OFDM (Orthogonal Frequency Division Multiplexing) system time-frequency synchronization method, device and equipment based on ZC sequence and medium

Abstract

The invention provides an OFDM system time-frequency synchronization method, device and equipment based on a ZC sequence and a medium, and the method comprises the steps: carrying out the signal receiving of an input signal based on a continuous receiving window with the time length of NTs, and carrying out the PSS detection and first time offset measurement in combination with the matched filtering processing result of each continuous Npsssymb receiving window, and obtaining a first time offset measurement result; and adjusting the starting time of the receiving window according to the first time offset measurement result, receiving the input signal again based on the continuous receiving window with the time length of NTs, and performing SSS detection, time offset tau norm measurement and frequency offset alpha norm measurement in combination with the matched filtering processing result of each continuous Nsssymb receiving window to obtain a time offset measurement result and a frequency offset measurement result. According to the invention, the time-frequency synchronization capability of the OFDM system can be effectively improved, and time-frequency synchronization under the condition that the frequency offset is lower than 1% of the synchronization signal bandwidth can be supported.

Description

Technical Field

[0001] This application relates to the field of wireless communication, and more particularly, to a time-frequency synchronization method, apparatus, device, and medium for an OFDM (Orthogonal Frequency Division Multiplexing) system based on ZC (Zadoff-Chu) sequences. Background Art

[0002] Due to its good anti-multipath delay characteristics and support for flexible time-frequency resource allocation, OFDM technology is currently widely used in broadband wireless communication systems. Wireless communication protocol standards such as LTE, 5GNR, and WIFI are all based on OFDM technology. However, OFDM technology is extremely sensitive to frequency offset of signals, and a small frequency offset can cause a sharp decline in the performance of the entire system. Therefore, a more efficient time-frequency synchronization method is urgently needed. Summary of the Invention

[0003] This application aims to provide a time-frequency synchronization method, apparatus, device, and medium for an OFDM system based on ZC sequences, so as to solve the problem that the conventional time-frequency synchronization method for OFDM systems is difficult to achieve time-frequency synchronization of OFDM systems in scenarios with large frequency offsets in a low-complexity manner.

[0004] This application provides a time-frequency synchronization method for an OFDM system based on ZC sequences, including:

[0005] Receiving an input signal based on a receiving window with a continuous time length of NT s and jointly performing PSS detection and first time offset measurement on the matched filtering processing results of each continuous N pss_symb receiving windows to obtain a first time offset measurement result;

[0006] Adjusting the start time of the receiving window according to the first time offset measurement result, and then receiving the input signal again based on a receiving window with a continuous time length of NT s and jointly performing SSS detection, time offset τ sss_symb measurement, and frequency offset α norm measurement on the matched filtering processing results of each continuous N norm receiving windows to obtain a time offset measurement result and a frequency offset measurement result.

[0007] In some embodiments, the input signal includes a primary synchronization signal and a secondary synchronization signal with an interval not less than the subcarrier interval, where the primary synchronization signal is N pss_symb ZC sequences with a length of N zc , and the secondary synchronization signal is N sss_symb ZC sequences with a length of N zc .

[0008] In some embodiments, the root sequence number u of the primary synchronization signal pss is fixed to 1 or N zc -1.

[0009] In some embodiments, the root sequence number u of the secondary synchronization signal sss is fixed to round(N zc / 5 / FO max ) or N zc -round(N zc / 5 / FO max ), where FO max represents the maximum absolute value of the frequency offset.

[0010] In some embodiments, the PSS detection includes:

[0011] According to the input signal, the receiving end receives the time-domain signal corresponding to the OFDM symbol, performs matched filtering processing, and obtains the first matched filtering result;

[0012] According to the first matched filtering result and the PSS determination condition, perform PSS detection to obtain the first maximum pulse position;

[0013] Update the first maximum pulse position based on the matched filtering result;

[0014] According to the updated first maximum pulse position, calculate the first time offset measurement result.

[0015] In some embodiments, the SSS detection includes:

[0016] According to the input signal, the receiving end receives the time-domain signal corresponding to the OFDM symbol, performs matched filtering processing to obtain the second matched filtering result;

[0017] According to the second matched filtering result and the SSS determination condition, perform SSS detection to obtain the second maximum pulse position and the second time offset measurement result;

[0018] Perform frequency offset measurement according to the second maximum pulse position to obtain the frequency offset measurement result;

[0019] According to the first time offset measurement result and the second time offset measurement result, obtain the time offset measurement result.

[0020] In some embodiments, performing frequency offset measurement according to the second maximum pulse position to obtain the frequency offset measurement result satisfies:

[0021] α norm = α int + α dec ;

[0022]

[0023] Condition A:

[0024] where α norm is the frequency offset measurement result, n max is the second largest pulse position, N corr is the number of points for IFFT transformation when calculating the matched filter, N sc represents the number of subcarriers used for the synchronization signal, 0 ≤ N sc < N, N represents the number of points for FFT transformation and IFFT transformation in the OFDM system, u sss is the root sequence number of the input signal, R corr_sum () represents the cumulative sum sequence of the matched filter result.

