Preamble generation method, receiving method, system, device and medium

Abstract

The present application discloses a method for generating a preamble, a receiving method, a system, a device and a medium. The generating method includes obtaining a plurality of first short symbols and a plurality of second short symbols; the energy of the first short symbol and the second short symbol are different; the plurality of first short symbols and the plurality of second short symbols are interleaved to obtain a short training sequence; based on the short training sequence, the preamble is generated. The receiving method includes receiving the preamble, performing a cross-correlation operation on adjacent first short symbols in the plurality of first short symbols in each preamble, summing the results of all the cross-correlation operations to obtain a first value; summing the energy of all the second short symbols in the plurality of second short symbols in each preamble to obtain a second value; when the ratio of the first value to the second value is greater than a preset threshold, it is considered that the frame header of the signal is detected. The present application improves the number of OFDM transmission subcarriers, the data rate signal capture success rate, and the performance and robustness of time-frequency synchronization under low signal-to-noise ratio conditions.

Description

Technical Field

[0001] The present application relates to the field of communication technology, and in particular to a method for generating a preamble code, a method for receiving the preamble code, a system, a device and a medium. Background Art

[0002] The orthogonal frequency division multiplexing (OFDM) preamble design in the prior art is a key part to ensure that the wireless communication system can correctly receive and demodulate data, which mainly depends on the structure and function of the preamble. The OFDM preamble design in the prior art has some disadvantages:

[0003] All short preamble training sequences in the prior art are completely periodically repeated, and the feature identification is relatively simple. Although the short training sequence in the OFDM preamble can quickly achieve coarse synchronization and automatic gain control (AGC), its short length also makes it susceptible to noise interference. Noise may cause inaccurate detection of correlation peaks, thereby affecting the accuracy of synchronization.

[0004] The OFDM preamble design in the prior art is formulated for specific application scenarios and performance requirements, so it may lack sufficient flexibility when facing different communication environments and requirements. For example, in some special application scenarios, a longer training sequence may be required to improve the performance of synchronization and channel estimation, but this may not be directly achieved in the prior art. Summary of the invention

[0005] In view of the shortcomings of OFDM preamble design in the prior art, the present application provides a preamble generation method, a reception method, a system, a device and a medium.

[0006] The present application discloses a method for generating a preamble, which comprises:

[0007] Acquire a plurality of first short symbols and a plurality of second short symbols; the first short symbols and the second short symbols have different energies;

[0008] Alternately arrange a plurality of the first short symbols and a plurality of the second short symbols to obtain a short training sequence;

[0009] Based on the short training sequence, a preamble is generated.

[0010] Further, the energy of the first short symbol is greater than the energy of the second short symbol.

[0011] Further, the generating a preamble code based on the short training sequence includes:

[0012] Add a cyclic prefix to the front of the short training sequence to obtain a short preamble;

[0013] The preamble code is generated based on the short preamble header.

[0014] Further, the generating the preamble code based on the short preamble header includes:

[0015] The short preamble and the long preamble are arranged in sequence to obtain the preamble code.

[0016] Furthermore, the method for obtaining the long preamble includes:

[0017] A plurality of long training sequences are obtained, and a cyclic prefix is ​​added to the front of the plurality of long training sequences to obtain a long preamble.

[0018] Further, the acquiring of multiple long training sequences includes:

[0019] The time domain samples of a single long training sequence are repeated multiple times to form multiple consecutive long training sequences.

[0020] Furthermore, the energy of each of the first short symbols is the result of an inner product operation of each of the first short symbols and its own conjugate; the energy of each of the second short symbols is the result of an inner product operation of each of the second short symbols and its own conjugate.

[0021] The present application also discloses a method for receiving a preamble, which comprises:

[0022] receiving a preamble code, wherein the preamble code includes a short training sequence, wherein the short training sequence is composed of a plurality of first short symbols and a plurality of second short symbols arranged alternately, and the first short symbols and the second short symbols have different energies;

[0023] For each received preamble code, performing a cross-correlation operation on adjacent first short symbols among a plurality of first short symbols in each preamble code, and summing all the obtained results of the cross-correlation operation to obtain a first value;

[0024] summing the energies of all the second short symbols in the plurality of the second short symbols in each of the preamble codes to obtain a second value;

[0025] When the ratio of the first value to the second value is greater than a preset threshold, it is considered that the frame header of the signal is detected.

[0026] Furthermore, it also includes:

[0027] Performing a cross-correlation operation on adjacent second short symbols in the plurality of second short symbols in each of the preamble codes, and summing all the obtained results of the cross-correlation operation to obtain a third value;

[0028] summing the first value and the third value to obtain a fourth value;

[0029] When the fourth value takes the maximum value, it is considered that the signal has reached and matched the starting position of the signal frame.

[0030] Further, it also includes: obtaining the position determined by the coarse synchronization timing;

[0031] The obtaining of the position determined by the coarse synchronization timing comprises:

[0032] Starting from the start position of the signal frame, the sliding window is slid by the length of a single short symbol each time, and a correlation operation is performed on the signal corresponding to the sliding window before the sliding and the signal corresponding to the sliding until the sliding length is the length of a single short training sequence, and the results of the correlation operation are accumulated; the short training sequence is composed of a plurality of the first short symbols and a plurality of the second short symbols arranged alternately;

[0033] The starting position of the signal frame is moved backward by one data bit, so that the sliding window slides by the length of a single short symbol each time, and the signal corresponding to the sliding window before sliding and the signal corresponding to the sliding window after sliding are correlated until the sliding length is the length of a single short training sequence, and the results of the correlation operation are accumulated;

[0034] Until each data bit of the signal is traversed, the maximum value among all accumulated results corresponds to the position determined by the coarse synchronization timing; the size of the sliding window is the length of a single short symbol; the length of a single short symbol is the length of any short symbol in the short training sequence.

