A timing synchronization detection method and system under an OFDM system

Abstract

The application discloses a timing synchronization detection method and system in an OFDM system, and relates to the technical field of communication. The technical problem that the performance of synchronization detection is insufficient when the signal-to-noise ratio is low and it is difficult to reduce the influence of frequency offset is solved. The method comprises the following steps: locally storing a received complex sequence; delaying a scrambled short training field to obtain first redundancy information, second redundancy information and third redundancy information, and performing segmentation processing; calculating a timing metric function value Mn1 of a first time domain sampling complex point and a timing metric function value Mn2, and respectively judging whether the timing metric function value Mn1 and the timing metric function value Mn2 pass; calculating a timing metric function value Mn1 of a second time domain sampling complex point to a L-Ls time domain sampling complex point and a timing metric function value Mn2; and updating a first threshold cumulative value CountCn1 and a second threshold cumulative value CountCn2. The application improves the synchronization detection performance under a low signal-to-noise ratio condition, and solves the influence of frequency offset change on the detection performance.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and in particular to a timing synchronization detection method and system in an OFDM system. Background Technology

[0002] OFDM (Orthogonal Frequency-Division Multiplexing) boasts advantages such as high spectral efficiency, resistance to frequency-selective fading, and strong resistance to multipath interference, making it a hot application area in communication technology. Besides conventional applications, it is also used in low-power wireless communication and power line carrier communication, such as the State Grid's dual-mode interconnection high-speed wireless OFDM standard. The high efficiency of OFDM requires strict orthogonality between subcarriers. Once orthogonality is broken, system performance deteriorates rapidly, leading to a significant increase in inter-symbol interference and inter-carrier interference. Synchronization determines the reliability and correctness of data transmission; therefore, synchronization detection is necessary for OFDM.

[0003] Compared to non-data-assisted methods, data-assisted training field synchronization detection algorithms utilize the correlation of training sequences to estimate the timing synchronization of OFDM symbols. They offer advantages such as fast acquisition speed, accurate estimation, and ease of implementation, leading to their widespread use. For example, Figure 1 As shown, the short leading training field is obtained by repeating a complex-valued sample of length S 10 times. The information labeling is relatively simple, so structural optimization is often performed on short training fields. Scrambling is an effective and common method, such as... Figure 2 The image shows the pair. Figure 1 The short training field is scrambled with a pseudo-random bit sequence of 1111-1-1111-1. Then, the cumulative energy value of the received sequence delay autocorrelation is calculated. cumulative energy value of autocorrelation with received sequence The M value is obtained by comparing the values ​​of the two signals, and then the maximum peak synchronization point d is obtained by using threshold decision. However, for the scrambled short training field, the M value only performs well when the signal-to-noise ratio is high. When the signal-to-noise ratio decreases, the performance cannot achieve satisfactory results. At the same time, synchronization is the first step in reception, and it is impossible to calculate and compensate for frequency offset. Although it can improve the judgment performance, it cannot effectively reduce the impact of frequency offset.

[0004] In the process of realizing this invention, the inventors discovered at least the following problems in the prior art:

[0005] Synchronous detection in OFDM systems cannot achieve satisfactory performance when the signal-to-noise ratio decreases, and it is also difficult to reduce the impact of frequency offset, making it difficult to meet the requirements of OFDM systems. Summary of the Invention

[0006] The purpose of this invention is to provide a timing synchronization detection method for OFDM systems, addressing the technical problems in existing OFDM systems where synchronization detection performance fails to meet expectations when the signal-to-noise ratio decreases, and where it is difficult to reduce frequency offset effects, thus failing to meet the requirements of OFDM systems. The various technical effects of the preferred solutions among the many technical solutions provided by this invention are detailed below.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a timing synchronization detection method for an OFDM system, comprising the following steps:

[0009] S100: Receive complex sequences of length L Perform local storage; S200: Based on the received complex sequence The scrambled short training field is delayed by different numbers of short symbols to obtain first redundancy information, second redundancy information, and third redundancy information. Different segmentation processing is then applied to the short symbols of the scrambled short training field and the short symbols of the first, second, and third redundancy information. S300: The received complex sequence under the first, second, and third redundancy information is calculated respectively. S400: Sample the timing metric function values ​​Mn1 and Mn2 at the first time-domain complex point; S500: Determine whether the timing metric function values ​​Mn1 and Mn2 pass based on the first threshold threshold1 and the second threshold threshold2 respectively. If they pass, increment the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 by 1. If they fail, keep the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 unchanged; S600: Calculate the received complex sequence under the first redundancy information, the second redundancy information, and the third redundancy information respectively. From the second complex sampling point in the time domain to the (L-Ls)th complex sampling point, the timing metric function values ​​Mn1 and Mn2 of each complex sampling point in the time domain are determined, where Ls is the length of the scrambled short training field; S600: Based on the first threshold threshold1 and the second threshold threshold2, determine whether the timing metric function values ​​Mn1 and Mn2 of each complex sampling point in the time domain pass, and update the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 in the same way as in step S400, and perform synchronous detection based on the updated first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2.

[0010] Preferably, in step S200, the first redundancy information, the second redundancy information, and the third redundancy information are obtained by delaying the scrambled short training field by 1 short symbol length, 2 short symbol lengths, and 3 short symbol lengths, respectively.

[0011] Preferably, in step S200, when segmenting the first redundant information, the second redundant information, and the third redundant information, the data symbols of each short symbol in the scrambled short training field and the delayed scrambled short training field are consistent.

[0012] Preferably, in step S200, the scrambled pseudo-random bit sequence corresponding to the scrambled short training field is 1111-1-1111-1; in the first redundancy information, the short symbols of bits 2-4, 5, 6, 7, 8-9, and 10 of the scrambled short training field are each taken as a segment, and the short symbols of bits 1-3, 4, 5, 6, 7-8, and 9 of the delayed short training field are each taken as a segment; in the second redundancy information, the scrambled short training field... The 2nd to 3rd, 4th to 5th, 6th to 7th, 8th, and 9th short training symbols are each considered as one segment, and the 1st to 2nd, 3rd to 4th, 5th to 6th, 7th, and 8th short training symbols of the delayed short training field are each considered as one segment; in the third redundant information, the 4th, 5th to 6th, 7th, 8th to 9th, and 10th short training symbols of the scrambled short training field are each considered as one segment, and the 1st, 2nd to 3rd, 4th, 5th to 6th, and 7th short training symbols of the delayed short training field are each considered as one segment.

[0013] Preferably, in step S300, the formula for calculating the timing measurement function value Mn1 is:

[0014]

[0015] ^2,

[0016] in This represents the total energy value of the delayed autocorrelation sequence of the first redundant information. This represents the total energy value of the delayed autocorrelation sequence of the first redundant information. This represents the total energy value of the delayed autocorrelation sequence of the first redundant information, where D takes the value of 1, 2, or 3. Indicates autocorrelation delay, This represents the relevant window length, with a value of 144. When D=1, Dn=16; when D=2, Dn=32; when D=3, Dn=48.

[0017] The formula for calculating the timing measurement function value Mn2 is as follows:

[0018] ,

[0019] in, The method involves first adding the delayed autocorrelation function values ​​Cn1 of the first redundancy information, Cn2 of the second redundancy information, and Cn3 of the third redundancy information together as complex numbers, and then taking the modulus. The method involves first taking the modulus of the time-delayed autocorrelation function values ​​Cn1 (first redundant information), Cn2 (second redundant information), and Cn3 (third redundant information), and then summing them together.

[0020] Preferably, in step S400 or S600, if the timing measurement function value Mn1 is greater than the first threshold threshold1, it is determined to pass; if the timing measurement function value Mn2 is greater than the second threshold threshold2, it is determined to pass.

