TDCS-OFDM covert communication method and device

Abstract

The invention discloses a TDCS-OFDM covert communication method and equipment, and relates to the technical field of communication. The method comprises the following steps: sampling an electromagnetic environment to generate a primary function; carrying out coding interleaving on transform domain communication system TDCS information needing to be communicated; modulating the coded and interleaved TDCS data by using cyclic code shift keying (CCSK) to generate a frequency domain TDCS signal loaded on a first subcarrier, the first subcarrier being a subcarrier within an available spectral range determined based on a primary function; carrying out coding interleaving on orthogonal frequency division multiplexing (OFDM) information needing to be communicated; performing quadrature amplitude modulation on the coded and interleaved OFDM information to generate a frequency domain OFDM signal loaded on a second subcarrier, wherein the second subcarrier is in an available spectral range and is different from the first subcarrier; and sequentially performing frequency domain synthesis, inverse fast Fourier transform and cyclic prefix addition on the frequency domain TDCS signal and the frequency domain OFDM signal to form a TDCS-OFDM signal. According to the invention, the communication rate and the anti-interception capability of covert communication are improved.

Description

Technical Field

[0001] This invention relates to the field of communication technology, specifically to a TDCS-OFDM covert communication method and device. Background Technology

[0002] Currently, research on OFDM-TDCS (Orthogonal Frequency Division Multiplexing-Transform Domain Communication System) includes: coding interleaving, synchronization, modulation and demodulation, as well as the influence of the channel on the system, and the influence of random subcarriers and continuous subcarriers on the system. However, there is little analysis on how to ensure both a certain communication rate and secure communication during the transmission process of wireless communication systems.

[0003] While OFDM-TDCS systems can avoid interference and select available frequency bands for data communication, improving transmission reliability, their characteristic of sacrificing high-frequency spectrum resources for communication stability results in a very low communication rate in actual communication. Furthermore, if there is more complex interference in the environment, the remaining available frequency bands may be even smaller, leading to an even lower communication rate and making accurate exchange of large amounts of information impossible. Summary of the Invention

[0004] This invention addresses the shortcomings of existing covert communication methods, such as low communication rates and easy detection by eavesdroppers with strong signal processing capabilities. It provides a TDCS-OFDM covert communication method and device, which improves the communication rate and anti-interception capability of covert communication.

[0005] The present invention is achieved through the following technical solution.

[0006] Firstly, a TDCS-OFDM covert communication method is provided, the method comprising:

[0007] The electromagnetic environment is sampled to obtain spectrum sensing results, and basis functions are generated based on the spectrum sensing results;

[0008] Encode and interleave the TDCS information of the transform domain communication system that needs to communicate;

[0009] Cyclic Code Shift Keying (CCSK) is used to modulate the coded and interleaved TDCS data, and based on the basis function and the preset subcarrier allocation, a frequency domain TDCS signal for the modulated TDCS data is generated and loaded on the first subcarrier. The first subcarrier is a subcarrier within the available spectrum range determined based on the basis function.

[0010] Encode and interleave the Orthogonal Frequency Division Multiplexing (OFDM) information that needs to be communicated;

[0011] The coded and interleaved OFDM information is subjected to orthogonal amplitude modulation to generate a frequency domain OFDM signal loaded on a second subcarrier, which is a subcarrier different from the first subcarrier within the available spectrum range determined based on the basis function.

[0012] The frequency domain TDCS signal loaded on the first subcarrier and the frequency domain OFDM signal loaded on the second subcarrier are sequentially synthesized in the frequency domain, subjected to inverse fast Fourier transform, and a cyclic prefix is ​​added to form a TDCS-OFDM signal.

[0013] In some embodiments, the electromagnetic environment is sampled to obtain spectrum sensing results, and basis functions are generated based on the spectrum sensing results, including:

[0014] Based on the sampling results of the electromagnetic environment, the environmental spectral power spectral density is calculated to obtain the environmental spectral amplitude;

[0015] The ambient spectrum amplitude is compared with a preset threshold to determine the frequency band location occupied by the interference, and the basis function amplitude vector is obtained.

