A distributed secure transmission method and communication system based on smart reflective surfaces

Abstract

The application discloses a kind of distributed security transmission methods and communication systems based on intelligent reflecting surface, the method includes: transmitter carries out series-parallel conversion to binary data to be transmitted, obtains odd bit bit string and even bit bit string, and selects one bit string to carry out binary phase shift keying BPSK modulation, obtains BPSKI signal and sends.The BPSKI signal sent by transmitter reaches intelligent reflecting surface, IRS calculates phase offset coefficient, and the incident BPSKI signal is phase-shifted and reflected to obtain BPSKII signal, and BPSKII signal is reflected to receiver.The receiver superimposes the BPSKI signal directly from transmitter and the BPSKII signal reflected by IRS, and the signal obtained is the quaternary phase shift keying modulation QPSK signal carrying expected data, and the receiver recovers expected data using QPSK demodulation method.The application makes transmitter only send part data information, and signal is transmitted in two ways, which can effectively prevent the leakage of expected data information, thereby improving the security of communication system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wireless communication, and further relates to a distributed secure transmission method based on an intelligent reflecting surface and a communication system. BACKGROUND

[0002] Wireless communication technology develops rapidly and constantly meets the increasing demand of user quantity and data service. Wireless communication takes open space as a transmission medium, and its broadcast nature makes the communication of legal users face the threat of eavesdropping and tampering from attackers within its signal coverage range, that is, the confidentiality and integrity of legal communication may be destroyed. At the same time, wireless networks and mobile services are increasingly widely used in personal life and enterprise operations, and a large amount of sensitive data information containing personal privacy and business secrets is transmitted in a wireless mobile environment. Once the signal carrying these data is intercepted and obtained by malicious users, great loss will be caused. Therefore, secure communication (SC) is an important part of wireless communication technology and is also the key to more widely applied future wireless data services. Wireless communication technology based on physical layer security has received extensive attention in recent years.

[0003] The technologies related to physical layer security include: existing technology one: artificial noise (AN) technology is to use part of the power of the legitimate transmitter (Tx) to generate an interference signal, which is called AN, and the legitimate transmitter sends AN and legitimate communication signals at the same time. AN can reduce the signal-to-noise ratio of the eavesdropper, but the legitimate receiver can eliminate the influence of AN and recover the information of the legitimate communication from the received mixed signal. Tang Yanqun, Wei Jibo, Ma Dongtang, and Zhang Xiaoying. Robust artificial noise aided transmit designs for physical layer security [C] / / National Doctoral Academic Forum on Information and Communications Technology, 2013: 21-23. The robustness of artificial noise aided physical layer security is studied, considering the multiple-input single-output single-antenna eavesdropping scenario and the multiple-input multiple-output multi-antenna eavesdropping scenario. Under the constraints of the signal-to-noise ratio of the eavesdropping receiver and the signal-to-noise ratio of the legitimate receiver, a security transmission method is designed to minimize the total transmission power, and AN is added to enhance the physical layer security. The advantage of the physical layer security mechanism based on AN is to artificially worsen the channel quality of the eavesdropping channel and improve the security communication rate of the legitimate communication system. Existing technology two: beamforming technology is to adjust the spatial characteristics of the signal sent by the legitimate transmitter, so that the legitimate signal is constructive at its desired receiver, thereby maximizing the signal-to-interference-plus-noise ratio (SINR) of the legitimate receiver, while reducing the SINR of the eavesdropper. X. Chen, S. Han, and J. Wang. Analysis of Physical Layer Security Based on Correlated Channels in Opportunistic Beamforming Technology [C] / / IEEE Vehicular Technology Conference (VTC), 2021: 27-30. Random beamforming technology is used to achieve secure communication, and the greater the correlation between the legitimate user and the eavesdropper, the lower the security transmission rate. The advantage of beamforming technology is to fully utilize the spatial degrees of freedom to increase the difference between the legitimate communication channel and the eavesdropping channel, thereby enhancing the security of the legitimate communication signal. Existing technology three: cooperative interference technology.Cooperative jamming technology takes advantage of a third-party transmitter to send interference to the eavesdropper while the legitimate user receives the signal to reduce the communication quality of the eavesdropping channel. Li B, Wu W, Zhao W, et al. Security Enhancement With a Hybrid Cooperative NOMA Scheme for MEC System[J]. IEEE Transactions on Vehicular Technology, 70(3), 2021, 2635-2648. Cooperative jamming technology uses the cooperative interference between non-orthogonal multiple access (NOMA) users to improve the security of the mobile-edge computing (MEC) system. The advantage of cooperative jamming technology is to use a large number of transmitting devices to cooperatively transmit interference signals to weaken the quality of the eavesdropping channel and improve the security performance.

