A method and system for covert information transmission based on RIS regulation channel

Abstract

The present application belongs to the technical field of wireless communication, and particularly relates to a covert information transmission method based on RIS regulation of a channel. The purpose of the present application is to face the static channel scene, utilize the RIS regulation of the channel characteristics, enhance the terminal communication performance, and realize the specific information covert transmission in the RIS coverage area. By controlling the RIS to use two kinds of gain different directional pattern steering to regulate the channel environment, the amplitude change virtual amplitude shift keying modulation generated thereby is utilized to perform the unique information covert transmission, and it is not necessary to establish synchronization with the communication party through a control link. On the one hand, the RIS is utilized to construct an enhanced beam according to the node position to realize the signal enhancement of the receiving party, and on the other hand, the information is carried through the steering RIS directional pattern, the terminal can perceive the change of the channel environment by utilizing the existing channel estimation module, the information transmitted by the RIS is distinguished, and the receiving demodulation of the data stream of the normal communication party is not interfered.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, and in particular relates to a method and system for covert information transmission based on a RIS control channel for covert transmission of specific information within a RIS coverage area. Background Technology

[0002] Covert communication, also known as low-probability-of-detection communication, refers to the transmission of covert information superimposed on public information, making it difficult or even impossible for eavesdroppers to detect the covert information, thus greatly improving information security. With the increasing demand for robust security and privacy from 5G wireless networks and the Internet of Things (IoT), covert communication has attracted significant interest from researchers. Existing research mainly focuses on the fundamental limitations of concealing wireless transmission, namely, the amount of information that can be secretly transmitted from transmitter Alice to legitimate receiver Bob with a specific probability of being detected by eavesdropper Eve. Existing covert communication technologies can be broadly categorized into three areas: time domain, spatial domain, and frequency domain. Facing the challenges and technical bottlenecks of existing covert communication technologies, reconfigurable wireless environments and real-time adjustable individual array elements offer new solutions.

[0003] Passive beamforming and information transmission based on Reconfigurable Intelligent Surfaces (RIS) is a publicly available technology closest to this patent. The main feature of this technology is that it uses the switching states of RIS units to simulate spatial modulation techniques to transmit specific information or achieve covert communication. However, since the switching states of RIS units are used as index information for information transmission, some RIS units must be in the off state, resulting in the inability to fully utilize the beamforming-assisted communication capabilities of RIS. Therefore, this scheme essentially sacrifices some auxiliary communication capabilities in exchange for the RIS's information transmission capabilities. Finally, at the receiving and demodulation ends, due to the superposition of additional information with the modulated signal, this scheme involves a two-step information detection problem, which is inefficient and difficult. The shortcomings of existing technologies are: first, they cannot fully utilize the beamforming capabilities of RIS, resulting in a small increase in channel capacity due to information transmission; second, RIS needs to cooperate with the communicating party to complete information transmission, and the demodulation method is complex and inefficient. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art. It proposes a covert information transmission method based on RIS modulation channel, which can enable the terminal to obtain additional data streams in addition to normal signal reception by simply adjusting the RIS pattern without adding any additional transmission components and occupying very little frequency band resources.

[0005] The purpose of this invention is to address static channel scenarios by utilizing the channel modulation characteristics of RIS (Radio Frequency Identification) to enhance terminal communication performance while enabling the covert transmission of specific information (such as environmental information collected by sensors, control commands to the terminal, etc.) within the RIS coverage area.

[0006] This invention controls the RIS board to use two different gain patterns to agilely regulate the channel environment, utilizing the resulting amplitude variation virtual amplitude shift keying (ASK) modulation for covert information transmission without requiring synchronization with the communicating party via a control link. On one hand, the RIS board components construct an enhanced beam based on the node location to amplify the receiver's signal. On the other hand, by carrying information through the agile RIS pattern, the terminal can use its existing channel estimation module to sense changes in the channel environment and determine the information transmitted by the RIS, without interfering with the reception and demodulation of the normal communicating party's data stream.

