Probability shaping method, signal transmission method and signal transmission system based on dual-mode index modulation

Abstract

The invention discloses a probability shaping method based on dual-mode index modulation, a signal transmission method and a signal transmission system in the technical field of magnetic communication, and the method comprises the steps: obtaining underwater noise of a magnetic induction communication target area, constructing a constellation codebook compiled by a QPSK constellation A and a QPSK constellation B based on two different transmitting powers, the QPSK constellation A is an inner side mapping constellation with small transmitting power, and the QPSK constellation B is an outer side mapping constellation with large transmitting power; and performing serial-parallel conversion on the bit stream of the original data to obtain a matrix, and performing index selection and constellation mapping according to the matrix and the constellation codebook to obtain a matrix after probability shaping. The novel probability shaping method based on dual-mode index modulation is low in complexity, does not introduce redundancy, and is high in flexibility; through real-time monitoring of underwater noise and a method of adjusting the mapping frequency ratio of an inner side mapping constellation to an outer side mapping constellation, probability distribution of any shape is flexibly realized, and system performance is optimized.

Description

Technical Field

[0001] The present invention relates to a probability shaping method, a signal transmission method and a signal transmission system based on dual-mode index modulation, and belongs to the technical field of magnetic communication. Background Art

[0002] With the development of modern industry, the demand for communications in the civil, industrial, and defense fields has gradually expanded to underwater and underground areas. Underground, wired communications are susceptible to geological changes, resulting in damage and difficulties in repair. Underwater, acoustic communications suffer from severe multipath effects, while optical communications are susceptible to absorption and scattering, and electromagnetic wave power consumption is high. In contrast, magnetic induction communication has become a leading candidate technology for multi-habitat communications due to its significant resistance to multipath effects, low absorption and scattering losses, low power consumption, and simple equipment structure. Although magnetic induction communication systems have strong transmission capabilities, their bandwidth is narrow, so the transmission rate is very limited.

[0003] Index modulation is considered a novel modulation technique for improving the spectral efficiency (SE) of orthogonal frequency division multiplexing (OFDM) systems. This technique utilizes not only OFDM subcarriers but also their positions for data transmission. By specifying the positions of active subcarriers, their positions carry additional bits of information. However, due to the presence of idle subcarriers, the SE of index modulation is relatively limited at higher modulation orders. The emergence of dual-mode index modulation addresses this limitation in improving SE.

[0004] Due to the complex underwater environment, communications are much more affected by turbulence than in air. Therefore, probabilistic shaping technology is often used in underwater magnetic communications. Probabilistic shaping does not change the shape of the constellation diagram, but maintains the minimum Euclidean distance between constellation points. By changing the transmission probability of each constellation point—increasing the transmission probability of constellation points with lower internal energy and decreasing the transmission probability of constellation points with higher external energy—it reduces the average energy, improves the quality factor of the constellation diagram, and achieves gain. This effectively counters Gaussian noise interference and is attracting increasing attention as a typical modulation format optimization technique. Traditional probabilistic shaping methods require the use of labels, channel coding, or distribution matchers to convert uniformly distributed binary sequences into symbol sequences with the desired distribution. This increases the redundancy of the transmitted data, and the mathematical structure of the distribution matcher is very complex, making its implementation difficult. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a probability shaping method, a signal transmission method and a signal transmission system based on dual-mode index modulation.

[0006] In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions.

[0007] In a first aspect, the present invention discloses a probability shaping method based on dual-mode index modulation, comprising: Obtaining the underwater channel matrix of the magnetic induction communication target area; Constructing a constellation codebook based on two QPSK constellations A and QPSK constellations B with different transmit powers according to the underwater channel matrix, wherein the QPSK constellation A is an inner mapping constellation A with low transmit power, and the QPSK constellation B is an outer mapping constellation B with high transmit power, and mapping probability distribution of the inner mapping constellation A and the outer mapping constellation B is determined according to the underwater channel matrix; The bit stream of the original data is serial-to-parallel converted into a matrix, and index selection and constellation mapping are performed according to the matrix and the constellation codebook to obtain a probability-shaped matrix.

