Time-frequency synchronization method and device in orthogonal frequency division multiplexing large frequency offset scenario

Abstract

This application provides a time-frequency synchronization method and apparatus for large frequency offset scenarios in orthogonal frequency division multiplexing (OFDM). The transmitting end configures a long training structure based on ZC sequence pairs in the radio frequency signal, leveraging the constant amplitude, low peak-to-average power ratio (PAPR), and excellent autocorrelation characteristics of the ZC sequences to significantly enhance resistance to frequency offset and noise. The receiving end employs a two-dimensional time-frequency sliding search to construct a two-dimensional time-frequency correlation matrix, jointly estimating the frequency offset and timing offset to avoid the error accumulation problem of the "timing first, then frequency offset" process. A dual-position constraint mechanism is introduced in the peak detection stage to effectively filter false peaks generated by channel noise and multipath interference. Voting fusion of multi-frame data further improves synchronization stability, making the synchronization between the receiving and transmitting ends more accurate and stable. This significantly improves the robustness and estimation accuracy of the synchronization process in large frequency offset scenarios and effectively suppresses performance degradation caused by frequency offset.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to a time-frequency synchronization method and apparatus for orthogonal frequency division multiplexing with large frequency offset. Background Technology

[0002] In Orthogonal Frequency-Division Multiplexing (OFDM) systems, cross-correlation synchronization of long training sequence pairs is the core method for achieving symbol timing and carrier frequency synchronization. Correlation techniques often employ conventional structured long training sequences (such as PN sequences and pseudo-random sequences), and typically use a separate process of "timing estimation first, then frequency estimation." However, conventional structured long training sequences suffer from problems such as autocorrelation attenuation due to frequency offset, synchronization error accumulation, and weak anti-interference capabilities under large frequency offset scenarios. This reduces the energy difference between spurious peaks and true synchronization peaks, making them difficult to distinguish and resulting in poor signal synchronization performance. Summary of the Invention

[0003] In view of this, the purpose of this application is to propose a time-frequency synchronization method and device for orthogonal frequency division multiplexing with large frequency offset. By building a radio frequency signal adapted to the large frequency offset scenario at the transmitting end, the receiving end constructs a two-dimensional correlation matrix by performing frequency offset search and cross-correlation operation on the radio frequency signal, and then locks the effective synchronization point by using dual position constraint verification, so as to achieve time-frequency synchronization of the radio frequency signal.

[0004] To achieve the above objectives, this application provides a time-frequency synchronization method for orthogonal frequency division multiplexing (OFDM) scenarios with large frequency offset, applied at the receiving end, comprising:

[0005] The set of candidate frequency offset compensation values ​​is determined based on the preset frequency offset search step size and the large frequency offset tolerance range; The local ZC sequence is frequency offset compensated according to the candidate frequency offset compensation value set to obtain the local sequence set; A two-dimensional time-frequency correlation matrix is ​​constructed based on the radio frequency signal transmitted by the transmitting end and the local sequence set; Based on the theoretical interval and preset threshold value in the radio frequency signal, peak detection with dual position constraints is performed on the time-frequency two-dimensional correlation matrix to obtain candidate effective synchronization points; A voting method is used to fuse and decide on candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point. The radio frequency signals are then subjected to frequency offset correction processing based on the optimal effective synchronization point to obtain a time-frequency synchronization signal.

[0006] Optionally, determining the candidate frequency offset compensation value set based on a preset frequency offset search step size and a large frequency offset tolerance range includes: The frequency search interval is determined based on the aforementioned large frequency offset tolerance range; In response to the frequency offset search step size satisfying the accuracy division condition, the frequency search interval is divided sequentially according to the frequency offset search step size, starting from the lower boundary frequency of the frequency search interval, and then sequentially marked according to the division order to obtain the candidate frequency offset compensation value set.

[0007] Optionally, the step of performing frequency offset compensation on the local ZC sequence based on the candidate frequency offset compensation value set to obtain a local sequence set includes: The frequency offset compensation factor is determined based on the sampling period and the candidate frequency offset compensation value in the candidate frequency offset compensation value set; the frequency offset compensation factor set is also defined. The local ZC sequence is frequency offset compensated according to each frequency offset compensation factor in the set of frequency offset compensation factors to obtain a local sequence set.

[0008] Optionally, constructing a two-dimensional time-frequency correlation matrix based on the radio frequency signal transmitted by the transmitting end and the local sequence set includes: Determine the receiving sequence corresponding to the radio frequency signal; Perform a time-domain sliding cross-correlation operation on each local sequence in the local sequence set and the received sequence to obtain the cross-correlation function value corresponding to the candidate frequency offset compensation value; Using the candidate frequency offset compensation value as the row index and the timing sliding offset of the local sequence relative to the received sequence as the column index, the cross-correlation function value is filled into a preset initial correlation matrix as a matrix element to obtain the time-frequency two-dimensional correlation matrix.

[0009] Optionally, performing a time-domain sliding cross-correlation operation on the local sequence and the received sequence to obtain the cross-correlation function value corresponding to the candidate frequency offset compensation value includes: Using the local sequence as a sliding window and a preset maximum search value as a timed sliding constraint, a window sequence corresponding to the sliding window is determined in the received sequence. Perform cross-correlation operation on each window sequence and the local sequence to obtain the cross-correlation function value of the target candidate frequency offset compensation value corresponding to the local sequence.

[0010] Optionally, the step of performing dual-position-constrained peak detection on the time-frequency two-dimensional correlation matrix based on the theoretical interval and a preset threshold value in the radio frequency signal to obtain candidate valid synchronization points includes: The peak position is determined based on the row and column indices of the time-frequency two-dimensional correlation matrix, and the cross-correlation function value corresponding to the peak position is determined. The peak positions where the cross-correlation function value is greater than or equal to the threshold value are determined as valid peak positions; Based on the theoretical interval and the time-frequency two-dimensional correlation matrix, peak detection with dual position constraints is performed on the effective peak position to obtain the candidate effective synchronization point.

[0011] Optionally, the step of performing dual-position constraint peak detection on the effective peak positions based on the theoretical interval and the time-frequency two-dimensional correlation matrix to obtain the candidate effective synchronization points includes: The next retrieval position of the effective peak position is determined based on the theoretical interval; The first cross-correlation function value corresponding to the next retrieval position is determined based on the time-frequency two-dimensional correlation matrix. In response to the first cross-correlation function value being greater than the threshold value, the effective peak position is determined as the candidate effective synchronization point.

[0012] Optionally, the step of using a voting method to fuse candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point includes: Determine the candidate cross-correlation function value for each of the candidate valid synchronization points, determine the maximum candidate cross-correlation function value among the candidate cross-correlation function values, and determine the candidate valid synchronization point corresponding to the maximum candidate cross-correlation function value as the valid synchronization point of a single frame radio frequency signal; The optimal effective synchronization point with the most votes is determined from the effective synchronization points of multiple frames of radio frequency signals using a voting method.

[0013] Based on the same inventive concept, this application also provides a time-frequency synchronization method for orthogonal frequency division multiplexing with large frequency offset, applied at the transmitting end, including: Remove the standard long training sequence from the initial radio frequency signal to obtain the missing sequence; The sequence generation parameters are determined based on the user's input parameters, and the same first ZC sequence and second ZC sequence are generated based on the sequence generation parameters; wherein the first ZC sequence, the second ZC sequence and the local sequence of the receiving end are the same; According to the preset frame structure, the first ZC sequence and the second ZC sequence are deployed into the missing sequence to obtain the radio frequency signal to be sent to the receiving end; The theoretical interval is determined by the first position index of the first ZC sequence in the radio frequency signal and the second position index of the second ZC sequence in the radio frequency signal, and the radio frequency signal carrying the theoretical interval is sent to the receiving end.