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for covert information transmission based on RIS-controlled channels is provided, based on the following system, which includes a base station, a terminal, and a third-party transmitter. The third-party transmitter includes a signal generation module and a RIS information control module. The signal generation module includes an information generation module and a channel coding module. The RIS information control module includes a RIS control module and a RIS board. The terminal includes an antenna module, an A / D sampling module, and a signal processing module. The signal processing module includes a channel estimation module, a channel equalization module, a channel demodulation module, a base station channel decoding module for acquiring base station data streams, a timing synchronization module, a sampling decision module, a frame synchronization module, and a third-party transmitter channel decoding module for acquiring third-party transmitter data streams.

[0009] The steps to implement this method are as follows:

[0010] Step 1) Obtain channel state information and the optimal phase shift coefficient for the enhanced terminal direction based on the locations of the base station, terminal, and third-party transmitter;

[0011] Step 2) When the third-party transmitter does not send information, the base station processes the information to be sent to generate a high-speed data stream and sends it to the terminal. The RIS control module configures the RIS unit phase shift of the RIS board to the optimal phase shift coefficient to enhance the terminal direction signal.

[0012] Step 3) When a third-party sender needs to send information to a terminal, perform the following operations:

[0013] Step 3.1) The third-party sending end generates a binary sequence of the information to be sent using the information generation module and groups it into groups;

[0014] Step 3.2) Each binary sequence is channel coded by the channel coding module. After obtaining the baseband signal, a synchronization header is added to each baseband signal to generate a data frame. The data frame is sent to the RIS control module to adjust the phase shift of the RIS unit, thereby sending a low-speed data stream to the terminal.

[0015] Step 4) When the terminal receives information sent by the base station and the third-party sender, it performs the following operations:

[0016] Step 4.1) The high-speed data stream and low-speed data stream sent to the terminal are processed by the receiving antenna module and the A / D sampling module and then sent to the signal processing module;

[0017] Step 4.2) The channel estimation module performs channel estimation on the received data to obtain a weighted channel estimate.

[0018] Step 4.3) The weighted channel estimate is processed by the channel equalization module, the channel demodulation module, and the base station channel decoding module to obtain the information transmitted by the base station;

[0019] Step 4.4) The weighted channel estimate is synchronized with the symbols transmitted by the third-party transmitter and the base station by the timing synchronization module, the sampling decision is performed by the sampling decision module, the frame start position is determined by the frame synchronization module, and the information transmitted by the third-party transmitter is obtained by the decoding by the third-party transmitter channel decoding module.

[0020] Preferably, channel state information is obtained based on the locations of the base station, terminal, and third-party transmitter. The channel state information of the base station-terminal direct link is denoted as follows: The channel state information of the base station-RIS board is denoted as The channel state information of the RIS board-terminal is denoted as The optimal phase shift coefficient of the RIS board is obtained by satisfying: And obtain the phase shift coefficient that deviates from the terminal direction.

[0021] Preferably, the baseband signal contains an information sequence and a check sequence, and the data frame contains a synchronization sequence, an information sequence, and a check sequence. The data frame sequence is sent to the RIS control module, and then the phase shift of the RIS unit is adjusted according to the "0" and "1" in the input data frame sequence. When the input is "0", the RIS board is configured with a phase shift coefficient that deviates from the terminal direction; when the input is "1", the RIS board is configured with the optimal phase shift coefficient.

[0022] Preferably, timed synchronization includes the following steps:

[0023] a) Use a sliding sampling method to continuously sample 2K weighted channel estimates. And the amplitude values ​​of adjacent sampling points Compare;

[0024] b) If the amplitude values ​​of the j-th sampling point and the (j+1)-th sampling point satisfy the following condition Where A is the amplitude decision threshold, if the K sampling points after the (j+1)th sampling point (including the (j+1)th sampling point) are within a RIS transmission symbol interval, then proceed to step c); otherwise, continue to step a).

[0025] c) The (j+1)th sampling point is used as the timing synchronization point, and the subsequent K consecutive sampling points are regarded as sampling of a RIS transmitted symbol for subsequent symbol decision.

