High-definition video stable transmission system based on OFDM modulation

Abstract

The invention discloses a high-definition video stable transmission system based on OFDM modulation, and belongs to the technical field of communication data processing. The system comprises a high-definition video signal acquisition and preprocessing module, a data processing and encryption module, an OFDM modulation and signal transmission module, an error correction demodulation module and a decryption and video recovery module. Sampling frequency and gain are dynamically adjusted according to power grid electromagnetic interference intensity monitored in real time, collected analog high-definition video signals are converted into digital signals, and coded video data streams are obtained according to real-time monitoring and dichotomy of the current OFDM channel state. Therefore, the video data is adaptive to the characteristics of the power grid channel before entering the transmission link, the stability of video data transmission is improved, and the problems that the video data transmission is easy to interfere and the stability is insufficient due to the fact that early-stage processing is not fully combined with the condition of the power grid channel in the prior art are effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of communication data processing, and in particular to a high-definition video stable transmission system based on OFDM modulation. Background Art

[0002] As the power system strides towards intelligence, the safe and stable operation of the power grid is becoming more and more important, and the demand for real-time monitoring is becoming more and more urgent. Traditional monitoring methods are difficult to meet the actual needs of comprehensive and timely monitoring of the power grid due to low efficiency and many geographical restrictions. Video surveillance technology has made great progress in recent years, and the power grid happens to have widely distributed channel resources, so using the power grid channel to transmit surveillance video has gradually become a feasible and popular option.

[0003] Nowadays, the technology of transmitting surveillance video through power grid channels is indeed developing. The application of OFDM modulation technology has improved the transmission quality and anti-interference ability of video signals in power grid channels to a certain extent. Many power companies have also begun to use it in the monitoring of key parts such as transmission lines and substations, and realized the real-time transmission of high-definition surveillance video through power grid channels.

[0004] However, in the process of implementing the technical solution of the invention in the embodiments of the present application, the present application found that the above technology has at least the following technical problems:

[0005] In the prior art, the power grid environment itself is relatively complex and there are many interference factors. During the transmission of video data, it is often unable to resist these interference factors, resulting in frequent freezes, screen distortions, and even interruptions in the transmitted video. For example, in some scenarios that rely on power grid channels to transmit surveillance videos, the screen often has problems such as short pauses and image distortions without any regularity, which seriously affects the continuity of video data transmission. There is a problem that video data transmission is susceptible to interference and lacks stability due to the lack of sufficient pre-processing based on the power grid channel conditions. Summary of the invention

[0006] In view of the above problems, the present invention is proposed. Therefore, the problem to be solved by the present invention is that in the prior art, there is a problem that video data transmission is susceptible to interference and lacks stability due to insufficient pre-processing in combination with the power grid channel conditions.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions: a high-definition video stable transmission system based on OFDM modulation, which includes: a high-definition video signal acquisition and preprocessing module, a data processing and encryption module, an OFDM modulation and signal transmission module, an error correction demodulation module, and a decryption and video recovery module;

[0008] The high-definition video signal acquisition and preprocessing module is used to convert the acquired analog high-definition video signal into a digital signal, and obtain an encoded video data stream according to the digital signal and the current OFDM channel state;

[0009] The data processing and encryption module is used to group the encoded video data stream according to the encoded video data stream, the estimated value of the multipath delay spread of the power grid and the frequency domain distribution of electromagnetic interference, and map it to the OFDM subcarrier to obtain frequency domain subcarrier data, and perform channel coding and encryption processing on the frequency domain subcarrier data to obtain encrypted data;

[0010] The OFDM modulation and signal transmission module is used to perform OFDM modulation on the encrypted data according to the real-time frequency fluctuation, phase noise and multipath fading change rate of the power grid, add a cyclic prefix to obtain the signal to be transmitted and transmit it through the power grid channel, and when the receiving end receives the transmitted signal, restore the OFDM symbol signal with the cyclic prefix, and obtain the frequency domain signal after removing the cyclic prefix;

[0011] The error correction demodulation module is used to perform error correction on the frequency domain signal based on the LSTM long short-term memory network model, demodulate the error-corrected data to obtain the original data block that has been channel-coded and encrypted, and also to perform channel decoding on the demodulated data block, restore the data block before coding according to the check matrix during coding, and reorganize it into a complete coded video data stream;

[0012] The decryption and video recovery module is used to decrypt the encoded video data stream and recover the original digital video signal.

