Sound-imitating underwater covert communication method and device based on hopping pulse position coding

Abstract

The invention discloses a sound-imitating underwater covert communication method and device based on jump group pulse position coding, and the method comprises the steps: generating a large number of different whale animal sound groups and time delay difference value groups which can be used for coding according to the distribution rule of signal types and time intervals in a real marine animal sound string from a bionic angle, and carrying out the coding of the whale animal sound groups and the time delay difference value groups; a mode including but not limited to a pseudo-random sequence and the like is used, and group skipping is carried out on a whale animal sound group and a delay difference group by taking a code element as a unit during coding; the coded bionic communication signal string contains abundant and varied whale sound and delay difference values which conform to the real whale sound string distribution rule, so that the communication camouflage is improved. The device comprises a processor and a memory. According to the invention, a bionic camouflage covert communication string highly similar to a real marine animal sound signal string is constructed, and high-covert transmission of communication information is realized.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to an acoustic underwater covert communication method and device based on hopping group pulse position coding. Background Art

[0002] As the most effective means of underwater communication, underwater acoustic communication technology is widely used in submarine-based communication, submarine-to-submarine communication, submarine communication, underwater measurement and control, underwater LAN interconnection, maritime remote control and telemetry, and underwater communication and navigation integration. In recent years, with the increasingly fierce competition among countries in the ocean field, underwater acoustic communication technology has played an increasingly important role in the fields of maritime rights protection and sea area protection. However, with the development of marine stealth technology in various countries, the concealment and security of underwater acoustic communication systems are facing increasingly severe challenges. In order to ensure the covert transmission of information from underwater military platforms, various countries have carried out a lot of research work on underwater acoustic covert communication in recent years.

[0003] Traditional covert underwater acoustic communication methods mainly use low probability of interception (LPI) and low probability of detection (LPD) technologies. LPI mainly changes the parameters of artificial communication signals through frequency hopping, time hopping and other technologies to increase the difficulty of underwater detection systems to intercept communication information, thereby achieving the purpose of covert communication. However, the communication signals used in this method are still traditional underwater communication signals such as single-frequency signals and linear frequency modulation signals, which have obvious artificial characteristics and are easy to attract the attention of the detection system, resulting in the positioning of underwater military platforms. The core idea of ​​LPD is to try to reduce the signal-to-noise ratio of communication signals and hide the communication signals in noise to increase the difficulty of the detection system to detect the communication signals. However, this low signal-to-noise ratio covert communication method will limit the communication distance of the communication system, resulting in the reliability and effectiveness of long-distance covert communication being difficult to guarantee. Different from traditional covert underwater acoustic communication methods, the bionic camouflage covert underwater acoustic communication method uses or imitates the calls of marine animals as communication signals. It has the advantage of realizing covert transmission of communication information without reducing the signal-to-noise ratio, and shows outstanding potential in communication concealment and reliability.

[0004] Patent document CN207312015U discloses a bionic underwater acoustic communication method based on differential pattern delay difference coding, which uses the dolphin whistle signal itself and the delay difference between them to transmit communication information. The signal types and time interval types of this communication method are fixed, and its communication signal string does not conform to the diversity law of real dolphin whistle signals and the time intervals between them. The time interval distribution is also different from the real dolphin whistle signal string, which will lead to its limited concealment performance. Patent document CN103401619A discloses an underwater acoustic communication method based on virtual time reversal mirror M-element bionic signal coding, which has higher reliability than patent document CN207312015U, but its communication signal types and time interval types are still fixed, and it also has the problem of not conforming to the diversity law of real dolphin signal strings and limited concealment performance. Patent document CN118300707A discloses an underwater acoustic covert communication method imitating a pistol shrimp signal, which has a higher communication rate than patent document CN207312015U, but it still does not improve the concealment of this type of method from the perspective of the diversity of signals and time intervals.

