Hidden underwater acoustic communication method supporting non-detectable feature

Abstract

The invention discloses a hidden underwater acoustic communication method supporting non-detectable characteristics, which comprises the following steps: collecting marine environment noise as an information carrier in real time, and carrying out broadband filtering to obtain an original band-limited noise signal; performing steganography modulation on the original band-limited noise signal to generate an information bearing signal; adding the information bearing signal and the original band-limited noise signal to generate a covert communication signal; a receiving end collects and receives signals in real time; carrying out resampling to obtain a received signal after Doppler compensation; a receiving end adopts different optimal modulation parameter combinations to carry out steganography demodulation on each compensated signal to obtain a correlation value matrix; and judging according to the maximum value of the absolute value of the correlation value matrix to complete the receiving of the communication information. According to the method disclosed by the invention, the communication signal can be submerged in the environmental noise, any repeatedly transmitted signal cannot occur, detectable features such as cyclic spectrum and cepstrum are eliminated, non-feature detectability is really realized, and high concealment of underwater acoustic communication is ensured.

Description

Technical Field

[0001] The invention belongs to the field of underwater communication, relates to a covert underwater acoustic communication technology, and specifically relates to a covert underwater acoustic communication method supporting non-detectable features. Background Art

[0002] Underwater communication mainly uses sound waves as a carrier, which can achieve long-distance information transmission. Due to the openness of underwater acoustic channel propagation, other non-cooperative parties can monitor and decipher the transmitted information, and even detect the location of the communication partner, reducing information security and platform concealment.

[0003] With the development of the ocean, application scenarios are constantly expanding, and the security of underwater information transmission is becoming more and more important. At present, multiple underwater application scenarios have continuously increased the requirements for the concealment of communication activities to protect the security of information and platforms. Therefore, covert underwater acoustic communication technology has become an important research direction in the field of underwater acoustic technology. In particular, for the special requirements for concealment underwater, it is necessary to study covert underwater acoustic communication with undetectable features according to the special circumstances of the application scenario to prevent eavesdropping of information and exposure of the platform.

[0004] Considering the particularity of the underwater acoustic environment, covert underwater acoustic communication technology is mainly divided into three categories, namely low intercept, low detection and bionic covert underwater acoustic communication technology. Low intercept covert underwater acoustic communication technology mainly adopts encryption and coding methods to protect the security of information. Even if the non-cooperative party detects the communication activity, it cannot decipher the transmitted information. Low intercept method usually cannot guarantee the safety of the platform. The emission source level is high, and there is a greater risk of platform exposure, which does not meet the special requirements of underwater covert transmission. Low detection covert underwater acoustic communication technology mainly adopts spread spectrum and multi-carrier communication system, which reduces the power spectrum density by expanding the spectrum to achieve the purpose of submerging the signal in the background noise. It is difficult for non-cooperative parties to identify the communication activities of low detection methods through energy detection. However, since the signals of such methods are usually artificial signals, the communication signal characteristics can be detected by means of cyclic spectrum, high-order spectrum and inverse spectrum, and then the communication party can be located and identified. Bionic covert communication technology mainly uses the calls of marine organisms as information carriers. The important assumption of this method is that non-cooperative parties regard bionic communication signals as biological activities, so that both parties can avoid detection and interception. Similar to the low detection method, because the information symbol corresponds to a specific and fixed transmission signal during the modulation process, the communication signal of this method has obvious characteristics and can be detected by means such as cyclic spectrum. In addition, its emission source is very high. Once the assumption is not established, the risk of platform exposure will be greatly increased. In order to ensure the safety of underwater information transmission and underwater long-term working platforms, it is of great research significance and application value to study a new type of covert underwater acoustic communication technology to eliminate any detectable characteristics. Summary of the invention

[0005] Purpose of the invention: In order to overcome the deficiencies in the prior art, a covert underwater acoustic communication method that supports no detectable features is provided, which can achieve the goal of drowning the communication signal in the environmental noise, and no repeated transmitted signals will appear, eliminating detectable features such as cyclic spectrum and inverse spectrum, truly realizing no feature detectable, and ensuring the high concealment of underwater acoustic communication.

