A direct satellite user downlink synchronization method adapting to the high dynamics of low-orbit satellites

Abstract

The present invention discloses a downlink synchronization method for a direct-connected satellite user that is adaptable to the high dynamics of a low-orbit satellite. The method comprises: dividing the downlink synchronization to obtain an initial synchronization phase and a synchronization tracking phase; in the initial synchronization phase, when the user can obtain ephemeris information, using an ephemeris pre-compensation method to perform initial synchronization; when the user cannot obtain ephemeris information, using a multi-step integer frequency division method to perform initial synchronization; in the synchronization tracking phase, using a preset synchronization tracking model to perform synchronization tracking to achieve downlink synchronization of the direct-connected satellite user. The method of the present invention can be applied to downlink synchronization of direct-connected satellite users in a high dynamic environment, with high synchronization accuracy and low complexity.

Description

Technical Field

[0001] The present invention relates to the field of satellite communication technology, and in particular to a downlink synchronization method for directly connected satellite users adapting to the high dynamics of low-orbit satellites. Background Art

[0002] At present, the technology of mobile phone direct connection to satellite has become the research and development focus of academia and industry at home and abroad. In the future, mobile phone direct connection to satellite will be characterized by mobile phones equipped with miniaturized built-in satellite antennas and supporting broadband data and communication services. In order to provide mobile phone direct connection to satellite broadband services, it is necessary to design a constellation system based on low-orbit satellites. However, the high-speed flight state of low-orbit satellites has a great impact on the continuity of satellite-to-ground link communications, delay stability and operating frequency stability. The extremely high time-frequency deviation changes under the high-dynamic motion of low-orbit satellites far exceed the adaptability of the existing ground mobile communication 5G transmission system. The large frequency deviation of low-orbit satellites affects the search for synchronization signals of the downlink of mobile phone direct connection to satellites, resulting in slow or even difficult synchronization of the satellite-mobile phone downlink. Therefore, it is necessary to focus on the downlink synchronization problem under the influence of large frequency deviation caused by high dynamics. Summary of the invention

[0003] The technical problem to be solved by the present invention is that, in order to solve the problem that the large frequency deviation of low-orbit satellites affects the search for synchronization signals of the downlink of the direct-connected satellite by mobile phones, resulting in slow or even difficult synchronization of the satellite-mobile phone downlink, a downlink synchronization method for direct-connected satellite users that is adaptable to the high dynamics of low-orbit satellites is proposed. In particular, an initial synchronization method based on multi-step integer frequency division is designed for the case where the user cannot obtain the ephemeris.

[0004] In order to solve the above technical problems, an embodiment of the present invention discloses a downlink synchronization method for a direct-connected satellite user adapting to the high dynamics of a low-orbit satellite, the method comprising:

[0005] S1, divide the downlink synchronization into an initial synchronization phase and a synchronization tracking phase;

[0006] S2, in the initial synchronization stage, when the user can obtain ephemeris information, the ephemeris pre-compensation method is used for initial synchronization; when the user cannot obtain ephemeris information, the multi-step integer frequency division method is used for initial synchronization;

[0007] S3, in the synchronization tracking stage, synchronization tracking is performed using a preset synchronization tracking model to achieve downlink synchronization of directly connected satellite users.

[0008] As an optional implementation manner, in the embodiment of the present invention, when the user cannot obtain ephemeris information, the initial synchronization is performed using a multi-step integer frequency division method, including:

[0009] S21, obtaining a received signal;

[0010] S22, generating 2N+1 groups of PSS time domain sequence groups with integer frequency offsets, each group including 3 PSS time domain sequences with different index numbers, where N is a positive integer;

[0011] PSS (Primary Synchronization Signal) is the primary synchronization signal;

[0012] S23, preprocessing the PSS time domain sequence to obtain a preprocessed PSS time domain sequence;

[0013] S24, processing the received signal and the pre-processed PSS time domain sequence to obtain initial synchronization information of the received signal to achieve initial synchronization;

[0014] The initial synchronization information includes starting position information, integer multiple frequency offset value and fractional multiple fine frequency offset estimation value.

