CN104753561B - Direct sequence spread spectrum modulation method for suppressing multipath interference in underwater acoustic communication - Google Patents

Abstract

The invention provides a direct sequence spread spectrum modulation method for suppressing multi-channel interference in underwater acoustic communication. The direct sequence spread spectrum modulation method uses a complementary sequence pair as a pseudo-random sequence of direct sequence spread spectrum modulation, introduces underwater acoustic communication, and utilizes The ideal correlation function in the zero-correlation window constructed by it has better multi-path suppression ability than ordinary finite-length random sequences, and can completely suppress multi-path interference in underwater acoustic spread spectrum communication; according to actual needs, two kinds of The combination method of "complementary sequence" pairs constructs the pseudo-random sequence of direct sequence spread spectrum modulation: the time-division orthogonal combination method can reduce the transmission duty cycle, thereby cooling the power amplifier. It is not sensitive to the carrier phase and does not require precise carrier phase synchronization; the information transmission efficiency of the carrier phase orthogonal combination method is consistent with that of ordinary m-sequence, Gold sequence and other pseudo-random sequence spread spectrum modulation. When the signal-to-noise ratio is high, The demodulation error rate of this mode is better.

Description

A Direct Sequence Spread Spectrum Modulation Method for Suppressing Multi-path Interference in Underwater Acoustic Communication

technical field

The invention belongs to the technical field of underwater acoustic spread spectrum communication, in particular to a direct sequence spread spectrum modulation method for suppressing multipath interference in underwater acoustic communication.

Background technique

In underwater acoustic communication, the inter-symbol interference (ISI) caused by the multipath effect is the main reason for limiting the information transmission rate. In this regard, the use of direct sequence spread spectrum modulation can not only increase the transmission distance of the signal, but also have a strong inhibitory effect on multi-path signals with a delay greater than one spread spectrum chip according to the sharp autocorrelation characteristics of the PRN code. Therefore, underwater acoustic communication based on DSSS modulation scheme has been extensively studied. In DSSS modulation technology, commonly used spread spectrum codes include m-sequence, Gold code, chaos code and so on. However, in engineering applications, only limited-length spreading codes can be used for signal modulation and demodulation. However, from the Welch bound given in the document "Welch L R. Lower bounds on the maximum cross-correlation of signals [J]. IEEETransactions Information Theory, 1974, 20:397-399." , the ideal autocorrelation or cross-correlation function cannot be obtained. Therefore, non-ideal auto-correlation and cross-correlation make the spread spectrum system unable to completely suppress inter-symbol interference (ISI) and multiple access interference (MAI), improving the correlation characteristics of random sequences has become one of the effective means to suppress multi-path interference.

In order to reduce or even eliminate intersymbol interference (ISI) and multiple access interference (MAI), in the document "Sta′nczak S. Boche H. Haardt M. Are LAS-codes a miracle? [J]. Global Telecommunications Conference, 2001. GLOBECOM' 01. IEEE, 2001, 1:589-593." provides the LS codes for the LAS-CDMA system. The LS code is a "complementary series" with a zero-correlation window (IFW). Within the zero-correlation window, the pair of "complementary sequences" has ideal autocorrelation and cross-correlation functions. The proposal of this spreading code is mainly used in mobile wireless communication networks to reduce the intersymbol interference (ISI) and multiple access interference (MAI) of the CDMA system and improve the capacity of the cellular network.

Contents of the invention

The purpose of the present invention is to provide a direct sequence spread spectrum modulation method for suppressing multi-path interference in underwater acoustic communication in order to solve the technical problem that the existing direct sequence spread spectrum modulation method cannot completely suppress multi-path interference in underwater acoustic communication, The direct sequence spread spectrum modulation method uses the complementary sequence pair as the pseudo-random sequence of the direct sequence spread spectrum modulation, introduces underwater acoustic communication, and uses the ideal correlation function in the zero correlation window constructed by it to achieve better performance than ordinary finite-length random sequences. multipath suppression capability.

