Fast synchronization and frequency offset estimation method for burst signals of physical layer of ad hoc network

Abstract

The invention relates to a fast synchronization and frequency offset estimation method for a burst signal of a physical layer of an ad hoc network, a sending end sends a wireless signal, the wireless signal is generated by adopting a synchronization sequence, and the synchronization sequence comprises a synchronization segment and a control segment; a receiving end receives and analyzes the wireless signal to obtain an IQ sequence and preprocesses the IQ sequence; extracting the local synchronization sequence to obtain a local extraction sequence; performing cross-correlation operation on the preprocessed sequence and a local extraction sequence to obtain a cross-correlation sequence; obtaining a cross-correlation power sequence according to the cross-correlation sequence; segmenting the cross-correlation power sequence, calculating the peak-to-average ratio of each segment of the cross-correlation power sequence, and obtaining a coarse synchronization index position according to the peak-to-average ratio; and generating a plurality of fine synchronization matching sequences based on the coarse synchronization index position and the IQ sequence, performing correlation operation on each fine synchronization matching sequence and a local synchronization sequence to obtain a second correlation sequence, determining a fine synchronization index position based on an average power value of the second correlation sequence, and further obtaining a synchronization symbol and a control symbol.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless frame synchronization and frequency offset estimation, and particularly to a method for fast synchronization and frequency offset estimation of burst signals in the physical layer of an ad hoc network. Background Art

[0002] Wireless frame synchronization and frequency offset estimation are the first steps in wireless signal frame reception, and the quality of their performance directly affects the correct rate of reception and decoding. It is also a topic that the communication industry has been researching. Currently, traditional synchronization methods include:

[0003] 1. Timing synchronization and frequency offset estimation method based on cyclic prefix.

[0004] The disadvantage is that the multipath effect causes multiple delayed path signals to be superimposed, and these path-related peaks interfere with each other, resulting in deviation in the synchronization position estimation.

[0005] 2. Sch-Cox timing synchronization method.

[0006] This method has a simple principle and is easy to implement, but there is a relatively wide flat peak on the decision curve, which is not conducive to the determination of sampling points. In order to obtain good decision performance, the cyclic prefix length has to be reduced, but it will affect the inter-symbol anti-interference performance.

[0007] 3. Minn timing synchronization method.

[0008] In the case of good signal-to-noise ratio, due to the existence of negative values in the Minn synchronization sequence, a spike may appear at the sampling point, but there will be side lobes on both sides of the ideal sampling point, and there will be two synchronization-related peaks when the OFDM symbol length is 4 times the cyclic prefix. In the case of low signal-to-noise ratio, missed detection and misdetection are likely to occur.

[0009] 4. Park timing synchronization method.

[0010] Due to the existence of symmetric training symbols and conjugate training symbols in this training sequence, the decision curve at the ideal sampling point will have a sharper peak. The disadvantage is that there are two relatively large side lobes, and there will be two peaks when the OFDM symbol length is 2 times the cyclic prefix length. When the signal-to-noise ratio is low, missed detection and misdetection are likely to occur.

[0011] 5. Blind estimation method without data assistance

[0012] Estimation is carried out by using the special structure of the signal or by analyzing the frequency-domain signal of the received signal. The advantage of blind estimation is high spectrum utilization rate and no need for additional pilot symbol overhead. The disadvantage is that it is greatly affected by multipath interference. In order to obtain high-precision estimation, dozens or even hundreds of OFDM symbol blocks need to be accumulated, and the capture time is long.

[0013] 6. Adopt the method of joint estimation of synchronization and frequency offset

[0014] For two consecutive symbols within the search window, the sampling points of the CP of the first OFDM symbol are conjugated and multiplied with the sampling points that are N sampling points away from the tail of this symbol, and then the average value 1 is obtained. The sampling points of the CP of the second OFDM symbol are conjugated and multiplied with the sampling points that are N sampling points away from it in the previous OFDM symbol, and then the average value 2 is obtained. The average value 1 and the average value 2 are added to obtain the average value 3. For M OFDM symbols in the window, calculate the average value 3 between adjacent two symbols according to the above steps in turn. By sliding the window to calculate the maximum value position, the synchronization position of the OFDM symbol is obtained, and then the frequency offset is calculated. This method requires accumulating a large number of OFDM symbols to accurately capture synchronization. Summary of the Invention

[0015] In view of the above analysis, embodiments of the present invention aim to provide a method for fast synchronization and frequency offset estimation of ad hoc network physical layer burst signals, so as to solve the problems that existing classical synchronization methods for signals with low signal-to-noise ratio are prone to misjudgment and a large number of OFDM symbols need to be accumulated to accurately capture the synchronization position.