[0004] Security problems in the prior art: Although the above-mentioned physical layer security technologies one, two and three improve the security of wireless communication to a certain extent, they are all based on the traditional centralized modulation (CM) method to load all the data information of the user onto one physical signal for transmission, that is, the signal sent by the legitimate transmitter Tx carries the complete user data. Once the eavesdropper intercepts the physical signal and processes it, the user information can be recovered from the intercepted signal with the help of its computing power, thereby destroying the confidentiality of the communication. And the artificial noise technology needs to artificially generate noise signals, which not only wastes the power of the legitimate transmitter, but also affects other nearby legitimate communications. The beamforming technology needs to configure multiple antennas for the communication device to control the beam, which increases the hardware cost of the device, and when the position and channel state information of the eavesdropper are unknown, it is difficult to accurately design the beam for secure communication. The cooperative jamming technology depends on the specific communication scenario. For a randomly moving wireless communication system, the specific implementation of cooperative jamming needs to be adapted, and cooperative jamming requires independent interference devices and power overhead.

[0005] The application provides a method for realizing distributed secure transmission by using an IRS. A transmitter divides data to be transmitted into two parts. The transmitter modulates one part of the data and directly transmits a first modulated signal to a receiver. An intelligent reflecting surface IRS also receives the first modulated signal. The IRS performs controllable phase shift reflection on the first modulated signal to obtain a second modulated signal. The first modulated signal and the second modulated signal reach a legitimate receiver. The legitimate receiver can recover the expected data information from the mixed signal. For an eavesdropper, intercepting one signal can only recover part of the user data information without complete meaning. Meanwhile, intercepting and accurately combining two physical signals requires the eavesdropper to accurately know the propagation characteristics of the two physical signals, which is difficult to achieve in practice, thereby increasing the difficulty of eavesdropping and realizing secure transmission of legitimate user data. The application only uses one transmitter and utilizes the passive characteristics of the IRS to realize secure data transmission without increasing the transmission power consumption. Moreover, the application does not rely on the use of spatial degrees of freedom, i.e., it does not need to design a spatial beam to realize secure transmission, thereby avoiding the multi-antenna overhead at the transmitter and the receiver. SUMMARY

[0006] The application provides a distributed secure transmission method and a communication system based on an intelligent reflecting surface, aiming to realize secure communication.

[0007] The application converts binary data to be transmitted by a legitimate transmitter into an odd bit string and an even bit string through serial-parallel conversion, selects one of the bit strings for binary phase shift keying (BPSK) modulation, and obtains a BPSK I signal for transmission. The BPSK I signal transmitted by the transmitter reaches an intelligent reflecting surface. The IRS calculates a phase offset coefficient and performs phase shift reflection on the incident BPSK I signal to obtain a BPSK II signal. The BPSK II signal is reflected to a receiver. The receiver superimposes the BPSK I signal directly from the transmitter and the BPSK II signal reflected by the IRS to obtain a quaternary phase shift keying (QPSK) signal carrying expected data. The receiver can recover the expected data using a conventional QPSK demodulation method.

[0008] Further, the distributed secure transmission method based on an intelligent reflecting surface includes the following specific steps:

[0009] The secure communication system includes a legitimate transmitter Tx, an intelligent reflecting surface IRS controlled by the Tx, a legitimate receiver Rx, and an eavesdropper Eve. The Tx is equipped with N T root transmitting antennas, the Rx and the Eve are each equipped with N R root receiving antennas, and the IRS includes M reflecting elements.