[0008] Furthermore, the mapping probability distribution of the inner mapping constellation A and the outer mapping constellation B is determined according to the underwater channel matrix, including: An optimal probability parameter is obtained by using convex optimization according to the underwater channel matrix, and a mapping frequency ratio of an inner mapping constellation to an outer mapping constellation is adjusted according to the optimal probability parameter.

[0009] Furthermore, the obtaining of an optimal probability parameter by convex optimization according to the underwater channel matrix, and adjusting the mapping frequency ratio of the inner mapping constellation to the outer mapping constellation according to the optimal probability parameter, includes: The underwater channel is estimated using the minimum mean square error estimation method to obtain the underwater channel matrix H, with the number of rows and columns both being M*N2; the probability shaping parameter is expressed as the matrix A, with the number of rows and columns both being M*N2; The transmitted signal is a column vector x, the number of columns is M*N2, then the signal power after probability shaping is x T Ax, T represents the conjugate transpose of the vector; The received signal is a column vector y, the number of columns is M*N2, and the channel noise power is expressed as x T A T HAx-y T y; The optimization problem is expressed as: ; Both H and A are symmetric positive definite matrices. This optimization problem is a typical semidefinite programming problem. The optimization problem is solved to obtain the optimal solution Ax with the minimum channel noise power. A is the mapping probability corresponding to each symbol. A is used to obtain the ratio of the mapping times of the inner mapping constellation to the outer mapping constellation. The symbol is used to carry the amplitude and phase information of the subcarrier.

[0010] Furthermore, the constellation codebook is constructed, including: The mapping probability distribution is n:1, the number of inner mapping constellation mappings is n times, the number of outer mapping constellation mappings is once, and n is a positive integer; The mapping probability of the four points of the inner mapping constellation A is n / 4(n+1), and the mapping probability of the four points of the outer mapping constellation B is 1 / 4(n+1); The constructed constellation codebook includes n+1 symbols, each symbol contains two bits, and the correspondence between each symbol and the key bit is arbitrarily modified under the condition that the ratio of the number of constellation A mappings to the number of constellation B mappings is n:1, thereby obtaining the constellation index mapping rule.

[0011] 5. The probability shaping method based on dual-mode index modulation according to claim 4, wherein the step of converting the bit stream of the original data into a matrix by serial-to-parallel conversion, and performing index selection and constellation mapping according to the matrix and the constellation codebook to obtain a probability distribution comprises: Convert the original data of the binary bit stream into an M×N1 matrix by serial-parallel conversion, where M represents the rows of the M×N1 matrix and N1 represents the columns of the M×N1 matrix; The bits on the row vector of the M×N1 matrix are divided into constellation mapping groups and index selection groups, with the ratio of constellation mapping groups to index selection groups being (n+1):1. The first (n+1)N1 / (n+2) columns are constellation mapping groups, and the last N1 / (n+2) columns are index selection groups. Every two bits on the index selection group are mapped one-to-one to n+1 symbols on the constellation codebook, and then the bits of the constellation mapping group corresponding to the index selection group are mapped according to the constellation mapping order corresponding to the symbols on the constellation codebook selected by every two bits of the index selection group, to obtain an M×N2 matrix after probability shaping, where N2=(n+1)N1 / (n+2), and N2 represents the column of the M×N2 matrix; the column vector of the M×N2 matrix after probability shaping is the transmitted subcarrier, each subcarrier carries M constellation-mapped symbols, and the symbol carries the frequency domain signal of the subcarrier, and the frequency domain signal includes amplitude and phase information.

