Cell search method, apparatus, and ground terminal

Abstract

The present disclosure provides a cell search method, device and ground terminal, wherein the method comprises: determining a baseband signal of a synchronization signal transmitted by a low-orbit satellite; determining a Doppler frequency offset and a frequency offset change rate between the low-orbit satellite and the ground terminal according to a current satellite position of the low-orbit satellite and a current terminal position of the ground terminal; compensating the baseband signal according to the Doppler frequency offset and the frequency offset change rate to obtain a compensated baseband signal; accurately determining a fine synchronization point of a primary synchronization signal PSS based on a coarse synchronization point of the primary synchronization signal PSS in the compensated baseband signal, and performing cell search based on the fine synchronization point. Thus, the ground terminal can conveniently and quickly perform cell search in a larger Doppler frequency shift environment, and the performance of cell search of the ground terminal is improved.

Description

Technical Field

[0001] This disclosure relates to the field of satellite communication technology, and in particular to a cell search method, apparatus and ground terminal. Background Technology

[0002] In low-Earth orbit (LEO) satellite communication scenarios, LEO satellites move at high speeds and are relatively far from ground terminals. Therefore, enabling ground terminals to quickly and conveniently perform cell searches is crucial for ground terminals to access LEO satellites. Summary of the Invention

[0003] This disclosure provides a method, apparatus, and ground terminal for determining line timing advance, enabling the ground terminal to conveniently and quickly perform cell search in environments with large Doppler frequency shift, thereby improving the cell search performance of the ground terminal.

[0004] In a first aspect, embodiments of this disclosure provide a cell search method applied in a ground terminal, which involves: determining the baseband signal of a synchronization signal transmitted by a low-Earth orbit (LEO) satellite; determining the Doppler frequency offset and frequency offset rate of change between the LEO satellite and the ground terminal based on the current satellite position and the current terminal position of the ground terminal; compensating the baseband signal based on the Doppler frequency offset and the frequency offset rate of change to obtain a compensated baseband signal; determining multiple coarse synchronization points of the primary synchronization signal (PSS) in the compensated baseband signal; determining the fine synchronization point of the PSS based on the multiple coarse synchronization points; and performing a cell search based on the fine synchronization point.

[0005] In one embodiment of this disclosure, before the baseband signal is compensated according to the Doppler frequency offset and the frequency offset change rate to obtain the compensated baseband signal, the method further includes: performing low-pass filtering on the baseband signal.

[0006] In one embodiment of this disclosure, the method further includes: estimating the frequency offset of the PSS based on the precise synchronization point to obtain an estimated value of the frequency offset of the PSS.

[0007] In one embodiment of this disclosure, determining multiple coarse synchronization points of the primary synchronization signal (PSS) in the compensated baseband signal includes: dividing the compensated baseband signal into multiple segmented signals using a sliding window, wherein the preset length of the sliding window is the length N of the cyclic prefix (CP) of the Orthogonal Frequency Division Multiplexing (OFDM) symbol. CP The result is obtained by summing the number of sampling points N of the Fast Fourier Transform; for each segmented signal, a length of N is truncated from the beginning of the segmented signal. CPThe first segmented signal is extracted, and a segment of length N is extracted from the specified position of the segmented signal. CP The second intercepted signal, wherein the length between the specified position and the end position of the segmented signal is equal to N. CP Determine the correlation between the first truncated signal and the second truncated signal; from the correlation between the first truncated signal and the second truncated signal of all the segmented signals, obtain multiple target correlations with a correlation greater than a preset correlation threshold; take the starting position of the segmented signal corresponding to each target correlation as the coarse synchronization point of the main synchronization signal PSS in the compensated baseband signal.

[0008] In one embodiment of this disclosure, determining the correlation between the first intercepted signal and the second intercepted signal includes: segmenting the first intercepted signal to obtain a first segmented signal sequence; segmenting the second intercepted signal to obtain a second segmented signal sequence; and summing the correlation values ​​between the i-th segmented signal in the first segmented signal sequence and the i-th segmented signal in the second segmented signal sequence to obtain the correlation between the first intercepted signal and the second intercepted signal, wherein i is an integer greater than or equal to 1 and less than H, and H represents the total number of segmented signals in the first segmented signal sequence.

[0009] In one embodiment of this disclosure, determining the fine synchronization point of the PSS based on the plurality of coarse synchronization points includes: performing Fast Fourier Transform on the plurality of target correlations respectively to obtain Fast Fourier Transform results corresponding to the plurality of target correlations; determining the maximum value of each of the Fast Fourier Transform results; taking the maximum value among the maximum values ​​as the target maximum value; obtaining the target coarse synchronization point corresponding to the target maximum value from the plurality of coarse synchronization points, and taking the target coarse synchronization point as the fine synchronization point of the main synchronization signal PSS.

[0010] In one embodiment of this disclosure, the step of estimating the frequency offset of the PSS based on the precise synchronization point to obtain the frequency offset estimate of the PSS includes: obtaining the point value of the target maximum value corresponding to the precise synchronization point; determining whether the point value is greater than the number of sampling points of the fast Fourier transform; if the point value is less than or equal to the number of sampling points of the fast Fourier transform, then determining the frequency offset estimate of the PSS based on the point value, the number of sampling points of the fast Fourier transform, and the sampling frequency of the intermediate frequency signal.

[0011] In one embodiment of this disclosure, the method further includes: if the point value is greater than the number of sampling points of the fast Fourier transform, then the difference obtained by subtracting the point value from the number of sampling points of the fast Fourier transform is used as the target point value; and the frequency offset estimate of the primary synchronization signal PSS in the compensated baseband signal is determined based on the target point value, the number of sampling points of the fast Fourier transform, and the sampling frequency of the intermediate frequency signal.

[0012] The cell search method of this disclosure determines the baseband signal of the synchronization signal transmitted by a low-Earth orbit (LEO) satellite; determines the Doppler frequency offset and frequency offset rate of change between the LEO satellite and the ground terminal based on the current satellite position and the current terminal position of the ground terminal; compensates the baseband signal based on the Doppler frequency offset and frequency offset rate of change to obtain a compensated baseband signal; accurately determines the fine synchronization point of the primary synchronization signal (PSS) based on the coarse synchronization point in the compensated baseband signal, and performs cell search based on the fine synchronization point. This enables the ground terminal to conveniently and quickly perform cell search even in environments with large Doppler frequency shifts, improving the cell search performance of the ground terminal.

[0013] Secondly, embodiments of this disclosure provide a cell search device, which is applied in a ground terminal. The device includes: a first determining module, used to determine the baseband signal of a synchronization signal transmitted by a low-Earth orbit satellite; a second determining module, used to determine the Doppler frequency offset and frequency offset rate of change between the low-Earth orbit satellite and the ground terminal based on the current satellite position of the low-Earth orbit satellite and the current terminal position of the ground terminal; a compensation module, used to compensate the baseband signal based on the Doppler frequency offset and the frequency offset rate of change to obtain a compensated baseband signal; a third determining module, used to determine multiple coarse synchronization points of the primary synchronization signal (PSS) in the compensated baseband signal; and a cell search module, used to determine the fine synchronization point of the PSS based on the multiple coarse synchronization points and perform cell search based on the fine synchronization point.