[0035] Furthermore, it also includes: coarse frequency offset estimation;

[0036] The coarse frequency offset estimation includes:

[0037] When the modulus of the maximum value among all the accumulated results is the largest, obtaining the relationship between the angle value and the coarse frequency offset estimation value;

[0038] Obtaining a range of coarse frequency offset estimation according to a relationship between the angle value and the coarse frequency offset estimation value;

[0039] A time domain coarse frequency offset compensation signal is obtained according to the range of the coarse frequency offset estimation and the time domain sample point signal before compensation.

[0040] Further, it also includes: precise timing synchronization;

[0041] The precise timing synchronization includes:

[0042] The long training sequence in the signal is subjected to conjugate cross-correlation operation with the local long training sequence respectively, and the position of the maximum value among all the cross-correlation operation results is taken as the position of precise timing synchronization.

[0043] Furthermore, it also includes: precise frequency offset estimation and residual frequency offset compensation;

[0044] The precise frequency offset estimation and residual frequency offset compensation include:

[0045] Performing cross-correlation operations on adjacent long training sequences among a plurality of long training sequences, summing up all the cross-correlation operation results, and performing phase extraction on the summation result to obtain a precise frequency offset estimation;

[0046] Perform timing adjustments, estimate residual frequency offset using consecutive OFDM symbols, and perform residual frequency offset compensation.

[0047] Furthermore, the method further includes: calculating a residual frequency offset and accumulating a residual frequency offset error.

[0048] Furthermore, it also includes:

[0049] A remaining sequence after removing the long training sequence is extracted from the signal, and the remaining sequence is re-adjusted into a matrix containing a cyclic prefix and transmission data, and a transmission data sequence without the cyclic prefix is ​​extracted from the matrix and subjected to frequency domain transformation.

[0050] Furthermore, it also includes:

[0051] The multiple long training sequences are converted into the frequency domain, and the channel estimation results of the multiple long training sequences are averaged to obtain the channel estimation result.

[0052] Furthermore, it also includes:

[0053] Using the channel estimation result, performing channel equalization on the data subcarrier to obtain an estimated value of the data subcarrier;

[0054] Perform channel equalization on the residual frequency offset using the pilot signal to obtain a residual phase offset;

[0055] Residual phase compensation is performed according to the estimated value of the data subcarrier and the residual phase offset.

[0056] The present application also discloses a preamble generation system, which comprises:

[0057] A short symbol acquisition module, configured to acquire a plurality of first short symbols and a plurality of second short symbols; the first short symbols and the second short symbols have different energies;

[0058] A short training sequence acquisition module, used for interleaving a plurality of the first short symbols and a plurality of the second short symbols to obtain a short training sequence;

[0059] The preamble generation module is used to generate a preamble based on the short training sequence.

[0060] The present application also discloses a preamble receiving system, which comprises:

[0061] A receiving module, configured to receive a preamble, wherein the preamble includes a short training sequence, wherein the short training sequence is composed of a plurality of first short symbols and a plurality of second short symbols arranged alternately, and the first short symbols and the second short symbols have different energies;

[0062] A first calculation module, configured to perform a cross-correlation operation on adjacent first short symbols among the plurality of first short symbols in each of the preamble codes, and sum all the obtained results of the cross-correlation operation to obtain a first value;

[0063] A second calculation module, configured to sum the energies of all the second short symbols in the plurality of the second short symbols in each of the preamble codes to obtain a second value;

[0064] The frame header judgment module is used to determine that a frame header of a signal is detected when the ratio of the first value to the second value is greater than a preset threshold.

[0065] The present application also discloses an electronic device, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the method for generating a preamble code described in any one of the above items is implemented, or the method for receiving a preamble code described in any one of the above items is implemented.

[0066] The present application also discloses a computer-readable storage medium, which includes a computer program or instructions. When the computer program or instructions are executed on a computer, the computer executes any of the above-mentioned methods for generating a preamble code, or implements any of the above-mentioned methods for receiving a preamble code.

[0067] Due to the adoption of the above-mentioned technical scheme, the present application has the following advantages: the preamble code structure design proposed in the present invention has good timing and energy periodicity, can achieve high-precision synchronization under low signal-to-noise ratio conditions, and can use a simple algorithm to achieve high-precision synchronization, which can effectively reduce the implementation complexity of the receiving system. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of the present application. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0069] Figure 1 A schematic diagram of a flow chart of a method for generating a preamble code according to an embodiment of the present application;

[0070] Figure 2 A schematic diagram of a flow chart of a method for designing a short preamble according to an embodiment of the present application;

[0071] Figure 3 A detailed schematic diagram of the data frame format of an embodiment of the present application;

[0072] Figure 4 This is a schematic diagram of a capture probability diagram of an embodiment of the present application in which only the existing 802.11a solution is changed to 667 subcarrier transmission;

[0073] Figure 5 A schematic diagram of the probability of successful capture of a symbol leading data frame according to an embodiment of the present application;

[0074] Figure 6 A schematic diagram of the average Doppler frequency deviation estimation error according to an embodiment of the present application;

[0075] Figure 7 A flowchart of a method for receiving a preamble code according to an embodiment of the present application is provided. DETAILED DESCRIPTION

[0076] The present application is further described in conjunction with the accompanying drawings and embodiments, and the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field should fall within the scope of protection of the embodiments of the present application.

[0077] In the process of signal reception, in order to overcome the high-speed movement of the transmitter, a large Doppler frequency shift will be generated. Figure 1 , an embodiment of the present application provides a method for generating a preamble, which includes:

[0078] A plurality of first short symbols and a plurality of second short symbols are obtained; the energy of the first short symbol and the energy of the second short symbol are different; it should be noted that the first short symbol and the second short symbol are both a sequence.

[0079] Alternately arranging a plurality of first short symbols and a plurality of second short symbols to obtain a short training sequence;

[0080] Based on the short training sequence, a preamble is generated.