[0005] This concealment problem will bring great security risks to the communication method. Patent document CN112530443B has disclosed a method for identifying camouflaged communication signals based on delay difference coding and imitating cetacean calls to address this concealment defect. The method extracts the time intervals between signals in the received bionic camouflaged communication signal string and calculates the probability density function of the extracted time interval to distinguish between the bionic camouflaged communication signal string and the real marine animal call string. It can be seen that this problem will bring great concealment risks to this type of bionic camouflaged communication method. Summary of the invention

[0006] The present invention provides a bionic underwater covert communication method and device based on hopping group pulse position coding. The present invention overcomes the problem of limited concealment performance caused by the lack of diversity of signal types and time intervals of real marine animal call signal strings, and constructs a bionic camouflage covert communication string that is highly similar to the real marine animal call signal string, thereby realizing high-covert transmission of communication information. See the following description for details:

[0007] In the first aspect, a method for acoustic underwater covert communication based on group hopping pulse coding is provided, the method comprising:

[0008] From a bionic perspective, based on the distribution of signal types and time intervals in real marine animal call strings, a large number of different cetacean call groups and time delay difference groups that can be used for encoding are generated to form a cetacean call group library and a time delay difference group library;

[0009] And using methods including but not limited to pseudo-random sequences, the cetacean call groups and time delay difference groups are grouped in units of code elements during encoding, so that the encoded bionic communication signal string contains rich and varied cetacean calls and time delay differences that conform to the distribution law of real cetacean call strings, so as to improve the communication camouflage.

[0010] The constructed cetacean call signal group includes: cetacean call signals with better autocorrelation and cetacean call signals with better cross-correlation.

[0011] Wherein, the cetacean call signal with better autocorrelation is selected as follows:

[0012] Extract n cetacean call signals s1(t) to s1(t) from the real cetacean call signal string based on short-term energy n (t);

[0013]

[0014] Calculate the cetacean call signal s1(t) to s n The autocorrelation function A1(t) to A n (t), where t is the time delay, according to the main lobe width t of the autocorrelation function x and side lobe level η s , for all the cetacean call signals s1(t) to s n (t) is screened to obtain the main lobe width t x Small side lobe level η s Small n' cetacean call signals s'1(t) to s' n' (t).

[0015] Wherein, the method of screening multiple groups of cetacean call signals with poor mutual correlation is:

[0016] pass:

[0017]

[0018] Computing cetacean call signals s' with high timing accuracy i (t) and s' j The cross-correlation matrix c of (t) ij , where t is the time delay and the correlation coefficient matrix c ij is an n' by n' square matrix, the element in the i-th row and j-th column of the square matrix is ​​C ij .

[0019] Construct the set S1 and transform the mutual correlation coefficient matrix c ij The first row in the 11 To C1n' Compare with the mutual correlation coefficient screening threshold ε in turn. If C 11 is less than ε, put s'1(t) into the set S1. If C 12 Less than ε, put s'2(t) into the set S1 until C is completed 1n' Compared with ε, the number of signals in set S1 is recorded as NS1, and NS1 is the sum of s'1(t) to s' n' The total number of signals in (t) whose correlation coefficient with s'1(t) is lower than ε;

[0020] Construct the set S2 and convert the mutual correlation coefficient matrix c ij The second row in the 21 To C 2n' The set S2 is constructed by comparing them with the mutual correlation coefficient screening threshold ε in turn, and the number of signals in the set S2 is recorded as NS2, which is the sum of s'1(t) to s' n' The total number of signals in (t) whose correlation coefficient with s'2(t) is lower than ε, and the number of signals in the set Sn' is recorded as NSn';

[0021] Find the maximum value NSm from NS1 to NSn' and get the corresponding cetacean call signal s' m (t), the call signal s' m (t) being placed in a first group of the set of real cetacean call signals for encoding as the first signal of the first group of the set of real cetacean call signals;

[0022] Find the cetacean call signal with the largest NS value in the set Sm as the second signal of the first group, find the third signal in the set corresponding to the second signal, and so on, to screen out the first group of cetacean call signals with poor mutual correlation;

[0023] Put 2 in the first group N The NS corresponding to the signal is excluded, and the maximum value is found in the remaining NS. According to the previous step, the second to Mth groups of cetacean call signals with poor mutual correlation are constructed, where each group contains 2 N A signal used to encode N bits of information.

