OFDM packet detection control method and system for delay correlation and length maintenance

Abstract

The invention discloses an OFDM (Orthogonal Frequency Division Multiplexing) packet detection control method and system with delay correlation and length maintenance, and relates to the technical field of secure communication, and the method comprises the following steps: a receiving end caches an input signal and extracts current receiving data and delay receiving data; calculating a delay correlation value of the current receiving data and the delay receiving data; calculating a signal energy value of the received data in the delay window period; normalizing the ratio of the delay correlation value to the signal energy value; and when the judgment variable is greater than the detection condition of the preset threshold value, and it is verified that the judgment variable continuously meets the condition that the duration reaches the preset length threshold value, OFDM grouping detection is carried out. The technical problems that in the prior art, under the complex channel environment, OFDM grouping detection precision is low, the anti-interference capacity is weak, and the communication link safety is poor due to the fact that grouping detection faces misjudge multipath interference are solved, and the technical effect of improving the anti-interference capacity of grouping detection and the stability of safety communication is achieved.

Description

Technical Field

[0001] The present application relates to the technical field related to packet detection control, and in particular to an OFDM packet detection control method and system with delay correlation and length retention. Background Art

[0002] Orthogonal frequency division multiplexing (OFDM) technology, at the core of modern communications, splits high-speed data streams into multiple parallel, lower-speed sub-data streams, which are transmitted simultaneously via multiple orthogonal subcarriers, significantly improving transmission performance. However, in actual communication environments, OFDM struggles to cope with complex channel conditions, such as multipath propagation, noise interference, and frequency offset. These problems can cause signal distortion and delay during transmission, which in turn affects the receiver's ability to accurately detect OFDM packets. Existing OFDM packet detection is primarily based on sliding window energy detection, cyclic prefix (CP), or preamble sequences. However, in complex channel environments, detection suffers from low detection accuracy and weak anti-interference capabilities. For example, in a multipath channel, signals from different paths arrive at the receiver at different times, disrupting the periodicity of the preamble sequence and making it difficult for cyclic prefix-based detection to accurately determine the starting position of the packet. In the presence of noise interference, traditional methods are prone to misjudgment, reducing the accuracy and reliability of data transmission.

[0003] Therefore, in the current related technologies, there are technical problems such as low OFDM packet detection accuracy, weak anti-interference ability, and misjudgment of packet detection in the face of multipath interference in complex channel environments, resulting in poor security of the communication link. Summary of the Invention

[0004] The present application solves the technical problems in the prior art of low OFDM packet detection accuracy, weak anti-interference capability, and misjudgment of packet detection in the face of multipath interference, which leads to poor security of the communication link, by providing an OFDM packet detection control method and system with delay correlation and length retention. The method achieves the technical effect of improving the anti-interference capability of packet detection and the stability of secure communication.

[0005] The present application provides an OFDM packet detection control method with delay correlation and length retention, the method comprising: a receiving end caching an input signal and extracting current received data and delayed received data, the input signal comprising a periodic preamble structure; calculating a delay correlation value between the current received data and the delayed received data according to the periodic preamble structure; calculating a signal energy value of the received data within a delay window period between the current received data and the delayed received data; obtaining a decision variable by normalizing the ratio of the delay correlation value to the signal energy value; triggering a preliminary detection when the decision variable is greater than a detection condition of a preset threshold, verifying that the duration for which the decision variable continuously satisfies the detection condition reaches a preset length threshold, confirming that the group starting position has been reached, and performing OFDM packet detection, wherein the preset length threshold comprises one or more lengths.

[0006] In a possible implementation, the delay-correlated and length-maintained OFDM packet detection control method further performs the following processing: designing a periodic preamble structure, wherein the periodic preamble structure is a periodic structure formed by N segments of the same short training sequence, where N is a positive integer; adding the periodic preamble structure to the front end of the OFDM packet signal and sending it to the receiving end through the transmitting end.

[0007] In a possible implementation, the delay correlation plus length preservation OFDM packet detection control method further performs the following processing: the short training sequence is an identical short training sequence with a length of 16.

[0008] In a possible implementation, the delay-correlation plus length-preservation OFDM packet detection control method further performs the following processing: obtaining L currently received data and L data received D times ago based on the short training sequence length L of the periodic preamble structure; and using the delay-correlation formula: , calculate the cross-correlation between the L data currently received and the L data received D times ago, and obtain the delayed correlation value, Indicates that the signal is received at the current moment n With delay D similarity.

[0009] In a possible implementation, the delay-correlated and length-maintained OFDM packet detection control method further performs the following processing: using the formula: , calculate and obtain the decision variable, where, is the decision variable, is the delay-related value, is the signal energy value.