[0081] The embodiment of the present application designs a short training sequence based on periodic repeatability and energy asymmetry. The embodiment of the present application introduces the energy asymmetry design of the short preamble to break the traditional single periodic repeatability feature, so that the short training sequence has additional features, which helps the receiving end to quickly and accurately identify the target signal among multiple signal sources. Figure 3 , short symbols STF1, STF3, STF5, STF7, STF9 are completely identical sequences, short symbols STF2, STF4, STF6, STF8, STF10 are completely identical sequences, and the corresponding sequence signal energies of STF1, STF3, STF5, STF7, STF9 are higher than those of STF2, STF4, STF6, STF8, STF10. Through the above design, the combination of energy asymmetry and periodic repeatability of the short training sequence is achieved. This design can make the detection algorithm at the receiving end more efficient.

[0082] In one embodiment of the present application, the energy of the first short symbol is greater than the energy of the second short symbol. The preamble sequence design in the embodiment of the present application combines the characteristics of periodicity and asymmetric structure, the first short symbol and the second short symbol are periodically repeated with one interval, and the energy of adjacent short symbols is inconsistent (the energy of the previous sequence needs to be higher than the energy of the subsequent sequence).

[0083] In one embodiment of the present application, generating a preamble based on a short training sequence includes:

[0084] Add a cyclic prefix to the front of the short training sequence to obtain a short preamble;

[0085] Generate a preamble based on the short preamble header.

[0086] The short training sequence has both periodic repeatability and energy asymmetry, and can be used for signal detection and rough frequency offset estimation. At the same time, the short preamble has a cyclic prefix (CP) to make up for the lack of robustness of existing solutions to synchronization and capture errors. The energy asymmetric structure used greatly improves the success rate of signal capture.

[0087] In one embodiment of the present application, generating a preamble code based on a short preamble header includes:

[0088] The short preamble and the long preamble are arranged in sequence to obtain a preamble code.

[0089] The embodiment of the present application adopts a dual cyclic prefix design, and cyclic prefixes are added to both the short preamble and the long preamble to improve the performance and robustness of time-frequency synchronization under low signal-to-noise ratio conditions.

[0090] Compared with the preamble design of the IEEE 802.11a protocol, the preamble code design proposed in the embodiment of the present application significantly enhances the performance and flexibility of the communication system in complex environments. In view of the shortcomings of the OFDM preamble design in the above-mentioned IEEE 802.11a protocol, the embodiment of the present application greatly increases the number of OFDM transmission subcarriers to simultaneously increase the data rate and the preamble length, thereby taking into account both the time-frequency synchronization accuracy and a certain transmission rate.

[0091] In one embodiment of the present application, a method for obtaining a long preamble includes:

[0092] A plurality of long training sequences are obtained, and cyclic prefixes are added to the front of the plurality of long training sequences to obtain a long preamble.

[0093] The embodiments of the present application are directed to the prior art (such as the 802.11a protocol), which usually only includes the design of the cyclic prefix of the data part, and generally does not insert the cyclic prefix at the short training sequence, and lacks effective robustness and coping ability for large frequency deviation and synchronization capture deviation under low signal-to-noise ratio conditions. In view of this, a dual cyclic prefix structure based on the preamble is designed, that is, an additional cyclic prefix (CP) is added to both the short preamble and the long preamble, and the periodicity of the preamble code and the cyclic prefix data structure design are combined to achieve high-precision correction of large Doppler frequency deviation and large synchronization capture deviation under low signal-to-noise ratio.

[0094] In one embodiment of the present application, obtaining multiple long training sequences includes:

[0095] The time domain samples of a single long training sequence are repeated multiple times to form multiple continuous long training sequences.

[0096] In a possible implementation of the present application, a long training sequence (LTS) is designed for symbol alignment, precise frequency offset estimation and channel estimation, specifically: the time domain sample value of a single long training sequence is repeated twice to form two consecutive long training sequences. Figure 3 As shown, each data preamble sequence HT-LTF (long preamble header) includes a cyclic prefix CP and two LTSs.

[0097] In one embodiment of the present application, obtaining a plurality of first short symbols and a plurality of second short symbols includes:

[0098] Two short sequences are randomly selected and inverse Fourier transformed to obtain a first short symbol and a second short symbol, and the first short symbol and the second short symbol are repeated multiple times to obtain multiple first short symbols and multiple second short symbols. The short sequence can be any frequency domain signal of any length.

[0099] In one embodiment of the present application, the energy of each first short symbol is the result of an inner product operation of each first short symbol and its own conjugate; the energy of each second short symbol is the result of an inner product operation of each second short symbol and its own conjugate.

[0100] In a possible implementation of the present application, see Figure 2 , generate two short sequences sq1 and sq2, and perform IFFT operations on them to obtain two short symbols sq ifft1 and sq ifft2 (short symbol sq ifft1 and sq ifft2 It can be any frequency domain signal of any length). Repeat the short symbol with higher energy among the two short symbols 5 times, and then repeat the other short symbol with lower energy 5 times, and then cross-arrange them together to form a complete short training sequence, which forms part of the preamble. The energy of the short symbol here refers to the result of the inner product operation of the short symbol and its own conjugate. Among them, the short training sequence consists of a series of short symbols, see Figure 3 Specifically, it usually consists of 10 short symbols STF1 to STF10. STF1, STF3, STF5, STF7, and STF9 are completely identical sequences. STF2, STF4, STF6, STF8, and STF10 are completely identical sequences. The corresponding energies of STF1, STF3, STF5, STF7, and STF9 are higher than the corresponding energies of STF2, STF4, STF6, STF8, and STF10. The energy inconsistency of short symbols is mainly achieved by controlling the size of the real and imaginary parts in sq1 and sq2 (for example, taking 0 elements, 1 elements, or -1 elements). Through the above design, the combination of energy asymmetry and periodic repeatability of short training sequences is achieved.

