A shared dictionary based physical layer spread spectrum camouflage module

Abstract

The application relates to a shared-dictionary-based physical layer spread spectrum camouflage module, belonging to the field of deep-sea covert communication. 16 The module comprises a shared waveform dictionary, a random mapping encoder, a power spectrum shaping filter and an adaptive power controller; the dictionary contains not less than two mutually different spread spectrum sequences, each sequence having a mutually different chip rate, which fundamentally suppresses the cyclostationary characteristics of a traditional spread spectrum signal; the random mapping encoder maps encrypted information into a spread spectrum waveform through pseudo-random selection, each communication waveform being randomly different, so that physical layer one-time pad is realized; power spectrum shaping makes the signal indistinguishable from deep-sea background magnetic noise, and adaptive power control makes the signal submerged in environmental noise; the module can reliably communicate under the condition that the signal-to-noise ratio is as low as -10 dB, and provides physical layer security protection for deep-sea communication nodes.

Description

Technical Field

[0001] This invention relates to the field of deep-sea covert communication and physical layer security technology, and in particular to a physical layer spread spectrum camouflage module based on a shared dictionary. Background Technology

[0002] To improve the probability of interception, existing underwater covert communication systems typically employ direct sequence spread spectrum or frequency hopping techniques, using pseudo-random codes to reduce the signal power spectral density below the background noise level. However, the inherent periodicity and binary nature of direct sequence spread spectrum signals, along with other cyclostationary characteristics, allow them to be identified and exploited by eavesdroppers under long-term observation or high-order spectral analysis.

[0003] A review published in the *Journal of Communications* in 2025 systematically analyzed the current status, challenges, and solutions for chaotic LPI communication. Classical LPI communication methods such as direct sequence spread spectrum and frequency hopping face the risk of interception. Improved schemes such as multi-carrier DCSK and indexed modulation DCSK still struggle to address the degradation in anti-interception capability and security caused by the introduction of a reference sequence. Chaotic communication waveforms exhibit shortcomings in security, transmission efficiency, and reliability, and their engineering implementation presents difficulties.

[0004] In deep-sea communication nodes where energy and computing power are limited, existing physical layer security technologies face challenges. A camouflage scheme is needed to eliminate cyclic stationary characteristics at the physical layer and achieve reliable communication with a negative signal-to-noise ratio without complex synchronization.

[0005] This module is a sub-module of the parent invention patent "Integrated System for Full-Link Low Physical Characteristics Communication Based on Deep-Sea Hydrostatic Pressure Driven", providing physical layer secure communication for deep-sea communication nodes.

[0006] This invention provides a spread spectrum camouflage scheme that solves the signal detectability problem at the physical layer, making the transmitted waveform indistinguishable from deep-sea background noise through a shared dictionary and pseudo-random selection. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide a physical layer spread spectrum camouflage module based on a shared dictionary. By pseudo-randomly selecting spread spectrum sequences with different chip rates, the cyclic stationary characteristics of traditional spread spectrum signals are suppressed, and the signal is statistically indistinguishable from the magnetic noise of the deep sea background, thus providing physical layer secure communication guarantee for deep-sea communication nodes.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is: a physical layer spread spectrum masquerading module based on a shared dictionary, the innovation of which is: comprising: A shared waveform dictionary, pre-installed at both the transmitter and authorized receiver, contains no fewer than 2... 16 Each of the following spread spectrum sequences is different from the others, and each sequence has a different chip rate; The random mapping encoder divides the encrypted information bit stream into fixed-length groups and uses a key-driven pseudo-random number generator to randomly select a spreading sequence from a dictionary to map each group of information. A power spectrum shaping filter is used to make the fitting error between the power spectral density of the output signal and the deep-sea magnetic noise spectrum less than 10%. An adaptive power controller adjusts the transmit power based on channel quality.