[0021] Preferably, in step S600, if the first threshold cumulative value CountCn1 meets the exit condition, the synchronization detection is exited, the timed synchronization is successful, and the time-domain sampling complex point position d corresponding to the maximum value of the timed synchronization is returned.

[0022] Preferably, in step S600, if the second threshold cumulative value CountCn2 meets the exit condition, the timing synchronization position corresponding to the maximum value is updated until all time-domain sampling complex points of length L-Ls are calculated, and the time-domain sampling complex point position d' corresponding to the synchronized maximum value is returned.

[0023] Preferably, in step S600, the first threshold value is 0.6, the second threshold value is 60, the exit condition for the first threshold cumulative value CountCn1 is greater than 1, and the exit condition for the second threshold cumulative value CountCn2 is greater than 6.

[0024] A timing synchronization detection system for an OFDM system, used to run any of the timing synchronization detection methods for an OFDM system described above.

[0025] Implementing one of the above-described technical solutions of the present invention has the following advantages or beneficial effects:

[0026] This embodiment increases the amount of delay autocorrelation information by using first, second, and third redundancy information. The three sets of redundancy information are weighted according to their respective characteristics, and threshold decisions are made using timing metric function values ​​Mn1 and Mn2. This improves synchronization detection performance under low signal-to-noise ratio (SNR) conditions and addresses the impact of frequency offset variations on detection performance while maintaining performance gain under low SNR. Simultaneously, the short symbols of the first, second, and third redundancy information are segmented differently. Segmentation reduces the amount of complex calculations, thereby reducing the computational load of the synchronization detection algorithm and significantly shortening the synchronization detection time. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0028] Figure 1 This is a schematic diagram of the structure of existing short leading training fields;

[0029] Figure 2 This is a schematic diagram of the structure of the existing short preamble training field after scrambling;

[0030] Figure 3 This is a flowchart of a timing synchronization detection method in an OFDM system according to an embodiment of the present invention;

[0031] Figure 4 This is a segmented schematic diagram of the first redundancy information, the second redundancy information, and the third redundancy information in a timing synchronization detection method under an OFDM system according to Embodiment 1 of the present invention;

[0032] Figure 5 This is a schematic diagram of the segmentation of the scrambled existing short preamble training field in a timing synchronization detection method under an OFDM system according to Embodiment 1 of the present invention;

[0033] Figure 6 This is a schematic diagram illustrating the calculation process of timing metric function values ​​Mn1 and Mn2 in a timing synchronization detection method under an OFDM system according to Embodiment 1 of the present invention.

[0034] Figure 7 This is a simulation diagram of a timing synchronization detection method in an OFDM system according to Embodiment 1 of the present invention and an existing synchronization detection method under different signal-to-noise ratios.

[0035] Figure 8This is a simulation diagram of a timing synchronization detection method in an OFDM system according to Embodiment 1 of the present invention and a synchronization detection method under different signal-to-noise ratios when affected by different frequency offsets. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, various exemplary embodiments described below will be referenced to the accompanying drawings, which form part of the exemplary embodiments, illustrating various exemplary embodiments that may be used to implement the present invention. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. It should be understood that they are merely examples of processes, methods, and apparatuses consistent with some aspects of the present invention disclosed as detailed in the appended claims, and other embodiments may be used, or structural and functional modifications may be made to the embodiments listed herein without departing from the scope and spirit of the present invention.

[0037] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," etc., indicate the orientation or positional relationship based on the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the referred element must have a specific orientation, or be constructed and operated in a specific orientation. The terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. The term "multiple" means two or more. The terms "connected" and "linked" should be interpreted broadly, for example, they can be fixed connections, detachable connections, integral connections, mechanical connections, electrical connections, communication connections, direct connections, indirect connections through an intermediate medium, and can be the internal connection of two elements or the interaction relationship between two elements. The term "and / or" includes any and all combinations of one or more of the related listed items. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0038] To illustrate the technical solution described in this invention, specific embodiments are described below, showing only the parts related to the embodiments of this invention.