[0101] In the design of the preamble sequence, periodicity is a very important characteristic in signal design, which refers to the pattern of the signal repeating in time, which means that certain bit patterns in the sequence will repeat at certain time intervals. Periodic signals make it easier for the receiving end to find the starting point of the signal, that is, the position of the frame header. By detecting the recurring pattern, the receiving end can quickly adjust its internal clock to synchronize with the transmitting end. Based on the particularity of the frame header structure, the short symbols of odd numbers usually contain higher energy, while the short symbols of even numbers contain lower energy. This application utilizes the periodic repetition characteristics and energy asymmetry of the short preamble header, and calculates the ratio of the sum of the periodic cross-correlations of the short symbols of adjacent odd numbers to the sum of the energy of the short symbol signals of the even numbers to determine the arrival of the frame header. When the frame header arrives, the ratio will increase significantly.

[0102] By combining periodic repeatability with energy asymmetry, the preamble design not only retains the characteristics of periodic repeatability, but also enhances the uniqueness and recognition of the signal through energy asymmetry. This dual characteristic enables the receiver to accurately identify the arrival of the frame header in a shorter time and in a more complex environment, thereby significantly improving the probability of successful capture. Figure 7 , an embodiment of the present application provides a method for receiving a preamble code, which includes:

[0103] receiving a preamble code, the preamble code comprising a short training sequence, the short training sequence being composed of a plurality of first short symbols and a plurality of second short symbols arranged alternately, and the first short symbols and the second short symbols having different energies;

[0104] Performing a cross-correlation operation on adjacent first short symbols among the multiple first short symbols in each preamble code, and summing all the obtained results of the cross-correlation operation to obtain a first value;

[0105] summing the energies of all second short symbols in the plurality of second short symbols in each preamble code to obtain a second value;

[0106] When the ratio of the first value to the second value is greater than a preset threshold, it is considered that the frame header of the signal is detected.

[0107] In a possible implementation of the present application, the frame header (preamble) is captured, and the periodic cycle and asymmetry characteristics of the short header are used to calculate the ratio of the arithmetic sum of the cross-correlation of adjacent odd-numbered short symbols (STF1, STF3, STF5, STF7, STF9) and the energy sum of the even-numbered short symbols (STF2, STF4, STF6, STF8, STF10). Among them, the sum of the periodic correlation of adjacent odd-numbered short symbols is M ( n ), the total energy of the even-numbered short symbols is P ( n ), as follows:

[0108]

[0109]

[0110] here, S 1( n ) indicates a short symbol signal, N 1 is the length of a single short symbol, Used to find the conjugate of a complex number. The specific calculation formula for the energy ratio is as follows:

[0111]

[0112] When the frame header arrives, due to the special structure of the short training sequence, the arithmetic sum of the cross-correlation of the adjacent odd-numbered short symbols is significantly larger than the energy arithmetic sum of the corresponding even-numbered short symbols. NM ( n ) will increase significantly when the frame header arrives.

[0113] In the embodiment of the present application, in terms of frame header detection, when the frame header arrives, the energy sum of the short symbols (multiple first short symbols) with odd numbers will increase significantly, while the energy sum of the short symbols (multiple second short symbols) with even numbers will be lower than before. Therefore, it is possible to determine whether the frame header has arrived by estimating the corresponding energy ratio, which significantly improves the problem that the short training sequence may not be sufficient to achieve fast and stable symbol header capture in harsh environments, such as low signal-to-noise ratio or high multipath interference, and greatly improves the success rate of symbol header capture in low signal-to-noise ratio environments, ensuring the accuracy and reliability of data transmission.

[0114] In one embodiment of the present application, it also includes:

[0115] Performing a cross-correlation operation on adjacent second short symbols among the multiple second short symbols in each preamble code, and summing all the obtained results of the cross-correlation operation to obtain a third value;

[0116] The first value and the third value are summed to obtain a fourth value;

[0117] When the fourth value takes the maximum value, it is considered that the signal has reached and matched the starting position of the signal frame.

[0118] Based on the possible implementation methods mentioned above in this application, try to find the short training sequence in the signal through a loop (a loop refers to performing a correlation operation with a certain data bit as the starting position, and the starting data bit should be moved back and correlated next time). In the loop, the sum of the cross-correlation operations between the adjacent short symbols with odd numbers is calculated (for example, STF1 and STF3, STF3 and STF5 are adjacent short symbols with odd numbers), and the sum of the energy of the short symbols with even numbers is calculated. At the same time, the ratio of the above two accumulated values ​​is calculated.

[0119] In order to automatically detect the arrival of the frame header, the threshold of the above ratio can be set as .when NM ( n ) exceeds the threshold, that is, when NM ( n )> When the signal frame header arrives, it is considered that the signal frame header has arrived. After the signal frame header arrives, coarse timing synchronization is performed, as shown in the following formula:

[0120]

[0121] In order to increase the coarse timing accuracy, the coarse timing synchronization needs to sum the correlation of each segment data sequence in more cycles. Note that in order to reduce the complexity of the operation, only the cross-correlation between adjacent short symbols in odd-numbered short symbols (STF1, STF3, STF5, STF7, STF9) and the cross-correlation between adjacent short symbols in even-numbered short symbols (STF2, STF4, STF6, STF8, STF10) need to be calculated, without calculating the signal energy and the ratio. M 1( n ) reaches its maximum value when the real signal arrives and matches the starting position;

[0122] Once a starting position that satisfies the conditions is found, the loop ends and the starting index is recorded index start .

[0123] Based on the energy asymmetry and periodic repetitiveness of the short training sequence, the embodiment of the present application designs a frame header detection algorithm based on the accumulated energy ratio, which has better performance than the existing scheme through the threshold judgment of the correlation operation result of a single sequence. Figure 4 and Figure 5 By comparison, it can be seen that the present application can significantly improve the symbol capture probability under low signal-to-noise ratio conditions.