[0016] On the one hand, embodiments of the present invention provide a method for fast synchronization of ad hoc network physical layer burst signals. The sending end sends a wireless signal, and the wireless signal is generated using a synchronization sequence, and the synchronization sequence includes: a synchronization segment and a control segment;

[0017] The receiving end receives the wireless signal and parses it to obtain an IQ sequence, and performs preprocessing to obtain a preprocessed sequence; extracts the local synchronization sequence to obtain a local extraction sequence; performs a cross-correlation operation on the preprocessed sequence and the local extraction sequence to obtain a cross-correlation sequence; obtains a cross-correlation power sequence according to the cross-correlation sequence; segments the cross-correlation power sequence, calculates the peak-to-average ratio of each segment of the cross-correlation power sequence, and obtains the rough synchronization index position according to the peak-to-average ratio; generates a plurality of fine synchronization matching sequences based on the rough synchronization index position and the IQ sequence, performs a correlation operation on each fine synchronization matching sequence and the local synchronization sequence to obtain a corresponding second correlation sequence, and determines the fine synchronization index position based on the average power value of the second correlation sequence, and then obtains the synchronization symbol and the control symbol.

[0018] Further, the generating a plurality of fine synchronization matching sequences based on the rough synchronization index position and the IQ sequence includes:

[0019] Taking the points within a set interval range before and after the rough synchronization index position as the starting points, sliding windows on the received IQ sequence to generate a plurality of fine synchronization matching sequences.

[0020] Further, the determining the fine synchronization index position based on the average power value of the second correlation sequence includes:

[0021] Calculate the average power value of each second correlation sequence, and use the position of the first point of the fine synchronization matching sequence corresponding to the second correlation sequence with the largest average power value as the fine synchronization index position.

[0022] Further, the preprocessing of the received IQ sequence includes in turn: AGC processing, decimation, and polyphase filtering; divide the IQ sequence after AGC processing into groups of k data starting from the beginning, extract the data at the first position in each group, and then average the data in each group and superimpose it on the data extracted from the current group to obtain the sequence after polyphase filtering, where the range of k is [6, 10].

[0023] Further, the preprocessing further includes: quantizing the sequence after polyphase filtering to 16 bits, comparing the quantized data to obtain the maximum peak value of the quantized data. If the maximum peak value is greater than Use the ratio of the maximum peak value to as the scaling factor, and divide each number in the sequence after polyphase filtering by the scaling factor to obtain the data after clipping processing; if the maximum peak value is less than or equal to Do not perform clipping processing.

[0024] Further, segment the cross-correlation power sequence, calculate the peak-to-average ratio of each segment of the cross-correlation power sequence, and obtain the coarse synchronization index position according to the peak-to-average ratio, including: divide the cross-correlation power sequence into segments of M data each, first search for the peak points of the data within each segment, perform peak suppression filtering by removing m data before and after the peak points within each segment, accumulate and average the M / 2 data before and after each peak point in the filtered cross-correlation power sequence to obtain the average value of the M data before and after each peak point, divide each peak point by the average value of its corresponding M data before and after to obtain the peak-to-average ratio of each segment, compare multiple peak-to-average ratios to obtain the maximum peak-to-average ratio, and the position of the peak point corresponding to the maximum peak-to-average ratio is the coarse synchronization index position, where the range of m is [3, 6], and the range of M / 2 is [28, 36].

[0025] Further, the synchronization sequence generated by the transmitter is a low peak-to-average ratio sequence, which is generated using the following calculation formula:

[0026]

[0027] where: u is the root index number, n is the sequence index number, and the value range of n is from 0 to 61;

[0028] Load the du(n) sequence onto the subcarriers, perform inverse Fourier transform on the subcarriers and add a cyclic prefix CP to obtain a synchronization sequence for transmission.

[0029] On the other hand, an embodiment of the present invention provides a frequency offset estimation method based on the fast synchronization method. After obtaining the synchronization symbol, intercept the cyclic prefix CP of the synchronization symbol, remove the first and last 5 points of the CP to obtain the anti-aliased cyclic prefix, perform a correlation operation on the anti-aliased cyclic prefix and the corresponding sampling points at the tail within the present synchronization symbol to obtain the CP correlation sequence, take the mean value of each point in the CP correlation sequence to obtain the mean value of the CP correlation sequence, and calculate the phase difference of the synchronization symbol according to the I and Q components of the mean value;

[0030] Use the same method as the method for obtaining the phase difference of the synchronization symbol to obtain the phase difference of the control symbol;

[0031] Based on the phase difference of the synchronization symbol and the phase difference of the control symbol, obtain the frequency offset of the synchronization symbol and the frequency offset of the control symbol respectively.