[0010] The application realizes the following steps:

[0011] Step 1, the transmitter Tx serial-to-parallel (S / P) converts the expected data code d(t) to be transmitted to obtain an odd bit bit string d0(t) and an even bit bit string d1(t), and the transmitter Tx selects the odd bit bit string d0(t) to perform binary phase shift keying (BPSK) modulation with a phase of {0, π} to obtain a BPSKI signal, and sends the BPSKI signal to the receiver Rx, wherein the expected data code d(t) is a binary bit string;

[0012] Step 2, the BPSKI signal sent by the transmitter Tx reaches the intelligent reflecting surface IRS, the Tx calculates a phase offset coefficient θ, θ ∈ (-π, π], and controls the IRS to perform phase shift reflection on the BPSKI signal, so that the reflected signal is a BPSKII signal modulated by the even bit bit string d1(t) with a phase of , and the IRS reflects the BPSKII signal to the receiver Rx;

[0013] Step 3, the BPSKI signal transmitted by the transmitter Tx and the BPSKII signal reflected by the IRS are superimposed on each other at the receiver Rx, and the superimposed signal is a modulated signal obtained by performing quaternary phase shift keying (QPSK) modulation on the bit string d(t) with a phase of , and the receiver Rx demodulates the expected data using the modulated QPSK signal.

[0014] Further, the step 1 specifically includes:

[0015] (1a) the transmitter Tx serial-to-parallel (S / P) converts the expected data code d(t) to be transmitted to obtain an odd bit bit string d0(t) and an even bit bit string d1(t);

[0016] (1b) the transmitter Tx selects d0(t) to multiply a carrier signal cos(ω c t) to obtain a BPSKI signal s A (t) with a phase of 0 or π, s A (t) = d0(t)cos(ω c t), and the Tx sends s A (t) to the receiver Rx and the intelligent reflecting surface IRS through an antenna.

[0017] Further, the step 2 specifically includes:

[0018] (2a) the transmitter Tx calculates the bit information of d0(t) and d1(t) at time t, and performs BPSKI signal with a phase of {0, π} and BPSKII signal with a phase of a phase difference of the BPSKII signal, and calculating a phase offset coefficient θ required for the intelligent reflecting surface IRS to phase-shift reflect the incident BPSKII signal according to the phase difference i , where i ∈ {1, …, M};

[0019] (2b) the transmitter Tx controls the intelligent reflecting surface IRS to controllably phase-shift reflect the BPSKII signal from the Tx through the IRS controller, at this time the receiver Rx receives the BPSKII signal reflected from the IRS as r IB (t) = h IB Φh AI s A (t), where is a reflection coefficient matrix of the IRS, diag(·) represents a diagonal matrix obtained by diagonalizing a vector, the intelligent reflecting surface IRS is provided with M reflection elements, β i and θ i respectively represent the amplitude reflection coefficient and the phase offset coefficient of the i-th IRS reflection element to the incident signal, and β M and θ M respectively represent the amplitude reflection coefficient and the phase offset coefficient of the M-th IRS reflection element to the incident signal. All β i are set to 1, θ i ∈ (-π, π] is calculated by the transmitter Tx in step (2a); represents a channel coefficient vector from the Tx to the IRS, represents a channel coefficient vector from the IRS to the Rx.

[0020] Further, the step 3 specifically comprises:

[0021] (3a) the receiver Rx receives the BPSKII signal directly from the Tx, which is represented as: r AB (t) = h AB s A (t), where represents a channel coefficient from the Tx to the Rx, and the receiver Rx receives a superimposed signal from the Tx and the IRS as r B (t) = h AB s A (t) + h IB Φh AI s A (t) + n B , where the noise n B received by the receiver Rx is a Gaussian random variable with a mean of 0 and a variance of ;

[0022] (3b) the receiver Rx selects as the filtering coefficient, from rB (t) the QPSK modulated signal waveform is obtained, and the Rx uses the QPSK signal demodulation to recover the expected data bit string d(t).

[0023] The application aims to provide a distributed secure transmission method and communication system based on intelligent reflecting surface.

[0024] The application has the advantages and positive effects that:

[0025] An IRS-aided distributed modulation based secure communication (IRS-DMSC) is proposed. Compared with the traditional centralized modulation, the IRS-DMSC splits the data information to be transmitted into two parts at the transmitting end, and the transmitter only modulates one part of the data to obtain a first modulated signal and transmits it. The first modulated signal is not only transmitted directly to the legitimate receiver, but also reflected by the intelligent reflecting surface (IRS). The IRS performs controllable phase shift reflection on the first modulated signal and reflects a second modulated signal to the legitimate receiver. Finally, at the legitimate receiver, the first modulated signal and the second modulated signal are superimposed on each other, and the legitimate receiver can recover the expected data information from the superimposed signal. The method realizes the security of the signal transmission process, that is, the first modulated signal and the second modulated signal only carry part of the data information. If an eavesdropper intercepts one of the signals, he can only recover part of the user data information which has no complete meaning. If the eavesdropper intercepts both physical signals and accurately combines them, he needs to accurately know the propagation characteristics of the two physical signals, which is difficult to achieve in practice, thus increasing the difficulty of eavesdropping and realizing the secure transmission of legitimate user data. The application only uses one transmitter and utilizes the passive characteristics of the IRS to realize secure data transmission without increasing the transmission power consumption. Moreover, the application does not rely on the use of spatial degrees of freedom, that is, it does not need to design spatial beams to realize secure transmission, thus avoiding the multi-antenna overhead at the transmitter and receiver. In addition, the application is not only suitable for secure communication of single-input single-output systems, but also suitable for secure communication of multiple-input multiple-output systems. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a flowchart of a distributed secure transmission method and communication system based on intelligent reflecting surface provided by the application;

[0027] Figure 2 is a system model schematic diagram of a distributed secure transmission method and communication system based on intelligent reflecting surface provided by the application;

[0028] Figure 3is the change of the channel capacity of the IRS-DMSC method and the CM method proposed in the application with the signal-to-noise ratio η.

[0029] Figure 4 is the change of the symbol error rate of the IRS-DMSC method and the CM method proposed in the application with the signal-to-noise ratio η.

[0030] Figure 5 is the change of the secure capacity of the IRS-DMSC method and the CM method proposed in the application with the signal-to-noise ratio η. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0032] The present application aims to solve the implementation of physical layer security in the field of wireless communication, and the problem of transmission signals being illegally eavesdropped. A legal transmitter modulates a part of original expected data to be transmitted to obtain a first modulated signal for transmission, and the first modulated signal is transmitted to a legal receiver and an IRS. The IRS performs controllable phase shift reflection on the first modulated signal to obtain a second modulated signal, and then reflects the second modulated signal to the legal receiver. The first modulated signal and the second modulated signal are superimposed at the legal receiver, and the legal receiver can recover the original expected data from the superimposed signal by using a conventional demodulation method.

[0033] The difficulty and significance of solving the above technical problems: because wireless channels have a broadcast characteristic, wireless communication signals are extremely vulnerable to illegal eavesdropping. The present application proposes a distributed secure transmission method (IRS-DMSC) based on IRS. A legal transmitter only adjusts and transmits a part of an original data sequence to be transmitted. The transmitted signal is transmitted directly to a legal receiver and is incident to an IRS and is phase-modulated by the IRS, and then is reflected to the legal receiver. The signal directly from the legal transmitter and the signal reflected by the IRS are superimposed at the legal receiver, and the legal receiver demodulates the mixed signal to recover the original expected data. Compared with the traditional centralized transmission mode, all data information of a user is modulated into a physical signal for transmission. Once the physical signal is intercepted, the confidentiality of the user's communication will be threatened. The present application takes the characteristics of wireless channels into the modulation process, can fully utilize the randomness of wireless channels to prevent eavesdropping, and provides security protection for the data transmission of legal users.

[0034] The application principle of the present application will be described in detail below with reference to the accompanying drawings:

[0035] As Figure 1As shown, the distributed secure transmission method based on the intelligent reflecting surface provided by the embodiment of the application comprises the following steps:

[0036] S101: The distributed communication system is composed of 1 transmitter Alice, 1 receiver Bob and 1 IRS, the transmitter is configured with N T = 1 transmitting antenna, the receiver is configured with N R = 1 receiving antenna, and the IRS is configured with M intelligent reflecting units. The transmitter Alice performs serial-parallel conversion on the expected data to be transmitted d(t) to obtain an odd bit bit string d0(t) and an even bit bit string d1(t), the transmitter Tx selects the odd bit bit string d0(t) to perform binary phase shift keying BPSK modulation with a phase of {0, π} to obtain a BPSK I signal, and transmits the BPSK I signal to the receiver Rx, wherein the expected data d(t) is a binary bit string;

[0037] S102: The BPSK I signal transmitted by the transmitter Alice reaches the intelligent reflecting surface IRS, the Alice calculates a phase offset coefficient θ, θ ∈ (-π, π], and controls the IRS to perform phase shift reflection on the BPSK I signal, so that the reflected signal becomes an even bit bit string d1(t) to perform BPSK modulation with a phase of , and the IRS reflects the BPSK II signal to the receiver Bob;

[0038] S103: The BPSK I signal transmitted by the transmitter Alice and the BPSK II signal reflected by the IRS are superimposed on each other at the receiver Bob, and the superimposed signal is a modulated signal obtained by performing quaternary phase shift keying QPSK modulation on the bit string d(t) with a phase of , and the receiver Bob demodulates the expected data using the modulated QPSK signal.