[0026] Preferably, a false synchronization detection step is set between step b) and step c): for K consecutive sampling points after the (j+1)th sampling point, there exist any two sampling points that satisfy... If the result is a false synchronization caused by sudden interference, then the search is repeated and step a) is executed; otherwise, it is determined to be frame synchronization and step c) is executed.

[0027] Preferably, the sampling decision module performs the sampling decision process as follows: Calculate the average amplitude value of K consecutive sampling points within a RIS transmitted symbol. Then we get the binary sequence. .

[0028] A system for implementing the covert information transmission method based on the RIS control channel as described above, the system comprising a base station, a terminal, and a third-party transmitter;

[0029] The third-party transmitter includes a signal generation module and a RIS information control module. The signal generation module includes an information generation module and a channel coding module; the RIS information control module includes a RIS control module and a RIS board.

[0030] The terminal includes an antenna module, an A / D sampling module, and a signal processing module. The signal processing module includes a channel estimation module, a channel equalization module, a channel demodulation module, a base station channel decoding module for acquiring base station data streams, a timing synchronization module, a sampling decision module, a frame synchronization module, and a third-party transmitter channel decoding module for acquiring third-party transmitter data streams.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] The advantage of this invention lies in the fact that, without affecting the normal communication process from the base station to the terminal, and without adding extra transmission components or occupying very little frequency band resources, the third-party transmitter uses a RIS (Radio Relay System) to carry information on the wireless channel to complete additional information transmission. That is, the terminal can simultaneously receive both base station-to-terminal and third-party transmitter-to-terminal information. Therefore, compared to traditional technologies that require a legitimate party to remotely control the virtual space modulation of the RIS unit's switching state before information transmission, this invention can improve terminal signal quality while providing an information transmission method that requires no cooperation from the communicating party and is simple to detect.

[0033] Furthermore, the information transmitted from the third-party transmitter to the terminal can only be detected within the coverage area of ​​the RIS information control module, possessing a certain degree of concealment. This technology is applicable to scenarios where a third party sends control commands or external environmental information to terminals within a designated area. Compared to traditional technologies, this invention can fully utilize the beamforming-assisted communication capabilities of the RIS unit without increasing additional cost or power consumption, and it is also simpler for the terminal to receive the data. Attached Figure Description

[0034] Figure 1 This is a system model diagram of an embodiment of the present invention.

[0035] Figure 2 This is a block diagram of the terminal Bob receiving device according to an embodiment of the present invention.

[0036] Figure 3 This is the data frame format of an embodiment of the present invention.

[0037] Figure 4(a) is a schematic diagram of timing synchronization failure in an embodiment of the present invention.

[0038] Figure 4(b) is a schematic diagram of timing synchronization in an embodiment of the present invention.

[0039] Figure 5 This is a schematic diagram of the timing synchronization algorithm in an embodiment of the present invention.

[0040] Figure 6 This is a flowchart of the signal processing for terminal Bob in an embodiment of the present invention. Detailed Implementation

[0041] To clarify the advantages of the present invention, the following detailed description is provided in conjunction with specific embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0042] See appendix Figure 1A method for covert information transmission based on a RIS-controlled channel is proposed. The system comprises three types of nodes: a base station Alice, a terminal Bob, and a third-party transmitter Carol. Both Alice and Bob are equipped with a single antenna. Alice transmits high-speed data to Bob. Carol, the third-party transmitter, is deployed close to Bob and is equipped with a RIS board and control module. When Carol is not transmitting covert information, the high-speed data received by Bob from Alice can be enhanced by controlling the RIS board. When Carol sends covert information at the third-party sending end, Carol controls the RIS board to transmit low-rate data to Bob at the terminal. .

[0043] Specifically, the third-party transmitter Carol includes a signal generation module and a RIS information control module. The signal generation module includes an information generation module and a channel coding module. The information generation module generates a binary sequence of the information that the third-party transmitter Carol needs to transmit. The channel coding module adds redundant information to the binary sequence from the information generation module, and the redundant encoding is not limited to using LDPC codes, convolutional codes, BCH codes, etc.