[0025] In a second aspect, the present application provides a time-frequency synchronization device for an OFDM system based on a ZC sequence, including:

[0026] A PSS detection module, configured to receive an input signal based on a reception window with a continuous time length of NT s , and perform PSS detection and first time offset measurement by combining the matched filter processing results of each continuous N pss_symb reception windows, to obtain a first time offset measurement result;

[0027] An SSS detection module, configured to adjust the start time of the reception window according to the first time offset measurement result, and again receive the input signal based on a reception window with a continuous time length of NT s , and perform SSS detection, time offset τ sss_symb measurement and frequency offset α norm measurement by combining the matched filter processing results of each continuous N norm reception windows, to obtain a time offset measurement result and a frequency offset measurement result.

[0028] In a third aspect, the present application provides an electronic device, including: a memory, a processor;

[0029] The memory stores computer-executable instructions;

[0030] The processor executes the computer-executable instructions stored in the memory, so that the processor executes the method as in the first aspect.

[0031] In a fourth aspect, the present application provides a computer-readable storage medium, in which computer-executable instructions are stored, and when the computer-executable instructions are executed by a processor, they are used to implement the method as in the first aspect.

[0032] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present application are:

[0033] Based on the root sequence number u pss Fixed to 1 or N zc Design of the primary synchronization signal of the repeated ZC sequence with -1. Among them, the root sequence number u pss Fixed to 1 or N zc The design with -1 can ensure that under the condition of large frequency offset, the pulse peaks in the matched filtering result are concentrated in a specific region τ norm -N corr / N zc ~τ norm +N corr / N zc , and then the fractional multiple OFDM symbol time offset result τ can be detected through the pulse peak position pss_dec ; The design of the repeated ZC sequence can avoid the scenario where the complete OFDM symbol carrying the PSS cannot be completely received within the reception window, and the detection performance can be enhanced by combining the matched filtering results.

[0034] Based on the root sequence number u sss Fixed to round(N zc / 5 / FO max ) or N zc -round(N zc / 5 / FO max ) of the repeated ZC sequence for the design of the auxiliary synchronization signal. Among them, u sss Fixed to round(N zc / 5 / FO max ) or N zc -round(N zc / 5 / FO max ) of the design can ensure that under the condition of large frequency offset, the pulse peaks in the matched filtering result are shifted to τ affected by the frequency offset norm +round(α norm )u sss N corr / N zc nearby, and then the frequency offset result α norm and the accurate fractional multiple OFDM symbol time offset result τ sss_dec can be detected through the pulse peak position; The design of the repeated ZC sequence can support the measurement of the integer multiple OFDM symbol time-frequency offset result.

[0035] Based on the SSS-based frequency offset measurement mechanism, the frequency offset measurement result α can be obtained based on the pulse peak position in the matched filtering result norm .

[0036] The time offset measurement mechanism based on SSS can obtain a more accurate fractional multiple OFDM symbol time offset result based on the pulse peak position in the matched filtering result, and can obtain an integer multiple OFDM symbol time offset result based on the pulse peak magnitudes of multiple consecutive matched filtering results, thereby obtaining an accurate time offset.

[0037] Through the above improvements, this method can effectively improve the time-frequency synchronization ability of the OFDM system and support time-frequency synchronization under the condition that the frequency offset is lower than 1% of the synchronization signal bandwidth. Brief Description of the Drawings

[0038] Figure 1 It is a schematic diagram of a communication system model using OFDM technology provided by this application;

[0039] Figure 2 It is a schematic diagram of the time synchronization processing timing based on multi-receiving window scanning;

[0040] Figure 3 It is a schematic diagram of the process of a time-frequency synchronization method for an OFDM system based on ZC sequences provided by an embodiment of this application;

[0041] Figure 4 It is a schematic diagram of a two-stage synchronization signal design based on ZC sequences provided by an embodiment of this application;

[0042] Figure 5 It is a schematic diagram of the time-frequency synchronization processing timing at the receiving end of an OFDM system based on ZC sequences provided by an embodiment of this application;

[0043] Figure 6 It is a schematic diagram of PSS detection processing provided by an embodiment of this application;

[0044] Figure 7 It is a schematic diagram of SSS detection processing provided by an embodiment of this application;

[0045] Figure 8 It is a schematic diagram of the structure of a time-frequency synchronization device for an OFDM system based on ZC sequences provided by an embodiment of this application;

[0046] Figure 9 It is a schematic diagram of the structure of an electronic device provided by this application. Detailed Embodiments

[0047] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. Usually, the components of the embodiments of this application described and illustrated here can be arranged and designed in various different configurations.

[0048] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the present application.