[0032] Furthermore, calculate the respective corresponding frequency offsets according to the sampling frequency when the receiving end receives the IQ sequence and the phase difference of the synchronization symbol or the control symbol. The formula is:

[0033]

[0034] where F S is the sampling frequency when the receiving end receives the IQ sequence, is the phase difference of the synchronization symbol or the control symbol, and N is the number of points of the inverse Fourier transform.

[0035] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0036] 1. For the fast synchronization method of the self-organizing network physical layer burst signal of the present invention, when the receiving end receives the IQ sequence, preprocess it to obtain the preprocessed sequence; extract the local synchronization sequence to obtain the local extracted sequence; perform a cross-correlation operation on the preprocessed sequence and the local extracted sequence to obtain the cross-correlation sequence; obtain the cross-correlation power sequence according to the cross-correlation sequence; segment the cross-correlation power sequence, calculate the peak-to-average ratio of each segment of the cross-correlation power sequence, and obtain the rough synchronization index position according to the peak-to-average ratio; generate multiple fine synchronization matching sequences based on the rough synchronization index position and the IQ sequence, perform a correlation operation on each fine synchronization matching sequence and the local synchronization sequence to obtain the corresponding second correlation sequence, and determine the fine synchronization index position based on the average power value of the second correlation sequence, thereby obtaining the synchronization symbol and the control symbol. By adopting the two-stage synchronization algorithm of rough synchronization and fine synchronization based on the pseudo-random sequence, the fast synchronization of the burst radio frame can be completed within one OFDM symbol period.

[0037] 2. In a fast synchronization method for burst signals in the physical layer of an ad hoc network according to the present invention, during the process of obtaining the coarse synchronization index position, every M data in the cross-correlation power sequence are divided into a segment. First, the peak point of the data is searched within each segment. Then, m data before and after the peak point are removed within each segment for peak suppression filtering. After the peak suppression filtering is performed on the cross-correlation power sequence, the mean value of M data before and after each peak point is obtained by accumulating and averaging M / 2 data before and after each peak point in each segment, that is, the influence of the peak point on the average value of the cross-correlation power of each segment is excluded during the calculation of the peak-to-average ratio of each segment of the cross-correlation power sequence, which can more accurately reflect the background energy of the signal and measure the peak characteristics of the signal, and better adapt to the influence of multipath, asymmetry, and uneven energy distribution of different types of signals. This process adopts segmented calculation, which can reduce the computing pressure and storage pressure of the processor. The segmented calculation can analyze the signal changes more precisely, improve the synchronization accuracy in a multipath channel or an environment with high noise, and suppress noise and interference through segmented calculation, thereby improving the robustness of this synchronization method.

[0038] 3. In a fast synchronization method for burst signals in the physical layer of an ad hoc network according to the present invention, the preprocessing sequentially includes: AGC processing, decimation, polyphase filtering, and clipping processing; after decimation, the coarse synchronization index position can be quickly found. Polyphase filtering makes up for the signal defect caused by decimation. Clipping processing can prevent the result of the cross-correlation operation between the preprocessed sequence and the local decimated sequence from overflowing, and prevent misjudgment or missing judgment of the coarse synchronization index position caused by the overflow.

[0039] 4. For the frequency offset estimation method based on the fast synchronization method for burst signals in the physical layer of an ad hoc network according to the present invention, after obtaining the synchronization symbol, the cyclic prefix CP of the synchronization symbol is intercepted, and the first and last 5 points of the CP are removed to obtain the de-aliased cyclic prefix. The de-aliased cyclic prefix is correlated with the corresponding sampling points at the tail within the same synchronization symbol to obtain the CP correlation sequence. The mean value of each point in the CP correlation sequence is obtained to get the mean value of the CP correlation sequence. The phase difference of the synchronization symbol is calculated according to the I and Q components of the mean value; the phase difference of the control symbol is obtained by using the same method as the method for obtaining the phase difference of the synchronization symbol; the frequency offset of the synchronization symbol and the frequency offset of the control symbol are respectively obtained based on the phase difference of the synchronization symbol and the phase difference of the control symbol. The frequency offset estimation of the wireless frame is completed within two OFDM symbol periods.

[0040] In the present invention, the above technical solutions can also be combined with each other to realize more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification or understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained from the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference signs denote the same components.

