An Orthogonal Chaotic Constellation Modulation Multicarrier Spread Spectrum Underwater Acoustic Communication Method

Abstract

An orthogonal chaotic constellation modulation multi-carrier spread-spectrum underwater acoustic communication method. The present invention relates to an orthogonal chaotic constellation modulation multi-carrier spread-spectrum underwater acoustic communication method, belonging to the technical field of underwater acoustic communication. The purpose of the present invention is to solve the problems of weak confidentiality and high bit error rate under deep sea channels in existing methods. The specific process is as follows: 1: Obtain a group of chaotic sequences; each group of Quadratic chaotic sequence groups includes M chaotic sequences with a length of N, and each chaotic sequence can carry log2M bits of information; 2: Obtain IN chaotic constellation symbols; 3: Obtain the interleaved IN chaotic constellation symbol sequences; 4: Transform the baseband signal into a passband multi-carrier signal; use a linear frequency modulation signal as the preamble signal, first transmit the preamble signal, and then transmit the passband multi-carrier signal; 5: Obtain the received signal after passive time reversal; 6: Sample the received signal after fast Fourier transform; 7: Demodulate the I groups of chaotic constellation symbol sequences contained in the sampled values to obtain information bits.

Description

Technical Field

[0001] The present invention relates to an orthogonal chaotic constellation modulation multi - carrier spread - spectrum underwater acoustic communication method, belonging to the technical field of underwater acoustic communication. Background Art

[0002] Underwater acoustic communication technology is a core technology with an important position in the ocean field and plays an important supporting role in underwater observation and operation. However, underwater acoustic communication using sound waves has openness and broadcast characteristics. While receiving and transmitting signals, it may be acquired and damaged by non - cooperative parties. The security of underwater acoustic communication is extremely important. When designing an underwater acoustic communication system, not only the rate and reliability but also the security need to be considered.

[0003] Due to its non - binary characteristics and non - periodic behavior, chaotic spread - spectrum sequences have application prospects in secure and covert communication. Chaotic spread - spectrum communication replaces the pseudo - random spread - spectrum code with a chaotic sequence, effectively solving the limitation of the periodicity of the pseudo - random spread - spectrum code. However, the quantized chaotic sequence still has binary characteristics. To achieve physical - layer encryption on the transmitted constellation diagram, a chaotic phase - modulation sequence is disclosed in Chinese Patent CN110266344A. The phase - modulation sequence is an unquantized complex - valued sequence, overcoming the disadvantages of the periodicity and binary nature of the pseudo - random sequence. Literature [Yue Ao, Li Wei, Ma Dongtang, etc. Physical - layer encryption transmission algorithm combining Latin array and amplitude - phase transformation. Signal Processing, 2016] uses a Latin array to scramble the positions of constellation points and obtains a more complex transmitted constellation diagram based on a key - encryption method. However, the encryption method controlled by the key requires key interaction and negotiation. The secure communication method of encrypting at the transmitter and decrypting at the receiver requires accurate compensation for the channel impact, and the complex multipath structure of the underwater acoustic channel increases the implementation difficulty of this type of method. The encryption method for underwater acoustic communication needs to be implemented in combination with the characteristics of the underwater acoustic channel. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of weak confidentiality and high bit - error rate in deep - sea channels of existing methods, and to propose an orthogonal chaotic constellation modulation multi - carrier spread - spectrum underwater acoustic communication method.

[0005] A specific process of an orthogonal chaotic constellation modulation multi - carrier spread - spectrum underwater acoustic communication method is as follows:

[0006] Step 1: Binomial Quadratic sequence q se The initial value is a randomly generated random number, and the binomial Quadratic sequence q se The recursive calculation formula is

[0007]

[0008] The parameters a and b satisfy the condition 3 / 4 < ab < 2;

[0009] Randomly generate M initial values, and substitute the M initial values into the recursive calculation formula of the binomial Quadratic sequence q se to generate M Quadratic chaotic sequences. The M Quadratic chaotic sequences form a chaotic sequence group;

[0010] Each group of Quadratic chaotic sequence groups includes M chaotic sequences of length N, and each chaotic sequence can carry log 2 M bits of information;

[0011] Step 2: Evenly divide the information bit sequence transmitted by the transmitter into two groups. Take out the information bits in the first group of information bit sequences as the first string of information bits; take out the information bits in the second group of information bit sequences as the second string of information bits; process the first string of information bits to obtain a chaotic sequence; process the second string of information bits to obtain a chaotic sequence; combine the chaotic sequences as the real part and the imaginary part respectively to obtain N chaotic constellation symbols S chaos Based on the N chaotic constellation symbols S chaos obtain IN chaotic constellation symbols;