[0014] Based on the same inventive concept, this application also provides a time-frequency synchronization device for orthogonal frequency division multiplexing with large frequency offset, comprising: The transmitting end is configured to: remove the standard long training sequence from the initial radio frequency signal to obtain a missing sequence; determine sequence generation parameters according to user input parameters, and generate the same first ZC sequence and second ZC sequence according to the sequence generation parameters; wherein the first ZC sequence, the second ZC sequence and the local sequence of the receiving end are the same; deploy the first ZC sequence and the second ZC sequence into the missing sequence according to a preset frame structure to obtain a radio frequency signal to be transmitted to the receiving end; determine the theoretical interval by the first position index of the first ZC sequence in the radio frequency signal and the second position index of the second ZC sequence in the radio frequency signal, and transmit the radio frequency signal carrying the theoretical interval to the receiving end; The receiving end is configured to: determine a set of candidate frequency offset compensation values ​​based on a preset frequency offset search step size and a large frequency offset tolerance range; perform frequency offset compensation on the local ZC sequence based on the set of candidate frequency offset compensation values ​​to obtain a local sequence set; construct a time-frequency two-dimensional correlation matrix based on the radio frequency signal transmitted by the transmitting end and the local sequence set; perform peak detection with dual position constraints on the time-frequency two-dimensional correlation matrix based on the theoretical interval in the radio frequency signal and a preset threshold value to obtain candidate effective synchronization points; use a voting method to perform fusion decision on the candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point, and perform frequency offset correction processing on the radio frequency signal based on the optimal effective synchronization point to obtain a time-frequency synchronization signal.

[0015] As can be seen from the above, the time-frequency synchronization method and apparatus for large frequency offset scenarios in orthogonal frequency division multiplexing provided in this application can determine a set of candidate frequency offset compensation values ​​based on a preset frequency offset search step size and a large frequency offset tolerance range; perform frequency offset compensation on the local ZC sequence based on the candidate frequency offset compensation value set to obtain a local sequence set; construct a two-dimensional time-frequency correlation matrix based on the radio frequency signal transmitted by the transmitter and the local sequence set; perform peak detection with dual position constraints on the two-dimensional time-frequency correlation matrix based on the theoretical interval in the radio frequency signal and a preset threshold value to obtain candidate effective synchronization points; use a voting method to perform fusion decision on the candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point; and perform frequency offset correction processing on the radio frequency signal based on the optimal effective synchronization point to obtain a time-frequency synchronized signal. The transmitter configures a long training structure based on ZC sequence pairs in the radio frequency signal, which significantly enhances the anti-frequency offset and anti-noise capabilities by utilizing the constant amplitude, low peak-to-average power ratio, and excellent autocorrelation characteristics of the ZC sequence. The receiver improves the synchronization accuracy in scenarios with large frequency offset by using a two-dimensional time-frequency search, and reduces the error caused by the maximum peak value by using known location information, thereby improving the overall performance of the system.

[0016] The receiver, based on the RF signal transmitted by the transmitter and the local sequence set after frequency offset compensation, constructs a two-dimensional time-frequency correlation matrix using a two-dimensional sliding search. This jointly estimates the frequency offset and timing offset, avoiding the error accumulation problem of the "timing first, then frequency offset" process. In the peak detection stage, a dual-position constraint mechanism is introduced. Based on the ZC sequence pairs in the RF signal, the true synchronization point is verified at fixed theoretical intervals to obtain candidate effective synchronization points, effectively filtering false peaks caused by channel noise and multipath interference. Finally, by fusing multi-frame data through voting, a more accurate optimal effective synchronization point is determined from the candidate effective synchronization points, further improving synchronization stability and making the synchronization between the receiver and transmitter more accurate and stable. This significantly improves the robustness and estimation accuracy of the synchronization process under large frequency offset scenarios and effectively suppresses performance degradation caused by frequency offset. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a time-frequency synchronization method applied to a large frequency offset scenario in orthogonal frequency division multiplexing at the receiving end, according to an embodiment of this application. Figure 2 This is a schematic diagram of the PPDU frame structure according to an embodiment of this application; Figure 3 This is a flowchart illustrating a time-frequency synchronization method applied to a large frequency offset scenario in orthogonal frequency division multiplexing at the receiving end, according to an embodiment of this application. Figure 4 This is a schematic diagram illustrating the calculation process of the cross-correlation function value in an embodiment of this application; Figure 5 This is a schematic diagram of a two-dimensional time-frequency correlation matrix according to an embodiment of this application; Figure 6 This is a schematic diagram showing the peak position and theoretical interval in an embodiment of this application; Figure 7 This is a schematic diagram of the algorithm simulation results in the embodiments of this application; Figure 8 This is a schematic diagram of the simulation results of the two-dimensional search algorithm in the embodiments of this application; Figure 9 This is a schematic diagram illustrating the joint voting results of an embodiment of this application; Figure 10 This is a schematic diagram of a time-frequency synchronization device in a large frequency offset scenario of orthogonal frequency division multiplexing according to an embodiment of this application; Figure 11This is a schematic diagram of an electronic device according to an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0020] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0021] In this article, it is important to understand that any number of elements in the accompanying figures is for illustrative purposes and not for limitation, and any naming is for distinction only and has no limiting meaning.

[0022] Based on the above background description, the following situations also exist in the related technologies: Conventional structured long training sequences in related technologies often employ a separate process of "time estimation first, then frequency estimation." However, in scenarios with large frequency offsets, this separate process suffers from the following three drawbacks: First, the autocorrelation of long training sequences in a split process is easily attenuated by frequency offset, and cross-correlation operations are easily affected by channel noise and multipath interference, resulting in false maxima. Second, the separate estimation process ignores the coupling relationship between frequency offset and timing offset. Frequency offset will cause timing peak offset, and timing error will affect the accuracy of frequency offset estimation, ultimately leading to the accumulation of synchronization error. Third, the peak-to-average power ratio of traditional long training sequences is relatively high, which further reduces the anti-interference ability of synchronization algorithms, making it difficult to distinguish between false peaks and real synchronization peaks.

[0023] In related technologies, simply increasing the cross-correlation threshold or using smoothing filters to remove spurious peaks does not solve the problem of frequency and timing coupling estimation, leading to insufficient synchronization accuracy and poor robustness in scenarios with large frequency offsets. Meanwhile, ZC (Zadoff-Chu) sequences, as sequences with constant envelope, low peak-to-average power ratio, good autocorrelation, and cross-correlation, possess natural advantages in resisting frequency offsets and noise, but have not yet been applied to long training structures in OFDM systems. Furthermore, a technical solution combining two-dimensional joint estimation and position verification mechanisms to address the dual problems of "spurious peaks + coupled estimation" in scenarios with large frequency offsets is still lacking. Therefore, a synchronization technique that integrates the characteristics of ZC sequences, two-dimensional joint estimation, and position verification mechanisms is urgently needed to improve synchronization performance in scenarios with large frequency offsets.

