Acquisition method and system in carrier synchronization based on ephemeris

Abstract

The invention relates to a capturing method and system in carrier synchronization based on ephemeris. The method comprises the following steps: acquiring ephemeris, a receiving signal and a local pseudo code of a satellite to be captured; according to the ephemeris, Doppler frequency offset of the satellite signal to be captured is obtained; obtaining an initial search range of the satellite signal to be captured according to the Doppler frequency offset; generating a local signal through the initial search range; obtaining the phase of the satellite signal to be captured according to the local pseudo code and the received signal; obtaining the correlation of the received signal and the local signal in a time domain through the received signal and the local signal; and capturing the satellite signal to be captured according to the correlation and the phase. According to the method, the problems that in the related technology, satellite signal capturing is not accurate enough and capturing efficiency is not high enough are solved, the purpose of reducing the calculation amount is achieved by reducing the search range, and the efficiency and precision of satellite signal capturing are improved.

Description

Technical Field

[0001] The invention relates to the field of satellite communication, in particular to a capture method and system in carrier synchronization based on ephemeris. Background Art

[0002] Low-orbit satellite communication systems have attracted extensive attention in the fields of civil and military communications in recent years due to their wide communication range, low communication delay, and freedom from terrain and environmental factors. In the application of low-orbit satellites, there is a large relative speed and acceleration between the low-orbit satellite and the ground terminal, which will cause a large Doppler frequency deviation with high-order time-varying characteristics, making it impossible for the receiver to complete accurate carrier frequency capture and thus unable to maintain communication.

[0003] Traditional carrier frequency capture faces problems such as poor robustness, low capture accuracy, high complexity and low applicability. In low signal-to-noise ratio environments, traditional carrier capture algorithms are easily affected by noise and interference, resulting in capture failure or significant performance degradation. In high-speed mobile environments, the Doppler shift of the signal will cause frequency changes. Traditional algorithms often have difficulty adapting to rapidly changing frequencies, resulting in unstable capture. In the case of weak signals or strong interference, traditional carrier capture methods may not be able to accurately estimate the actual frequency of the signal. In high-speed mobile communication environments, the signal will shift in frequency due to the Doppler effect. If the algorithm cannot accurately estimate this frequency change, accurate carrier capture cannot be achieved. Traditional carrier capture algorithms have limitations in sensitivity and resolution in their design, which limits their capture accuracy in complex signal environments. Some traditional carrier capture algorithms require complex mathematical operations and may only consider specific signal environments when designed. When faced with variable signal conditions, the algorithm needs to be further adjusted and optimized, which increases complexity. Therefore, it is of great significance to improve the efficiency and accuracy of carrier frequency capture. Summary of the invention

[0004] In view of the defects in the prior art, the present invention provides a capture method and system for carrier synchronization based on ephemeris, and solves the problem of insufficient accuracy and efficiency in capturing satellite signals in the related art.

[0005] One aspect of the present invention provides a capture method in carrier synchronization based on ephemeris, including: obtaining the ephemeris, received signal and local pseudo code of the satellite to be captured; obtaining the Doppler frequency deviation of the satellite signal to be captured according to the ephemeris; obtaining the initial search range of the satellite signal to be captured based on the Doppler frequency deviation; generating a local signal through the initial search range; obtaining the phase of the satellite signal to be captured according to the local pseudo code and the received signal; obtaining the correlation between the received signal and the local signal in the time domain through the received signal and the local signal; and capturing the satellite signal to be captured according to the correlation and the phase.

[0006] The initial search range is finally determined based on the ephemeris. Through this method, the search range is reduced during the satellite signal capture process, thereby reducing the amount of calculation. According to the search range, the satellite signal receiver generates a corresponding local signal, thereby improving the efficiency and accuracy of satellite signal capture.

[0007] Optionally, according to the ephemeris, the Doppler frequency deviation of the satellite signal to be captured is obtained, including: using the ephemeris to obtain a first velocity and a first position of the satellite in a geocentric inertial coordinate system; determining a second velocity and a second position of the satellite in a geocentric coordinate system through the first velocity and the first position; determining a third velocity and a third position of the satellite relative to a ground terminal through the second velocity and the second position; and obtaining the Doppler frequency deviation of the satellite signal to be captured according to the third velocity and the third position.

[0008] The satellite's position in the geocentric inertial coordinate system is ultimately converted into the relative position and velocity between the satellite signal receiver and the satellite. The Doppler frequency deviation is caused by the relative motion between the satellite signal receiver and the satellite, making the calculation of the Doppler frequency deviation more convenient.