[0015] As an optional implementation manner, in an embodiment of the present invention, preprocessing the PSS time domain sequence to obtain a preprocessed PSS time domain sequence includes:

[0016] S231, performing sliding correlation calculation on the PSS time domain sequence and the received signal to obtain autocorrelation information;

[0017] S232, processing the autocorrelation information to obtain a modulus value of the autocorrelation information;

[0018] S233, the modulus value of the autocorrelation information is normalized to obtain a preprocessed PSS time domain sequence.

[0019] As an optional implementation manner, in an embodiment of the present invention, the processing of the received signal and the preprocessed PSS time domain sequence to obtain initial synchronization information of the received signal includes:

[0020] S241, performing sliding correlation calculation on the received signal and the pre-processed PSS time domain sequence to obtain starting position information and integer frequency offset value;

[0021] S242, processing the received signal and the PSS time domain sequence to obtain a fractional fine frequency offset estimation value.

[0022] As an optional implementation manner, in an embodiment of the present invention, performing sliding correlation calculation on the received signal and the preprocessed PSS time domain sequence to obtain starting position information and integer frequency offset values ​​includes:

[0023] S2411, performing sliding correlation calculation on the received signal and the pre-processed PSS time domain sequence to obtain sliding related information;

[0024] S2412, performing peak detection on the sliding related information to obtain a maximum related peak value;

[0025] S2413, when the maximum correlation peak value is greater than a preset decision threshold, detecting a position offset corresponding to the maximum correlation peak value to obtain starting position information;

[0026] S2414, processing the PSS time domain sequence corresponding to the maximum correlation peak to obtain an integer frequency offset value.

[0027] As an optional implementation manner, in an embodiment of the present invention, the processing of the PSS time domain sequence corresponding to the maximum correlation peak to obtain an integer frequency offset value includes:

[0028] Using a detection metric function, the PSS time domain sequence corresponding to the maximum correlation peak is processed to obtain an integer frequency deviation value;

[0029] The detection metric function expression is:

[0030]

[0031] Among them, Alpha(idx,icfo,d) is the detection metric function, r(n) is the received signal, p idx,icfo (n) is the PSS time domain sequence, * indicates taking the conjugate, idx is the sector ID value, icfo is the integer frequency offset value, L indicates the sampling point length of PSS in a single subframe, and d is the position offset corresponding to the maximum correlation peak, that is, the starting position information.

[0032] As an optional implementation manner, in an embodiment of the present invention, the processing of the received signal and the PSS time domain sequence to obtain a fractional multiple fine frequency offset estimate includes:

[0033] S2421, performing conjugate calculation on the PSS time domain sequence to obtain a conjugate PSS time domain sequence;

[0034] S2422, using a frequency offset estimation model, processing the received signal and the conjugate PSS time domain sequence to obtain a fractional fine frequency offset estimation value;

[0035] The frequency offset estimation model expression is:

[0036]

[0037] Among them, C i is the fractional multiple frequency offset estimate of the ith antenna, N′ is the FFT sample length of the OFDM symbol, r pss,i (n) is the received signal received by the ith antenna; s pss(n) is the PSS time domain sequence, and * indicates conjugation.

[0038] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0039] The present invention realizes a direct satellite user downlink synchronization method that adapts to the high dynamics of low-orbit satellites. In the initial synchronization stage, when the user can obtain ephemeris information, the ephemeris pre-compensation method is used for initial synchronization; when the user cannot obtain ephemeris information, an initial synchronization method based on multi-step integer frequency division is designed. In the synchronization tracking stage, the short-period characteristics of the reference signal are used to estimate the residual frequency difference, so as to accurately estimate the Doppler frequency deviation to achieve synchronization tracking. The method of the present invention can realize the downlink synchronization of mobile phones directly connected to satellites under the condition of large frequency deviation caused by the high dynamics of low orbits, with low complexity and meeting the real-time requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0041] Figure 1 It is a flow chart of a downlink synchronization method for a direct-connected satellite user that is adaptable to the high dynamics of a low-orbit satellite disclosed in an embodiment of the present invention;

[0042] Figure 2 It is a flow chart of another method for downlink synchronization of directly connected satellite users that is adaptable to the high dynamics of low-orbit satellites disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] The terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, device, product or equipment that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units that are inherent to these processes, methods, products or equipment.