[0012] In a second aspect, the present invention discloses a signal transmission method based on probability shaping of dual-mode index modulation. On the sending side, this includes: Obtaining a probability-shaped M×N2 matrix obtained by the probability shaping method described in the first aspect; Set an M×1024 empty matrix, insert the frequency domain signal of the probability-shaped matrix into the first N2 columns of the M×1024 empty matrix in columns to obtain a frequency domain signal matrix; Perform inverse Fourier transform on the frequency domain signal matrix column by column to convert the frequency domain signal into a time domain signal matrix of size M×1024; Adding cyclic prefixes and suffixes before and after the M×1024 time domain signal matrix to obtain an M×1320 time domain signal matrix, performing frequency conversion interpolation on the M×1320 time domain signal matrix, and converting the frequency conversion interpolation into a magnetic induction signal through a magnetic induction coil; On the receiving end, this includes: The magnetic induction signal sent by the transmitter after underwater transmission is received, the cyclic prefix and suffix of the magnetic induction signal are removed, the signal is deinterpolated through frequency conversion, and then converted into a frequency domain signal through Fourier transform. The M×N2 matrix after probability shaping is restored, and the original data is restored from the M×N2 matrix after probability shaping.

[0013] Furthermore, the restoration of the probability-shaped M×N2 matrix to obtain the original data includes: The M×N2 matrix after probability shaping is divided into M×N2 groups, each of which hides two bits of index information; Determine the mapped QPSK constellation through the constellation mapping group, and then determine the constellation mapping order; According to the constellation index mapping rule, all bits of the index selection group are obtained through the constellation mapping sequence; Then, demodulate each symbol one by one according to the mapping constellation corresponding to each symbol to obtain a constellation mapping group; The constellation mapping group is combined with the index selection group to obtain the original data of the binary bit stream.

[0014] In a third aspect, the present invention discloses a signal transmission system based on probability shaping of dual-mode index modulation, comprising: A transmitting end, configured to obtain a probability-shaped M×N2 matrix obtained by the probability shaping method described in the first aspect; Set an M×1024 empty matrix, insert the frequency domain signal of the probability-shaped matrix into the first N2 columns of the M×1024 empty matrix in columns to obtain a frequency domain signal matrix; Perform inverse Fourier transform on the frequency domain signal matrix column by column to convert the frequency domain signal into a time domain signal matrix of size M×1024; Adding cyclic prefixes and suffixes before and after the M×1024 time domain signal matrix to obtain an M×1320 time domain signal matrix, performing frequency conversion interpolation on the M×1320 time domain signal matrix, and converting the frequency conversion interpolation into a magnetic induction signal through a magnetic induction coil; The receiving end is used to receive the magnetic induction signal sent by the transmitting end after underwater transmission, remove the cyclic prefix and suffix of the magnetic induction signal, perform frequency conversion deinterpolation, and then convert it into a frequency domain signal through Fourier transform, restore the M×N2 matrix after probability shaping, and restore the M×N2 matrix after probability shaping to obtain the original data.

[0015] The beneficial effects achieved by the present invention are: Probabilistic shaping is performed using dual-mode index modulation. Compared to traditional probabilistic shaping methods, this new method offers reduced complexity, no redundancy, and increased flexibility. By monitoring underwater noise in real time and utilizing convex optimization to determine optimal probability parameters, the system can flexibly achieve arbitrary probability distributions by adjusting the ratio of the inner and outer mapping constellations as needed, significantly improving receiver sensitivity and optimizing system performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of a signal transmission method based on a novel probability shaping of dual-mode index modulation; Figure 2 This is a schematic diagram of the implementation process of probabilistic shaping; Figure 3 is the received signal constellation diagram; Figure 4 This is a comparison chart of the bit error rate curves after the original data is restored using the new probability shaping method and the ordinary 8QAM transmission signal; Figure 5 It is the 8QAM constellation diagram without probability shaping; Figure 6 It is the probabilistically shaped 8QAM constellation diagram. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0018] Embodiment 1: This embodiment introduces a probability shaping method based on dual-mode index modulation, including: Acquire underwater noise in the target area of ​​magnetic induction communication; Constructing a constellation codebook based on QPSK constellation A and QPSK constellation B with two different transmit powers according to the underwater noise, wherein QPSK constellation A is an inner mapping constellation with low transmit power, QPSK constellation B is an outer mapping constellation with high transmit power, and mapping probability distribution of the inner mapping constellation and the outer mapping constellation is determined according to the underwater noise; The bit stream of the original data is serial-to-parallel converted into a matrix, and index selection and constellation mapping are performed according to the matrix and the constellation codebook to obtain a probability-shaped matrix.