[0039] Example 1:

[0040] like Figure 3 As shown, the present invention provides a timing synchronization detection method in an OFDM system, comprising the following steps: S100: receiving a complex sequence of length L. For local storage, in OFDM systems, signals are typically represented in complex baseband form, i.e., complex numbers composed of in-phase / quadrature components. This representation can fully describe the amplitude and phase information of the signal. This complex number sequence... It is a discrete complex baseband signal obtained after RF down-conversion, low-pass filtering, and ADC sampling, receiving a complex sequence. It is a sampled digital signal containing a scrambled short training field. S200: Based on the received complex sequence. The scrambled short training field is delayed by different numbers of short symbols. The scrambled short training field is obtained by scrambling a pseudo-random bit sequence on a complex sample of length S repeated 10 times, thereby changing the statistical characteristics of the signal. Each short symbol corresponds to 16 complex sampling points in the time domain, and the duration of one short symbol is 16 × 50 ns = 0.8 μs. First redundancy information, second redundancy information, and third redundancy information are obtained. Compared with the scrambled short training field, the first, second, and third redundancy information are delayed by different numbers of short symbols (one short symbol is one delay unit, or a delay of different numbers of 16 complex sampling points in the time domain, or a delay of different numbers of 0.8 μs). The short symbols of the scrambled short training field and the short symbols of the first, second, and third redundancy information are segmented differently. Segmentation reduces the amount of complex calculations, thereby reducing the computational load of the synchronization detection algorithm and significantly reducing the synchronization detection time. S300: Calculate the received complex sequence under the first, second, and third redundancy information respectively. The timing metric function values ​​Mn1 and Mn2 are sampled at the first time domain complex point. These values ​​reflect the degree of deviation between the received signal and the local timing reference signal. S400: Based on the first threshold 1 and the second threshold 2, it is determined whether the timing metric function values ​​Mn1 and Mn2 pass. If they pass, the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 are incremented by 1. If they fail, the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 remain unchanged. S500: The received complex sequence under the first redundancy information, the second redundancy information, and the third redundancy information are calculated respectively. From the second time-domain complex sampling point to the L-Ls-th time-domain complex sampling point, the timing metric function values ​​Mn1 and Mn2 of each time-domain complex sampling point are determined, where Ls is the length of the scrambled short training field, such as 10 short symbols or the length of 160 time-domain complex sampling points. S600: Based on the first threshold threshold1 and the second threshold threshold2, it is determined whether the timing metric function values ​​Mn1 and Mn2 of each time-domain complex sampling point pass, and the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 are updated in the same way as in step S400. Synchronous detection is performed based on the updated first threshold cumulative value CountCn1 and second threshold cumulative value CountCn2. This embodiment increases the amount of delay autocorrelation information by using first, second, and third redundancy information. The three sets of redundancy information are weighted according to their respective characteristics, and threshold decisions are made using timing metric function values ​​Mn1 and Mn2. This improves synchronization detection performance under low signal-to-noise ratio (SNR) conditions and addresses the impact of frequency offset variations on detection performance while maintaining performance gain under low SNR. Simultaneously, the short symbols of the first, second, and third redundancy information are segmented differently. Segmentation reduces the amount of complex calculations, thereby reducing the computational load of the synchronization detection algorithm and significantly shortening the synchronization detection time.

