A method for underwater acoustic modulation and demodulation based on frequency hopping and direct sequence spread spectrum

Abstract

The present invention discloses a method for underwater acoustic modulation and demodulation of frequency hopping combined with direct sequence spread spectrum, belonging to the field of underwater acoustic communication. The method comprises the following steps: setting system parameters for modulation at the transmitting end and demodulation at the receiving end; the transmitting end performs source modulation based on frequency hopping combined with direct sequence spread spectrum; the receiving end performs demodulation based on frequency hopping combined with direct sequence spread spectrum to obtain source data. The method is based on a spread spectrum scheme, combines frequency hopping technology and direct sequence spread spectrum technology, realizes frequency band selection by frequency hopping, and performs direct sequence spread spectrum modulation on different frequency bands, which can effectively improve the transmission rate of spread spectrum underwater acoustic communication, and has good confidentiality performance and strong anti-interference ability.

Description

Technical Field

[0001] The invention belongs to the field of underwater acoustic communication, and in particular relates to an underwater acoustic modulation and demodulation method combining frequency hopping with direct sequence spread spectrum. Background Art

[0002] Due to the special nature of water, long-distance wireless transmission of underwater data can only be achieved through sound waves. The underwater acoustic communication technology was initially implemented through analog communication, and with the advancement of technology, it has gradually developed into a digital communication-based implementation. However, when sound waves are transmitted underwater, they are affected by the complex underwater acoustic channel, and the multipath effect and complex environmental noise will reduce the signal quality and affect the efficiency of underwater acoustic communication.

[0003] Spread spectrum communication technology expands the bandwidth of the transmitted information before transmission. The signal bandwidth of the transmission is much larger than the minimum bandwidth required for the transmitted information. It has strong anti-interference and anti-multipath capabilities, low bit error rate, and strong confidentiality. It is widely used in the field of underwater acoustic communication. The spread spectrum modulation at the transmitting end is completed using an independent code sequence and implemented through coded modulation; the receiving end uses the same code sequence for despreading and recovers the transmitted information. Common spread spectrum systems usually include direct sequence spread spectrum, frequency hopping spread spectrum, time hopping spread spectrum, wideband linear frequency modulation, hybrid methods, etc., which exchange signal-to-noise ratio gain by widening the signal bandwidth. However, the bandwidth of the underwater acoustic channel is limited and the information transmission rate is low. For underwater acoustic spread spectrum technology, the anti-interference ability is improved by widening the bandwidth of the transmitted signal, which will further reduce the information transmission rate. In order to improve the transmission rate of spread spectrum communication technology, the present invention proposes an underwater acoustic modulation and demodulation method of frequency hopping combined with direct sequence spread spectrum. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing methods and propose a method for underwater acoustic modulation and demodulation combining frequency hopping and direct sequence spread spectrum, which uses frequency hopping to achieve frequency band selection and performs direct sequence spread spectrum modulation on different frequency bands. At the transmitting end, the system bandwidth is divided into several sub-bands, and sub-band selection is achieved based on frequency hopping modulation technology. Different sub-bands correspond to different transmission information; direct sequence spread spectrum modulation is performed in each frequency band, and different spread spectrum codes correspond to transmission information. At the receiving end, the received signal is demodulated to restore the frequency hopping modulation information; direct sequence spread spectrum despreading is performed on each sub-band to restore the spread spectrum code information. The present invention can effectively improve the transmission rate of spread spectrum underwater acoustic communication, and has good confidentiality performance and strong anti-interference ability.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0006] A method for underwater acoustic modulation and demodulation of frequency hopping combined with direct sequence spread spectrum comprises the following steps: S1: setting system parameters for modulation at a transmitting end and demodulation at a receiving end; S2: the transmitting end performs source modulation based on frequency hopping combined with direct sequence spread spectrum; S3: the receiving end performs demodulation based on frequency hopping combined with direct sequence spread spectrum to obtain source data.

[0007] In some embodiments, the system parameter setting for the modulation at the transmitting end and the demodulation at the receiving end in step S1 includes: defining the system bandwidth as B, dividing the system bandwidth B into sub-bands, is an integer power of 2, and the bandwidth of each sub-band is , the center frequency of the sub-band is recorded as , then each different frequency band can carry bits of information; Y m sequences are used as PN codes, denoted as , then each different PN code can carry J bits of information, Y is a power of 2.