[0016] In some embodiments, CCSK is used to modulate the coded and interleaved TDCS data, and based on the basis function and a preset subcarrier allocation, a frequency-domain TDCS signal for the modulated TDCS data is generated and loaded onto a first subcarrier, including:

[0017] The TDCS data, after being interleaved with binary codes, is converted into decimal data and used as the transmission symbol;

[0018] The transmitted symbols are subjected to CCSK modulation to generate a frequency domain TDCS signal;

[0019] A random phase vector of the same length as the basis function amplitude vector is generated by a random phase generator. Then, the random phase vector is multiplied by the basis function amplitude vector to obtain the frequency domain expression of the basis function.

[0020] Based on the frequency domain TDCS signal and the frequency domain expression of the basis function, the frequency domain TDCS signal is loaded onto the first subcarrier using the preset subcarrier allocation.

[0021] In some embodiments, the method further includes: performing orthogonal amplitude modulation on the coded and interleaved OFDM information to obtain a frequency domain OFDM signal, adding artificial noise to the frequency domain OFDM signal, and then loading the frequency domain OFDM signal with added artificial noise onto the second subcarrier.

[0022] In some embodiments, the frequency domain OFDM signal with the added artificial noise is:

[0023]

[0024] The added artificial noise is represented as: , The null space matrix representing the channel state information of the main channel. Represents the vector corresponding to artificial noise; Represents a data signal matrix; Precoding matrix representing the secret signal The submatrix formed by the first r columns.

[0025] In some embodiments, singular value decomposition is performed on the channel state information. , and The value of .

[0026] In some embodiments, 1 / 2 bitrate convolutional coding is used to encode the TDCS information and the OFDM information.

[0027] In some embodiments, the power of the frequency domain OFDM signal is greater than the power of the frequency domain TDCS signal.

[0028] Secondly, a TDCS-OFDM covert communication device is provided, the device comprising:

[0029] The basis function generation module is used to: sample the electromagnetic environment to obtain spectrum sensing results, and generate basis functions based on the spectrum sensing results;

[0030] The TDCS information encoding and interleaving module is used to encode and interleave TDCS information of a transform domain communication system that needs to communicate.

[0031] The frequency domain TDCS signal generation module is used to: modulate the coded and interleaved TDCS data using cyclic code shift keying (CCSK), and generate a frequency domain TDCS signal for the modulated TDCS data loaded on a first subcarrier based on the basis function and a preset subcarrier allocation, wherein the first subcarrier is a subcarrier within the available spectrum range determined based on the basis function.

[0032] The OFDM information encoding and interleaving module is used to encode and interleave Orthogonal Frequency Division Multiplexing (OFDM) information that needs to be communicated.

[0033] The frequency domain OFDM signal generation module is used to: perform orthogonal amplitude modulation on the coded and interleaved OFDM information to generate a frequency domain OFDM signal loaded on a second subcarrier, wherein the second subcarrier is a subcarrier different from the first subcarrier within the available spectrum range determined based on the basis function;

[0034] The TDCS-OFDM signal generation module is used to: sequentially perform frequency domain synthesis, inverse fast Fourier transform, and add a cyclic prefix on the frequency domain TDCS signal loaded on the first subcarrier and the frequency domain OFDM signal loaded on the second subcarrier to form a TDCS-OFDM signal.

[0035] Thirdly, a TDCS-OFDM covert communication device is provided, the device comprising:

[0036] At least one processor;

[0037] At least one memory coupled to the at least one processor and storing instructions for execution by the at least one processor, the instructions implementing the method described in any of the above when executed by the at least one processor.

[0038] Compared with existing technologies, this invention has the following advantages and beneficial effects: It divides the frequency-domain mapped TDCS and OFDM signals into portions of the available frequency band, forming a completely new TDCS-OFDM joint waveform. The OFDM signal power is higher than the TDCS power to ensure communication quality. Simultaneously, artificial noise is added to the OFDM signal to achieve anti-interception functionality. Furthermore, TDCS can select multiple different subcarrier mapping methods on continuously available frequency bands. Based on the actual situation on the frequency band, the communicating parties agree on a certain mapping method for communication, or transmit these multiple mapping methods according to a certain pattern, thereby deceiving the enemy and making the TDCS signal difficult to detect, increasing the concealment and reliability of communication, and achieving reliable covert communication. Even if the OFDM signal is severely interfered with and cannot be demodulated, basic communication can still be completed using the TDCS signal. When interference is not severe, the communication rate will be greatly improved due to the perfect separation of OFDM and TDCS signals. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a flowchart of a TDCS-OFDM covert communication method according to an embodiment of the present invention.