[0041] As an optional implementation method, such as Figure 4 As shown, in step S200, the first, second, and third redundancy information are obtained by delaying the scrambled short training field by 1 short symbol length (i.e., delaying 16 time-domain complex sampling points), 2 short symbol lengths (i.e., delaying 32 time-domain complex sampling points), and 3 short symbol lengths (i.e., delaying 48 time-domain complex sampling points), respectively. When segmenting the first, second, and third redundancy information, the data symbols of each short symbol segment in the scrambled short training field and the delayed scrambled short training field are consistent, that is, short symbol S or short symbol -S each appear in one segment, and short symbol S and short symbol -S will not appear simultaneously in one segment, thereby simplifying the complex number calculation. The scrambled pseudo-random bit sequence corresponding to the scrambled short training field is 1111-1-1111-1, so the short training field is SSSSSSSSSS, and the scrambled short training field is SSSS-S-SSSS-S, as shown. Figure 1 , Figure 2 As shown. Figure 3As shown, in the first redundancy information, the short symbols of the 2nd to 4th, 5th, 6th, 7th, 8th to 9th, and 10th bits of the scrambled short training field are each considered as one segment, and the short symbols of the 1st to 3rd, 4th, 5th, 6th, 7th to 8th, and 9th bits of the delayed short training field are each considered as one segment, for a total of 6 segments; in the second redundancy information, the short symbols of the 2nd to 3rd, 4th to 5th, 6th to 7th, 8th, and 9th bits of the scrambled short training field are each considered as one segment, and the short symbols of the 1st to 2nd, 3rd to 4th, 5th to 6th, 7th, and 8th bits of the delayed short training field are each considered as one segment, for a total of 5 segments; in the third redundancy information, the short symbols of the 4th, 5th to 6th, 7th, 8th to 9th, and 10th bits of the scrambled short training field are each considered as one segment, and the short symbols of the 1st, 2nd to 3rd, 4th, 5th to 6th, and 7th bits of the delayed short training field are each considered as one segment, for a total of 5 segments. In existing delayed autocorrelation methods (Schmidl and Cox synchronization algorithms), assuming a window length N (16... If the data length is L and the autocorrelation is calculated point by point with a 16-point delay, then Cn and Pn need to be calculated for approximately N complex multiplications and complex additions. 2 If L = 800 and N = 144, then approximately 230,400 calculations are required. However, if all relevant values ​​in the first calculation window length N (N > 16) are summed to obtain the relevant value value1, then calculating complex multiplication and complex addition each requires approximately N... For the second instance, starting from the second data point, the autocorrelation value only needs to be added to the autocorrelation value of the new point after the window length, and then subtracted from the autocorrelation value of the first point in the window, such as value2=value1+data(N+1). conj(data(N+17))-data(1) conj(data(17)), ..., up to point L, each operation involves 2 complex multiplications and 2 complex additions, and the data length is L. Therefore, the total computational complexity is: 2 N+L 2. If L=800 and N=144, then the number of calculations for complex multiplication and complex addition is approximately 2. N+L 2 = 1888, thus reducing the computational complexity from a product of window length and data length to a linear increase. Since scrambling disrupts the consistency of symbols in the existing short training field structure, the above-mentioned method for simplifying computation cannot be directly implemented. Therefore... Figure 5After segmentation, the consistency of symbols within each segment can be guaranteed, allowing the simplified implementation method to be used, thus saving computational load. The results of the six segments are then summed to obtain Cn and Pn, and finally Mn is calculated. The window length remains 48+16+16+16+32+16=144. Therefore, although the first, second, and third redundant information in this embodiment are scrambled, by performing different segmentation processing on their respective short symbols, the simplified implementation algorithm described above can still be used. This reduces the computational load of the synchronization detection algorithm while maintaining the same window length, thereby significantly reducing the synchronization detection time.

[0042] As an optional implementation, in step S300, the formula for calculating the timing measurement function value Mn1 is:

[0043]

[0044] ^2,

[0045] in This represents the total energy value of the delayed autocorrelation sequence of the first redundant information. This represents the total energy value of the delayed autocorrelation sequence of the first redundant information. This represents the total energy value of the delayed autocorrelation sequence of the first redundant information, where D takes the value of 1, 2, or 3. Indicates autocorrelation delay, This represents the relevant window length, with a value of 144. When D=1, Dn=16; when D=2, Dn=32; when D=3, Dn=48.