[0019] The mapping probability distribution of the inner mapping constellation and the outer mapping constellation is determined based on underwater noise, including: An optimal probability parameter is obtained by using convex optimization according to the underwater noise, and a mapping frequency ratio of an inner mapping constellation to an outer mapping constellation is adjusted according to the optimal probability parameter.

[0020] The method of obtaining an optimal probability parameter by using convex optimization according to the underwater noise and adjusting the mapping frequency ratio of the inner mapping constellation to the outer mapping constellation according to the optimal probability parameter comprises: The channel is estimated using the minimum mean square error estimation method to obtain the channel matrix H, with the number of rows and columns both being M*N2; the probability parameter can be expressed as the matrix A, with the number of rows and columns both being M*N2. To optimize the signal quality, we require that the sum of the channel noise power after probability shaping be minimized. The transmitted signal is a column vector x, with the number of columns being M*N2. The signal power after probability shaping is x T Ax, T represents the conjugate transpose of the vector; the received signal is a column vector y, the number of columns is M*N2, and the channel noise power can be expressed as x T A T HAx-y T y. At this time, the optimization problem can be expressed as: ; Because both the channel matrix and the probability shaping parameter matrix are symmetric and positive definite, this optimization problem is a typical semidefinite programming problem. Matlab's CVX function is used to find the optimal solution Ax that minimizes noise power. A represents the mapping probability corresponding to each symbol. This matrix allows us to determine the optimal ratio of the inner and outer mapping constellations.

[0021] The constellation codebook is constructed, comprising: The mapping probability distribution is 4:1, the inner mapping constellation is mapped 4 times, the outer mapping constellation is mapped once, and 4 is a positive integer; The mapping probability of the four points of the inner mapping constellation A is 4 / 20, and the mapping probability of the four points of the outer mapping constellation B is 1 / 20. There are four symbols in the constellation codebook, and each symbol can accommodate two bits. The corresponding relationship with the key bit is that when the index bit is 00, the corresponding original data is mapped four times on the A constellation and then mapped once on the B constellation; when the key bit is 01, the corresponding original data is first mapped once on the A constellation, then once on the B constellation, and finally mapped three times on the A constellation; when the key bit is 10, the corresponding original data is first mapped three times on the A constellation, then once on the B constellation, and finally mapped once on the A constellation; when the key bit is 11, the corresponding original data is first mapped twice on the A constellation, then once on the B constellation, and finally mapped twice on the A constellation. There are four combinations in total, and the constellation index mapping rule is obtained. The serial-to-parallel conversion of the bit stream of the original data into a matrix, performing index selection and constellation mapping according to the matrix and the constellation codebook to obtain a probability distribution includes: Convert the original data of the binary bit stream into a 240×66 matrix by serial-to-parallel conversion, where 240 represents the rows of the 240×66 matrix and 66 represents the columns of the 240×66 matrix; The bits on the row vector of the M×N1 matrix are divided into constellation mapping groups and index selection groups, with the first 55 columns being the constellation mapping group and the last 11 columns being the index selection group; Each two bits on the index selection group are mapped one-to-one to five symbols on the constellation codebook, and then the bits of the constellation mapping group corresponding to the index selection group are mapped according to the constellation mapping order corresponding to the symbols on the constellation codebook selected by each two bits of the index selection group, to obtain a probability-shaped 240×55 matrix, where 55 represents a column of the 240×55 matrix; the column vectors of the probability-shaped 240×55 matrix are transmitted subcarriers, each subcarrier carries 240 constellation-mapped symbols, and the symbols carry the frequency domain signals of the subcarriers, where the frequency domain signals include amplitude and phase information.