[0008] In some embodiments, the PN code bandwidth is equal to the sub-band bandwidth, the PN codes are orthogonal to each other, and the period of each PN code is .

[0009] In some embodiments, the transmitting end in step S2 performs source modulation based on frequency hopping combined with direct sequence spread spectrum, including: S2-1: the transmitting end groups the source; S2-2: the transmitting end performs frequency hopping modulation on the grouped source; S2-3: the transmitting end performs direct sequence spread spectrum modulation on the signal after frequency hopping modulation; S2-4: the transmitting end performs carrier modulation on the signal after direct sequence spread spectrum modulation.

[0010] In some embodiments, the sending end of step S2-1 groups the information sources as follows:

[0011] Define the binary bit information data stream to be sent by the sender as b n , b n The value is 0 or 1, and n is a positive integer, that is, According to the system parameters set in step S1, the binary bit information data stream is grouped into groups of P=U+(K-1)J bits each. The binary bit information data stream can be divided into ; Among them, the binary bit information data stream can be divided into the first U bit frequency hopping groups, denoted as b (n-1)P+1 , b (n-1)P+2 , …, b (n-1)P+U After bit direct sequence spread spectrum group, denoted as b (n-1)P+U+1 , b (n-1)P+U+2 , …, bnP ;

[0012] The transmitting end of step S2-2 performs frequency hopping modulation on the grouped information source as follows:

[0013] Perform frequency hopping modulation on the first U bit frequency hopping groups, write the first U bit frequency hopping groups into binary numbers, and then convert them into decimal numbers , ;according to Select the serial number Central bandwidth The sub-band is set to 0;

[0014] for Non-zero sub-bands , the transmitter generates the carrier with the corresponding center bandwidth from low to high frequency , the number of carriers corresponding to the center bandwidth is , complete frequency hopping modulation;

[0015] The transmitting end of step S2-3 performs direct sequence spread spectrum modulation on the frequency hopping modulated signal as follows:

[0016] After bit direct sequence spread spectrum group performs direct sequence spread spectrum modulation, each A group of group, after The bit direct sequence spread spectrum groups are written as corresponding binary numbers and then converted into decimal numbers respectively. ,in ;according to choose PN code , complete direct sequence spread spectrum modulation;

[0017] The transmitting end of step S2-4 performs carrier modulation on the signal after direct sequence spread spectrum modulation as follows:

[0018] For each binary bit information data stream b n , and PN code and The carriers are multiplied and filtered to smooth the transmitted waveform. After smoothing, the waveform is sent for superposition to complete a The modulation waveform; finally, each The modulated waveforms are serially spliced, and after adding a synchronization header, they are sent to the receiving end as the transmitting signal of the transmitting end.

[0019] In some embodiments, With serial number Central bandwidth is a one-to-one correspondence, or With serial number Central bandwidth This is done by setting the frequency hopping pattern.

[0020] In some embodiments, the receiving end in step S3 performs demodulation based on frequency hopping combined with direct sequence spread spectrum to obtain source data, including: S3-1: the receiving end performs frequency hopping demodulation on the received signal; S3-2: the receiving end performs direct sequence spread spectrum demodulation on the signal after frequency hopping demodulation; S3-3: the receiving end recovers the source information.

[0021] In some embodiments, the receiving end of step S3-1 performs frequency hopping demodulation on the received signal as follows:

[0022] After receiving the signal sent by the transmitter, the receiver performs desynchronization processing to obtain the modulated signal waveform; The modulation waveform length is used for frequency discrimination; no transmission signal is obtained in a sub-band. The sub-band carries the transmitted signal; according to the center frequency corresponding to the 0 signal sub-band Serial number , convert it into a binary number, denoted as b (n-1)P+1 b (n-1)P+2 …b (n-1)P+U , the first U bits of information can be obtained;

[0023] The receiving end of step S3-2 performs direct sequence spread spectrum demodulation on the frequency hopping demodulated signal as follows:

[0024] For the frequency discrimination sub-bands, from low to high in frequency, the corresponding center frequency is , perform bandpass filtering in turn to obtain the signal corresponding to each sub-band, and down-convert it to the baseband to obtain the corresponding PN code ; Despread and obtain the binary number corresponding to each PN code, which is recorded as b (n-1)P+U+1 b (n-1)P+U+2 …b (n-1)P+U+J , b (n-1)P+U+J+1 b (n-1)P+U+J+2 …b (n-1)P+U+2J , …, b (n-1)P+U+(K-2)J+1 b (n-1)P+U+(K-2)J+2 …b nP , a total of bits of information;

[0025] The receiving end of step S3-3 recovers the source information in the following way:

[0026] For one The modulation waveform length is obtained by demodulating the U bits of information obtained by the serial step S3-1 and the information obtained by demodulating the step S3-2. bits of information to get bits of information; finally, each The demodulated bit information is serially concatenated to restore the binary bit information data stream sent by the transmitter.

[0027] Compared with the existing methods, the present invention is based on a spread spectrum scheme, combines frequency hopping technology and direct sequence spread spectrum technology, uses frequency hopping to achieve frequency band selection, and performs direct sequence spread spectrum modulation on different frequency bands, which effectively improves the transmission rate of spread spectrum underwater acoustic communication, and has good confidentiality performance and strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 It is a schematic diagram of the steps of a frequency hopping combined with direct sequence spread spectrum underwater acoustic modulation and demodulation method of the present invention;

[0030] Figure 2 It is a basic flow chart of the underwater acoustic modulation and demodulation method of the present invention combining frequency hopping with direct sequence spread spectrum;

[0031] Figure 3 The present invention Schematic diagram of frequency hopping combined with direct sequence spread spectrum modulation and demodulation at the transmitting end. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; the technical features designed in different implementation modes of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "lateral", "up", "down", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more. In addition, the term "including" and any variation thereof all mean "at least including".

[0034] See also Figure 1 and Figure 2 , Figure 1 It is a flow chart of a frequency hopping combined with direct sequence spread spectrum underwater acoustic modulation and demodulation method of the present invention, Figure 2 The basic flow chart of the frequency hopping combined with direct sequence spread spectrum underwater acoustic modulation and demodulation method of the present invention is shown in the figure. As shown in the figure, the frequency hopping combined with direct sequence spread spectrum underwater acoustic modulation and demodulation method comprises the following steps:

[0035] S1: Set system parameters for modulation at the transmitter and demodulation at the receiver;

[0036] S2: The transmitter performs source modulation based on frequency hopping combined with direct sequence spread spectrum;

[0037] S3: The receiving end performs demodulation based on frequency hopping combined with direct sequence spread spectrum to obtain the source data.

[0038] The transmitter first groups the binary data stream, and then performs frequency hopping modulation and direct sequence spread spectrum modulation to obtain the transmission signal, and after adding the synchronization header information, it is sent out through the transducer. The receiver first removes the synchronization header of the signal received by the transducer, and then performs frequency discrimination to obtain the frequency hopping modulation information, and performs direct sequence spread spectrum despreading on the signal after frequency discrimination to obtain the direct sequence spread spectrum modulation information. Finally, the frequency hopping modulation information and the direct sequence spread spectrum modulation information are combined into the transmitted information stream output.

[0039] The system parameter setting for the modulation at the transmitting end and the demodulation at the receiving end in step S1 includes: defining the system bandwidth as B, dividing the system bandwidth B into sub-bands, is an integer power of 2, and the bandwidth of each sub-band is , the center frequency of the sub-band is recorded as , then each different frequency band can carry bits of information; Y m sequences are used as PN codes, denoted as , then each different PN code can carry J bits of information, Y is an integer power of 2. The PN code bandwidth is equal to the sub-band bandwidth, the PN codes are orthogonal to each other, and the period of each PN code is .

[0040] The transmitting end in step S2 performs source modulation based on frequency hopping combined with direct sequence spread spectrum, including:

[0041] S2-1: The sender groups the information sources;

[0042] S2-2: The transmitter performs frequency hopping modulation on the grouped signal source;

[0043] S2-3: The transmitting end performs direct sequence spread spectrum modulation on the frequency hopping modulated signal;

[0044] S2-4: The transmitter performs carrier modulation on the signal after direct sequence spread spectrum modulation.