[0042] Figure 1 Flowchart of the method for obtaining synchronization symbols and control symbols of a fast synchronization method for self-organizing network physical layer burst signals according to the present invention;

[0043] Figure 2 IQ complex plane diagram of the ZC sequence of a fast synchronization method for self-organizing network physical layer burst signals according to the present invention;

[0044] Figure 3 Schematic diagram of the synchronization signal resource allocation of a fast synchronization method for self-organizing network physical layer burst signals according to the present invention;

[0045] Figure 4 Absolute value diagram of the correlation operation result between the fine synchronization matching sequence and the local synchronization sequence of a fast synchronization method for self-organizing network physical layer burst signals according to the present invention;

[0046] Figure 5 Graph of the power result obtained by the correlation operation between the fine synchronization matching sequence and the local synchronization sequence of a fast synchronization method for self-organizing network physical layer burst signals according to the present invention. Detailed implementation manners

[0047] The following will specifically describe the preferred embodiments of the present invention in conjunction with the accompanying drawings, in which the accompanying drawings form a part of this application and are used together with the embodiments of the present invention to explain the principle of the present invention, and are not used to limit the scope of the present invention.

[0048] A specific embodiment of the present invention discloses a fast synchronization method for self-organizing network physical layer burst signals, as Figure 1 shown, specifically including steps S1 - S4.

[0049] Step S1: The transmitting end sends a wireless signal, and the wireless signal is generated by using a synchronization sequence, and the synchronization sequence includes: a synchronization segment and a control segment.

[0050] The synchronization segment uses 1 OFDM symbol, and the control segment uses at least 1 OFDM symbol.

[0051] The synchronization sequence generated by the transmitting end is a low peak-to-average power ratio sequence, and is generated by using the following calculation formula:

[0052]

[0053] where: u is the root index number, n is the sequence index number, and the value range of n is from 0 to 61;

[0054] Load the du(n) sequence onto the subcarriers, perform inverse Fourier transform on the subcarriers and add a cyclic prefix CP to obtain a synchronization sequence for transmission.

[0055] The IQ complex plane diagram of the ZC sequence is as Figure 2 shown.

[0056] Specifically, the synchronization sequence uses a ZC complex sequence. The ZC complex sequence is a kind of Euler complex sequence, which is a sequence composed of points on the unit circle in the complex plane, and each point corresponds to a pair of (I, Q) values. This sequence has good autocorrelation and has a constant envelope. The advantages are low peak-to-average ratio (both the time domain and frequency domain of the ZC sequence are ZC sequences and the amplitude is constant), which is beneficial for the radio frequency power amplifier signal to exert the maximum efficiency.

[0057] In formula (1), u is the root index number. In this embodiment, numbers that are relatively prime to 63 in the range of 1 - 62 are taken, and 63 is the sequence length. n is the sequence index number, and its value range is from 0 to 61, corresponding to 62 subcarriers. This sequence helps the terminal determine the starting position of the OFDM symbol and helps the terminal determine the carrier frequency offset. And by detecting the PSS sequence, the PSS index is determined, that is, a part of the information of the physical layer cell identifier is determined.

[0058] The synchronization of the system has a total of 72 subcarriers, referring to the ZC sequence of PSS in LTE. This ZC sequence is composed of 62 symbols (the amplitude is constantly 1 and the phase satisfies a specific functional relationship), and 5 subcarriers are left on each side as protection. The schematic diagram of the synchronization signal resource allocation is as Figure 3 shown.

[0059] Step S2: The receiving end receives the wireless signal and parses it to obtain an IQ sequence, and performs preprocessing to obtain a preprocessed sequence; the local synchronization sequence is extracted to obtain a local extraction sequence.

[0060] Specifically, the radio frequency wireless signal received by the receiving end passes through a zero-IF transceiver, and the radio frequency signal is converted into a baseband signal, which then becomes IQ component data, that is, an IQ sequence.

[0061] The preprocessing of the received IQ sequence includes in turn: AGC processing, extraction, and polyphase filtering; the IQ sequence after AGC processing is divided into groups of every k data starting from the beginning, the data at the first position in each group is extracted, and then the data in each group is averaged and superimposed on the data extracted from the current group to obtain a polyphase-filtered sequence, where the range of k is in [6, 10].

[0062] Specifically, at the receiving end, in order to reduce the complexity of synchronization signal detection, first, the IQ sequence is filtered and downsampled by 8 times (8-fold extraction). The passband of the filter is 2 MHz bandwidth.

[0063] Quantize the sequence after polyphase filtering to 16 bits, compare the quantized data, and obtain the maximum peak value of the quantized data. If the maximum peak value is greater than Take the ratio of the maximum peak value to as the scaling factor, and divide each number in the sequence after polyphase filtering by the scaling factor to obtain the data after amplitude limiting processing; if the maximum peak value is less than or equal to No amplitude limiting processing is performed.