[0010] In a possible implementation, the delay-related and length-retained OFDM packet detection control method further performs the following processing: configuring a two-stage shift register, the two-stage shift register including a first-length shift register and a second-length shift register, wherein the first length is smaller than the second length; when the receiving end receives the input signal, the input signal is stored in a cache module, the input signal is stored bit by bit through the first-length shift register, and shifted step by step according to the first length to realize a first-length delay cache; based on the cache processing of the first-length shift register, the signal data is subjected to a second-length shift processing through the second-length shift register to obtain another set of signal data having a second-length time interval with the current data.

[0011] In a possible implementation, the delay correlation plus length maintenance OFDM packet detection control method also performs the following processing: setting the first length and the second length of the short training sequence, the first length is smaller than the second length; using the periodic preamble structure of the first length and the second length respectively to calculate the first delay correlation value and the second delay correlation value; calculating the energy of the first delay correlation value and the second delay correlation value respectively, and setting the correlation energy threshold of the first delay and the correlation energy threshold of the second delay; when the first delay correlation energy exceeds the correlation energy threshold of the first delay and the second delay correlation energy exceeds the correlation energy threshold of the second delay, it is determined that the packet starts.

[0012] In a possible implementation, the delay correlation plus length-maintained OFDM packet detection control method further performs the following processing: calculating the conjugate product of the current received data and the delayed received data; summing the conjugate product results of the continuous data during the delay window to calculate the window accumulation result; taking the absolute values of the real part and the imaginary part of the window accumulation result respectively and adding them to obtain the delay correlation value.

[0013] In a possible implementation, the delay-correlated and length-maintained OFDM packet detection control method further performs the following processing: calculating the static noise power spectrum density and change rate at the receiving end; updating the background noise estimate using recursive least mean square based on the noise power spectrum density and change rate; and dynamically adjusting and setting the decision variable threshold using the exponential decay law based on the trend of the estimated value change.

[0014] The present application also provides an OFDM packet detection and control system with delay correlation and length retention, the system comprising: an input signal buffer unit, for caching the input signal at the receiving end and extracting the current received data and the delayed received data, the input signal comprising a periodic preamble structure; a delay correlation value calculation unit, for calculating the delay correlation value of the current received data and the delayed received data according to the periodic preamble structure; a signal energy value calculation unit, for calculating the signal energy value of the received data within the delay window period of the current received data and the delayed received data; a decision variable acquisition unit, for obtaining the decision variable by normalizing the ratio of the delay correlation value to the signal energy value; and a packet detection unit, for triggering preliminary detection when the decision variable is greater than the detection condition of a preset threshold, and verifying that the duration for which the decision variable continuously meets the detection condition reaches a preset length threshold, confirming that the packet starting position has been reached, and performing OFDM packet detection.

[0015] The OFDM packet detection control method and system proposed in this application with delay correlation plus length retention is designed to cache the input signal at the receiving end and extract the current received data and the delayed received data; calculate the delay correlation value between the current received data and the delayed received data; calculate the signal energy value of the received data during the delay window; perform normalization processing by the ratio of the delay correlation value to the signal energy value; when the decision variable is greater than the detection condition of the preset threshold, verify that the decision variable continuously meets the detection condition for a duration that reaches the preset length threshold, confirm that the packet starting position has been reached, and perform OFDM packet detection. This solves the technical problems existing in the prior art of low OFDM packet detection accuracy, weak anti-interference ability, and misjudgment of packet detection in the face of multipath interference in complex channel environments, resulting in poor communication link security, and achieves the technical effect of improving the anti-interference ability of packet detection and the stability of secure communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the accompanying drawings of the embodiments of the present disclosure are briefly introduced below. Flowcharts are used in this application to illustrate the operations performed by the systems according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed in precise order. Instead, various steps may be processed in reverse order or simultaneously as needed. Furthermore, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0017] Figure 1 A flowchart of the delay-correlated and length-preserving OFDM packet detection control method provided in an embodiment of the present application.

[0018] Figure 2 Schematic diagram of the structure of the OFDM packet detection control system with delay correlation and length retention provided in an embodiment of the present application.

[0019] Description of the reference numerals: input signal buffer unit 10 , delay correlation value calculation unit 20 , signal energy value calculation unit 30 , decision variable acquisition unit 40 , group detection unit 50 . DETAILED DESCRIPTION

[0020] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below.