[0041] Figure 2This is a block diagram of a signal model for TDCS-OFDM covert communication according to an embodiment of the present invention.

[0042] Figure 3 This is a diagram of a TDCS-OFDM covert communication architecture according to an embodiment of the present invention.

[0043] Figure 4 This is a graph showing the relationship between SNR (signal-to-noise ratio) and BER (bit error rate) for TDCS-OFDM covert communication according to an embodiment of the present invention.

[0044] Figure 5 This is a structural block diagram of a TDCS-OFDM covert communication device according to an embodiment of the present invention.

[0045] Figure 6 This is a schematic diagram of the structure of a TDCS-OFDM covert communication device according to an embodiment of the present invention. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0047] Combining Transform Domain Communication System (TDCS) with Artificial Noise (AN) technology is an innovative approach to improve the security and anti-interference capabilities of the physical layer of wireless communication.

[0048] TDCS employs noise-like basis function modulation to achieve low intercept characteristics. Its core principle is sensing the spectral environment and selecting idle frequency bands to generate basis functions. The pseudo-random phase sequence design within these basis functions is inextricably linked to LPI characteristics. Simultaneously, the generation and injection strategies for artificial noise are deeply integrated with the TDCS's spectral sensing results. The energy of the artificial noise is intelligently injected into the "spectral space" or dimensions (such as space, frequency, and time) that have the least impact on legitimate receivers, maximizing security gains while minimizing negative impacts on legitimate communication.

[0049] The combination of TDCS and artificial noise is essentially a deep integration and synergistic innovation of the three major technical advantages of "dynamic spectrum utilization", "inherent low intercept waveform" and "active controllable interference", aiming to build a more intelligent, more covert and more efficient physical layer secure transmission system.

[0050] Based on the above analysis, the present invention provides a TDCS-OFDM covert communication method. Figure 1 This is a flowchart of a TDCS-OFDM covert communication method according to an embodiment of the present invention. Figure 2This is a signal model block diagram of a TDCS-OFDM covert communication according to an embodiment of the present invention, showing the signal processing modules of the transmitting end with M transmitting antennas and the signal processing modules of the receiving end with N receiving antennas. Figure 2 The functional modules shown can implement the TDCS-OFDM covert communication method of this invention. (Reference) Figure 1 The TDCS-OFDM covert communication method includes: S10 to S60.

[0051] The following combination Figure 1 and Figure 2 Detailed explanations are provided for S10 to S60.

[0052] In S10, the electromagnetic environment is sampled to obtain spectrum sensing results, and basis functions are generated based on the spectrum sensing results.

[0053] For example, sampling the electromagnetic environment to obtain spectrum sensing results and generating basis functions based on the spectrum sensing results includes: calculating the environmental spectrum power spectral density based on the sampling results of the electromagnetic environment to obtain the environmental spectrum amplitude; comparing the environmental spectrum amplitude with a preset threshold to determine the frequency band location occupied by the interference and obtaining the basis function amplitude vector.

[0054] Specifically, the electromagnetic environment can be sampled using a transmitter, and then the power spectral density of the electromagnetic environment can be calculated based on the sampled data. The Welch algorithm can be used to calculate the power spectral density.

[0055] (1)

[0056] in, As a normalization factor, it is indispensable for ensuring that the power spectrum estimation is asymptotically unbiased. In this invention, the sampled signal... Divided into Segments, each segment is [length missing] Add a rectangular window to each data segment. Let be the i-th sampling point in the N-th data segment. These are the basis functions of the Fourier transform. It is the angular frequency. In the Welch algorithm and The choice of [aspect] directly affects the performance of spectral estimation.

[0057] Then, by comparing the obtained environmental spectrum amplitude with a set threshold, the location of the frequency band occupied by the interference can be determined, thereby obtaining the amplitude information of the basis functions. For example, the flat amplitude shaping method can be chosen to generate the amplitude spectrum of the basis functions, and its mathematical model is as follows:

[0058] (2)

[0059] in, For the selected threshold value, This is the result of environmental spectrum estimation. If the value is less than or equal to the threshold, it means that the frequency band is not occupied and can be used to transmit signals. The amplitude of the basis function in this segment is set to 1. Otherwise, it is set to 0. This is how the basis function is determined.

[0060] In S20, the Transform Domain Communication System (TDCS) information that needs to be communicated is encoded and interleaved. For example, 1 / 2 code rate convolutional coding can be used to encode the TDCS information.