[0049] Embodiment

[0050] Figure 1 It is a schematic diagram of a communication system model using OFDM technology provided for the present application. Considering that the frequency offset may exceed 0.5 times the subcarrier spacing, the starting subcarrier at reception is offset by round(α):

[0051]

[0052] Where X(l,k) represents the signal transmitted by the transmitting end on the k-th subcarrier of the l-th OFDM symbol, 0 ≤ l < L, 0 ≤ k < N;

[0053] Y(l,k) represents the signal received by the receiving end on the k-th subcarrier of the l-th OFDM symbol, 0 ≤ l < L, 0 ≤ k < N;

[0054] W(l,k) represents the noise received by the receiving end on the k-th subcarrier of the l-th OFDM symbol, which can be approximately considered to follow a complex Gaussian distribution, 0 ≤ l < L, 0 ≤ k < N;

[0055] N represents the number of points for FFT transformation and IFFT transformation in the OFDM system, generally defaulting to not exceeding 8192;

[0056] N CP represents the number of CP points used for each OFDM symbol;

[0057] L represents the number of OFDM symbols transmitted;

[0058] N sc represents the number of subcarriers used for the valid signal, 0 ≤ N sc < N;

[0059] N start represents the starting subcarrier serial number used for the valid signal, 0 ≤ N start < N, 0 ≤ N start + N sc < N;

[0060] T s and T s ' respectively represent the sampling time interval of the transmitting end and the sampling time interval of the receiving end, with the measurement unit being s. In the current engineering implementation, it is very difficult to ensure T s and Ts 'Strictly equal, but the error can be guaranteed to be in the order of 0.1 - 1 ppm, that is, T s ' / T s <10 -6 ;

[0061] Δf = NT s represents the sub - carrier spacing, with the unit of measurement being Hz;

[0062] τ max represents the maximum time delay, with the unit of measurement being s. During system design, it is necessary to ensure that τ max <N CP T s , τ max <N CP T s ';

[0063] α min and α max respectively represent the minimum Doppler frequency - shift factor and the maximum Doppler frequency - shift factor caused by the relative movement of the transceiver. They are the ratios of the minimum Doppler frequency - shift and the maximum Doppler frequency - shift to Δf. In a conventional OFDM system, it is necessary to ensure - 0.1 < α min ≤α max <0.1;

[0064] h equ (τ, α) represents the equivalent channel attenuation factor corresponding to the transmission path with a time delay of τ and a Doppler frequency - shift of α, where 0 ≤ τ < τ max , α min ≤α < α max , which takes into account the influence of the deviation between T s and T s ', as well as the influence of phase noise at the receiving end. For the convenience of analysis, it is assumed that h equ (τ, α) is constant within the duration of a single OFDM symbol;

[0065] round(α) represents rounding α;

[0066] f N0,N1 (x) represents the following function, which is the sum of a constant - modulus geometric complex - number sequence. As |x| increases, it shows a trend of decreasing fluctuations:

[0067]

[0068] It can be seen that the deviation between T s ' and T s can cause an inter - carrier interference effect similar to frequency offset and a phase - shift effect similar to time delay. However, considering that the frequency accuracy of current crystal oscillators is mostly at the level of 0.1 - 1 ppm, that is, T s' / T s <10 -6 and N generally can only reach 10 4 order of magnitude. Then the above formula can be approximated as follows. It can be seen that the inter-carrier interference effect similar to frequency offset caused by it can be approximately ignored:

[0069]

[0070] Obviously, the first part in Y(l,k) is the effective signal part, and the second part shows the inter-carrier interference (ICI). It can be seen that the power of ICI has a positive correlation with α. Through simulation, it can be found that when α > 0.1, ICI cannot be ignored and can lead to a significant degradation in demodulation performance.

[0071] Most of the time-frequency synchronization in current OFDM systems is completed based on training sequences. Most of the training sequences are designed based on gold sequences or ZC sequences. They utilize the autocorrelation and cross-correlation characteristics of the training sequences, complete time synchronization based on matched filtering processing, and calculate the frequency offset based on the phase difference between two received signals to complete frequency synchronization. The general process is as follows:

[0072] Step 1: Determine the normalized time offset τ based on the pulse amplitude of the autocorrelation function norm (Considering the existence of multipath effects in the communication scenario, the normalized time offset is used to characterize the time offset), where l ss represents the OFDM symbol with a training sequence, and N start and N sc represent the starting position and the number of subcarriers occupied by the training sequence respectively:

[0073]

[0074] Step 2: Calculate the normalized frequency offset α based on the phase difference between two received signals norm (Considering the existence of multipath effects in the communication scenario, the normalized frequency offset is used to characterize the frequency offset), where l ss0 and l ss1 represent the serial numbers of two OFDM symbols with training sequences (l ss0 < l ss1 ):

[0075]

[0076] The above method has limitations on the time offset and frequency offset ranges:

[0077] The maximum time delay τ max shall not exceed N CP T s ;

[0078] Absolute value of the maximum frequency offset FO max = max{|α min |,|α max |} shall not exceed 2π(l ss1 -l ss0 )N / (N + N CP );

[0079] For the limitation of the maximum time delay τ max , the conventional approach is to overcome it based on the multi - receive window scanning mechanism. Figure 2 As shown in the time - synchronization processing timing diagram for multi - receive window scanning, Figure 2 if the receiver does not know the value of l ss (l ss represents the OFDM symbol with a training sequence), the signal is received at intervals of N CP and subjected to FFT (Fast Fourier Transform) processing. Then, based on the above - mentioned matched - filtering processing procedure (Step 1), τ max can be scanned. At this time, theoretically, τ max can be positive infinity and is also supported.