[0064] Specifically, amplitude limiting processing can prevent the result of the cross-correlation operation between the preprocessed sequence and the local decimated sequence from overflowing, and prevent misjudgment or missed judgment of the coarse synchronization index position caused by overflow.

[0065] The decimation multiple of the local synchronization sequence to obtain the local decimated sequence is the same as the decimation multiple in the preprocessing of the received IQ sequence.

[0066] Step S3: Perform a cross-correlation operation on the preprocessed sequence and the local decimated sequence to obtain a cross-correlation sequence; obtain a cross-correlation power sequence according to the cross-correlation sequence. Segment the cross-correlation power sequence, calculate the peak-to-average ratio of each segment of the cross-correlation power sequence, and obtain the coarse synchronization index position according to the peak-to-average ratio.

[0067] Specifically, perform a cross-correlation calculation on the decimated received IQ sequence and the local decimated sequence to obtain a cross-correlation sequence, then calculate the cross-correlation power value of each data in the cross-correlation sequence to obtain a cross-correlation power sequence. The calculation formula of the cross-correlation power sequence is:

[0068]

[0069] where, R xy (k) is the result of the cross-correlation calculation of the decimated received IQ sequence and the local decimated sequence, and P xy (k) is the k-th item of the cross-correlation power sequence.

[0070] Segment the cross-correlation power sequence, calculate the peak-to-average ratio of each segment of the cross-correlation power sequence, and obtain the coarse synchronization index position, including: divide every M data in the cross-correlation power sequence into one segment. First, search for the data peak point within each segment. Remove m data before and after the peak point within each segment for peak suppression filtering. In the filtered cross-correlation power sequence, accumulate M / 2 data before and after each peak point in each segment and take the average to obtain the average of M data before and after each peak point in each segment. Divide the peak point of each segment by the average of its corresponding M data before and after to obtain the peak-to-average ratio of each segment. Compare multiple peak-to-average ratios to obtain the maximum peak-to-average ratio. The position of the peak point corresponding to the maximum peak-to-average ratio is the coarse synchronization index position, where the range of m is [3, 6], and the range of M / 2 is [28, 36].

[0071] In a specific embodiment of the present invention, the cross-correlation power sequence is divided into segments of 64 points each (AGC is adjusted every 512 points, and after 8-fold sampling, it is 64 points per segment). For each segment, the peak point of the cross-correlation power and the index position corresponding to the peak point are searched. With the peak point of each segment as the center, a peak-to-average ratio window is set (first, m data before and after the peak point in each segment are removed for peak suppression filtering to exclude the influence of the peak point on the average value of the cross-correlation power of each segment), and the average power of the cross-correlation power in the peak-to-average ratio window (including the front and back windows of the peak point) is calculated. According to the average power of the cross-correlation power of each segment, the peak-to-average ratio of each segment is calculated.

[0072] Calculating the cross-correlation power and the peak-to-average ratio of each segment of the cross-correlation power realizes peak detection and noise suppression of the signal. Segment processing and taking the average within the window improve the efficiency and accuracy of the algorithm.

[0073] Step S4: Based on the coarse synchronization index position and the IQ sequence, generate multiple fine synchronization matching sequences. Perform correlation operations on each fine synchronization matching sequence and the local synchronization sequence to obtain the corresponding second correlation sequences. Determine the fine synchronization index position based on the average power values of the second correlation sequences, and then obtain the synchronization symbol and the control symbol.

[0074] The specific process is as Figure 1 shown.

[0075] Taking the points within the set interval range before and after the coarse synchronization index position as the starting points, slide the window of the received IQ sequence to generate multiple fine synchronization matching sequences.

[0076] Specifically, find the point corresponding to the coarse synchronization index position in the received IQ sequence (that is, the coarse synchronization index position in the decimated sequence needs to be restored to the non-decimated IQ sequence), perform local search near this point, and obtain the correlation operation results of each fine synchronization matching sequence and the local synchronization sequence. The absolute value graph of the correlation operation results is as Figure 4 shown.

[0077] The set interval range is from 2k points before the coarse synchronization index position to 2k points after the coarse synchronization index position, where k is the decimation multiple in the preprocessing of the received IQ sequence; the window size is 512; that is, the length of the fine synchronization matching sequence obtained by sliding the window of the IQ sequence is 512.

[0078] When performing the correlation operation between the fine synchronization matching sequence and the local synchronization sequence, intercept the first 512 points of the local synchronization sequence as a template, and calculate the correlation between this template and each fine synchronization matching sequence to obtain the second correlation sequence.