[0045] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0046] The present invention discloses a method for downlink synchronization of directly connected satellite users that adapts to the high dynamics of low-orbit satellites. The method includes: dividing downlink synchronization to obtain an initial synchronization stage and a synchronization tracking stage; in the initial synchronization stage, when the user can obtain ephemeris information, using an ephemeris pre-compensation method for initial synchronization; when the user cannot obtain ephemeris information, using a multi-step integer frequency division method for initial synchronization; in the synchronization tracking stage, using a preset synchronization tracking model for synchronization tracking to achieve downlink synchronization of directly connected satellite users. The method of the present invention can be applied to downlink synchronization of directly connected satellite users in a high dynamic environment, with high synchronization accuracy and low complexity. The following are detailed descriptions.

[0047] Embodiment 1

[0048] See also Figure 1 , Figure 1 The embodiment of the present invention discloses a flow chart of a method for downlink synchronization of a direct satellite user adapted to the high dynamics of a low-orbit satellite. Figure 1 The described method for downlink synchronization of direct satellite users adapted to the high dynamics of low-orbit satellites is applied to the field of satellite communication technology to solve the problem that the large frequency deviation of low-orbit satellites affects the search for synchronization signals of the downlink of the mobile phone directly connected to the satellite, resulting in slow or even difficult synchronization of the satellite-mobile phone downlink. The embodiments of the present invention are not limited thereto. Figure 1 As shown, the direct satellite user downlink synchronization method adapted to the high dynamics of low-orbit satellites may include the following operations:

[0049] S1, divide the downlink synchronization into an initial synchronization phase and a synchronization tracking phase;

[0050] S2, in the initial synchronization stage, when the user can obtain ephemeris information, the ephemeris pre-compensation method is used for initial synchronization; when the user cannot obtain ephemeris information, the multi-step integer frequency division method is used for initial synchronization;

[0051] The ephemeris pre-compensation method is to jointly calculate the current Doppler frequency difference based on the satellite trajectory and the user terminal position in the ephemeris broadcast, and then pre-compensate the large Doppler estimated by the ephemeris in the RF unit, while reducing the integer frequency division step to quickly complete the large frequency difference search range and complete the initial synchronization process (that is, when there is ephemeris, the integer frequency deviation range N value can be reduced to reduce the search range);

[0052] S3, in the synchronization tracking stage, synchronization tracking is performed using a preset synchronization tracking model to achieve downlink synchronization of directly connected satellite users.

[0053] The preset synchronous tracking model is used for synchronous tracking to achieve downlink synchronization of directly connected satellite users. That is, the short-period characteristics of the CSI-RS (channel state information reference signal) reference signal are used to estimate the residual frequency difference, thereby accurately estimating the Doppler frequency deviation to achieve synchronous tracking.

[0054] Optionally, when the user can obtain ephemeris information, performing initial synchronization using an ephemeris pre-compensation method includes:

[0055] The current downlink Doppler frequency difference is jointly calculated based on the satellite trajectory and the user terminal position in the ephemeris broadcast;

[0056] Pre-compensation of the Doppler of the ephemeris estimate is performed in the radio frequency unit;

[0057] By utilizing the operation of the present invention, the large frequency difference search range can be quickly completed by reducing the integer multiple frequency deviation range N value.

