A method and device for capturing low-orbit satellite signals

Abstract

The present application belongs to the field of signal capture technology, and relates to a method and device for capturing low-orbit satellite signals. The method includes: acquiring a radio frequency signal sent by a low-orbit satellite to obtain a zero intermediate frequency signal; acquiring the orbital parameters, current time, and current positioning of the low-orbit satellite, and predicting the entry and exit time, minimum Doppler frequency shift, and maximum Doppler frequency shift; if it is determined that the current time is within the entry and exit time of the low-orbit satellite, obtaining a conjugate multiplication result based on the zero intermediate frequency signal; obtaining a discrete Fourier transform result based on the conjugate multiplication result, the minimum Doppler frequency shift within the entry and exit time, and the maximum Doppler frequency shift within the entry and exit time; making a judgment based on the discrete Fourier transform result, if it is determined that the capture is successful, calculating the Doppler frequency deviation result obtained by the capture, and outputting the Doppler frequency deviation result, the pilot segment of the zero intermediate frequency signal, and the data segment of the zero intermediate frequency signal as the capture result. The present application has a small amount of calculation and low power consumption for capturing low-orbit satellite signals.

Description

Technical Field

[0001] The present application relates to the field of signal capture technology, and in particular to a method and device for capturing low-orbit satellite signals. Background Art

[0002] As the number of Internet users continues to increase worldwide, the demand for high-speed, low-latency and global coverage communication services is growing.

[0003] Low-orbit satellite communication systems have faster satellite movement and shorter signal propagation distances, enabling them to provide these services and meet user needs. Furthermore, advancements in low-orbit satellite communication technology have continuously expanded its application areas. In addition to traditional communication services, low-orbit satellites are also used in the Internet of Things, intelligent transportation, telemedicine, navigation enhancement, environmental monitoring and other fields. The growth in demand in these areas has driven market expansion.

[0004] However, low-orbit satellites also face challenges, such as the greater Doppler effect caused by faster speeds and the shorter transit time of low-orbit satellites. These factors bring considerable challenges and difficulties to ground terminals in capturing low-orbit satellite signals.

[0005] Generally speaking, in low-orbit satellite communication systems, in order for the ground low-orbit satellite signal receiving end to quickly estimate the carrier frequency difference and bit deviation, each frame usually carries a known preamble, that is, a pilot sequence. The receiving end uses this known pilot sequence to capture the low-orbit satellite signal, that is, signal arrival detection and rough estimation of the phase and frequency of the received signal.

[0006] In the current ground receiver low-orbit satellite signal acquisition method, most ground low-orbit satellite signal receivers are always in the power-on acquisition state to prevent missing the signals transmitted by low-orbit satellites to the ground during the short satellite transit time.

[0007] However, these methods have high requirements on the power consumption of the receiver and the complexity of the acquisition algorithm. Summary of the Invention

[0008] Based on this, it is necessary to provide a low-orbit satellite signal capture method and device to address the above technical problems, so as to reduce the computational complexity and power consumption of low-orbit satellite signal capture.

[0009] A low-orbit satellite signal acquisition method, comprising:

[0010] Acquire the radio frequency signal sent by the low-orbit satellite and obtain the zero intermediate frequency signal based on the radio frequency signal;

[0011] Obtain the orbital parameters, current time, and current position of the low-orbit satellite, and predict the entry and exit time of the low-orbit satellite relative to the ground from the current time to multiple hours in the future, the minimum Doppler shift during the entry and exit time, and the maximum Doppler shift during the entry and exit time;

[0012] A judgment is made based on the current time and the entry and exit time of the low-orbit satellite. If it is determined that the current time is within the entry and exit time of the low-orbit satellite, a conjugate multiplication result is obtained based on the zero intermediate frequency signal; a discrete Fourier transform result is obtained based on the conjugate multiplication result, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time;

[0013] A judgment is made based on the discrete Fourier transform result. If the capture is successful, the Doppler frequency deviation result obtained by the capture is calculated, and the Doppler frequency deviation result, the pilot segment of the zero intermediate frequency signal, and the data segment of the zero intermediate frequency signal are output as the capture result.