In order to achieve the above object, the present invention provides a direct sequence spread spectrum modulation method for suppressing multi-channel interference in underwater acoustic communication, the direct sequence spread spectrum modulation method comprising:

Step 1) Construct two sequences that satisfy the "complementary sequence" pair relationship;

Step 2) Perform orthogonal combination of the two sequences obtained in step 1) to generate a pseudo-random sequence, and use the pseudo-random sequence as a spreading code;

Step 3) Calculate the duration of a single spread code chip according to the transmission bandwidth of the spread spectrum signal, calculate the duration of a single information chip according to the information transmission rate, and then calculate the spread spectrum corresponding to a single information chip The number of code chips;

Step 4) According to the result calculated in step 3), the transmitted information chips are respectively multiplied by modulo 2 with the pseudo-random sequence obtained in step 2) according to the corresponding number relationship, and combined to generate a complex baseband spread spectrum signal;

Step 5) Multiply the complex baseband spread spectrum signal obtained in step 4) by the signal carrier and take the real part to obtain the spread spectrum transmission signal.

As a further improvement of the above technical solution, each sequence generated in step 1) is represented in the continuous time domain as:

Among them, the length of the sequence is N, t represents time, c _n represents the sequence value of the nth pseudo-random sequence, rect( ) is a square wave function T _C represents the duration of a single chip of the pseudo-random sequence;

The correlation function of the "complementary sequence" pair is defined as:

Among them, τ represents the delay of sequences A _i and A _j , A _i , A _j , B _i , B _j are all pseudo-random sequences satisfying the relationship of "complementary sequence". When i=j, the above formula describes the autocorrelation characteristic ; i≠j describes the cross-correlation characteristics.

As a further improvement of the above technical solution, the information chips transmitted in step 4) are expressed as:

Among them, d _n represents the value of the nth information sequence, t represents time, and T _d represents the duration of a single information sequence.

As a further improvement of the above technical solution, the signal carrier in step 5) is expressed as:

in, Indicates the imaginary unit, ω is the carrier angular frequency, is the initial phase of the carrier, and t represents the time.

As a further improvement of the above technical solution, in the step 2) the orthogonal combination generates a pseudo-random sequence in a time-division manner. After the two sequences are arranged in chronological order, a certain length of value 0 is added between the two sequences sequence, the obtained pseudo-random sequence is expressed as:

Among them, A _n and B _n represent sequences, W represents the number of 0s added between the two sequences, S represents a pseudo-random sequence, and its length is 2(N+W);

According to the definition of the correlation function, the correlation function of formula (5) is expressed as:

Among them, A _i , A _j , B _i , and B _j are all pseudo-random sequences satisfying the "complementary sequence" relationship. When i=j, the above formula describes the autocorrelation characteristic; i≠j describes the cross-correlation characteristic.

As a further improvement of the above technical solution, the spread spectrum transmission signal obtained in step 5) is expressed as:

Among them, T _C represents the duration of a single chip of the pseudo-random sequence, t represents the time, Indicates the information chip, with Indicates the sequence, ω is the carrier angular frequency is the initial phase of the carrier, and T _d represents the duration of a single information sequence.

As a further improvement of the above technical solution, in the step 2) the orthogonal combination generates the pseudo-random sequence using the carrier phase quadrature method, and the two sequences are respectively adjusted to the orthogonal carrier with a phase difference of 90 degrees, and the pseudo-random sequence obtained is A random sequence is expressed as:

CS＝A _n + jB _n (8)

Among them, A _n and B _n represent sequences, Represents the imaginary number unit, CS represents the pseudo-random sequence in complex number form after combination, and its length is N;

According to the definition of correlation function, the correlation function of formula (8) is:

The real part of the correlation function Expressed as:

The imaginary part of the correlation function Expressed as:

Among them, A _i , A _j , B _i , and B _j are all pseudo-random sequences satisfying the "complementary sequence" relationship. When i=j, the above formula describes the autocorrelation characteristic; i≠j describes the cross-correlation characteristic.