[0046] The formula for calculating the timing measurement function value Mn2 is:

[0047] ,

[0048] like Figure 6 As shown, where, The method involves first summing the time-delayed autocorrelation function values ​​Cn1 (first redundant information), Cn2 (second redundant information), and Cn3 (third redundant information) using complex numbers. Cn1, Cn2, and Cn3 are all complex numbers. The summation is performed using the rules of complex number addition. The real part is the sum of the real parts of the three complex numbers Cn1, Cn2, and Cn3, and the imaginary part is the sum of the imaginary parts of the three complex numbers Cn1, Cn2, and Cn3. Then, the modulus is taken to obtain the positive square root of the sum of the squares of the real and imaginary parts of the summed complex number. The time-delay autocorrelation function values ​​Cn1 (first redundancy information), Cn2 (second redundancy information), and Cn3 (third redundancy information) are first moduloed separately, that is, the modulo of each of the three complex numbers Cn1, Cn2, and Cn3 is calculated individually, and then summed. In other words, the final timing measurement function value Mn2 is obtained by summing the moduli of the three complex numbers Cn1, Cn2, and Cn3. , The weighted summation.

[0049] As an optional implementation, in step S400 or S600, if the timing metric function value Mn1 is greater than the first threshold threshold1, it is judged as passing, that is, if the timing metric function value Mn1 is greater than the first threshold threshold1, the scrambled short training field is detected and the synchronization detection is successful; if the timing metric function value Mn2 is greater than the second threshold threshold2, it is judged as passing, that is, if the timing metric function value Mn2 is greater than the second threshold threshold2, the scrambled short training field is detected and the synchronization detection is successful.

[0050] As an optional implementation, in step S600, if the first threshold cumulative value CountCn1 meets the exit condition, the synchronization detection exits, the timing synchronization is successful, and the time-domain sampling complex point position d corresponding to the maximum value of the timing synchronization is returned. That is, when the first threshold cumulative value CountCn1 is not unique in terms of the value greater than the threshold, the largest value among all values ​​greater than the threshold is updated by comparison to obtain the OFDM symbol starting sampling point index. This is mainly applicable to high signal-to-noise ratio situations, where the signal is clear, noise is negligible, and the detection difficulty is low. Therefore, the exit condition for the first threshold cumulative value CountCn1 is greater than 1, that is, the synchronization detection can be judged to be successful when the timing metric function value Mn1 is greater than the first threshold threshold1 for the first time it is detected.

[0051] As an optional implementation, in step S600, if the second threshold cumulative value CountCn2 meets the exit condition, the timing synchronization position corresponding to the maximum value is updated until all time-domain sampling complex points of length L-Ls are calculated, and the time-domain sampling complex point position d corresponding to the maximum value of synchronization is returned. That is, by comparing and updating, the largest time-domain sampling complex point among all values ​​where the second threshold cumulative value CountCn2 is greater than the threshold is obtained, so as to obtain the OFDM symbol starting sampling point index. This is mainly applicable to the case of low signal-to-noise ratio, where the signal is severely submerged by noise and the detection is difficult. Therefore, it is necessary to calculate all time-domain sampling complex points of length L-Ls and then select the timing synchronization position corresponding to the maximum value to complete the synchronization detection.

[0052] As an optional implementation, in step S600, the first threshold is 0.6 and the second threshold is 60; the exit condition for the first threshold cumulative value CountCn1 is greater than 1, and the exit condition for the second threshold cumulative value CountCn2 is greater than 6. In this embodiment, the exit condition for the second threshold cumulative value CountCn2 is obtained based on simulation analysis, which facilitates the rapid acquisition of the timing synchronization position under low signal-to-noise ratio.