[0024] Among them, the delay difference group is:

[0025] Statistically analyzing the distribution of time intervals in real cetacean call signal strings, obtaining time interval samples F in real cetacean call signal strings, and the probability density function of sample F is f(x);

[0026] Generate a pseudo-random sample G with uniform distribution using the pseudo-random sequence generation method, and the corresponding probability density function is g(x);

[0027] Based on f(x) and g(x), the pseudo-random sample G is sampled using acceptance-rejection sampling to obtain a pseudo-random sequence numerical sample F' that conforms to the distribution of f(x); F' is used as the total sample of the encoded delay difference to construct a group of delay difference values ​​P for encoding.

[0028] Among them, the communication signal string is highly similar to the real marine animal call signal string, realizing highly concealed transmission of communication information.

[0029] The delay difference is consistent with the distribution law of time intervals in real cetacean call strings.

[0030] The method matches any real marine animal call string pattern, and constructs multiple groups of real cetacean call signal groups for encoding.

[0031] In the second aspect, an acoustic underwater covert communication device based on hopping group pulse coding is provided, the device comprising: a processor and a memory, the memory storing program instructions, the processor calling the program instructions stored in the memory to enable the device to execute any one of the methods described in the first aspect.

[0032] The beneficial effects of the technical solution provided by the present invention are:

[0033] (1) The delay difference values ​​used for encoding in the communication signal string are rich and varied, and conform to the distribution law of time intervals in the real cetacean call string: based on the distribution law of time intervals in the real cetacean call string, multiple delay difference value group libraries for encoding are constructed, and the delay difference value group used for encoding is continuously changed in units of code elements by means of group hopping including but not limited to pseudo-random sequences, thereby controlling the distribution law of time intervals in the generated communication signal string;

[0034] (2) The real cetacean call signals used for encoding in the communication signal string are rich and diverse: Based on the diversity of the call signals in the real cetacean call string, multiple cetacean call group libraries used for encoding are constructed, and the cetacean call group libraries used for encoding are continuously changed in units of code elements by means of group hopping including but not limited to pseudo-random sequences, thereby achieving the richness and diversity of the signals used in the communication signal string;

[0035] (3) It can flexibly match the regularity of any real marine animal call string: It can match the regularity of any real marine animal call string by only modifying the cetacean call group library and the delay difference group library. There is no need to modify the communication method, and the regularity matching is relatively flexible. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1A schematic diagram showing a real cetacean call signal string in the present invention;

[0037] Figure 2 It is a schematic diagram of the communication coding method based on the group hopping of real cetacean call signals in the present invention;

[0038] Figure 3 It is a schematic diagram of a communication coding method based on delay difference group hopping group in the present invention;

[0039] Figure 4 A schematic diagram showing a communication transmission platform in the present invention;

[0040] Figure 5 A schematic diagram showing a communication receiving platform in the present invention;

[0041] Figure 6 A schematic diagram showing the distribution of time intervals in a real cetacean call signal train;

[0042] Figure 7 Show a section with Figure 6 The cetacean call signal string is used as the imitation object, and the schematic diagram of the distribution law of the time interval in the bionic communication signal string obtained by encoding without using the group skipping method;

[0043] Figure 8 Show a section with Figure 6 The cetacean call signal string is used as the simulation object. A schematic diagram of the distribution law of the time interval in the bionic communication signal string encoded by the hopping group method is shown.

[0044] In the attached figure, the list of components is as follows:

[0045] Figure 4 In the figure: 1 is the call signal group and the delay difference value group library; 2 is the pseudo-random sequence; 3 is the communication information to be transmitted; 4 is the communication encoder; 5 is the underwater acoustic transducer.

[0046] Figure 5 In the figure: 6 is a hydrophone; 7 is a copy correlator; 8 is a communication decoder; 9 is a communication information outputter. DETAILED DESCRIPTION

[0047] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0048] To solve this problem, the embodiment of the present invention proposes a method and device for underwater covert communication based on pulse position coding by hopping group. From the perspective of bionics, the cetacean call group and time delay difference group used for coding are hopped in units of code elements by using methods including but not limited to pseudo-random sequences, so that the cetacean call group and time delay difference group used for coding are constantly changed to ensure the diversity of the cetacean calls and time delay differences used, so that they are close to the characteristics of the real cetacean call string, and further improve the communication camouflage.