As a further improvement of the above technical solution, the spread spectrum transmission signal obtained in step 5) is expressed as:

Among them, T _C represents the duration of a single chip of the pseudo-random sequence, t represents the time, Indicates the information chip, with represents a sequence, Indicates the combined pseudo-random sequence in the form of complex numbers, ω is the carrier angular frequency, is the initial phase of the carrier, and T _d represents the duration of a single information sequence.

As a further improvement of the above technical solution, the "complementary sequence" pair adopts LS code.

The advantages of a direct sequence spread spectrum modulation method for suppressing multi-path interference in underwater acoustic communication of the present invention are:

The present invention adopts the "complementary sequence" pair as a pseudo-random sequence in underwater acoustic spread spectrum communication, which can construct ideal autocorrelation and cross-correlation functions, and can completely suppress multi-path interference in underwater acoustic spread spectrum communication in theory; Provide two combination methods of "complementary sequence" pairs, which can be selected according to the specific situation: 1) Time-division orthogonal combination method: the sequence with a value of 0 added between complementary sequences can reduce the emission duty cycle, thereby cooling The role of the power amplifier; this kind of signal is not sensitive to the carrier phase when using quadrature demodulation, and does not require precise carrier phase synchronization; when the signal-to-noise ratio is low, the demodulation error rate of this method is better than that of mode 2); 2) Carrier phase quadrature combination method: The information transmission efficiency of this method is consistent with that of ordinary m-sequence, Gold sequence and other pseudo-random sequence spread spectrum modulation, which is more efficient than method 1); when the signal-to-noise ratio is high, this method The demodulation bit error rate is better than mode 1).

Description of drawings

Fig. 1 is a flowchart of a direct sequence spread spectrum modulation method for suppressing multi-path interference in underwater acoustic communication according to the present invention.

Fig. 2 is a schematic diagram of the structure of the "complementary sequence" pair in the present invention, which is orthogonally combined to generate a pseudo-random sequence in a time-division manner.

Fig. 3 is the autocorrelation function of pseudo-random sequence generated by orthogonal combination in time-division mode in the present invention.

Fig. 4 is the cross-correlation function of pseudo-random sequence generated by orthogonal combination in time-division mode in the present invention.

Fig. 5 is the autocorrelation function of the pseudo-random sequence generated by the quadrature combination of carrier phase quadrature in the present invention.

Fig. 6 is the cross-correlation function of the pseudo-random sequence generated by the quadrature combination of carrier phase quadrature in the present invention.

FIG. 7 is a three-dimensional diagram of the CZT time-frequency search of the lake test CZT time-frequency search based on the time-division method in the present invention.

FIG. 8 is a three-dimensional diagram of the CZT time-frequency search of the lake test CZT time-frequency search of the spread spectrum transmission signal obtained based on the carrier phase quadrature method in the present invention.

detailed description

A direct sequence spread spectrum modulation method for suppressing multi-path interference in underwater acoustic communication according to the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in Fig. 1, a kind of direct sequence spread spectrum modulation method of the present invention suppresses multi-path interference in underwater acoustic communication, described direct sequence spread spectrum modulation method comprises:

Step 1) Construct two sequences A code and B code that satisfy the "complementary sequence" pair relationship, that is, the two sequences are mutually orthogonal sequences, and the aperiodic autocorrelation or cross-correlation function of A code and the autocorrelation or The cross-correlation functions are equal at zero delay, and are equal in absolute value and opposite in sign elsewhere;

Step 2) Perform orthogonal combination of the two sequences obtained in step 1) to generate a pseudo-random sequence, and use the pseudo-random sequence as a spreading code;

Step 3) Calculate the duration of a single spread code chip according to the transmission bandwidth of the spread spectrum signal, calculate the duration of a single information chip according to the information transmission rate, and then calculate the spread spectrum corresponding to a single information chip The number of code chips;

Step 4) According to the result calculated in step 3), the transmitted information chips are respectively multiplied by modulo 2 with the pseudo-random sequence obtained in step 2) according to the corresponding number relationship, and combined to generate a complex baseband spread spectrum signal;

Step 5) Multiply the complex baseband spread spectrum signal obtained in step 4) by the signal carrier and take the real part to obtain the spread spectrum transmission signal.