[0006] Technical solution: To achieve the above-mentioned purpose, the present invention provides a covert underwater acoustic communication method supporting no detectable features, comprising the following steps:

[0007] S1: The transmitter collects ocean environmental noise in real time as an information carrier, and then performs broadband filtering on the collected ocean environmental noise according to the working frequency band to obtain the original band-limited noise signal x(t);

[0008] S2: According to the information to be transmitted, the optimal modulation parameter combination is selected to perform steganographic modulation on the original band-limited noise signal x(t) to generate the information-bearing signal C(x(t));

[0009] S3: Add the information-bearing signal C(x(t)) to the original band-limited noise signal x(t) to generate a covert communication signal s(t)=x(t)+C(x(t)), which is then transmitted into the ocean environment by the transmitting transducer after passing through a power amplifier;

[0010] S4: The receiving end collects the received signal r(t) in real time;

[0011] S5: According to the Doppler factor sequence {a n ,n=1,...,N a}, the receiving end resamples the real-time collected signal for each Doppler factor to obtain the Doppler compensated received signal r (n) (t);

[0012] S6: The receiving end uses N φ Different optimal modulation parameter combinations, for each compensated signal r (n) (t) Perform steganalysis demodulation to obtain the correlation value matrix ρ;

[0013] S7: Make a decision based on the absolute maximum value of the correlation value matrix ρ, and select the index corresponding to the maximum value. Complete the reception of communication information.

[0014] Furthermore, the ocean environmental noise in step S1 includes biological calls, ship noise, signals naturally generated by the ocean, radiation noise from other underwater platforms, and signals emitted by other underwater platforms.

[0015] Furthermore, the method of steganographic modulation in step S2 includes: dividing the band-limited noise signal into even-numbered sub-signals in the time domain according to the division mode, a total of 2N b segment, denoted as {x n (t),n=-N b ,...,-1,1,...,N b}, and perform time domain inversion to obtain {x -n (-t),n=-N b ,...,-1,1,...,N b}; According to the symbol information b to be transmitted and the optimal modulation condition, select the steganographic parameter, that is, the rotation phase combination φ, and multiply the rotation phase with each signal segment for symbol modulation to obtain the information carrying signal C(x(t)); The number of rotation phase combinations φ is consistent with the number of symbol information, which is N φ .

[0016] Furthermore, in step S2, the rotation phase combination For the MPSK communication system, the total Rotating phase combination {φ (m) ,m=1,...,N φ},{φ n ,n=-N b ,...,-1,1,...,N b} is the optimal modulation parameter, which is selected mainly based on the symbol information b to be transmitted. The optimal modulation parameter selection method is as follows:

[0017]

[0018] in, is the phase of the symbol information b, {K n ,n=1,...,N b} is an integer.

[0019] Furthermore, the information bearing signal C(x(t)) in step S2 is expressed as follows:

[0020]

[0021] Among them, {x n (t),n=-N b ,...,-1,1,...,N b} is the N obtained by evenly dividing x(t) b signal fragment.

[0022] Furthermore, the steganalysis demodulation method in step S6 includes:

[0023] A1: Use Nφ The steganalysis parameters are used to compensate the signal r (n) (t) Perform the same processing as step S2 to obtain the intermediate signal {z m (t),m=1,...,N φ};

[0024] A2: The receiving end will φ The intermediate signals are respectively compared with the Doppler compensated signal r (n) (t) is processed by correlation to obtain the correlation value vector [ρ(n,1),...,ρ(n,N φ )];

[0025] A3: For each Doppler compensated signal r (n) (t) are all processed in step A2 to obtain the correlation value matrix ρ.

[0026] Furthermore, the intermediate signal of step A1 is expressed as follows:

[0027]

[0028] φ n =φ (m) [n]

[0029] Furthermore, the operation of the relevant value vector in step A2 is expressed as follows:

[0030]

[0031] Furthermore, the expression for making a decision according to the maximum absolute value of the correlation value matrix ρ in step S7 is as follows:

[0032]

[0033] in and Represent the estimated Doppler value index and symbol information index respectively, The corresponding symbol information is the transmitted information, and demodulation is completed.

[0034] The method of the present invention first collects ocean environmental noise as an information carrier, and performs broadband filtering according to the working frequency band to obtain the original band-limited noise signal. Secondly, according to the symbol information to be transmitted and the optimal modulation parameters, the corresponding steganographic parameters are selected, and the original band-limited noise signal is steganographically modulated to obtain an information-carrying signal, which is added to the original band-limited noise signal to generate a transmitted communication signal. At the receiving end, after resampling the received signal, different intermediate signals are obtained according to the combination of the optimal modulation parameters, and then the intermediate signal is correlated with the received signal. Finally, information judgment is made according to the size of the correlation value to complete the communication.