[0021] In order to make the purpose, technical solutions and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limiting this application. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0022] In the following description, reference is made to “some embodiments”, which describes a subset of all possible embodiments, but it will be understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict, and the terms “first\second” involved are merely used to distinguish similar objects and do not represent a specific ordering of the objects. The terms “including” and “having” and any variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or modules that are not clearly listed or that are inherent to these processes, methods, products or devices. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used herein are for the purpose of describing the embodiments of this application only.

[0023] The embodiment of the present application provides a delay-correlated and length-maintained OFDM packet detection control method, such as Figure 1 As shown, the method includes: In step S100 , the receiving end buffers an input signal and extracts currently received data and delayed received data, wherein the input signal includes a periodic preamble structure.

[0024] Step S100 further includes that the short training sequence is an identical short training sequence with a length of 16.

[0025] Preferably, the receiving end caches the input signal, that is, the input signal is temporarily stored in a temporary storage area, and delayed processing of the data is achieved through a two-stage shift register, wherein the input signal includes a periodic preamble structure, that is, from T1 to T10, they are all short training sequences of length 16, and the 16 short training sequences are exactly the same. The preamble structure is a pre-designed special signal sequence, usually located at the beginning of the OFDM packet signal, providing the receiving end with synchronization information, channel estimation information, etc., so that the receiving end can better perform data decoding of the input signal. The periodic preamble structure indicates that the preamble sequence appears repeatedly. For example, a preamble sequence of length N is repeated once every certain time interval T.

[0026] Preferably, the shift register is a digital circuit composed of multiple triggers connected in series, and is composed of multiple triggers cascaded. In each clock cycle, the data in the register will shift one position to the right or left in turn, new data will be input from one end, and the oldest data will be output from the other end. Among them, the latest input data of the shift register is the currently received data, which is extracted by connecting the input port of the shift register; for example, a shift register with a length of 16 will delay the input data by 16 levels, that is, when the 16th clock cycle arrives, the data originally input into the shift register will be moved to the output end of the register, and then the data is obtained by connecting the output end of the shift register, which is the data after 16 levels of delay, that is, delayed received data.

[0027] Furthermore, step S100 also includes step S101, designing a periodic preamble structure, wherein the periodic preamble structure is a periodic structure formed by N segments of the same short training sequence, where N is a positive integer; and step S102, adding the periodic preamble structure to the front end of the OFDM packet signal and sending it to the receiving end through the transmitting end.

[0028] Preferably, a periodic preamble structure is designed, which consists of N identical short training sequences, where N is a positive integer, so that the preamble structure is repeated periodically in time. For example, when N=3, the preamble structure is composed of three identical short training sequences arranged in sequence. The short training sequences may be used for coarse synchronization and channel estimation. Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation technology used to split a high-speed data stream into multiple parallel low-speed sub-data streams. Each sub-data stream is modulated onto mutually orthogonal sub-carriers for transmission. A periodic preamble structure is added to the front end of the OFDM packet signal, that is, the periodic preamble structure and the OFDM packet signal are spliced together. For example, the digital sequence of the preamble structure and the digital sequence of the OFDM packet signal are stored in a buffer in sequence and then converted into analog signals through a digital-to-analog converter (DAC); the receiver can determine whether a new OFDM packet has arrived by detecting the periodic characteristics of the periodic preamble structure. The preamble structure can be used to achieve time and frequency synchronization between the receiver and the transmitter; the receiver can use the information in the preamble structure to estimate channel fading, noise, etc. Finally, the transmitter processes the OFDM packet signal with a periodic preamble structure, including modulation (such as QPSK, 16QAM, etc.), coding (such as convolutional coding, Turbo coding, etc.), up-conversion, etc., and then sends it to the receiver, where it performs down-conversion, demodulation, decoding and other operations to restore the signal to a digital sequence.

[0029] Furthermore, step S100 also includes step S110, configuring a two-stage shift register, the two-stage shift register including a first-length shift register and a second-length shift register, wherein the first length is smaller than the second length; step S120, when the receiving end receives the input signal, the input signal is stored in the cache module, the input signal is stored bit by bit through the first-length shift register, and the signal is shifted step by step according to the first length to realize a first-length delay cache; step S130, based on the cache processing of the first-length shift register, the signal data is shifted by the second-length shift register to obtain another set of signal data with a second-length time interval with the current data.

[0030] Preferably, a two-stage shift register is configured, including a first-length shift register and a second-length shift register, wherein the length of the first-length shift register is relatively short, denoted as , used to perform preliminary delay buffering processing on the input signal, the length of the second length shift register is recorded as , and the first length Less than the second length , further signal delay shift is performed based on the processing result of the first length shift register; after the receiving end receives the input signal, it is stored in the cache module, and the input signal is stored bit by bit through the first length shift register. Specifically, every time a clock pulse comes, the data in the register shifts one bit to the right (or left), and the new input signal data enters from one end and is shifted according to the first length. Shift step by step, when passing After a clock cycle, the first length delay buffer of the input signal is realized. For example, if =16, then after 16 clock cycles, the data initially entering the register will be moved to the other end of the register, and the output data at this time is the signal data after 16 levels of delay.