[0053] In an AWGN (Additive White Gaussian Noise Channel) channel, a simulation was performed using a sequence of 500 noise points, 240 signal points, and 300 noise points (all points are complex time-domain samples). The first 160 points of the 240 signal points constituted a short training field, and the last 80 points formed a long training sequence (following the short training field, primarily used for accurate channel estimation and fine frequency offset estimation). The noise ranged from -10 dB to 0 dB, and the white Gaussian noise was generated at a signal-to-noise ratio (SNR) of 10 dB. The simulation was run 5000 times, and the step-out rate at different SNRs was statistically analyzed. The results are as follows: Figure 7 As shown. Existing synchronization detection methods: autocorrelation delay D is 16 points, correlation window length is 144 points; the detection method in this embodiment: autocorrelation delay D is 16, 32, or 48 points, correlation window length N is 144, 128, or 112 points, threshold1 is 0.6, threshold2 is 60, the exit condition for CountCn1 is greater than 1, and the exit condition for CountCn2 is greater than 6. The sampling rate of the OFDM system is set to 54000Hz, and the length of the time-domain sample points processed by the Fast Fourier Transform (FFT) is 32 points, resulting in a subcarrier spacing of fscs = 54000 / 32 = 1688Hz. Subcarrier spacings with different frequency offsets are set, received data is generated, and the performance impact of different frequency offsets on this optimized scheme is simulated. The simulation is performed 5000 times, and the results are as follows. Figure 8 As shown. By Figure 7 The results show that when the step loss rate is less than 1%, the method in this embodiment improves the signal-to-noise ratio (SNR) by 1.8 dB compared to existing methods; Figure 8 The results show that when the step-out rate is less than 1%, the frequency offset of different multiples of carrier spacing has little impact on the improved method, and the signal-to-noise ratio (SNR) still improves by 1 to 1.8 dB. Furthermore, a digital signal processing (DSP) was used to implement this embodiment and the existing method. According to tests, the method in this embodiment reduces the computational load by 60% compared to the existing method.

[0054] The embodiment is merely a specific example and does not indicate that this is the only way to implement the present invention.

[0055] Example 2:

[0056] A timing synchronization detection system under an OFDM system is disclosed, used to run the timing synchronization detection method under an OFDM system described in Embodiment 1. This embodiment increases the amount of delay autocorrelation information by using first, second, and third redundant information, and performs weighted calculations on the three sets of redundant information according to their respective characteristics. Timing metric function values ​​Mn1 and Mn2 are used for threshold decision, improving synchronization detection performance under low signal-to-noise ratio (SNR) conditions. While maintaining performance gain under low SNR, the impact of frequency offset variations on detection performance is addressed. Simultaneously, the short symbols of the first, second, and third redundant information are processed in different segments. Segmentation reduces the amount of complex calculations, thereby reducing the computational load of the synchronization detection algorithm and significantly reducing the synchronization detection time.

[0057] The above description is merely a preferred embodiment of the present invention. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A timing synchronization detection method in an OFDM system, characterized in that, Includes the following steps: S100: Receive complex sequences of length L Perform local storage; S200: Based on received complex sequence Different numbers of short symbols are delayed on the scrambled short training field to obtain the first redundancy information, the second redundancy information, and the third redundancy information. Different segmentation processing is then performed on the short symbols of the scrambled short training field and the short symbols of the first redundancy information, the second redundancy information, and the third redundancy information. S300: Calculate the received complex sequence under the first redundancy information, the second redundancy information, and the third redundancy information respectively. The timing metric function values ​​Mn1 and Mn2 are sampled at the first complex point in the time domain. S400: Based on the first threshold threshold1 and the second threshold threshold2, determine whether the timing measurement function value Mn1 and the timing measurement function value Mn2 pass. If they pass, the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 are incremented by 1 respectively. If they fail, the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 remain unchanged. S5 00: Calculate the received complex sequences under the first redundancy information, the second redundancy information, and the third redundancy information respectively. The timing metric function values ​​Mn1 and Mn2 for each time-domain sampling complex point from the second time-domain sampling complex point to the L-Ls time-domain sampling complex point, where Ls is the length of the scrambled short training field; S600: Based on the first threshold threshold1 and the second threshold threshold2, determine whether the timing metric function value Mn1 and timing metric function value Mn2 of each time-domain sampling complex point pass, and update the first threshold cumulative value CountCn1 and the second threshold cumulative value CountCn2 in the same way as step S400. Perform synchronization detection based on the updated first threshold cumulative value CountCn1 and second threshold cumulative value CountCn2.