[0049] Compared with the existing bionic covert communication method, the embodiment of the present invention has the following advantages: (1) The delay difference values ​​used for encoding in the communication signal string are rich and diverse, and conform to the distribution law of time intervals in the real cetacean call string: based on the distribution law of time intervals in the real cetacean call string, it constructs a plurality of delay difference value group libraries for encoding, and continuously changes the delay difference value group used for encoding in units of code elements by means of hopping groups including but not limited to pseudo-random sequences, thereby controlling the distribution law of time intervals in the generated communication signal string; (2) The real cetacean call signals used for encoding in the communication signal string are rich and diverse: based on the diversity law of call signals in the real cetacean call string, it constructs a plurality of cetacean call group libraries for encoding, and continuously changes the cetacean call group libraries used for encoding in units of code elements by means of hopping groups including but not limited to pseudo-random sequences, thereby achieving the richness and diversity of the signals used in the communication signal string. (3) It can flexibly match the regularity of any real marine animal call string: It can match the regularity of any real marine animal call string by only modifying the cetacean call group library and the delay difference group library. There is no need to modify the communication method, and the regularity matching is relatively flexible.

[0050] The embodiment of the present invention provides an acoustic underwater covert communication method and device based on group hopping pulse position coding. Figure 1 shows a real cetacean call signal string, composed of Figure 1 It can be seen that the calls of cetaceans and the time intervals between their calls vary greatly. The call signal itself and the time delay difference between the calls can be used to encode communication information, and the copy correlation algorithm can be used to identify the call signal and solve the time position of the call signal to achieve information decoding of the communication method. At the same time, in order to match the diversity of the call signals and their time intervals in the real cetacean call string, the cetacean call group and the delay difference group used for encoding are jumped using methods including but not limited to pseudo-random sequences to further improve the communication camouflage.

[0051] The first step is to construct a set of real cetacean call signals for encoding:

[0052] First, based on the short-time energy, n cetacean call signals s1(t) to s1(t) are extracted from the real cetacean call signal string.n (t);

[0053] Further, by:

[0054]

[0055] Calculate the cetacean call signal s1(t) to s n The autocorrelation function A1(t) to A n (t), where t is the time delay. Then according to the main lobe width t of the autocorrelation function x and side lobe level η s , for all the cetacean call signals s1(t) to s n (t) is screened to obtain the main lobe width t x Small side lobe level η s Small n' cetacean call signals s'1(t) to s' n' (t), mark these cetacean call signals as cetacean call signals with good autocorrelation. For example, 10% of the shortest duration of the call signal can be used as the main lobe width t x Screening threshold, use -3dB as the sidelobe level η s Screening threshold, screening cetacean call signals with good autocorrelation.

[0056] Since the embodiment of the present invention uses copy correlation to complete the calculation of the time position of the call, that is, by detecting the autocorrelation function A of the call signal of a certain cetacean i The maximum position of (t) determines the cetacean call signal s i (t) is the time position in the call pulse train. Therefore, the cetacean call signal with good autocorrelation can be considered to have high timing accuracy, that is, this step can also be considered to screen out the cetacean call signals s'1(t) to s' n' (t);

[0057] Further, by:

[0058]

[0059] Computing cetacean call signals s' with high timing accuracy i (t) and s' j The cross-correlation matrix c of (t) ij , where t is the time delay. From the formula, we can see that the mutual correlation coefficient matrix c ij is an n' by n' square matrix, the element in the i-th row and j-th column of the square matrix is ​​C ij .

[0060] Further, construct the set S1 and transform the mutual correlation coefficient matrix cij The first row in the 11 To C 1n' Compare with the mutual correlation coefficient screening threshold ε in turn. If C 11 is less than ε, put s'1(t) into the set S1. If C 12 If it is less than ε, put s'2(t) into the set S1, and so on until C is completed. 1n' Compared with ε, the number of signals in set S1 is recorded as NS1, and NS1 is the sum of s'1(t) to s' n' The total number of signals in s'(t) whose correlation coefficient with s'1(t) is less than ε.