[0013] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the step of obtaining the encoded video data stream according to the digital signal and the current OFDM channel state includes:

[0014] Monitor the current OFDM channel state Schannel in real time, and classify the current OFDM channel state Schannel into two states, namely, good and bad;

[0015] If the current OFDM channel status Schannel is good, the number of subcarriers N is set to a fixed value Ngood, the modulation order M is set to a fixed value Mgood, the quantization parameter QP is set to a fixed value QPgood, and the frame rate FR is set to a fixed value FRgood;

[0016] If the current OFDM channel status Schannel is poor, set the number of subcarriers N to a fixed value Nbad, Nbad<Ngood, the modulation order M to a fixed value Mbad, Mbad<Mgood, set the quantization parameter QP to a fixed value QPbad, QPbad>QPgood, and set the frame rate FR to a fixed value FRbad, FRbad<FRgood;

[0017] The digital signal Vdigital is encoded according to the OFDM modulation parameters and video encoding parameters determined above to obtain an encoded video data stream Vencoded.

[0018] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the step of grouping the encoded video data stream includes:

[0019] Obtain the current power grid channel multipath delay spread estimation range τe, divide it into m intervals, and record the interval number as w, each interval corresponds to a time interval adjustment coefficient kt,w;

[0020] Obtain the time interval Tb of the multipath delay spread value of the w-th interval, Tb=kt,w·τe;

[0021] Divide the encoded video data stream into Q equal-length data blocks Bq, and number the equal-length data blocks as q, q = 1, 2, ..., Q;

[0022]

[0023] in, Represents the total number of bits of the encoded video data stream, N is the number of subcarriers, and R is the amount of data that a subcarrier can transmit per unit time.

[0024] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the method for acquiring the frequency domain subcarrier data is as follows:

[0025] Obtain the electromagnetic interference frequency domain of the power grid and divide it into h frequency bands, calculate the electromagnetic interference intensity If and interference gradient change Gh=|If,h+1-If,h| of each frequency band, If,h+1 is the electromagnetic interference intensity of the h+1th frequency band, If,h is the electromagnetic interference intensity of the hth frequency band;

[0026] Divide the center frequency of the subcarrier frequency band into different groups, each group corresponds to a mapping priority P, P = k2*(1-Gh), k2 is the mapping priority coefficient;

[0027] According to the mapping priority, the equal-length data blocks Bq are mapped to the OFDM subcarrier frequency domain, a one-to-one mapping relationship is established, and the frequency-domain subcarrier data Scarrier is obtained.

[0028] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the channel coding of the frequency domain subcarrier data includes the following steps:

[0029] The real-time noise power spectrum density Npsd and noise correlation Cn of the power grid channel are collected, and the noise comprehensive index NI is calculated based on them:

[0030] NI=a1*Npsd+a2*Cn;

[0031] Among them, a1 is the weight coefficient of Npsd for NI, a2 is the weight coefficient of Cn for NI;

[0032] According to the noise comprehensive index and its corresponding low-density parity check code pattern, the frequency domain subcarrier data is channel coded to obtain the coded data C:

[0033] C = LDPCenhanced(D,Hg);

[0034] Wherein, D is the original data block of the frequency domain subcarrier data, Hg is the check matrix corresponding to the low-density parity-check code pattern, and LDPCenhanced represents the LDPC coding operation enhanced for the power grid environment.

[0035] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the step of performing OFDM modulation on the encrypted data includes:

[0036] The real-time frequency fluctuation Δf and phase noise of the power grid are Standardize the process;

[0037] Using high-speed carrier chips, according to the real-time frequency fluctuation Δf and phase noise of the power grid Dynamically optimize OFDM modulation parameters Mparam:

[0038]

[0039] Among them, M0 is the initial modulation parameter, b1 is the adjustment coefficient of Δf, and b2 is The adjustment factor of

[0040] The frequency domain data corresponding to the encrypted data E is converted into the time domain signal Tsignal through the inverse fast Fourier transform. The conversion formula is:

[0041]

[0042] Where Tsignal(t) is the time domain signal at time t, X(k) is the frequency domain signal of the kth subcarrier, k is the subcarrier number, N is the number of subcarriers, e is a natural constant, j is an imaginary unit, π is the circumference of a circle, t is the time index, and T is the symbol period, which is the length of time that an OFDM symbol lasts;

[0043] Real-time monitoring of the power grid multipath fading change rate ρmp, based on which the cyclic prefix length CPL is output:

[0044] CPL=c1+c2·ρmp;

[0045] Where c1 is the basic cyclic prefix length, c2 is the coefficient of influence of multipath fading on transmission performance;

[0046] The signal part with a length of CPL is intercepted from the tail of the OFDM time domain signal Tsignal, and copied and added to the front end of the time domain signal Tsignal to obtain the signal to be transmitted with a cyclic prefix

[0047] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the step of recovering the OFDM symbol signal with a cyclic prefix includes:

[0048] When the receiving end receives the transmission signal Rsignal, it obtains the grid frequency deviation Δfr and phase noise And the residual impact of multipath fading εmp, and perform normalization to calculate the synchronization error metric SE:

[0049]

[0050] Where d1 is the weight coefficient of Δfr for SE, d2 is For the weight coefficient of SE, d3 is the weight coefficient of εmp for SE.