[0009] Optionally, obtaining the initial search range of the satellite signal to be captured based on the Doppler frequency deviation includes: using the Doppler frequency deviation to obtain the maximum value and the minimum value of the Doppler frequency deviation; determining the center frequency and the search range of the satellite signal to be captured based on the maximum value and the minimum value; and obtaining the initial search range of the satellite signal to be captured through the center frequency and the search range.

[0010] In the calculation of the initial search range, compared to directly taking the maximum and minimum values ​​as the search range. This method centers the search range on the average frequency, which helps to quickly locate the center of the signal, thereby improving the search efficiency. At the same time, it reduces the risk of search failure caused by rapid changes or extreme values ​​of the signal. Even in the case of large changes in Doppler frequency shift, it can ensure that the search range covers all possible frequencies.

[0011] Optionally, generating a local signal through the initial search range includes: determining a frequency value range of the local signal through the initial search range; and generating the local signal according to the frequency value range of the local signal.

[0012] The frequency value range of the local signal is determined through the initial search range, and then the local signal is generated according to the frequency value range of the local signal, so that the local signal forms a one-to-one correspondence with the initial search range, making the signal capture more accurate.

[0013] Optionally, the correlation between the received signal and the local signal in the time domain is obtained through the received signal and the local signal, including: setting the length of a window, the window being used to select a portion of the received signal from the received signal; using the window to perform sliding sampling on the received signal, and extracting the sampling data of the window during each sliding process; obtaining the first frequency domain information for the first time based on the sampling data extracted for the first time; obtaining the current first frequency domain information through the first frequency domain information obtained for the previous time and the sampling data currently extracted, until the first frequency domain information for each time except the first time is obtained; obtaining the second frequency domain information of the local signal based on the local signal; calculating the product result of the first frequency domain information and the second frequency domain information based on the first frequency domain information and the second frequency domain information; and using the product result to obtain the correlation between the received signal and the local signal in the time domain.

[0014] According to the sliding sampling of the received signal, the received signal is divided into multiple signal segments and calculated separately, which simplifies the complex problem. At the same time, because there is a large overlap between the two slides, the calculation result of the latter can be updated based on the calculation result of the previous one, which greatly reduces the amount of calculation. Calculating the correlation between the local signal and the received signal in the time domain can accurately capture the signal.

[0015] Optionally, capturing the satellite signal to be captured according to the correlation and the phase includes: determining the point of strongest correlation between the received signal and the local signal according to the correlation; obtaining the frequency of the satellite signal to be captured through the point of strongest correlation; and capturing the satellite signal to be captured according to the frequency and the phase.

[0016] According to the obtained frequency and phase, the carrier generated by the local oscillator is made consistent with the carrier of the received signal in frequency and phase, so that the signal can be better demodulated and the purpose of capturing the signal is achieved.

[0017] Optionally, the first frequency domain information of the first time satisfies the following formula: in, is the frequency domain information, is the frequency index, To receive the signal, is the sample point of the received signal, is the length of the signal, is the orbital eccentricity.

[0018] The formula has a simple structure and is easy to calculate. Since the formula calculates the frequency domain information of a signal segment, the formula can simplify complex signal problems and play a huge role in improving calculation efficiency.

[0019] Optionally, the current first frequency domain information satisfies the following formula: in, is the current frequency domain information, is the frequency domain information of the previous one, is the frequency index, is the length of the signal, is the orbital eccentricity.

[0020] When calculating the current frequency domain information, this formula updates the current frequency domain information according to the previous frequency domain information, which reduces the amount of calculation and improves the calculation efficiency.

[0021] Optionally, the correlation data satisfies the following formula: in, is the correlation result in the time domain, is the sample point of the received signal, is the frequency index, is the length of the signal, is the product result, is the orbital eccentricity.

[0022] This formula has a simple structure and is easy to calculate.

[0023] Another aspect of the present invention provides a capture system in ephemeris-based carrier synchronization, comprising: a processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are interconnected, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute the capture method in ephemeris-based carrier synchronization described in the previous aspect of the present invention.

[0024] The capture system for carrier synchronization based on ephemeris of the present invention has a compact structure, stable performance, high integration and simple composition, and can stably execute the capture method for carrier synchronization based on ephemeris provided in the previous aspect of the present invention, further improving the overall applicability and practical application capability of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flowchart of a method for acquiring carrier synchronization based on ephemeris according to an embodiment of the present invention; Figure 2 The present invention provides an acquisition system for carrier synchronization based on ephemeris according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not need to be adopted to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, software or methods are not specifically described.