[0080] For the limitation of the absolute value of the maximum frequency offset FO max , the conventional approach is to select a sub - carrier interval Δf configuration and a training - sequence - located OFDM interval (l max <2π(l ss1 -l ss0 )N / (N + N CP ) to overcome it. If such a configuration cannot be selected, it can be overcome based on the blind - scan method. As shown in the following formula, it mainly enhances the process (Step 2) of calculating the normalized frequency offset from the phase difference of the two - segment received signals. The cost is a significant increase in the computational complexity. Among them, ss1 -l ss0 represents the circular convolution operation: represents the circular convolution operation:

[0081]

[0082] Among them, α int represents the integer - multiple frequency - offset factor, imag(x) represents the imaginary part of the complex number x, real(x) represents the real part of the complex number x, j represents the imaginary unit, and j * j = - 1.

[0083] Obviously, it is very difficult to complete the time - frequency synchronization of the OFDM system in the case of a large frequency offset in a low - complexity manner with the above - listed conventional algorithms.

[0084] AsFigure 3 as shown Figure 3 FIG. is a schematic flow chart of a time-frequency synchronization method for an OFDM system based on ZC sequences provided by an embodiment of the present application, which can support time-frequency synchronization of an OFDM system under the condition that the frequency offset is lower than 1% of the synchronization signal bandwidth. Specifically, the method includes the following steps:

[0085] Step 301: Receive an input signal based on a reception window with a continuous time length of NT s and perform PSS detection and first time offset measurement by combining the matched filtering processing results of each continuous N pss_symb reception windows to obtain a first time offset measurement result;

[0086] Step 302: Adjust the start time of the reception window according to the first time offset measurement result, and then receive the input signal again based on a reception window with a continuous time length of NT s and perform SSS detection, time offset τ sss_symb measurement, and frequency offset α norm measurement by combining the matched filtering processing results of each continuous N norm reception windows to obtain a time offset measurement result and a frequency offset measurement result.

[0087] Among them, Figure 4 is a schematic diagram of a two-stage synchronization signal design based on ZC sequences provided by an embodiment of the present application. As Figure 4 shown, the input signal can be a two-stage synchronization signal based on ZC sequences. Use N pss_symb ZC sequences with a length of N zc as the primary synchronization signal (PSS), and its corresponding OFDM symbol has no CP (i.e., N CP = 0), and the root sequence number u pss is fixed to 1 or N zc -1. The receiver can complete coarse time offset estimation based on this signal; use N sss_symb ZC sequences with a length of N zc as the secondary synchronization signal (SSS), and its corresponding OFDM symbol has no CP (i.e., N CP = 0), and the root sequence number u sss is fixed to round(N zc / 5 / FO max ) or N zc -round(N zc / 5 / FO max ), where FO max represents the maximum absolute value of the frequency offset; the interval (GP) between the PSS and the SSS is guaranteed to be not less than NT s .

[0088] Figure 5Schematic diagram of the time-frequency synchronization processing timing for the receiver of an OFDM system based on ZC sequences provided by the embodiments of this application, where N is set pss_symb = N sss_symb = 3, and the interval between PSS and SSS (GP) is equal to NT s . The receiver first receives signals based on a receiving window with a continuous time length of NT s , and jointly performs PSS detection and fractional multiple OFDM symbol time offset (τ pss_symb ) measurement based on the matched filtering processing results of every consecutive N pss_dec receiving windows. After detecting the PSS, immediately after adjusting the start time of the receiving window (delaying τ dec ), it starts receiving signals again based on a receiving window with a continuous time length of NT s , and jointly performs SSS detection and time offset (τ sss_symb ) measurement and frequency offset (α norm ) measurement based on the matched filtering processing results of every consecutive N norm receiving windows.

[0089] PSS detection may include:

[0090] According to the input signal, the receiving end receives the time-domain signal corresponding to the OFDM symbol, performs matched filtering processing, and obtains the first matched filtering result;

[0091] According to the first matched filtering result and the PSS determination condition, perform PSS detection to obtain the first maximum pulse position;

[0092] Update the first maximum pulse position based on the matched filtering result;

[0093] According to the updated first maximum pulse position, calculate the first time offset measurement result.

[0094] Exemplarily, the input and output of PSS detection may be:

[0095] Input:

[0096] The original PSS signal X PSS (k) generated by the receiving end, with a length of N sc , 0 ≤ k < N sc ;

[0097] The maximum number of PSS scanning windows L pss_scan ;

[0098] L pss_scan time-domain received signals r(l,n) corresponding to OFDM symbols;

[0099] Synchronization signal existence judgment threshold N relSum thr;

[0100] The number of subcarriers N occupied by PSS sc , 0 ≤ N sc < N;

[0101] The starting subcarrier serial number N occupied by PSS start , 0 ≤ N start < N, 0 ≤ N start + N sc < N;

[0102] The number of points N for FFT transformation and IFFT transformation in the OFDM system;

[0103] The number of points N for IFFT transformation when calculating the matched filtering corr , which should be not less than N sc .