[0012] Step 3: Interleave the IN chaotic constellation symbols to obtain an interleaved sequence of IN chaotic constellation symbols Place the interleaved sequence of IN chaotic constellation symbols on K subcarriers, where K = IN;

[0013] Step 4: Perform an inverse fast Fourier transform on the interleaved chaotic constellation symbol sequence of length K to obtain a transformed chaotic constellation symbol sequence. Add a zero-padding suffix to the transformed chaotic constellation symbol sequence to obtain a baseband signal; Transform the baseband signal s K to the passband multi-carrier signal x(t);

[0014] Use the chirp signal z(t) as the preamble signal, first transmit the preamble signal z(t), and then transmit the passband multi-carrier signal x(t);

[0015] Step 5: The receiving end obtains the received signal and processes the received signal to obtain the received signal after passive time reversal;

[0016] Step 6: Perform down-conversion, low-pass filtering, removing the zero-padding suffix, and fast Fourier transform on the received signal y ptr (t) in sequence to obtain a transformed received signal. Sample the transformed received signal at the baseband sampling rate B, and the sampling value is

[0017] Step 7: For the sampling value Demodulate the chaotic constellation symbol sequence in Group I included to obtain information bits.

[0018] The beneficial effects of the present invention are as follows:

[0019] The object of the present invention is to provide an orthogonal chaotic constellation modulation multi-carrier spread spectrum communication method that can achieve secure and reliable underwater acoustic communication. Orthogonal chaotic constellation modulation modulates information bits on two groups of chaotic sequences, and the two groups of chaotic sequences are orthogonally combined as the real part and the imaginary part respectively to enhance the confidentiality of underwater acoustic communication. The receiving end adopts an M-ary despreading method based on passive time reversal noise reduction to overcome the large time delay spread in the deep sea, performs time domain equalization by passive time reversal, and adopts a threshold noise reduction method to further reduce the influence of noise. This method transmits information with a chaotic constellation diagram, improves the bit error rate performance with passive time reversal noise reduction, and can achieve secure and reliable underwater acoustic communication.

[0020] The present invention utilizes the non-linear and unpredictable characteristics of the chaotic system, and uses a chaotic constellation diagram to transmit information to enhance the security of underwater acoustic communication. Aiming at the problem of insufficient security of general phase shift keying modulation and chaotic phase modulation, the present invention adopts orthogonal chaotic constellation modulation at the transmitting end. The transmitted constellation symbols are chaotic in both amplitude and phase, enhancing confidentiality. Aiming at the influence of the long time delay channel in the deep sea on the despreading at the receiving end, the present invention performs time domain equalization by passive time reversal and adopts a threshold noise reduction method to further reduce the influence of noise. The method of the present invention improves the security of underwater acoustic communication, and at the same time has good bit error rate performance, and has the advantages of good confidentiality and high reliability. Description of the Drawings

[0021] Figure 1 is a flowchart of an orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method;

[0022] Figure 2 is a schematic diagram of sub-carrier interleaving;

[0023] Figure 3 is a measured underwater acoustic channel diagram of the 110 km sound channel axis;

[0024] Figure 4 is an orthogonal chaotic constellation modulation constellation diagram;

[0025] Figure 5 is a diagram of the simulation result of the bit error rate performance under the 110 km sound channel axis underwater acoustic channel. Detailed Embodiments

[0026] Detailed Embodiment 1: The specific process of an orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method in this embodiment is as follows:

[0027] The transmitting end evenly divides the input information bit sequence into two groups, performs orthogonal chaotic constellation modulation on the real and imaginary parts of the chaotic constellation symbols, places the chaotic constellation symbols on subcarriers for multi-carrier modulation to obtain a passband multi-carrier signal to be transmitted, and adds a preamble signal before the passband multi-carrier signal for transmission. The receiving end performs time synchronization on the received underwater acoustic signal, extracts the channel using the preamble signal, then performs noise reduction processing on the extracted channel, and then performs passive time reversal. For the signal after passive time reversal, multi-carrier demodulation is performed to obtain a baseband signal, and finally, orthogonal chaotic constellation symbol demodulation is performed by a multi-path parallel correlator to obtain a binary sequence.