[0014] In one embodiment, a judgment is made based on the current time and the entry and exit time of the low-orbit satellite. If it is determined that the current time is within the entry and exit time of the low-orbit satellite, a conjugate multiplication result is obtained based on the zero intermediate frequency signal; a discrete Fourier transform result is obtained based on the conjugate multiplication result, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time, including:

[0015] Based on the current time and the entry and exit time of low-orbit satellites, determine whether the current time is within the entry and exit time of low-orbit satellites;

[0016] If it is determined that the current time is within the entry and exit time of the low-orbit satellite, the zero intermediate frequency signal and the pilot pseudo-random sequence are conjugate multiplied in the time dimension to obtain a conjugate multiplication result;

[0017] Based on the conjugate multiplication result, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time, a discrete Fourier transform calculation is performed in the frequency dimension to obtain a discrete Fourier transform result.

[0018] In one embodiment, a discrete Fourier transform is performed in the frequency dimension based on the conjugate multiplication result, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time to obtain a discrete Fourier transform result, including:

[0019] ;

[0020] Where, is the discrete Fourier transform result, is the number of points in the pilot pseudo-random sequence, is the conjugate multiplication result, is the imaginary number symbol, , where floor(.) is rounded down, ceil(.) is rounded up, and f step is the frequency search interval of discrete Fourier transform, f dn is the minimum Doppler frequency shift during the entry and exit time, f up is the maximum Doppler shift during the entry and exit time.

[0021] In one embodiment, a conjugate multiplication calculation is performed on the zero intermediate frequency signal and the pilot pseudo random sequence in the time dimension to obtain a conjugate multiplication result, including:

[0022] ;

[0023] Where, is the conjugate multiplication result, is the number of points in the pilot pseudo-random sequence, is a zero intermediate frequency signal, is the conjugate transformation, is the pilot pseudo-random sequence.

[0024] In one embodiment, if it is determined that the current time is not within the entry and exit time of the low-orbit satellite, the calculation channel of the conjugate multiplication result and the discrete Fourier transform result is closed.

[0025] In one embodiment, a determination is made based on a discrete Fourier transform result. If the capture is successful, a Doppler frequency offset result obtained by the capture is calculated, and the Doppler frequency offset result, a pilot segment of a zero intermediate frequency signal, and a data segment of the zero intermediate frequency signal are output as the capture result, including:

[0026] According to the discrete Fourier transform results, the peak value, mean value and peak index of the signal are obtained, and whether the capture is successful is determined;

[0027] If the capture is successful, the Doppler frequency deviation result obtained by the capture is calculated according to the peak index, and the Doppler frequency deviation result, the pilot segment of the zero intermediate frequency signal, and the data segment of the zero intermediate frequency signal are output as the capture result;

[0028] If it is determined that the capture has failed, the forecast is repeated and the next round of capture is carried out.

[0029] In one embodiment, the peak value, mean value, and peak index of the signal are obtained based on the discrete Fourier transform result, and whether the capture is successful is determined, including:

[0030] According to the discrete Fourier transform results, the peak value, mean value and peak index of the signal are obtained;

[0031] Based on the peak value and the mean value, the peak-to-average ratio is calculated;

[0032] Compare the peak-to-average ratio with the capture success threshold to determine whether the capture is successful.

[0033] In one embodiment, obtaining a radio frequency signal transmitted by a low-orbit satellite and obtaining a zero intermediate frequency signal based on the radio frequency signal includes:

[0034] Obtain the radio frequency signal sent by the low-orbit satellite, perform radio frequency down-conversion, and obtain the intermediate frequency signal;

[0035] Perform analog-to-digital conversion sampling on the intermediate frequency signal to obtain an intermediate frequency sampling signal;

[0036] The intermediate frequency sampling signal is digitally down-converted to zero intermediate frequency to obtain a zero intermediate frequency signal.

[0037] A low-orbit satellite signal capture device adopts a low-orbit satellite signal capture method, comprising: a front-end unit and a capture processing unit;

[0038] The front-end unit is used to obtain the radio frequency signal sent by the low-orbit satellite and obtain the zero intermediate frequency signal based on the radio frequency signal;

[0039] The capture processing unit includes: a control module, a positioning module, a storage module, a conversion module and a correlator module. The control module is connected to the positioning module, the storage module, the conversion module and the correlator module respectively, and the control module is also connected to the front unit;