[0051] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the demodulation of the error-corrected data includes the following steps:

[0052] The frequency domain signal after error correction corresponding to the kth subcarrier Perform channel compensation to eliminate the residual effects of multipath fading and obtain the compensated signal Dcomp(k);

[0053] According to the frequency deviation estimation value Δfr and the phase tracking information, frequency and phase compensation is performed on Dcomp(k) to obtain a phase-corrected signal Drorr(k);

[0054] Adaptive filtering or interference cancellation technology is used to process Dcorr(k) to remove the residual influence of electromagnetic interference and obtain the interference suppressed signal Dsupp(k);

[0055] Dsupp(k) is soft-demodulated, and the log-likelihood ratio of each bit is calculated to obtain the original data block after channel coding and encryption, that is, the demodulated data block.

[0056] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the acquisition of the complete encoded video data stream includes the following steps:

[0057] Channel decoding is performed on the demodulated data block, and a low-density parity check code decoding algorithm is used to restore the data block D′ before encoding through the decoding formula according to the check matrix Hg during encoding;

[0058]

[0059] Among them, D' is the decoded data, that is, the data block before encoding, and C' is the demodulated data block. is the decoding operation of the low-density parity-check code;

[0060] The restored data blocks before encoding are reassembled according to the grouping rules of the sending end to obtain a complete encoded video data stream Rencoded.

[0061] As a preferred solution of the OFDM-modulated high-definition video stable transmission system described in the present invention, the decrypting of the encoded video data stream to restore the original digital video signal includes the following steps:

[0062] The encryption key K generated during encryption is inversely transformed according to the formula K′=K>>s, and right-shifted by s bits to obtain the decryption key K′. D″ is the decrypted data, and E′ is the received encrypted data, which are decrypted to restore the original digital video signal Rdigital.

[0063] The beneficial effects of the present invention are as follows: the present invention converts the collected analog high-definition video signal into a digital signal by dynamically adjusting the sampling frequency and gain according to the real-time monitored electromagnetic interference intensity of the power grid, and obtains the encoded video data stream based on the real-time monitoring and binary classification of the current OFDM channel state, so that the video data is adapted to the power grid channel characteristics before entering the transmission link, thereby improving the stability of the initial stage of video data transmission, reducing the transmission instability caused by unreasonable early parameter settings in the subsequent transmission process, and effectively solving the problem in the prior art that the video data transmission is susceptible to interference and lacks stability due to insufficient early processing in combination with the power grid channel conditions.

[0064] The present invention obtains the estimated range of multipath delay spread of the current power grid channel and divides it into intervals, determines the time interval adjustment coefficient according to each interval, thereby dividing the encoded video data stream into equal-length data blocks, and simultaneously obtains the frequency domain distribution of power grid electromagnetic interference, calculates the relevant parameters of each frequency band to determine the mapping priority, and then maps the data block to the OFDM subcarrier frequency domain, and performs channel coding and encryption processing on the frequency domain subcarrier data, thereby achieving the reliability and security of data transmission in complex power grid channels, and reducing transmission errors or information leakage caused by factors such as channel interference and easy data theft.

[0065] The present invention constructs a LSTM long short-term memory network model to perform sequence analysis and error correction on the frequency domain signal, then obtains the demodulated data block according to the frequency domain signal after error correction, and then uses a low-density parity-check code decoding algorithm combined with the check matrix during encoding to perform channel decoding and data reorganization, and finally uses the inverse transformation of the encryption key to generate a decryption key for decryption operation, thereby comprehensively and accurately correcting various errors generated in the transmission process, achieving stable and accurate restoration of the original high-definition video signal, avoiding the inability to restore the original video due to transmission errors, and preventing data leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0067] Figure 1 This is a structural diagram of a high-definition video stable transmission system based on OFDM modulation in Example 1. DETAILED DESCRIPTION

[0068] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0069] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0070] The embodiment of the present application provides a high-definition video stable transmission system based on OFDM modulation, which solves the problem in the prior art that video data transmission is susceptible to interference and lacks stability due to insufficient pre-processing in combination with the power grid channel conditions. The sampling frequency and gain are dynamically adjusted according to the real-time monitored power grid electromagnetic interference intensity, the collected analog high-definition video signal is converted into a digital signal, and the encoded video data stream is obtained based on real-time monitoring and binary classification of the current OFDM channel status, so that the video data is adapted to the power grid channel characteristics before entering the transmission link, thereby improving the stability of the initial stage of video data transmission and reducing the transmission instability caused by unreasonable pre-parameter settings in the subsequent transmission process.