[0022] Example 2 is based on the same inventive concept as Example 1. This example introduces a signal transmission method based on a novel probability shaping of dual-mode index modulation, including: like Figure 1 As shown, first, a constellation codebook is designed using a 3:1 mapping probability allocation method. The original data is then converted from serial to parallel, and the bits on the matrix horizontal quantity are divided into a constellation mapping group and an index selection group. Every two bits on the index selection group are mapped one-to-one to four symbols on the constellation codebook, and then the bits of the constellation mapping group corresponding to the index selection group are mapped according to the constellation mapping order corresponding to the symbols on the constellation codebook selected by every two bits of the index selection group. After constellation mapping, a frequency domain signal is obtained, and the frequency domain signal is conjugated and merged. An inverse Fourier transform is then performed to obtain the OFDM transmission signal. After Fourier transform at the receiving end, the constellation modulation order of the signal is demodulated to obtain the bits of the index selection group, and then the constellation mapping group information is demodulated according to the constellation mapping order corresponding to the index selection group. The bits of the constellation mapping group and the index selection group are merged to obtain the original data.

[0023] (1) Constellation codebook design: The constellation codebook is composed of two QPSK constellations A and B with different transmission powers. The QPSK constellation with low transmission power is used as the inner mapping constellation A, and the QPSK constellation with high transmission power is used as the outer mapping constellation B. When designing the codebook, a mapping probability distribution of 3:1 is adopted. The QPSK constellation with low transmission power (inner mapping constellation A) is mapped three times, while the QPSK constellation with high transmission power (outer mapping constellation B) is mapped once. The mapping probability of the four points of the inner mapping constellation A is 3 / 16, and the mapping probability of the four points of the outer mapping constellation B is 1 / 16. There are four types of symbols in the constellation codebook, each of which can accommodate two bits. The corresponding relationship with the key bit is shown in Table 1. When the index bit is 00, the corresponding original data is mapped twice on the A constellation and once on the B constellation; when the key bit is 01, the corresponding original data is first mapped once on the A constellation, then mapped once on the B constellation, and finally mapped once on the A constellation. The superscripts (1), (2), and (3) represent the first, second, and third constellation points of A or B. By analogy, there are four combinations in total, and the specific mapping rules are given in Table 1.

[0024] Table 1 Constellation index mapping rules ; (2) Implementation of probabilistic shaping: The implementation process of probabilistic shaping is as follows Figure 2 As shown. The original data is a randomly generated binary bit stream, representing the initial signal to be transmitted. In this scheme, we take 21120 bits as an example. The original data is a 1×21120 bit stream. The bit stream is serial-to-parallel converted, and the binary data stream is converted from a 1×21120 matrix to a 240×44 matrix. The bits on the horizontal quantity of the matrix are divided into constellation mapping groups and index selection groups. Every two bits on the index selection group are mapped one-to-one to the four symbols on the constellation codebook, and then the bits of the constellation mapping group corresponding to the index selection group are mapped according to the constellation mapping order corresponding to the symbols on the constellation codebook selected by every two bits of the index selection group. That is, we get the following Figure 2 The probability distribution diagram is shown. After mapping, a 240×33 matrix is ​​obtained. The column vectors of the matrix are the transmitted subcarriers. Each subcarrier carries 240 symbols after constellation mapping. The symbols carry the subcarrier's amplitude and phase information, that is, the frequency domain signal.