[0040] The control module is used to obtain the orbital parameters of the low-orbit satellite, and in combination with the current time and the current positioning, predict the low-orbit satellite entry and exit time relative to the ground from the current time to multiple hours in the future, the minimum Doppler frequency shift during the entry and exit time, and the maximum Doppler frequency shift during the entry and exit time; it is also used to determine whether the current time is within the low-orbit satellite entry and exit time based on the current time and the low-orbit satellite entry and exit time; it is also used to send the zero intermediate frequency signal to the correlator module; it is also used to determine whether the capture is successful based on the discrete Fourier transform result, calculate the captured Doppler frequency deviation result when it is determined that the capture is successful, and output the Doppler frequency deviation result, the pilot segment of the zero intermediate frequency signal, and the data segment of the zero intermediate frequency signal as the capture result;

[0041] The positioning module is used to obtain the current time and current location;

[0042] The storage module is used to store the entry and exit time, the minimum Doppler frequency shift within the entry and exit time, and the maximum Doppler frequency shift within the entry and exit time;

[0043] The transformation module is used to obtain a discrete Fourier transform result according to the conjugate multiplication result, the minimum Doppler frequency shift within the entry and exit time, and the maximum Doppler frequency shift within the entry and exit time;

[0044] The correlator module is used to determine when the current time is within the entry and exit time of the low-orbit satellite, and obtain the conjugate multiplication result based on the zero intermediate frequency signal.

[0045] In one embodiment, the front-end unit includes: an acquisition module, a sampling module, and a frequency conversion module connected in sequence;

[0046] The acquisition module is used to acquire the radio frequency signal sent by the low-orbit satellite and obtain the intermediate frequency signal after the radio frequency down-conversion;

[0047] The sampling module is used to perform analog-to-digital conversion sampling on the intermediate frequency signal to obtain an intermediate frequency sampling signal;

[0048] The frequency conversion module is used to digitally down-convert the intermediate frequency sampling signal to zero intermediate frequency to obtain a zero intermediate frequency signal.

[0049] The above-mentioned low-orbit satellite signal acquisition method and device is a technology that predicts Doppler shift based on a satellite orbit motion model. By analyzing the orbital parameters and motion patterns of the low-orbit satellite, the entry and exit times and Doppler shift of the low-orbit satellite relative to the ground-based low-orbit satellite signal acquisition terminal in the future are predicted. Based on this, the ground-based low-orbit satellite signal acquisition terminal captures the low-orbit satellite's transmission signal. Compared with traditional methods, it can:

[0050] 1) Predict the entry and exit times and Doppler shift of low-orbit satellite signals in advance;

[0051] 2) The ground-based low-orbit satellite signal acquisition terminal can control the on / off of acquisition-related modules based on the predicted entry and exit times of low-orbit satellites to save power consumption;

[0052] 3) The ground-based low-orbit satellite signal acquisition terminal can configure the frequency search of the relevant acquisition module based on the predicted Doppler frequency shift during the entry and exit time of the low-orbit satellite. By using prior information (predicted entry and exit time and Doppler frequency shift), the number of frequency points to be searched is reduced, and the search range of the frequency points is shortened to reduce the search time and complexity in the frequency dimension, avoid interference introduced during full-frequency search, and reduce interference from irrelevant frequencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a diagram showing an application scenario of a low-orbit satellite signal acquisition method according to an embodiment;

[0054] Figure 2 1 is a flow chart of a method for capturing low-orbit satellite signals according to an embodiment;

[0055] Figure 3 This is a diagram of a frame format of a low-orbit satellite transmitting end in a low-orbit satellite signal acquisition method according to an embodiment;

[0056] Figure 4 is a structural block diagram of a low-orbit satellite signal acquisition device in one embodiment;

[0057] Figure 5 This is a partial working process diagram of a low-orbit satellite signal acquisition device in one embodiment. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for explaining this application and are not intended to limit this application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in this application without creative work are within the scope of protection of this application.

[0059] In addition, the terms "first," "second," and so on, used in this application are for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this application, "multiple groups" means at least two groups, such as two groups, three groups, and so on, unless otherwise specifically defined.

[0060] In this application, unless otherwise specified or limited, the terms "connect," "fix," etc. should be understood in a broad sense. For example, "fix" can mean a fixed connection, a detachable connection, or an integral connection; it can mean a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean internal communication between two elements or an interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0061] In addition, the technical solutions between the various embodiments of the present application can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0062] The present application provides a low-orbit satellite signal acquisition method that can be applied to Figure 1 In the application scenario diagram shown, the terminal 102 communicates with the server 104 via a network. The terminal 102 may include but is not limited to various personal computers, laptops, smart phones, tablet computers, and portable wearable devices. The server 104 may be a server corresponding to various portal websites or a backend of a work system.