[0079] In a specific embodiment of the present invention, the set interval range is to find the point corresponding to the coarse synchronization index position in the received IQ sequence, search 16 points forward and backward respectively (8-fold decimation), and sequentially use the 33 points including the point corresponding to the coarse synchronization index position as the starting point of the fine synchronization matching sequence. A fine synchronization matching sequence is intercepted from the IQ sequence in sequence with the above starting points, and the length of the fine synchronization matching sequence is 512 points. The power result diagram obtained by relevant operations is as Figure 5 shown.

[0080] Calculate the average power value of each second correlation sequence, and use the position of the first point of the fine synchronization matching sequence corresponding to the second correlation sequence with the largest average power value as the fine synchronization index position.

[0081] Specifically, in the received IQ sequence, intercept 1 OFDM symbol length backward from the fine synchronization index position to obtain a synchronization symbol, and intercept 1 OFDM symbol length starting from the next point after the end of the synchronization symbol to obtain a control symbol.

[0082] In a specific embodiment of the present invention, 1 OFDM symbol includes 64 points of cyclic prefix CP and 1024 points after the cyclic prefix CP, totaling 1088 points.

[0083] Another specific embodiment of the present invention discloses a frequency offset estimation method based on the above fast synchronization method for ad hoc network physical layer burst signals. The method includes: after obtaining the synchronization symbol, intercept the cyclic prefix CP of the synchronization symbol, remove the first 5 points and the last 5 points of the CP to obtain the de-aliased cyclic prefix, perform a correlation operation on the de-aliased cyclic prefix and the sampling points corresponding to the tail within the same synchronization symbol to obtain a CP correlation sequence, take the mean of each point in the CP correlation sequence to obtain the mean of the CP correlation sequence, and calculate the phase difference of the synchronization symbol according to the I and Q components of the mean;

[0084] Use the same method as the synchronization symbol phase difference acquisition method to obtain the phase difference of the control symbol;

[0085] Based on the phase difference of the synchronization symbol and the phase difference of the control symbol, obtain the frequency offset of the synchronization symbol and the frequency offset of the control symbol respectively.

[0086] Calculate the respective corresponding frequency offsets according to the sampling frequency when the receiving end receives the IQ sequence and the phase differences of the synchronization symbol or the control symbol. The formula is:

[0087]

[0088] where F S is the sampling frequency when the receiving end receives the IQ sequence, is the phase difference of the synchronization symbol or the control symbol, and N is the number of points of the inverse Fourier transform.

[0089] Specifically, frequency offset estimation is performed on the cyclic prefix CP of these two OFDM symbols, namely the synchronization segment and the control segment.

[0090] Extract the CP of the synchronization segment symbol and the part corresponding to the tail CP of the synchronization segment symbol, and calculate the phase difference phi according to the following formula:

[0091]

[0092] phi = -j2πΔfN (3)

[0093] Wherein, CP' in (2) is the anti-aliased cyclic prefix obtained by removing the first 5 points and the last 5 points from the cyclic prefix of the synchronization segment symbol, conj(Symbol) is the conjugate complex number of the part corresponding to the tail CP of the synchronization segment symbol, x(n) is the average value obtained after performing a correlation operation on the anti-aliased cyclic prefix and the part corresponding to the tail CP of the synchronization segment symbol to obtain a CP correlation sequence, N is the number of points of the inverse Fourier transform, and Δf is the frequency difference between the anti-aliased cyclic prefix and the part corresponding to the tail CP of the synchronization segment symbol.

[0094] Calculate the phase difference through the following formula (4): x(n) = real(phi) + j×image(phi),

[0095]

[0096] Combined with the quadrant of x(n), convert the value range of Phi_offset from to the interval range of (-π, π). The specific method is as follows:

[0097] When x(n) is in the first quadrant (real part > 0, imaginary part > 0), the phase value range: (0, +π / 2), no adjustment is required.

[0098] When x(n) is in the second quadrant (real part < 0, imaginary part > 0), the phase value range: (π / 2, +π), it is necessary to add π to the result (-π / 2, 0) of tan -1 .

[0099] When x(n) is in the third quadrant (real part < 0, imaginary part < 0), the phase value range: (-π, -π / 2), it is necessary to subtract π from the result (0, π / 2) of tan -1 .

[0100] When x(n) is in the fourth quadrant (real part > 0, imaginary part < 0), the phase value range: (-π / 2, 0), the result of tan -1 does not need to be adjusted.