[0028] The flowchart of the orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method provided by the present invention is as Figure 1 shown, and specifically includes the following steps:

[0029] Symbol description: Bold indicates a vector or matrix, represents conjugate transpose, The tilde represents the frequency domain. * represents convolution operation, Re represents taking the real part, Im represents taking the imaginary part, (·) * represents conjugate operation, E(·) represents mathematical expectation, j represents the imaginary unit, and π and e represent constants.

[0030] Step 1: The binomial Quadratic sequence q se The initial value is a randomly generated random number, and the recursive calculation formula of the binomial Quadratic sequence q se is

[0031]

[0032] The parameters a and b satisfy the condition 3 / 4 < ab < 2;

[0033] Randomly generate M initial values, and substitute the M initial values into the recursive calculation formula of the binomial Quadratic sequence q se respectively to generate M Quadratic chaotic sequences, and the M Quadratic chaotic sequences form a chaotic sequence group;

[0034] For example, randomly generate 10 initial values, and substitute the 10 initial values into the recursive calculation formula of the binomial Quadratic sequence q se respectively to generate 10 Quadratic chaotic sequences, and the 10 Quadratic chaotic sequences form a chaotic sequence group;

[0035] Each group of Quadratic chaotic sequence groups includes M chaotic sequences with a length of N (N is set), and each chaotic sequence can carry log 2 M bit information;

[0036] Step 2: Evenly divide the information bit sequence transmitted by the transmitter into two groups. Extract information bits from the first group of information bit sequences as the first string of information bits; extract information bits from the second group of information bit sequences as the second string of information bits; process the first string of information bits to obtain a chaotic sequence; process the second string of information bits to obtain a chaotic sequence; combine the chaotic sequences as the real part and the imaginary part respectively to obtain N chaotic constellation symbols S chaos , and based on the N chaotic constellation symbols S chaos obtain IN chaotic constellation symbols;

[0037] Step 3: Interleave the IN chaotic constellation symbols to obtain an interleaved sequence of IN chaotic constellation symbols The interleaving method is shown in Figure 2 , and place the interleaved sequence of IN chaotic constellation symbols on K subcarriers, where K = IN;

[0038] Step 4: Perform an inverse fast Fourier transform (IFFT) on the interleaved chaotic constellation symbol sequence of length K to obtain a transformed chaotic constellation symbol sequence. Add a zero-padding suffix to the transformed chaotic constellation symbol sequence to obtain a baseband signal; transform the baseband signal s K to a passband multi-carrier signal x(t);

[0039] Use a chirp signal z(t) as the preamble signal. First transmit the preamble signal z(t), and then transmit the passband multi-carrier signal x(t);

[0040] Step 5: The receiving end obtains the received signal and processes the received signal to obtain the received signal after passive time reversal;

[0041] Step 6: Perform down-conversion, low-pass filtering, removing the zero-padding suffix, and fast Fourier transform on the received signal y ptr (t) in sequence to obtain a transformed received signal. Sample the transformed received signal at the baseband sampling rate B, and the sampling values are

[0042] Step 7: Demodulate the I groups of chaotic constellation symbol sequences contained in the sampling values to obtain information bits.

[0043] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that in step 2, the information bit sequence transmitted by the transmitter is evenly divided into two groups. Information bits are taken out from the first group of information bit sequences as the first string of information bits; information bits are taken out from the second group of information bit sequences as the second string of information bits; the first string of information bits is processed to obtain a chaotic sequence; the second string of information bits is processed to obtain a chaotic sequence; the chaotic sequences are combined as the real part and the imaginary part respectively to obtain N chaotic constellation symbols S chaos , based on the N chaotic constellation symbols S chaos obtain IN chaotic constellation symbols;

[0044] The specific process is as follows:

[0045] Step 21: Evenly divide the information bit sequence transmitted by the transmitter into two groups; the process is as follows:

[0046] Take the first half of the information bit sequence as the first group of information bit sequences, and take the second half of the information bit sequence as the second group of information bit sequences to obtain two groups of information bit sequences;

[0047] For example, if the information bit sequence is 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, it is evenly divided into two groups. The first group is 0, 1, 0, 1, 0, and the second group is 1, 1, 0, 0, 1;

[0048] Step 22: Take out log 2 M information bits in sequence (in sequence means in the order of 1, 2, 3, 4, 5) from the first group of information bit sequences as the first string of information bits;

[0049] Take out log 2 M information bits in sequence (in sequence means in the order of 1, 2, 3, 4, 5) from the second group of information bit sequences as the second string of information bits;

[0050] Step 23: Convert the first string of information bits into a decimal number, and obtain the corresponding chaotic sequence c i (n) in the chaotic sequence group with the decimal number as the index;