[0014] The cell search apparatus of this disclosure determines the baseband signal of the synchronization signal transmitted by a low-Earth orbit (LEO) satellite; determines the Doppler frequency offset and frequency offset rate of change between the LEO satellite and the ground terminal based on the current satellite position and the current terminal position of the ground terminal; compensates the baseband signal based on the Doppler frequency offset and frequency offset rate of change to obtain a compensated baseband signal; accurately determines the fine synchronization point of the primary synchronization signal (PSS) based on the coarse synchronization point in the compensated baseband signal, and performs cell search based on the fine synchronization point. This enables the ground terminal to conveniently and quickly perform cell search even in environments with large Doppler frequency shifts, improving the cell search performance of the ground terminal.

[0015] Thirdly, embodiments of this application provide a ground terminal, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the cell search method as described in the first aspect of this disclosure.

[0016] Fourthly, embodiments of this application provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the cell search method as described in the first aspect of this disclosure.

[0017] Fifthly, embodiments of this application provide a computer program product that, when executed by an instruction processor, implements the cell search method as described in the first aspect of this disclosure.

[0018] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this disclosure will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, in which:

[0020] Figure 1 This is a schematic diagram of a low-Earth orbit satellite communication system provided in an embodiment of the present disclosure;

[0021] Figure 2 This is a flowchart illustrating another cell search method provided in an embodiment of the present disclosure;

[0022] Figure 3 This is a flowchart illustrating another cell search method provided in an embodiment of the present disclosure;

[0023] Figure 4 This is a flowchart illustrating another cell search method provided in an embodiment of the present disclosure;

[0024] Figure 5 This is a schematic flowchart illustrating another cell search method provided in an embodiment of this disclosure;

[0025] Figure 6 This is a flowchart illustrating another cell search method provided in an embodiment of the present disclosure;

[0026] Figure 7 This is a flowchart illustrating another cell search method provided in an embodiment of the present disclosure;

[0027] Figure 8 An example diagram illustrating the probability of detecting error in the PSS fine synchronization point and cell group ID number under different signal-to-noise ratios provided in this embodiment of the disclosure;

[0028] Figure 9 This is an example diagram of the root mean square error of the overall frequency offset provided in an embodiment of this disclosure.

[0029] Figure 10 This is a schematic diagram of the structure of a cell search device provided in an embodiment of the present disclosure;

[0030] Figure 11 This is a block diagram illustrating a ground terminal for implementing a cell search method according to an exemplary embodiment. Detailed Implementation

[0031] Embodiments of this disclosure are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this disclosure, and should not be construed as limiting this disclosure.

[0032] Please see Figure 1 , Figure 1 This is a schematic diagram of the architecture of a low-Earth orbit (LEO) satellite communication system provided in an embodiment of this disclosure. The LEO satellite communication system may include, but is not limited to, a LEO satellite and a ground terminal. Figure 1 The number and form of the devices shown are for illustrative purposes only and do not constitute a limitation on the embodiments of this disclosure. In actual applications, it may include two or more low-orbit satellites and two or more ground terminals. Figure 1 The low-Earth orbit satellite communication system shown is an example consisting of a low-Earth orbit satellite 101 and a ground terminal 102.

[0033] In this embodiment of the disclosure, the low-orbit satellite 101 is an entity used for transmitting or receiving signals.

[0034] In this disclosure, the ground terminal 102 refers to a processing device used for communication with low-Earth orbit satellites within the coverage beam range of the low-Earth orbit satellite. For example, the ground terminal can be a car, smart car, mobile phone, wearable device, tablet computer, etc., equipped with satellite communication capabilities. This disclosure does not limit the specific technology or device form used in the ground terminal.

[0035] In the aforementioned low-Earth orbit (LEO) satellite communication systems, during the process of a ground terminal accessing a LEO satellite, the LEO satellite moves at a very high speed relative to the ground terminal. Therefore, even if the ground terminal receiving the satellite signal remains in the same position, a significant Doppler frequency shift will occur between the received signal frequency and the carrier frequency of the LEO satellite. Furthermore, the distance between the LEO satellite and the ground base station is much greater than that of the LEO satellite, resulting in a very low signal-to-noise ratio (SNR). This large frequency shift and low SNR place more stringent requirements on cell search in LEO satellite communication systems.

[0036] In this embodiment, the baseband signal of the synchronization signal transmitted by the low-Earth orbit satellite is determined; based on the current satellite position and the current terminal position of the ground terminal, the Doppler frequency offset and frequency offset rate of change between the low-Earth orbit satellite and the ground terminal are determined; based on the Doppler frequency offset and frequency offset rate of change, the baseband signal is compensated to obtain a compensated baseband signal; based on the coarse synchronization point of the primary synchronization signal (PSS) in the compensated baseband signal, the fine synchronization point of the PSS is accurately determined, and cell search is performed based on the fine synchronization point. This allows the ground terminal to conveniently and quickly perform cell search even in environments with large Doppler frequency shifts, improving the cell search performance of the ground terminal.

[0037] It is understood that the low-orbit satellite communication system described in this disclosure is for the purpose of more clearly illustrating the technical solutions of this disclosure, and does not constitute a limitation on the technical solutions provided in this disclosure. As those skilled in the art will know, with the evolution of system architecture and the emergence of new business scenarios, the technical solutions provided in this disclosure are also applicable to similar technical problems.

[0038] The cell search method, apparatus, and ground terminal of this disclosure are described below with reference to the accompanying drawings.

[0039] Figure 2 This is a schematic flowchart of a cell search method provided in an embodiment of the present disclosure.

[0040] like Figure 2 As shown, the cell search method may include the following steps:

[0041] Step 201: Determine the baseband signal of the synchronization signal transmitted by the low-orbit satellite.

[0042] It should be noted that the cell search method in this embodiment is applied in a cell search device, which can be implemented by software and / or hardware. The cell search device in this embodiment can be a ground terminal or can be configured in a ground terminal. This embodiment does not specifically limit this.

[0043] In some exemplary embodiments, the ground terminal may receive synchronization signals transmitted by low-Earth orbit satellites.

[0044] In this example, the synchronization signal can be the Synchronization Signal and PBCH block (SSB) signal. PBCH is short for Physical Broadcast Channel.

[0045] The SSB signal is composed of three parts: the primary synchronization signal (PSS), the secondary synchronization signal (SSS), and the PBCH.

[0046] Correspondingly, after receiving the synchronization signal from the low-Earth orbit satellite, the synchronization signal can be down-converted to obtain at least one intermediate frequency (IF) signal. Different IF signals correspond to different frequency points, and there is a frequency interval between these points. For example, the frequency interval Δf = 1.44 × 10⁻⁶. 6 It is understood that this is merely an example of frequency spacing, and the frequency spacing can also be other values; this embodiment does not specifically limit this.

[0047] In this example, one of the intermediate frequency signals mentioned above can be further down-converted to obtain the baseband signal of the synchronization signal.

[0048] As an example, the received synchronization signal can be directly down-converted to obtain the baseband signal of the synchronization signal.

[0049] Step 202: Determine the Doppler frequency offset and frequency offset rate between the low-Earth orbit satellite and the ground terminal based on the current satellite position and the current terminal position of the ground terminal.