[0101] Compared with the prior art, a fast synchronization method for self-organizing network physical layer burst signals provided by this embodiment is as follows: the receiving end receives an IQ sequence and performs preprocessing to obtain a preprocessed sequence; the local synchronization sequence is decimated to obtain a local decimated sequence; the preprocessed sequence and the local decimated sequence are subjected to cross-correlation operation to obtain a cross-correlation sequence; a cross-correlation power sequence is obtained according to the cross-correlation sequence; the cross-correlation power sequence is segmented, the peak-to-average ratio of each segment of the cross-correlation power sequence is calculated, and the coarse synchronization index position is obtained according to the peak-to-average ratio; based on the coarse synchronization index position and the IQ sequence, multiple fine synchronization matching sequences are generated, each fine synchronization matching sequence is subjected to correlation operation with the local synchronization sequence to obtain a corresponding second correlation sequence, and the fine synchronization index position is determined based on the average power value of the second correlation sequence, thereby obtaining the synchronization symbol and the control symbol. By adopting a two-stage synchronization algorithm of coarse synchronization and fine synchronization based on pseudo-random sequences, the fast synchronization of the burst wireless frame can be completed within one OFDM symbol period. In the fast synchronization method for self-organizing network physical layer burst signals provided by this embodiment, during the acquisition process of the coarse synchronization index position, every M data of the cross-correlation power sequence are divided into one segment. In each segment, the data peak point is first searched, m data before and after the peak point are removed in each segment for peak suppression filtering, and after the peak suppression filtering of the cross-correlation power sequence, the mean value of M data before and after each peak point is obtained by accumulating M / 2 data before and after each peak point in each segment and then taking the mean value, that is, the influence of the peak point on the average value of the cross-correlation power of each segment is excluded during the calculation of the peak-to-average ratio of each segment of the cross-correlation power sequence, which can more accurately reflect the background energy of the signal and measure the peak characteristics of the signal, and better adapt to the influence of multipath, asymmetry and uneven energy distribution of different types of signals. This process adopts segmented calculation, which can reduce the operation pressure and storage pressure of the processor. The segmented calculation analyzes the signal change more finely, improves the synchronization accuracy in a multipath channel or a noisy environment, and can suppress noise and interference through segmented calculation, thereby improving the robustness of this synchronization method. In the fast synchronization method for self-organizing network physical layer burst signals provided by this embodiment, the preprocessing sequentially includes: AGC processing, decimation, polyphase filtering, and clipping processing; after decimation, the coarse synchronization index position can be quickly found, the polyphase filtering makes up for the signal defect caused by decimation, and the clipping processing can prevent the result of the cross-correlation operation between the preprocessed sequence and the local decimated sequence from overflowing, and prevent the misjudgment or missed judgment of the coarse synchronization index position caused by the overflow.Based on the frequency offset estimation method of the fast synchronization method for the self-organizing network physical layer burst signal provided in this embodiment, after obtaining the synchronization symbol, intercept the cyclic prefix CP of the synchronization symbol, remove the first 5 points and the last 5 points of the CP to obtain the anti-aliased cyclic prefix, perform a correlation operation on the anti-aliased cyclic prefix and the sampling points corresponding to the tail within this synchronization symbol to obtain the CP correlation sequence, take the mean value of each point in the CP correlation sequence to obtain the mean value of the CP correlation sequence, and calculate the phase difference of the synchronization symbol according to the I and Q components of the mean value; use the same method as the method for obtaining the phase difference of the synchronization symbol to obtain the phase difference of the control symbol; respectively obtain the frequency offset of the synchronization symbol and the frequency offset of the control symbol based on the phase difference of the synchronization symbol and the phase difference of the control symbol. The frequency offset estimation of the wireless frame is completed within two OFDM symbol periods.

[0102] Those skilled in the art can understand that all or part of the processes for implementing the methods of the above embodiments can be completed by instructing relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium. Among them, the computer-readable storage medium is a disk, an optical disc, a read-only memory or a random access memory, etc.

[0103] The above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A fast synchronization method for self-organizing network physical layer burst signals, characterized in that The transmitting end sends a wireless signal, and the wireless signal is generated by using a synchronization sequence, where the synchronization sequence includes a synchronization segment and a control segment. The receiving end receives the wireless signal, parses it to obtain an IQ sequence, and performs preprocessing to obtain a preprocessed sequence; extracts the local synchronization sequence to obtain a local extraction sequence; performs a cross-correlation operation on the preprocessed sequence and the local extraction sequence to obtain a cross-correlation sequence; obtains a cross-correlation power sequence according to the cross-correlation sequence; segments the cross-correlation power sequence, calculates the peak-to-average ratio of each segment of the cross-correlation power sequence, and obtains a coarse synchronization index position according to the peak-to-average ratio; generates a plurality of fine synchronization matching sequences based on the coarse synchronization index position and the IQ sequence, performs a correlation operation on each fine synchronization matching sequence and the local synchronization sequence to obtain a corresponding second correlation sequence, and determines the fine synchronization index position based on the average power value of the second correlation sequence, thereby obtaining a synchronization symbol and a control symbol.