[0027] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or subcombination. In addition, it should be understood by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale.

[0028] In one embodiment of the present invention, a method for acquiring carrier synchronization based on ephemeris is provided. It should be noted that, Figure 1 As shown, the steps of the flowchart representing the method can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be performed in an order different from that herein.

[0029] Figure 1 Flow chart of a method for capturing carrier synchronization based on ephemeris according to an embodiment of the present invention, as shown in FIG. Figure 1 As shown, the method comprises the following steps: Step S1, obtaining the ephemeris, received signal and local pseudo code of the satellite to be captured.

[0030] In this embodiment, the satellite ephemeris is a data table or data set that records in detail the satellite's orbital information in space and its changing patterns over time. In simple terms, it is like a "schedule" and "position record" for the satellite, which contains the corresponding relationship between the satellite's position, speed and other parameters and time, and provides key data support for ground equipment to track and use satellites.

[0031] The ephemeris mainly includes Kepler orbit parameters, time parameters and perturbation parameters. Among them, Kepler orbit parameters include semi-major axis, eccentricity, orbit inclination, right ascension of ascending node, argument of perigee and mean anomaly.

[0032] Orbital semi-major axis: half of the major axis of the satellite's elliptical orbit. It determines the size of the satellite orbit and also reflects the average distance of the satellite from the earth. The larger the semi-major axis, the farther the satellite orbit is from the earth.

[0033] Eccentricity: It is used to describe the degree of difference between the shape of a satellite orbit and a circle. Its value range is between 0 and 1, where e=0 represents a circular orbit, and the closer e is to 1, the more elliptical the orbit. Earth observation satellites often use near-circular orbits with a small eccentricity to ensure observations at a relatively stable altitude.

[0034] Orbital inclination: It is the angle between the satellite orbit plane and the Earth's equatorial plane. This angle determines the inclination of the satellite orbit relative to the Earth. For example, the orbital inclination of polar-orbiting satellites is close to 90°, which can cover the Earth's polar regions well, and is crucial for tasks such as polar observation and weather forecasting.

[0035] Ascending node right ascension: The angle from the vernal equinox to the ascending node of the satellite orbit (the point where the satellite crosses the equatorial plane from the southern hemisphere into the northern hemisphere). It is used to determine the orientation of the satellite orbit plane in space, just like setting a starting angle for the satellite orbit in the space coordinate system.

[0036] Argument of perigee: The angle from the ascending node along the direction of satellite movement to the perigee of the satellite orbit (the point where the satellite is closest to the earth), which is used to more accurately describe the position of the satellite in the orbital plane.

[0037] Mean anomaly: It is an angle parameter related to the position of the satellite in orbit, which changes evenly over time. Combined with Kepler's equation, it can be used to calculate the change of the satellite's position over time on the elliptical orbit, where the mean anomaly satisfies the following formula: in, is the Earth's gravitational constant, is the average motion, is the elliptical orbit period, is the semi-major axis of the orbit, is the Earth's gravitational constant; For the moment of perigee, is the mean anomaly angle.

[0038] Time parameters are also important information. For example, the reference time is a reference time point for the ephemeris data. All orbital parameters are based on this time. For example, the ephemeris may give the satellite orbit parameters at a certain coordinated universal time, and the subsequent orbit predictions and calculations are based on this starting time for time extrapolation. In addition, the satellite ephemeris is not permanently valid because the satellite orbit changes over time. The ephemeris will contain information about the validity period, such as how many hours or days it is valid. At the same time, there will also be content about the update cycle, which is used to explain how often the satellite ground control system will update the ephemeris data. For example, the ephemeris update cycle of some navigation satellites may be several hours to ensure that ground users can obtain more accurate satellite orbit information for positioning.

[0039] Since the earth is not an ideal sphere, there are non-spherical gravitational perturbations, as well as the influence of various factors such as the gravitational pull of the sun and the moon, and atmospheric drag, which will cause the satellite orbit to change slightly. The orbital perturbation parameters in the ephemeris are used to describe these changes. For example, atmospheric drag will gradually reduce the orbital altitude of low-orbit satellites, and the atmospheric drag coefficient related parameters in the ephemeris can help predict the attenuation of the orbital altitude.

[0040] The received signal refers to the signal obtained by the ground receiving equipment from the electromagnetic waves transmitted by the satellite.

[0041] The local pseudo code is a coding sequence generated inside the receiver that has the same structure and characteristics as the pseudo random code in the satellite transmission signal. The pseudo random code is a binary sequence that appears to be random but is actually generated according to a certain rule and has good autocorrelation and cross-correlation.