[0050] As an example, a ground terminal can determine its current location by using its own Global Navigation Satellite System (GNSS).

[0051] The current terminal location is used to indicate the current location of the ground terminal.

[0052] The current satellite position is used to indicate the current location of low-orbit satellites.

[0053] In some exemplary implementations, the current terminal location L UE =[X UE ,Y UE Z UECorrespondingly, the current satellite position L SAT =[X SAT ,Y SAT Z SAT Correspondingly, based on the current terminal value and the current satellite position, the Doppler frequency offset f between the low-orbit satellite and the ground terminal is calculated. u Its calculation expression is as follows:

[0054]

[0055] Among them, f c The carrier frequency used when a low-Earth orbit satellite transmits a synchronization signal is c = 3.0 * 10⁻⁶. 8 m / s.

[0056] In some exemplary implementations, the current terminal location L UE =[X UE ,Y UE Z UE Correspondingly, the current satellite position L SAT =[X SAT ,Y SAT Z SAT Correspondingly, based on the current terminal value and the current satellite position, the frequency offset rate f′ between the low-orbit satellite and the ground terminal is calculated. u Its calculation expression is as follows:

[0057]

[0058] The description of the relevant parameters in this formula can be found in the description of the relevant parameters in the previous formula, and this embodiment does not impose any specific limitations on them.

[0059] Step 203: Based on the Doppler frequency offset and the frequency offset change rate, the baseband signal is compensated to obtain the compensated baseband signal.

[0060] In some exemplary embodiments, to reduce the impact of noise on subsequent processing, the baseband signal can be low-pass filtered before compensation processing. This filters out noise from the baseband signal, reducing its impact on subsequent processing.

[0061] In some exemplary implementations, for example, y2(n) represents the processed baseband signal, and the ground terminal calculates the Doppler frequency offset f using a preset ephemeris and the terminal's position. u and the rate of change of frequency deviation f′ u Then, the signal y2(n) is compensated to obtain the signal r(n), and its calculation expression is:

[0062]

[0063] Where n ranges from 1 to L_data. Where L_data represents the length of the processed baseband signal, and f... s This indicates the sampling frequency of the intermediate frequency (IF) signal. The IF signal uses f... s It is obtained by sampling the time-domain signal corresponding to the intermediate frequency signal.

[0064] Step 204: Determine multiple coarse synchronization points of the primary synchronization signal PSS in the compensated baseband signal.

[0065] In some exemplary embodiments, coarse synchronization processing is performed on the compensated baseband signal to obtain multiple coarse synchronization points of the master synchronization signal PSS in the compensated baseband signal.

[0066] Step 205: Based on multiple coarse synchronization points, determine the fine synchronization point of the PSS, and perform cell search based on the fine synchronization point.

[0067] In some exemplary implementations, multiple coarse synchronization points are captured based on a preset capture algorithm to obtain the fine synchronization point of the PSS. It can be understood that the fine synchronization point is one of the multiple coarse synchronization points.

[0068] In some exemplary implementations, one of a plurality of coarse synchronization points can be arbitrarily selected as the fine synchronization point of the PSS.

[0069] Correspondingly, the PSS-based fine synchronization point extracts the PSS from the compensated baseband signal and performs cell search based on the extracted PSS.

[0070] The description of cell search based on the extracted PSS can be implemented using the methods in the subsequent embodiments of this disclosure or the methods in related technologies. This embodiment does not specifically limit the method.

[0071] The cell search method provided in this disclosure determines the baseband signal of the synchronization signal transmitted by a low-Earth orbit (LEO) satellite; determines the Doppler frequency offset and frequency offset rate of change between the LEO satellite and the ground terminal based on the current satellite position and the current terminal position of the ground terminal; compensates the baseband signal based on the Doppler frequency offset and frequency offset rate of change to obtain a compensated baseband signal; accurately determines the fine synchronization point of the primary synchronization signal (PSS) based on the coarse synchronization point in the compensated baseband signal, and performs cell search based on the fine synchronization point. This enables the ground terminal to conveniently and quickly perform cell search even in environments with large Doppler frequency shifts, improving the cell search performance of the ground terminal.

[0072] To enable ground terminals to accurately process signals other than the PSS signal (such as SSS and PBCH) in the synchronization signal, as well as subsequent received downlink signals, frequency offset estimation of the PSS can be performed based on the fine synchronization point to obtain the estimated frequency offset value of the PSS. This facilitates subsequent processing of other signals in the synchronization signal and downlink signals transmitted by low-Earth orbit satellites during access to low-Earth orbit satellites, based on the determined estimated frequency offset value.

[0073] As an example, the PSS can be extracted from the compensated baseband signal based on the fine synchronization point of the primary synchronization signal (PSS). Correspondingly, frequency offset estimation can be performed based on the extracted PSS to obtain the residual frequency offset value after ephemeris compensation. Other possible implementations of frequency offset estimation of the PSS based on the fine synchronization point to obtain the estimated frequency offset value of the PSS will be described exemplarily in subsequent embodiments.

[0074] To clearly illustrate how multiple coarse synchronization points of the primary synchronization signal PSS in the compensated baseband signal are determined in the above embodiments, this disclosure proposes another cell search method.

[0075] Figure 3 This is a schematic flowchart of another cell search method provided in an embodiment of the present disclosure.

[0076] like Figure 3 As shown, the cell search method may include the following steps:

[0077] Step 301: Determine the baseband signal of the synchronization signal transmitted by the low-orbit satellite.

[0078] Step 302: Perform low-pass filtering on the baseband signal to obtain the processed baseband signal.

[0079] Step 303: Determine the Doppler frequency offset and frequency offset rate between the low-Earth orbit satellite and the ground terminal based on the current satellite position and the current terminal position of the ground terminal.

[0080] Step 304: Based on the Doppler frequency offset and the frequency offset change rate, the processed baseband signal is compensated to obtain the compensated baseband signal.

[0081] It should be noted that the specific implementation methods of steps 301 to 304 can be found in the relevant descriptions of the embodiments of this disclosure, and will not be repeated here.

[0082] Step 305: Divide the compensated baseband signal into multiple segmented signals using a sliding window. The preset length of the sliding window is the length N of the cyclic prefix CP of the Orthogonal Frequency Division Multiplexing (OFDM) symbol. CPIt is obtained by summing the number of sampling points N of the Fast Fourier Transform.

[0083] As an example, for the compensated baseband signal, a sliding window of preset length can be used, sliding with a preset sliding step size until the end position of the signal in the sliding window is the same as the end position of the compensated baseband signal, at which point the sliding window stops sliding. Correspondingly, during the sliding process of the sliding window on the baseband signal, the baseband signal within the sliding window after each sliding can be considered as a segmented signal.

[0084] The preset sliding step size is a step size pre-set in the cell search device. For example, the preset sliding step size can be 1. It is understood that in practical applications, the preset sliding step size can be set according to the actual application requirements, and this embodiment does not specifically limit it.

[0085] It should be noted that in this example, the length of an Orthogonal Frequency Division Multiplexing (OFDM) symbol is equal to the length N of the cyclic prefix (CP) of the OFDM symbol. CP This is the sum of the number of sampling points N in the Fast Fourier Transform. In other words, in this example, the length of the sliding window is the same as the length of the OFDM symbol.