[0061] Further, construct set S2 and convert the mutual correlation coefficient matrix c ij The second row in the 21 To C 2n' The set S2 is constructed by comparing them with the mutual correlation coefficient screening threshold ε in turn, and the number of signals in the set S2 is recorded as NS2, which is the sum of s'1(t) to s' n' The total number of signals in (t) whose correlation coefficient with s'2(t) is lower than ε. This process is repeated until the set Sn' is constructed and the number of signals in the set Sn' is recorded as NSn'.

[0062] Further, find the maximum value NSm among NS1 to NSn' and obtain the corresponding cetacean call signal s' m (t), s' m (t) is placed in the first group of the real cetacean call signal group for encoding as the first signal of the first group of the real cetacean call signal group. Then, the cetacean call signal with the largest NS value is continuously searched in the set Sm as the second signal of the first group, and then the third signal is searched in the set corresponding to the second signal, and so on, to screen out the first group of cetacean call signals with poor mutual correlation, which group includes 2 N A signal used to encode N bits of information.

[0063] Furthermore, the first group of 2 N The NS corresponding to the signal is excluded, and the maximum value is found in the remaining NS. According to the previous step, the second to Mth groups of cetacean call signals with poor mutual correlation are constructed, where each group contains 2 N A signal used to encode N bits of information.

[0064] Among the M groups of signals obtained by this method, any call signal is related to the other 2 in the same group. N-1 call signal shows low cross-correlation, which makes it easy for the receiving end to judge which call signal in the group is used for encoding by copying the correlation result. There is no requirement for the cross-correlation between different groups of signals. For example, if 100 groups of cetacean call signals with poor cross-correlation are screened, each group contains 8 signals, and any of these 8 signals shows a cross-correlation coefficient lower than the screening threshold ε with the other 7 call signals in the same group. There is no requirement for the cross-correlation between different groups, for example, between the 8 signals in the first group and the 8 signals in the second group.

[0065] Step 2: Construct a delay difference group for encoding:

[0066] Firstly, the distribution of time intervals in the real cetacean call signal string is statistically analyzed to obtain the time interval sample F in the real cetacean call signal string, and the probability density function of sample F is f(x);

[0067] Furthermore, a large number of pseudo-random samples G with uniform distribution are generated by using a pseudo-random sequence generation method, and the probability density function of the pseudo-random sample G is g(x);

[0068] Furthermore, based on f(x) and g(x), the acceptance-rejection sampling method is used to sample G, and a pseudo-random sequence numerical sample F' that conforms to the distribution of f(x) is obtained from G. Since f(x) is the distribution of the time intervals in the real cetacean call signal string, the distribution law of F' can be considered to be the same as the distribution law of the time intervals in the real cetacean call signal string;

[0069] Furthermore, taking F' as the total sample of the delay difference value to be encoded, construct the delay difference value groups P for encoding, where each group contains 2 Q Different delay differences are used to encode Q bits of information.

[0070] Step 3: Design communication coding method:

[0071] First, the groups of real cetacean call signals and delay difference values ​​used in encoding each symbol are determined. Specifically, for the nth symbol, the nth element x in the pseudo-random sequence X distributed between 0 and 1 is used. n The size of

[0072]

[0073] Get the group number m of the real cetacean call signal group used by this code element n , where For example, if there are 100 cetacean call signal groups, for the first code element, if the first element x in the pseudo-random sequence X is nis 0.1, then the group number m of the cetacean call signal group n It can be calculated as 11 by the above formula, that is, the code element is encoded using the 11th group of cetacean call signals.

[0074] At the same time, according to the nth element y in the pseudo-random sequence Y distributed between 0 and 1 n The size of

[0075]

[0076] Get the group number p of the delay difference group used by the codeword n .

[0077] Furthermore, for each code element, according to the information to be encoded, a corresponding call signal is selected from its corresponding real cetacean call signal group as the communication signal, and a corresponding delay difference value is selected from its corresponding delay difference value group as the time interval between the communication signal and the previous communication signal.

[0078] Furthermore, a real cetacean call signal with high timing accuracy is selected as the communication synchronization code SC, and the SC is combined with all the encoded communication code elements to form a final communication signal string z(t).

[0079] Step 4: Design the decoding method for the communication information receiving end:

[0080] Firstly, synchronization timing is performed by processing the copy correlation of the synchronization code SC, and the end time of SC is used as the time reference of the first code element S1 in the bionic communication signal string z(t).