[0124] In one embodiment of the present application, it further includes: acquiring a position determined by the coarse synchronization timing;

[0125] Get the position determined by the coarse synchronization timing, including:

[0126] Starting from the start position of the signal frame, the sliding window is slid by the length of a single short symbol each time, and a correlation operation is performed on the signal corresponding to the sliding window before and after the sliding window is slid, until the sliding length is the length of a single short training sequence, and the results of the correlation operation are accumulated;

[0127] The starting position of the signal frame is moved backward by one data bit, so that the sliding window slides the length of a single short symbol each time, and the corresponding signal before the sliding window slides and the corresponding signal after the sliding window slides are correlated until the sliding length is the length of a single short training sequence, and the results of the correlation operation are accumulated;

[0128] Until each data bit of the signal is traversed, the maximum value of all accumulated results corresponds to the position determined by the coarse synchronization timing; the size of the sliding window is the length of a single short symbol; the length of a single short symbol is the length of any short symbol in the short training sequence.

[0129] Based on the possible implementation methods mentioned above in this application, the size of the sliding window is set to the length of a single short symbol in the short training sequence for subsequent correlation processing. Fix the starting position estimated by the frame header capture process, let the data window slide a single short symbol length each time, perform correlation operations on the received signal before and after each slide, and calculate the arithmetic sum to obtain the sum of the autocorrelation operations before and after the sequence at different data window sliding positions, and store its value in the array sum max Each calculation process mentioned above M 1( n ). After that, the estimated frame start position is moved back by one data bit (single short symbol length), the same data window sliding correlation and summation operation is repeated, and the new result is stored in the array sum max After repeating the above operation several times, the array sum max Therefore, the array sum max Stores the arithmetic sum of the sliding correlation of the data window at different starting estimation positions. sum max The maximum subscript index in index temp It is the position determined by the coarse synchronization timing.

[0130] In one embodiment of the present application, it further includes: coarse frequency offset estimation;

[0131] Coarse frequency offset estimation, including:

[0132] When the modulus of the maximum value among all accumulated results is the largest, the relationship between the angle value and the coarse frequency offset estimation value is obtained;

[0133] According to the relationship between the angle value and the rough frequency offset estimation value, the range of the rough frequency offset estimation is obtained;

[0134] A time domain coarse frequency offset compensation signal is obtained according to the range of coarse frequency offset estimation and the time domain sample point signal before compensation.

[0135] Based on the possible implementation methods mentioned above in this application, after the coarse timing synchronization, the coarse frequency offset estimation is performed. sum max The peak index in index temp And the corresponding forward and backward autocorrelation values, calculate the coarse frequency offset estimate FO ets1and the time interval of each sample (received signal) (the time interval of each sample in seconds), calculate the phase compensation sequence to compensate for the coarse frequency deviation. When , the above formula can be rewritten as follows:

[0136]

[0137] in, T s Indicates the sampling period. M 2( n )The moment when the modulus value is the largest is the corresponding coarse timing estimated position, as shown in the following formula:

[0138]

[0139] right M The angle at the maximum value of 2 modulus is calculated as follows:

[0140]

[0141] in, Used to calculate the phase angle of a complex number, The start position of the short training sequence determined for coarse timing synchronization.

[0142] The rough frequency deviation calculation formula can be obtained as follows:

[0143]

[0144] Since the angle estimation range is , the approximate range of the coarse frequency offset estimation can be calculated. After estimating the coarse frequency offset, the coarse frequency offset compensation in the time domain is first performed. The compensation method is as follows:

[0145]

[0146] here, It is the time domain sampling signal before compensation; the time domain sampling signal refers to the signal obtained by sampling the received signal.

[0147] In one embodiment of the present application, it also includes: precise timing synchronization;

[0148] Precise timing synchronization, including:

[0149] The long training sequence in the signal is subjected to conjugate cross-correlation operation with the local long training sequence respectively, and the position of the maximum value among all the cross-correlation operation results is taken as the position of precise timing synchronization.

[0150] Based on the possible implementation methods mentioned above in this application, after the coarse frequency offset compensation, precise timing synchronization is performed to initialize an array SumMax To store the results of the cross-correlation. Through a cycle, precise timing synchronization uses the received long preamble and the local long preamble for conjugate cross-correlation, and calculates the cross-correlation between the signal and the local long training sequence, as shown in the following formula:

[0151]

[0152] in, S 2( n ) represents the long training sequence vector, Represents the synchronization signal saved locally. Find the index of the element with the largest absolute value in the array and calculate the precise symbol timing deviation TO est When the received sequence and the sequence in the local preamble are completely aligned, a peak value of the correlation operation will appear. The peak position is the position of precise timing synchronization.

[0153] In one embodiment of the present application, it further includes: precise frequency offset estimation and residual frequency offset compensation;

[0154] Precise frequency offset estimation and residual frequency offset compensation, including:

[0155] Performing cross-correlation operations on adjacent long training sequences among the multiple long training sequences, summing up all the cross-correlation operation results, and performing phase extraction on the summation result to obtain a precise frequency offset estimation;

[0156] Perform timing adjustments, estimate residual frequency offset using consecutive OFDM symbols, and perform residual frequency offset compensation.

[0157] On the basis of the possible implementation methods mentioned above in the present application, after the precise timing is completed, at the peak timing position, the cycle characteristics of the long training sequence before and after are also used to perform precise frequency offset estimation. When the system is designed, in order to improve the frequency offset estimation accuracy under low signal-to-noise ratio, a long training sequence with 4 cycles is designed. In order to fully improve the frequency offset estimation accuracy, a long training sequence with 4 cycles is used for frequency offset estimation, as shown in the following formula:

[0158]

[0159] in, N2 is the length of a long training sequence, n max It is the starting position of the long training sequence determined by precise timing synchronization.

[0160] Afterwards, MMM Extract the phase as shown in the following formula:

[0161]

[0162] T s Refers to the duration of a data bit. Therefore, the following precise frequency deviation estimation formula can be obtained:

[0163]

[0164] To make a timing adjustment, two consecutive OFDM symbols are used (by multiplying their IFFT outputs and taking the angle) to estimate the residual frequency offset. FO ets2 , and perform residual frequency offset compensation.

[0165] The embodiments of the present application significantly increase the number of OFDM transmission subcarriers to simultaneously increase the data transmission rate and the preamble length, thereby taking into account both the data transmission rate and the synchronization performance.