[0051] Convert the second string of information bits into a decimal number, and obtain the corresponding chaotic sequence u i (n) in the chaotic sequence group with the decimal number as the index;

[0052] Step 24: Combine the chaotic sequences c i (n) and u i (n) as the real part and the imaginary part respectively to obtain N chaotic constellation symbols S chaos ; The expression is:

[0053] Schaos c(n) = c i c(n) + ju(n) i c(n), n = 1...N

[0054] Step 25: Repeat Steps 22 to 24 for I times to obtain I groups of chaotic constellation symbol sequences. Each group of chaotic constellation symbols includes N chaotic constellation symbols, obtaining a total of IN chaotic constellation symbols, as well as the chaotic sequence c(n) and the chaotic sequence u(n); I c(n) and the chaotic sequence u(n) I c(n);

[0055] c I c(n) = c 1 c(n), …, c i c(n), …, c I c(n);

[0056] u I u(n) = u 1 u(n), …, u i u(n), …, u I u(n).

[0057] Other steps and parameters are the same as those in the first specific implementation manner.

[0058] Third specific implementation manner: The difference between this implementation manner and the first or second specific implementation manner is that in Step 3, the IN chaotic constellation symbols are interleaved to obtain an interleaved sequence of IN chaotic constellation symbols. The interleaving method is shown in , and the interleaved sequence of IN chaotic constellation symbols Figure 2 is placed on K subcarriers, where K = IN; The specific process is as follows:

[0059] Take the first chaotic constellation symbol in each group of chaotic constellation symbol sequences to form a new first group of chaotic constellation symbol sequences (including N chaotic constellation symbols);

[0060] Take the second chaotic constellation symbol in each group of chaotic constellation symbol sequences to form a new second group of chaotic constellation symbol sequences (including N chaotic constellation symbols);

[0061] Until taking the Nth chaotic constellation symbol in each group of chaotic constellation symbol sequences to form a new Nth group of chaotic constellation symbol sequences (including N chaotic constellation symbols);

[0062] Connect the new first group of chaotic constellation symbol sequences to the new Nth group of chaotic constellation symbol sequences to obtain an interleaved sequence of IN chaotic constellation symbols

[0063]

[0064] ​Place the interleaved sequence of IN chaotic constellation symbols on K sub - carriers, where K = IN.

[0065] Other steps and parameters are the same as those in the first or second specific implementation manner.

[0066] Specific implementation manner four: The difference between this implementation manner and one of the first to third specific implementation manners is that in step 4, the interleaved chaotic constellation symbol sequence of length K is subjected to an inverse fast Fourier transform (IFFT) to obtain a transformed chaotic constellation symbol sequence. A zero - padding suffix is added to the transformed chaotic constellation symbol sequence to obtain a baseband signal; the baseband signal s K is transformed into a pass - band multi - carrier signal x(t);

[0067] Using a chirp signal z(t) as a preamble signal, first transmit the preamble signal z(t), and then transmit the pass - band multi - carrier signal x(t);

[0068] The specific process is as follows:

[0069] Step 41: Perform an inverse fast Fourier transform (IFFT) on the interleaved chaotic constellation symbol sequence of length K to obtain a transformed chaotic constellation symbol sequence. A zero - padding suffix is added to the transformed chaotic constellation symbol sequence, and the length of zero - padding is v, to obtain a baseband signal as

[0070] where F zp is a (v + K)×K matrix, F K is a K×K inverse fast Fourier transform (IFFT) matrix, denotes conjugate transpose;

[0071] Step 42: Let f c be the carrier center frequency, B be the operating bandwidth, T d be the multi - carrier block data length, and T d = K / B;

[0072] Transform the baseband signal s K into a pass - band multi - carrier signal x(t);

[0073] The expression of the pass - band transmitted signal x(t) is:

[0074]

[0075] where Re represents taking the real part; represents a chaotic constellation symbol in the interleaved chaotic constellation symbol sequence; j represents the imaginary unit; π and e represent constants; g(t) represents a rectangular window; T zp represents the time length of the zero-padding suffix; t represents time;

[0076] The rectangular window g(t) is

[0077]

[0078] Step 43: Use the chirp signal z(t) as the preamble signal. First, transmit the preamble signal z(t), and then transmit the passband multi-carrier signal x(t).

[0079] Other steps and parameters are the same as those in one of the specific embodiments one to three.