[0063] This application provides a low-orbit satellite signal acquisition method, such as Figure 2The flow chart shown in FIG. 1 shows an embodiment of the present invention. Figure 1 The following example illustrates the terminal in the example, including:

[0064] Step 202: Acquire a radio frequency signal sent by a low-orbit satellite, and obtain a zero intermediate frequency signal based on the radio frequency signal.

[0065] Specifically:

[0066] Obtain the radio frequency signal sent by the low-orbit satellite, and obtain the intermediate frequency signal after radio frequency down-conversion;

[0067] Performing analog-to-digital conversion (ADC) on the intermediate frequency signal to obtain an intermediate frequency sampling signal;

[0068] The intermediate frequency sampling signal is digitally down-converted to zero intermediate frequency to obtain a zero intermediate frequency signal.

[0069] In this step, if Figure 3 The frame format shown in the figure shows the LEO satellite transmitter. The pilot sequence used for acquisition in the frame header of the LEO satellite transmission frame is a pseudo-random (PN) sequence known to both the sender and receiver, known as a pilot pseudo-random sequence (which can be obtained using existing technologies). Bit "0" in the pilot and data segments undergoes bipolar IQ conversion to "+1," while bit "1" undergoes bipolar IQ conversion to "-1." The sequence is then modulated onto a carrier wave and transmitted from the LEO satellite antenna. The ground-based LEO satellite signal acquisition terminal detects the presence of the pilot segment in the frame signal arriving from the LEO satellite and estimates the starting data position and Doppler offset of the LEO satellite transmission frame.

[0070] Step 204, obtain the orbital parameters, current time and current position of the low-orbit satellite, and predict the entry and exit time of the low-orbit satellite relative to the ground from the current time to multiple hours in the future, the minimum Doppler shift during the entry and exit time, and the maximum Doppler shift during the entry and exit time.

[0071] In this step, the orbital parameters of the low-orbit satellite, that is, the two-row element number of the low-orbit satellite, can be obtained according to the existing technology.

[0072] The specific forecasting process is an existing technology, for example, using a satellite forecasting model (such as the SGP4 (Simplified General Perturbations Version 4th) satellite orbit motion model) for forecasting, which includes the motion laws of low-orbit satellites.

[0073] The minimum Doppler shift within the entry and exit time and the maximum Doppler shift within the entry and exit time constitute the Doppler shift range.

[0074] Step 206: Make a judgment based on the current time and the entry and exit time of the low-orbit satellite. If it is determined that the current time is within the entry and exit time of the low-orbit satellite, obtain the conjugate multiplication result based on the zero intermediate frequency signal; and obtain the discrete Fourier transform result based on the conjugate multiplication result, the minimum Doppler frequency shift within the entry and exit time, and the maximum Doppler frequency shift within the entry and exit time.

[0075] Specifically:

[0076] A judgment is made based on the current time and the entry and exit time of the low-orbit satellite. If it is determined that the current time is within the entry and exit time of the low-orbit satellite, the zero-intermediate-frequency signal and the pilot pseudo-random sequence are conjugate multiplied in the time dimension to obtain a conjugate multiplication result.

[0077] Based on the conjugate multiplication result, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time, a discrete Fourier transform calculation is performed in the frequency dimension to obtain a discrete Fourier transform result.

[0078] More specifically:

[0079] Based on the current time and the entry and exit time of low-orbit satellites, determine whether the current time is within the entry and exit time of low-orbit satellites;

[0080] If the current time is determined to be within the entry and exit time of the low-orbit satellite, the zero-IF signal and the pilot pseudo-random sequence are conjugate multiplied in the time dimension to obtain the conjugate multiplication result:

[0081] ;

[0082] Where, is the conjugate multiplication result, is the number of points in the pilot pseudo-random sequence, is a zero intermediate frequency signal, is the conjugate transformation, is a pilot pseudo-random sequence (which can be obtained by the existing technology);

[0083] Based on the conjugate multiplication result, the minimum Doppler shift during the entry and exit time, and the maximum Doppler shift during the entry and exit time, a discrete Fourier transform (DFT) calculation is performed in the frequency dimension to obtain the discrete Fourier transform result:

[0084] ;

[0085] Where, is the discrete Fourier transform result, is the number of points of the pilot pseudo-random sequence, that is, the coherent integration length of DFT, is the conjugate multiplication result, is the imaginary number symbol, , where floor(.) is rounded down, ceil(.) is rounded up, and f step is the frequency search interval of discrete Fourier transform, f dn is the minimum Doppler frequency shift during the entry and exit time, f up is the maximum Doppler shift during the entry and exit time.