[0044] The RIS information control module includes a RIS control module and a RIS board. The RIS control module can control the cell states of the RIS board via FPGA / serial port and receive binary sequences from the signal generation module. The RIS board consists of N cells and can control the phase of the incident electromagnetic signal. The phase shift of the RIS cell is denoted as... ,in .

[0045] See appendix Figure 2 As shown, the terminal Bob includes an antenna module, an A / D sampling module, and a signal processing module. The antenna module is used to receive radio signals and amplify and filter them. The A / D sampling module is used to convert the analog signals received from the antenna module into digital signals and send them to the signal processing module. The signal processing module is used to separate and demodulate the two data streams sent by Alice and Carol. It includes a channel estimation module, a channel equalization module for acquiring the base station data stream, a channel demodulation module, a base station channel decoding module, a timing synchronization module, a sampling decision module, a frame synchronization module, and a third-party sender channel decoding module for acquiring the third-party sender data stream.

[0046] Base station Alice and third-party transmitter Carol each send high-speed data streams to terminal Bob. and low-speed data stream And follow these steps:

[0047] 1. Base station Alice performs the following operations:

[0048] The base station Alice generates a high-speed data stream from the information to be transmitted through channel coding, modulation, amplification, and other methods. And send it to Bob's terminal. The symbol period is The sending rate is .

[0049] 2. Carol, the third-party sender, performs the following operations:

[0050] 1) Initially, statistical CSI (Channel State Information) is obtained based on the positions of three nodes: base station Alice, third-party transmitter Carol (RIS), and terminal Bob. The statistical CSI of the Alice-Bob direct link is denoted as... Alice-RIS's statistical CSI is denoted as The statistical CSI of RIS-Bob is denoted as Then the optimal phase shift design of the RIS board Configuration meets: Furthermore, the phase shift coefficient configuration deviating from the terminal Bob direction is given. ;

[0051] 2) When the third-party transmitter Carol does not send data, the RIS unit phase shift is configured via the RIS control module. This enhances the signal in the Bob direction at the terminal.

[0052] 3) When the third-party sender Carol needs to send a message to the terminal Bob, perform the following operations:

[0053] ① The low-speed data stream that needs to be transmitted The information generation module generates binary sequences and groups them;

[0054] ② The channel coding module performs channel coding on each sequence. In this embodiment, LDPC codes are used for redundancy coding to obtain the baseband signal. ,but It contains an information sequence and a check sequence; for each group of baseband signals A synchronization header (using a Gold code sequence in this embodiment) is added to generate a data frame. ,like Figure 3 As shown. Specifically, data frames. It contains a synchronization sequence, an information sequence, and a verification sequence;

[0055] ③ Transfer the data frame The sequence is sent to the RIS control module, and then based on the input data frame... The "0" and "1" in the sequence, according to the sign period, are The rate of adjustment controls the phase shift of the RIS unit, where, when the input is "0", the RIS phase shift coefficient is configured as follows: When you input "1", the RIS phase shift coefficient is configured as follows: Then the data stream sent by the third-party sender Carol The rate is .

[0056] 3. Terminal Bob receives two streams of information and performs the following operations:

[0057] To simultaneously obtain high-speed data from base station Alice and low-speed covert information from third-party transmitter Carol, terminal Bob needs to obtain the communication protocols, such as communication rates and encoding methods, of both base station Alice and third-party transmitter Carol beforehand. Furthermore, since Carol's transmission rate is much lower than Alice's transmission rate, it can be assumed that Alice's transmission rate is an integer multiple of Carol's transmission rate. K is any integer. Here Bob uses... Figure 6 The steps shown separate the two data streams received. and :

[0058] 1) The antenna module receives radio signals and amplifies and filters them;

[0059] 2) The A / D sampling module is used to convert the received analog signal into a digital signal and send it to the signal processing module;

[0060] 3) After receiving the digital signal, the signal processing module first performs channel estimation via the channel estimation module. By using the public pilot symbols, it obtains the weighted channel estimate g from Alice to Bob. Then, for g, it performs steps 4 and 5 as follows to separate and demodulate the data stream using different methods. and ;

[0061] 4) Perform channel equalization on the weighted channel estimate g and complete the subsequent data stream. Demodulation mainly includes the following steps: First, the received data is channel-equalized using the obtained CSI through the channel equalization module. Then, the data is demodulated and decoded by the signal demodulation module and the base station channel decoding module, respectively, to obtain the information sent by Alice.