[0080] Specific embodiment five: The difference between this embodiment and one of the specific embodiments one to four is that in step 5, the receiving end obtains the received signal and processes the received signal to obtain the received signal after passive time reversal;

[0081] The specific process is as follows:

[0082] Step 51: The passband signal x(t) is transmitted through the underwater acoustic channel to obtain the received signal y(t);

[0083] Step 52: Perform time synchronization, estimate the Doppler of the preamble signal z(t) to obtain the Doppler spread factor; based on the Doppler spread factor, resample and Doppler compensate the received signal y(t) to obtain the preamble signal after resampling Doppler compensation as z r (t);

[0084] The passband multi-carrier signal received by the receiving end is x r (t);

[0085] Step 54: Assume that the impulse response function of the channel is h(t);

[0086] Step 55: Perform matched filtering on the preamble signals z(t) and z r (t) to extract the channel. The extracted channel h′(t) is expressed as

[0087] h′(t) = z r (t) * z * (-t) = h(t) * [z(t) * z * (-t)] + w z (t) * z * (-t)

[0088] where, * represents the convolution operation, (·) * represents the conjugate operation, w z(t) represents the leading signal z r the noise of (t);

[0089] Step 56: Denoise the extracted channel h′(t) to obtain the denoised channel The process is as follows:

[0090] From the threshold Γ h clip the small paths in h′(t), and the denoising operation is expressed as

[0091]

[0092] where Γ h represents the threshold;

[0093] The threshold Γ h is divided into a hard threshold and a soft threshold;

[0094] The hard threshold is expressed as Γ h = ωmax(|h′(t)|), ω represents the denoising parameter, which is selected according to the empirical value;

[0095] The soft threshold is the mean value of the extracted channel, and the soft threshold is expressed as Γ h = E(|h′(t)|), E(·) represents the mathematical expectation;

[0096] When the prior information of the channel is known, use the hard threshold for denoising, otherwise use the soft threshold for denoising;

[0097] Step 57: Perform passive time reversal on the passband signal x r (t) received at the receiving end to obtain the received signal y ptr (t) after passive time reversal; The process is as follows:

[0098] Convolve the passband signal x r (t) received at the receiving end with to obtain the received signal y ptr (t) after passive time reversal, and the expression is:

[0099]

[0100] where w ptr (t) represents the noise in the passband signal x r (t) received after passive time reversal;

[0101] h ptr (t) represents the passive time reversal channel, and the expression is:

[0102] h ptr (t) = h(t) * h * (-t) * z(t) * z* (-t)

[0103] At the time delay of the strongest path (h ptr (t) maximum value) at time 0, time synchronization is performed on the received signal y ptr (t) that has undergone passive time reversal.

[0104] Other steps and parameters are the same as those in any one of the first to fourth specific embodiments.

[0105] Specific embodiment six: The difference between this embodiment and any one of the first to fifth specific embodiments is that in step 6, the received signal y ptr (t) that has undergone passive time reversal is successively down-converted, low-pass filtered, zero-suffix removed, and fast Fourier transformed to obtain the transformed received signal, and the transformed received signal is sampled at the baseband sampling rate B, and the sampling value is

[0106] Sampling value Is expressed as

[0107]

[0108] Among them, Represents the amplitude coefficient of the strongest path of the passive time-reversal channel, Represents the interference of the passive time-reversal channel, Represents after passive time reversal The noise in.

[0109] Other steps and parameters are the same as those in any one of the first to fifth specific embodiments.

[0110] Specific embodiment seven: The difference between this embodiment and any one of the first to sixth specific embodiments is that in step 7, the I-group chaotic constellation symbol sequence included in the sampling value Is demodulated to obtain information bits; the specific process is as follows:

[0111] Step 71: Set two groups (Re path and Im path) of parallel correlators for frequency-domain despreading, and each group has M correlators;

[0112] Step 72: For the i-th received constellation symbol sequence in the transmitted I-group chaotic constellation symbol sequence, from The real and imaginary parts at the corresponding positions are used to calculate the test statistics And The expression is:

[0113]

[0114] Among them, Represents the (i + Nn)-th sampled value in; c q (n) represents the spreading sequence corresponding to the q-th correlator on the Re path; represents the (i + Nn)-th in the interference of the passive time-reversal channel; represents after passive time-reversal the (i + Nn)-th in the noise in;

[0115] Im represents taking the imaginary part, u p (n) represents the spreading sequence corresponding to the p-th correlator on the Im path;

[0116] Step 73: According to c i (n) = c q when it is the maximum, u when (n) = u i (n) = u p when it is the maximum, the process of despreading according to the criterion of obtaining the maximum is as follows: Record the indexes q and p of the correlators that make

[0117] and and the maximum, and convert q and p into a binary information bit sequence.