Based on the above direct sequence spread spectrum modulation method, assuming that the length of the sequence is N, the two sequences satisfying the "complementary sequence" pair relationship can be expressed in the continuous time domain as:

Among them, t represents time, c _n represents the sequence value of the nth pseudo-random sequence, rect( ) is a square wave function T _C represents the duration of a single chip of the pseudo-random sequence.

The correlation function of the "complementary sequence" pair can be defined as:

Among them, τ represents the delay of sequences A _i and A _j , A _i , A _j , B _i , B _j are all pseudo-random sequences satisfying the relationship of "complementary sequence". When i=j, the above formula describes the autocorrelation characteristic ; i≠j describes the cross-correlation characteristics. It can be seen from the formula (2) that the autocorrelation and cross-correlation characteristics of the constructed correlation function of the "complementary sequence" are ideal, that is, the autocorrelation has a pulse at 0 delay; Both correlation and cross-correlation are 0.

In addition, the information chips transmitted in step 4) can be expressed as:

Among them, d _n represents the value of the nth information sequence, t represents time, and T _d represents the duration of a single information sequence.

The signal carrier in the step 5) can be expressed as:

in, Indicates the imaginary unit, ω is the carrier angular frequency, is the initial phase of the carrier, and t represents the time. In the present invention, there are many pairs of "complementary sequences" that can be used as pseudo-random sequences and their construction methods. In this embodiment, the LS code is taken as an example as a "complementary sequence" pair spreading code for underwater acoustic spread spectrum communication. Assuming (c _N ,s _N ) and (c′ _N ,s′ _N ) are the same complementary sequence pair, when N=2, the basic complementary sequence pair code group can be expressed as:

According to the following tree iteration, each iteration can obtain a complementary sequence pair code group whose length is doubled.

After n times of expansion, 2 ⁿ pairs of "complementary sequence" pairs with a coding length of 2 ⁿ N can be obtained.

Since the non-periodic autocorrelation function of C code and the autocorrelation function of S code are equal at zero delay, the absolute value is equal in other places, and the sign is opposite. Therefore, the C code and the S code are combined in a certain way, and in the orthogonal interval of the C code and the S code, the correlation functions are superimposed to form a "zero correlation window", thereby forming the LS code.

In order to construct the ideal correlation function of the sequence A code and B code (the sequence value of A code and B code can only take +1 or -1) in the "complementary sequence" pair in the zero correlation window, it is necessary to ensure that the sequence A code and B code Correlation operations cannot occur, that is, sequence A code and B code are orthogonal in a certain sense. In order to achieve the purpose of orthogonality during modulation, the present invention provides two feasible methods:

1) Time-division method: Arrange the sequence A code and B code in the "complementary sequence" pair in chronological order, and add a sequence with a certain length of 0 between the sequence A code and B code, thereby realizing two The orthogonal combination of sequence A code and B code generates a pseudo-random sequence. The structure of the pseudo-random sequence shown in Figure 1 can be expressed as:

Among them, A _n and B _n represent sequences, W represents the number of 0s added between the two sequences, S represents a pseudo-random sequence, and its length is 2(N+W);

According to the definition of the correlation function, the correlation function of formula (7) is expressed as:

Among them, A _i , A _j , B _i , and B _j are all pseudo-random sequences satisfying the "complementary sequence" relationship. When i=j, the above formula describes the autocorrelation characteristic; i≠j describes the cross-correlation characteristic.

Obviously, when the time delay |τ|<W, the ideal correlation function can be obtained for the pseudo-random sequence formed by the "complementary sequence" pair orthogonally combined in a time-division manner.