[0024] The time-frequency synchronization method and apparatus for large frequency offset scenarios in orthogonal frequency division multiplexing (OFDM) provided in this application can determine a set of candidate frequency offset compensation values ​​based on a preset frequency offset search step size and a large frequency offset tolerance range; perform frequency offset compensation on the local ZC sequence based on the candidate frequency offset compensation value set to obtain a local sequence set; construct a two-dimensional time-frequency correlation matrix based on the radio frequency signal transmitted by the transmitter and the local sequence set; perform peak detection with dual position constraints on the two-dimensional time-frequency correlation matrix based on the theoretical interval in the radio frequency signal and a preset threshold value to obtain candidate effective synchronization points; use a voting method to perform fusion decision on the candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point; and perform frequency offset correction processing on the radio frequency signal based on the optimal effective synchronization point to obtain a time-frequency synchronized signal. The transmitter configures a long training structure based on ZC sequence pairs in the radio frequency signal, which significantly enhances the anti-frequency offset and anti-noise capabilities by utilizing the constant amplitude, low peak-to-average power ratio, and excellent autocorrelation characteristics of the ZC sequence. The receiver improves the synchronization accuracy in large frequency offset scenarios through two-dimensional time-frequency search, reduces the error caused by maximum peak values ​​by utilizing known position information, and improves the overall performance of the system.

[0025] The receiver, based on the RF signal transmitted by the transmitter and the local sequence set after frequency offset compensation, constructs a two-dimensional time-frequency correlation matrix using a two-dimensional sliding search. This jointly estimates the frequency offset and timing offset, avoiding the error accumulation problem of the "timing first, then frequency offset" process. In the peak detection stage, a dual-position constraint mechanism is introduced. Based on the ZC sequence pairs in the RF signal, the true synchronization point is verified at fixed theoretical intervals to obtain candidate effective synchronization points, effectively filtering false peaks caused by channel noise and multipath interference. Finally, by fusing multi-frame data through voting, a more accurate optimal effective synchronization point is determined from the candidate effective synchronization points, further improving synchronization stability and making the synchronization between the receiver and transmitter more accurate and stable. This significantly improves the robustness and estimation accuracy of the synchronization process under large frequency offset scenarios and effectively suppresses performance degradation caused by frequency offset.

[0026] The following describes in detail, with reference to the accompanying drawings, the time-frequency synchronization method for orthogonal frequency division multiplexing with large frequency offset provided by the embodiments of this application.

[0027] In some embodiments, such as Figure 1 As shown, a time-frequency synchronization method for orthogonal frequency division multiplexing (OFDM) scenarios with large frequency offset is applied at the transmitting end, including: Step 101: Remove the standard long training sequence from the initial radio frequency signal to obtain the missing sequence.

[0028] In practice, the initial radio frequency signal is composed of Physical Layer Protocol Data Units (PPDUs). PPDUs are the basic unit of physical layer data transmission in wireless network communication, and their frame structure design is crucial for ensuring reliable data transmission. A PPDU consists of a synchronization header, a physical layer frame header, and a physical layer payload. The synchronization header includes a training sequence (also called a preamble) and a start-of-frame delimiter. The training sequence is typically a specific bit sequence (such as all 0s or all 1s) used by the receiving device for clock synchronization and signal locking. The start-of-frame delimiter is a specific bit pattern that marks the end of the preamble sequence and the beginning of the actual frame data. The physical layer frame header includes the frame length and rate / signaling. The frame length indicates the length of the subsequent physical layer payload so that the receiver knows how much data to receive. The rate / signaling specifies the data transmission rate and modulation / coding scheme used in the payload portion, which the receiver adjusts the demodulation parameters accordingly. The physical layer payload is the actual data content to be transmitted, originating from the upper-layer MAC layer protocol data unit, and its length is variable.

[0029] The specific format of PPDU varies depending on different wireless communication standards (such as the IEEE 802.11 series), mainly in the design of the preamble and frame header: IEEE 802.11b / g (2.4GHz band): Defines two formats: long preamble and short preamble. Long preamble has better compatibility, while short preamble is more efficient. The SIGNAL field in its frame header indicates the data transmission rate (e.g., 1, 2, 5.5, 11 Mbps).

[0030] IEEE 802.11a / g / n / ac (OFDM technology): Employs more complex training sequences. The preamble contains a short training sequence (for coarse synchronization) and a long training sequence (for precise channel estimation), and its SIGNAL field (using the most robust BPSK modulation) contains the data rate that determines the modulation and coding scheme of the subsequent data fields.

[0031] The PPDU frame structure in orthogonal frequency division multiplexing is as follows: Figure 2The image shows the frame structure using the IEEE 802.11a standard, with a total duration of 16 μs. The training sequence consists of 10 cycles of repeated short training symbols (STS, corresponding to...). Figure 2 (t1-t10) and two cycles of repeated long training symbols (LTS, corresponding to Figure 2 The training symbol interval consists of T1-T2, with the short training symbol interval being 1 / 4 of the normal OFDM symbol interval and the long training symbol interval being consistent with the normal OFDM symbol interval. The following is connected to the "SIGNAL" field (1 normal OFDM symbol length) which contains key information such as modulation type, coding rate, and data length.

[0032] To introduce ZC sequences, the original structure and function of the short training symbols (used for coarse synchronization and coarse carrier frequency offset estimation) are retained. Only the long training symbol part is replaced, that is, the original standard long training sequence is removed, and ZC sequence pairs (two identical ZC sequences) are deployed at the time domain positions corresponding to T1 and T2. This ensures that the total duration of the frame header and the timing relationship of each domain are completely consistent with the IEEE 802.11a standard, without the need to adjust the frame structure parsing logic of the receiver.

[0033] Step 102: Determine the sequence generation parameters based on the user's input parameters, and generate the same first ZC sequence and second ZC sequence based on the sequence generation parameters; wherein the first ZC sequence, the second ZC sequence and the local sequence of the receiving end are the same.

[0034] In practical implementation, based on the OFDM system parameters of the IEEE 802.11a standard and the requirements of large frequency offset scenarios, the core parameters of the ZC sequence are determined. The selected number of subcarriers is N=64 (as specified in the IEEE 802.11a standard), the normal OFDM symbol period is 3.2μs, and the sampling period T... s =0.05μs (sampling frequency 20MHz), sequence length L =64 (equal to the number of subcarriers N), ensuring full compatibility with OFDM subcarriers, while matching the time domain length requirement of long training symbols, the root index u is selected as 1, satisfying coprime with the number of subcarriers N.

[0035] Based on the above core parameters (u=1, L=64), two ZC sequences with completely identical parameters are generated, which are defined as the first ZC sequence (Z1) and the second ZC sequence (Z2) respectively, forming a ZC sequence pair. The two sequences maintain constant amplitude and low peak-to-average ratio characteristics.

[0036] Step 103: Deploy the first ZC sequence and the second ZC sequence into the missing sequence according to the preset frame structure to obtain the radio frequency signal to be sent to the receiving end.

[0037] In practice, according to the timing requirements of the PPDU frame header, the first ZC sequence (Z1) is deployed at the beginning of the original long training symbol T1, and the second ZC sequence (Z2) is deployed at the beginning of the original long training symbol T2, so as to obtain the radio frequency signal to be sent to the receiving end.

[0038] Step 104: Determine the theoretical interval by using the first position index of the first ZC sequence in the radio frequency signal and the second position index of the second ZC sequence in the radio frequency signal, and send the radio frequency signal carrying the theoretical interval to the receiving end.

[0039] In practice, the theoretical interval position ΔS = 64 sampling points of the ZC sequence pair is calculated based on the deployment location. That is, the theoretical interval is determined by the first position index of the first ZC sequence in the radio frequency signal and the second position index of the second ZC sequence in the radio frequency signal. The corresponding time domain interval is 3.2μs, which is consistent with the normal OFDM symbol interval, providing a clear position reference for dual position constraint detection at the receiver.