[0058] Optionally, when the user cannot obtain ephemeris information, performing initial synchronization using a multi-step integer frequency division method includes:

[0059] S21, obtaining a received signal;

[0060] S22, generating 2N+1 groups of PSS (primary synchronization signal) time domain sequence groups with integer frequency offsets, each group including 3 PSS time domain sequences with different index numbers, where N is a positive integer;

[0061] S23, preprocessing the PSS time domain sequence to obtain a preprocessed PSS time domain sequence;

[0062] S24, processing the received signal and the pre-processed PSS time domain sequence to obtain initial synchronization information of the received signal to achieve initial synchronization;

[0063] The initial synchronization information includes starting position information, integer multiple frequency offset value and fractional multiple fine frequency offset estimation value.

[0064] Optionally, preprocessing the PSS time domain sequence to obtain a preprocessed PSS time domain sequence includes:

[0065] S231, performing sliding correlation calculation on the PSS time domain sequence and the received signal to obtain autocorrelation information;

[0066] S232, processing the autocorrelation information to obtain a modulus value of the autocorrelation information;

[0067] S233, the modulus value of the autocorrelation information is normalized to obtain a preprocessed PSS time domain sequence.

[0068] Sliding correlation calculation is a prior art in the art.

[0069] The normalization process is to divide the modulus of the autocorrelation information by the amplitude of the received signal.

[0070] Optionally, the processing the received signal and the preprocessed PSS time domain sequence to obtain initial synchronization information of the received signal includes:

[0071] S241, performing sliding correlation calculation on the received signal and the pre-processed PSS time domain sequence to obtain starting position information and integer frequency offset value;

[0072] S242, processing the received signal and the PSS time domain sequence to obtain a fractional fine frequency offset estimation value.

[0073] Optionally, performing sliding correlation calculation on the received signal and the preprocessed PSS time domain sequence to obtain starting position information and integer frequency offset values ​​includes:

[0074] S2411, performing sliding correlation calculation on the received signal and the pre-processed PSS time domain sequence to obtain sliding related information;

[0075] S2412, performing peak detection on the sliding related information to obtain a maximum related peak value;

[0076] S2413, when the maximum correlation peak value is greater than a preset decision threshold, detecting a position offset corresponding to the maximum correlation peak value to obtain starting position information;

[0077] The preset decision threshold is set according to experiments and is not limited in this embodiment;

[0078] S2414, processing the PSS time domain sequence corresponding to the maximum correlation peak to obtain an integer frequency offset value.

[0079] Step S2414 specifically includes detecting the sector number and integer frequency offset value corresponding to the PSS time domain sequence corresponding to the maximum correlation peak.

[0080] Optionally, the processing of the PSS time domain sequence corresponding to the maximum correlation peak to obtain an integer frequency offset value includes:

[0081] Using a detection metric function, the PSS time domain sequence corresponding to the maximum correlation peak is processed to obtain an integer frequency deviation value;

[0082] The detection metric function expression is:

[0083]

[0084] Among them, Alpha(idx,icfo,d) is the detection metric function, r(n) is the received signal, p idx,icfo (n) is the PSS time domain sequence, * indicates taking the conjugate, idx is the sector ID value, icfo is the integer frequency offset value, L indicates the sampling point length of PSS in a single subframe, and d is the position offset corresponding to the maximum correlation peak, that is, the starting position information.

[0085] Optionally, the processing the received signal and the PSS time domain sequence to obtain a fractional multiple fine frequency offset estimate includes:

[0086] S2421, performing conjugate calculation on the PSS time domain sequence to obtain a conjugate PSS time domain sequence;

[0087] S2422, using a frequency offset estimation model, processing the received signal and the conjugate PSS time domain sequence to obtain a fractional fine frequency offset estimation value;

[0088] The frequency offset estimation model expression is:

[0089]

[0090] Among them, C i is the fractional multiple frequency offset estimate of the ith antenna, N′ is the fast Fourier transform (FFT) sample length of the orthogonal frequency division multiplexing (OFDM) symbol, r pss,i (n) is the received signal received by the ith antenna; s pss (n) is the PSS time domain sequence, and * indicates conjugation.