[0086] For example, the length of the sliding window and the length of the preset sliding step are both equal to the length N of the cyclic prefix CP of the OFDM symbol. CP The sum of the number of sampling points N in the Fast Fourier Transform, or in other words, the length of the sliding window and the length of the preset sliding step are both equal to the length of the OFDM symbol. Correspondingly, when using this sliding window and sliding with the preset sliding step on the compensated baseband signal r(n) of data length L_data, the segment signal s(n) corresponding to the k-th segment is s(n) = r(k·(N+N) cp )+1:(k+1)·(N+N cp In the formula, k·(N+N) cp )+1:(k+1)·(N+N cp ) represents the value of n in the segmented signal corresponding to the k-th segment, ranging from k·(N+N). cp (k+1) to (k+1)·(N+N) cp ).

[0087] For example, the length of the sliding window is equal to the length N of the cyclic prefix CP of the OFDM symbol. CPGiven the sum of the number of sampling points N in the Fast Fourier Transform, and a preset sliding step size of 1, when using this sliding window, the compensated baseband signal r(n) with a preset sliding step size is slid along the data length L_data until the end position of the signal in the sliding window is the same as the end position of the compensated baseband signal, and then the sliding window is stopped, the corresponding segment signal s(n) for the k-th segment is s(n) = r(k:k+N+N). cp In the formula, k: k + N + N cp This indicates that the value of n in the segmented signal corresponding to the k-th segment ranges from k to k+N+N. cp Among them, k+N+N cp The value of is less than or equal to . Correspondingly, the total number of segmented signals K corresponding to the baseband signal after L_data compensation is K = L_data - (N + N cp )+1.

[0088] Step 306: For each segmented signal, truncate it forward by a length of N from the beginning of the segmented signal. CP The first segmented signal is extracted, and a segment of length N is extracted from the specified position of the segmented signal. CP The second intercept signal, wherein the length between the specified position and the end position of the segmented signal is equal to N. CP .

[0089] In other words, for each segmented signal, a segment of length N can be extracted from that segmented signal s(n). cp The first intercepted signal and the corresponding OFDM symbol's final length N cp The second intercept signal.

[0090] It can be understood that the first intercepted signal is the signal corresponding to the cyclic prefix (CP) of the corresponding OFDM symbol.

[0091] The length of the segmented signal s(n) is (N+N) cp ).

[0092] Step 307: Determine the correlation between the first intercepted signal and the second intercepted signal.

[0093] It is understandable that the methods for determining the correlation between the first and second intercepted signals differ in different application scenarios, as illustrated below:

[0094] As an example, the correlation between the first and second intercepted signals can be calculated directly to obtain the correlation between the first and second intercepted signals.

[0095] As another example, the first and second intercepted signals can be input into a preset correlation calculation model to determine the correlation between the first and second intercepted signals.

[0096] Other possible methods for determining the correlation between the first intercepted signal and the second intercepted signal will be described by way of example in subsequent embodiments.

[0097] Step 308: From the correlation between the first and second truncated signals of all segmented signals, obtain multiple target correlations with a correlation greater than a preset correlation threshold.

[0098] The preset relevance threshold is a critical value of relevance that is pre-set in the cell search device according to actual needs, and this embodiment does not specifically limit it.

[0099] Step 309: Take the starting position of the segmented signal corresponding to each target correlation as the coarse synchronization point of the main synchronization signal PSS in the compensated baseband signal.

[0100] Step 310: Based on multiple coarse synchronization points, determine the fine synchronization point of the PSS, and perform cell search based on the fine synchronization point.

[0101] In some exemplary implementations, the correlation of each segment signal corresponding to each coarse synchronization point can be obtained, and the target correlation with the highest correlation can be obtained, and the coarse synchronization point corresponding to the target correlation can be used as the fine synchronization point of the PSS.

[0102] In this example, the compensated baseband signal is divided into multiple segments using a sliding window, and a segment of length N is truncated from the beginning of each segment. CP The first intercepted signal is obtained, and the correlation between the first and second intercepted signals in the segmented signal is determined. Therefore, based on the correlation between the first and second intercepted signals of all segmented signals, the coarse synchronization point of the primary synchronization signal (PSS) in the compensated baseband signal can be accurately determined. This improves the accuracy of the fine synchronization point determined based on the coarse synchronization point, thereby enabling the ground terminal to perform accurate cell search and improving the accuracy of cell search for the ground terminal.

[0103] In some exemplary embodiments, in order to accurately determine the correlation between the first intercepted signal and the second intercepted signal, the first intercepted signal and the second intercepted signal can be segmented respectively, and the correlation between the first intercepted signal and the second intercepted signal can be determined based on the segmentation results corresponding to each of the first intercepted signal and the second intercepted signal. To clearly understand this process, the following describes... Figure 4The process of determining the correlation between the first intercepted signal and the second intercepted signal in the embodiments of this disclosure will be described.

[0104] Figure 4 This is a schematic flowchart of another cell search method provided in an embodiment of the present disclosure.

[0105] like Figure 4 As shown, an exemplary implementation of determining the correlation between the first intercepted signal and the second intercepted signal may include the following steps:

[0106] Step 401: Segment the first intercepted signal to obtain a first segmented signal sequence.

[0107] In other words, in this example, the first intercepted signal can be segmented, and the segmented signals can be sorted to obtain the first segmented signal sequence.

[0108] As an exemplary implementation, the first intercepted signal can be segmented according to a preset number of segments to obtain a preset number of segmented signals, and the preset number of segmented signals can be sorted according to the order of each segment in the first intercepted signal to obtain a first segmented signal sequence.

[0109] The preset number of segments is a value preset in the cell search device, such as 6 or 8 segments.

[0110] Step 402: The second intercepted signal is segmented to obtain a second segmented signal sequence.

[0111] In other words, in this example, the second intercepted signal can be segmented, and the segmented signals can be sorted to obtain a second segmented signal sequence.

[0112] As an exemplary implementation, the second intercepted signal can be segmented according to a preset number of segments to obtain a preset number of segmented signals, and the preset number of segmented signals can be sorted according to the order of each segment in the second intercepted signal to obtain a second segmented signal sequence.

[0113] Step 403: Sum the correlation values ​​between the i-th segment signal in the first segment signal sequence and the i-th segment signal in the second segment signal sequence to obtain the correlation between the first truncated signal and the second truncated signal.

[0114] Where i is an integer greater than or equal to 1 and less than H, and H represents the total number of segmented signals in the first segmented signal sequence.

[0115] As an example, for the segmented signal corresponding to the Kth segment, it can be derived from the segmented signal pair of length N+N. cp The data s(n) takes a length of N. cp CP data and the corresponding OFDM symbol's final length N cp The data is then divided into M segments of length . Data; then, the segmented data undergoes relevant operations and accumulation, and the calculation expression is:

[0116]

[0117] The ·* operation represents multiplying corresponding data. The formula contains... This represents the signal corresponding to the m-th segment in the first intercepted signal. This represents the signal corresponding to the m-th segment in the second intercepted signal; This indicates that the value of n in the first intercepted signal ranges from arrive Correspondingly, This indicates that the value of n in the second intercepted signal ranges from arrive The value of m ranges from 1 to N. cp / M-1. Wherein, N cp / M represents the total number of segments corresponding to the segmentation of the first intercepted signal, i.e., H = N cp / M. M represents the preset number of segments. This means that the total number of segments corresponding to the segmentation of the second captured signal is also equal to N. cp / M. In this example, N is used. cp The description will be based on the example where / M is an integer.