[0062] 5) Obtain the data stream based on the amplitude difference of the weighted channel estimate g. It mainly includes the following steps:

[0063] ① Timing synchronization. Timing synchronization is performed based on the amplitude changes of the weighted channel estimate g. First, 2K channel estimates are continuously sampled. (Hereinafter referred to as sampling point 1, sampling point 2, ..., sampling point 2K) to achieve synchronization between Carol's transmitted symbols and Alice's transmitted symbols, as shown in Figure 4(b). When the current K sampling points fall within the symbol 1 interval, timing synchronization can be considered complete; as shown in Figure 4(a), when the current K sampling points fall across the intervals of symbol 1 and symbol 2, timing synchronization is required. Since the RIS board and Alice transmit information asynchronously, timing synchronization is necessary. Specifically, it includes the following steps:

[0064] a) Continuous sampling is performed using a sliding method, and the amplitude values ​​of adjacent sampling points are compared. Compare;

[0065] b) If the amplitude values ​​of the j-th sampling point and the (j+1)-th sampling point satisfy the following condition Where A is the amplitude decision threshold, it is determined that the K sampling points after the (j+1)th sampling point (including the (j+1)th sampling point) may be within one RIS transmission symbol interval, such as Figure 5 As shown, proceed to step c); otherwise, continue to step a).

[0066] c) For any K consecutive sampling points after the (j+1)th sampling point, there exist any two sampling points that satisfy... If the problem is identified as a false synchronization caused by sudden interference, the search is restarted and step a) is executed; otherwise, it is identified as frame synchronization and step d) is executed.

[0067] d) The (j+1)th sampling point is used as the timing synchronization point, and the subsequent K consecutive sampling points (including the (j+1)th sampling point) are regarded as sampling of a RIS transmitted symbol for subsequent symbol decision.

[0068] ②Sampling decision. Calculate the average amplitude value of K consecutive sampling points within a transmitted symbol. Then we get the binary sequence. .

[0069] ③ Frame synchronization header capture. The frame synchronization position is determined by utilizing the autocorrelation characteristics of the synchronization sequence, thereby determining the frame start position.

[0070] ④ Channel decoding. Based on the frame start position, the data sequence in a frame is sent to a third-party transmitter channel decoding module, such as an LDPC decoder, to obtain the information sent by Carol.