[0009] Furthermore, the shared waveform dictionary is generated using cascaded chaotic mapping, with the main mapping being a Logistic mapping with parameter r=4, and the auxiliary mapping being a Chebyshev mapping. A chaotic sequence with uniform statistical characteristics is generated through nonlinear coupling. The peak cross-correlation coefficient between different spreading sequences in the dictionary is less than 0.01. The KL divergence between the transmitted signal and the deep-sea background magnetic noise is less than 0.1. The random mapping encoder supports an M-sequence superposition mode, simultaneously selecting M spreading sequences and summing them with equal power weights to output a synthesized waveform.

[0010] Furthermore, the method for constructing and presetting the shared waveform dictionary is as follows: Step 1: Chaotic Sequence Generation: An initial sequence is generated using a cascaded chaotic mapping; the main mapping is the Logistic mapping. The secondary mapping is the Chebyshev mapping. By nonlinearly coupling the outputs of the two, a chaotic sequence with more uniform statistical properties is generated, enhancing the unpredictability of the waveform. The second step is waveform generation: Chaotic mapping is run with 256 different initial seeds, which are derived from the master key, and Nc = 1024 chaotic values ​​are output each time. These values ​​are mapped onto bipolar BPSK symbols, with positive values ​​being +1 and negative values ​​being -1, resulting in a spread spectrum sequence of length 1024. The sequence is then pulse-shaped using a raised cosine filter with a roll-off factor of 0.5 to generate a baseband spread spectrum waveform. Each waveform is randomly assigned a chip rate Rc, which is a pseudo-random value uniformly distributed in the range of 1kHz to 50kHz. The time domain length Tw = Nc / Rc of each waveform varies accordingly. The third step is cross-correlation optimization: calculate the peak cross-correlation coefficient between all waveforms in the waveform library, and replace or rotate the phase of waveform pairs with a cross-correlation coefficient greater than 0.01 to optimize the orthogonality between waveforms. The fourth step is secure distribution: the generated waveform library, waveform index mapping table, and waveform chip rate parameters are packaged, encrypted using AES-256, and written to the non-volatile memory of each node through a secure channel.

[0011] Furthermore, the transmitting end processing flow is as follows: Step A: The length of the data frame to be transmitted is 128 bits, which is encrypted using AES-128 and denoted as information vector b; Step B: Use the current key (Kenc) to derive a random number seed rseed, and combine it with the first 64 bits of b to determine the modulated waveform index; Step C: Extract the waveform corresponding to index i from the dictionary. To enhance robustness, select M waveforms and sum them using equal power weights: ,in Normalization coefficient; Step D: Input s(t) into a 10th-order IIR digital filter. The filter coefficients are designed based on the target power spectrum curve, which is determined based on the environmental noise spectrum parameters estimated from the current water temperature and salinity. Step E: Adjust the power amplifier through the adaptive power controller to amplify the signal to the target transmission power and then radiate it through the triaxial orthogonal loop coil.

[0012] Furthermore, the demodulation process at the receiving end is as follows: Step A: After the received signal is amplified and sampled with low noise, parallel sliding correlation matched filtering is performed on all waveforms in the dictionary simultaneously; let the received signal be... The output of the matched filter is ; Step B: The peak detector finds the peak with the largest absolute value, ymax, and its corresponding waveform index, imax; Step C: Extract time synchronization information using peak positions to correct clock drift at the receiver; Step D: Obtain the information bit best through the waveform index imax inverse mapping; if the M-sequence superposition mode is used, the orthogonal matching pursuit algorithm is needed to estimate the contribution coefficient of each waveform before making a decision.

[0013] An innovative deep-sea communication beacon includes a spread spectrum camouflage module, a dual-resonant magnetic coupling communication unit, and a PSIC power generation unit. When transmitting regular data, the information stream is encrypted using AES-128 and then input to a shared dictionary encoder. The shaped spread spectrum waveform is processed by a power spectrum shaping filter and then radiated by a triaxial orthogonal loop coil group driven by an adaptive power controller. At the receiving end, the signal is collected from the triaxial loop coil group and fed to a matched filter demodulator. The decrypted data is used by the beacon's master controller or re-encoded and forwarded via relay logic.