[0071] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0072] Example 1

[0073] Reference Figure 1 , which is the first embodiment of the present invention, and provides a high-definition video stable transmission system based on OFDM modulation, the system comprising: a high-definition video signal acquisition and preprocessing module, a data processing and encryption module, an OFDM modulation and signal transmission module, an error correction demodulation module, and a decryption and video recovery module;

[0074] The high-definition video signal acquisition and preprocessing module is used to convert the acquired analog high-definition video signal into a digital signal, and obtain an encoded video data stream according to the digital signal and the current OFDM channel state;

[0075] The data processing and encryption module is used to group the encoded video data stream according to the encoded video data stream, the estimated value of the multipath delay spread of the power grid and the frequency domain distribution of electromagnetic interference, and map it to the OFDM subcarrier to obtain frequency domain subcarrier data, and perform channel coding and encryption processing on the frequency domain subcarrier data to obtain encrypted data;

[0076] The OFDM modulation and signal transmission module is used to perform OFDM modulation on the encrypted data according to the real-time frequency fluctuation, phase noise and multipath fading change rate of the power grid, add a cyclic prefix to obtain the signal to be transmitted and transmit it through the power grid channel, and when the receiving end receives the transmitted signal, restore the OFDM symbol signal with the cyclic prefix, and obtain the frequency domain signal after removing the cyclic prefix;

[0077] The error correction demodulation module is used to perform error correction on the frequency domain signal based on the LSTM long short-term memory network model, demodulate the error-corrected data to obtain the original data block that has been channel-coded and encrypted, and also to perform channel decoding on the demodulated data block, restore the data block before coding according to the check matrix during coding, and reorganize it into a complete coded video data stream;

[0078] The decryption and video recovery module is used to decrypt the encoded video data stream and recover the original digital video signal.

[0079] It needs to be explained that converting the acquired analog high-definition video signal into a digital signal means:

[0080] Real-time monitoring of the electromagnetic interference intensity I of the power grid, I∈[Imin,Imax], Imin is the minimum electromagnetic interference intensity, Imax is the maximum electromagnetic interference intensity;

[0081] Divide [Imin, Imax] into r intervals and number the interval as i;

[0082] When the electromagnetic interference intensity of the power grid is in the i-th interval, the sampling frequency fs and gain g are adjusted:

[0083]

[0084] Where fs0 is the initial sampling frequency, Δfs is the adjustment step, g0 is the initial gain, and k1 is the gain adjustment coefficient;

[0085] Convert the analog signal Voriginal into a digital signal Vdigital:

[0086] Vdigital=ADC(Voriginal), where ADC(...) is an ADC analog-to-digital converter.

[0087] Furthermore, the step of obtaining the encoded video data stream according to the digital signal and the current OFDM channel state includes:

[0088] Monitor the current OFDM channel state Schannel in real time, and classify the current OFDM channel state Schannel into two states, namely, good and bad;

[0089] When the current OFDM channel status Schannel is good, the number of subcarriers N is set to a fixed value Ngood, the modulation order M is set to a fixed value Mgood, the quantization parameter QP is set to a fixed value QPgood, and the frame rate FR is set to a fixed value FRgood;

[0090] If the current OFDM channel status Schannel is poor, set the number of subcarriers N to a fixed value Nbad, Nbad<Ngood, the modulation order M to a fixed value Mbad, Mbad<Mgood, set the quantization parameter QP to a fixed value QPbad, QPbad>QPgood, and set the frame rate FR to a fixed value FRbad, FRbad<FRgood;

[0091] The digital signal Vdigital is encoded according to the OFDM modulation parameters and video encoding parameters determined above to obtain an encoded video data stream Vencoded.

[0092] In this embodiment, an OFDM channel characteristic feature data set is collected. The OFDM channel characteristic features include the channel fading degree and the noise level. The OFDM channel characteristic feature data set has been marked with data in "good" or "bad" status, and preprocessing work such as data cleaning, feature selection, and proportional division into test sets and test sets is performed.

[0093] The CART algorithm is used to initialize the decision tree model, and key hyperparameters such as the maximum depth, minimum sample division, and division criteria are set. The channel feature data of the training set and the corresponding channel state labels are input into the initialized decision tree model so that it can build a tree structure according to the division criteria to learn the classification rules. The trained decision tree model is then evaluated using the test set to obtain a binary classification model.

[0094] The current OFDM channel state is input into the binary classification model and the channel state label is output. The channel state label includes good and bad.