[0025] (3) OFDM system transmission: A 240×1024 empty matrix is ​​created, and the 240×33 frequency domain signal is inserted column-by-column into the first 33 columns of the empty matrix. The frequency domain signal matrix is ​​then conjugated and inserted column-by-column into the last 33 columns of the empty matrix. This ensures that the inverse Fourier transform yields a real matrix. The resulting matrix is ​​then inverse Fourier transformed column-by-column to convert the frequency domain signal into a time domain signal, reducing the matrix size to 240×1024. Next, a cyclic prefix and suffix are added before and after the matrix to reduce crosstalk between symbol points. A cyclic prefix length of 128 and a suffix length of 40 are chosen. This matrix then becomes a 240×1320 time domain signal. The time domain signal matrix is ​​then subjected to frequency conversion interpolation to enhance its anti-interference capabilities. After frequency conversion interpolation, the signal is converted into a magnetic induction signal via a magnetic induction coil. After the magnetic induction signal is transmitted underwater, the cyclic prefix and suffix are removed, the signal is deinterpolated by frequency conversion, and then converted into a frequency domain signal by Fourier transform. The effective data matrix of 240×33 is restored to obtain the constellation points of the received signal. The constellation diagram is as follows: Figure 3 shown.

[0026] (4) Signal reception and demodulation: The received 240×33 constellation point matrix is ​​divided into 240×33 groups, each containing a two-bit index. The constellation point information is used to determine the mapped QPSK constellation and, in turn, the constellation mapping order. Following the constellation index mapping rules in Table 1, all bits of the index selection group can be obtained from the constellation mapping order. Each symbol is then demodulated one by one according to the mapped constellation to obtain the constellation mapping group. Finally, the constellation mapping group is combined with the index selection group to produce a 1×21120 raw binary data stream.

[0027] (5) Result analysis: In order to verify the performance of the proposed probabilistic shaping scheme, we compared the bit error rates of the transmitted signals before and after probabilistic shaping. Figure 4 The comparison of the bit error rate curves of the new probability shaping method and the ordinary 8QAM transmission signal after recovering the original data is shown respectively. BER is the bit error rate and SNR is the signal-to-noise ratio. Figure 5 , is a common 8QAM constellation diagram without probability shaping. It can be seen that the mapping probabilities of each constellation point are close. Figure 6 This is a constellation diagram of a new type of probability shaping using dual-mode index modulation. As can be seen from the figure, after probability shaping, the mapping probability of the middle constellation point becomes significantly higher. After using the new probability shaping method and the ordinary 8QAM transmission signal through the additive white Gaussian noise channel with the same signal-to-noise ratio, it can be seen that after probability shaping, the transmission probability of the constellation points with low transmission power within the constellation is significantly improved, which will effectively reduce the interference of additive white Gaussian noise. Figure 4As can be seen from the data, the new probabilistic shaping method is the first to reach the FEC bit error rate threshold and outperforms conventional 8QAM transmission at any signal-to-noise ratio. Furthermore, the new probabilistic shaping method achieves a sensitivity gain of 0.38dB at the FEC threshold bit error rate of 3.8×10⁻³. This demonstrates that the new probabilistic shaping method has excellent robustness against additive white Gaussian noise and holds great promise for future applications in underwater magnetic communication systems.

[0028] Embodiment 3, based on the same inventive concept as the other embodiments, introduces a signal transmission system based on probability shaping of dual-mode index modulation, including: A transmitting end, configured to obtain a probability-shaped M×N2 matrix obtained by the probability shaping method described in Example 1; Set an M×1024 empty matrix, insert the frequency domain signal of the probability-shaped matrix into the first N2 columns of the M×1024 empty matrix in columns to obtain a frequency domain signal matrix; Perform inverse Fourier transform on the frequency domain signal matrix column by column to convert the frequency domain signal into a time domain signal matrix of size M×1024; Adding cyclic prefixes and suffixes before and after the M×1024 time domain signal matrix to obtain an M×1320 time domain signal matrix, performing frequency conversion interpolation on the M×1320 time domain signal matrix, and converting the frequency conversion interpolation into a magnetic induction signal through a magnetic induction coil; The receiving end is used to receive the magnetic induction signal sent by the transmitting end after underwater transmission, remove the cyclic prefix and suffix of the magnetic induction signal, perform frequency conversion deinterpolation, and then convert it into a frequency domain signal through Fourier transform, restore the M×N2 matrix after probability shaping, and restore the M×N2 matrix after probability shaping to obtain the original data.