[0042] Step S2: obtaining the Doppler frequency deviation of the to-be-captured satellite signal according to the ephemeris.

[0043] Wherein, obtaining the Doppler frequency deviation of the to-be-captured satellite signal according to the ephemeris specifically includes the following sub-steps: Step S201, using the ephemeris to obtain a first velocity and a first position of the satellite in a geocentric inertial coordinate system.

[0044] In this embodiment, the geocentric inertial coordinate system refers to a coordinate system with the center of the earth as the origin, and the coordinate axes remain unchanged relative to distant stars, ignoring the influence of the earth's rotation and other forces, providing an idealized reference frame. The geocentric inertial coordinate system plays an important role in studying the motion of celestial bodies, satellite orbits, etc. It provides a relatively stable and easy-to-calculate reference system for these studies. The X-axis points to the vernal equinox, which is the intersection of the ecliptic and the equator in astronomy. The Y-axis is orthogonal to the X-axis, usually in a direction with an angle of 90 degrees with the X-axis, specifically pointing to the positive direction in the ecliptic plane, and the Z-axis is perpendicular to the XY plane and points to the direction of the North Star.

[0045] In step S201, the first position and the first velocity in the geocentric inertial coordinate system satisfy the following formulas respectively: in, is the position in the geocentric inertial coordinate system, is the velocity in the geocentric inertial coordinate system, is the orbital eccentricity, is the Earth's gravitational constant, is the semi-major axis of the orbit, represents the approach angle, represents the direction cosine vector, Represents the direction cosine vector.

[0046] Then the vector The expression is: in, Argument of perigee, is the right ascension of the ascending node, is the orbital inclination.

[0047] Step S202: Determine a second speed and a second position of the satellite in an earth-fixed coordinate system based on the first speed and the first position.

[0048] In this embodiment, the earth-fixed coordinate system is a coordinate system fixed on the earth and rotates with the earth. The earth-centered inertial coordinate system is converted to the earth-fixed coordinate system so that the relative position and velocity of the satellite can be described by latitude and longitude. It is necessary to use the relationship between the earth-centered inertial coordinate system and the instantaneous mean equatorial coordinate system, the instantaneous mean equatorial coordinate system and the instantaneous true equatorial coordinate system, the instantaneous true equatorial coordinate system and the quasi-earth-fixed coordinate system, and the quasi-earth-fixed coordinate system and the earth-fixed coordinate system to convert. To solve the position and velocity of the terminal in the earth-fixed coordinate system, the position and velocity conversion matrix should be set as , Therefore, the position and velocity of the satellite in the Earth-fixed coordinate system satisfy the following formulas: in, is the position in the Earth-fixed coordinate system, is the velocity in the Earth-fixed coordinate system, is the position transformation matrix, is the position in the geocentric inertial coordinate system, is the velocity conversion matrix, is the velocity in the Earth-centered inertial coordinate system.

[0049] Typically, longitude ( ),latitude( )、Elevation( ) to represent the geographic position of the receiver, then the vector in the earth-fixed coordinate system is Satisfies the following formula: in, It represents the position of the receiving device in the earth-fixed coordinate system. The definitions of other symbols in the formula are the same as those mentioned above and will not be repeated here.

[0050] Based on the position of the receiving device in the ground-fixed coordinate system Similarly, the speed of the receiving device in the ground-fixed coordinate system can be obtained .

[0051] Step S203, determining a third speed and a third position of the satellite relative to the ground terminal according to the second speed and the second position; In this embodiment, the relative third speed and third position refer to the relative speed and relative position between the satellite and the ground terminal. The relative speed and relative position respectively satisfy the following formulas: in, is the relative position, is the relative speed. The definitions of other symbols in the formula are the same as those mentioned above and will not be repeated here.

[0052] Step S204: Obtain the Doppler frequency deviation of the to-be-captured satellite signal according to the third speed and the third position.

[0053] In this embodiment, Doppler frequency deviation refers to the phenomenon that the frequency received by the receiver differs from the frequency sent by the satellite due to the relative motion between the satellite and the signal receiver. The principle of Doppler frequency deviation is that when the satellite and the receiver are close to each other, the frequency received by the receiver will increase; when the satellite and the receiver are far away from each other, the frequency received by the receiver will decrease.

[0054] Among them, the Doppler frequency deviation satisfies the following formula: in, is the Doppler frequency deviation, is the nominal RF frequency of the received signal, is the speed of light, is the relative speed, is the velocity vector With position vector The angle between.

[0055] Step S3: obtaining an initial search range of the satellite signal to be captured according to the Doppler frequency deviation.