[0086] In this step, if it is determined that the current time is not within the entry and exit time of the low-orbit satellite, the calculation channels of the conjugate multiplication result and the discrete Fourier transform result are closed.

[0087] Step 208: make a judgment based on the discrete Fourier transform result. If the capture is successful, calculate the captured Doppler frequency offset result, and output the Doppler frequency offset result, the pilot segment of the zero intermediate frequency signal, and the data segment of the zero intermediate frequency signal as the capture result.

[0088] Specifically: based on the discrete Fourier transform results, the peak value, mean value and peak index of the signal are obtained, and it is determined whether the capture is successful; if the capture is successful, the Doppler frequency deviation result obtained by the capture is calculated based on the peak index, and the Doppler frequency deviation result, the pilot segment of the zero intermediate frequency signal and the data segment of the zero intermediate frequency signal are output as the capture result; if the capture is determined to be unsuccessful, the forecast is re-performed and the next round of capture is carried out.

[0089] Among them: according to the discrete Fourier transform result, the peak value, mean value and peak index of the signal are obtained, and whether the capture is successful is judged, including: according to the discrete Fourier transform result, the peak value, mean value and peak index of the signal are obtained; according to the peak value and mean value, the peak-to-average ratio is calculated; the peak-to-average ratio is compared with the capture success threshold to judge whether the capture is successful.

[0090] In this step, the capture success threshold is an empirical value, which can be set or adjusted by software according to existing technology. How to judge whether the capture is successful belongs to existing technology and will not be described in detail here.

[0091] The above-mentioned low-orbit satellite signal acquisition method is a technology that predicts Doppler shift based on the satellite orbit motion model. By analyzing the orbital parameters and motion patterns of the low-orbit satellite, the entry and exit times and Doppler shift of the low-orbit satellite relative to the ground low-orbit satellite signal acquisition terminal in the future are predicted. Based on this, the ground low-orbit satellite signal acquisition terminal captures the low-orbit satellite's transmission signal. Compared with traditional methods, it can:

[0092] 1) Predict the entry and exit times and Doppler shift of low-orbit satellite signals in advance;

[0093] 2) The ground-based low-orbit satellite signal acquisition terminal can control the on / off of acquisition-related modules based on the predicted entry and exit times of low-orbit satellites to save power consumption;

[0094] 3) The ground-based low-orbit satellite signal acquisition terminal can configure the frequency search of the relevant acquisition module based on the predicted Doppler frequency shift during the entry and exit time of the low-orbit satellite. By using prior information (predicted entry and exit time and Doppler frequency shift), the number of frequency points to be searched is reduced, and the search range of the frequency points is shortened to reduce the search time and complexity in the frequency dimension, avoid interference introduced during full-frequency search, and reduce interference from irrelevant frequencies.

[0095] It should be understood that although Figure 2 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. In addition, Figure 2 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0096] This application also provides a low-orbit satellite signal acquisition device, such as Figure 4 As shown, in one embodiment, it includes: a front-end unit and a capture processing unit.

[0097] The front-end unit is used to acquire radio frequency signals transmitted by low-orbit satellites and derive a zero-intermediate frequency (ZIF) signal from the radio frequency signals. The front-end unit includes an acquisition module, a sampling module, and a frequency conversion module. Within the front-end unit, the acquisition module, sampling module, and frequency conversion module are connected in sequence.

[0098] The acquisition module is used to acquire the radio frequency signal sent by the low-orbit satellite and perform radio frequency down-conversion on the radio frequency signal to obtain an intermediate frequency signal.

[0099] The sampling module is used to perform analog-to-digital conversion sampling on the intermediate frequency signal to obtain an intermediate frequency sampling signal.

[0100] The frequency conversion module is used to digitally down-convert the intermediate frequency sampling signal to zero intermediate frequency to obtain a zero intermediate frequency signal.