2. The timing synchronization detection method in an OFDM system according to claim 1, characterized in that, In step S200, the first redundancy information, the second redundancy information, and the third redundancy information are obtained by delaying the scrambled short training field by 1 short symbol length, 2 short symbol lengths, and 3 short symbol lengths, respectively.

3. The timing synchronization detection method in an OFDM system according to claim 2, characterized in that, In step S200, when segmenting the first redundant information, the second redundant information, and the third redundant information, the data symbols of each short symbol in the scrambled short training field and the delayed scrambled short training field are consistent.

4. The timing synchronization detection method in an OFDM system according to claim 3, characterized in that, In step S200, the scrambled pseudo-random bit sequence corresponding to the scrambled short training field is 1111-1-1111-1; in the first redundancy information, the short symbols of bits 2-4, 5, 6, 7, 8-9, and 10 of the scrambled short training field are each taken as a segment, and the short symbols of bits 1-3, 4, 5, 6, 7-8, and 9 of the delayed short training field are each taken as a segment; in the second redundancy information, the scrambled short training field 2... The short training symbols of bits 3, 4-5, 6-7, 8, and 9 are each considered as one segment, and the short training symbols of bits 1-2, 3-4, 5-6, 7, and 8 of the delayed short training field are each considered as one segment; in the third redundancy information, the short training symbols of bits 4, 5-6, 7, 8-9, and 10 of the scrambled short training field are each considered as one segment, and the short training symbols of bits 1, 2-3, 4, 5-6, and 7 of the delayed short training field are each considered as one segment.

5. The timing synchronization detection method in an OFDM system according to claim 1, characterized in that, In step S300, the formula for calculating the timing measurement function value Mn1 is as follows: ^2， in This represents the total energy value of the delayed autocorrelation sequence of the first redundant information. This represents the total energy value of the delayed autocorrelation sequence of the second redundant information. The value of D represents the total energy of the delayed autocorrelation sequence of the third redundant information, where D takes the value of 1, 2, or 3. Indicates autocorrelation delay, This represents the relevant window length, with a value of 144. When D=1, Dn=16; when D=2, Dn=32; when D=3, Dn=48. The formula for calculating the timing measurement function value Mn2 is as follows: ， in, The method involves first adding the delayed autocorrelation function values ​​Cn1 of the first redundancy information, Cn2 of the second redundancy information, and Cn3 of the third redundancy information together as complex numbers, and then taking the modulus. The method involves first taking the modulus of the time-delayed autocorrelation function values ​​Cn1 (first redundant information), Cn2 (second redundant information), and Cn3 (third redundant information), and then summing them together.

6. The timing synchronization detection method in an OFDM system according to claim 1, characterized in that, In step S400 or S600, if the timing measurement function value Mn1 is greater than the first threshold threshold1, it is determined to pass; if the timing measurement function value Mn2 is greater than the second threshold threshold2, it is determined to pass.

7. The timing synchronization detection method in an OFDM system according to claim 1, characterized in that, In step S600, if the first threshold cumulative value CountCn1 meets the exit condition, the synchronization detection is exited, the time synchronization is successful, and the time domain sampling complex point position d corresponding to the maximum value of the time synchronization is returned.

8. The timing synchronization detection method in an OFDM system according to claim 1, characterized in that, In step S600, if the second threshold cumulative value CountCn2 meets the exit condition, the timing synchronization position corresponding to the maximum value is updated until all time-domain sampling complex points of length L-Ls are calculated, and the time-domain sampling complex point position d' corresponding to the synchronized maximum value is returned.

9. The timing synchronization detection method in an OFDM system according to claim 1, characterized in that, In step S600, the first threshold threshold1 is 0.6, and the second threshold threshold2 is 60; the exit condition for the first threshold cumulative value CountCn1 is greater than 1, and the exit condition for the second threshold cumulative value CountCn2 is greater than 6.

10. A timing synchronization detection system under an OFDM system, characterized in that, This method is used to run a timed synchronization detection method under an OFDM system according to any one of claims 1-9.

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