[0056] Wherein, obtaining the initial search range of the to-be-captured satellite signal according to the Doppler frequency deviation specifically includes the following sub-steps: Step S301: using the Doppler frequency shift, obtain the maximum value and the minimum value of the Doppler frequency shift.

[0057] In this embodiment, when the satellite moves on the predetermined orbit, there will be relative motion between the satellite and the receiver. A relative velocity will be generated between the satellite and the receiver at any time. At the same time, according to the relative position and velocity, the angle between the velocity vector and the position vector can be obtained. According to the calculation formula of Doppler frequency deviation, the maximum value of Doppler frequency deviation can be calculated. and minimum value .

[0058] Step S302: determining the center frequency and search range of the satellite signal to be captured according to the maximum value and the minimum value.

[0059] In this embodiment, the satellite center frequency refers to the center frequency of the frequency band during satellite communication or satellite signal transmission. It is a key reference point of the entire signal frequency band and is used to determine the position of the signal in the spectrum. Low earth orbit satellites are close to the earth and have a short signal transmission path, but in order to achieve global coverage, multiple satellites are required to form a network, and the frequencies they use may be different, and frequency coordination between satellites needs to be considered.

[0060] The center frequency of the satellite is half of the sum of the maximum value of the Doppler frequency deviation and the minimum value of the Doppler frequency deviation. Therefore, the center frequency satisfies the following formula: In the formula, is the center frequency, is the maximum value of the Doppler frequency deviation, is the minimum value of Doppler frequency deviation.

[0061] The search range is the difference between the maximum and minimum values ​​of the Doppler frequency deviation. Therefore, the search range satisfies the following formula: In the formula, is the search scope, is the maximum value of the Doppler frequency deviation, is the minimum value of Doppler frequency deviation.

[0062] Step S303: obtaining an initial search range of the to-be-captured satellite signal through the center frequency and the search range.

[0063] In this embodiment, the initial search range refers to the range of parameters such as frequency, phase, and time delay that may exist in the signal that is initially set when performing satellite signal search or other similar signal processing tasks. Reasonable setting of this range is crucial for quickly and accurately capturing signals. If the initial search range is too large, the search time and computing resource consumption will increase; if the range is too small, the signal may be missed, resulting in failure to successfully capture.

[0064] The initial search range of the satellite signal to be captured is determined according to the center frequency and the search range. The specific initial search range is set to the center frequency plus or minus half of the search range. Among them, the initial search range of the satellite signal to be captured satisfies the following formula: In the formula, is the initial search range, is the center frequency, is the search scope.

[0065] In the calculation of the initial search range, compared to directly taking the maximum and minimum values ​​as the search range. This method centers the search range on the average frequency, which helps to quickly locate the center of the signal, thereby improving the search efficiency. At the same time, it reduces the risk of search failure caused by rapid changes or extreme values ​​of the signal. Even in the case of large changes in Doppler frequency shift, it can ensure that the search range covers all possible frequencies.

[0066] Step S4: Generate a local signal through the initial search range.

[0067] The step of generating a local signal through the initial search range specifically includes the following sub-steps: Step S401, determining the frequency value range of the local signal through the initial search range; In this embodiment, in satellite signal reception, since the satellite signal frequency is usually high, it is more complicated to directly process the high-frequency signal. The local signal is mainly used for down-conversion operation. An accurate local signal can effectively reduce the bit error rate in the demodulation process. If the carrier frequency or phase of the local signal is inconsistent with that of the satellite signal, the demodulated signal will be distorted, increasing the bit error.

[0068] Local signals help achieve time synchronization and frequency synchronization in satellite signal reception. In satellite communication systems, there is a delay in signal transmission. In order to accurately receive and process signals, the receiving end needs to be consistent with the time and frequency reference of the satellite signal. The local signal can be used as a reference to synchronize the clock and frequency of the receiving end with the satellite signal source by comparing and adjusting with the received satellite signal.

[0069] Therefore, through the initial search range, multiple local signal value ranges corresponding to the search range can be determined to better identify and capture satellite signals.

[0070] Step S402: Generate the local signal according to the frequency value range of the local signal.

[0071] In this embodiment, the core component for generating the local signal is a local oscillator. It is an electronic circuit that can generate a stable frequency signal. It is usually achieved by using the piezoelectric effect of a quartz crystal. The quartz crystal will generate mechanical vibration under the action of an electric field, and its vibration frequency is very stable.

[0072] As described above, based on the determined frequency value range of the local signal, the receiving device generates a plurality of local signals corresponding to the search range one by one.