[0045] The sending end of step S2-1 groups the information sources in the following way:

[0046] Define the binary bit information data stream to be sent by the sender as b n , b n The value is 0 or 1, and n is a positive integer, that is, According to the system parameters set in step S1, the binary bit information data stream is grouped into groups of P=U+(K-1)J bits each, so the binary bit information data stream Can be divided into ; Among them, the binary bit information data stream (each ) can be divided into the first U bit frequency hopping groups, denoted as b (n-1)P+1 , b (n-1)P+2 , …, b (n-1)P+U After bit direct sequence spread spectrum group, denoted as b (n-1)P+U+1 , b (n-1)P+U+2 , …, b nP ;

[0047] The transmitting end of step S2-2 performs frequency hopping modulation on the grouped information source as follows:

[0048] For each group The first U bit frequency hopping group Perform frequency hopping modulation, write the first U bit frequency hopping group into binary numbers, and then convert them into decimal numbers , ;according to Select the serial number Central bandwidth The sub-bands of are set to 0; With serial number Central bandwidth is a one-to-one correspondence, or With serial number Central bandwidth Confidentiality is improved by setting a frequency hopping pattern to correspond.

[0049] for Non-zero sub-bands , the transmitter generates the carrier with the corresponding center bandwidth from low to high frequency , the number of carriers corresponding to the center bandwidth is , complete frequency hopping modulation;

[0050] The transmitting end of step S2-3 performs direct sequence spread spectrum modulation on the frequency hopping modulated signal as follows:

[0051] For each group After bit DSSS group Direct sequence spread spectrum modulation is performed, each A group of group, after The bit direct sequence spread spectrum groups are written as corresponding binary numbers and then converted into decimal numbers respectively. ,in ;according to choose PN code , complete direct sequence spread spectrum modulation;

[0052] The transmitting end of step S2-4 performs carrier modulation on the signal after direct sequence modulation and spread spectrum as follows:

[0053] For each binary bit information data stream b n , and PN code and The carriers are multiplied and filtered to smooth the transmitted waveform. After smoothing, the waveform is sent for superposition to complete a The modulation waveform; finally, each The modulated waveforms are serially spliced, and after adding a synchronization header, they are sent as the transmitting end signal.

[0054] The receiving end in step S3 performs demodulation based on frequency hopping combined with direct sequence spread spectrum to obtain the source data, including:

[0055] S3-1: The receiving end performs frequency hopping demodulation on the received signal;

[0056] S3-2: The receiving end performs direct sequence spread spectrum demodulation on the frequency hopping demodulated signal;

[0057] S3-3: The receiving end recovers the source information.

[0058] The receiving end of step S3-1 performs frequency hopping demodulation on the received signal as follows:

[0059] After receiving the signal sent by the transmitter, the receiver performs desynchronization processing to obtain the modulated signal waveform; The modulation waveform length is used for frequency discrimination; no transmission signal is obtained in a sub-band. The sub-band carries the transmitted signal; according to the center frequency corresponding to the 0 signal sub-band Serial number , convert it into a binary number, denoted as b (n-1)P+1 b (n-1)P+2 …b (n-1)P+U , the first U bits of information can be obtained;

[0060] The receiving end of step S3-2 performs direct sequence spread spectrum demodulation on the frequency hopping demodulated signal as follows:

[0061] For the frequency discrimination sub-bands, from low to high in frequency, the corresponding center frequency is , perform bandpass filtering in turn to obtain the signal corresponding to each sub-band, and down-convert it to the baseband to obtain the corresponding PN code ; Despread and obtain the binary number corresponding to each PN code, which is recorded as b (n-1)P+U+1 b (n-1)P+U+2 …b (n-1)P+U+J , b (n-1)P+U+J+1 b (n-1)P+U+J+2 …b (n-1)P+U+2J , …, b (n-1)P+U+(K-2)J+1 b (n-1)P+U+(K-2)J+2 …b nP , a total of bits of information;

[0062] The receiving end of step S3-3 recovers the source information in the following way:

[0063] For one The modulation waveform length is obtained by demodulating the U bits of information obtained by the serial step S3-1 and the information obtained by demodulating the step S3-2. bits of information to get bits of information; finally, each The demodulated bit information is serially concatenated to restore the binary bit information data stream sent by the transmitter.