[0029] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, 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 magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0030] 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 flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, 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 flowcharts and / or block diagrams. 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.

[0031] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work 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 The function specified in one or more boxes.

[0032] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0033] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A probability shaping method based on dual-mode index modulation, characterized in that: include: Obtaining the underwater channel matrix of the magnetic induction communication target area; Constructing a constellation codebook based on two QPSK constellations A and QPSK constellations B with different transmit powers according to the underwater channel matrix, wherein the QPSK constellation A is an inner mapping constellation A with low transmit power, and the QPSK constellation B is an outer mapping constellation B with high transmit power, and mapping probability distribution of the inner mapping constellation A and the outer mapping constellation B is determined according to the underwater channel matrix; The bit stream of the original data is serial-to-parallel converted into a matrix, and index selection and constellation mapping are performed according to the matrix and the constellation codebook to obtain a probability-shaped matrix.

2. The probability shaping method based on dual-mode index modulation according to claim 1, characterized in that: The mapping probability distribution of the inner mapping constellation A and the outer mapping constellation B is determined according to the underwater channel matrix, including: An optimal probability parameter is obtained by using convex optimization according to the underwater channel matrix, and a mapping frequency ratio of an inner mapping constellation to an outer mapping constellation is adjusted according to the optimal probability parameter.

3. The probability shaping method based on dual-mode index modulation according to claim 2, characterized in that: The method of obtaining an optimal probability parameter by using convex optimization according to the underwater channel matrix and adjusting the mapping frequency ratio of the inner mapping constellation to the outer mapping constellation according to the optimal probability parameter comprises: The underwater channel is estimated using the minimum mean square error estimation method to obtain the underwater channel matrix H, with the number of rows and columns both being M*N2; the probability shaping parameter is expressed as the matrix A, with the number of rows and columns both being M*N2; The transmitted signal is a column vector x, the number of columns is M*N2, then the signal power after probability shaping is x T Ax, T represents the conjugate transpose of the vector; The received signal is a column vector y, the number of columns is M*N2, and the channel noise power is expressed as x T A T HAx-y T y; The optimization problem is expressed as: ； Both H and A are symmetric positive definite matrices. This optimization problem is a typical semidefinite programming problem. The optimization problem is solved to obtain the optimal solution Ax with the minimum channel noise power. A is the mapping probability corresponding to each symbol. A is used to obtain the ratio of the mapping times of the inner mapping constellation to the outer mapping constellation. The symbol is used to carry the amplitude and phase information of the subcarrier.

4. The probability shaping method based on dual-mode index modulation according to claim 1, characterized in that: The constellation codebook is constructed, comprising: The mapping probability distribution is n:1, the number of inner mapping constellation mappings is n times, the number of outer mapping constellation mappings is once, and n is a positive integer; The mapping probability of the four points of the inner mapping constellation A is n / 4(n+1), and the mapping probability of the four points of the outer mapping constellation B is 1 / 4(n+1); The constructed constellation codebook includes n+1 symbols, each symbol contains two bits, and the correspondence between each symbol and the key bit is arbitrarily modified under the condition that the ratio of the number of constellation A mappings to the number of constellation B mappings is n:1, thereby obtaining the constellation index mapping rule.