[0101] The capture processing unit includes: a control module, a positioning module, a storage module, a conversion module and a correlator module. In the capture processing unit, the control module is connected to the positioning module, the storage module, the conversion module and the correlator module respectively, and is also connected to the front unit.

[0102] The control module is used to obtain the orbital parameters of the low-orbit satellite, and in combination with the current time and the current positioning, predict the low-orbit satellite entry and exit time relative to the ground from the current time to multiple hours in the future, the minimum Doppler frequency shift during the entry and exit time, and the maximum Doppler frequency shift during the entry and exit time; it is also used to determine whether the current time is within the low-orbit satellite entry and exit time based on the current time and the low-orbit satellite entry and exit time; it is also used to send the zero intermediate frequency signal to the correlator module; it is also used to determine whether the capture is successful based on the discrete Fourier transform result, calculate the captured Doppler frequency deviation result when it is determined that the capture is successful, and output the Doppler frequency deviation result, the pilot segment of the zero intermediate frequency signal, and the data segment of the zero intermediate frequency signal as the capture result;

[0103] The positioning module is used to obtain the current time and current location of the capture device (i.e. the current latitude and longitude information);

[0104] The storage module is used to store the entry and exit time, the minimum Doppler frequency shift within the entry and exit time, and the maximum Doppler frequency shift within the entry and exit time;

[0105] The transformation module is used to obtain a discrete Fourier transform result according to the conjugate multiplication result, the minimum Doppler frequency shift within the entry and exit time, and the maximum Doppler frequency shift within the entry and exit time;

[0106] The correlator module is used to determine when the current time is within the entry and exit time of the low-orbit satellite, and obtain the conjugate multiplication result based on the zero intermediate frequency signal.

[0107] The working process of a low-orbit satellite signal acquisition device (the low-orbit satellite signal acquisition device serves as a ground low-orbit satellite signal acquisition terminal) is as follows:

[0108] 1) The front-end unit receives the RF signal sent by the low-orbit satellite and converts the received RF signal r(t) to an intermediate frequency signal r d (t).

[0109] 2) For the intermediate frequency signal r d (t) Perform analog-to-digital conversion sampling to obtain the intermediate frequency sampling signal s IF (n).

[0110] 3) Sampling the intermediate frequency signal s IF (n) is digitally down-converted to zero intermediate frequency to obtain a zero intermediate frequency signal s(n) (this signal is a digital signal).

[0111] 4) Input the zero intermediate frequency digital signal s(n) into the capture processing unit and enter the low-orbit satellite signal capture processing flow, as follows: Figure 5 shown.

[0112] 4.1) The acquisition processing unit uses the control module and the positioning module (e.g., the Global Navigation Satellite System (GNSS) module) to calculate the low-orbit satellite signal relative to the ground from the current time to the next N hours (the parameter N can be set), the low-orbit satellite entry and exit time (i.e., entry and exit time) t0~t1 of the acquisition terminal, and the minimum Doppler frequency shift f within the entry and exit time t0~t1. dn and the maximum Doppler shift f up and the entry and exit time t0~t1, the minimum Doppler frequency shift f dn and the maximum Doppler shift f up Store in storage module.

[0113] 4.2) The capture processing unit obtains the current time and current position of the low-orbit satellite signal capture device through the positioning module, obtains the stored low-orbit satellite entry and exit time through the storage module, and uses the control module to determine whether the current time is within the low-orbit satellite entry and exit time. If the current time is not within the low-orbit satellite entry and exit time, the control module turns off the conversion module and the correlator module, and enters a loop judgment state (continuously judging whether the current time is within the low-orbit satellite entry and exit time). If the current time is within the low-orbit satellite signal entry and exit time, the conversion module and the correlator module are turned on and calculations are performed.

[0114] 4.3) The control module sends the zero intermediate frequency signal s(n) to the correlator module. The correlator module performs conjugate multiplication calculation on s(n) and the known pilot pseudo-random sequence in the time dimension to obtain the conjugate multiplication result. .

[0115] 4.4) After the correlator module completes the calculation, the control module calculates the result of the correlator, i.e. the conjugate multiplication result And the minimum Doppler frequency shift f stored in the storage module dn and the maximum Doppler shift f up Passed to the transformation module, the transformation module uses the minimum Doppler frequency shift f dn and the maximum Doppler shift f up ,Will Perform discrete Fourier transform calculation in the frequency dimension to obtain the discrete Fourier transform result After the discrete Fourier transform is calculated, the peak value peek, mean value mean, and peak index idx of the discrete Fourier transform of the signal segment are obtained and the results are passed to the control module. The control module calculates the peak-to-average ratio based on the peak value peek and mean value mean, and compares it with the capture success threshold threshold to determine whether the capture is successful.