[0091] It can be seen that the present invention realizes a direct satellite user downlink synchronization method that adapts to the high dynamics of low-orbit satellites. In the initial synchronization stage, when the user can obtain ephemeris information, the ephemeris pre-compensation method is used for initial synchronization; when the user cannot obtain ephemeris information, an initial synchronization method based on multi-step integer frequency division is designed. In the synchronization tracking stage, the short-period characteristics of the reference signal are used to estimate the residual frequency difference, so as to accurately estimate the Doppler frequency deviation to achieve synchronization tracking. The method of the present invention can realize the downlink synchronization of mobile phones directly connected to satellites under the condition of large frequency deviation caused by the high dynamics of low orbits, with low complexity and can meet real-time requirements.

[0092] Embodiment 2

[0093] See also Figure 2 , Figure 2 1 is a flow chart of another method for downlink synchronization of direct-connected satellite users that is adaptable to the high dynamics of low-orbit satellites disclosed in an embodiment of the present invention. Figure 2 The described method for downlink synchronization of direct satellite users adapted to the high dynamics of low-orbit satellites is applied to the field of satellite communication technology to solve the problem that the large frequency deviation of low-orbit satellites affects the search for synchronization signals of the downlink of the mobile phone directly connected to the satellite, resulting in slow or even difficult synchronization of the satellite-mobile phone downlink. The embodiments of the present invention are not limited thereto. Figure 2 As shown, the direct satellite user downlink synchronization method adapted to the high dynamics of low-orbit satellites may include the following operations:

[0094] In order to solve the problem that the large frequency deviation of low-orbit satellites affects the search for synchronization signals of the downlink of the mobile phone directly connected to the satellite, resulting in slow or even difficult synchronization of the satellite-mobile phone downlink, the present invention proposes a downlink synchronization method for direct-satellite users that is adaptable to the high dynamics of low-orbit satellites. In particular, an initial synchronization method based on multi-step integer frequency division is designed for the case where the user cannot obtain the ephemeris.

[0095] The present invention discloses a downlink synchronization method for a direct-connected satellite user adapting to the high dynamics of a low-orbit satellite, which specifically includes:

[0096] Step S1, downlink synchronization includes two steps: initial synchronization and synchronization tracking;

[0097] Step S2, when the user can obtain ephemeris information, an ephemeris pre-compensation method is used to perform initial synchronization;

[0098] Step S3, when the user cannot obtain ephemeris information, an initial synchronization method based on multi-step integer frequency division is used, the method comprising the following steps:

[0099] Step S31, using the time-frequency characteristics of the PSS sequence (constant amplitude, zero autocorrelation), locally generate 2N+1 groups of PSS time-domain sequence groups with integer frequency offsets, each group containing 3 PSS time-domain sequences with different index numbers (local PSS sequences);

[0100] Step S32, performing sliding correlation modulo calculation on all local PSS sequences and the received signal, and then dividing by the amplitude of the received signal to complete normalization processing, thereby obtaining 2N+1 local PSS replica groups;

[0101] Step S33, sliding correlation is performed between the received signal and 2N+1 local PSS replica groups. When the maximum correlation peak is greater than the preset decision threshold, the position offset corresponding to the maximum correlation peak is obtained as the timing point of receiving the time domain data, that is, the starting position of the received signal PSS sequence (received signal), the sector number corresponding to the local PSS sequence with the largest correlation and the integer frequency deviation; the designed algorithm detection metric function is as follows:

[0102]

[0103] Among them, Alpha(idx,icfo,d) is the detection metric function, r(n) is the received signal, p idx,icfo (n) is the PSS time domain sequence, * indicates taking the conjugate, idx is the sector ID value, icfo is the integer frequency offset value, L indicates the sampling point length of PSS in a single subframe, and d is the position offset corresponding to the maximum correlation peak, that is, the starting position information.