[0061] In S30, cyclic code shift keying (CCSK) is used to modulate the coded and interleaved TDCS data, and a frequency-domain TDCS signal for the modulated TDCS data is generated on the first subcarrier based on the basis function and a preset subcarrier allocation. The first subcarrier is a subcarrier within the available spectrum range determined based on the basis function.

[0062] For example, the coded interleaved TDCS data is modulated using CCSK, and a frequency domain TDCS signal for the modulated TDCS data is generated and loaded onto the first subcarrier based on the basis function and a preset subcarrier allocation, including: S31 to S34.

[0063] In S31, the binary encoded interleaved TDCS data is converted into decimal data and used as the transmission symbol. The binary bit information is converted into decimal numbers as the transmission symbol. Then, modulation is performed.

[0064] In S32, the transmitted symbols are CCSK modulated to generate a frequency-domain TDCS signal. For example, CCSK modulation is performed using the following formula:

[0065] (3)

[0066] In S33, a random phase vector of the same length as the basis function amplitude vector is generated by a random phase generator. Then, the random phase vector is multiplied by the basis function amplitude vector to obtain the frequency domain expression of the basis function.

[0067] In S34, based on the frequency domain expression of the frequency domain TDCS signal and the basis function, the frequency domain TDCS signal is loaded onto the first subcarrier using a preset subcarrier allocation.

[0068] The transmitted symbols and basis functions are mapped, and the frequency-domain TDCS signal is loaded onto the first subcarrier based on a preset subcarrier allocation. TDCS can select multiple different subcarrier mapping methods on continuously available frequency bands. Depending on the actual situation on the frequency band, the communicating parties agree on a certain mapping method for communication, or transmit these multiple mapping methods according to a certain pattern, thereby deceiving the enemy and making the TDCS signal difficult to detect, increasing the concealment and reliability of communication, and completing reliable covert communication. Even if the OFDM signal is severely interfered with and cannot be demodulated, basic communication can still be completed using the TDCS signal. When the interference is not severe, the communication rate will be greatly improved due to the perfect separation of OFDM and TDCS signals. After subcarrier allocation of data symbols and basis functions, the power of the basis functions is adjusted, and then an inverse Fourier transform is performed to obtain the time-domain expression of the TDCS transmitted signal:

[0069] (4)

[0070] in, The number of subcarriers, Spectral vector The number of 1s, the scaling value The power was normalized. It is a random phase. This demonstrates multiple access capability. For the first A modulated number.

[0071] In S40, the Orthogonal Frequency Division Multiplexing (OFDM) information that needs to be communicated is encoded and interleaved. For example, convolutional coding with a 1 / 2 code rate can be used.

[0072] In S50, the encoded and interleaved OFDM information is subjected to quadrature amplitude modulation (QAM) to generate a frequency-domain OFDM signal loaded on a second subcarrier. The second subcarrier is a subcarrier different from the first subcarrier within the available spectrum range determined based on the basis function. For example, 4QAM (quadrature amplitude modulation) modulation can be used. During OFDM modulation, the TDCS signal and the OFDM signal are mapped to different consecutive subcarriers, achieving complete separation in the frequency domain. By using IFFT and adding a cyclic prefix, the joint waveform can still achieve independent transmission in the frequency domain even under time-domain convolution.

[0073] In some embodiments, the TDCS-OFDM covert communication method further includes: after performing orthogonal amplitude modulation on the coded and interleaved OFDM information to obtain a frequency-domain OFDM signal, adding artificial noise to the frequency-domain OFDM signal, and then loading the frequency-domain OFDM signal with added artificial noise onto a second subcarrier to improve the OFDM signal's anti-interception capability. The added artificial noise, superimposed on the useful signal, can result in a high bit error rate at the illegal receiver without affecting the reception at the legitimate receiver, thereby deceiving the enemy and enabling covert communication.

[0074] Assume the total power of the transmitted signal is The number of transmitted data streams is The data signal power ratio is That is, the data communication power is Then the power of artificial noise is Then the OFDM data transmitted in the frequency domain is:

[0075] (5)

[0076] The added artificial noise is , M and N are the number of transmitting antennas and receiving antennas, respectively; Let be a data signal matrix, and let the i-th element follow a function with expectation of 0 and variance of . Gaussian distribution; precoding matrix of secure signal To extract the matrix (pre-encoded matrix) The submatrix formed by the first r columns.