[0118] In this example, the first and second truncated signals are segmented separately, and the correlation between them is determined based on the segmentation results for each signal. This reduces the impact of noise on the correlation calculation and improves the accuracy of the determined correlation between the first and second truncated signals.

[0119] In one embodiment of this disclosure, to clearly illustrate how the fine synchronization point of the PSS is determined based on multiple coarse synchronization points, the following is a detailed explanation. Figure 5 The process of determining the fine synchronization point of the PSS based on multiple coarse synchronization points in the embodiments of this disclosure will be described by way of example.

[0120] like Figure 5 As shown in this example, determining the fine synchronization point of PSS based on multiple coarse synchronization points can include:

[0121] Step 501: Perform Fast Fourier Transform on the correlation of multiple targets respectively to obtain the Fast Fourier Transform results corresponding to the correlation of multiple targets.

[0122] For example, for the k-th target relevance among multiple target relevances, assuming xcorr_data(k) represents the k-th target relevance, a Fast Fourier Transform (FFT) operation can be performed on the number of sampling points fft_num of the Fast Fourier Transform. The calculation formula is: fft_data(k) = FFT(xcorr_data(k), fft_num), where k takes values ​​from 1 to F, and F represents the total number of target relevances.

[0123] Step 502: Determine the maximum value of each Fast Fourier Transform result.

[0124] Following the previous example, correspondingly, taking the maximum value from fft_data(k), the expression for calculating the maximum value p_max_data(k) and the corresponding position p_max(k) is as follows:

[0125]

[0126] Here, abs(*) represents the absolute value operation; max(*) is the maximum value operation; and mean(*) is the average value operation.

[0127] Step 503: Take the maximum value among all the maximum values ​​as the target maximum value.

[0128] Step 504: From multiple coarse synchronization points, obtain the target coarse synchronization point corresponding to the target maximum value, and use the target coarse synchronization point as the fine synchronization point of the main synchronization signal PSS.

[0129] In this example, by combining multiple target correlations with a correlation greater than a preset correlation threshold, the fine synchronization point of the primary synchronization signal PSS in the compensated baseband signal is accurately determined.

[0130] Correspondingly, in Figure 5 Based on the illustrated embodiment, in order to accurately determine the frequency offset estimate of the primary synchronization signal (PSS) in the compensated baseband signal, the above-described possible implementation method of estimating the frequency offset of PSS based on the fine synchronization point to obtain the frequency offset estimate of PSS is as follows: Figure 6 As shown, it may include:

[0131] Step 601: Obtain the point value of the target maximum value corresponding to the precision synchronization point.

[0132] Step 602: Determine whether the point value is greater than the number of sampling points of the Fast Fourier Transform. If yes, proceed to step 603; otherwise, proceed to steps 604 to 605.

[0133] Step 603: Determine the frequency offset estimate of the main synchronization signal PSS in the compensated baseband signal based on the point value, the number of sampling points of the fast Fourier transform, and the sampling frequency of the intermediate frequency signal.

[0134] In some exemplary implementations, the numerical value, the number of sampling points of the fast Fourier transform, and the sampling frequency of the intermediate frequency signal can be input into a preset calculation function to obtain the frequency offset estimate of the main synchronization signal PSS in the compensated baseband signal.

[0135] In one exemplary implementation, frequency offset estimation is performed based on the point value, the number of sampling points in the Fast Fourier Transform, and the sampling frequency of the intermediate frequency signal to calculate the estimated frequency offset value f of the primary synchronization signal PSS in the compensated baseband signal. est The calculation formula is as follows:

[0136]

[0137] In the formula, fo_direct1 is a preset value, for example, fo_direct1 = -1. Correspondingly, fft_num represents the number of sampling points in the Fast Fourier Transform, and fo_poe represents the point value. s This indicates the sampling frequency of the intermediate frequency signal.

[0138] Step 604: Subtract the point value from the number of sampling points in the Fast Fourier Transform and use the difference as the target point value.

[0139] In other words, the target number of points fo_poe = fft_num - poe, where poe is the number of points and fft_num represents the number of sampling points in the Fast Fourier Transform.

[0140] Step 605: Determine the frequency offset estimate of the main synchronization signal PSS in the compensated baseband signal based on the target point value, the number of sampling points of the fast Fourier transform, and the sampling frequency of the intermediate frequency signal.

[0141] In some exemplary embodiments, the frequency offset estimate f is calculated. est The calculation formula is:

[0142]

[0143] In the formula, fo_direct2 is a preset value, for example, fo_direct2 = 1; fo_poe represents the target point value, fft_num represents the number of sampling points in the Fast Fourier Transform, and correspondingly, fo_poe represents the point value, f s This indicates the sampling frequency of the intermediate frequency signal.

[0144] It is understandable that, in this example, the residual frequency offset value after ephemeris compensation is accurately determined, which facilitates the subsequent processing of the signal after PSS in the synchronization signal based on this frequency offset value, as well as the frequency offset compensation of the subsequent downlink signals sent by the low-Earth orbit satellite during the access process.

[0145] To make this clearer, let's combine the following... Figure 7 The cell search method of this embodiment will be described exemplarily.

[0146] Figure 7 This is a schematic flowchart of another cell search method provided in an embodiment of this disclosure.

[0147] like Figure 7 As shown, the cell search method may include:

[0148] Step 701: The SSB signal transmitted by the low-orbit satellite is down-converted to obtain an intermediate frequency signal y(n) with frequency point f0, and the intermediate frequency signal is down-converted to zero frequency to obtain a baseband signal y1(n).

[0149] Where n takes values ​​in the range (0, L_data-1), and L_data represents the data length of the baseband signal y1(n).

[0150] The initial value of frequency point f0 is the minimum frequency point in the bandwidth allocated by the low-orbit satellite to the ground terminal.

[0151] The formula for calculating the baseband signal y1(n) by down-converting the intermediate frequency signal y(n) to zero frequency is as follows:

[0152]

[0153] Where exp(*) is the exponential function;

[0154] Among them, f s Indicates the sampling frequency.

[0155] Specifically, y(n) is obtained through the sampling frequency f. s It is obtained by sampling the time-domain signal y(t) with frequency f0.

[0156] Step 702: The baseband signal y1(n) is low-pass filtered to obtain signal y2(n).

[0157] Correspondingly, the computational expression for y2(n) is obtained as follows:

[0158]

[0159] Where ∑(*) is the summation function; h is the coefficient of the L-order low-pass filter.

[0160] In some exemplary embodiments, in order for the low-pass filter in the ground terminal to be adaptable to different parameters such as bandwidth and subcarrier spacing, the low-pass filter coefficient h needs to be as follows:

[0161] h = firls(L-1,f,a,w)

[0162] Where L is the order of the low-pass filter;

[0163] The parameter f is generated as follows: SCS stands for Subcarrier Spacing, supporting 60kHz, 120kHz, and 240kHz.