[0118] Step 74: Repeat Step 72 to Step 73 until the demodulation of all a total of I groups of chaotic constellation symbols is completed, and a total of I × 2 × log 2 M information bits are obtained.

[0119] Other steps and parameters are the same as those in any one of the specific embodiments one to six.

[0120] The following embodiments are used to verify the beneficial effects of the present invention:

[0121] Embodiment 1:

[0122] The following conducts a simulation performance analysis in conjunction with the accompanying drawings. To verify the security and reliability of the present invention for underwater acoustic communication, a multi-carrier spread-spectrum underwater acoustic communication system is built, including K = 512 subcarriers, with a frequency band of 2 - 4 kHz, a sampling rate f s = 48 kHz, a signal length of 256 ms, a guard interval of 64 ms, and an M-ary spread-spectrum parameter of 64. The simulation uses the 110 km channel of the sound channel axis measured in a deep-sea test, as shown in the attached Figure 3 , and the channel delay spread reaches 200 ms. When the spreading code length N = 64, the constellation diagram drawn by the 512 chaotic constellation symbols obtained is shown in the attached Figure 4 . It can be seen from the attached drawings that the transmitted constellation symbols are randomly distributed in a certain area, enhancing the confidentiality of underwater acoustic communication.

[0123] Compare the bit error rate performance of three encryption methods, including: orthogonal chaotic constellation modulation, abbreviated as chaotic modulation; chaotic phase modulation; chaotic quantization; amplitude and phase transformation encryption controlled by a key, abbreviated as key encryption. The communication rates of various methods under different parameter configurations are: chaotic modulation 64, spreading code length 64, rate 300 bps; chaotic modulation 32, spreading code length 32, rate 600 bps; chaotic phase modulation 64, spreading code length 64, rate 150 bps; chaotic phase modulation 32, spreading code length 32, rate 300 bps; key encryption, spreading code length 64, rate 300 bps. The bit error rate simulation results are shown in the appendix Figure 5 。It can be seen from the attached drawings that the orthogonal chaotic constellation modulation multi-carrier spread-spectrum underwater acoustic communication method provided by the present invention can work stably in the deep-sea channel axis channel, with a communication rate of 300 bps, reaching about 10 at a signal-to-noise ratio of 0 dB -3 bit error rate. At the same rate, the bit error rate performance of the provided chaotic modulation method is better than the existing chaotic phase modulation and key encryption methods, reflecting the advantages of the present invention.