[0031] Preferably, after the first length shift register completes the first length delay buffer, the signal data enters the second length shift register, which also works under the control of the clock signal and performs a shift operation (bit by bit storage) on the signal data that has passed through the first length delay buffer. After a clock cycle, the second length of the current data is obtained. Another set of signal data at time intervals, for example, if =32, the data output from the second-length shift register is the signal data after 32 levels of delay relative to the current input data. The delayed data generated by shift registers of different lengths can then be used to synchronize signals. By comparing the current data with data of different delays, the starting position of the signal, symbol boundaries, and other information can be determined, thereby achieving synchronization between the receiving and transmitting ends.

[0032] Step S200: Calculate the delay correlation value between the current received data and the delayed received data according to the periodic preamble structure.

[0033] Step S200 further includes step S210, obtaining the currently received L data and the L data received D times ago according to the short training sequence length L of the periodic preamble structure; step S220, using the delay correlation formula: , calculate the cross-correlation between the L data currently received and the L data received D times ago, and obtain the delayed correlation value, Indicates that the signal is received at the current moment n With delay D similarity.

[0034] Preferably, the periodic preamble structure is composed of multiple identical short training sequences, so that the signals containing the preamble structure received at different times have similarity, and the short training sequence is a signal sequence with a specific length L. By calculating the correlation between the current received data and the data received after a delay, the periodic characteristics can be captured, thereby determining whether the preamble structure of the OFDM packet is received, and then determining the starting position of the packet. Specifically, after receiving the input signal, the receiving end caches the signal, and according to the length L of the short training sequence, the receiving end obtains L consecutive data received at the current time, which is recorded as [ ,…, ], n represents the current moment, and simultaneously obtains L consecutive data received before D moments, recorded as [ ,…, ], D represents the delay duration; then according to the delay-related formula: , calculate the cross-correlation between the L data currently received and the L data received D times ago, and obtain the delayed correlation value, where, Indicates that the signal is received at the current moment n With delay D The delay-related value of is the n-kth data received at the current moment, It is the complex conjugate of the n-k-Dth data received D times ago. The communication signal is usually in complex form. Taking the complex conjugate makes it easier to consider the phase information of the signal when calculating the correlation. It reflects the similarity between the signal received at the current time n and the signal received at the delayed time D.

[0035] Furthermore, step S200 also includes step S210, calculating the conjugate product of the current received data and the delayed received data; step S220, summing the conjugate product results of the continuous data during the delay window and calculating the window accumulation result; step S230, taking the absolute values of the real part and the imaginary part of the window accumulation result respectively and adding them to obtain the delay related value.

[0036] Preferably, the current received data and the delayed received data are recorded as DataA and DataB respectively, and DataB is DataA after being delayed by 16 time units. The data are output synchronously through the shift register to ensure that the time of DataA and DataB corresponds. DataA and DataB are both complex data, including real and imaginary parts. Assume that DataA is represented by (in, is the real part, is the imaginary part), DataB is expressed as (in, is the real part, is the imaginary part), using 4 multipliers for parallel calculation 、 、 and Four products, according to the operation rules of complex number multiplication , combine the four products calculated into the real part of the complex number and the imaginary part , take the absolute value of the complex multiplication results for 16 consecutive times and accumulate them to obtain the final result of the delay correlation value. Each time, the similarity score of a pair of signals is calculated, and the total score of 16 consecutive similarities is counted. The higher the total score, the stronger the periodicity of the signal.

[0037] Step S300 , calculating the signal energy value of the data received during the delay window period between the current received data and the delayed received data.

[0038] Preferably, the delay window refers to the time interval from the delay moment to the current moment of receiving data based on the current receiving moment. For example, if the delay is D sampling cycles and the current moment is n, the delay window is the time period from n-D to n. Then, according to the current moment n, the delay D and the calculated length L, the signal data is determined from the received signal buffer, that is, [ ,…, ], and then calculate the signal energy through the formula: , calculate the signal energy value of the data received during the delay window between the current received data and the delayed received data, where the signal energy value Reflects the signal strength, that is, the signal energy value of the received data during the delay window. For discrete-time signals, it is the cumulative sum of the squares of the signal sample amplitudes, indicating the energy carried by the signal during the delay window. represents the signal value received at time n−k−D, where k is the index value within a calculation range of length L, ranging from 0 to L−1. When a complex number is multiplied by its complex conjugate, the square of the modulus (amplitude) of the complex number is calculated, that is, ; By calculating the signal energy value, it can be determined whether a signal has arrived. That is, when the received signal energy exceeds the threshold, it indicates that there may be a valid signal reaching the receiving end.