[0095] Furthermore, the step of grouping the encoded video data stream includes:

[0096] Obtain the current power grid channel multipath delay spread estimation range τe, divide it into m intervals, and record the interval number as w, each interval corresponds to a time interval adjustment coefficient kt,w;

[0097] Obtain the time interval Tb of the multipath delay spread value of the w-th interval, Tb=kt,w·τe;

[0098] Divide the encoded video data stream into Q equal-length data blocks Bq, and number the equal-length data blocks as q, q = 1, 2, ..., Q;

[0099]

[0100] Among them, Datasize encoded Represents the total number of bits of the encoded video data stream, and R is the amount of data that can be transmitted by the subcarrier per unit time.

[0101] Furthermore, the method for acquiring the frequency domain subcarrier data is:

[0102] Obtain the electromagnetic interference frequency domain of the power grid and divide it into h frequency bands, calculate the electromagnetic interference intensity If and interference gradient change Gh=|If,h+1-If,h| of each frequency band, If,h+1 is the electromagnetic interference intensity of the h+1th frequency band, If,h is the electromagnetic interference intensity of the hth frequency band;

[0103] Divide the center frequency of the subcarrier frequency band into different groups, each group corresponds to a mapping priority P, P = k2*(1-Gh), k2 is the mapping priority coefficient;

[0104] According to the mapping priority, the equal-length data blocks Bq are mapped to the OFDM subcarrier frequency domain, a one-to-one mapping relationship is established, and the frequency-domain subcarrier data Scarrier is obtained.

[0105] Further, the channel coding of the frequency domain subcarrier data comprises the following steps:

[0106] The real-time noise power spectrum density Npsd and noise correlation Cn of the power grid channel are collected, and the noise comprehensive index NI is calculated based on them:

[0107] NI=a1*Npsd+a2*Cn;

[0108] Among them, a1 is the weight coefficient of Npsd for NI, a2 is the weight coefficient of Cn for NI;

[0109] According to the noise comprehensive index and its corresponding low-density parity check code pattern, the frequency domain subcarrier data is channel coded to obtain the coded data C:

[0110] C = LDPCenhanced(D,Hg);

[0111] Wherein, D is the original data block of the frequency domain subcarrier data, Hg is the check matrix corresponding to the low-density parity-check code pattern, and LDPCenhanced represents the LDPC encoding operation on the frequency domain subcarrier data.

[0112] In this embodiment, the specific steps of LDPCenhanced performing channel coding operation on frequency domain subcarrier data are as follows:

[0113] First, the corresponding generator matrix G is constructed according to the LDPC code type and generator matrix parameters corresponding to the noise comprehensive index. The generator matrix has a specific mathematical relationship with the check matrix Hg for subsequent conversion.

[0114] Next, the original data block D is regarded as a row vector and multiplied with the generating matrix G in a binary finite field. According to the rule of C=D*G, the encoded data C with redundant check bits added is obtained, thereby giving the data error correction capability to cope with the influence of power grid channel noise.

[0115] It should be explained that the specific steps of obtaining the encrypted data through encryption processing are:

[0116] The unique identification information of the power grid Igrid is hashed to obtain the hash value Hgrid, and the encryption key K is generated according to the hash value:

[0117]

[0118] Among them, K0 is the initial encryption key, represents a bitwise XOR operation, << s represents shifting the hash value left by s bits, where s is the number of shift bits determined according to the length of the power grid identity information and the encryption strength requirements;

[0119] Encrypt the encoded data C to obtain encrypted data E;

[0120] E=AESgrid(C)

[0121] Among them, AESgrid represents the AES encryption operation.

[0122] In this embodiment, the steps of AESgrid encrypting the encoded data are:

[0123] The encoded data C is divided into fixed-length data blocks of usually 128 bits. Taking the generated encryption key K as a parameter, each data block is subjected to multiple rounds of operations such as byte substitution, row shift, column confusion and round key addition included in the AES encryption algorithm. Finally, the encrypted ciphertext data blocks are combined to form the encrypted data E to ensure the confidentiality of data transmission.