2) Carrier Phase Orthogonal Mode: The sequence A code and B code in the "complementary sequence" pair are respectively adjusted to two orthogonal carriers with a phase difference of 90 degrees, thereby realizing the orthogonal combination generation of the two sequences pseudorandom sequence. The obtained pseudo-random sequence can be expressed as:

CS＝A _n + jB _n (9)

Among them, A _n and B _n represent sequences, Represents the imaginary number unit, CS represents the pseudo-random sequence in complex number form after combination, and its length is N;

According to the definition of the correlation function, the correlation function of formula (9) is expressed as:

real part of the correlation function Expressed as:

imaginary part of the correlation function Expressed as:

Among them, A _i , A _j , B _i , and B _j are all pseudo-random sequences satisfying the "complementary sequence" relationship. When i=j, the above formula describes the autocorrelation characteristic; i≠j describes the cross-correlation characteristic.

Obviously, from the correlation function of the real part of formula (11), it can be seen that the real part of the correlation function of the pseudo-random sequence formed by the "complementary sequence" pair orthogonally combined in the carrier phase quadrature method has Ideal autocorrelation and cross-correlation functions.

It can be seen from the formula (12) that the imaginary part of the correlation function of the spread spectrum codes orthogonally combined in the carrier phase quadrature mode represents the result of the cross-correlation between the sequence A code and B code in the "complementary sequence", although Its value is not always equal to 0 in any delay area, but because the sequence A code and B code are orthogonal, the magnitude of the imaginary part is very small, and the impact on the entire correlation function is also small. In order to make full use of the ideal correlation characteristics of the combination code, for the correlation demodulation of this spreading code, only the real part of the correlation result needs to be taken out as an effective output result.

According to the direct sequence spread spectrum modulation method of the spread spectrum signal, when the time division method is adopted, the spread spectrum transmitted signal obtained by combining the formulas (1), (3) and (7) is expressed as:

When the carrier phase quadrature method is adopted, the spread spectrum transmission signal obtained by combining formulas (1), (3) and (9) is expressed as:

According to the basic theory of spread spectrum communication, assuming that there is at least one complete pseudo-random spread spectrum sequence in one information chip, the correlation of the spread spectrum transmitted signal on the baseband calculated by formula (13) and formula (14) characteristics, which are determined by the correlation functions of Equation (3) and Equation (4), respectively.

The specific embodiment of the present invention will be further described in detail below in combination with the actual transmission signal of a certain lake test.

The parameters of the spread spectrum transmitted signal based on the LS code transmitted in the experiment are as follows:

Signal bandwidth: 4KHz ~ 8KHz, center frequency: 6KHz.

Step 201): Generate the sequence A code and B code of the "complementary sequence" pair. This step can generate the required length of the "complementary sequence" pair C code and S code according to the iterative method of formulas (5) and (6).

Step 202): According to the "complementary sequence" in step 201), the C code and the S code are orthogonally combined to generate a pseudo-random sequence, and two pseudo-random spread spectrum sequences are obtained: 1) Generate a C code with a length of 512 chips and S code, 512 chips of 0 are inserted between the C code and the S code, and combined into a spreading code with a length of 2048 chips according to the time-division orthogonal form; 2) Generate a C code and an S code with a length of 1024 chips , combined into a complex spreading code with a length of 1024 chips according to the carrier phase orthogonal form.

Step 203): Calculate the duration T _C of a single spread spectrum code chip according to the transmission bandwidth of the spread spectrum signal; calculate the duration T _d of a single information chip according to the information transmission rate; then calculate a single information chip The number of chips of the corresponding spreading sequence.

Step 204): According to the result calculated in step 203), the transmitted information chips are multiplied by modulo 2 with the two pseudo-random spread spectrum sequences obtained in step 202) according to the corresponding number relationship, and according to the formula (7 ) and (9) to combine to generate a complex baseband spread spectrum signal.