[0064] In order to facilitate understanding of the entire process of the frequency hopping combined with direct sequence spread spectrum underwater acoustic modulation and demodulation method described in the present invention, the following will take U=4, J=4 as an example for illustration (this example is not intended to limit the present invention). Figure 3 To understand, an example is given below:

[0065] Figure 3 The schematic diagram of the frequency hopping combined direct sequence spread spectrum modulation and demodulation at the transmitting end when K=4 and Y=4 is given. According to the system parameter settings, U=2, J=2, P=8, and the system bandwidth is divided into sub-bands, carrying U=2 bits of information; containing Y=4 PN codes, each PN code carries bits of information.

[0066] As shown in the figure, the information flow to be sent is: “001001000110001111000110110100111000111000001001010001001111010000111000011100011101100000010010…”. The modulation process is as follows:

[0067] The first step is to group the information flow to be sent. The bits are grouped into “'00100100''01100011''11000110''11010011''10001110''00001001''01000100''11110100''00111000''01110001''11011000''00010010'…”. Each group of bit data is then divided into the first U=2 bit frequency hopping group and the second U=2 bit frequency hopping group. The number of bits of direct sequence spread spectrum group is: "'00 100100''01100011''11 000110''11 010011''10 001110''00 001001''01 000100''11 110100''00111000''01 110001''11 011000''00 010010'…".

[0068] In the second step, frequency modulation is performed based on the first U=2 bits of the frequency hopping group data stream of each group: "'00''01''11''11''10''00''01''11''00''01''11''00'...", and the frequency hopping group data stream is converted into decimal numbers in the order of 0, 1, 3, 3, 2, 0, 1, 3, 0, 1, 3, 0. This embodiment is demonstrated according to the one-to-one correspondence between the sequence number and the center bandwidth. In actual situations, it can be modified according to a certain frequency hopping pattern to improve confidentiality. At this time, for each group, the 0 carrier is: ", the generated non-zero carrier is: " , , , , , , , , , , , …”.

[0069] The third step is to The DSSS group is composed of a number of bits: "100100"'100011"'000110"'010011"'001110"'001001"'000100"'110100"'111000"'110001"'011000"'010010'…", and the DSSS is used for modulation. A group can be divided into 01 00'…". The PN codes for each group are: "'10 01 00''10 00 11''00 01 10''01 00 11''00 11 10''00 10 01''00 01 00''11 01 00''11 10 00''11 00 01''01 10 00''01 00 10'…". Converted into decimal numbers, they are: "'2 1 0''2 0 3''0 1 2''1 0 3''0 3 2''0 2 1''0 1 0''3 1 0''3 2 0''3 0 1''1 20''1 0 2'…". 3 PN 2 PN 1 ''PN 3 PN 1 PN 4 ''PN 1 PN 2 PN 3 ''PN2 PN 1 PN 4 ‘‘PN 1 PN 4 PN 3 ‘‘PN 1 PN 3 PN 2 ‘‘PN 1 PN 2 PN 1 ‘‘PN 4 PN 2 PN 1 ‘‘PN 4 PN 3 PN 1 ‘‘PN 4 PN 1 PN 2 ‘‘PN 2 PN 3 PN 1 ‘‘PN 2 PN1 PN 3 ’…”。

[0070] Step 4: Sequentially, the PN codes: “‘PN 3 PN 2 PN 1 ‘‘PN 3 PN 1 PN 4 ‘‘PN 1 PN 2 PN 3 ‘‘PN 2 PN 1 PN 4 ‘‘PN 1 PN 4 PN 3 ‘‘PN 1 PN 3 PN 2 ‘‘PN 1 PN 2 PN 1 ‘‘PN 4 PN 2 PN 1 ‘‘PN 4 PN 3 PN 1 ‘‘PN 4 PN 1 PN 2 ‘‘PN 2 PN 3 PN 1 ‘‘PN 2 PN1 PN 3'…" and non-zero carrier: " , , , , , , , , , , , …” and then pass through shaping filtering to smooth the transmitted waveform. Then the multiplied signals of each group are superimposed, that is, for the first group, 'PN 3 PN 2 PN 1 'With frequency The carrier waves of the sub-groups are multiplied and superimposed to form a sub-group modulation waveform. After all sub-group modulation is completed, all group modulation waveforms are serially spliced, and after adding a synchronization header, they are sent as the transmitting end signal, and the modulation is completed.