[0081] Furthermore, according to the pseudo-random sequences X and Y that are the same as those of the transmitting end, the real cetacean call signal group number m1 and the delay difference group number p1 of the first code element S1 are obtained.

[0082] Furthermore, S1 is subjected to copy correlation processing with all the call signals in the m1-th call signal group, the call signal used by the code element is determined, and the communication information i1 encoded by the code element through the call signal is solved.

[0083] Furthermore, the starting time of the call signal in S1 is compared with the time base of the first code element S1, the delay difference used by the first code element S1 is determined, the communication information j1 ​​encoded by the delay difference of the first code element is solved, and the time base is adjusted to the end time of the call signal in the code element.

[0084] Furthermore, the above decoding steps are repeated until all code elements are decoded to obtain communication information i1 to i n , j1 to j n .

[0085] Furthermore, i1 to i n , j1 to j n By combining them, all communication information can be obtained, thus realizing communication decoding.

[0086] Step 5: Implementation of communication transmitting and receiving platform:

[0087] The communication launch platform is implemented as follows:

[0088] like Figure 4 As shown, the call signal group and delay difference group library 1 transmits the constructed cetacean call signal group and delay difference group to the communication encoder 4, the communication encoder 4 reads the pseudo-random sequence 2 and the communication information 3 to be transmitted, and constructs a bionic communication signal string according to the communication coding method in the embodiment of the present invention, and transmits the bionic communication signal string to the underwater acoustic transducer 5, which converts it into a sound wave signal and sends it into the water to realize the transmission of the communication information.

[0089] The communication receiving platform is implemented as follows:

[0090] like Figure 5 As shown, a hydrophone 6 is used to collect a cetacean call signal string carrying communication information and convert it into an electrical signal for transmission to a copy correlator 7. The copy correlator 7 synchronizes and times the received signal and sends it to a communication decoder 8. The communication decoder 8 decodes the received signal based on the communication decoding method in the embodiment of the present invention, and finally outputs the decoded communication information through a communication information outputter 9, thereby realizing decoding of the communication information.

[0091] An acoustic underwater covert communication device based on hopping group pulse position coding, the device comprises: a processor and a memory, the memory stores program instructions, the processor calls the program instructions stored in the memory to make the device perform the following method steps:

[0092] From a bionic perspective, based on the distribution of signal types and time intervals in real marine animal call strings, a large number of different cetacean call groups and time delay difference groups that can be used for encoding are generated to form a cetacean call group library and a time delay difference group library;

[0093] And using methods including but not limited to pseudo-random sequences, the cetacean call groups and time delay difference groups are grouped in units of code elements during encoding, so that the encoded bionic communication signal string contains rich and varied cetacean calls and time delay differences that conform to the distribution law of real cetacean call strings, so as to improve the communication camouflage.

[0094] Among them, the constructed cetacean call signal group includes: cetacean call signals with better autocorrelation and cetacean call signals with better cross-correlation.

[0095] Among them, the cetacean call signals with better autocorrelation are:

[0096] Extract n cetacean call signals s1(t) to s1(t) from the real cetacean call signal string based on short-term energy n (t);

[0097]

[0098] Calculate the cetacean call signal s1(t) to s n The autocorrelation function A1(t) to A n (t), where t is the time delay, according to the main lobe width t of the autocorrelation function x and side lobe level η s , for all the cetacean call signals s1(t) to s n (t) is screened to obtain the main lobe width t x Small side lobe level η s Small n' cetacean call signals s'1(t) to s' n' (t).

[0099] Among them, the cetacean call signals for screening mutual correlation are:

[0100] pass:

[0101]

[0102] Computing cetacean call signals s' with high timing accuracy i (t) and s' j The mutual correlation coefficient matrix c of (t) ij , where t is the time delay and the correlation coefficient matrix c ij is an n' by n' square matrix, the element in the i-th row and j-th column of the square matrix is ​​C ij .