[0166] In one embodiment of the present application, the method further includes: calculating a residual frequency offset and accumulating a residual frequency offset error.

[0167] In one embodiment of the present application, it also includes:

[0168] The remaining sequence after removing the long training sequence is extracted from the signal, and the remaining sequence is re-adjusted into a matrix containing a cyclic prefix and transmission data. The transmission data sequence without the cyclic prefix is ​​extracted from the matrix and subjected to frequency domain transformation (FFT transformation).

[0169] In one embodiment of the present application, it also includes:

[0170] The multiple long training sequences are converted into the frequency domain, and the channel estimation results of the multiple long training sequences are averaged to obtain the channel estimation result.

[0171] Based on the possible implementation methods mentioned above in this application, a frequency domain LS estimation (Least Squares Estimation) algorithm is performed on the long training sequence, as shown in the following formula:

[0172]

[0173] Wherein, P(k) is the frequency domain sequence of the transmitted long training sequence, Y(k) is the frequency domain sequence of the received long training sequence, and H(k) is the estimated channel.

[0174] In order to improve the accuracy of channel estimation, the channel estimation results of the four preceding and succeeding long training sequences are averaged, as shown in the following formula:

[0175]

[0176] in, represents the frequency domain signal of receiving a long training sequence, Indicates the frequency domain signal of sending a long training sequence.

[0177] In one embodiment of the present application, it also includes:

[0178] Using the channel estimation result, channel equalization is performed on the data subcarrier to obtain an estimated value of the data subcarrier;

[0179] Perform channel equalization on the residual frequency offset using the pilot signal to obtain a residual phase offset;

[0180] Residual phase compensation is performed based on the estimated value of the data subcarrier and the residual phase offset.

[0181] Based on the possible implementation methods mentioned above in the present application, the data subcarrier is firstly subjected to the first channel equalization using the above channel estimation result, as shown in the following formula, wherein: X 1( k ) is the estimated value of the data subcarrier.

[0182]

[0183] At the same time, in order to compensate for the influence of residual frequency offset, the pilot is used to perform a second channel equalization on the residual phase frequency offset, that is, phase tracking and correction, which can ensure that the demodulated signal constellation diagram remains correctly in the ideal constellation and ensure the demodulation performance. Therefore, the received signal of the pilot subcarrier can be expressed as:

[0184]

[0185] in, is the pilot signal, is the residual phase offset.

[0186] The following phase calculation formula is obtained:

[0187]

[0188] The estimated residual phase offset is used to perform a second residual phase compensation on the equalized data subcarrier, as shown in the following formula:

[0189]

[0190] in, is the residual phase offset.

[0191] The number of carriers in the embodiment of the present application can reach more than one thousand, which significantly improves the transmission speed and the length of the leading head, thereby taking into account both the transmission rate and the synchronization performance. The embodiment of the present application can be used in the transmission system of the satellite Internet of Things to achieve high-performance time-frequency synchronization and high-precision decoding under Doppler frequency deviation; the present application can also be used in the leading head design based on the DVB-S2 satellite communication system to achieve high-precision time-frequency synchronization under low signal-to-noise ratio.

[0192] The above-mentioned embodiments of the present application can be applied to OFDM systems under low signal-to-noise ratio conditions, which can improve the synchronization accuracy and efficiency of the OFDM system and reduce synchronization complexity and resource consumption.

[0193] In order to explain the present application more clearly, specific examples of the present application in practical application are provided below.

[0194] 1. Design of preamble and pilot:

[0195] The frame structure of the transmission signal used in this embodiment is composed of Figure 3 It includes a short preamble sequence HT-STF, a long preamble header HT-LTF, a sequence HT-Sig and a sequence HT-Data. Among them, the short preamble sequence HT-STF is used for the automatic gain control (AGC) setting, antenna selection and timing synchronization of the receiving end; the long preamble header HT-LTF is used for channel estimation and equalization; the sequence HT-Sig is used to transmit the signaling information of the frame indication; the sequence HT-Data is responsible for transmitting the upper layer user data.

[0196] like Figure 3 As shown, in the design of the short preamble sequence HT-STF in this embodiment, the total length of the short symbol STF is the length of a single OFDM symbol, CP is a cyclic prefix, and the lengths of STF1 to STF10 are the same and are arranged to form the short preamble sequence HT-STF.

[0197] In addition, in the design of the long preamble HT-LTF in this embodiment, CP is a cyclic prefix, and the total length of HT-LTF is the number of points of FFT (Fast Fourier Transform); the preamble is transmitted in the data subcarrier.

[0198] 2. For simulation results:

[0199] The key simulation parameters of the OFDM system are as follows:

[0200] 1. The number of FFT points is 1024, which means that in the frequency domain, each OFDM symbol has 1024 subcarriers. The total length of the short preamble is the length of one OFDM symbol, and the length of a single long preamble is also the length of an OFDM symbol. The cyclic prefix lengths of the short and long preambles are both 256.

[0201] 2. The subcarrier bandwidth is 30kHz, which means that the interval between subcarriers is 30kHz.

[0202] 3. The Doppler frequency deviation is 52 kHz, and the frequency deviation change rate is 750 Hz / s.

[0203] 4. Duration of OFDM symbols

[0204] Data portion duration = 1024 points / symbol rate = 1024 / 30.72M = 33.33us

[0205] CP2 (2 cyclic prefixes) part duration = 128 points / symbol rate = 128 / 30.72M = 4.16us

[0206] Total duration = Data duration + CP2 duration = 33.33us + 4.16us = 37.49us

[0207] 5. The actual number of subcarriers is 609, which means that out of 1024 subcarriers, only 609 subcarriers are used to transmit data and pilots.

[0208] 6. The number of pilot signals is 76, which are used for channel estimation and tracking.

[0209] 7. The number of data subcarriers is 533, the actual number of subcarriers - the number of pilots = 609-76 = 533, which is used to transmit user data.