[0104] Output:

[0105] The fractional - multiple OFDM symbol time - offset measurement result τ dec ;

[0106] The OFDM symbol serial number l where PSS is detected pss_dect ;

[0107] The PSS detection reliability result SINR pss_dect .

[0108] Figure 6 This is the schematic diagram of PSS detection processing provided by the embodiment of the present application. As shown in the figure, the PSS detection steps may include:

[0109] Step 601: Initialize l = 0, the cumulative sum sequence R of the matched filtering result corr_sum (n)=0, 0 ≤ n < N; the fractional - multiple OFDM symbol time - offset measurement result (the first time - offset measurement result) τ pss_dec =0; the PSS detection reliability result SINR pss_dec =-1; the OFDM symbol serial number l where PSS is detected pss_dect =-1;

[0110] Step 602: If l < the maximum number of PSS scanning windows L pss_scan , continue to execute Step 603; otherwise, end the PSS detection and return the PSS detection result;

[0111] Step 603: The receiving end receives the time - domain signal r(l,n) corresponding to the l - th OFDM symbol and performs matched filtering processing as shown in the following formula:

[0112]

[0113] The matched filtering result is denoted as R corr (l,n), which is a sequence of length N corr . Here, n represents the serial number of the matched filtering result, and N sc represents the number of subcarriers used for the synchronization signal, and N start represents the starting subcarrier serial number used for the synchronization signal, where 0 ≤ N start < N, 0 ≤ N start + N sc < N, N corr represents the number of points for the IFFT transformation when calculating the matched filtering, which should be not less than N sc , and X PSS (k) represents the transmitted PSS signal, carried in the frequency domain as a ZC sequence, where 0 ≤ k < N sc .

[0114] Step 604: Update R corr_sum (n) as shown in the following formula:

[0115]

[0116] Step 605: Perform PSS detection. If the following formula is satisfied, it is determined that the PSS detection is successful; if the detection is successful, record the maximum pulse position n max and the PSS detection reliability SINR pss_dect , and continue to execute Step 606; otherwise, jump to Step 608;

[0117] SINR pss_dect > N relSum_thr

[0118]

[0119] Step 6: Perform PSS detection verification, update the maximum pulse position n max , the PSS detection reliability SINR pss_dect and the OFDM symbol serial number l of the detected PSS pss_dect , and they are updated only when |R corr_sum_next (n max_next )| 2 >|R corr_sum (n max )| 2 , where n max_next represents the maximum pulse position found based on |R corr_sum_next (n max_next )| 2 ,

[0120]

[0121] Step 607: Calculate the fractional multiple OFDM symbol timing offset measurement result τ pss_dec , and according to the following formula, then end the PSS detection and return the corresponding result,

[0122]

[0123] Step 608: l = l + 1, and jump to Step 602.

[0124] The SSS detection may include:

[0125] Based on the input signal, the receiving end receives the time-domain signal corresponding to the OFDM symbol, and performs matched filtering processing to obtain the second matched filtering result;

[0126] Based on the second matched filtering result and the SSS determination condition, perform SSS detection to obtain the second maximum pulse position and the second timing offset measurement result;

[0127] Based on the second maximum pulse position, perform frequency offset measurement to obtain the frequency offset measurement result;

[0128] Based on the first timing offset measurement result and the second timing offset measurement result, obtain the timing offset measurement result.

[0129] Exemplarily, the input and output of the SSS detection process may be:

[0130] Input:

[0131] The original SSS signal X SSS (k) generated by the receiving end, carried in the frequency domain, is a ZC sequence with a length of N sc , 0 ≤ k < N sc ;

[0132] The fractional multiple OFDM symbol timing offset measurement result τ pss_dec ;

[0133] The OFDM symbol number l where the PSS is detected pss_dect ;

[0134] The maximum number of SSS scanning windows L sss_scan ;

[0135] L sss_scan time-domain received signals r(l,n) corresponding to OFDM symbols;

[0136] The synchronization signal existence determination threshold N relSum_thr ;

[0137] The number of subcarriers N occupied by the SSS sc , 0 ≤ Nsc <N;

[0138] The starting subcarrier serial number N occupied by SSS start , 0 ≤ N start <N, 0 ≤ N start +N sc <N;

[0139] The number of points N for FFT and IFFT transforms in the OFDM system;

[0140] The number of sampling points N for the interval between PSS and SSS GP , which should be an integer multiple of N;

[0141] The time domain sampling time interval T s ;

[0142] The number of points N for IFFT transform when calculating the matched filter corr , which should be not less than N sc .

[0143] Output:

[0144] The time offset measurement result τ norm ;

[0145] The frequency offset measurement result α norm ;

[0146] The SSS detection reliability result SINR sss_dect .