[0103] Construct the set S1 and transform the mutual correlation coefficient matrix c ij The first row in the 11 To C 1n' Compare with the mutual correlation coefficient screening threshold ε in turn. If C 11 is less than ε, put s'1(t) into the set S1. If C 12 Less than ε, put s'2(t) into the set S1 until C is completed 1n' Compared with ε, the number of signals in set S1 is recorded as NS1, which is the number of s'1(t) to s' n' The total number of signals in (t) whose correlation coefficient with s'1(t) is lower than ε;

[0104] Construct the set S2 and convert the mutual correlation coefficient matrix c ij The second row in the 21 To C 2n' The set S2 is constructed by comparing them with the mutual correlation coefficient screening threshold ε in turn, and the number of signals in the set S2 is recorded as NS2, which is the sum of s'1(t) to s' n' The total number of signals in (t) whose correlation coefficient with s'2(t) is lower than ε, and the number of signals in the set Sn' is recorded as NSn';

[0105] Find the maximum value NSm from NS1 to NSn' and get the corresponding cetacean call signal s' m (t), the call signal s' m (t) being placed in a first group of the set of real cetacean call signals for encoding as the first signal of the first group of the set of real cetacean call signals;

[0106] Find the cetacean call signal with the largest NS value in the set Sm as the second signal of the first group, find the third signal in the set corresponding to the second signal, and so on, to screen out the first group of cetacean call signals with poor mutual correlation;

[0107] Put 2 in the first group N The NS corresponding to the signal is excluded, and the maximum value is found in the remaining NS. According to the previous step, the second to Mth groups of cetacean call signals with poor mutual correlation are constructed, where each group contains 2 N A signal used to encode N bits of information.

[0108] The delay difference value group is:

[0109] Statistically analyzing the distribution of time intervals in real cetacean call signal strings, obtaining time interval samples F in real cetacean call signal strings, and the probability density function of sample F is f(x);

[0110] Generate a pseudo-random sample G with uniform distribution using the pseudo-random sequence generation method, and the corresponding probability density function is g(x);

[0111] Based on f(x) and g(x), the pseudo-random sample G is sampled using acceptance-rejection sampling to obtain a pseudo-random sequence numerical sample F' that conforms to the distribution of f(x); F' is used as the total sample of the encoded delay difference to construct a group of delay difference values ​​P for encoding.

[0112] Among them, the communication signal string is highly similar to the real marine animal call signal string, realizing highly concealed transmission of communication information.

[0113] Among them, the delay difference is consistent with the distribution law of time intervals in real cetacean call strings.

[0114] The device matches any real marine animal call string pattern, and constructs multiple groups of real cetacean call signal groups for encoding.

[0115] It should be pointed out here that the device description in the above embodiment corresponds to the method description in the embodiment, and the embodiment of the present invention will not be described in detail here.

[0116] The execution subjects of the above-mentioned processor and memory can be devices with computing functions such as computers, single-chip microcomputers, and microcontrollers. In specific implementation, the embodiments of the present invention do not limit the execution subjects and are selected according to the needs of actual applications.

[0117] The data signal is transmitted between the memory and the processor via a bus, which is not described in detail in the embodiment of the present invention.

[0118] Unless otherwise specified, the models of the components in the embodiments of the present invention are not limited, and any device that can perform the above functions may be used.

[0119] Those skilled in the art will appreciate that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for acoustic underwater covert communication based on hopping group pulse coding, characterized in that: The method comprises: From a bionic perspective, based on the distribution of signal types and time intervals in real marine animal call strings, a large number of different cetacean call groups and time delay difference groups that can be used for encoding are generated to form a cetacean call group library and a time delay difference group library; During encoding, the cetacean call groups and time delay difference groups are group-hopped in units of code elements, so that the encoded bionic communication signal string contains cetacean calls and time delay differences that conform to the distribution law of real cetacean call strings, so as to improve communication camouflage.

2. The method for acoustic underwater covert communication based on group-hopping pulse coding according to claim 1, characterized in that: The cetacean call group comprises: screening cetacean call signals with better autocorrelation and screening multiple groups of cetacean call signals with poor mutual correlation.