[0116] 4.5) If the capture is successful, the control module calculates the captured Doppler frequency offset result fdopper based on the peak index of the discrete Fourier transform (how to calculate it is known in the art), stores the zero-IF data s(n) containing the pilot segment and data segment into the storage module, and outputs it as the capture result. If the capture is unsuccessful, indicating that the signal segment does not contain the pilot signal of the low-orbit satellite signal, the process proceeds to 4.1 and loops for the next capture round (the capture process is moment-to-moment capture).

[0117] For the specific definition of a low-orbit satellite signal acquisition device, please refer to the definition of a low-orbit satellite signal acquisition method above, and will not be repeated here. Each module in the above-mentioned device can be implemented in whole or in part by software, hardware, or a combination thereof. Each of the above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to each of the above modules.

[0118] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0119] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0120] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for capturing low-orbit satellite signals, characterized in that: include: Acquire the radio frequency signal sent by the low-orbit satellite and obtain the zero intermediate frequency signal based on the radio frequency signal; Obtain the orbital parameters, current time, and current position of the low-orbit satellite, and predict the entry and exit time of the low-orbit satellite relative to the ground from the current time to multiple hours in the future, the minimum Doppler shift during the entry and exit time, and the maximum Doppler shift during the entry and exit time; The current time and the entry and exit time of the low-orbit satellite are judged. If the current time is judged to be within the entry and exit time of the low-orbit satellite, the conjugate multiplication result is obtained according to the zero intermediate frequency signal; The discrete Fourier transform result is obtained according to the conjugate multiplication result, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time; A judgment is made based on the discrete Fourier transform result. If the capture is successful, the Doppler frequency deviation result obtained by the capture is calculated, and the Doppler frequency deviation result, the pilot segment of the zero-IF signal, and the data segment of the zero-IF signal are output as the capture result; If it is determined that the current time is not within the entry and exit time of the low-orbit satellite, the calculation channel of the conjugate multiplication result and the discrete Fourier transform result is closed.

2. The method for capturing low-orbit satellite signals according to claim 1, wherein: The current time and the entry and exit time of the low-orbit satellite are judged. If the current time is judged to be within the entry and exit time of the low-orbit satellite, the conjugate multiplication result is obtained according to the zero intermediate frequency signal; The discrete Fourier transform results are obtained based on the conjugate multiplication results, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time, including: Based on the current time and the entry and exit time of low-orbit satellites, determine whether the current time is within the entry and exit time of low-orbit satellites; If it is determined that the current time is within the entry and exit time of the low-orbit satellite, the zero intermediate frequency signal and the pilot pseudo-random sequence are conjugate multiplied in the time dimension to obtain a conjugate multiplication result; Based on the conjugate multiplication result, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time, a discrete Fourier transform calculation is performed in the frequency dimension to obtain a discrete Fourier transform result.

3. The method for capturing low-orbit satellite signals according to claim 2, wherein: Based on the conjugate multiplication result, the minimum Doppler shift within the entry and exit time, and the maximum Doppler shift within the entry and exit time, a discrete Fourier transform calculation is performed in the frequency dimension to obtain the discrete Fourier transform results, including: Where, is the discrete Fourier transform result, is the number of points in the pilot pseudo-random sequence, is the conjugate multiplication result, is the imaginary number symbol, k =floor(f dn / f step ), floor(f dn / f step )+1,…,ceil(f up / f step ), where floor(.) is rounded down, ceil(.) is rounded up, and f step is the frequency search interval of discrete Fourier transform, f dn is the minimum Doppler frequency shift during the entry and exit time, f up is the maximum Doppler shift during the entry and exit time.

4. The method for capturing low-orbit satellite signals according to claim 3, wherein: Perform conjugate multiplication calculation on the zero intermediate frequency signal and the pilot pseudo-random sequence in the time dimension to obtain the conjugate multiplication result, including: Where, is the conjugate multiplication result, is the number of points in the pilot pseudo-random sequence, is a zero intermediate frequency signal, is the conjugate transformation, is the pilot pseudo-random sequence.