[0147] Figure 7 This is the schematic diagram of SSS detection processing provided by the embodiments of the present application. As shown in the figure, the SSS detection processing process may include:

[0148] Step 701: Initialize l = l pss_dect +N GP / N; R corr_sum (n) = 0, 0 ≤ n < N; τ norm = 0; α norm = 0;

[0149] SINR sss_dect = 0, and the receiving end delays the starting time point of the received time domain signal by round(τ pss_dec / T s ) sampling points;

[0150] Step 702: If l < L sss_scan , continue to execute Step 703; otherwise, end the SSS detection and return the SSS detection result

[0151] Step 703: The receiving end receives the time-domain signal r(l,n) corresponding to the l-th OFDM symbol and performs matched filtering processing as shown in the following formula:

[0152]

[0153] The matched filtering result is denoted as R corr (l,n), which is a sequence of length N corr , and n represents the serial number of the matched filtering result.

[0154] Step 704: Update R corr_sum (n) as shown in the following formula

[0155]

[0156] Step 5: Perform SSS detection as shown in the following formula. If the following conditions are met, it is determined that the SSS detection is successful; if the detection is successful, record the maximum pulse position n max and the SSS detection reliability SINR sss_dect , and continue to execute Step 706; otherwise, jump to Step 708.

[0157] SINR sss_dect >N relSum_thr

[0158]

[0159] Step 706: Perform frequency offset measurement as shown in the following formula to obtain the frequency offset measurement result α norm

[0160] α norm =α int +α dec ;

[0161]

[0162] Condition A:

[0163] Step 707: Perform time offset measurement as shown in the following formula to obtain the time offset measurement result τ norm , then end the SSS detection and return the corresponding result,

[0164] τ norm =τ pss_dec +τ sss_dec +τ sss_int

[0165]

[0166] Step 708: l = l + 1, and jump to Step 702.

[0167] The meanings of the parameters are summarized as follows:

[0168] X PSS (k) represents the transmitted PSS signal, carried in the frequency domain, which is a ZC sequence, 0 ≤ k < N sc ;

[0169] X SSS (k) represents the transmitted SSS signal, carried in the frequency domain, which is a ZC sequence, 0 ≤ k < N sc ;

[0170] Y(l, k) represents the signal received by the receiver on the l-th OFDM symbol and the k-th subcarrier, 0 ≤ l < L, 0 ≤ k < N;

[0171] r(l, n) represents the signal received by the receiver on the l-th OFDM symbol and the n-th sampling point, 0 ≤ l < L, 0 ≤ n < N;

[0172] R corr (l, n) represents the matched filtering result corresponding to the l-th OFDM symbol;

[0173] R corr_sum (n) represents the cumulative sum sequence of the matched filtering results, 0 ≤ n < N;

[0174] N represents the number of points for FFT and IFFT transforms in the OFDM system, generally defaulting to no more than 8192;

[0175] N CP represents the number of CP points used for each OFDM symbol. For the synchronization signal designed in this scheme, it is fixed at 0;

[0176] N sc represents the number of subcarriers used for the synchronization signal, 0 ≤ N sc < N;

[0177] N start represents the starting subcarrier serial number used for the synchronization signal, 0 ≤ N start < N, 0 ≤ N start + N sc < N;

[0178] N corr represents the number of points for IFFT transform when calculating the matched filtering, which should be not less than N sc ;

[0179] L pss_scan represents the maximum number of received windows for PSS detection;

[0180] L sss_scan Indicates the maximum number of received windows for PSS detection.

[0181] A time-frequency synchronization method for an OFDM system based on ZC sequences provided by an embodiment of the present application:

[0182] Based on the root sequence number u pss Fixed to 1 or N zc Design of the primary synchronization signal of the repeated ZC sequence of -1. Among them, the root sequence number u pss Fixed to 1 or N zc The design of -1 can ensure that under the condition of large frequency offset, the pulse peaks in the matched filtering result are concentrated in a specific area τ norm -N corr / N zc ~τ norm +N corr / N zc , and then the fractional multiple OFDM symbol time offset result τ can be detected through the pulse peak position pss_dec ; The design of the repeated ZC sequence can avoid the scenario where the complete OFDM symbol carrying PSS cannot be completely received within the received window, and the detection performance can be enhanced by combining the matched filtering results.

[0183] Based on the root sequence number u sss Fixed to round(N zc / 5 / FO max ) or N zc -round(N zc / 5 / FO max ) design of the auxiliary synchronization signal of the repeated ZC sequence. Among them, u sss Fixed to round(N zc / 5 / FO max ) or N zc -round(N zc / 5 / FO max ) design can ensure that under the condition of large frequency offset, the pulse peaks in the matched filtering result are shifted to τ affected by the frequency offset norm +round(α norm )u sss N corr / N zc nearby, and then the frequency offset result α norm and the accurate fractional multiple OFDM symbol time offset result τ sss_dec can be detected through the pulse peak position; The design of the repeated ZC sequence can support the measurement of the integer multiple OFDM symbol time-frequency offset result.