[0039] The application will be further described below in combination with the drawings and specific embodiments.

[0040] As shown in the drawings, Figure 2 the application adopts a communication system comprising 1 legal transmitter Alice, 1 legal receiver Bob and an IRS as a system model. The transmitter is configured with N T = 1 transmitting antenna, the receiver is configured with N R = 1 receiving antenna, and the IRS is configured with M intelligent reflecting units. The application uses h xy and h xy to represent the channel coefficients and vectors of legal communication, uses g xy and g xy to represent the eavesdropping channel coefficients and vectors, and the subscript xy represents a communication device x and y, specifically, denote the channel coefficient from Alice to Bob, and denote the channel coefficient vectors from Alice to IRS and from IRS to Bob, respectively, and denote the eavesdropping channel coefficient from Alice to Eve and the eavesdropping channel coefficient and vector from IRS to Eve, respectively. All channels are spatially uncorrelated Rayleigh flat fading channels, i.e., h xy , g xy , h xy , g xy The elements in h xy , g xy , h xy , g xy can be modeled as independent and identically distributed (i.i.d.) complex Gaussian random variables with zero mean and unit variance. Moreover, all channels have block fading property, i.e., the channel coefficients remain constant in a block consisting of several consecutive time slots and vary randomly between adjacent blocks. Since the IRS is controlled by Alice, Alice can accurately obtain the channel fading coefficient vector h AI between itself and the IRS. In addition, Bob can accurately estimate h AB and h IB and feed back these information to Alice through a low-rate error-free link. In this invention, Alice selects half of the data to be transmitted to be directly BPSK modulated and transmitted. The modulated BPSK signal (denoted as BPSK I) is transmitted to Bob directly on the one hand, and is incident on the IRS on the other hand, and the modulated BPSK signal (denoted as BPSK II) carrying the other half of the data is generated by the IRS through controllable phase shift modulation and transmitted to Bob. The two-way BPSK signals are superimposed into a QPSK signal at Bob, and Bob can recover the original expected data information from the mixed signal using QPSK demodulation method.

[0041] The specific steps of the distributed secure transmission method based on intelligent reflecting surface provided by the embodiment of the invention are as follows:

[0042] The system consists of one transmitter Alice, one receiver Bob and one intelligent reflecting surface IRS. The transmitter Alice is configured with N T = 1 transmitting antenna, the receiver Bob is configured with N R = 1 receiving antenna, and Bob can accurately estimate the channel state information between itself and Alice and feed back to Alice. Alice can also accurately obtain the channel fading information between itself and the IRS. The implementation steps are as follows:

[0043] Step 1, the transmitter Alice performs serial-to-parallel conversion on the expected data to be transmitted d(t) to obtain an odd bit bit string d0(t) and an even bit bit string d1(t), and selects the odd bit bit string d0(t) to perform binary phase shift keying (BPSK) modulation with a phase of {0, π} to obtain a BPSK I signal, and sends the BPSK I signal to the receiver Bob, wherein the expected data d(t) is a binary bit string;

[0044] Step 1a, the transmitter Alice performs S / P conversion on the expected data to be transmitted d(t) to obtain an odd bit bit string d0(t) and an even bit bit string d1(t);

[0045] Step 1b, the transmitter Alice selects d0(t) to multiply a carrier signal cos(ω c t) to obtain a BPSK I signal s A (t) with a phase of 0 or π, s A (t) = d0(t)cos(ω c t), and the transmitter Alice sends s A (t) to the receiver Bob and the intelligent reflecting surface (IRS) through an antenna.

[0046] Step 2, the BPSK I signal sent by the transmitter Alice reaches the intelligent reflecting surface (IRS), the transmitter Alice calculates a phase offset coefficient θ, θ ∈ (-π, π], and controls the IRS to perform phase shift reflection on the BPSK I signal, so that the reflected signal becomes an even bit bit string d1(t) to perform BPSK modulation with a phase of , and the IRS reflects a modulated signal BPSK II signal to the receiver Bob;

[0047] Step 2a, the transmitter Alice calculates the bit information of d0(t) and d1(t) at time t, and performs a phase difference between a BPSK I signal with a phase of {0, π} and a BPSK II signal with a phase of , and calculates a phase offset coefficient θ i required by the intelligent reflecting surface (IRS) to perform phase shift reflection on the incident BPSK I signal according to the phase difference, wherein i ∈ {1, …, M}, and the phase reflection coefficient θ i is as shown in Table 1.