2. The fast synchronization method according to claim 1, wherein The generating a plurality of fine synchronization matching sequences based on the coarse synchronization index position and the IQ sequence includes: Sliding a window on the received IQ sequence with points within a set interval range before and after the coarse synchronization index position as the starting point to generate a plurality of fine synchronization matching sequences.

3. The rapid synchronization method according to claim 2, wherein The set interval range is from 2k points before the coarse synchronization index position to 2k points after the coarse synchronization index position, where k is the extraction multiple in the preprocessing of the received IQ sequence; the window size is 512. When performing the correlation operation between the fine synchronization matching sequence and the local synchronization sequence, intercept the first 512 points of the local synchronization sequence as a template, and calculate the correlation between the template and each fine synchronization matching sequence to obtain a second correlation sequence.

4. The fast synchronization method according to claim 2, wherein The determining the fine synchronization index position based on the average power value of the second correlation sequence includes: Calculating the average power value of each second correlation sequence, and taking the position of the first point of the fine synchronization matching sequence corresponding to the second correlation sequence with the largest average power value as the fine synchronization index position.

5. The rapid synchronization method according to claim 1, wherein The preprocessing of the received IQ sequence includes, in sequence: AGC processing, extraction, and polyphase filtering; dividing the IQ sequence after AGC processing into groups of k data starting from the beginning, extracting the data at the first position in each group, and then averaging the data in each group and adding it to the extracted data of the current group to obtain a polyphase-filtered sequence, where the range of k is [6, 10].

6. The fast synchronization method according to claim 5, wherein The preprocessing further includes: quantizing the sequence after polyphase filtering to 16 bits, comparing the quantized data to obtain the maximum peak value of the quantized data, and if the maximum peak value is greater than taking the ratio of the maximum peak value to as the scaling factor, and dividing each number in the sequence after polyphase filtering by the scaling factor to obtain the data after amplitude limiting processing; if the maximum peak value is less than or equal to no amplitude limiting processing is performed.

7. The fast synchronization method according to claim 1, wherein Segmenting the cross-correlation power sequence, calculating the peak-to-average ratio of each segment of the cross-correlation power sequence, and obtaining the coarse synchronization index position according to the peak-to-average ratio includes: dividing the cross-correlation power sequence into segments of M data each, searching for data peak points within each segment, performing peak suppression filtering by removing m data before and after the peak point within each segment, adding up the M / 2 data before and after each peak point in the filtered cross-correlation power sequence and taking the average to obtain the average of the M data before and after each peak point, dividing each segment peak point by the average of its corresponding M data before and after to obtain the peak-to-average ratio of each segment, comparing multiple peak-to-average ratios to obtain the maximum peak-to-average ratio, and the position of the peak point corresponding to the maximum peak-to-average ratio is the coarse synchronization index position, where the range of m is [3, 6], and the range of M / 2 is [28, 36].

8. The fast synchronization method according to claim 1, wherein The synchronization sequence generated by the transmitting end is a low peak-to-average power ratio sequence, which is generated by using the following calculation formula: Where: u is the root index number, n is the sequence index number, and the value range of n is from 0 to 61; Load the du(n) sequence onto the subcarriers, perform an inverse Fourier transform on the subcarriers and add a cyclic prefix CP to obtain a synchronization sequence for transmission.

9. A frequency offset estimation method for the fast synchronization method according to claims 1-8, characterized in that After obtaining the synchronization symbol, intercept the cyclic prefix CP of the synchronization symbol, remove the first 5 points and the last 5 points of the CP to obtain an anti-aliased cyclic prefix, perform a correlation operation on the anti-aliased cyclic prefix and the sampling points corresponding to the tail within this synchronization symbol to obtain a CP correlation sequence, take the average of each point in the CP correlation sequence to obtain the average value of the CP correlation sequence, and calculate the phase difference of the synchronization symbol according to the I and Q components of the average value; Use the same method as the synchronization symbol phase difference acquisition method to obtain the phase difference of the control symbol; Based on the phase differences of the synchronization symbol and the control symbol, obtain the frequency offset of the synchronization symbol and the frequency offset of the control symbol respectively.

10. The frequency offset estimation method according to claim 9, characterized in that, Calculate the respective corresponding frequency offsets according to the sampling frequency when the receiving end receives the IQ sequence and the phase differences of the synchronization symbol or the control symbol. The formula is: Among them, F S is the sampling frequency at which the receiving end receives the IQ sequence, is the phase difference of the synchronization symbol or the phase difference of the control symbol, and N is the number of points of the inverse Fourier transform.

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