[0040] In some embodiments, such as Figure 3 As shown, a time-frequency synchronization method for orthogonal frequency division multiplexing (OFDM) scenarios with large frequency offset is applied at the receiver, including: Step 301: Determine the set of candidate frequency offset compensation values ​​based on the preset frequency offset search step size and large frequency offset tolerance range.

[0041] In practice, in order to achieve time and frequency synchronization, the receiving end needs to generate multiple candidate frequency offset compensation values ​​that cover the system's tolerance range for large frequency offset, taking into account the application scenarios of high-speed mobile communication and long-distance transmission.

[0042] In some embodiments, determining a set of candidate frequency offset compensation values ​​based on a preset frequency offset search step size and a large frequency offset tolerance range includes: Determine the frequency search range based on the large frequency deviation tolerance range; In response to the frequency offset search step size satisfying the accuracy division condition, the frequency search interval is divided sequentially according to the frequency offset search step size, starting from the lower boundary frequency of the frequency search interval, and then sequentially marked according to the division order to obtain a set of candidate frequency offset compensation values.

[0043] In practice, based on the operating bandwidth of the OFDM system, carrier frequency stability, and application scenario requirements, the large frequency offset tolerance range is determined and used as the frequency search interval. Δf∈ [ 50kHz, 50kHz]; The frequency search range represents the maximum allowable frequency offset range of the system. Time and frequency synchronization is only performed within the frequency search range. Scenarios outside the frequency search range are not considered and are regarded as fault scenarios that require manual repair.

[0044] To ensure accurate frequency offset estimation while achieving comprehensive coverage of a large frequency offset range, a reasonable frequency offset search step size needs to be set. A step size that is too small will divide the frequency search interval into too many sub-intervals, increasing computational load, synchronization delay, and providing only a small improvement in synchronization accuracy. Conversely, a step size that is too large will divide the frequency search interval into fewer sub-intervals, reducing computational load, but each sub-interval corresponds to a large range, failing to achieve comprehensive coverage of the large frequency offset range and resulting in a significant decrease in synchronization accuracy. Therefore, a reasonable frequency offset search step size needs to be set to divide the frequency search interval.

[0045] Optionally, a selection range can be used to determine the precision partitioning condition. For example, if the selection range is [4,6], and the frequency offset search step size is within the selection range (i.e., the frequency offset search step size is less than or equal to the upper boundary value of the selection range and greater than or equal to the lower boundary value of the selection range), then the precision partitioning condition is satisfied. If the frequency offset search step size is outside the selection range (i.e., the frequency offset search step size is greater than the upper boundary value of the selection range or less than the lower boundary value of the selection range), then the precision partitioning condition is not satisfied.

[0046] For example, setting the frequency offset search step size Δf A step size of 5kHz ensures both the accuracy of frequency offset estimation and comprehensive coverage of a large frequency offset range, based on the frequency offset search step size. Δf Step 1: Divide the frequency search interval and generate a set of candidate frequency offset compensation values ​​F. F={F0,F1,...,F k}; The calculation method for the candidate frequency offset compensation value is as follows; F i =Δf_min+i×Δf_step(i=0,1,...,k); Where i is the order label of the candidate frequency offset compensation value; Δf_min is the lower boundary value of the frequency search interval, that is, the minimum frequency within the frequency search interval, for example... 50kHz; k is the maximum order marker of the candidate frequency offset compensation value, k=(Δf_max-Δf_min) / Δf_step, Δf_max is the upper boundary value of the frequency search interval, that is, the maximum frequency within the frequency search interval, for example, 50kHz, then k=(50+50) / 5=20.

[0047] Step 302: Perform frequency offset compensation on the local ZC sequence based on the candidate frequency offset compensation value set to obtain the local sequence set.

[0048] In practice, to reduce computational complexity, the receiver adopts a scheme of compensating for the local ZC sequence (instead of directly compensating for the received signal). The receiver pre-stores a local ZC sequence s_local with parameters completely identical to those of the transmitter. The core parameters of the local ZC sequence are the root index (u=1) and the sequence length (L=64). Since the length of the local ZC sequence (64 sampling points) is shorter than the sequence segment length of the received RF signal, in order to reduce the amount of computation and ensure the accuracy of correlation value calculation, the receiver adopts a strategy of compensating the candidate frequency offset compensation value to the local ZC sequence.

[0049] In some embodiments, frequency offset compensation is performed on the local ZC sequence according to the candidate frequency offset compensation value set to obtain a local sequence set, including: The frequency offset compensation factor is determined based on the sampling period and the candidate frequency offset compensation values ​​in the candidate frequency offset compensation value set; The local ZC sequence is frequency offset compensated according to each frequency offset compensation factor in the frequency offset compensation factor set to obtain the local sequence set.

[0050] In practice, for each candidate frequency offset compensation value F i First, determine the frequency offset compensation factor based on the sampling period and the candidate frequency offset compensation values ​​in the candidate frequency offset compensation value set. Among them, T s =0.05μs, which is the sampling period, and j represents the imaginary unit.

[0051] Then, frequency offset compensation is performed on the local ZC sequence according to each frequency offset compensation factor in the frequency offset compensation factor set, resulting in a local sequence set. This is achieved by multiplying the frequency offset compensation factor by the local ZC sequence point by point, resulting in multiple compensated local sequences, which form the local sequence set. The formula for calculating the frequency offset compensation of the local ZC sequence according to each frequency offset compensation factor in the frequency offset compensation factor set is as follows: ; in, This is the local ZC sequence before frequency offset compensation. This is the compensated local sequence.

[0052] After performing cross-correlation between the compensated local sequence and the received radio frequency signal, the modulus of the cross-correlation value is taken to ensure that the magnitude of the correlation value is not affected, thus greatly reducing the computational complexity.

[0053] Step 303: Construct a two-dimensional time-frequency correlation matrix based on the radio frequency signal transmitted by the transmitter and the local sequence set.

[0054] In specific implementation, for the receiving end, after receiving the radio frequency signal carrying the theoretical interval, optionally, the radio frequency signal can be preprocessed first. This preprocessing includes down-conversion, analog-to-digital conversion, and low-pass filtering to obtain the baseband digital signal. This signal has already undergone coarse synchronization and DC component removal through a short training sequence to ensure the accuracy of subsequent processing. After preprocessing, a two-dimensional time-frequency correlation matrix is ​​constructed by cross-correlation calculation of the radio frequency signal and the local sequence set. The process of constructing the two-dimensional time-frequency correlation matrix is ​​shown in the following embodiment.

[0055] In some embodiments, a two-dimensional time-frequency correlation matrix is ​​constructed based on the radio frequency signal transmitted by the transmitter and the local sequence set, including: Determine the receiving sequence corresponding to the radio frequency signal; Perform a time-domain sliding cross-correlation operation on each local sequence and the received sequence in the local sequence set to obtain the cross-correlation function value corresponding to the candidate frequency offset compensation value; Using the candidate frequency offset compensation value as the row index and the timing sliding offset of the local sequence relative to the received sequence as the column index, the cross-correlation function value is filled into the preset initial correlation matrix as a matrix element to obtain a two-dimensional time-frequency correlation matrix.

[0056] In practice, the radio frequency (RF) signal is first digitized to obtain the corresponding received sequence. The RF signal is essentially a physical quantity carrying information. It describes a continuously changing pattern, typically a function of time, but can also be a function of space (such as an image) or other independent variables.