[0071] The demodulation process is the opposite of the modulation process. After the receiving end receives the signal sent by the transmitting end, it performs desynchronization processing to obtain the modulated signal waveform. The details are as follows:

[0072] Step 1: Perform frequency discrimination according to the modulation waveform length of a small group from the received signal waveform. Figure 2 As shown, the demodulation results show that the 0-frequency carriers of each group are: Therefore, the corresponding frequency hopping modulation information is: "'00''01''11''11''10''00''01''11''00''01''11''00'…", that is, the frequency hopping modulation information demodulation is completed. The non-0 carriers are: , , , , , , , , , , , …”.

[0073] Step 2: According to the non-zero carrier information, each group of modulated waveforms is narrow-band filtered and down-converted to obtain the baseband data under the non-zero carrier: "PN 3 PN 2 PN 1 ''PN 3 PN 1 PN 4 ''PN 1 PN2 PN 3 ''PN 2 PN 1 PN 4 ''PN 1 PN 4 PN 3 ''PN 1 PN 3 PN 2 ''PN 1 PN 2 PN 1 ''PN 4 PN 2 PN 1 ''PN 4 PN 3 PN 1 ''PN 4 PN 1 PN 2 ''PN 2 PN 3 PN 1 ''PN 2 PN1 PN 3 '…".

[0074] The third step is to perform direct sequence spread spectrum despreading on the baseband data to obtain the direct sequence spread spectrum modulation information: “'10 01 00''10 00 11''00 01 10''01 00 11''00 11 10''00 10 01''00 01 00''11 0100''11 10 00''11 00 01''01 10 00''01 00 10'…”.

[0075] Step 4: Combine the recovered frequency hopping modulation information and direct sequence spread spectrum modulation information to obtain the information stream transmitted by the transmitter: “001001000110001111000110110100111000111000001001010001001111010000111000011100011101100000010010…”, and the demodulation is completed.

[0076] Compared with the existing methods, the present invention is based on a spread spectrum scheme, combines frequency hopping technology and direct sequence spread spectrum technology, uses frequency hopping to achieve frequency band selection, and performs direct sequence spread spectrum modulation on different frequency bands, which effectively improves the transmission rate of spread spectrum underwater acoustic communication, and has good confidentiality performance and strong anti-interference ability.

[0077] In addition, those skilled in the art should understand that, although there are many problems in the prior art, each embodiment or technical solution of the present invention can be improved in only one or several aspects, without having to solve all the technical problems listed in the prior art or background technology at the same time. Those skilled in the art should understand that the content not mentioned in a claim should not be used as a limitation on the claim.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A frequency hopping combined with direct sequence spread spectrum underwater acoustic modulation and demodulation method, characterized in that: The following steps are involved: S1: Set system parameters for modulation at the transmitter and demodulation at the receiver; S2: The transmitter performs source modulation based on frequency hopping combined with direct sequence spread spectrum; S3: The receiving end performs demodulation based on frequency hopping combined with direct sequence spread spectrum to obtain the source data; The system parameter setting for the modulation at the transmitting end and the demodulation at the receiving end in step S1 includes: defining the system bandwidth as B, dividing the system bandwidth B into sub-bands, is an integer power of 2, and the bandwidth of each sub-band is , the center frequency of the sub-band is recorded as , then each different frequency band can carry bits of information; Y m sequences are used as PN codes, denoted as , then each different PN code can carry J bits of information, Y is a power of 2; The transmitting end in step S2 performs source modulation based on frequency hopping combined with direct sequence spread spectrum, including: S2-1: The sender groups the information sources; S2-2: The transmitter performs frequency hopping modulation on the grouped signal source; S2-3: The transmitting end performs direct sequence spread spectrum modulation on the frequency hopping modulated signal; S2-4: The transmitting end performs carrier modulation on the signal after direct sequence spread spectrum modulation; The sending end of step S2-1 groups the information sources in the following way: Define the binary bit information data stream to be sent by the sender as b n , b n The value is 0 or 1, n is a positive integer, and according to the system parameters set in step S1, the binary bit information data stream is grouped according to each P=U+(K-1)J bits, so the binary bit information data stream can be divided into ; Among them, the binary bit information data stream can be divided into the first U bit frequency hopping groups, denoted as b (n-1)P+1 , b (n-1)P+2 , …, b (n-1)P+U After bit direct sequence spread spectrum group, denoted as b (n-1)P+U+1 , b (n-1)P+U+2 , …, b nP ; The transmitting end of step S2-2 performs frequency hopping modulation on the grouped information source as follows: Perform frequency hopping modulation on the first U bit frequency hopping groups, write the first U bit frequency hopping groups into binary numbers, and then convert them into decimal numbers , ;according to Select the serial number Central bandwidth The sub-band is set to 0; for Non-zero sub-bands , the transmitter generates the carrier with the corresponding center bandwidth from low to high frequency , the number of carriers corresponding to the center bandwidth is , complete frequency hopping modulation; The transmitting end of step S2-3 performs direct sequence spread spectrum modulation on the frequency hopping modulated signal as follows: After bit direct sequence spread spectrum group performs direct sequence spread spectrum modulation, each A group of group, after The bit direct sequence spread spectrum groups are written as corresponding binary numbers and then converted into decimal numbers respectively. ,in ;according to choose PN code , complete direct sequence spread spectrum modulation; The transmitting end of step S2-4 performs carrier modulation on the signal after direct sequence spread spectrum modulation as follows: For each binary bit information data stream b n , and PN code and The carriers are multiplied and filtered to smooth the transmitted waveform. After smoothing, the waveform is sent for superposition to complete a The modulation waveform; finally, each The modulated waveforms are serially spliced, and after adding a synchronization header, they are sent to the receiving end as the transmitting signal of the transmitting end.