[0014] The advantages of this invention are: 1) First, suppress cyclostationary characteristics; by using the random mapping information of sequences with different chip rates, the cyclostationary characteristics of traditional spread spectrum signals are fundamentally suppressed, and eavesdroppers cannot detect the presence of the signal through cyclospectral analysis; Second, statistical indistinguishability; the transmitted signal, after being shaped and randomly modulated by the Wenz spectrum, has a KL divergence of less than 0.1, making it statistically indistinguishable from deep-sea background magnetic noise. Third, the probability of interception is extremely low; the dictionary contains no fewer than 2 entries. 16 The signal strength is such that eavesdroppers cannot exhaustively match it; the cross-correlation coefficient between each waveform is less than 0.01, and the signal power can be controlled below the level of ambient magnetic noise, achieving deep signal-to-noise ratio concealment.

[0015] Fourth, energy efficiency; no complex chaotic synchronization or channel estimation is required, and legitimate receivers only need matched filtering for demodulation.

[0016] Fifth, key-driven security. The mapping rules change with the key, and the key space is no less than 2. 128 Physical layer security does not depend on algorithm confidentiality. Attached Figure Description

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is a block diagram illustrating the principle of a shared dictionary spread spectrum modulation transmitter for a physical layer spread spectrum masquerading module based on a shared dictionary, according to the present invention.

[0019] Figure 2 This is a schematic diagram comparing the cyclic spectral density of signals from a traditional DSSS (left) and a shared dictionary scheme (right) in a physical layer spread spectrum masquerading module based on a shared dictionary, according to the present invention.

[0020] Figure 3 This is a flowchart of the matched filtering demodulation process at the receiver of a physical layer spread spectrum masquerading module based on a shared dictionary according to the present invention.

[0021] Figure 4 This is a comparison curve of the transmit signal power spectrum and Wenz noise spectrum of a physical layer spread spectrum camouflage module based on a shared dictionary according to the present invention.

[0022] Figure 5 This invention provides a dictionary construction and pre-setting process for a physical layer spread spectrum masquerading module based on a shared dictionary. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] like Figures 1 to 5 The physical layer spread spectrum masquerading module based on a shared dictionary shown includes: A shared waveform dictionary, pre-installed at both the transmitter and authorized receiver, contains no fewer than 2... 16 Each of the following spread spectrum sequences is different from the others, and each sequence has a different chip rate; The random mapping encoder divides the encrypted information bit stream into fixed-length groups and uses a key-driven pseudo-random number generator to randomly select a spreading sequence from a dictionary to map each group of information. A power spectrum shaping filter is used to make the fitting error between the power spectral density of the output signal and the deep-sea magnetic noise spectrum less than 10%. An adaptive power controller adjusts the transmit power based on channel quality.

[0026] The shared waveform dictionary is generated using cascaded chaotic mapping, with the main mapping being a Logistic mapping with parameter r=4 and the auxiliary mapping being a Chebyshev mapping. A chaotic sequence with uniform statistical characteristics is generated through nonlinear coupling. The peak cross-correlation coefficient between different spreading sequences in the dictionary is less than 0.01. The KL divergence between the transmitted signal and the deep-sea background magnetic noise is less than 0.1. The random mapping encoder supports an M-sequence superposition mode, simultaneously selecting M spreading sequences and summing them with equal power weights to output a synthesized waveform.

[0027] like Figure 5 As shown: The methods for constructing and presetting a shared waveform dictionary are as follows: Step 1: Chaotic Sequence Generation: An initial sequence is generated using a cascaded chaotic mapping; the main mapping is the Logistic mapping. The secondary mapping is the Chebyshev mapping. By nonlinearly coupling the outputs of the two, a chaotic sequence with more uniform statistical properties is generated, enhancing the unpredictability of the waveform. The second step is waveform generation: Chaotic mapping is run with 256 different initial seeds, which are derived from the master key, and Nc = 1024 chaotic values ​​are output each time. These values ​​are mapped onto bipolar BPSK symbols, with positive values ​​being +1 and negative values ​​being -1, resulting in a spread spectrum sequence of length 1024. The sequence is then pulse-shaped using a raised cosine filter with a roll-off factor of 0.5 to generate a baseband spread spectrum waveform. Each waveform is randomly assigned a chip rate Rc, which is a pseudo-random value uniformly distributed in the range of 1kHz to 50kHz. The time domain length Tw = Nc / Rc of each waveform varies accordingly. The third step is cross-correlation optimization: calculate the peak cross-correlation coefficient between all waveforms in the waveform library, and replace or rotate the phase of waveform pairs with a cross-correlation coefficient greater than 0.01 to optimize the orthogonality between waveforms. The fourth step is secure distribution: the generated waveform library, waveform index mapping table, and waveform chip rate parameters are packaged, encrypted using AES-256, and written to the non-volatile memory of each node through a secure channel.