[0057] A sequence is a set of sequentially ordered, indexed numerical values. It is an abstract concept in mathematics and computer science. The index n is a function of the integer n. It is discrete. The sequence itself is discrete and digitized. It is the "embodiment" of a signal when it is processed in a digital system.

[0058] A sequence is typically the digital result of a continuous signal after sampling and quantization. This process is called analog-to-digital conversion (A / D conversion): on a continuous time axis, at fixed time intervals T... s The sampling period is one instantaneous value of the signal. This transforms the continuous time variable t into a discrete integer index n (n = 0, 1, 2, ...). The sampled continuous amplitude values ​​are approximated as finite-precision numbers (e.g., represented by 16-bit binary numbers). This results in a discrete-time, discrete-amplitude digital sequence.

[0059] Radio frequency (RF) signals are analog signals in the form of high-frequency electromagnetic waves propagating in the air. The received sequence is a digital representation of the RF signal after a series of processing steps in a digital processor (such as an FPGA, DSP, or CPU), ultimately allowing it to be directly processed by algorithms, resulting in the received sequence corresponding to the RF signal. Each local sequence in the local sequence set corresponds to a frequency-offset local sequence stored at the receiver. Each local sequence has a different frequency offset; the actual frequency offset is determined by comparing local sequences with different frequency offsets and the received sequence, providing a data basis for synchronization. This comparison process is achieved through cross-correlation calculations.

[0060] In some embodiments, a time-domain sliding cross-correlation operation is performed on the local sequence and the received sequence to obtain the cross-correlation function value corresponding to the candidate frequency offset compensation value, including: The difference between the length of the first sequence of the received sequence and the length of the second sequence of the local sequence is determined as the maximum search value; Using the local sequence as a sliding window and the maximum search value as a timed sliding constraint, a window sequence corresponding to the sliding window is determined in the received sequence; Perform cross-correlation calculations on each window sequence and the local sequence to obtain the cross-correlation function value of the target candidate frequency offset compensation value corresponding to the local sequence.

[0061] In practice, for any target frequency offset compensation value F i The corresponding local sequence, when used as a window, results in a sliding window of length 64. When the sliding window is aligned with the first and last characters of the received sequence, the corresponding τ... p =0 indicates no sliding. Since the sliding window length is 64, when sliding to the maximum search value N_search, the tail of the sliding window is already aligned with the last bit of the received sequence. Continuing to slide would result in blank spaces within the sliding window, causing severe distortion of the sequence and loss of synchronization capability, so sliding stops. The maximum search value is the length of a single data frame of the received communication signal. Since the sliding step size is 1 sampling point, the maximum search value represents the maximum number of times the sliding window can move, and is the timing sliding offset τ. p The maximum value of τ is then the timing sliding offset. p The search range is τ∈[0, N_search].

[0062] If the sliding window has a length of 64, then as the sliding window slides within the received sequence, there will always be 64 window sequences within the window. A cross-correlation operation is performed on each window sequence and the local sequence, and the cross-correlation function value corresponding to the target candidate frequency offset compensation value of the local sequence is obtained. That is, the time-domain sliding step size of the compensated local sequence relative to the received sequence is 1 sampling point. For each timing sliding offset τ... p,refer to Figure 4 The cross-correlation function between the modulo-taken received sequence and the compensated local sequence is: ; in, The frequency offset compensation value is F. i The timing sliding offset is τ p The cross-correlation function value at time N represents the sequence length, for example, 64, then n represents the variable from 0 to 64. This represents the conjugate operation, which sums the correlation values ​​of each sampling point within the sequence length to obtain the cross-correlation function value.

[0063] When the sliding window slides to the position corresponding to the first ZC sequence, since the local sequence is the same as the first and second ZC sequences, the calculated cross-correlation function value is relatively large compared to other sliding positions, thus providing a data basis for locating the synchronization point.

[0064] While calculating the cross-correlation function value at the receiving end, an initial two-dimensional correlation matrix (with empty elements) is simultaneously constructed in time and frequency. Then, the candidate frequency offset compensation value F is used. i For row index, the timing slide offset of the local sequence relative to the received sequence. As column indices, the cross-correlation function values ​​are used as matrix elements to fill the preset initial correlation matrix, that is, each (F i , The cross-correlation function values ​​corresponding to the combination The elements are used to fill the initial correlation matrix one by one, resulting in the time-frequency two-dimensional correlation matrix R.

[0065] Step 304: Perform peak detection with dual position constraints on the time-frequency two-dimensional correlation matrix based on the theoretical interval and preset threshold value in the radio frequency signal to obtain candidate effective synchronization points.

[0066] In specific implementation, refer to Figure 5 By performing cross-correlation operations between the local sequence and the received sequence to construct a two-dimensional time-frequency correlation matrix, the synchronization matching degree under different time-frequency combinations is intuitively presented, providing clear data visualization support for subsequent peak detection. Through the above process, the receiver successfully transforms the time-frequency coupled synchronization problem into a two-dimensional matrix matching problem, laying a solid foundation for accurately selecting effective synchronization points.

[0067] During the peak detection phase, based on the preset theoretical interval positions of sequence pairs in the received sequence, it is determined whether the correlation values ​​of the current peak position and the corresponding theoretical interval position both exceed a preset threshold. If the dual position constraint condition is met, it is determined as a candidate valid synchronization point. The process for determining the candidate valid synchronization point is as follows.

[0068] In some embodiments, peak detection with dual position constraints is performed on the time-frequency two-dimensional correlation matrix based on the theoretical interval in the radio frequency signal and a preset threshold value to obtain candidate valid synchronization points, including: The peak position is determined based on the row and column indices of the time-frequency two-dimensional correlation matrix, and the cross-correlation function value corresponding to the peak position is determined. The peak positions where the cross-correlation function value is greater than or equal to the threshold value are determined as valid peak positions; Based on the theoretical interval and the two-dimensional correlation matrix of time and frequency, peak detection with dual position constraints is performed on the effective peak position to obtain candidate effective synchronization points.

[0069] Specifically, peak detection with dual position constraints is performed on the effective peak positions based on the theoretical interval and the two-dimensional time-frequency correlation matrix to obtain candidate effective synchronization points, including: The next retrieval position of the effective peak position is determined based on the theoretical interval; The value of the first cross-correlation function corresponding to the next retrieval position is determined based on the time-frequency two-dimensional correlation matrix. In response to the first cross-correlation function value being greater than the threshold value, the effective peak position is determined as a candidate effective synchronization point.

[0070] In practice, the frame structure parameters preset by the sending end are retrieved to obtain the theoretical interval ΔS of the ZC sequence pairs. Based on the theoretical interval ΔS, the retrieval offset corresponding to the theoretical interval is determined. The retrieval offset has a linear relationship with ΔS, and the retrieval offset = ΔS × F. s , of which F s This is the system sampling frequency.

[0071] refer to Figure 6 Ideally, during the cross-correlation operation and time-series search, due to the specific training sequence structure (the local sequence is identical to the first and second ZC sequences in the received sequence), the following will occur: Figure 6 The two peaks shown have a fixed difference in position, representing the theoretical interval. Therefore, the known theoretical interval information can be used to verify and eliminate the influence of accidental maximum peaks on the entire synchronization process. For example, to reduce computational load, the peak positions where the cross-correlation function value is greater than or equal to the threshold value are determined as valid peak positions, eliminating the influence of invalid data.