3. The method for underwater covert communication based on pulse position coding based on group hopping according to claim 2, characterized in that: The cetacean call signal for screening for better autocorrelation is: Extract n cetacean call signals s1(t) to s1(t) from the real cetacean call signal string based on short-term energy n (t); Calculate the cetacean call signal s1(t) to s n The autocorrelation function A1(τ) to A n (τ), where τ is the time delay, according to the main lobe width τ of the autocorrelation function x and side lobe level η s , for all the cetacean call signals s1(t) to s n (t) is screened to obtain the main lobe width τ x Small side lobe level η s Small n' cetacean call signals s'1(t) to s' n' (t).

4. The method for acoustic underwater covert communication based on group-hopping pulse coding according to claim 2 is characterized in that: The screening of multiple groups of cetacean call signals with poor mutual correlation is as follows: pass: Computing cetacean call signals s' with high timing accuracy i (t) and s' j The mutual correlation coefficient matrix c of (t) ij , where τ is the time delay and the correlation coefficient matrix c ij is an n' by n' square matrix, the element in the i-th row and j-th column of the square matrix is ​​C ij ; Construct the set S1 and transform the mutual correlation coefficient matrix c ij The first row in the 11 To C 1n' Compare with the mutual correlation coefficient screening threshold ε in turn. If C 11 is less than ε, put s'1(t) into the set S1. If C 12 Less than ε, put s'2(t) into the set S1 until C is completed 1n' Compared with ε, the number of signals in set S1 is recorded as NS1, and NS1 is the sum of s'1(t) to s' n' The total number of signals in (t) whose correlation coefficient with s'1(t) is lower than ε; Construct the set S2 and convert the mutual correlation coefficient matrix c ij The second row in the 21 To C 2n' The set S2 is constructed by comparing them with the mutual correlation coefficient screening threshold ε in turn, and the number of signals in the set S2 is recorded as NS2, which is the sum of s'1(t) to s' n' The total number of signals in (t) whose correlation coefficient with s'2(t) is lower than ε, and the number of signals in the set Sn' is recorded as NSn'; Find the maximum value NSm from NS1 to NSn' and get the corresponding cetacean call signal s' m (t), the call signal s' m (t) being placed in a first group of the set of real cetacean call signals for encoding as the first signal of the first group of the set of real cetacean call signals; Find the cetacean call signal with the largest NS value in the set Sm as the second signal of the first group, find the third signal in the set corresponding to the second signal, and so on, to screen out the first group of cetacean call signals with poor mutual correlation; Put 2 in the first group N The NS corresponding to the signal is excluded, and the maximum value is found in the remaining NS. According to the previous step, the second to Mth groups of cetacean call signals with poor mutual correlation are constructed, where each group contains 2 N A signal used to encode N bits of information.

5. The method for underwater covert communication based on pulse position coding based on group hopping according to claim 1, characterized in that: The delay difference value group is: Statistically analyzing the distribution of time intervals in real cetacean call signal strings, obtaining time interval samples F in real cetacean call signal strings, and the probability density function of sample F is f(x); Generate a pseudo-random sample G with uniform distribution using the pseudo-random sequence generation method, and the corresponding probability density function is g(x); Based on f(x) and g(x), the pseudo-random sample G is sampled using acceptance-rejection sampling to obtain a pseudo-random sequence numerical sample F' that conforms to the distribution of f(x); F' is used as the total sample of the encoded delay difference to construct a group of delay difference values ​​P for encoding.

6. The method for underwater covert communication based on pulse position coding based on group hopping according to claim 1, characterized in that: The communication signal string is highly similar to a real marine animal call signal string, thereby achieving highly concealed transmission of communication information.

7. The method for acoustic underwater covert communication based on group-hopping pulse coding according to claim 5 is characterized in that: The delay difference is consistent with the distribution law of time intervals in real cetacean call strings.

8. The method for underwater covert communication based on pulse position coding based on group hopping according to claim 5, characterized in that: The method can match any real marine animal call string pattern.

9. The method for acoustic underwater covert communication based on group-hopping pulse coding according to claim 4, characterized in that: The method constructs multiple sets of real cetacean call signal sets for encoding.

10. An acoustic underwater covert communication device based on group-hopping pulse position coding, characterized in that: The device comprises: a processor and a memory, wherein program instructions are stored in the memory, and the processor calls the program instructions stored in the memory to enable the device to execute the method according to any one of claims 1 to 9.

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