[0124] Furthermore, the step of performing OFDM modulation on the encrypted data includes:

[0125] The real-time frequency fluctuation Δf and phase noise of the power grid are Standardize the process;

[0126] Using high-speed carrier chips, according to the real-time frequency fluctuation Δf and phase noise of the power grid Dynamically optimize OFDM modulation parameters Mparam:

[0127]

[0128] Among them, M0 is the initial modulation parameter, b1 is the adjustment coefficient of Δf, and b2 is The adjustment factor of

[0129] The frequency domain data corresponding to the encrypted data E is converted into the time domain signal Tsignal through the inverse fast Fourier transform. The conversion formula is:

[0130]

[0131] Where Tsignal(t) is the time domain signal at time t, X(k) is the frequency domain signal of the kth subcarrier, k is the subcarrier number, e is a natural constant, j is an imaginary unit, π is the circumference of a circle, t is the time index, and T is the symbol period, which is the length of time that an OFDM symbol lasts;

[0132] Real-time monitoring of the power grid multipath fading change rate ρmp, based on which the cyclic prefix length CPL is output:

[0133] CPL=c1+c2·ρmp;

[0134] Where c1 is the basic cyclic prefix length, c2 is the coefficient of influence of multipath fading on transmission performance;

[0135] The signal part with a length of CPL is intercepted from the tail of the OFDM time domain signal Tsignal, and copied and added to the front end of the time domain signal Tsignal to obtain the signal to be transmitted with a cyclic prefix

[0136] It should be explained that adding the cyclic prefix to obtain the signal to be transmitted and transmitting it through the power grid channel specifically means: transmitting the signal to be transmitted through the power grid channel at the allowed transmission frequency, wherein the allowed transmission frequency is [2MH, 18MH].

[0137] Furthermore, the step of recovering the OFDM symbol signal with a cyclic prefix includes:

[0138] When the receiving end receives the transmission signal Rsignal, it obtains the grid frequency deviation Δfr and phase noise And the residual impact of multipath fading εmp, and perform normalization to calculate the synchronization error metric SE:

[0139]

[0140] Where d1 is the weight coefficient of Δfr for SE, d2 is For the weight coefficient of SE, d3 is the weight coefficient of εmp for SE. The residual impact of multipath fading is estimated by using a channel estimator at the receiving end to estimate the channel characteristics. Assume that the transmitted pilot signal is P(k) and the received pilot signal is Rp(k). In the ideal case where noise is not considered, the relationship between the received pilot signal and the transmitted pilot signal can be expressed as Rp(k)=H(k)*P(k), where H(k) is the channel frequency response on the kth subcarrier.

[0141] According to the least squares method, the estimated value of the channel frequency response on the kth subcarrier is obtained

[0142] After obtaining the estimated value of the channel frequency response, it is converted into the channel impulse response h(n) through inverse discrete Fourier transform, and the formula is: Where n is the time domain sampling index.

[0143] The synchronization parameters are adjusted according to SE to achieve symbol synchronization and carrier synchronization between the receiving end and the transmitting end, and the signal is received and processed; after down-conversion, filtering and amplification operations, noise and interference are removed, the OFDM symbol signal with a cyclic prefix is ​​restored, and the time domain signal is obtained after removing the cyclic prefix.

[0144] The receiving end collects dynamic change data of the electromagnetic interference spectrum, divides the electromagnetic interference spectrum of the receiving end into different frequency bands, and adjusts the filter parameter Ffilt according to the change ΔIr of the interference intensity of each frequency band:

[0145] Ffilt(ΔIr)=F0+e1·ΔIr;

[0146] Among them, F0 is the initial filtering parameter, and e1 is the filtering parameter adjustment coefficient determined by experiments to ensure the accuracy and stability of signal recovery;

[0147] After removing the cyclic prefix, the time domain signal is converted back to the frequency domain signal Rcarrier through fast Fourier transform. The conversion formula is:

[0148]

[0149] Wherein, x(t) is the time domain signal after removing the cyclic prefix.

[0150] It should be explained that the steps of performing error correction and demodulation on the frequency domain signal based on the LSTM long short-term memory network model include:

[0151] Construct a LSTM long short-term memory network model, with the frequency domain signal Rcarrier and historical received signal features as input, where the historical received signal features are the feature extraction results of the received signal within a certain time window in the past, including statistical features such as signal amplitude and phase;

[0152] The LSTM model performs sequence analysis and error correction on Rcarrier by learning a large number of noisy signal and correct signal samples, and outputs the frequency domain signal after error correction.

[0153] Further, demodulating the error-corrected data refers to: demodulating the data on each subcarrier of the error-corrected frequency domain signal to obtain the original data block that has been channel-coded and encrypted, including the following steps:

[0154] The frequency domain signal after error correction corresponding to the kth subcarrier Channel compensation is performed to eliminate the residual influence of multipath fading and obtain the compensated signal Dcomp(k).

[0155] According to the frequency deviation estimation value Δfr and the phase tracking information, frequency and phase compensation are performed on Dcomp(k) to obtain a phase-corrected signal Drorr(k).

[0156] Adaptive filtering or interference cancellation technology is used to process Dcorr(k) to remove the residual influence of electromagnetic interference and obtain the interference suppressed signal Dsupp(k).