[0124] The present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. An orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method, characterized in that: The specific process of the method is: Step 1: Binomial Quadratic Sequence q se The initial value is a randomly generated random number, the binomial Quadratic sequence q se The recursive calculation formula is: Parameters a and b satisfy the condition 3 / 4<ab<2; Randomly generate M initial values ​​and bring them into the binomial Quadratic sequence q se The recursive calculation formula generates M Quadratic chaotic sequences, and M Quadratic chaotic sequences form a chaotic sequence group; Each Quadratic chaotic sequence group includes M chaotic sequences of length N, and each chaotic sequence can carry log2M bits of information; Step 2: Divide the information bit sequence transmitted by the transmitter into two groups on average, take out information bits from the first group of information bit sequences as the first string of information bits; take out information bits from the second group of information bit sequences as the second string of information bits; process the first string of information bits to obtain a chaotic sequence; process the second string of information bits to obtain a chaotic sequence; combine the chaotic sequences as the real part and the imaginary part respectively to obtain N chaotic constellation symbols S chaos , based on N chaotic constellation symbols S chaos Get IN Chaos Constellation symbols; Step 3: Interleave IN chaotic constellation symbols to obtain an interleaved IN chaotic constellation symbol sequence The IN chaotic constellation symbol sequences after interleaving Placed on K subcarriers, K = IN; Step 4: Interleaved chaotic constellation symbol sequence of length K Perform inverse fast Fourier transform to obtain the transformed chaotic constellation symbol sequence, add zero-filling suffix to the transformed chaotic constellation symbol sequence to obtain the baseband signal; K Transform to passband multi-carrier signal x(t); Using the linear frequency modulation signal z(t) as the pilot signal, the pilot signal z(t) is transmitted first, and then the passband multi-carrier signal x(t) is transmitted; Step 5: The receiving end obtains a received signal, and processes the received signal to obtain a passively time-reversed received signal; Step 6: Passively time-reversed received signal y ptr (t) Down-conversion, low-pass filtering, zero-padding removal, and fast Fourier transform are performed in sequence to obtain the transformed received signal, and the transformed received signal is sampled at the baseband sampling rate B, and the sampling value is Step 7: Sample values Demodulating the I group of chaotic constellation symbol sequences contained in to obtain information bits; In step 2, the information bit sequence transmitted by the transmitting end is evenly divided into two groups, information bits are taken from the first group of information bit sequences as the first string of information bits; information bits are taken from the second group of information bit sequences as the second string of information bits; the first string of information bits is processed to obtain a chaotic sequence; the second string of information bits is processed to obtain a chaotic sequence; the chaotic sequences are combined as real parts and imaginary parts respectively to obtain N chaotic constellation symbols S chaos , based on N chaotic constellation symbols S chaos Get IN Chaos Constellation symbols; The specific process is: Step 21: Divide the information bit sequence transmitted by the transmitter into two groups on average; the process is: The first half of the information bit sequence is used as the first group of information bit sequences, and the second half of the information bit sequence is used as the second group of information bit sequences, thereby obtaining two groups of information bit sequences; Step 22: sequentially extract log2M information bits from the first group of information bit sequences as the first string of information bits; Sequentially taking out log2M information bits from the second group of information bit sequences as the second string of information bits; Step 23: Convert the first string of information bits into decimal numbers, and use the decimal number as the index to obtain the corresponding chaotic sequence c in the chaotic sequence group. i (n); Convert the second string of information bits into decimal numbers, and use the decimal number as the index to obtain the corresponding chaotic sequence u in the chaotic sequence group. i (n); Step 24: Chaotic Sequence c i (n) and u i (n) are combined as the real part and the imaginary part respectively to obtain N chaotic constellation symbols S chaos ; The expression is: S chaos (n)=c i (n)+you i (n),n=1...N Step 25: Repeat steps 22 to 24 I times to obtain I groups of chaotic constellation symbol sequences, each group of chaotic constellation symbols includes N chaotic constellation symbols, and a total of IN chaotic constellation symbols and chaotic matrix C are obtained. I (n) and the chaos matrix U I (n); C I (n)=c1(n),…,c i (n),…,c I (n); YOU I (n)=u1(n),…,u i (n),…,u I (a).

2. According to claim 1, an orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method is characterized by: In step 3, IN chaotic constellation symbols are interleaved to obtain an interleaved IN chaotic constellation symbol sequence The IN chaotic constellation symbol sequences after interleaving Placed on K subcarriers, K = IN; The specific process is: Taking the first chaotic constellation symbol in each group of chaotic constellation symbol sequences to form a new first group of chaotic constellation symbol sequences; Taking the second chaotic constellation symbol in each group of chaotic constellation symbol sequences to form a new second group of chaotic constellation symbol sequences; Until the Nth chaotic constellation symbol in each group of chaotic constellation symbol sequences is taken to form a new Nth group of chaotic constellation symbol sequences; Connect the new first group of chaotic constellation symbol sequences to the new Nth group of chaotic constellation symbol sequences to obtain IN interleaved chaotic constellation symbol sequences The IN chaotic constellation symbol sequences after interleaving Placed on K subcarriers, K=IN.

3. According to claim 2, an orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method is characterized by: The chaotic constellation symbol sequence after interleaving with a length of K in step 4 Perform inverse fast Fourier transform to obtain the transformed chaotic constellation symbol sequence, add zero-filling suffix to the transformed chaotic constellation symbol sequence to obtain the baseband signal; K Transform to passband multi-carrier signal x(t); Using the linear frequency modulation signal z(t) as the pilot signal, the pilot signal z(t) is transmitted first, and then the passband multi-carrier signal x(t) is transmitted; The specific process is: Step 41: Interleaved chaotic constellation symbol sequence of length K Perform inverse fast Fourier transform to obtain the transformed chaotic constellation symbol sequence, add a zero-padding suffix to the transformed chaotic constellation symbol sequence, and the zero-padding length is v, and the baseband signal is obtained as Among them, F zp is a (v+K)×K matrix, F K is the K×K inverse fast Fourier transform matrix, represents conjugate transpose; Step 42: Set f c is the carrier center frequency, B is the operating bandwidth, T d is the multi-carrier block data length, T d =K / B; The baseband signal s K Transform to passband multi-carrier signal x(t); The expression of the passband transmission signal x(t) is: Among them, Re means taking the real part; represents a chaotic constellation symbol in the interleaved chaotic constellation symbol sequence; j represents an imaginary unit; π and e represent constants; g(t) represents a rectangular window; T zp Indicates the time length of the zero-filled suffix; t indicates time; The rectangular window g(t) is Step 43: Using the linear frequency modulation signal z(t) as a pilot signal, first transmit the pilot signal z(t) and then transmit the passband multi-carrier signal x(t).