[0048] Table 1: IRS phase offset under different transmitted data

[0049]

[0050] Step 2b, the transmitter Alice controls the IRS to reflect the BPSK I signal from Alice with a controllable phase shift, at this time the receiver Bob receives the BPSK II signal reflected from the IRS as r IB (t) = h IB Φh AI s A (t), set all β i = 1, θ i ∈ (-π, π] which is calculated by the transmitter Alice in step 2a.

[0051] Step 3, the BPSK I signal transmitted by the transmitter Alice and the BPSK II signal reflected by the IRS are superimposed on each other at the receiver Bob, and the superimposed signal is a modulated signal obtained by performing quaternary phase shift keying (QPSK) modulation on the bit string d(t) with a phase of , and the receiver Bob demodulates the expected data using the modulated QPSK signal.

[0052] Step 3a, the receiver Bob receives the BPSK I signal directly from Alice, which is represented as: r AB (t) = h AB s A (t), where represents the channel coefficient from Alice to Bob, and the superimposed signal received by Bob from Alice and the IRS is r B (t) = h AB s A (t) + h IB Φh AI s A (t) + n B , where the noise n B received by the receiver Bob is a Gaussian random variable with a mean of 0 and a variance of ;

[0053] Step 3b, the receiver Bob selects as the filter coefficient to obtain the QPSK modulated signal waveform from r B (t), and Bob uses the QPSK signal to demodulate and recover the expected data bit string d(t).

[0054] The application effect of the present application is described in detail below in combination with simulation.

[0055] I. Simulation conditions:

[0056] The performance of the present application is evaluated below. We assume that the communication system includes 1 transmitter Alice, 1 receiver Bob, and M smart reflecting units. The transmitter is configured with NT = 1 transmitting antenna, and N receiving antennas R =1. Set the symbol rate to R. s =1.2×10 8 Baud, carrier frequency is f c =2.4GHz. Define Alice's transmit power P. T noise power Normalized parameters In the simulation, η∈[-5,30]dB is taken. In the simulation, 5000 channel coefficients h are independently and randomly generated using the combination method. xy With the eavesdropping channel coefficient g xy 200 QPSK symbols are transmitted under each group of channel coefficients.

[0057] This invention simulates the channel capacity, security capacity, and symbol error rate for different transmission methods. Channel capacity is measured by the maximum average mutual information, and its calculation formula is as follows: Where x is the transmitted data symbol. Let P(x) be the probability of the data symbol estimated by the receiver. The probability of the transmitter sending x is P(x), and the probability of the receiver receiving x is... The probability is The joint probability density of the two is The maximum average mutual information c between Alice and Bob can be obtained from the channel capacity formula. B The maximum average mutual information c between Alice and Eve E Security capacity is defined as the maximum transmission rate of a legitimate communication pair when an eavesdropper cannot obtain any legitimate user information. Its calculation formula is: c s =max{c B -c E ,0}.

[0058] Simulations were performed on IRS-DMSC and traditional centralized modulation (CM).

[0059] II. Simulation Content:

[0060] Figure 3 The legal channel capacity c obtained by different transmission methods is given. B and eavesdropping channel capacity c E How it changes with η. For example... Figure 3 As shown, CM and IRS-DMSC have the same c B This is because both transmission methods can obtain the same standard QPSK constellation point at Bob as the constellation point of the desired data. As η increases, the c of CM and IRS-DMSC... B All gradually approach the maximum channel capacity of 2 bits / symbol QPSK modulation. This is because when η is high, Bob's expression changes from r...B (t) The probability of correctly recovering the data symbols is close to 1. For the eavesdropping channel capacity, the IRS-DMSC gives c E always 0.