[0184] Based on the frequency offset measurement mechanism of SSS, the frequency offset measurement result α can be obtained based on the pulse peak position in the matched filtering resultnorm 。

[0185] Based on the time offset measurement mechanism of SSS, the fractional multiple OFDM symbol time offset result can be obtained more accurately based on the pulse peak position in the matched filtering result, and the integer multiple OFDM symbol time offset result can be obtained based on the pulse peak magnitudes of multiple consecutive matched filtering results, so as to obtain an accurate time offset.

[0186] Through the above improvements, this method can effectively improve the time-frequency synchronization ability of the OFDM system and support time-frequency synchronization under the condition that the frequency offset is lower than 1% of the synchronization signal bandwidth.

[0187] Figure 8 This is a schematic structural diagram of an OFDM system time-frequency synchronization device 80 provided by an embodiment of the present application. As Figure 8 shown, it includes:

[0188] A PSS detection module 801, configured to receive an input signal through a reception window with a continuous time length of NT s and perform PSS detection and first time offset measurement by combining the matched filtering processing results of every continuous N pss_symb reception windows to obtain a first time offset measurement result;

[0189] An SSS detection module 802, configured to adjust the start time of the reception window according to the first time offset measurement result, and then receive the input signal through a reception window with a continuous time length of NT s again, and perform SSS detection, time offset τ sss_symb measurement and frequency offset α norm measurement by combining the matched filtering processing results of every continuous N norm reception windows to obtain a time offset measurement result and a frequency offset measurement result.

[0190] In some embodiments, the PSS detection module 801 is further configured to:

[0191] Receive the time-domain signal corresponding to the OFDM symbol at the receiving end according to the input signal, perform matched filtering processing to obtain a first matched filtering result;

[0192] Perform PSS detection according to the first matched filtering result and the PSS determination condition to obtain a first maximum pulse position;

[0193] Update the first maximum pulse position based on the matched filtering result;

[0194] Calculate the first time offset measurement result according to the updated first maximum pulse position.

[0195] In some embodiments, the SSS detection module 802 is further configured to:

[0196] According to the input signal, the receiving end receives the time-domain signal corresponding to the OFDM symbol, and performs matched filtering processing to obtain a second matched filtering result;

[0197] According to the second matched filtering result and the SSS determination component, perform SSS detection to obtain a second maximum pulse position and a second time offset measurement result;

[0198] Perform frequency offset measurement according to the second maximum pulse position to obtain a frequency offset measurement result;

[0199] According to the first time offset measurement result and the second time offset measurement result, obtain a time offset measurement result.

[0200] In some embodiments, the SSS detection module 802 is further configured to:

[0201] Satisfy:

[0202] α norm = α int + α dec ;

[0203]

[0204] Condition A:

[0205] Wherein, α norm is the frequency offset measurement result, n max is the second maximum pulse position, N corr is the number of points for IFFT transformation when calculating the matched filter, N sc represents the number of subcarriers used by the synchronization signal, 0 ≤ N sc < N, N represents the number of points for FFT transformation and IFFT transformation of the OFDM system, u sss is the root sequence number of the input signal, R corr_sum () represents the cumulative sum sequence of the matched filter result.

[0206] The time-frequency synchronization device of the OFDM system based on the ZC sequence provided in this embodiment can execute the method provided in the above method embodiment, and its implementation principle and technical effect are similar, which will not be elaborated here in this embodiment.

[0207] Figure 9 This is a schematic structural diagram of an electronic device provided by this application. As Figure 9 shown, the electronic device 90 provided in this embodiment includes: at least one processor 901 and a memory 902. Optionally, the device 90 further includes a communication component 903. Among them, the processor 901, the memory 902, and the communication component 903 are connected through a bus 904.

[0208] In the specific implementation process, at least one processor 901 executes the computer-executable instructions stored in the memory 902, so that at least one processor 901 executes the above-mentioned method.

[0209] For the specific implementation process of the processor 901, reference may be made to the above method embodiments. Their implementation principles and technical effects are similar, and will not be elaborated here in this embodiment.

[0210] In the above embodiments, it should be understood that the processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), etc. The general-purpose processor may be a microprocessor or any conventional processor, etc. The steps of the method disclosed in combination with the application can be directly implemented by the execution of the hardware processor, or by a combination of hardware and software modules in the processor.

[0211] The memory may include a high-speed random access memory (RAM), and may also include non-volatile memory (NVM), such as at least one disk memory.

[0212] The bus may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. For the sake of convenience of representation, the bus in the drawings of this application is not limited to only one bus or one type of bus.

[0213] This application also provides a computer program product, including a computer program, which implements the above method when executed by a processor.

[0214] This application also provides a computer-readable storage medium, in which computer-executable instructions are stored. When the processor executes the computer-executable instructions, the above method is implemented.

[0215] The above-readable storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, a magnetic disk, or an optical disk. The readable storage medium can be any available medium accessible by a general-purpose or special-purpose computer.

[0216] An exemplary readable storage medium is coupled to the processor, enabling the processor to read information from and write information to the readable storage medium. Of course, the readable storage medium can also be a component of the processor. The processor and the readable storage medium can be located in an application specific integrated circuit (ASIC). Of course, the processor and the readable storage medium can also exist as discrete components in a device.