[0073] Step S5, obtaining the phase of the satellite signal to be captured according to the local pseudo code and the received signal.

[0074] In this embodiment, the satellite signal phase refers to the state of the electromagnetic wave signal emitted by the satellite at a certain moment. In the fields of satellite communication and navigation, phase is an important parameter, which is related to factors such as the propagation time, frequency and relative position between the satellite and the receiving station of the signal.

[0075] Local pseudo code is a locally generated code similar to a random code sequence used in satellite communications and satellite navigation systems. It is a binary code sequence with a specific pattern, usually generated by a shift register or other circuit through a specific feedback logic.

[0076] The sliding correlation algorithm sets a different rate for the pseudo code generator than the received signal, thereby achieving relative sliding between the two. In a correlation cycle, the pseudo code generally slides half a chip, and the sliding continues until the two code sequences are phase-aligned, at which point the phase of the received pseudo code is obtained. For the convenience of analysis and without loss of generality, it is assumed that the pseudo code phase has been aligned.

[0077] Among them, the pseudo-code generator is a device or software module that can generate a pseudo-random code sequence. Pseudo-random code is a binary code sequence that appears to be random but is actually generated according to a certain rule. Its basic principle is to generate a sequence through one or more shift registers combined with specific feedback logic.

[0078] Step S6: Obtain the correlation between the received signal and the local signal in the time domain through the received signal and the local signal.

[0079] Wherein, obtaining the correlation between the received signal and the local signal in the time domain by using the received signal and the local signal specifically includes the following sub-steps: Step S601, setting the length of a window, wherein the window is used to select a portion of the received signal from the received signal.

[0080] In this embodiment, when the window slides on the received signal, this is a signal processing technique. The received signal can be regarded as a time series, and the window is a fixed-length interval that moves step by step along this time series. The signal sliding window length refers to a fixed-length observation interval in the signal processing process. This interval is like a "window" that can slide along the signal sequence, which is used to analyze, process or extract features from the signal within the window.

[0081] Step S602: Sliding sampling is performed on the received signal using the window, and sampling data of the window in each sliding process is extracted.

[0082] In this embodiment, the sliding of the window is performed in a certain step, that is, each sliding is performed for a fixed length, and after each sliding, the corresponding data in the window is extracted.

[0083] The step size of each window movement is related to the speed of change of the relevant signal. A larger window sliding step size can be used for a slowly changing signal, because the signal does not change much over a long period of time, and a larger step size can speed up the processing without losing key information. Similarly, for a rapidly changing signal, a smaller window sliding step size is required.

[0084] The step size of the window movement is also related to the length of the window itself. When the window length is short, a relatively small window sliding step size can usually be used to ensure full coverage of the signal. However, if the processing purpose is to extract the long-term trend of the signal or perform coarse-grained feature extraction, a larger window sliding step size can be used even if the window length is long.

[0085] In addition, when computing resources are limited, in order to reduce the amount of calculation, it may be necessary to increase the window sliding step. For signal processing tasks with high real-time requirements, it may be necessary to appropriately increase the window sliding step, but at the same time ensure that important target information is not missed due to excessive step size.

[0086] Step S603: obtaining the first frequency domain information of the first time according to the sampled data extracted for the first time.

[0087] In this embodiment, as in the above step S5, the pseudo code phase has been aligned, the first sampling before the window starts sliding, and the sampled signal represented in the time domain is converted into a frequency domain representation to obtain the first frequency domain information for the first time, wherein the first frequency domain information for the first time satisfies the following formula: in, is the frequency domain information, is the frequency index, To receive the signal, is the sample point of the received signal, is the length of the signal.

[0088] Step S604: Obtain the current first frequency domain information through the first frequency domain information obtained last time and the sampling data currently extracted, until the first frequency domain information is obtained each time except the first time.

[0089] In this embodiment, in order to improve efficiency, the frequency domain information of the sampled signal is usually not recalculated after each window movement. Instead, the frequency domain information of the previous sampled signal can be used to update the frequency domain information of the current window sampled signal, which can significantly reduce the amount of calculation. This method can reduce the computational complexity and the capture time at the same time.

[0090] Among them, the current first frequency domain information satisfies the following formula: in, is the current frequency domain information, is the frequency domain information of the previous one, is the frequency index, is the length of the signal.

[0091] It should be noted that the first frequency domain information in step S603 and the first frequency domain information in step S604 have the same concept but do not have the same attribute value. That is, the first frequency domain information represents the result obtained by converting each sampled signal represented in the time domain into a frequency domain representation, but among these result data, the amplitude of each data in the frequency domain representation may be different.