[0035] In the present invention, the ocean environmental noise is random and belongs to a broadband signal. When used as an information carrier, it does not have its own inherent characteristics, such as cyclic spectrum characteristics. At the same time, in order to eliminate high-order characteristics such as cyclic spectrum, when modulating information, a special modulation and demodulation method is designed so that the information modulation does not depend on a specific carrier, so that any section of environmental noise can be used as a carrier for information transmission, so that communication activities will not have identifiable characteristics due to signal repetition. A special modulation method plus environmental noise as a carrier can obtain a concealed underwater acoustic communication method with superior concealment.

[0036] Beneficial effects: Compared with the prior art, the present invention adopts ocean environmental noise as an information carrier and proposes a covert underwater acoustic communication method based on steganography technology. Steganography technology is mainly used for modulation and demodulation of information. By hiding the symbol information in the steganographic parameters, it avoids the need to use a fixed signal mode to transmit the same information, so that any information can be transmitted using any signal. In practical applications, the transmitter can generate a communication signal through steganography technology based on the background noise of the ocean environment recorded anytime and anywhere on site, and the receiver can also achieve synchronization and demodulation at the same time based on the steganography technology. It can achieve the goal of submerging the communication signal in the environmental noise, and there will be no repeated transmitted signals, eliminating detectable features such as cyclic spectrum and inverse spectrum, truly achieving featureless detection and ensuring the high concealment of underwater acoustic communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the process of the present invention;

[0038] Figure 2 It is a schematic diagram of the demodulation process at the receiving end in the method of the present invention;

[0039] Figure 3 This is a performance simulation curve diagram obtained in this embodiment;

[0040] Figure 4 A comparison diagram of signal cepstrum characteristics of the traditional direct sequence spread spectrum and the method of the present invention;

[0041] Figure 5 It is a comparison diagram of the signal cyclic spectrum characteristics of the traditional direct sequence spread spectrum and the method of the present invention. DETAILED DESCRIPTION

[0042] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0043] like Figure 1 As shown, the present invention provides a covert underwater acoustic communication method supporting no detectable features, comprising the following steps:

[0044] S1: The transmitter collects ocean environmental noise in real time as an information carrier, and then performs broadband filtering on the collected ocean environmental noise according to the working frequency band to obtain the original band-limited noise signal x(t);

[0045] Marine environmental noise signals are any sound signals existing in the marine environment, including biological calls, ship noise, signals generated by the ocean, radiation noise from other underwater platforms, signals emitted by other underwater platforms, etc.

[0046] S2: According to the information to be transmitted, the optimal modulation parameter combination is selected to perform steganographic modulation on the original band-limited noise signal x(t) to generate the information-bearing signal C(x(t));

[0047] The method of steganographic modulation includes: dividing the band-limited noise signal into even-numbered sub-signals in the time domain according to the division mode, a total of 2N b segment, denoted as {x n (t),n=-N b ,...,-1,1,...,N b}, and perform time domain inversion to obtain {x -n (-t),n=-N b ,...,-1,1,...,N b}; According to the symbol information b to be transmitted and the optimal modulation condition, select the steganographic parameter, that is, the rotation phase combination φ, and multiply the rotation phase with each signal segment for symbol modulation to obtain the information carrying signal C(x(t)); The number of rotation phase combinations φ is consistent with the number of symbol information, which is N φ .

[0048] Rotating Phase Combination total Rotating phase combination {φ (m) ,m=1,...,N φ},{φ n ,n=-N b ,...,-1,1,...,N b} is the optimal modulation parameter, which is selected mainly based on the symbol information b to be transmitted. The optimal modulation parameter selection method is as follows:

[0049]

[0050] in, is the phase of the symbol information b, {K n ,n=1,...,N b} is an integer;

[0051] The information-carrying signal C(x(t)) is expressed as follows:

[0052]

[0053] Among them, {x n (t),n=-N b ,...,-1,1,...,N b} is the N obtained by evenly dividing x(t) b signal fragment.

