture is successful, otherwise it is determined that the capture fails.

3. The high-sensitivity rapid capture method for satellite-ground dynamic environment according to claim 1, characterized in that: The sideband interval is a frequency interval outside the capture range corresponding to a group of baseband signals corresponding to the last frequency point of the first frequency search interval of two adjacent frequency search intervals and a group of baseband signals corresponding to the first frequency point of the second frequency search interval.

4. The high-sensitivity rapid capture method for satellite-ground dynamic environment according to claim 3 is characterized in that: The sideband interval estimation is specifically as follows: preset a normalized threshold T hz , the difference between the detection value of the baseband signal corresponding to the last frequency point of the first frequency search interval and the detection value of the baseband signal corresponding to the first frequency point of the second frequency search interval in two adjacent frequency search intervals is calculated; if the difference is greater than the normalization threshold T hz , then perform FFT-IFFT capture judgment within the estimation interval 1; if the difference is less than the negative value of the normalization threshold -T hz , then the FFT-IFFT capture decision is performed in the estimation interval three; otherwise, the FFT-IFFT capture decision is performed in the estimation interval two.

5. The high-sensitivity rapid capture method for satellite-ground dynamic environment according to claim 4 is characterized in that: The method for determining the estimation interval is: The baseband signal corresponding to the last frequency point of the first frequency search interval in two adjacent frequency search intervals is subtracted from the non-coherent accumulation result of the baseband signal corresponding to the first frequency point of the second frequency search interval to obtain a difference curve between the two, and the part of the difference curve between the two in the sideband interval is taken to obtain a monotonically decreasing curve; the monotonically decreasing curve exceeds the normalization threshold T hz The frequency interval corresponding to the part is the estimated interval 1, which is less than the negative value of the normalization threshold -T hz The frequency interval corresponding to the part is estimated interval three, and the frequency interval corresponding to the rest is estimated interval two.

6. The high-sensitivity rapid capture method for satellite-ground dynamic environment according to claim 2, characterized in that: By designing timing constraints, the FFT processing process of the baseband spread spectrum signal and the FFT processing process of the local pseudo code are performed simultaneously, and the FFT results of the two are output synchronously.

7. The high-sensitivity rapid capture method for satellite-ground dynamic environment according to claim 1, characterized in that: After the FFT-IFFT capture is successful, the pseudo-code phase and carrier frequency rough estimation results of the communication signal are obtained, and then the pseudo-code phase fine tracking and carrier frequency fine tracking are turned on, the tracked signal is synchronized with the code elements, and the code elements are decoded.

8. A high-sensitivity rapid acquisition system for use in a satellite-ground dynamic environment, used to implement the method according to any one of claims 1 to 7, characterized in that: include: Signal transceiver module: used for the transmitter to obtain a communication signal that meets the target communication frequency after pulse code modulation, spread spectrum, and frequency modulation of the communication data, and transmit it, and the receiver receives the communication signal; FFT-IFFT capture and judgment module: used to generate a number of local signals with different frequencies in the frequency search interval through the local parallel digital control oscillator NCO group, and perform FFT-IFFT capture and judgment on the communication signal; Sideband interval estimation module: used to perform sideband interval estimation on two adjacent frequency search intervals, and perform FFT-IFFT capture judgment based on the sideband interval estimation results.

9. A high-sensitivity rapid acquisition system for use in a satellite-ground dynamic environment, characterized in that: The signal transceiver module, the FFT-IFFT capture and determination module and the sideband interval estimation module are all implemented on an FPGA chip.

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