[0104] Step S34, under the condition of obtaining the position offset corresponding to the maximum correlation peak and the sector number and integer frequency offset corresponding to the local PSS sequence with the maximum correlation, the received time domain PSS symbol (received signal) is multiplied by the conjugate point multiplication of the local PSS sequence in the time domain, and then divided into two parts and summed respectively, and finally the frequency offset size is estimated:

[0105]

[0106] Among them, C i is the fractional multiple frequency offset estimate of the ith antenna, N′ is the fast Fourier transform (FFT) sample length of the orthogonal frequency division multiplexing (OFDM) symbol, r pss,i (n) is the received signal received by the ith antenna; s pss (n) is the locally generated PSS sequence (PSS time domain sequence), and * indicates conjugation. If the receiver uses two antennas, the correlation operation results are combined into C = C 1 +C 2 At the same time, we can also jointly estimate C with multiple PSS signals acc =∑ l C (l) , C (l) represents the fractional multiple frequency deviation estimate of the lth antenna, C acc is the joint estimation result of multiple PSS signals, from which the normalized fractional frequency deviation ε is calculated f for:

[0107]

[0108] Where angle(·) is a function for finding the angle of a complex number, thereby achieving initial synchronization.

[0109] Step S4, using the short period characteristic of the CSI-RS reference signal to estimate the residual frequency difference, thereby accurately estimating the Doppler frequency offset to achieve synchronous tracking.

[0110] The short period characteristic of the CSI-RS reference signal is used to estimate the residual frequency difference, so as to accurately estimate the Doppler frequency offset and achieve synchronous tracking. Carrier frequency estimation can be completed by estimating the phase change of the channel estimation of the channel state information demodulation reference signal at two different symbol positions in the same time slot. The specific estimation method is as follows: the channel estimation of the reference signal at two different symbol positions after interpolation in the same time slot is defined as in is the number of downlink resource blocks RB, and the phase calculation formula is defined as:

[0111]

[0112] The correlation operation within the entire frequency domain DMRS reference symbol is:

[0113]

[0114] Next, we calculate the frequency estimate Δfs est The steps are:

[0115] S41, find the angle of Ds(1):

[0116]

[0117] S42, by in:

[0118]

[0119] Where fs in the above formula is the signal sampling rate, FFT NSIZE is the number of FFT points, CP_LEN1 is the CP length of the OFDM symbol, ΔL is the number of symbols between two reference symbols in the time domain, and atan is the inverse tangent angle calculation;

[0120] S43, averaging Δfs in one frame M times can obtain the frequency mean value:

[0121]

[0122] It can be seen that the present invention realizes a direct satellite user downlink synchronization method that adapts to the high dynamics of low-orbit satellites. In the initial synchronization stage, when the user can obtain ephemeris information, the ephemeris pre-compensation method is used for initial synchronization; when the user cannot obtain ephemeris information, an initial synchronization method based on multi-step integer frequency division is designed. In the synchronization tracking stage, the short-period characteristics of the reference signal are used to estimate the residual frequency difference, so as to accurately estimate the Doppler frequency deviation to achieve synchronization tracking. The method of the present invention can realize the downlink synchronization of mobile phones directly connected to satellites under the condition of large frequency deviation caused by the high dynamics of low orbits, with low complexity and can meet real-time requirements.

[0123] The device embodiments described above are only illustrative, wherein the modules described as separate components may or may not be physically separated, and the components displayed as modules may or may not be physical modules, i.e., they may be located in one place, or they may be distributed on multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Those of ordinary skill in the art may understand and implement it without creative work.

[0124] Through the specific description of the above embodiments, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the above technical solution can be essentially or partly contributed to the prior art in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, and the storage medium includes a read-only memory (ROM), a random access memory (RAM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), a one-time programmable read-only memory (OTPROM), an electronically erasable rewritable read-only memory (EEPROM), a compact disc (CD-ROM) or other optical disc storage, magnetic disk storage, magnetic tape storage, or any other computer-readable medium that can be used to carry or store data.