[0157] Dsupp(k) is soft-demodulated, and the log-likelihood ratio of each bit is calculated to obtain the original data block after channel coding and encryption, that is, the demodulated data block.

[0158] Furthermore, the step of obtaining a complete encoded video data stream comprises the following steps:

[0159] Channel decoding is performed on the demodulated data block, and a low-density parity check code decoding algorithm is used to restore the data block D′ before encoding through the decoding formula according to the check matrix Hg during encoding;

[0160]

[0161] Among them, D' is the decoded data, that is, the data block before encoding, and C' is the demodulated data block. is the decoding operation of the low-density parity-check code;

[0162] The restored data blocks before encoding are reassembled according to the grouping rules of the sending end to obtain a complete encoded video data stream Rencoded.

[0163] Furthermore, decrypting the encoded video data stream to restore the original digital video signal includes the following steps:

[0164] The encryption key K generated during encryption is inversely transformed according to the formula K′=K>>s, and right-shifted by s bits to obtain the decryption key K′. D″ is the decrypted data, and E′ is the received encrypted data, which are decrypted to restore the original digital video signal Rdigital.

[0165] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0166] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0167] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0168] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0169] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0170] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high-definition video stable transmission system based on OFDM modulation, characterized in that: include: High-definition video signal acquisition and preprocessing module, data processing and encryption module, OFDM modulation and signal transmission module, error correction and demodulation module, decryption and video recovery module; The high-definition video signal acquisition and preprocessing module is used to convert the acquired analog high-definition video signal into a digital signal, and obtain an encoded video data stream according to the digital signal and the current OFDM channel state; The data processing and encryption module is used to group the encoded video data stream according to the encoded video data stream, the estimated value of the multipath delay spread of the power grid and the frequency domain distribution of electromagnetic interference, and map it to the OFDM subcarrier to obtain frequency domain subcarrier data, and perform channel coding and encryption processing on the frequency domain subcarrier data to obtain encrypted data; The OFDM modulation and signal transmission module is used to perform OFDM modulation on the encrypted data according to the real-time frequency fluctuation, phase noise and multipath fading change rate of the power grid, add a cyclic prefix to obtain the signal to be transmitted and transmit it through the power grid channel, and when the receiving end receives the transmitted signal, restore the OFDM symbol signal with the cyclic prefix, and obtain the frequency domain signal after removing the cyclic prefix; The error correction demodulation module is used to perform error correction on the frequency domain signal based on the LSTM long short-term memory network model, demodulate the error-corrected data to obtain the original data block that has been channel-coded and encrypted, and also to perform channel decoding on the demodulated data block, restore the data block before coding according to the check matrix during coding, and reorganize it into a complete coded video data stream; The decryption and video recovery module is used to decrypt the encoded video data stream and recover the original digital video signal.

2. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: The step of obtaining the encoded video data stream according to the digital signal and the current OFDM channel state comprises: Monitor the current OFDM channel state Schannel in real time, and classify the current OFDM channel state Schannel into two states, namely, good and bad; If the current OFDM channel status Schannel is good, the number of subcarriers N is set to a fixed value Ngood, the modulation order M is set to a fixed value Mgood, the quantization parameter QP is set to a fixed value QPgood, and the frame rate FR is set to a fixed value FRgood; If the current OFDM channel status Schannel is poor, set the number of subcarriers N to a fixed value Nbad, Nbad<Ngood, the modulation order M to a fixed value Mbad, Mbad<Mgood, set the quantization parameter QP to a fixed value QPbad, QPbad>QPgood, and set the frame rate FR to a fixed value FRbad, FRbad<FRgood; The digital signal Vdigital is encoded according to the OFDM modulation parameters and video encoding parameters determined above to obtain an encoded video data stream Vencoded.

3. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: The step of grouping the encoded video data stream comprises: Obtain the current power grid channel multipath delay spread estimation range τe, divide it into m intervals, and record the interval number as w, each interval corresponds to a time interval adjustment coefficient kt,w; Obtain the time interval Tb of the multipath delay spread value of the w-th interval, Tb=kt,w·τe; Divide the encoded video data stream into Q equal-length data blocks Bq, and number the equal-length data blocks as q, q = 1, 2, ..., Q; Among them, Datasize encoded Represents the total number of bits of the encoded video data stream, N is the number of subcarriers, and R is the amount of data that a subcarrier can transmit per unit time.

4. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: The method for acquiring the frequency domain subcarrier data is: Obtain the electromagnetic interference frequency domain of the power grid and divide it into h frequency bands, calculate the electromagnetic interference intensity If and interference gradient change Gh=|If,h+1-If,h| of each frequency band, If,h+1 is the electromagnetic interference intensity of the h+1th frequency band, If,h is the electromagnetic interference intensity of the hth frequency band; Divide the center frequency of the subcarrier frequency band into different groups, each group corresponds to a mapping priority P, P = k2*(1-Gh), k2 is the mapping priority coefficient; According to the mapping priority, the equal-length data blocks Bq are mapped to the OFDM subcarrier frequency domain, a one-to-one mapping relationship is established, and the frequency-domain subcarrier data Scarrier is obtained.

5. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: The channel coding of the frequency domain subcarrier data comprises the following steps: The real-time noise power spectrum density Npsd and noise correlation Cn of the power grid channel are collected, and the noise comprehensive index NI is calculated based on them: NI=a1*Npsd+a2*Cn; Among them, a1 is the weight coefficient of Npsd for NI, a2 is the weight coefficient of Cn for NI; According to the noise comprehensive index and its corresponding low-density parity check code pattern, the frequency domain subcarrier data is channel coded to obtain the coded data C: C = LDPCenhanced(D,Hg); Wherein, D is the original data block of the frequency domain subcarrier data, Hg is the check matrix corresponding to the low-density parity-check code pattern, and LDPCenhanced represents the LDPC coding operation enhanced for the power grid environment.

6. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: The step of performing OFDM modulation on the encrypted data comprises: The real-time frequency fluctuation Δf and phase noise of the power grid are Standardize the process; Using high-speed carrier chips, according to the real-time frequency fluctuation Δf and phase noise of the power grid Dynamically optimize OFDM modulation parameters Mparam: Among them, M0 is the initial modulation parameter, b1 is the adjustment coefficient of Δf, and b2 is The adjustment factor of The frequency domain data corresponding to the encrypted data E is converted into the time domain signal Tsignal through the inverse fast Fourier transform. The conversion formula is: Where Tsignal(t) is the time domain signal at time t, X(k) is the frequency domain signal of the kth subcarrier, k is the subcarrier number, N is the number of subcarriers, e is a natural constant, j is an imaginary unit, π is the circumference of a circle, t is the time index, and T is the symbol period, which is the length of time that an OFDM symbol lasts; Real-time monitoring of the power grid multipath fading change rate ρmp, based on which the cyclic prefix length CPL is output: CPL=c1+c2·ρmp; Where c1 is the basic cyclic prefix length, c2 is the coefficient of influence of multipath fading on transmission performance; The signal part with a length of CPL is intercepted from the tail of the OFDM time domain signal Tsignal, and copied and added to the front end of the time domain signal Tsignal to obtain the signal to be transmitted with a cyclic prefix Tsignal CP .

7. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: The step of recovering an OFDM symbol signal with a cyclic prefix comprises: When the receiving end receives the transmission signal Rsignal, it obtains the grid frequency deviation Δfr and phase noise And the residual impact of multipath fading εmp, and perform normalization to calculate the synchronization error metric SE: Where d1 is the weight coefficient of Δfr for SE, d2 is For the weight coefficient of SE, d3 is the weight coefficient of εmp for SE.

8. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: Demodulating the error-corrected data comprises the following steps: The frequency domain signal after error correction corresponding to the kth subcarrier Perform channel compensation to eliminate the residual effects of multipath fading and obtain the compensated signal Dcomp(k); According to the frequency deviation estimation value Δfr and the phase tracking information, frequency and phase compensation is performed on Dcomp(k) to obtain a phase-corrected signal Drorr(k); Adaptive filtering or interference cancellation technology is used to process Dcorr(k) to remove the residual influence of electromagnetic interference and obtain the interference suppressed signal Dsupp(k); Dsupp(k) is soft-demodulated, and the log-likelihood ratio of each bit is calculated to obtain the original data block after channel coding and encryption, that is, the demodulated data block.

9. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: The acquisition of the complete encoded video data stream comprises the following steps: Channel decoding is performed on the demodulated data block, and a low-density parity check code decoding algorithm is used to restore the data block D′ before encoding through the decoding formula according to the check matrix Hg during encoding; Among them, D' is the decoded data, that is, the data block before encoding, and C' is the demodulated data block. is the decoding operation of the low-density parity-check code; The restored data blocks before encoding are reassembled according to the grouping rules of the sending end to obtain a complete encoded video data stream Rencoded.

10. A high-definition video stable transmission system based on OFDM modulation as claimed in claim 1, characterized in that: Decrypting the encoded video data stream to restore the original digital video signal comprises the following steps: The encryption key K generated during encryption is inversely transformed according to the formula K′=K>>s, and right-shifted by s bits to obtain the decryption key K′. D″ is the decrypted data, and E′ is the received encrypted data, which are decrypted to restore the original digital video signal Rdigital.

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