[0072] The core logic of the dual-position constraint is: for any valid peak position detected in the time-frequency two-dimensional correlation matrix (F... i , τ p ), it is necessary to determine the next retrieval position of the effective peak position (F) based on the theoretical interval. i , τ p +ΔS), and at the effective peak position (F) during retrieval. i , τp At the same time, the next search position (F) needs to be verified. i , τ p Whether the first cross-correlation function value corresponding to ΔS meets the preset threshold requirement. When the correlation values ​​of both the effective peak position itself and the next search position exceed the preset threshold, it is determined that the dual position constraint condition is met. Since the correlation value of the effective peak position has been determined to be greater than the threshold value, when the first cross-correlation function value is greater than the threshold value of the cross-correlation function value, the effective peak position (F) is... i , τ p () was identified as a candidate valid synchronization point.

[0073] Optionally, a two-way decision strategy can also be used to determine whether the dual-position constraint condition is met: for any effective peak position (F) detected in the time-frequency two-dimensional correlation matrix i , τ p ), it is necessary to determine the previous retrieval position of the effective peak position (F) based on the theoretical interval. i , τ p ΔS) and the next retrieval position (F) i , τ p +ΔS), and at the effective peak position (F) during retrieval. i ,τ p At the same time, the next search position (F) needs to be verified. i , τ p The first cross-correlation function value of +ΔS and the previous search position (F) i , τ p The second cross-correlation function value (determined according to the deployment order of the ZC sequence pairs) of ΔS is checked against a threshold value. Only when the correlation values ​​of the current position and the preceding / following search position both exceed the preset threshold is the dual-position constraint condition satisfied. That is, when there is a cross-correlation function value greater than the threshold value in either the first or second cross-correlation function value, the effective peak position (F) is determined. i , τ p () was identified as a candidate valid synchronization point.

[0074] Optionally, the threshold value Th is determined as follows: .

[0075] in, This is the threshold coefficient.

[0076] During the peak detection phase, the receiver first performs a traversal scan of the time-frequency two-dimensional correlation matrix, identifying each valid peak position whose amplitude exceeds a threshold. Each peak position is denoted as (Fi, τ_p) in coordinate form, where Fi is the candidate frequency offset compensation value corresponding to the valid peak position, and τ_p is the timing sliding offset corresponding to the valid peak position. Subsequently, the receiver retrieves the frame structure parameters preset by the transmitter to accurately obtain the theoretical interval between the first and second ZC sequences in the received sequence pair. The theoretical interval is determined by the transmitter during frame structure configuration and communicated to the receiver in advance to ensure consistency between the transmitting and receiving ends. The corresponding theoretical interval is located in the time-frequency two-dimensional correlation matrix, and the cross-correlation function value corresponding to the theoretical interval is extracted. The extracted cross-correlation function value is compared with a preset threshold to determine whether it meets the condition. If the cross-correlation function value at the peak position exceeds the threshold Th, and the first cross-correlation function value at the subsequent search position is less than the threshold Th, then the peak position is determined to be a false peak and is removed. If the cross-correlation function value at the peak position exceeds the threshold Th, and the first cross-correlation function value at the subsequent search position is also greater than the threshold Th, then the effective peak position is determined to satisfy the dual position constraint condition, and the effective peak position is confirmed as a potential effective synchronization point, and is entered into the subsequent synchronization point optimization and screening process as a candidate effective synchronization point.

[0077] By identifying candidate valid synchronization points and utilizing the fixed-position correlation characteristics of ZC sequence pairs in the received signal, false peaks caused by factors such as channel noise and multipath interference are effectively filtered out, ensuring the accuracy and reliability of subsequent synchronization points.

[0078] Step 305: Use a voting method to fuse and decide on the candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point, and perform frequency offset correction processing on the radio frequency signals based on the optimal effective synchronization point to obtain the time-frequency synchronization signal.

[0079] After completing the traversal scan of the two-dimensional time-frequency correlation matrix, the true effective synchronization point is selected from all potential effective synchronization points. According to the maximum likelihood principle, the cross-correlation value is maximized only when the time delay and frequency compensation are aligned with the actual frequency offset. Therefore, the frequency offset value and time delay value corresponding to the maximum peak value are selected as the effective synchronization point based on the magnitude of the cross-correlation value of the candidate points. The process of determining the effective synchronization point is shown in the following embodiment.

[0080] In some embodiments, a voting method is used to fuse candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point, including: Determine the candidate cross-correlation function value for each candidate valid synchronization point, determine the maximum candidate cross-correlation function value among the candidate cross-correlation function values, and determine the candidate valid synchronization point corresponding to the maximum candidate cross-correlation function value as the valid synchronization point of a single frame radio frequency signal; The optimal effective synchronization point with the most votes is determined from the effective synchronization points of multiple frames of radio frequency signals using a voting method.

[0081] In practice, the candidate cross-correlation function value of each candidate valid synchronization point is determined. The maximum candidate cross-correlation function value is then identified, and the candidate valid synchronization point corresponding to the maximum candidate cross-correlation function value is determined as the valid synchronization point of a single frame of RF signal. Figure 5 The point with the highest mid-peak value is taken as the effective synchronization point. Then, the optimal effective synchronization point with the most votes is determined from the effective synchronization points of multiple frames of RF signals using a voting method. For example, in the case of 3 frames, the effective synchronization point of the first frame is (F... 10 , τ2); the effective synchronization point of the second frame is (F 10 , τ2); the effective synchronization point of the third frame is (F 11 If τ2), then the effective synchronization point with the most votes is (F 10 If τ2), then the effective synchronization point (F) 10 , τ2) is the optimal effective synchronization point, and the positioning accuracy of the optimal synchronization point is further improved by voting on the frame.

[0082] The timing slip offset τ_ corresponding to the optimal effective synchronization point As the optimal timing estimate, τ_ The corresponding sampling time is used as the starting position of the OFDM symbol to complete symbol timing synchronization and ensure that the receiver can accurately extract the effective data segment of each OFDM symbol; the candidate frequency offset compensation value F_ corresponding to the optimal effective synchronization point is used. As the optimal frequency offset estimate, F_ As a carrier frequency offset compensation, it performs frequency offset correction processing on the received radio frequency signal to counteract the destruction of signal orthogonality by large frequency offset and complete carrier frequency synchronization.

[0083] According to such Figure 7 The simulation results of the algorithm shown show that, compared with the cross-correlation algorithm in the related technology, the time-frequency synchronization method provided by the embodiment of this application in the orthogonal frequency division multiplexing large frequency offset scenario has a synchronization performance that is about 1dB better under the same conditions. The horizontal axis represents the signal-to-noise ratio.

[0084] like Figure 8The simulation results of the two-dimensional search algorithm shown in this application demonstrate that the time-frequency synchronization method (also known as the two-dimensional search algorithm) for orthogonal frequency division multiplexing with large frequency offset provided in this application embodiment can improve the system synchronization accuracy in scenarios with large frequency offset. The performance curves show that the traditional cross-correlation algorithm is greatly affected by frequency offset, especially in scenarios with large frequency offset, which will greatly affect the algorithm performance. However, the two-dimensional search algorithm can avoid this impact, and the algorithm accuracy is related to the search step size.

[0085] like Figure 9 The voting joint decision results shown demonstrate that after single-frame time-frequency synchronization is completed, multi-frame joint decision-making is performed. A voting method is used to fuse and decide on a preset number of candidate synchronization points for each frame, selecting the optimal effective synchronization point. Using multi-frame joint decision-making can significantly improve overall performance, with a threshold of 10... -3 Based on this, a performance improvement of about 3dB is also achieved when the combined frame count M=3.