[0210] Figure 5 It reflects the relationship between the capture probability and signal-to-noise ratio of a signal receiving system. As the SNR increases, when the SNR is -8dB, the capture probability is close to 0.2; when the SNR is -2dB, the capture probability gradually increases from a lower value to a value close to 1; when the SNR is greater than -2dB, the capture probability is 1. Figure 4 This is a capture probability diagram that only changes the existing scheme to 667 subcarrier transmission. It can be seen that the capture probability of the technical scheme proposed in this application under low signal-to-noise ratio conditions is significantly better than the existing technical scheme, and can significantly improve the symbol capture success rate under low signal-to-noise ratio conditions.

[0211] Figure 6 It reflects the trend of the average frequency offset estimation error changing with the signal-to-noise ratio. Among them, the SNR value range is from -8dB to 6dB. It can be clearly seen that with the increase of SNR, the average frequency offset estimation error shows a downward trend. This shows that under higher signal-to-noise ratio conditions, the average frequency offset estimation error is smaller. Because the noise component in the signal is reduced under high signal-to-noise ratio, the signal itself is easier to be accurately identified and processed. Therefore, the accuracy of frequency offset estimation is also improved.

[0212] Judging from the above simulation results, the preamble code structure design proposed in this application has good timing and energy periodicity, can achieve high-precision synchronization under low signal-to-noise ratio conditions, and can use simple algorithms to achieve high-precision synchronization, which can effectively reduce the implementation complexity of the receiving system.

[0213] The present application provides a system for generating a preamble, which includes:

[0214] A short symbol acquisition module, used for acquiring a plurality of first short symbols and a plurality of second short symbols; the first short symbols and the second short symbols have different energies;

[0215] A short training sequence acquisition module, used for interleaving a plurality of first short symbols and a plurality of second short symbols to obtain a short training sequence;

[0216] The preamble generation module is used to generate a preamble based on a short training sequence.

[0217] The embodiment of the present application provides a system for receiving a preamble code, which includes:

[0218] A receiving module, used for receiving a preamble, wherein the preamble includes a short training sequence, wherein the short training sequence is composed of a plurality of first short symbols and a plurality of second short symbols arranged alternately, and the energy of the first short symbol and the second short symbol is different;

[0219] A first calculation module, configured to perform a cross-correlation operation on adjacent first short symbols among a plurality of first short symbols in each preamble code, and sum all the obtained results of the cross-correlation operation to obtain a first value;

[0220] A second calculation module, configured to sum the energies of all second short symbols in the plurality of second short symbols in each preamble code to obtain a second value;

[0221] The frame header judgment module is used to determine that a frame header of a signal is detected when the ratio of the first value to the second value is greater than a preset threshold.

[0222] An embodiment of the present application provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the method for generating a preamble code described in the above embodiment is implemented, or the method for receiving a preamble code described in the above embodiment is implemented.

[0223] An embodiment of the present application provides a computer-readable storage medium, which includes a computer program or instructions. When the computer program or instructions are executed on a computer, the computer executes the method for generating a preamble code described in the above embodiment, or implements the method for receiving a preamble code described in the above embodiment.

[0224] It should be noted that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0225] Those skilled in the art should clearly understand that, for the convenience and brevity of description, the specific working processes of the preamble code generation system and the preamble code receiving system, the electronic device and the computer-readable storage medium described in the above embodiments can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0226] A person of ordinary skill in the art will appreciate that all or part of the steps to implement the above embodiments may be accomplished by hardware, or may be accomplished by instructing the relevant hardware through a program, and the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a disk, or an optical disk, etc.

[0227] The above are only optional embodiments of the present application, which are only used to illustrate the technical solution of the present application rather than to limit it. Without departing from the spirit and scope of the present application, modifications, equivalent substitutions, improvements, etc. to the specific implementation methods of the present application should all be included in the protection scope of the present application.

Claims

1. A method for generating a preamble, characterized in that: include: Acquire a plurality of first short symbols and a plurality of second short symbols; The first short symbol and the second short symbol have different energies, the energy of the first short symbol is greater than the energy of the second short symbol, the energy of each of the first short symbols is the result of an inner product operation of each of the first short symbols and its own conjugate, and the energy of each of the second short symbols is the result of an inner product operation of each of the second short symbols and its own conjugate; Alternately arrange a plurality of the first short symbols and a plurality of the second short symbols to obtain a short training sequence; Based on the short training sequence, a preamble is generated.

2. The method for generating a preamble according to claim 1, wherein: The generating a preamble code based on the short training sequence comprises: Add a cyclic prefix to the front of the short training sequence to obtain a short preamble; The preamble code is generated based on the short preamble header.

3. The method for generating a preamble according to claim 2, wherein: The generating the preamble code based on the short preamble header includes: The short preamble and the long preamble are arranged in sequence to obtain the preamble code.

4. The method for generating a preamble according to claim 3, wherein: The method for obtaining the long leading header includes: A plurality of long training sequences are obtained, and a cyclic prefix is ​​added to the front of the plurality of long training sequences to obtain a long preamble.

5. The method for generating a preamble according to claim 4, wherein: The acquiring of multiple long training sequences comprises: The time domain samples of a single long training sequence are repeated multiple times to form multiple consecutive long training sequences.

6. A method for receiving a preamble, characterized in that: include: Receive a preamble, where the preamble includes a short training sequence, where the short training sequence is composed of a plurality of first short symbols and a plurality of second short symbols arranged alternately, where the first short symbols and the second short symbols have different energies, where the energy of the first short symbol is greater than the energy of the second short symbol, where the energy of each of the first short symbols is a result of an inner product operation of each of the first short symbols and its own conjugate, and where the energy of each of the second short symbols is a result of an inner product operation of each of the second short symbols and its own conjugate; Performing a cross-correlation operation on adjacent first short symbols among the plurality of first short symbols in each of the preamble codes, and summing all the obtained results of the cross-correlation operation to obtain a first value; summing the energies of all the second short symbols in the plurality of the second short symbols in each of the preamble codes to obtain a second value; When the ratio of the first value to the second value is greater than a preset threshold, it is considered that the frame header of the signal is detected.