5. The probability shaping method based on dual-mode index modulation according to claim 4, characterized in that: The serial-to-parallel conversion of the bit stream of the original data into a matrix, performing index selection and constellation mapping according to the matrix and the constellation codebook to obtain a probability distribution includes: Convert the original data of the binary bit stream into an M×N1 matrix by serial-parallel conversion, where M represents the rows of the M×N1 matrix and N1 represents the columns of the M×N1 matrix; The bits on the row vector of the M×N1 matrix are divided into constellation mapping groups and index selection groups, with the ratio of constellation mapping groups to index selection groups being (n+1):

1. The first (n+1)N1 / (n+2) columns are constellation mapping groups, and the last N1 / (n+2) columns are index selection groups. Every two bits on the index selection group are mapped one-to-one to n+1 symbols on the constellation codebook, and then the bits of the constellation mapping group corresponding to the index selection group are mapped according to the constellation mapping order corresponding to the symbols on the constellation codebook selected by every two bits of the index selection group, to obtain an M×N2 matrix after probability shaping, where N2=(n+1)N1 / (n+2), and N2 represents the column of the M×N2 matrix; the column vector of the M×N2 matrix after probability shaping is the transmitted subcarrier, each subcarrier carries M constellation-mapped symbols, and the symbol carries the frequency domain signal of the subcarrier, and the frequency domain signal includes amplitude and phase information.

6. A signal transmission method based on probability shaping of dual-mode index modulation, characterized in that: On the sending side, this includes: Obtaining a probability-shaped M×N2 matrix obtained by the probability shaping method according to claim 5; Set an M×1024 empty matrix, insert the frequency domain signal of the probability-shaped matrix into the first N2 columns of the M×1024 empty matrix in columns to obtain a frequency domain signal matrix; Perform inverse Fourier transform on the frequency domain signal matrix column by column to convert the frequency domain signal into a time domain signal matrix of size M×1024; Adding cyclic prefixes and suffixes before and after the M×1024 time domain signal matrix to obtain an M×1320 time domain signal matrix, performing frequency conversion interpolation on the M×1320 time domain signal matrix, and converting the frequency conversion interpolation into a magnetic induction signal through a magnetic induction coil; On the receiving end, this includes: The magnetic induction signal sent by the transmitter after underwater transmission is received, the cyclic prefix and suffix of the magnetic induction signal are removed, the signal is deinterpolated through frequency conversion, and then converted into a frequency domain signal through Fourier transform. The M×N2 matrix after probability shaping is restored, and the original data is restored from the M×N2 matrix after probability shaping.

7. The signal transmission method based on probability shaping of dual-mode index modulation according to claim 6, characterized in that: The method of restoring the probability-shaped M×N2 matrix to obtain the original data includes: The M×N2 matrix after probability shaping is divided into M×N2 groups, each of which hides two bits of index information; Determine the mapped QPSK constellation through the constellation mapping group, and then determine the constellation mapping order; According to the constellation index mapping rule, all bits of the index selection group are obtained through the constellation mapping sequence; Then, demodulate each symbol one by one according to the mapping constellation corresponding to each symbol to obtain a constellation mapping group; The constellation mapping group is combined with the index selection group to obtain the original data of the binary bit stream.

8. A signal transmission system based on probability shaping of dual-mode index modulation, characterized in that: include: A transmitting end, configured to obtain a probability-shaped M×N2 matrix obtained by the probability shaping method according to claim 5; Set an M×1024 empty matrix, insert the frequency domain signal of the probability-shaped matrix into the first N2 columns of the M×1024 empty matrix in columns to obtain a frequency domain signal matrix; Perform inverse Fourier transform on the frequency domain signal matrix column by column to convert the frequency domain signal into a time domain signal matrix of size M×1024; Adding cyclic prefixes and suffixes before and after the M×1024 time domain signal matrix to obtain an M×1320 time domain signal matrix, performing frequency conversion interpolation on the M×1320 time domain signal matrix, and converting the frequency conversion interpolation into a magnetic induction signal through a magnetic induction coil; The receiving end is used to receive the magnetic induction signal sent by the transmitting end after underwater transmission, remove the cyclic prefix and suffix of the magnetic induction signal, perform frequency conversion deinterpolation, and then convert it into a frequency domain signal through Fourier transform, restore the M×N2 matrix after probability shaping, and restore the M×N2 matrix after probability shaping to obtain the original data.

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