[0077] for , and The value of can be obtained by performing singular value decomposition on the channel. Assume the transmitter receives data and obtains its channel state information (from transmitter to receiver). ,Right now:

[0078] (6)

[0079] in, Main channel The null space matrix satisfies ,in, For the precoding matrix of the confidential signal, This is the deprecation precoding matrix (left singular matrix) for the corresponding receiver. Let be the noise subspace matrix of the channel. It is a diagonal matrix composed of the channel singular values.

[0080] In S60, the frequency domain TDCS signal loaded on the first subcarrier and the frequency domain OFDM signal loaded on the second subcarrier are sequentially synthesized in the frequency domain, subjected to inverse fast Fourier transform, and a cyclic prefix is ​​added to form a TDCS-OFDM signal.

[0081] In some embodiments, the power of the frequency domain OFDM signal is set to be greater than that of the frequency domain TDCS signal to ensure communication quality.

[0082] At the receiving end (receiver), the received signal undergoes OFDM reception, CCSK demodulation, and decoding sequentially to obtain the useful information transmitted by the transmitter. The CCSK demodulation method uses the same basis functions as the transmitter to perform correlation demodulation on the TDCS demodulated signal back-mapped from the subcarrier. This invention employs a multi-element orthogonal modulation correlation demodulation method. The input signal is correlated with M reference signals, and the detection value with the largest correlation amplitude is selected as the estimated value of the signal.

[0083] Figure 3 This is a diagram of a TDCS-OFDM covert communication architecture according to an embodiment of the present invention. The inversely mapped OFDM signal is compared using maximum likelihood detection to determine the difference in bit error rate between the receiving user Bob and the eavesdropping device Eve, i.e.:

[0084] (7)

[0085] in, It is a matrix truncation The submatrix formed by the top left of the first r rows and r columns, The received signal obtained from the user end after channel equalization. This represents the channel matrix from the transmitter Alice to the eavesdropping device Eve.

[0086] Figure 4 This diagram illustrates the relationship between SNR (Signal-to-Noise Ratio) and BER (Bit Error Rate) in TDCS-OFDM covert communication according to an embodiment of the present invention. As the SNR increases, the receiver's bit error rate decreases, and the eavesdropping end's bit error rate remains consistently high. When the SNR reaches a certain level, the difference in bit error rates between Bob and Eve can exceed 30 dB. In this case, the addition of artificial noise can effectively reduce the possibility of the eavesdropping end intercepting information, achieving the goal of concealing the OFDM signal and improving the communication rate.

[0087] In this invention, frequency-domain mapped TDCS and OFDM signals each occupy a portion of the available frequency band, forming a novel TDCS-OFDM joint waveform. The OFDM signal power is higher than the TDCS power to ensure communication quality. Simultaneously, artificial noise is added to the OFDM signal to achieve anti-interception functionality. Furthermore, TDCS can select multiple subcarrier mapping methods across continuously available frequency bands. Depending on the actual situation in the frequency band, the communicating parties agree on a certain mapping method for communication, or transmit these multiple mapping methods according to a certain pattern, thereby deceiving the enemy and making the TDCS signal difficult to detect, increasing the stealth and reliability of communication, and achieving reliable covert communication. Even if the OFDM signal is severely interfered with and cannot be demodulated, basic communication can still be completed using the TDCS signal. When interference is not severe, the communication rate will be significantly increased due to the perfect separation of OFDM and TDCS signals.

[0088] On the other hand, the present invention provides a TDCS-OFDM covert communication device. Figure 5 This is a structural block diagram of a TDCS-OFDM covert communication device according to an embodiment of the present invention. (Reference) Figure 5 The device includes: a basis function generation module, a TDCS information encoding and interleaving module, a frequency domain TDCS signal generation module, an OFDM information encoding and interleaving module, a frequency domain OFDM signal generation module, and a TDCS-OFDM signal generation module.

[0089] The basis function generation module is used to: sample the electromagnetic environment to obtain spectrum sensing results, and generate basis functions based on the spectrum sensing results.

[0090] The TDCS information encoding and interleaving module is used to encode and interleave TDCS information of a transform domain communication system that needs to communicate.

[0091] The frequency domain TDCS signal generation module is used to: modulate the coded and interleaved TDCS data using Cyclic Code Shift Keying (CCSK), and generate a frequency domain TDCS signal for the modulated TDCS data loaded on a first subcarrier based on the basis function and a preset subcarrier allocation. The first subcarrier is a subcarrier within the available spectrum range determined based on the basis function.