7. The method for receiving a preamble according to claim 6, wherein: Also includes: Performing a cross-correlation operation on adjacent second short symbols in the plurality of second short symbols in each of the preamble codes, and summing all the obtained results of the cross-correlation operation to obtain a third value; summing the first value and the third value to obtain a fourth value; When the fourth value takes the maximum value, it is considered that the signal has reached and matched the starting position of the signal frame.

8. The method for receiving a preamble according to claim 6 or 7, characterized in that: Also includes: Obtaining the position determined by the coarse synchronization timing; The obtaining of the position determined by the coarse synchronization timing comprises: Starting from the starting position of the signal frame, the sliding window is made to slide by the length of a single short symbol each time, and a correlation operation is performed on the signal before the sliding window slides and the signal after the sliding window slides, until the sliding length is the length of a single short training sequence, and the results of the correlation operation are accumulated; the starting position of the signal frame is moved backward by one data bit, and the sliding window is made to slide by the length of a single short symbol each time, and a correlation operation is performed on the signal before the sliding window slides and the signal after the sliding window slides, until the sliding length is the length of a single short training sequence, and the results of the correlation operation are accumulated; Until each data bit of the signal is traversed, the maximum value among all accumulated results corresponds to the position determined by the coarse synchronization timing; the size of the sliding window is the length of a single short symbol; The length of a single short symbol is the length of any short symbol in the short training sequence.

9. The method for receiving a preamble according to claim 8, wherein: Also includes: Coarse frequency offset estimation; The coarse frequency offset estimation comprises: When the modulus of the maximum value among all the accumulated results is the largest, obtaining the relationship between the angle value and the coarse frequency offset estimation value; Obtaining a range of coarse frequency offset estimation according to a relationship between the angle value and the coarse frequency offset estimation value; A time domain coarse frequency offset compensation signal is obtained according to the range of the coarse frequency offset estimation and the time domain sample point signal before compensation.

10. The method for receiving a preamble according to claim 6 or 7, characterized in that: Also includes: Precise timing synchronization; The precise timing synchronization includes: The long training sequence in the signal is subjected to conjugate cross-correlation operation with the local long training sequence respectively, and the position of the maximum value among all the cross-correlation operation results is taken as the position of precise timing synchronization.

11. The method for receiving a preamble according to claim 6 or 7, characterized in that: Also includes: Precise frequency offset estimation and residual frequency offset compensation; The precise frequency offset estimation and residual frequency offset compensation include: Performing cross-correlation operations on adjacent long training sequences among a plurality of long training sequences, summing up all the cross-correlation operation results, and performing phase extraction on the summation result to obtain a precise frequency offset estimation; Perform timing adjustments, estimate residual frequency offset using consecutive OFDM symbols, and perform residual frequency offset compensation.

12. The method for receiving a preamble according to claim 6 or 7, characterized in that: Also includes: Calculate the residual frequency offset and accumulate the residual frequency offset error.

13. The method for receiving a preamble according to claim 6 or 7, characterized in that: Also includes: A remaining sequence after removing the long training sequence is extracted from the signal, and the remaining sequence is re-adjusted into a matrix containing a cyclic prefix and transmission data, and a transmission data sequence without the cyclic prefix is ​​extracted from the matrix and subjected to frequency domain transformation.

14. The method for receiving a preamble according to claim 6 or 7, characterized in that: Also includes: The multiple long training sequences are converted into the frequency domain, and the channel estimation results of the multiple long training sequences are averaged to obtain the channel estimation result.

15. The method for receiving a preamble according to claim 14, characterized in that: Also includes: Using the channel estimation result, performing channel equalization on the data subcarrier to obtain an estimated value of the data subcarrier; Perform channel equalization on the residual frequency offset using the pilot signal to obtain a residual phase offset; Residual phase compensation is performed according to the estimated value of the data subcarrier and the residual phase offset.

16. A system for generating a preamble, characterized in that: include: A short symbol acquisition module, used to acquire a plurality of first short symbols and a plurality of second short symbols; The first short symbol and the second short symbol have different energies, the energy of the first short symbol is greater than the energy of the second short symbol, the energy of each of the first short symbols is the result of an inner product operation of each of the first short symbols and its own conjugate, and the energy of each of the second short symbols is the result of an inner product operation of each of the second short symbols and its own conjugate; A short training sequence acquisition module, used for interleaving a plurality of the first short symbols and a plurality of the second short symbols to obtain a short training sequence; The preamble generation module is used to generate a preamble based on the short training sequence.

17. A preamble receiving system, characterized in that: include: a receiving module, configured to receive a preamble, wherein the preamble includes a short training sequence, wherein the short training sequence is composed of a plurality of first short symbols and a plurality of second short symbols arranged alternately, wherein the first short symbols and the second short symbols have different energies, wherein the energy of the first short symbol is greater than the energy of the second short symbol, wherein the energy of each of the first short symbols is a result of an inner product operation of each of the first short symbols and its own conjugate, and the energy of each of the second short symbols is a result of an inner product operation of each of the second short symbols and its own conjugate; A first calculation module, configured to perform a cross-correlation operation on adjacent first short symbols among the plurality of first short symbols in each of the preamble codes, and sum all the obtained results of the cross-correlation operation to obtain a first value; A second calculation module, configured to sum the energies of all the second short symbols in the plurality of the second short symbols in each of the preamble codes to obtain a second value; The frame header judgment module is used to determine that a frame header of a signal is detected when the ratio of the first value to the second value is greater than a preset threshold.

18. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the computer program is executed by the processor, the method for generating a preamble according to any one of claims 1 to 5 is implemented, or the method for receiving a preamble according to any one of claims 6 to 15 is implemented.

19. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a computer program or instructions, and when the computer program or instructions are executed on a computer, the computer executes the method for generating a preamble code according to any one of claims 1 to 5, or implements the method for receiving a preamble code according to any one of claims 6 to 15.

Images