[0039] Step S400 , obtaining a decision variable by normalizing the ratio of the delay correlation value to the signal energy value.

[0040] Step S400 further includes, by formula: , calculate and obtain the decision variable, where, is the decision variable, is the delay-related value, is the signal energy value.

[0041] Preferably, the delay-related value and signal energy value The numerical range and magnitude of the delay correlation value vary greatly, so normalization is performed on it. That is, by calculating the ratio of the delay correlation value to the signal energy value (i.e., Cn / Pn), it is converted to a relatively unified scale to eliminate the dimensional difference between the delay correlation value and the signal energy value. At the same time, it reduces the interference of different channel conditions, transmit power, etc. on the decision variable, and improves the stability and reliability of detection. Then, through the formula: , calculate the decision variable, that is, first take the absolute value of the delay correlation value , and then divided by the signal energy value , get the decision variable , where the decision variable combines the correlation and energy information of the signal. When the received signal contains a periodic preamble structure, the delay correlation value Larger, calculated decision variable is relatively large, and when there is no leading structure or the signal is weak, the decision variable is smaller, and is used to determine whether an OFDM packet signal is received.

[0042] Step S500, when the decision variable is greater than the detection condition of the preset threshold, a preliminary detection is triggered, and when it is verified that the duration for which the decision variable continuously meets the detection condition reaches the preset length threshold, it is confirmed that the starting position of the group has been reached, and OFDM group detection is performed, wherein the preset length threshold includes one or more lengths.

[0043] Preferably, the preset threshold is a reference value set according to actual needs. When the decision variable is greater than the detection condition of the preset threshold, it means that the received signal meets the group detection condition in terms of correlation and energy. Specifically, when the leading structure of the OFDM packet arrives, the periodicity of the signal will increase the delay correlation value, and the signal energy is also at an appropriate level, causing the decision variable to exceed the preset threshold, at which time the preliminary detection is triggered; then verify whether the duration of the decision variable continuously meeting the detection condition (the decision variable is greater than the preset threshold) reaches the preset length threshold, because there may be noise interference that causes the decision variable to accidentally exceed the threshold, and once the decision variable Being greater than a preset threshold is not sufficient to confirm that the starting position of the packet has been reached, where the preset length threshold is a pre-set time length. When the duration for which the decision variable is continuously greater than the preset threshold reaches the preset length threshold, it is confirmed that the preamble structure of the OFDM packet has been received, that is, the starting position of the packet has been reached; the receiving end then performs OFDM packet detection, including using information such as the short training sequence in the preamble structure to achieve time synchronization and frequency synchronization between the receiving end and the transmitting end, and ensure accurate sampling and demodulation of OFDM; based on the signal characteristics of the preamble structure, the channel fading, noise, etc. are estimated in order to make corresponding compensation and adjustments.

[0044] Preferably, the preset length threshold includes one or more lengths. Specifically, a dual-length training sequence (e.g., length 16+32) forms a composite signal signature whose combined pattern (e.g., timing relationship and energy distribution) is unique and difficult for malicious parties to fully imitate. Furthermore, the transmitter can dynamically switch the combined pattern of the dual-length sequence (e.g., 16+32, 24+48), which the receiver verifies using preset rules to form a lightweight physical layer key. The introduction of composite signal signatures and dynamic pattern switching significantly enhances defenses against malicious imitation sequences. For example, the difficulty of counterfeiting is doubled (requiring simultaneous cracking of the timing and energy characteristics of the dual sequences), a dynamic key mechanism (the combined pattern can be dynamically updated to resist replay attacks), and a foundation for defense in depth (cooperating with upper layers to build a multi-layered security system). Finally, the data portion of the OFDM packet is demodulated and decoded to recover the original data sent by the transmitter.

[0045] Furthermore, step S500 also includes step S501, calculating the static noise power spectrum density and change rate of the receiving end; step S502, using recursive least mean square to update the background noise estimation value based on the noise power spectrum density and change rate; step S503, dynamically adjusting and setting the decision variable threshold using the exponential decay law based on the change trend of the estimation value.