[0092] In the above step S603 and step S604, the results of the two steps have the same properties, but the implementation methods are different. In step S603, the entire sampled data is calculated, while step S604 is different. Step S604 updates the current window based on the calculation result of the previous sampled data. The reason for this is that when the window slides, the step is usually small, and the current sample extracted after each slide has a large overlap area with the sample extracted last time. Therefore, the size of the window sliding sampling step will affect the accuracy of step S604. The smaller the step, the higher the accuracy.

[0093] Step S605: obtaining second frequency domain information of the local signal according to the local signal.

[0094] In this embodiment, a plurality of local signal data are regarded as a continuous data stream, and the data stream represented in the time domain is converted to a frequency domain representation to obtain second frequency domain information of the local signal.

[0095] Step S606: Calculate a product of the first frequency domain information and the second frequency domain information according to the first frequency domain information and the second frequency domain information.

[0096] In this embodiment, the first frequency domain information and the second frequency domain information are multiplied to obtain a product result of the first frequency domain information and the second frequency domain information.

[0097] Step S607: using the multiplication result, obtain the correlation between the received signal and the local signal in the time domain.

[0098] In this embodiment, the correlation between the local signal and the received signal in the time domain refers to performing correlation processing on the local signal and the received signal in the time domain, and evaluating their correlation by calculating the similarity between them. This correlation analysis is widely used in satellite communication systems.

[0099] By converting the product result in the frequency domain to the time domain, the correlation between the local signal and the received signal in the time domain is obtained. In order to correctly receive and process satellite signals, the receiving end needs to maintain time synchronization with the satellite signal. Time domain correlation can serve as an important basis for time synchronization.

[0100] In step S607, the correlation data satisfies the following formula: in, is the correlation result in the time domain, is the sample point of the received signal, is the frequency index, is the length of the signal, is the product result.

[0101] Step S7: capturing the to-be-captured satellite signal according to the correlation and the phase.

[0102] Step S701: Determine, based on the correlation, a point at which the correlation between the received signal and the local signal is strongest.

[0103] In this embodiment, based on the correlation, the point with the largest amplitude in the time domain in the correlation data can be found, that is, the point where the correlation between the received signal and the local signal is the strongest. The point with the strongest correlation represents the best matching point between the received signal and the local signal, that is, the frequency and phase differences between them are the smallest.

[0104] Step S702: obtaining the frequency of the satellite signal to be captured through the point with the strongest correlation.

[0105] In this embodiment, when the correlation between the local signal and the received satellite signal reaches the strongest, it means that the two have achieved the best match in time and frequency. In an ideal situation, when the local signal and the satellite signal have the same frequency, their correlation will reach a peak at a certain time delay, and this peak is the point with the strongest correlation.

[0106] Step S703: Capture the satellite signal to be captured according to the frequency and the phase.

[0107] In this embodiment, the frequency and phase of the local oscillator are adjusted to be aligned with the carrier frequency and phase of the satellite signal, thereby achieving capture of the satellite signal.

[0108] In general, there is a close relationship between the received signal and the local signal. In carrier synchronization, the local signal is usually designed to be in the same frequency and phase as the expected received signal, so that the information carried in the received signal can be correctly demodulated. The purpose of carrier synchronization is to ensure that the carrier generated by the local oscillator of the receiver is consistent with the carrier of the received signal in frequency and phase, thereby allowing the signal to be correctly demodulated. In practical applications, since the received signal may be affected by various factors during the transmission process (such as multipath effect, frequency offset, phase noise, etc.), the received signal may not be completely in the same frequency and phase as the local signal. At this time, it is necessary to estimate the frequency and phase difference between the received signal and the local signal through correlation analysis, and make corresponding adjustments. The specific operation is: the local oscillator first generates a local signal that is expected to be close to the carrier frequency of the received signal. The received signal and the local signal are correlated, which is usually performed by multiplying the frequency domain information of the received signal with the conjugate of the frequency domain information of the local signal. The correlation result in the time domain is obtained by representing the multiplication result in the time domain, and the peak is found in the result. The location of the peak indicates the best match between the received signal and the local signal, that is, the frequency and phase differences between them are minimal. Based on the location of this peak, we can estimate the frequency and phase differences between the received signal and the local signal and adjust the local oscillator accordingly to achieve precise carrier synchronization.

[0109] like Figure 2 As shown, on the other hand, the present invention also provides a capture system in ephemeris-based carrier synchronization, comprising: a processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are interconnected, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute relevant steps of a relevant embodiment of a capture method in ephemeris-based carrier synchronization of the present invention.