[0164] The parameter 'a' takes the following values: a = [1, 1, 0, 0]

[0165] The parameter w takes the value: w = [1, 0.8].

[0166] Step 703: Calculate the Doppler frequency offset f based on the current terminal position of the ground terminal and the current satellite position of the low-Earth orbit satellite. u and frequency deviation rate f′ u Then, the signal y2(n) is compensated to obtain the signal r(n).

[0167] The formula for calculating r(n) is:

[0168] Specifically, the Doppler frequency offset f is calculated based on the current terminal position of the ground terminal and the current satellite position of the low-orbit satellite. u and the rate of change of frequency deviation f′ u An exemplary implementation is as follows: the current satellite position coordinates are L SAT =[X SAT ,Y SAT Z SAT The corresponding current terminal location coordinates are L. UE =[X UE ,Y UE Z UE ]; among which, Doppler frequency offset f u The corresponding calculation expression is:

[0169]

[0170] Among them, f c Let c be the carrier frequency used by the low-Earth orbit satellite when transmitting synchronization signals, and c = 3.0 * 10⁻⁶. 8 m / s.

[0171] Correspondingly, the Doppler frequency shift f′ u The calculation expression is as follows:

[0172]

[0173] Step 704: Truncate the received signal r(n) of length L_data to a length of N+N. cp , so as to obtain the k-th segment signal.

[0174] The expression for the k-th segment signal s(n) is:

[0175] s(n)=r(k:k+N+N cp -1). Here, the initial value of k is 0, and correspondingly, the maximum value of k is L_data-(N+N). cp ); where k:k+N+N cp -1 indicates that the value of n ranges from k to k+N+N. cp -1.

[0176] Where, N cp is the length of the OFDM symbol cyclic prefix CP; N is the number of FFT points.

[0177] It should be noted that in this example, N+N cp The resulting sum is the same as the length of the OFDM symbol.

[0178] Step 705: Take a segment of length N from the k-th segment signal. cp CP data and the corresponding OFDM symbol's final length N cp The data is then divided into M segments of length . The data is then processed and accumulated in segments to obtain the autocorrelation result of the k-th segment signal.

[0179] It can be understood that the data length of the k-th segment of the signal is N+N. cp .

[0180] The formula for calculating the autocorrelation result xcorr_data(k) of the k-th segment signal is as follows:

[0181]

[0182] The ·* operation represents multiplying the corresponding data.

[0183] Step 706: Determine whether the absolute value of the autocorrelation result xcorr_data(k) of the k-th segmented signal is greater than a preset correlation threshold. If not, execute Step 707; otherwise, execute Step 708.

[0184] Step 707: k = k + 1. If k + N + N cp > L_data or k ≥ K, then f0 = f0 + Δf, and return to Step 701. If k < K, then return to Step 704.

[0185] In some exemplary embodiments, when the updated f0 is less than the maximum frequency point of the bandwidth allocated by the low-earth orbit satellite to the ground terminal, return to Step 701.

[0186] Where, K represents the total number of segments obtained after segmenting the signal r(n). As an example, when using a sliding window of length N + N cp and the sliding step of the sliding window is 1, K = L - (N + N cp ).

[0187] Where, Δf represents the frequency point interval. For example, Δf can be 1.44 * 10 6 .

[0188] Step 708: Perform a fast Fourier transform on the autocorrelation result of the k-th segmented signal to obtain the fast Fourier transform result of the k-th segmented signal.​​​​​​​​​​​​​​​​​​​​Here, abs(*) represents the absolute value operation; max(*) is the maximum value operation; and mean(*) is the average value operation.

[0196] Step 710: If p_max_data(k) > x_max, then the position corresponding to the maximum point is poe = p_max(k), and the value corresponding to the maximum point is x_max = p_max_data(k).

[0197] Step 711, k = k + 1, if k + N + N cp If L_data > or k ≥ K, then proceed to step 708; otherwise, proceed to step 712.

[0198] Step 712: Take the maximum value of p_max_data(k), and the position of the maximum value is the position toa of the required PSS precision synchronization point.

[0199] Correspondingly, the calculation of the starting position toa is expressed as follows:

[0200] [~,toa]=max(p_max_data(k)) 1≤k≤L_data-(N+N cp )

[0201] Step 713: If poe > fft_num, then fo_poe = fft_num - poe, fo_direct = 1; otherwise, fo_poe = poe, fo_direct = -1.

[0202] Step 714: Perform frequency offset estimation based on fo_poe and fo_direct to obtain the frequency offset estimate f. est .

[0203] Among them, f est The calculation expression is:

[0204]

[0205] In this example, based on the pre-compensation of ephemeris frequency offset, the correlation between the cyclic prefix (CP) segment and the data segment with the last length of CP of the corresponding OFDM symbol is accumulated to obtain the correlation. When the correlation is greater than the preset correlation threshold, the "capture-frequency offset estimation" algorithm is used to achieve the integration of obtaining the synchronization point of the baseband signal and frequency offset estimation. This achieves both precise synchronization and obtains the residual frequency offset value after ephemeris compensation. This enables rapid cell search and improves the cell search performance of the ground terminal.

[0206] When the cell search method provided in this disclosure is applied to practice, the precise synchronization point location and cell group ID number (NI D2, values ​​1-3, representing 3 PSS sequences) of the primary synchronization signal (PSS) of the SSB block are obtained after detection using the method of this invention. An example diagram shows the probability of detection error for both under different signal-to-noise ratios. Figure 8 As shown. (Through) Figure 8 It can be seen that the detection error rate gradually decreases as the signal-to-noise ratio increases; the detection error rate of NI D2 is always lower than the probability of detecting errors at the PSS start position. This is because the determination of NI D2 is based on the PSS index corresponding to the peak of differential cross-correlation. The erroneous peak position may correspond to the correct index. Therefore, the detection of NI D2 has a certain fault tolerance.

[0207] Applying the cell search method provided in this disclosure to a practical application yields an example diagram of the root mean square error (RMSE) of the overall frequency offset, as shown below. Figure 4 As shown. To ensure the correctness of signal demodulation, the carrier frequency deviation needs to be less than 4% or even smaller than the carrier spacing. If we assume that a frequency deviation of 4% or less is negligible, then the maximum error between the estimated frequency deviation and the true value should be 600Hz, with a normalized value of 0.04. Figure 9 It can be seen that the critical value of signal-to-noise ratio (SNR) lies between 2dB and 4dB.

[0208] To implement the above embodiments, this disclosure also proposes a cell search device.

[0209] Figure 10 This is a schematic diagram of a cell search device provided in an embodiment of the present disclosure. It should be noted that the cell search device in this example is used in a ground terminal.

[0210] like Figure 10 As shown, the cell search device 1000 includes: a first determining module 1001, a second determining module 1002, a compensation module 1003, a third determining module 1004, and a cell search module 1005, wherein:

[0211] The first determining module 1001 is used to determine the baseband signal of the synchronization signal transmitted by the low-orbit satellite.

[0212] The second determining module 1002 is used to determine the Doppler frequency offset and frequency offset rate between the low-orbit satellite and the ground terminal based on the current satellite position of the low-orbit satellite and the current terminal position of the ground terminal.