[0046] Preferably, when there is no useful signal input at the receiving end (for example, in an idle time slot of a communication system), a spectrum analysis is performed on the received signal, and a power spectrum density estimate of the noise is obtained by performing a fast Fourier transform on noise samples over a period of time and calculating the power mean at each frequency. The noise power spectrum density calculated in adjacent time periods is compared to obtain its rate of change. For example, the difference or ratio of the power spectrum density at the current moment to the power spectrum density at the previous moment is calculated as a rate of change indicator to reflect the dynamic characteristics of the noise environment, such as burst noise or slowly changing interference. The recursive least mean square method updates the filter coefficients by minimizing the sum of squares of prediction errors. Specifically, the current received signal is decomposed into useful signal and noise, and then the mean square error between the estimated noise and the actual noise is minimized by continuously adjusting the estimator parameters. The initial noise estimate and the estimation error covariance matrix are set. For each new received sample, the gain vector and prediction error are calculated, and the noise estimate and covariance matrix are updated. Finally, according to the changing trend of the noise estimate, the decision variable threshold is dynamically adjusted using an exponential decay function. When the noise estimate increases, the threshold is correspondingly increased to reduce false detection; when the noise estimate decreases, the threshold is lowered to improve detection sensitivity, thereby triggering group detection to adaptively adapt to different noise environments, thereby more flexibly adapting to signal detection requirements under different noise intensities, and improving the reliability and stability of group detection.

[0047] Furthermore, step S500 also includes step S510, setting a first length and a second length of the short training sequence, where the first length is smaller than the second length; step S520, respectively using the periodic leading structure of the first length and the second length to calculate the first delay correlation value and the second delay correlation value; step S530, respectively calculating the energy of the first delay correlation value and the second delay correlation value, and setting the correlation energy threshold of the first delay and the correlation energy threshold of the second delay; step S540, when the first delay correlation energy exceeds the correlation energy threshold of the first delay and the second delay correlation energy exceeds the correlation energy threshold of the second delay, determining that the group starts.

[0048] Preferably, the first length and the second length of the short training sequence are set, and the first length is smaller than the second length. Assuming that the first length =16, second length =32, the length used is =16 short training sequence, calculate the 16 data currently received and The short-delay correlation value (the first delayed correlation value) is obtained by cross-correlating the 16 data received before the moment; the length is =32 long training sequence, calculate the 32 data currently received and The long delay correlation value (second delay correlation value) is obtained by cross-correlating the 32 data received before the moment; the first delay correlation value (short delay correlation value) and the second delay correlation value (long delay correlation value) are then processed respectively, that is, the square root of the square sum is taken to obtain the corresponding energy value, that is, the first delay correlation energy and the second time-delay related energy , which reflects the energy carried by the correlation value signal; then the correlation energy threshold of the first delay is set according to the actual performance requirements (short delay correlation energy threshold), second delay correlation energy threshold (Long delay correlation energy threshold), and then the first delay correlation energy and the second time-delay related energy , respectively, with the first delay-related energy threshold and the second time-delay related energy threshold When the first delay correlation energy at a certain position is compared , the second delay correlation energy ,at this time, > and > , that is, when the leading structure of the OFDM packet arrives, the periodicity of the signal will increase the energy of the correlation value under different delays, exceeding the preset threshold, and then triggering the packet start judgment. If the current position is 1000, the delay 、 , then the starting position of the group is 1000-32=968, that is, the delay time corresponding to the second length is pushed forward from the trigger judgment position to obtain the actual starting position of the group.

[0049] In the above, refer to Figure 1 The OFDM packet detection control method according to the embodiment of the present invention is described in detail. Figure 2 The OFDM packet detection and control system with delay correlation and length preservation according to an embodiment of the present invention is described.

[0050] The OFDM packet detection and control system with delay correlation and length retention according to the embodiment of the present invention is used to solve the technical problems existing in the prior art of low OFDM packet detection accuracy, weak anti-interference capability, and misjudgment of packet detection in the face of multipath interference in complex channel environments, resulting in poor communication link security, thereby achieving the technical effect of improving the anti-interference capability of packet detection and the stability of secure communications. Figure 2 As shown, the delay correlation plus length retention OFDM packet detection and control system includes: an input signal buffer unit 10, a delay correlation value calculation unit 20, a signal energy value calculation unit 30, a decision variable acquisition unit 40, and a packet detection unit 50.

[0051] An input signal buffer unit 10 is used for caching the input signal at the receiving end and extracting the current received data and the delayed received data, wherein the input signal includes a periodic preamble structure; a delay correlation value calculation unit 20 is used for calculating the delay correlation value of the current received data and the delayed received data based on the periodic preamble structure; a signal energy value calculation unit 30 is used for calculating the signal energy value of the received data within the delay window period of the current received data and the delayed received data; a decision variable acquisition unit 40 is used for obtaining the decision variable by normalizing the ratio of the delay correlation value to the signal energy value; a packet detection unit 50 is used for triggering preliminary detection when the decision variable is greater than the detection condition of a preset threshold, and verifying that the duration for which the decision variable continuously meets the detection condition reaches a preset length threshold, confirming that the group starting position has been reached, and performing OFDM packet detection, wherein the preset length threshold includes one or more lengths.