[0086] After synchronization is completed, the received signal after synchronization correction is output, providing a stable signal foundation for subsequent OFDM demodulation, channel decoding and other processes.

[0087] It should be noted that the method in this embodiment can be executed by a single device, such as a computer or server. The method can also be applied in a distributed scenario, where multiple devices cooperate to complete the task. In such a distributed scenario, one of these devices may execute only one or more steps of the method in this embodiment, and the multiple devices will interact with each other to complete the method described.

[0088] It should be noted that the above description describes some embodiments of this application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in a different order than that shown in the above embodiments and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0089] Based on the same inventive concept, and corresponding to any of the above embodiments, this application also provides a time-frequency synchronization device for orthogonal frequency division multiplexing with large frequency offset.

[0090] refer to Figure 10 The time-frequency synchronization device for orthogonal frequency division multiplexing with large frequency offset includes: Transmitter 10 is configured to: remove the standard long training sequence from the initial radio frequency signal to obtain a missing sequence; determine the sequence generation parameters according to the user's input parameters, and generate the same first ZC sequence and second ZC sequence according to the time-frequency sequence generation parameters; wherein the time-frequency first ZC sequence, second ZC sequence and the local sequence of the receiver are the same; deploy the time-frequency first ZC sequence and second ZC sequence into the time-frequency missing sequence according to the preset frame structure to obtain the radio frequency signal to be transmitted to the receiver; determine the theoretical interval by the first position index of the time-frequency first ZC sequence in the time-frequency radio frequency signal and the second position index of the time-frequency second ZC sequence in the time-frequency radio frequency signal, and transmit the radio frequency signal carrying the time-frequency theoretical interval to the receiver; The receiver 20 is configured to: determine a set of candidate frequency offset compensation values ​​based on a preset frequency offset search step size and a large frequency offset tolerance range; perform frequency offset compensation on the local ZC sequence based on the time-frequency candidate frequency offset compensation value set to obtain a local sequence set; construct a time-frequency two-dimensional correlation matrix based on the radio frequency signal transmitted by the transmitter and the time-frequency local sequence set; perform peak detection with dual position constraints on the time-frequency two-dimensional correlation matrix based on the theoretical interval in the time-frequency radio frequency signal and a preset threshold value to obtain candidate effective synchronization points; use a voting method to perform fusion decision on the candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point, and perform frequency offset correction processing on the time-frequency radio frequency signal based on the optimal effective synchronization point to obtain a time-frequency synchronization signal.

[0091] For ease of description, the above devices are described in terms of function, divided into various modules. Of course, in implementing this application, the functions of each module can be implemented in one or more software and / or hardware.

[0092] The apparatus described above is used to implement the time-frequency synchronization method for large frequency offset scenarios of orthogonal frequency division multiplexing in any of the foregoing embodiments, and has the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0093] Based on the same inventive concept, corresponding to the methods of any of the above embodiments, this application also provides an electronic device, 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 time-frequency synchronization method for large frequency offset scenarios of orthogonal frequency division multiplexing as described in any of the above embodiments.

[0094] Figure 11This embodiment illustrates a more specific hardware structure of an electronic device. The device may include a processor 1010, a memory 1020, an input / output interface 1030, a communication interface 1040, and a bus 1050. The processor 1010, memory 1020, input / output interface 1030, and communication interface 1040 are interconnected internally via the bus 1050.

[0095] The processor 1010 can be implemented using a general-purpose CPU (Central Processing Unit), microprocessor, application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this specification.

[0096] The memory 1020 can be implemented in the form of ROM (Read Only Memory), RAM (Random Access Memory), static storage device, dynamic storage device, etc. The memory 1020 can store the operating system and other applications. When the technical solutions provided in the embodiments of this specification are implemented by software or firmware, the relevant program code is stored in the memory 1020 and is called and executed by the processor 1010.

[0097] The input / output interface 1030 is used to connect input / output modules to realize information input and output. Input / output modules can be configured as components within the device (not shown in the figure) or externally connected to the device to provide corresponding functions. Input devices may include keyboards, mice, touchscreens, microphones, various sensors, etc., while output devices may include displays, speakers, vibrators, indicator lights, etc.

[0098] The communication interface 1040 is used to connect a communication module (not shown in the figure) to enable communication between this device and other devices. The communication module can communicate via wired means (such as USB, Ethernet cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.).

[0099] Bus 1050 includes a pathway for transmitting information between various components of the device, such as processor 1010, memory 1020, input / output interface 1030, and communication interface 1040.

[0100] It should be noted that although the above-described device only shows the processor 1010, memory 1020, input / output interface 1030, communication interface 1040, and bus 1050, in specific implementations, the device may also include other components necessary for normal operation. Furthermore, those skilled in the art will understand that the above-described device may only include the components necessary for implementing the embodiments of this specification, and not necessarily all the components shown in the figures.

[0101] The electronic devices described above are used to implement the time-frequency synchronization method for large frequency offset scenarios of orthogonal frequency division multiplexing in any of the foregoing embodiments, and have the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0102] Based on the same inventive concept, corresponding to the methods of any of the above embodiments, this application also provides a non-transitory computer-readable storage medium storing computer instructions, which are used to cause the computer to execute the time-frequency synchronization method in the orthogonal frequency division multiplexing large frequency offset scenario as described in any of the above embodiments.

[0103] The computer-readable medium of this embodiment includes permanent and non-permanent, removable and non-removable media, and information storage can be implemented by any method or technology. Information can be computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transfer medium that can be used to store information accessible by a computing device.

[0104] The computer instructions stored in the storage medium of the above embodiments are used to cause the computer to execute the time-frequency synchronization method in the orthogonal frequency division multiplexing large frequency offset scenario as described in any of the above embodiments, and have the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0105] Based on the same concept, corresponding to the methods of any of the above embodiments, this application also provides a computer program product, including computer program instructions. When the computer program instructions are run on a computer, the computer executes the time-frequency synchronization method in the orthogonal frequency division multiplexing large frequency offset scenario as described in any of the above embodiments, and has the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0106] It is understood that before using the technical solutions of the various embodiments in this application, users will be informed of the type, scope of use, and usage scenarios of the personal information involved in an appropriate manner, and user authorization will be obtained.

[0107] For example, upon receiving a user's active request, a prompt message is sent to the user to explicitly inform them that the requested operation will require the acquisition and use of the user's personal information. This allows the user to independently choose, based on the prompt message, whether to provide personal information to the software or hardware such as electronic devices, applications, servers, or storage media performing the operations described in this application.

[0108] As an optional but not limited implementation, in response to a user's active request, sending a prompt message to the user can be done via a pop-up window, where the prompt message can be presented in text format. Furthermore, the pop-up window can also include a selection control allowing the user to choose "agree" or "disagree" to provide personal information to the electronic device.

[0109] It is understood that the above notification and user authorization process is merely illustrative and does not limit the implementation of this application. Other methods that comply with relevant laws and regulations may also be applied to the implementation of this application.

[0110] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application is limited to these examples; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0111] Additionally, to simplify the description and discussion, and to avoid obscuring the embodiments of this application, the well-known power / ground connections to integrated circuit (IC) chips and other components may or may not be shown in the provided drawings. Furthermore, the apparatus may be shown in block diagram form to avoid obscuring the embodiments of this application, and this also takes into account the fact that the details of the implementation of these block diagram apparatuses are highly dependent on the platform on which the embodiments of this application will be implemented (i.e., these details should be fully understood by those skilled in the art). While specific details (e.g., circuits) have been set forth to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that the embodiments of this application can be implemented without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0112] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory architectures (e.g., dynamic RAM (DRAM)) may be used with the embodiments discussed.