[0110] In the acquisition system for carrier synchronization based on ephemeris provided by the present invention, each functional component can be integrated into one processing component, or each component can exist physically separately, or two or more components can be integrated into one component. The above-mentioned integrated components can be implemented in the form of hardware or in the form of software functions.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A capture method in carrier synchronization based on ephemeris, characterized in that: The method comprises: Obtain the ephemeris, received signal and local pseudo code of the satellite to be captured; Obtaining the Doppler frequency deviation of the to-be-captured satellite signal according to the ephemeris; Obtaining an initial search range of the to-be-captured satellite signal according to the Doppler frequency deviation; Generate a local signal through the initial search range; Obtaining the phase of the satellite signal to be captured according to the local pseudo code and the received signal; Obtaining, by using the received signal and the local signal, a correlation between the received signal and the local signal in the time domain; The to-be-captured satellite signal is captured according to the correlation and the phase.

2. The acquisition method in carrier synchronization based on ephemeris according to claim 1, characterized in that: The step of obtaining the Doppler frequency deviation of the to-be-captured satellite signal according to the ephemeris includes: Using the ephemeris, obtaining a first velocity and a first position of the satellite in a geocentric inertial coordinate system; Determining a second speed and a second position of the satellite in an earth-fixed coordinate system based on the first speed and the first position; Determine a third speed and a third position of the satellite relative to the ground terminal by using the second speed and the second position; The Doppler frequency deviation of the to-be-captured satellite signal is obtained according to the third speed and the third position.

3. The acquisition method in carrier synchronization based on ephemeris according to claim 1, characterized in that: The step of obtaining an initial search range of the to-be-captured satellite signal according to the Doppler frequency deviation comprises: Using the Doppler frequency deviation, obtaining a maximum value and a minimum value of the Doppler frequency deviation; Determine the center frequency and search range of the to-be-captured satellite signal according to the maximum value and the minimum value; The initial search range of the satellite signal to be captured is obtained through the center frequency and the search range.

4. The acquisition method in carrier synchronization based on ephemeris according to claim 1, characterized in that: The generating a local signal through the initial search range includes: Determining the frequency value range of the local signal through the initial search range; The local signal is generated according to a frequency value range of the local signal.

5. The acquisition method in carrier synchronization based on ephemeris according to claim 1, characterized in that: The obtaining, by using the received signal and the local signal, a correlation between the received signal and the local signal in the time domain comprises: Setting a length of a window, wherein the window is used to select a portion of the received signal from the received signal; Using the window to perform sliding sampling on the received signal, and extracting sampling data of the window in each sliding process; According to the sampled data extracted for the first time, obtaining the first frequency domain information for the first time; The current first frequency domain information is obtained by using the first frequency domain information obtained last time and the sampled data currently extracted, until the first frequency domain information is obtained each time except the first time; Obtaining second frequency domain information of the local signal according to the local signal; Calculate a product of the first frequency domain information and the second frequency domain information according to the first frequency domain information and the second frequency domain information; The correlation between the received signal and the local signal in the time domain is obtained by using the multiplication result.

6. The acquisition method in carrier synchronization based on ephemeris according to claim 1, characterized in that: The step of capturing the to-be-captured satellite signal according to the correlation and the phase includes: Determining, based on the correlation, a point where the correlation between the received signal and the local signal is strongest; Obtaining the frequency of the satellite signal to be captured through the point with the strongest correlation; The to-be-captured satellite signal is captured according to the frequency and the phase.

7. The acquisition method in carrier synchronization based on ephemeris according to claim 5, characterized in that: The first frequency domain information of the first time satisfies the following formula: in, is the frequency domain information, is the frequency index, To receive the signal, is the sample point of the received signal, is the length of the signal, is the orbital eccentricity.

8. The acquisition method in carrier synchronization based on ephemeris according to claim 5, characterized in that: The current first frequency domain information satisfies the following formula: in, is the current frequency domain information, is the frequency domain information of the previous one, is the frequency index, is the length of the signal, is the orbital eccentricity.

9. The acquisition method in carrier synchronization based on ephemeris according to claim 5, characterized in that: The correlation data satisfies the following formula: in, is the correlation result in the time domain, is the sample point of the received signal, is the frequency index, is the length of the signal, is the product result, is the orbital eccentricity.

10. An acquisition system for carrier synchronization based on ephemeris, characterized in that: include: A processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are connected to each other, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute the acquisition method in the carrier synchronization based on ephemeris according to any one of claims 1 to 9.

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