[0092] The OFDM information encoding and interleaving module is used to encode and interleave Orthogonal Frequency Division Multiplexing (OFDM) information that needs to be communicated.

[0093] The frequency domain OFDM signal generation module is used to: perform orthogonal amplitude modulation on the coded and interleaved OFDM information to generate a frequency domain OFDM signal loaded on a second subcarrier, wherein the second subcarrier is a subcarrier different from the first subcarrier within the available spectrum range determined based on the basis function.

[0094] The TDCS-OFDM signal generation module is used to: sequentially perform frequency domain synthesis, inverse fast Fourier transform, and add a cyclic prefix on the frequency domain TDCS signal loaded on the first subcarrier and the frequency domain OFDM signal loaded on the second subcarrier to form a TDCS-OFDM signal.

[0095] Other implementation details of this TDCS-OFDM covert communication device can be found in the previous description of the TDCS-OFDM covert communication method, and will not be repeated here.

[0096] In implementing the functions of the integrated modules described above in hardware, this embodiment of the invention provides a structure for the TDCS-OFDM covert communication device involved in the above embodiments. Figure 6 This is a schematic diagram of the structure of a TDCS-OFDM covert communication device according to an embodiment of the present invention. (Reference) Figure 6 The TDCS-OFDM covert communication device includes: at least one processor; and at least one memory. The at least one memory is coupled to the at least one processor and stores instructions for execution by the at least one processor, which, when executed by the at least one processor, implement the method described above.

[0097] A processor can be a set of logic blocks, modules, and circuits that implement or execute the various exemplary logic blocks, modules, and circuits described in connection with embodiments of the present invention. The processor can be a central processing unit, a general-purpose processor, a digital signal processor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. It can implement or execute the various exemplary logic blocks, modules, and circuits described in connection with embodiments of the present invention. A processor can also be a combination that implements computational functions, such as a combination of one or more microprocessors, a combination of a digital signal processor and a microprocessor, etc.

[0098] The memory may be read-only memory (ROM) or other types of static storage devices that can store static information and instructions, random access memory (RAM) or other types of dynamic storage devices that can store information and instructions, electrically erasable programmable read-only memory (EEPROM), disk storage media or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer, but is not limited thereto.

[0099] In one implementation, the memory can exist independently of the processor. The memory can be connected to the processor via a bus and used to store instructions or program code. When the processor calls and executes the instructions or program code stored in the memory, it can implement the method provided in the embodiments of the present invention. In another implementation, the memory can also be integrated with the processor.

[0100] On the other hand, the present invention also provides a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) storing computer program instructions that, when executed on a computer, cause the computer to perform the method as described in any of the above embodiments.

[0101] Exemplary examples show that the aforementioned computer-readable storage media may include, but are not limited to: magnetic storage devices (e.g., hard disks, floppy disks, or magnetic tapes), optical discs (e.g., compact disks (CDs), digital versatile disks (DVDs), etc.), smart cards, and flash memory devices (e.g., erasable programmable read-only memory (EPROMs), cards, sticks, or key drives, etc.). The various computer-readable storage media described in this invention may represent one or more devices and / or other machine-readable storage media for storing information. The term "machine-readable storage medium" may include, but is not limited to, wireless channels and various other media capable of storing, containing, and / or carrying instructions and / or data.

[0102] This invention provides a computer program that, when run on a computer, causes the computer to perform the method of any of the above embodiments.

[0103] This invention provides a computer program product containing instructions that, when run on a computer, cause the computer to perform the method of any of the above embodiments.

[0104] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A TDCS-OFDM covert communication method, characterized in that, The method includes: The electromagnetic environment is sampled to obtain spectrum sensing results, and basis functions are generated based on the spectrum sensing results; Encode and interleave the TDCS information of the transform domain communication system that needs to communicate; Cyclic Code Shift Keying (CCSK) is used to modulate the coded and interleaved TDCS data, and based on the basis function and the preset subcarrier allocation, a frequency domain TDCS signal for the modulated TDCS data is generated and loaded on the first subcarrier. The first subcarrier is a subcarrier within the available spectrum range determined based on the basis function. Encode and interleave the Orthogonal Frequency Division Multiplexing (OFDM) information that needs to be communicated; The coded and interleaved OFDM information is subjected to orthogonal amplitude modulation to generate a frequency domain OFDM signal loaded on a second subcarrier, which is a subcarrier different from the first subcarrier within the available spectrum range determined based on the basis function. The frequency domain TDCS signal loaded on the first subcarrier and the frequency domain OFDM signal loaded on the second subcarrier are sequentially synthesized in the frequency domain, subjected to inverse fast Fourier transform, and a cyclic prefix is ​​added to form a TDCS-OFDM signal.