[0071] The above specific implementation methods and embodiments are specific support for the technical concept of a covert information transmission method and system based on RIS control channel proposed by the present invention. They should not be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made on the basis of the technical solution according to the technical concept proposed by the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for covert information transmission based on RIS regulation channel, characterized in that: This method is based on a system that includes a base station, a terminal, and a third-party transmitter. The third-party transmitter includes a signal generation module and a RIS information control module. The signal generation module includes an information generation module and a channel coding module. The RIS information control module includes the RIS control module and the RIS board; The terminal includes an antenna module, an A / D sampling module, and a signal processing module; the signal processing module includes a channel estimation module, a channel equalization module, a channel demodulation module, a base station channel decoding module for acquiring base station data streams, a timing synchronization module, a sampling decision module, a frame synchronization module, and a third-party transmitter channel decoding module for acquiring third-party transmitter data streams. The steps to implement this method are as follows: Step 1) Obtain channel state information and the optimal phase shift coefficient for the enhanced terminal direction based on the locations of the base station, terminal, and third-party transmitter; Step 2) When the third-party transmitter does not send information, the base station processes the information to be sent to generate a high-speed data stream and sends it to the terminal. The RIS control module configures the phase shift of the RIS unit of the RIS board to the optimal phase shift coefficient to enhance the terminal direction signal. Step 3) When a third-party sender needs to send information to a terminal, perform the following operations: Step 3.1) The third-party sending end generates a binary sequence of the information to be sent using the information generation module and groups it into groups; Step 3.2) Each binary sequence is channel coded by the channel coding module. After obtaining the baseband signal, a synchronization header is added to each baseband signal to generate a data frame. The data frame is sent to the RIS control module to regulate the phase shift of the RIS unit, thereby sending a low-speed data stream to the terminal. Step 4) When the terminal receives information sent by the base station and the third-party sender, it performs the following operations: Step 4.1) The high-speed data stream and low-speed data stream sent to the terminal are processed by the receiving antenna module and the A / D sampling module and then sent to the signal processing module; Step 4.2) The channel estimation module performs channel estimation on the received data to obtain a weighted channel estimate. Step 4.3) The weighted channel estimate is processed by the channel equalization module, the channel demodulation module, and the base station channel decoding module to obtain the information transmitted by the base station; Step 4.4) The weighted channel estimate is synchronized with the symbols transmitted by the third-party transmitter and the base station by the timing synchronization module, the sampling decision module performs sampling decision, the frame synchronization module determines the frame start position, and the third-party transmitter channel decoding module decodes the information transmitted by the third-party transmitter. Channel state information is obtained based on the locations of the base station, terminal, and third-party transmitter. The channel state information of the base station-terminal direct link is denoted as follows: The channel state information of the base station-RIS board is denoted as The channel state information of the RIS board-terminal is denoted as The optimal phase shift coefficient of the RIS board is obtained by satisfying: And obtain the phase shift coefficient deviating from the terminal direction; The baseband signal contains an information sequence and a check sequence, and the data frame contains a synchronization sequence, an information sequence, and a check sequence; The data frame sequence is sent to the RIS control module, and then the phase shift of the RIS unit is adjusted according to the "0" and "1" in the input data frame sequence. When "0" is input, the RIS board is configured with a phase shift coefficient that deviates from the terminal direction; when "1" is input, the RIS board is configured with the optimal phase shift coefficient.

2. The method of claim 1, wherein the RIS-based channel regulation is used to control the covert information transmission. In step 4.4), the timing synchronization of the weighted channel estimate with the base station's transmitted symbols via the timing synchronization module includes the following steps: Step a) Continuously sample 2K weighted channel estimates using a sliding method. And the amplitude values ​​of adjacent sampling points Compare; Step b) If the amplitude values ​​of the j-th sampling point and the (j+1)-th sampling point satisfy the following condition Where A is the amplitude decision threshold, if the K sampling points after the (j+1)th sampling point are within a RIS transmission symbol interval, proceed to step c); otherwise, continue to step a). Step c) Take the (j+1)th sampling point as the timing synchronization moment, and treat the subsequent K consecutive sampling points as sampling of a RIS transmitted symbol for subsequent symbol decision.

3. The method of claim 2, wherein the RIS-based channel regulation is used to control the covert information transmission. A false synchronization detection step is set between step b) and step c): For the K consecutive sampling points after the (j+1)th sampling point, there exist any two sampling points that satisfy... If the result is a false synchronization caused by sudden interference, then the search is repeated and step a) is executed; otherwise, it is determined to be frame synchronization and step c) is executed.

4. The method for covert information transmission based on a RIS control channel according to claim 2, characterized in that: The sampling decision module performs the sampling decision process as follows: Calculate the average amplitude value of K consecutive sampling points within a RIS transmitted symbol. Then we get the binary sequence. .

5. A system for implementing the method for covert information transmission based on RIS regulation channel according to claim 1, characterized in that it comprises: The system includes a base station, a terminal, and a third-party transmitter; The third-party transmitter includes a signal generation module and a RIS information control module. The signal generation module includes an information generation module and a channel coding module. The RIS information control module includes the RIS control module and the RIS board; The terminal includes an antenna module, an A / D sampling module, and a signal processing module. The signal processing module includes a channel estimation module, a channel equalization module, a channel demodulation module, a base station channel decoding module for acquiring base station data streams, a timing synchronization module, a sampling decision module, a frame synchronization module, and a third-party transmitter channel decoding module for acquiring third-party transmitter data streams.

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