[0217] The division of units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces, and the indirect couplings or communication connections of devices or units can be in electrical, mechanical, or other forms.

[0218] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0219] In addition, the functional units in various embodiments of the present application can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit.

[0220] If a function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods in various embodiments of this application. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0221] Those of ordinary skill in the art can understand that all or part of the steps of implementing the above method embodiments can be completed by hardware related to program instructions. The foregoing program can be stored in a computer-readable storage medium. When this program is executed, it executes the steps including the above method embodiments; and the foregoing storage medium includes: various media such as ROMs, RAMs, magnetic disks, or optical discs that can store program codes.

[0222] The foregoing are only the preferred embodiments of this application and are not used to limit this application. For those skilled in the art, this application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. A time-frequency synchronization method for an OFDM system based on a ZC sequence, characterized in that: include: Based on the continuous time length of NT s The receiving window receives the input signal and combines each consecutive N pss_symb Perform PSS detection and first time offset measurement on the matched filtering processing result of each receiving window to obtain a first time offset measurement result; According to the first time offset measurement result, the start time of the receiving window is adjusted, and the continuous time length is NT s The receiving window receives the input signal and combines each consecutive N sss_symb The matched filtering results of the receiving windows are used for SSS detection and time deviation τ norm Measurement and frequency deviation α norm Measure and obtain the time offset measurement results and frequency offset measurement results.

2. The method for time-frequency synchronization of an OFDM system based on a ZC sequence according to claim 1, characterized in that: The input signal includes a primary synchronization signal and an auxiliary synchronization signal with an interval not less than the subcarrier interval, wherein the primary synchronization signal is N pss_symb The length is N zc The ZC sequence, the auxiliary synchronization signal is N sss_symb The length is N zc ZC sequence.

3. The method for time-frequency synchronization of an OFDM system based on a ZC sequence according to claim 2, characterized in that: The root sequence number u of the primary synchronization signal pss Fixed to 1 or N zc -1.

4. The OFDM system time-frequency synchronization method based on ZC sequence according to claim 2, characterized in that: The root sequence number u of the auxiliary synchronization signal sss Fixed to round(N zc / 5 / FO max ) or N zc -round(N zc / 5 / FO max ), where FO max Indicates the maximum absolute value of frequency deviation.

5. The method for time-frequency synchronization of an OFDM system based on a ZC sequence according to claim 1, characterized in that: The PSS detection includes: According to the input signal, the receiving end receives the time domain signal corresponding to the OFDM symbol, performs matched filtering processing, and obtains a first matched filtering result; Perform PSS detection according to the first matched filtering result and the PSS determination condition to obtain a first maximum pulse position; Updating a first maximum pulse position based on the matched filtering result; A first time offset measurement result is calculated according to the updated first maximum pulse position.

6. The method for time-frequency synchronization of an OFDM system based on a ZC sequence according to claim 1, characterized in that: The SSS detection includes: According to the input signal, the receiving end receives the time domain signal corresponding to the OFDM symbol and performs matched filtering to obtain a second matched filtering result; Perform SSS detection according to the second matched filtering result and the SSS determination element to obtain a second maximum pulse position and a second time offset measurement result; Perform frequency deviation measurement according to the second maximum pulse position to obtain a frequency deviation measurement result; A time offset measurement result is obtained according to the first time offset measurement result and the second time offset measurement result.

7. The method for time-frequency synchronization of an OFDM system based on a ZC sequence according to claim 6, characterized in that: The frequency deviation measurement is performed according to the second maximum pulse position to obtain a frequency deviation measurement result that satisfies: α norm ＝α int +α dec ； Condition A: Among them, α norm is the frequency offset measurement result, n max is the second largest pulse position, N corr is the number of points when performing IFFT transformation for calculating the matched filter, N sc represents the number of subcarriers used by the synchronization signal, 0 ≤ N sc < N, N represents the number of points for FFT transformation and IFFT transformation in the OFDM system, u sss is the root sequence number of the input signal, R corr_sum () represents the cumulative sum sequence of the matched filter result.

8. A time-frequency synchronization device for an OFDM system based on a ZC sequence, characterized in that: include: PSS detection module is used to detect the continuous time length NT s The receiving window receives the input signal and combines each consecutive N pss_symb Perform PSS detection and first time offset measurement on the matched filtering processing result of each receiving window to obtain a first time offset measurement result; The SSS detection module is used to adjust the start time of the receiving window according to the first time offset measurement result, and then adjust the start time of the receiving window based on the continuous time length NT s The receiving window receives the input signal and combines each consecutive N sss_symb The matched filtering results of the receiving windows are used for SSS detection and time deviation τ norm Measurement and frequency deviation α norm Measure and obtain the time offset measurement results and frequency offset measurement results.

9. An electronic device, characterized in that: include: Memory, processor; The memory stores computer-executable instructions; The processor executes the computer-executable instructions stored in the memory, so that the processor performs the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-executable instructions, which are used to implement the method according to any one of claims 1 to 7 when executed by a processor.

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