Step 205: Perform direct sequence spread spectrum modulation according to formula (13) or (14), multiply the complex baseband spread spectrum signal by the signal carrier and take the real part to obtain the spread spectrum transmit signal.

Figure 3 and Figure 4 show the autocorrelation and cross-correlation results of the pseudo-random sequence generated by the time-division orthogonal combination according to the above-mentioned lake test experiment, which consists of the C code and the S code with a length of 512 chips according to the time-division regularization Combination in the form of intersection, 512 chip-length 0s are inserted between the C code and the S code. It can be seen from the figure that the interval of the formed zero-correlation window (IFW) is (-512,512), and within the zero-correlation window, the combined code has ideal autocorrelation and cross-correlation functions.

Figure 5 and Figure 6 show the autocorrelation and cross-correlation results of the pseudo-random sequence generated by the orthogonal combination of the carrier phase orthogonal method according to the above-mentioned test experiment, which consists of the C code and the S code with a length of 1024 chips Combined in the form of real and imaginary parts of complex numbers. It can be seen from the figure that within any time delay, the real part of the correlation function of this combined code has ideal autocorrelation and cross-correlation values, which is consistent with the theoretical results described in formula (11).

Figure 7 and Figure 8 show the three-dimensional results obtained by CZT time-frequency search of two "complementary sequences" on the spread spectrum signal of the combined code according to the above-mentioned lake test. It can be seen that the area outside the main peak of the search results is very flat, which means that the two spread spectrum signals can have good correlation characteristics and can achieve good multi-path signal suppression capabilities.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent replacements to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all of them should be included in the scope of the present invention. within the scope of the claims.

Claims (9)