[0054] S3: Add the information-bearing signal C(x(t)) to the original band-limited noise signal x(t) to generate a covert communication signal s(t)=x(t)+C(x(t)), which is transmitted into the marine environment by the transmitting transducer;

[0055] S4: real-time acquisition of the received signal r(t) by the hydrophone at the receiving end;

[0056] S5: According to the Doppler factor sequence {a n ,n=1,...,N a}, the receiving end resamples the real-time collected signal for each Doppler factor to obtain the Doppler compensated received signal r (n) (t), by N a A compensation signal {r (n) (t),n=1,...,N a}; where the Doppler factor sequence is the maximum relative motion speed between the transmitter and the receiver |v max |, the equivalent sound speed c of the working sea area, and the Doppler factor range is set to [-|v max | / c,|v max | / c], the corresponding Doppler factor is

[0057] S6: The receiving end uses N φ Different optimal modulation parameter combinations, for each compensated signal r (n) (t) Perform steganalysis demodulation to obtain the correlation value matrix ρ;

[0058] Reference Figure 2 , according to the steganographic parameter φ adopted by the transmitter, the receiver a The same processing is performed on the Doppler compensated signal to obtain the intermediate signal z(t). The intermediate signal z(t) is respectively (n) (t) Perform correlation processing to obtain the correlation value. a Each compensation signal passes through N φ Steganalysis is processed and correlated to obtain the correlation value matrix Make a judgment on it, and the index corresponding to the maximum correlation value That is, to transmit information, complete information demodulation and reception;

[0059] Referring to the above, the methods of steganographic decoding include:

[0060] A1: Use N φ The steganalysis parameters are used to compensate the signal r (n) (t) Perform the same processing as step S2 to obtain the intermediate signal {z m (t),m=1,...,N φ}, expressed as follows:

[0061]

[0062] φ n =φ (m) [n]

[0063] A2: The receiving end will φ The intermediate signals are respectively compared with the Doppler compensated signal r (n) (t) is processed by correlation to obtain the correlation value vector [ρ(n,1),...,ρ(n,N φ )];

[0064] The operation expression of the relevant value vector is as follows:

[0065]

[0066] A3: For each Doppler compensated signal r (n) (t) are all processed in step A2 to obtain the correlation value matrix ρ.

[0067] S7: Make a decision based on the absolute maximum value of the correlation value matrix ρ, and select the index corresponding to the maximum value. Complete the reception of communication information.

[0068] The judgment was expressed as follows:

[0069]

[0070] in and Represent the estimated Doppler value index and symbol information index respectively, The corresponding symbol information is the transmitted information, and demodulation is completed.

[0071] Based on the above content, in order to verify the effectiveness and performance effect of the method of the present invention, this embodiment carried out corresponding performance simulation experiments, and the specific simulation parameters were set as follows:

[0072] 1. The original band-limited noise signal is obtained by broadband filtering of the real randomly collected ocean environmental noise and is used as a carrier. Its duration is 1s, the number of segments is 4, and it carries 2 symbols;

[0073] 2. The signal bandwidth is 4-8kHz, a total of 4 bits of information are transmitted, that is, 2 QPSK symbols, the overall communication rate is 4 bits / s, and the sampling rate is 64kHz;

[0074] 3. The interference noise is the real collected ocean environment noise;

[0075] 4. The transmitted communication signal is convolved with the measured hydroacoustic channel to simulate the real ocean environment.

[0076] In this embodiment, a communication bit error rate curve, that is, the relationship between the bit error rate BER and the signal-to-noise ratio SNR, is used as a performance evaluation method, which is defined as:

[0077]

[0078] Among them, K e is the number of bits demodulated incorrectly at the receiving end, K is the total number of bits transmitted, and P s is the power of the received signal, P n is the power of the interference noise.

[0079] During the simulation, the SNRs were set to {-20, -18, -16, -15, / 14, -13, -12, -11, -10, -9, -8, -7, -6, -5, -4}, respectively, in decibel (dB), and 2000 Monte Carlo simulations were performed for each SNR.

[0080] Figure 3 The simulation results show that under the condition of SNR of -6dB, the BER is about 10 -3 , which can be used for low-power transmission of information such as instructions of underwater long-term working platforms.

[0081] In order to prove that the covert underwater acoustic communication method provided by the present invention has no detectable features, feature detection methods such as cyclic spectrum and cepstrum are used to compare the features of the communication signal generated by the method with the traditional direct sequence spread spectrum signal. Figure 4 Comparing the cepstrum characteristics of the communication signal of the present invention with that of the direct sequence spread spectrum signal, it can be seen that the present invention does not have any cepstrum characteristics. Figure 5 By comparing the cyclic spectrum characteristics of the communication signal of the present invention with that of the direct sequence spread spectrum signal, it can be seen that the present invention does not have any cyclic spectrum characteristics.