[0052] The specific configuration of the input signal buffer unit 10 will be described in detail below. The input signal buffer unit 10 further includes: designing a periodic preamble structure, wherein the periodic preamble structure is a periodic structure formed by N segments of the same short training sequence, where N is a positive integer; adding the periodic preamble structure to the front end of the OFDM packet signal, and transmitting it from the transmitting end to the receiving end.

[0053] The specific configuration of the input signal buffer unit 10 will be described in detail below. The input signal buffer unit 10 further includes: the short training sequence is an identical short training sequence with a length of 16.

[0054] The specific configuration of the delay correlation value calculation unit 20 will be described in detail below. The delay correlation value calculation unit 20 further includes: obtaining the currently received L data and the L data received D times ago according to the short training sequence length L of the periodic preamble structure; using the delay correlation formula: , calculate the cross-correlation between the L data currently received and the L data received D times ago, and obtain the delayed correlation value, Indicates that the signal is received at the current moment n With delay D similarity.

[0055] The specific configuration of the decision variable obtaining unit 40 will be described in detail below. The decision variable obtaining unit 40 further includes: , calculate and obtain the decision variable, where, is the decision variable, is the delay-related value, is the signal energy value.

[0056] The specific configuration of the input signal buffer unit 10 will be described in detail below. The input signal buffer unit 10 further includes: configuring a two-stage shift register, the two-stage shift register including a first-length shift register and a second-length shift register, wherein the first length is less than the second length; when the receiving end receives the input signal, the input signal is stored in the buffer module, and the input signal is stored bit by bit through the first-length shift register, and shifted stage by stage according to the first length to achieve a first-length delay buffer; based on the buffering processing of the first-length shift register, the signal data is shifted by a second length through the second-length shift register to obtain another set of signal data with a second-length time interval from the current data.

[0057] The specific configuration of the packet detection unit 50 will be described in detail below. The packet detection unit 50 further includes: setting a first length and a second length of the short training sequence, wherein the first length is smaller than the second length; A first delay correlation value and a second delay correlation value are calculated using periodic preamble structures of a first length and a second length respectively; the energy of the first delay correlation value and the second delay correlation value are calculated respectively, and a first delay correlation energy threshold and a second delay correlation energy threshold are set; when the first delay correlation energy exceeds the first delay correlation energy threshold and the second delay correlation energy exceeds the second delay correlation energy threshold, the group start is determined.

[0058] The specific configuration of the delay correlation value calculation unit 20 will be described in detail below. The delay correlation value calculation unit 20 further includes: calculating the conjugate product of the current received data and the delayed received data; summing the conjugate product results of consecutive data within the delay window to calculate a window accumulation result; and taking the absolute values of the real and imaginary parts of the window accumulation result and adding them together to obtain the delay correlation value.

[0059] The specific configuration of the packet detection unit 50 will be described in detail below. The packet detection unit 50 further includes: calculating the static noise power spectrum density and rate of change at the receiving end; updating the background noise estimate using recursive least mean squares based on the noise power spectrum density and rate of change; and dynamically adjusting the decision variable threshold using the exponential decay rule based on the estimated value change trend.

[0060] The delay-correlated and length-maintained OFDM packet detection control system provided in the embodiment of the present invention can execute the delay-correlated and length-maintained OFDM packet detection control method provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method.

[0061] Although the present application makes various references to certain modules in the system according to the embodiments of the present application, any number of different modules may be used and run on the user terminal and / or server, and the various units and modules included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of the functional units are only for the convenience of distinguishing each other and are not used to limit the scope of protection of the present invention.

[0062] The above specific embodiments do not constitute a limitation on the scope of protection of this application. Those skilled in the art should understand that various modifications, combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application shall be included within the scope of protection of this application.

Claims

1. A delay-correlated and length-maintained OFDM packet detection control method, characterized in that: include: The receiving end buffers the input signal and extracts the current received data and the delayed received data, wherein the input signal includes a periodic preamble structure; Calculating a delay correlation value between current received data and delayed received data according to the periodic preamble structure; Calculate the signal energy value of the data received during the delay window between the current received data and the delayed received data; Obtaining a decision variable by normalizing the ratio of the delay correlation value to the signal energy value; When the decision variable is greater than the detection condition of the preset threshold, preliminary detection is triggered. When it is verified that the duration for which the decision variable continuously meets the detection condition reaches the preset length threshold, it is confirmed that the group starting position has been reached and OFDM group detection is performed, wherein the preset length threshold includes one or more lengths.