2. The method for underwater acoustic modulation and demodulation based on frequency hopping and direct sequence spread spectrum according to claim 1, characterized in that: The PN code bandwidth is equal to the sub-band bandwidth, and the PN codes are orthogonal to each other. The period of each PN code is .

3. The method for underwater acoustic modulation and demodulation based on frequency hopping and direct sequence spread spectrum according to claim 1, characterized in that: in, With serial number Central bandwidth is a one-to-one correspondence, or With serial number Central bandwidth This is done by setting the frequency hopping pattern.

4. The method for underwater acoustic modulation and demodulation using frequency hopping combined with direct sequence spread spectrum according to claim 1, characterized in that: The receiving end in step S3 performs demodulation based on frequency hopping combined with direct sequence spread spectrum to obtain the source data, including: S3-1: The receiving end performs frequency hopping demodulation on the received signal; S3-2: The receiving end performs direct sequence spread spectrum demodulation on the frequency hopping demodulated signal; S3-3: The receiving end recovers the source information.

5. The method for underwater acoustic modulation and demodulation based on frequency hopping and direct sequence spread spectrum according to claim 4 is characterized in that: The receiving end of step S3-1 performs frequency hopping demodulation on the received signal as follows: After receiving the signal sent by the transmitter, the receiver performs desynchronization processing to obtain the modulated signal waveform; The modulation waveform length is used for frequency discrimination; no transmission signal is obtained in a sub-band. The sub-band carries the transmitted signal; according to the center frequency corresponding to the 0 signal sub-band Serial number , convert it into a binary number, denoted as b (n-1)P+1 b (n-1)P+2 …b (n-1)P+U , the first U bits of information can be obtained; The receiving end of step S3-2 performs direct sequence spread spectrum demodulation on the frequency hopping demodulated signal as follows: For the frequency discrimination sub-bands, from low to high in frequency, the corresponding center frequency is , perform bandpass filtering in turn to obtain the signal corresponding to each sub-band, and down-convert it to the baseband to obtain the corresponding PN code ; Despread and obtain the binary number corresponding to each PN code, which is recorded as b (n-1)P+U+1 b (n-1)P+U+2 …b (n-1)P+U+J , b (n-1)P+U+J+1 b (n-1)P+U+J+2 …b (n-1)P+U+2J , …, b (n-1)P+U+(K-2)J+1 b (n-1)P+U+(K-2)J+2 …b nP , a total of bits of information; The receiving end of step S3-3 recovers the source information in the following way: For one The modulation waveform length is obtained by demodulating the U bits of information obtained by the serial step S3-1 and the information obtained by demodulating the step S3-2. bits of information to get bits of information; finally, each The demodulated bit information is serially concatenated to restore the binary bit information data stream sent by the transmitter.

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