[0028] like Figure 1 As shown: The transmitting end processing flow is as follows: Step A: The length of the data frame to be transmitted is 128 bits, which is encrypted using AES-128 and denoted as information vector b; Step B: Use the current key (Kenc) to derive a random number seed rseed, and combine it with the first 64 bits of b to determine the modulated waveform index; Step C: Extract the waveform corresponding to index i from the dictionary. To enhance robustness, select M waveforms and sum them using equal power weights: ,in Normalization coefficient; Step D: Input s(t) into a 10th-order IIR digital filter. The filter coefficients are designed based on the target power spectrum curve, which is determined based on the environmental noise spectrum parameters estimated from the current water temperature and salinity. Step E: Adjust the power amplifier through the adaptive power controller to amplify the signal to the target transmission power and then radiate it through the triaxial orthogonal loop coil.

[0029] like Figure 3 As shown: The demodulation process at the receiving end is as follows: Step A: After the received signal is amplified and sampled with low noise, parallel sliding correlation matched filtering is performed on all waveforms in the dictionary simultaneously; let the received signal be... The output of the matched filter is ; Step B: The peak detector finds the peak with the largest absolute value, ymax, and its corresponding waveform index, imax; Step C: Extract time synchronization information using peak positions to correct clock drift at the receiver; Step D: Obtain the information bit best through the waveform index imax inverse mapping; if the M-sequence superposition mode is used, the orthogonal matching pursuit algorithm is needed to estimate the contribution coefficient of each waveform before making a decision.

[0030] A deep-sea communication beacon includes a spread spectrum camouflage module; it also includes a dual-resonant magnetic coupling communication unit and a PSIC power generation unit, which work together to achieve covert communication that is undetectable at the physical layer; When transmitting regular data, the information stream is encrypted with AES-128 and then input into the shared dictionary encoder; the shaped spread spectrum waveform is processed by a power spectrum shaping filter and then radiated by a three-axis orthogonal loop coil group driven by an adaptive power controller; at the receiving end, the signal is collected from the three-axis loop coil group and fed to the matched filter demodulator; the decrypted data is used by the beacon master controller, or re-encoded and forwarded through relay forwarding logic; this adaptability ensures that the shared dictionary spread spectrum scheme can work seamlessly with the dual resonant magnetic coupling communication unit and the PSIC power supply unit.

[0031] Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A physical layer spread spectrum masquerading module based on a shared dictionary, characterized in that: include: A shared waveform dictionary, pre-installed at both the transmitter and authorized receiver, contains no fewer than 2... 16 Each of the following spread spectrum sequences is different from the others, and each sequence has a different chip rate; The random mapping encoder divides the encrypted information bit stream into fixed-length groups and uses a key-driven pseudo-random number generator to randomly select a spreading sequence from a dictionary to map each group of information. A power spectrum shaping filter is used to make the fitting error between the power spectral density of the output signal and the deep-sea magnetic noise spectrum less than 10%. An adaptive power controller adjusts the transmit power based on channel quality.

2. The physical layer spread spectrum masquerading module based on a shared dictionary according to claim 1, characterized in that: The shared waveform dictionary is generated using cascaded chaotic mapping, with the main mapping being a Logistic mapping with parameter r=4 and the auxiliary mapping being a Chebyshev mapping. A chaotic sequence with uniform statistical characteristics is generated through nonlinear coupling. The peak cross-correlation coefficient between different spreading sequences in the dictionary is less than 0.