[0213] The compensation module 1003 is used to compensate the baseband signal based on the Doppler frequency offset and the frequency offset change rate to obtain the compensated baseband signal.

[0214] The third determining module 1004 is used to determine multiple coarse synchronization points of the main synchronization signal PSS in the compensated baseband signal.

[0215] The cell search module 1005 is used to determine the fine synchronization point of the PSS based on multiple coarse synchronization points, and to perform cell search based on the fine synchronization point.

[0216] As one possible implementation of this disclosure, the apparatus may further include:

[0217] The low-pass filter processing module is used to perform low-pass filtering on the baseband signal.

[0218] As one possible implementation of this disclosure, the apparatus may further include:

[0219] The frequency offset estimation module is used to estimate the frequency offset of the PSS based on the fine synchronization point, so as to obtain the frequency offset estimate of the PSS.

[0220] As one possible implementation of this disclosure, the third determining module 1004 may include:

[0221] The segmentation unit is used to divide the compensated baseband signal into multiple segments using a sliding window. The preset length of the sliding window is the length N of the cyclic prefix CP of the Orthogonal Frequency Division Multiplexing (OFDM) symbol. CP It is obtained by summing the number of sampling points N of the Fast Fourier Transform;

[0222] The truncation unit is used to truncate each segmented signal by a length of N, starting from the beginning of the segment. CP The first segmented signal is extracted, and a segment of length N is extracted from the specified position of the segmented signal. CP The second intercept signal, wherein the length between the specified position and the end position of the segmented signal is equal to N. CP ;

[0223] The first determining unit is used to determine the correlation between the first intercepted signal and the second intercepted signal;

[0224] The acquisition unit is used to acquire multiple target correlations with a correlation greater than a preset correlation threshold from the correlation between the first and second truncated signals of all segmented signals.

[0225] The second determining unit is used to take the starting position of the segmented signal corresponding to each target correlation degree as the coarse synchronization point of the main synchronization signal PSS in the compensated baseband signal.

[0226] As one possible implementation of this disclosure, the first determining unit is specifically used for:

[0227] The first intercepted signal is segmented to obtain a first segmented signal sequence;

[0228] The second intercepted signal is segmented to obtain a second segmented signal sequence;

[0229] The correlation values ​​between the i-th segment signal in the first segment signal sequence and the i-th segment signal in the second segment signal sequence are summed to obtain the correlation between the first truncated signal and the second truncated signal, where i is an integer greater than or equal to 1 and less than H, and H represents the total number of segment signals in the first segment signal sequence.

[0230] As one possible implementation of this disclosure, the cell search module 1005 is specifically used for:

[0231] Perform Fast Fourier Transform on the correlation of multiple targets separately to obtain the Fast Fourier Transform results corresponding to the correlation of multiple targets;

[0232] Determine the maximum value of each Fast Fourier Transform result;

[0233] The maximum value among all the maximum values ​​is taken as the target maximum value;

[0234] From multiple coarse synchronization points, obtain the target coarse synchronization point corresponding to the target maximum value, and use the target coarse synchronization point as the fine synchronization point of the main synchronization signal PSS.

[0235] As one possible implementation of this disclosure, the frequency offset estimation module is specifically used for:

[0236] Get the point value corresponding to the maximum value;

[0237] Determine if the point value is greater than the number of sampling points in the Fast Fourier Transform;

[0238] If the point value is less than or equal to the number of sampling points of the Fast Fourier Transform, then the frequency offset estimate of the main synchronization signal PSS in the compensated baseband signal is determined based on the point value, the number of sampling points of the Fast Fourier Transform, and the sampling frequency of the intermediate frequency signal.

[0239] As one possible implementation of this disclosure, the frequency offset estimation module is further configured to:

[0240] If the point value is greater than the number of sampling points of the Fast Fourier Transform, the difference between the number of sampling points of the Fast Fourier Transform and the point value is taken as the target point value.

[0241] Based on the target point value, the number of sampling points of the Fast Fourier Transform, and the sampling frequency of the intermediate frequency signal, the frequency offset estimate of the main synchronization signal PSS in the compensated baseband signal is determined.

[0242] It should be noted that the foregoing explanation of the cell search method embodiment also applies to the cell search device in this embodiment, and this embodiment will not repeat the above.

[0243] The cell search apparatus of this disclosure determines the baseband signal of the synchronization signal transmitted by a low-Earth orbit (LEO) satellite; determines the Doppler frequency offset and frequency offset rate of change between the LEO satellite and the ground terminal based on the current satellite position and the current terminal position of the ground terminal; compensates the baseband signal based on the Doppler frequency offset and frequency offset rate of change to obtain a compensated baseband signal; accurately determines the fine synchronization point of the primary synchronization signal (PSS) based on the coarse synchronization point in the compensated baseband signal, and performs cell search based on the fine synchronization point. This enables the ground terminal to conveniently and quickly perform cell search even in environments with large Doppler frequency shifts, improving the cell search performance of the ground terminal.

[0244] It should be noted that the foregoing explanation of the cell search method embodiment also applies to the cell search device of this embodiment, and will not be repeated here.

[0245] To implement the above embodiments, this disclosure also proposes a ground terminal, such as... Figure 11 As shown, Figure 11 This is a block diagram illustrating a ground terminal for implementing a cell search method according to an exemplary embodiment.

[0246] like Figure 11 As shown, the aforementioned ground terminal 1100 includes:

[0247] The memory 1110 and the processor 1120 are connected by a bus 1130, which connects different components (including the memory 1110 and the processor 1120). The memory 1110 stores a computer program, which implements the cell search method of this disclosure embodiment when the processor 1120 executes the program.

[0248] Bus 1130 represents one or more of several bus architectures, including a memory bus or memory controller, a peripheral bus, a graphics acceleration port, a processor, or a local bus using any of the various bus architectures. For example, these architectures include, but are not limited to, the Industry Standard Architecture (ISA) bus, the Micro Channel Architecture (MAC) bus, the Enhanced ISA bus, the Video Electronics Standards Association (VESA) local bus, and the Peripheral Component Interconnect (PCI) bus.

[0249] Ground terminal 1100 typically includes a variety of ground terminal readable media. These media can be any available media that can be accessed by ground terminal 1100, including volatile and non-volatile media, and removable and non-removable media.

[0250] Memory 1110 may also include computer system readable media in the form of volatile memory, such as random access memory (RAM) 1140 and / or cache memory 1150. Ground terminal 1100 may further include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, storage system 1160 may be used to read and write non-removable, non-volatile magnetic media (… Figure 11 Not shown; usually referred to as a "hard drive"). Although Figure 11 Not shown, a disk drive for reading and writing to a removable non-volatile disk (e.g., a "floppy disk") and an optical disk drive for reading and writing to a removable non-volatile optical disk (e.g., a CD-ROM, DVD-ROM, or other optical media) may be provided. In these cases, each drive may be connected to bus 1130 via one or more data media interfaces. Memory 1110 may include at least one program product having a set (e.g., at least one) of program modules configured to perform the functions of the embodiments of this disclosure.