[0113] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the claims of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A time-frequency synchronization method for orthogonal frequency division multiplexing (OFDM) scenarios with large frequency offset, applied at the receiving end, characterized in that... include: The set of candidate frequency offset compensation values ​​is determined based on the preset frequency offset search step size and the large frequency offset tolerance range; The local ZC sequence is frequency offset compensated according to the candidate frequency offset compensation value set to obtain the local sequence set; A two-dimensional time-frequency correlation matrix is ​​constructed based on the radio frequency signal transmitted by the transmitting end and the local sequence set; Based on the theoretical interval and preset threshold value in the radio frequency signal, peak detection with dual position constraints is performed on the time-frequency two-dimensional correlation matrix to obtain candidate effective synchronization points; A voting method is used to fuse and decide on candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point. The radio frequency signals are then subjected to frequency offset correction processing based on the optimal effective synchronization point to obtain a time-frequency synchronization signal.

2. The method according to claim 1, characterized in that, The step of determining the candidate frequency offset compensation value set based on the preset frequency offset search step size and large frequency offset tolerance range includes: The frequency search interval is determined based on the aforementioned large frequency offset tolerance range; In response to the frequency offset search step size satisfying the accuracy division condition, the frequency search interval is divided sequentially according to the frequency offset search step size, starting from the lower boundary frequency of the frequency search interval, and then sequentially marked according to the division order to obtain the candidate frequency offset compensation value set.

3. The method according to claim 1, characterized in that, The step of performing frequency offset compensation on the local ZC sequence based on the candidate frequency offset compensation value set to obtain a local sequence set includes: The frequency offset compensation factor is determined based on the sampling period and the candidate frequency offset compensation value in the candidate frequency offset compensation value set; the frequency offset compensation factor set is also defined. The local ZC sequence is frequency offset compensated according to each frequency offset compensation factor in the set of frequency offset compensation factors to obtain a local sequence set.

4. The method according to claim 1, characterized in that, The step of constructing a two-dimensional time-frequency correlation matrix based on the radio frequency signal transmitted by the transmitting end and the local sequence set includes: Determine the receiving sequence corresponding to the radio frequency signal; Perform a time-domain sliding cross-correlation operation on each local sequence in the local sequence set and the received sequence to obtain the cross-correlation function value corresponding to the candidate frequency offset compensation value; Using the candidate frequency offset compensation value as the row index and the timing sliding offset of the local sequence relative to the received sequence as the column index, the cross-correlation function value is filled into a preset initial correlation matrix as a matrix element to obtain the time-frequency two-dimensional correlation matrix.

5. The method according to claim 4, characterized in that, The step of performing a time-domain sliding cross-correlation operation on each local sequence in the local sequence set and the received sequence to obtain the cross-correlation function value corresponding to the candidate frequency offset compensation value includes: Using the local sequence as a sliding window and a preset maximum search value as a timed sliding constraint, a window sequence corresponding to the sliding window is determined in the received sequence. Perform cross-correlation operation on each window sequence and the local sequence to obtain the cross-correlation function value of the target candidate frequency offset compensation value corresponding to the local sequence.

6. The method according to claim 1, characterized in that, The step of performing peak detection with dual position constraints on the time-frequency two-dimensional correlation matrix based on the theoretical interval and preset threshold value in the radio frequency signal to obtain candidate valid synchronization points includes: The peak position is determined based on the row and column indices of the time-frequency two-dimensional correlation matrix, and the cross-correlation function value corresponding to the peak position is determined. The peak positions where the cross-correlation function value is greater than or equal to the threshold value are determined as valid peak positions; Based on the theoretical interval and the time-frequency two-dimensional correlation matrix, peak detection with dual position constraints is performed on the effective peak position to obtain the candidate effective synchronization point.

7. The method according to claim 6, characterized in that, The step of performing dual-position constraint peak detection on the effective peak positions based on the theoretical interval and the time-frequency two-dimensional correlation matrix to obtain the candidate effective synchronization points includes: The next retrieval position of the effective peak position is determined based on the theoretical interval; The first cross-correlation function value corresponding to the next retrieval position is determined based on the time-frequency two-dimensional correlation matrix. In response to the first cross-correlation function value being greater than the threshold value, the effective peak position is determined as the candidate effective synchronization point.

8. The method according to claim 1, characterized in that, The process of using a voting method to fuse and decide on candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point includes: Determine the candidate cross-correlation function value for each of the candidate valid synchronization points, determine the maximum candidate cross-correlation function value among the candidate cross-correlation function values, and determine the candidate valid synchronization point corresponding to the maximum candidate cross-correlation function value as the valid synchronization point of a single frame radio frequency signal; The optimal effective synchronization point with the most votes is determined from the effective synchronization points of multiple frames of radio frequency signals using a voting method.

9. A time-frequency synchronization method for orthogonal frequency division multiplexing with large frequency offset, applied at the transmitting end, characterized in that... include: Remove the standard long training sequence from the initial radio frequency signal to obtain the missing sequence; The sequence generation parameters are determined based on the user's input parameters, and the same first ZC sequence and second ZC sequence are generated based on the sequence generation parameters; wherein the first ZC sequence, the second ZC sequence and the local sequence of the receiving end are the same; According to the preset frame structure, the first ZC sequence and the second ZC sequence are deployed into the missing sequence to obtain the radio frequency signal to be sent to the receiving end; The theoretical interval is determined by the first position index of the first ZC sequence in the radio frequency signal and the second position index of the second ZC sequence in the radio frequency signal, and the radio frequency signal carrying the theoretical interval is sent to the receiving end.

10. A time-frequency synchronization device for orthogonal frequency division multiplexing with large frequency offset, characterized in that, include: The transmitter is configured to remove the standard long training sequence from the initial radio frequency signal to obtain the missing sequence; The sequence generation parameters are determined based on the user's input parameters, and the same first ZC sequence and second ZC sequence are generated based on the sequence generation parameters; wherein the first ZC sequence, the second ZC sequence and the local sequence of the receiving end are the same; the first ZC sequence and the second ZC sequence are deployed into the missing sequence according to the preset frame structure to obtain the radio frequency signal to be transmitted to the receiving end; the theoretical interval is determined by the first position index of the first ZC sequence in the radio frequency signal and the second position index of the second ZC sequence in the radio frequency signal, and the radio frequency signal carrying the theoretical interval is transmitted to the receiving end; The receiving end is configured to: determine a set of candidate frequency offset compensation values ​​based on a preset frequency offset search step size and a large frequency offset tolerance range; perform frequency offset compensation on the local ZC sequence based on the set of candidate frequency offset compensation values ​​to obtain a local sequence set; construct a time-frequency two-dimensional correlation matrix based on the radio frequency signal transmitted by the transmitting end and the local sequence set; perform peak detection with dual position constraints on the time-frequency two-dimensional correlation matrix based on the theoretical interval in the radio frequency signal and a preset threshold value to obtain candidate effective synchronization points; use a voting method to perform fusion decision on the candidate effective synchronization points of multiple frames of radio frequency signals to obtain the optimal effective synchronization point, and perform frequency offset correction processing on the radio frequency signal based on the optimal effective synchronization point to obtain a time-frequency synchronization signal.

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