4. According to claim 3, an orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method is characterized by: In step 5, the receiving end obtains a received signal, and processes the received signal to obtain a passively time-reversed received signal; The specific process is: Step 51: The passband signal x(t) is transmitted through the underwater acoustic channel to obtain a received signal y(t); Step 52: Perform time synchronization, perform Doppler estimation on the pilot signal z(t), and obtain the Doppler expansion factor; perform resampled Doppler compensation on the received signal y(t) based on the Doppler expansion factor, and obtain the pilot signal after resampled Doppler compensation as z r (t); Step 53: The passband multi-carrier signal received by the receiving end is x r (t); Step 54: Assume the impulse response function of the channel is h(t); Step 55: For the pilot signal z(t) and z r (t) is subjected to matched filtering to extract the channel, and the extracted channel h′(t) is expressed as h′(t)=z r (t)*z * (-t)=h(t)*pz(t)*z * (-t)[+w z (t)*z * (-t) Among them, * represents the convolution operation, (·) * represents the conjugate operation, w z (t) represents the leading signal z r (t) noise; Step 56: Perform noise reduction processing on the extracted channel h′(t) to obtain the channel after noise reduction processing The process is: The noise reduction operation is expressed as Among them, Γ h Indicates threshold; Threshold Γ h Divided into hard threshold and soft threshold; The hard threshold is denoted as Γ h =ωmax(|h′(t)|), ω represents the noise reduction parameter; The soft threshold is denoted as Γ h =E(|h′(t)|), E(·) represents the mathematical expectation; When the channel prior information is known, hard threshold noise reduction is used, otherwise soft threshold noise reduction is used; Step 57: The passband signal received by the receiving end is x r (t) Passive time reversal is performed to obtain the passive time-reversed received signal y ptr (t); the process is: The passband signal received by the receiving end is x r (t) Convolution is performed to obtain the passive time-reversed received signal y ptr (t), the expression is: Among them, w ptr (t) represents the received passband signal x after passive time reversal r Noise in (t); h ptr (t) represents the passive time reversal channel, which is expressed as: h ptr (t)=h(t)*h * (-t)*z(t)*z * (-t) The received signal y after passive time reversal is measured at the time when the delay of the strongest path of the passive time reversal channel is 0. ptr (t) Perform time synchronization.

5. According to claim 4, an orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method is characterized by: In step 6, the passively time-reversed received signal y ptr (t) Down-conversion, low-pass filtering, zero-padding removal, and fast Fourier transform are performed in sequence to obtain the transformed received signal, and the transformed received signal is sampled at the baseband sampling rate B, and the sampling value is Sample value Expressed as in, represents the amplitude coefficient of the strongest path of the passive anti-channel, represents the interference of the backchannel when passive, Indicates passive time reversal The noise in the 6. According to claim 5, an orthogonal chaotic constellation modulation multi-carrier spread spectrum underwater acoustic communication method is characterized by: In step 7, the sampling value The I group of chaotic constellation symbol sequences contained in are demodulated to obtain information bits; the specific process is: Step 71: setting two groups of parallel correlators, each group having a total of M correlators; Step 72: For the i-th group of received constellation symbol sequences in the transmitted I groups of chaotic constellation symbol sequences, The test statistics are calculated for the real and imaginary parts of the corresponding positions in and The expression is: in, express The i+Nnth sample value in c q (n) represents the spread spectrum sequence corresponding to the qth correlator of Re path; represents the i+Nnth interference of the passive time-reversal channel; Indicates passive time reversal The i+Nnth noise in ; Im means taking the imaginary part, u p (n) represents the spreading sequence corresponding to the p-th correlator of Im path; Step 73: According to c i (n) = c q (n) Maximum, u i (n) = u p (n) The maximum criterion is used for despreading, and the process of obtaining the binary information bit sequence is: Recorder and The index q and p of the largest correlator, converting q and p into a binary information bit sequence; Step 74: Repeat step 72 to step 73 until all I groups of chaotic constellation symbols are demodulated and a total of I×2×log2M information bits are obtained.

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