5. A low-orbit satellite signal acquisition method according to any one of claims 1 to 4, characterized in that: The capture is determined based on the discrete Fourier transform result. If the capture is successful, the Doppler frequency offset result is calculated and the Doppler frequency offset result, the pilot segment of the zero-IF signal, and the data segment of the zero-IF signal are output as the capture result, including: According to the discrete Fourier transform results, the peak value, mean value and peak index of the signal are obtained, and whether the capture is successful is determined; If the capture is successful, the Doppler frequency deviation result obtained by the capture is calculated according to the peak index, and the Doppler frequency deviation result, the pilot segment of the zero intermediate frequency signal, and the data segment of the zero intermediate frequency signal are output as the capture result; If it is determined that the capture has failed, the forecast is repeated and the next round of capture is carried out.

6. The method for capturing low-orbit satellite signals according to claim 5, wherein: Based on the discrete Fourier transform results, the peak value, mean value, and peak index of the signal are obtained, and whether the capture is successful is determined, including: According to the discrete Fourier transform results, the peak value, mean value and peak index of the signal are obtained; Based on the peak value and the mean value, the peak-to-average ratio is calculated; Compare the peak-to-average ratio with the capture success threshold to determine whether the capture is successful.

7. A low-orbit satellite signal acquisition method according to any one of claims 1 to 4, characterized in that: Obtain the radio frequency signal sent by the low-orbit satellite and obtain the zero intermediate frequency signal based on the radio frequency signal, including: Obtain the radio frequency signal sent by the low-orbit satellite, and obtain the intermediate frequency signal after radio frequency down-conversion; Perform analog-to-digital conversion sampling on the intermediate frequency signal to obtain an intermediate frequency sampling signal; The intermediate frequency sampling signal is digitally down-converted to zero intermediate frequency to obtain a zero intermediate frequency signal.

8. A low-orbit satellite signal acquisition device, characterized in that: A low-orbit satellite signal capture method according to any one of claims 1 to 7, comprising: a front-end unit and a capture processing unit; The front-end unit is used to obtain the radio frequency signal sent by the low-orbit satellite and obtain the zero intermediate frequency signal based on the radio frequency signal; The capture processing unit includes: a control module, a positioning module, a storage module, a conversion module and a correlator module. The control module is connected to the positioning module, the storage module, the conversion module and the correlator module respectively, and the control module is also connected to the front unit; The control module is used to obtain the orbital parameters of the low-orbit satellite, and in combination with the current time and the current positioning, predict the low-orbit satellite entry and exit time relative to the ground from the current time to multiple hours in the future, the minimum Doppler frequency shift during the entry and exit time, and the maximum Doppler frequency shift during the entry and exit time; it is also used to determine whether the current time is within the low-orbit satellite entry and exit time based on the current time and the low-orbit satellite entry and exit time; it is also used to send the zero intermediate frequency signal to the correlator module; it is also used to determine whether the capture is successful based on the discrete Fourier transform result, calculate the captured Doppler frequency deviation result when it is determined that the capture is successful, and output the Doppler frequency deviation result, the pilot segment of the zero intermediate frequency signal, and the data segment of the zero intermediate frequency signal as the capture result; The positioning module is used to obtain the current time and current location; The storage module is used to store the entry and exit time, the minimum Doppler frequency shift within the entry and exit time, and the maximum Doppler frequency shift within the entry and exit time; The transformation module is used to obtain a discrete Fourier transform result according to the conjugate multiplication result, the minimum Doppler frequency shift within the entry and exit time, and the maximum Doppler frequency shift within the entry and exit time; The correlator module is used to determine when the current time is within the entry and exit time of the low-orbit satellite, and obtain the conjugate multiplication result based on the zero intermediate frequency signal.

9. The low-orbit satellite signal acquisition device according to claim 8, characterized in that: The front unit includes: an acquisition module, a sampling module and a frequency conversion module connected in sequence; The acquisition module is used to acquire the radio frequency signal sent by the low-orbit satellite, perform radio frequency down-conversion, and obtain the intermediate frequency signal; The sampling module is used to perform analog-to-digital conversion sampling on the intermediate frequency signal to obtain an intermediate frequency sampling signal; The frequency conversion module is used to digitally down-convert the intermediate frequency sampling signal to zero intermediate frequency to obtain a zero intermediate frequency signal.

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