[0125] Finally, it should be noted that the downlink synchronization method for directly connected satellite users that adapts to the high dynamics of low-orbit satellites disclosed in the embodiment of the present invention is only a preferred embodiment of the present invention, which is only used to illustrate the technical solution of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that it is still possible to modify the technical solutions recorded in the aforementioned embodiments, or to make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for downlink synchronization of direct satellite users adapting to the high dynamics of low-orbit satellites, characterized in that: The method comprises: S1, divide the downlink synchronization into an initial synchronization phase and a synchronization tracking phase; S2, in the initial synchronization stage, when the user can obtain ephemeris information, the ephemeris pre-compensation method is used for initial synchronization; when the user cannot obtain ephemeris information, the multi-step integer frequency division method is used for initial synchronization, including: S21, obtaining a received signal; S22, generating 2N+1 groups of PSS time domain sequence groups with integer frequency offsets, each group including 3 PSS time domain sequences with different index numbers, where N is a positive integer; S23, preprocessing the PSS time domain sequence to obtain a preprocessed PSS time domain sequence; S24, processing the received signal and the pre-processed PSS time domain sequence to obtain initial synchronization information of the received signal to achieve initial synchronization, including: S241, performing sliding correlation calculation on the received signal and the pre-processed PSS time domain sequence to obtain starting position information and integer frequency offset value, including: S2411, performing sliding correlation calculation on the received signal and the pre-processed PSS time domain sequence to obtain sliding related information; S2412, performing peak detection on the sliding related information to obtain a maximum related peak value; S2413, when the maximum correlation peak value is greater than a preset decision threshold, detecting a position offset corresponding to the maximum correlation peak value to obtain starting position information; S2414, processing the PSS time domain sequence corresponding to the maximum correlation peak to obtain an integer frequency offset value, including: Using a detection metric function, the PSS time domain sequence corresponding to the maximum correlation peak is processed to obtain an integer frequency deviation value; The detection metric function expression is: Among them, Alpha(idx,icfo,d) is the detection metric function, r(n) is the received signal, p idx,icfo (n) is the PSS time domain sequence, n is the time variable, * indicates taking the conjugate, idx is the sector ID value, icfo is the integer frequency offset value, L represents the sampling point length of the PSS in a single subframe, and d is the position offset corresponding to the maximum correlation peak, that is, the starting position information; S242, processing the received signal and the PSS time domain sequence to obtain a fractional fine frequency offset estimation value, including: S2421, performing conjugate calculation on the PSS time domain sequence to obtain a conjugate PSS time domain sequence; S2422, using a frequency offset estimation model, processing the received signal and the conjugate PSS time domain sequence to obtain a fractional fine frequency offset estimation value; The frequency offset estimation model expression is: Among them, C i is the fractional multiple frequency offset estimate of the ith antenna, N′ is the FFT sample length of the OFDM symbol, r pss,i (n) is the received signal received by the ith antenna; n is the time variable, s pss (n) is the PSS time domain sequence, * indicates conjugation; The initial synchronization information includes starting position information, integer multiple frequency offset value and fractional multiple fine frequency offset estimation value; S3, in the synchronization tracking stage, synchronization tracking is performed using a preset synchronization tracking model to achieve downlink synchronization of directly connected satellite users.

2. The method for downlink synchronization of direct-connected satellite users adapted to the high dynamics of low-orbit satellites according to claim 1, characterized in that: The preprocessing of the PSS time domain sequence to obtain a preprocessed PSS time domain sequence includes: S231, performing sliding correlation calculation on the PSS time domain sequence and the received signal to obtain autocorrelation information; S232, processing the autocorrelation information to obtain a modulus value of the autocorrelation information; S233, the modulus value of the autocorrelation information is normalized to obtain a preprocessed PSS time domain sequence.

Images