[0082] In summary, the covert underwater acoustic communication method of the present invention can achieve the communication signal being submerged in the ocean environment noise, and at the same time there are no detectable features. It is a very covert communication method, and can therefore be used for covert communication in long-distance and long-term underwater scenarios.

Claims

1. A method for covert underwater acoustic communication supporting no detectable features, characterized in that: The steps include: S1: The transmitter collects ocean environmental noise in real time as an information carrier, and then performs broadband filtering on the collected ocean environmental noise according to the working frequency band to obtain the original band-limited noise signal x(t); S2: According to the information to be transmitted, the optimal modulation parameter combination is selected to perform steganographic modulation on the original band-limited noise signal x(t) to generate the information-bearing signal C(x(t)); S3: Add the information-bearing signal C(x(t)) to the original band-limited noise signal x(t) to generate a covert communication signal s(t)=x(t)+C(x(t)), which is then transmitted into the ocean environment by the transmitting transducer after passing through a power amplifier; S4: The receiving end collects the received signal r(t) in real time; S5: According to the Doppler factor sequence {a n ,n=1,...,N a }, the receiving end resamples the real-time collected signal for each Doppler factor to obtain the Doppler compensated received signal r (n) (t); S6: The receiving end uses N φ Different optimal modulation parameter combinations, for each compensated signal r (n) (t) Perform steganalysis demodulation to obtain the correlation value matrix ρ; S7: Make a decision based on the absolute maximum value of the correlation value matrix ρ, and select the index corresponding to the maximum value. Complete the reception of communication information.

2. A method for supporting covert underwater acoustic communication without detectable features according to claim 1, characterized in that: The ocean environment noise in step S1 includes biological calls, ship noise, signals naturally generated by the ocean, radiation noise from other underwater platforms, and signals emitted by other underwater platforms.

3. A method for supporting covert underwater acoustic communication without detectable features according to claim 1, characterized in that: The method of steganographic modulation in step S2 includes: dividing the band-limited noise signal into even-numbered sub-signals in the time domain according to the division mode, a total of 2N b segment, denoted as {x n (t),n=-N b ,...,-1,1,...,N b }, and perform time domain inversion to obtain {x -n (-t),n=-N b ,...,-1,1,...,N b }; According to the symbol information b to be transmitted and the optimal modulation condition, select the steganographic parameter, that is, the rotation phase combination φ, and multiply the rotation phase with each signal segment for symbol modulation to obtain the information carrying signal C(x(t)); The number of rotation phase combinations φ is consistent with the number of symbol information, which is N φ .

4. A method for supporting covert underwater acoustic communication without detectable features according to claim 3, characterized in that: In step S2, the phase combination is rotated total Rotating phase combination {φ (m) ,m=1,...,N φ },{φ n ,n=-N b ,...,-1,1,...,N b } is the optimal modulation parameter, and the optimal modulation parameter selection method is as follows: in, is the phase of the symbol information b, {K n ,n=1,...,N b } is an integer.

5. A method for supporting covert underwater acoustic communication without detectable features according to claim 4, characterized in that: The information bearing signal C(x(t)) in step S2 is expressed as follows: Among them, {x n (t),n=-N b ,...,-1,1,...,N b } is the N obtained by evenly dividing x(t) b signal fragment.

6. A method for supporting covert underwater acoustic communication without detectable features according to claim 1, characterized in that: The method of steganographic demodulation in step S6 includes: A1: Use N φ The steganalysis parameters are used to compensate the signal r (n) (t) Perform the same processing as step S2 to obtain the intermediate signal {z m (t),m=1,...,N φ }; A2: The receiving end will φ The intermediate signals are respectively compared with the Doppler compensated signal r (n) (t) is processed by correlation to obtain the correlation value vector [ρ(n,1),...,ρ(n,N φ )]; A3: For each Doppler compensated signal r (n) (t) are all processed in step A2 to obtain the correlation value matrix ρ.

7. A method for supporting covert underwater acoustic communication without detectable features according to claim 6, characterized in that: The intermediate signal of step A1 is expressed as follows: f n =φ (m) [n]。 8. A method for supporting covert underwater acoustic communication without detectable features according to claim 6, characterized in that: The operation of the related value vector in step A2 is expressed as follows:

9. A method for supporting covert underwater acoustic communication without detectable features according to claim 1, characterized in that: The expression for making a decision based on the maximum absolute value of the correlation value matrix ρ in step S7 is as follows: in and Represent the estimated Doppler value index and symbol information index respectively, The corresponding symbol information is the transmitted information, and demodulation is completed.

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