2. The method according to claim 1, characterized in that, The electromagnetic environment is sampled to obtain spectrum sensing results, and basis functions are generated based on the spectrum sensing results, including: Based on the sampling results of the electromagnetic environment, the environmental spectral power spectral density is calculated to obtain the environmental spectral amplitude; The ambient spectrum amplitude is compared with a preset threshold to determine the frequency band location occupied by the interference, and the basis function amplitude vector is obtained.

3. The method according to claim 1, characterized in that, Modulating the coded and interleaved TDCS data using CCSK, and generating and loading a frequency-domain TDCS signal for the modulated TDCS data onto the first subcarrier based on the basis function and preset subcarrier allocation, including: The TDCS data, after being interleaved with binary codes, is converted into decimal data and used as the transmission symbol; The transmitted symbols are subjected to CCSK modulation to generate a frequency domain TDCS signal; A random phase vector of the same length as the basis function amplitude vector is generated by a random phase generator. Then, the random phase vector is multiplied by the basis function amplitude vector to obtain the frequency domain expression of the basis function. Based on the frequency domain TDCS signal and the frequency domain expression of the basis function, the frequency domain TDCS signal is loaded onto the first subcarrier using the preset subcarrier allocation.

4. The method according to any one of claims 1 to 3, characterized in that, The method further includes: performing orthogonal amplitude modulation on the coded and interleaved OFDM information to obtain a frequency domain OFDM signal, adding artificial noise to the frequency domain OFDM signal, and then loading the frequency domain OFDM signal with added artificial noise onto the second subcarrier.

5. The method according to claim 4, characterized in that, The frequency domain OFDM signal with the added artificial noise is: The added artificial noise is represented as: , The null space matrix representing the channel state information of the main channel. Represents the vector corresponding to artificial noise; Represents a data signal matrix; Precoding matrix representing the secret signal The submatrix formed by the first r columns.

6. The method according to claim 5, characterized in that, Singular value decomposition was performed on the channel state information. , and The value of .

7. The method according to claim 1, characterized in that, The TDCS information and the OFDM information are encoded using convolutional coding at a 1 / 2 bit rate.

8. The method according to claim 1, characterized in that, The power of the frequency domain OFDM signal is greater than the power of the frequency domain TDCS signal.

9. A TDCS-OFDM covert communication device, characterized in that, The device includes: The basis function generation module is used to: sample the electromagnetic environment to obtain spectrum sensing results, and generate basis functions based on the spectrum sensing results; The TDCS information encoding and interleaving module is used to encode and interleave TDCS information of a transform domain communication system that needs to communicate. The frequency domain TDCS signal generation module is used to: modulate the coded and interleaved TDCS data using cyclic code shift keying (CCSK), and generate a frequency domain TDCS signal for the modulated TDCS data loaded on a first subcarrier based on the basis function and a preset subcarrier allocation, wherein the first subcarrier is a subcarrier within the available spectrum range determined based on the basis function. The OFDM information encoding and interleaving module is used to encode and interleave Orthogonal Frequency Division Multiplexing (OFDM) information that needs to be communicated. The frequency domain OFDM signal generation module is used to: perform orthogonal amplitude modulation on the coded and interleaved OFDM information to generate a frequency domain OFDM signal loaded on a second subcarrier, wherein the second subcarrier is a subcarrier different from the first subcarrier within the available spectrum range determined based on the basis function; The TDCS-OFDM signal generation module is used to: sequentially perform frequency domain synthesis, inverse fast Fourier transform, and add a cyclic prefix on the frequency domain TDCS signal loaded on the first subcarrier and the frequency domain OFDM signal loaded on the second subcarrier to form a TDCS-OFDM signal.

10. A TDCS-OFDM covert communication device, characterized in that, The device includes: At least one processor; At least one memory coupled to the at least one processor and storing instructions for execution by the at least one processor, the instructions implementing the method of any one of claims 1 to 8 when executed by the at least one processor.

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