1. A direct sequence spread spectrum modulation method for suppressing multi-path interference in underwater acoustic communication, characterized in that, the direct sequence spread spectrum modulation method comprises: Step 1) Construct two sequences that satisfy the pair relationship of "complementary sequences", that is, the two sequences are mutually orthogonal sequences, and the aperiodic autocorrelation or cross-correlation function of one sequence and the autocorrelation or cross-correlation function of the other sequence Equal at zero delay, equal in absolute value and opposite in sign elsewhere; Step 2) carrying out orthogonal combination of the two sequences obtained in step 1) to generate a pseudo-random sequence, using the pseudo-random sequence as a spreading code; Step 3) Calculate the duration of a single spread spectrum code chip according to the transmission bandwidth of the spread spectrum signal, calculate the duration of a single information chip according to the information transmission rate, and then calculate the corresponding slave step of a single information chip 2) the number of chips of the spreading code obtained; Step 4) according to the result calculated in step 3), after the information chip of transmission is done modulus 2 multiplication with the pseudo-random sequence obtained in step 2) respectively according to the corresponding number relationship, the complex baseband spread spectrum signal is combined to generate; Step 5) multiplying the complex baseband spread spectrum signal obtained in step 4) by the signal carrier and taking the real part to obtain the spread spectrum transmission signal. 2. the direct-sequence spread spectrum modulation method that suppresses multi-path interference in underwater acoustic communication according to claim 1, is characterized in that, each sequence that generates in step 1) is represented as on continuous time domain: ${\mathrm{<span\; class="notranslate">\; C</span>}}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; rect</span>}}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; n</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Element;</span><span\; class="notranslate">\; \{</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ Among them, the length of the sequence is N, t represents time, c _n represents the sequence value of the nth pseudo-random sequence, rect( ) is a square wave function T _C represents the duration of a single chip of the pseudo-random sequence; The correlation function of the "complementary sequence" pair is defined as: ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; j</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&NotEqual;</span>\mathrm{<span\; class="notranslate">\; j</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; \&NotEqual;</span>\mathrm{<span\; class="notranslate">\; 0</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ Among them, τ represents the delay of sequences A _i and A _j , A _i , A _j , B _i , B _j are all pseudo-random sequences satisfying the relationship of "complementary sequence". When i=j, the above formula describes the autocorrelation characteristic , i≠j describes the cross-correlation characteristics. 3. the direct-sequence spread spectrum modulation method that suppresses multi-path interference in underwater acoustic communication according to claim 1, is characterized in that, described step 4) in the information chip that transmits is expressed as: ${\mathrm{<span\; class="notranslate">\; d</span>}}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; rect</span>}}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; n</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Element;</span><span\; class="notranslate">\; \{</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ Among them, d _n represents the value of the nth information sequence, t represents time, and T _d represents the duration of a single information sequence. 4. the direct sequence spread spectrum modulation method that suppresses multi-path interference in underwater acoustic communication according to claim 1, is characterized in that, the signal carrier in described step 5) is expressed as: in, Indicates the imaginary unit, ω is the carrier angular frequency, is the initial phase of the carrier, and t represents the time. 5. the direct-sequence spread spectrum modulation method that suppresses multi-path interference in underwater acoustic communication according to claim 1, is characterized in that, described step 2) in orthogonal combination generation pseudo-random sequence adopts time-division mode, two sequences After being arranged in chronological order, a sequence with a certain length of 0 is added between the two sequences, and the obtained pseudo-random sequence is expressed as: Among them, A _n and B _n represent sequences, W represents the number of 0s added between the two sequences, S represents a pseudo-random sequence, and its length is 2(N+W); According to the definition of the correlation function, the correlation function of formula (5) is expressed as: ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; j</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&NotEqual;</span>\mathrm{<span\; class="notranslate">\; j</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; W</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$ Among them, A _i , A _j , B _i , and B _j are all pseudo-random sequences satisfying the relationship of "complementary sequence". When i=j, the above formula describes the autocorrelation characteristic, and i≠j describes the cross-correlation characteristic. 6. according to claim 2,3,4 or 5, suppress the direct sequence spread spectrum modulation method of multi-path interference in the underwater acoustic communication, it is characterized in that, described step 5) obtain spread spectrum transmission signal and represent as: Among them, T _C represents the duration of a single chip of the pseudo-random sequence, t represents the time, Indicates the information chip, with Indicates the sequence, ω is the carrier angular frequency, is the initial phase of the carrier, and T _d represents the duration of a single information sequence. 7. the direct-sequence spread spectrum modulation method that suppresses multi-path interference in underwater acoustic communication according to claim 1, is characterized in that, described step 2) in orthogonal combination generation pseudo-random sequence adopts carrier phase quadrature mode, will The two sequences are respectively adjusted to the orthogonal carrier with a phase difference of 90 degrees, and the obtained pseudo-random sequence is expressed as: CS=A _n +jB _n (8) Among them, A _n and B _n represent sequences, Represents the imaginary number unit, CS represents the pseudo-random sequence in complex number form after combination, and its length is N; According to the definition of correlation function, the correlation function of formula (8) is: ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; CS</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{{\mathrm{<span\; class="notranslate">\; CS</span>}}^{<span\; class="notranslate">\; *</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; j</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$ The real part of the correlation function Expressed as: ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; j</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; N</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$ The imaginary part of the correlation function Expressed as: ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; -</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; mod</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$ Among them, A _i , A _j , B _i , and B _j are all pseudo-random sequences satisfying the relationship of "complementary sequence". When i=j, the above formula describes the autocorrelation characteristic, and i≠j describes the cross-correlation characteristic. 8. according to claim 2,3,4 or 7 described direct-sequence spread spectrum modulation method of suppressing multi-path interference in underwater acoustic communication, it is characterized in that, described step 5) obtain spread spectrum transmission signal and represent as: Among them, T _C represents the duration of a single chip of the pseudo-random sequence, t represents the time, Indicates the information chip, with represents a sequence, Indicates the combined pseudo-random sequence in the form of complex numbers, ω is the carrier angular frequency, is the initial phase of the carrier, and T _d represents the duration of a single information sequence. 9. The direct sequence spread spectrum modulation method for suppressing multi-channel interference in underwater acoustic communication according to claim 1, characterized in that, said "complementary sequence" pair adopts LS code.