01. The KL divergence between the transmitted signal and the deep-sea background magnetic noise is less than 0.

1. The random mapping encoder supports an M-sequence superposition mode, simultaneously selecting M spreading sequences and summing them with equal power weights to output a synthesized waveform.

3. A physical layer spread spectrum masquerading module based on a shared dictionary according to claim 2, characterized in that: The method for constructing and presetting the shared waveform dictionary is as follows: Step 1: Chaotic Sequence Generation: An initial sequence is generated using a cascaded chaotic mapping; the main mapping is the Logistic mapping. The secondary mapping is the Chebyshev mapping. By nonlinearly coupling the outputs of the two, a chaotic sequence with more uniform statistical properties is generated, enhancing the unpredictability of the waveform. The second step is waveform generation: run the chaotic mapping with 256 different initial seeds, which are derived from the master key, and output Nc=1024 chaotic values ​​each time. These values ​​are mapped onto bipolar BPSK symbols, with positive values ​​being +1 and negative values ​​being -1, resulting in a spread spectrum sequence of length 1024. The sequence is then pulse-shaped using a raised cosine filter with a roll-off factor of 0.5 to generate a baseband spread spectrum waveform. Each waveform is randomly assigned a chip rate Rc, which is a pseudo-random value uniformly distributed in the range of 1kHz to 50kHz. The time domain length Tw = Nc / Rc of each waveform varies accordingly. The third step is cross-correlation optimization: calculate the peak cross-correlation coefficient between all waveforms in the waveform library, and replace or rotate the phase of waveform pairs with a cross-correlation coefficient greater than 0.01 to optimize the orthogonality between waveforms. The fourth step is secure distribution: the generated waveform library, waveform index mapping table, and waveform chip rate parameters are packaged, encrypted using AES-256, and written to the non-volatile memory of each node through a secure channel.

4. A physical layer spread spectrum masquerading module based on a shared dictionary according to claim 1, characterized in that: The transmitting end processing flow is as follows: Step A: The length of the data frame to be transmitted is 128 bits, which is encrypted using AES-128 and denoted as information vector b; Step B: Use the current key (Kenc) to derive a random number seed rseed, and combine it with the first 64 bits of b to determine the modulated waveform index; Step C: Extract the waveform corresponding to index i from the dictionary. ; To enhance robustness, select M waveforms and sum them using equal power weights: ,in Normalization coefficient; Step D: Input s(t) into a 10th-order IIR digital filter. The filter coefficients are designed based on the target power spectrum curve, which is determined based on the environmental noise spectrum parameters estimated from the current water temperature and salinity. Step E: Adjust the power amplifier through the adaptive power controller to amplify the signal to the target transmission power and then radiate it through the triaxial orthogonal loop coil.

5. A physical layer spread spectrum masquerading module based on a shared dictionary according to claim 1, characterized in that: The demodulation process at the receiving end is as follows: Step A: After the received signal is amplified and sampled with low noise, parallel sliding correlation matched filtering is performed on all waveforms in the dictionary simultaneously; let the received signal be... The output of the matched filter is ; Step B: The peak detector finds the peak with the largest absolute value, ymax, and its corresponding waveform index, imax; Step C: Extract time synchronization information using peak positions to correct clock drift at the receiver; Step D: Obtain the information bit best through the waveform index imax inverse mapping; if the M-sequence superposition mode is used, the orthogonal matching pursuit algorithm is needed to estimate the contribution coefficient of each waveform before making a decision.

6. A deep-sea communication beacon, characterized in that, The system includes the spread spectrum camouflage module as described in any one of claims 1 to 5; it also includes a dual resonant magnetic coupling communication unit and a PSIC power generation unit; when transmitting regular data, the information stream is encrypted with AES-128 and then input to a shared dictionary encoder; the shaped spread spectrum waveform is processed by a power spectrum shaping filter and then radiated by a triaxial orthogonal loop coil group driven by an adaptive power controller; at the receiving end, the signal is collected from the triaxial loop coil group and fed to a matched filter demodulator; The decrypted data is used by the beacon master controller, or it is re-encoded and forwarded through relay forwarding logic.

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