2. The OFDM packet detection control method with delay correlation and length preservation according to claim 1, characterized in that: The receiving end buffers the input signal, which previously included: Designing a periodic preamble structure, wherein the periodic preamble structure is a periodic structure formed by N segments of the same short training sequence, where N is a positive integer; The periodic preamble structure is added to the front end of an OFDM packet signal and sent to a receiving end through a transmitting end.

3. The OFDM packet detection control method with delay correlation and length preservation according to claim 2, characterized in that: The short training sequence is an identical short training sequence with a length of 16.

4. The OFDM packet detection control method with delay correlation and length preservation according to claim 2, characterized in that: Calculating a delay correlation value between current received data and delayed received data according to the periodic preamble structure includes: According to the short training sequence length L of the periodic preamble structure, obtaining the currently received L data and the L data received D times ago; Through the delay related formula: , calculate the cross-correlation between the L data currently received and the L data received D times ago, and obtain the delayed correlation value, Indicates that the signal is received at the current moment n With delay D similarity.

5. The OFDM packet detection control method with delay correlation and length preservation according to claim 4, characterized in that: The obtaining of the decision variable comprises: By formula: , calculate and obtain the decision variable, where, is the decision variable, is the delay-related value, is the signal energy value.

6. The OFDM packet detection control method with delay correlation and length preservation according to claim 2, characterized in that: Confirmation of arrival at the group starting position, including: Setting a first length and a second length of a short training sequence, wherein the first length is smaller than the second length; Calculating a first delay correlation value and a second delay correlation value by using a periodic preamble structure of a first length and a periodic preamble structure of a second length respectively; Calculate the short-term window kurtosis corresponding to the first length and the long-term window stability corresponding to the second length respectively; When the short-term window kurtosis and the long-term window stability both meet the corresponding thresholds and the overlap between the two in the time domain exceeds the preset threshold, the grouping is determined to have started.

7. The OFDM packet detection control method with delay correlation and length preservation according to claim 1, characterized in that: The receiving end buffers the input signal, including: Configuring a two-stage shift register, the two-stage shift register comprising a first-length shift register and a second-length shift register, wherein the first length is smaller than the second length; After receiving the input signal, the receiving end stores the input signal in the cache module, stores the input signal bit by bit through the first length shift register, and shifts the input signal step by step according to the first length to achieve first length delay cache; Based on the cache processing of the first-length shift register, the signal data is subjected to a second-length shift processing through the second-length shift register to obtain another set of signal data that is time-spaced with the current data by a second length.

8. The OFDM packet detection control method with delay correlation and length preservation according to claim 1, characterized in that: Calculating the delay correlation value between the current received data and the delayed received data also includes: Calculate the conjugate product of the current received data and the delayed received data; Sum the conjugate product results of the continuous data during the delay window and calculate the window accumulation result; The real part and the imaginary part of the window accumulation result are taken as absolute values respectively and then added together to obtain the delay correlation value.

9. The OFDM packet detection control method with delay correlation and length preservation according to claim 1, characterized in that: When the decision variable is greater than a detection condition of a preset threshold, a preliminary detection is triggered, which also includes: Calculate the static noise power spectrum density and change rate at the receiving end; updating the background noise estimate using recursive least mean square according to the noise power spectral density and the rate of change; According to the changing trend of the estimated value, the threshold of the decision variable is dynamically adjusted using the exponential decay law.

10. OFDM packet detection and control system with delay correlation and length retention, characterized in that: The system is used to implement the delay-correlated and length-preserving OFDM packet detection control method according to any one of claims 1 to 9, and the system comprises: An input signal buffer unit, configured to buffer an input signal at a receiving end and extract current received data and delayed received data, wherein the input signal includes a periodic preamble structure; a delay correlation value calculation unit, configured to calculate a delay correlation value between current received data and delayed received data according to the periodic preamble structure; A signal energy value calculation unit, configured to calculate the signal energy value of the data received during the delay window between the current received data and the delayed received data; A decision variable obtaining unit, configured to obtain a decision variable by normalizing the ratio of the delay correlation value to the signal energy value; The packet detection unit is used to trigger preliminary detection when the decision variable is greater than the detection condition of a preset threshold, verify that the duration for which the decision variable continuously meets the detection condition reaches a preset length threshold, confirm that the starting position of the packet has been reached, and perform OFDM packet detection, wherein the preset length threshold includes one or more lengths.

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