[0251] A program / utility 1180 having a set (at least one) of program modules 1180 may be stored, for example, in memory 1110. Such program modules 1180 include, but are not limited to, an operating system, one or more application programs, other program modules, and program data. Each or some combination of these examples may include an implementation of a network environment. Program modules 1180 typically perform the functions and / or methods described in the embodiments of this disclosure.

[0252] Ground terminal 1100 can also communicate with one or more external devices 1190 (e.g., keyboard, pointing device, display, etc.), and with one or more devices that enable a user to interact with the ground terminal 1100, and / or with any device that enables the ground terminal 1100 to communicate with one or more other computing devices (e.g., network card, modem, etc.). This communication can be performed via input / output (I / O) interface 1192. Furthermore, ground terminal 1100 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) via network adapter 1193. Figure 11 As shown, network adapter 1193 communicates with other modules of ground terminal 1100 via bus 1130. It should be understood that, although... Figure 11 As not shown, other hardware and / or software modules can be used in conjunction with the ground terminal 1100, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0253] The processor 1120 performs various functional applications and data processing by running programs stored in the memory 1110.

[0254] It should be noted that the implementation process and technical principles of the ground terminal in this embodiment are explained in the foregoing description of the cell search method of this disclosure embodiment, and will not be repeated here.

[0255] To implement the above embodiments, this disclosure also proposes a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the cell search method of the above embodiments.

[0256] To implement the above embodiments, this disclosure also provides a computer program product that, when executed by an instruction processor, performs the cell search method of the above embodiments.

[0257] It should be noted that in the description of this disclosure, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more.

[0258] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of preferred embodiments of this disclosure includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the function involved, as will be understood by those skilled in the art to which embodiments of this disclosure pertain.

[0259] It should be understood that various parts of this disclosure can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0260] Those skilled in the art will understand that all or part of the steps of the methods described in the above embodiments can be implemented by a program instructing related hardware, and the program can be stored in a computer-readable storage medium. When executed, the program includes one or a combination of the steps of the method embodiments.

[0261] Furthermore, the functional units in the various embodiments of this disclosure can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0262] The storage media mentioned above can be read-only memory, disk, or optical disk, etc.

[0263] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0264] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A cell search method, characterized in that, The method is applied in a ground terminal, and the method includes: Determine the baseband signal of the synchronization signal transmitted by the low-Earth orbit satellite; Based on the current satellite position of the low-orbit satellite and the current terminal position of the ground terminal, determine the Doppler frequency offset and frequency offset rate between the low-orbit satellite and the ground terminal; The baseband signal is compensated based on the Doppler frequency offset and the frequency offset change rate to obtain a compensated baseband signal. Determine multiple coarse synchronization points of the primary synchronization signal PSS in the compensated baseband signal; Based on the multiple coarse synchronization points, the fine synchronization point of the PSS is determined, and cell search is performed based on the fine synchronization point; The method further includes: Based on the precise synchronization point, frequency offset is estimated for the PSS to obtain the estimated frequency offset value of the PSS; The determination of multiple coarse synchronization points of the primary synchronization signal PSS in the compensated baseband signal includes: The compensated baseband signal is divided into multiple segmented signals using a sliding window. The preset length of the sliding window is N, which is the length of the cyclic prefix (CP) of the Orthogonal Frequency Division Multiplexing (OFDM) symbol. CP It is obtained by summing the number of sampling points N of the Fast Fourier Transform; For each segmented signal, a length of N is truncated from the beginning of the segmented signal. CP The first segmented signal is extracted, and a segment of length N is extracted from the specified position of the segmented signal. CP The second intercepted signal, wherein the length between the specified position and the end position of the segmented signal is equal to N. CP ; Determine the correlation between the first intercepted signal and the second intercepted signal; From the correlation between the first and second truncated signals of all the segmented signals, obtain a plurality of target correlations whose correlation is greater than a preset correlation threshold; The starting position of the segmented signal corresponding to each of the target correlations is taken as the coarse synchronization point of the main synchronization signal PSS in the compensated baseband signal.

2. The method as described in claim 1, characterized in that, Before performing compensation processing on the baseband signal based on the Doppler frequency offset and the frequency offset change rate to obtain the compensated baseband signal, the method further includes: The baseband signal is subjected to low-pass filtering.

3. The method as described in claim 1, characterized in that, Determining the correlation between the first intercepted signal and the second intercepted signal includes: The first intercepted signal is segmented to obtain a first segmented signal sequence; The second intercepted signal is segmented to obtain a second segmented signal sequence; The correlation values ​​between the i-th segment signal in the first segment signal sequence and the i-th segment signal in the second segment signal sequence are summed to obtain the correlation between the first truncated signal and the second truncated signal, where i is an integer greater than or equal to 1 and less than H, and H represents the total number of segment signals in the first segment signal sequence.

4. The method as described in claim 1, characterized in that, The step of determining the fine synchronization point of the PSS based on the plurality of coarse synchronization points includes: Perform Fast Fourier Transform on each of the multiple target correlations to obtain the Fast Fourier Transform results corresponding to the multiple target correlations; Determine the maximum value for each of the aforementioned Fast Fourier Transform results; The maximum value among all the stated maximum values ​​shall be taken as the target maximum value; From the plurality of coarse synchronization points, obtain the target coarse synchronization point corresponding to the target maximum value, and use the target coarse synchronization point as the fine synchronization point of the main synchronization signal PSS.

5. The method as described in claim 4, characterized in that, The step of estimating the frequency offset of the PSS based on the precise synchronization point to obtain the estimated frequency offset value of the PSS includes: Obtain the point value of the target maximum value corresponding to the precise synchronization point; Determine whether the value of the point is greater than the number of sampling points of the fast Fourier transform; If the point value is less than or equal to the number of sampling points of the Fast Fourier Transform, then the frequency offset estimate of the PSS is determined based on the point value, the number of sampling points of the Fast Fourier Transform, and the sampling frequency of the intermediate frequency signal.

6. The method as described in claim 5, characterized in that, The method further includes: If the point value is greater than the number of sampling points of the Fast Fourier Transform, then the difference between the number of sampling points of the Fast Fourier Transform and the point value is taken as the target point value. The frequency offset estimate of the PSS is determined based on the target point value, the number of sampling points of the fast Fourier transform, and the sampling frequency of the intermediate frequency signal.

7. A cell search device, characterized in that, The device is used in a ground terminal, employing the cell search method as described in claim 1, and the device comprises: The first determining module is used to determine the baseband signal of the synchronization signal transmitted by the low-orbit satellite; The second determining module is used to determine the Doppler frequency offset and frequency offset rate of change between the low-orbit satellite and the ground terminal based on the current satellite position of the low-orbit satellite and the current terminal position of the ground terminal. The compensation module is used to perform compensation processing on the baseband signal based on the Doppler frequency offset and the frequency offset change rate to obtain the compensated baseband signal; The third determining module is used to determine multiple coarse synchronization points of the main synchronization signal PSS in the compensated baseband signal; The cell search module is used to determine the fine synchronization point of the PSS based on the multiple coarse synchronization points, and to perform cell search based on the fine synchronization point.

8. A ground terminal, characterized in that, include: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor, when executing the program, implements the cell search method as described in any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by the processor, the program implements the cell search method as described in any one of claims 1-6.

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