[0061] Figure 4 The variations of the symbol error rates of Bob and Eve with η under different transmission schemes are shown. As shown in the figure, Bob shows low (optimal) symbol error rate performance under both CM and IRS-DMSC schemes. For Eve, the symbol error rate is lowest under the CM scheme. The symbol error rate of Eve under IRS-DMSC is worst, about 50%, and does not decrease with the increase of η, which shows that when the legal communication adopts IRS-DMSC, the randomness of the channel makes the data information recovered by Eve completely random, i.e., Eve cannot accurately eavesdrop the data information of the legal communication.

[0062] Figure 5 The variations of the security capacities c s of different methods with η are shown. As shown in the figure, the c s of the CM scheme is always 0. The IRS-DMSC has a non-zero c s , and both increase with the increase of η, and finally gradually increase to the upper limit of the QPSK capacity of 2 bits / symbol.

[0063] The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A distributed secure transmission method based on a smart reflective surface, applicable to a wireless communication system comprising a transmitter Tx, a receiver Rx, and a smart reflective surface IRS, characterized in that, Includes the following steps: Step (1) The transmitter Tx performs serial-to-parallel conversion on the expected data encoding d(t) to be transmitted, and obtains an odd-numbered bit string d0(t) and an even-numbered bit string d1(t). The transmitter Tx selects the odd-numbered bit string d0(t) and performs binary phase shift keying (BPSK) modulation with a phase of {0,π} to obtain a BPSK1 signal, and sends it to the receiver Rx. The expected data encoding d(t) is a binary bit string. Step (2): The BPSKI signal sent by transmitter Tx arrives at the intelligent reflective surface IRS. Tx calculates the phase shift coefficient θ, θ∈(-π,π], and controls the IRS to perform phase shift reflection on the BPSKI signal, so that the reflected signal becomes an even-numbered bit string d1(t) with phase as... The modulated signal BPSKII obtained by BPSK modulation is reflected by the IRS to the receiver Rx. Step (3) The BPSKI signal transmitted by transmitter Tx and the BPSKI signal reflected by IRS are superimposed at receiver Rx. The superimposed signal is a phase-wise expression of the bit string d(t). The modulated signal obtained by quaternary phase shift keying (QPSK) modulation is used by receiver Rx to demodulate the desired data.

2. The distributed secure transmission method based on a smart reflective surface according to claim 1, characterized in that, Step (1) specifically includes: (1a) The transmitter Tx encodes the desired data to be transmitted d(t) into a serial-to-parallel transformation to obtain an odd-numbered bit string d0(t) and an even-numbered bit string d1(t); (1b) The transmitter Tx is selected with d0(t) and the carrier signal cos(ω). c Multiplying t) yields a BSK1 signal s with a phase of 0 or π. A (t), s A (t)=d0(t)cos(ω c t), Tx transmits s through the antenna A (t) is transmitted to the receiver Rx and the smart reflector IRS.

3. The distributed secure transmission method based on a smart reflective surface according to claim 1, characterized in that, Step (2) specifically includes: (2a) Transmitter Tx calculates the bit information of d0(t) and d1(t) at time t, and performs BSKI signal with phase {0,π} and phase respectively. The phase difference of the incident BPSKII signal is calculated, and the phase shift coefficient θ required for the intelligent reflective surface IRS to perform phase-shift reflection of the incident BPSKII signal is calculated based on the phase difference. i where i∈{1,…,M}; (2b) The transmitter Tx controls the IRS to perform controlled phase-shift reflection of the BPSKII signal from Tx through the intelligent reflective surface IRS controller. At this time, the receiver Rx receives the BPSKII signal reflected from the IRS as r. IB (t)=h IB Φh AI s A (t), where This is the reflection coefficient matrix of the IRS, where diag(·) represents the diagonal matrix obtained by diagonalizing the vector. The intelligent reflective surface IRS has M reflective elements, β... i and θ i Let β represent the amplitude reflection coefficient and phase shift coefficient of the incident signal for the i-th IRS reflective element, respectively. M and θ M These represent the amplitude reflection coefficient and phase shift coefficient of the incident signal for the Mth IRS reflecting element, respectively; set all β... i =1, θ i The ∈(-π,π] is calculated by the transmitter Tx in step (2a); This represents the channel coefficient vector from Tx to the IRS. This represents the channel coefficient vector from IRS to Rx.

4. The distributed secure transmission method based on a smart reflective surface according to claim 1, characterized in that, Step (3) specifically includes: (3a) The BPSKI signal received directly from Tx by receiver Rx is represented as: r AB (t)=h AB s A (t), where Let r represent the channel coefficient from Tx to Rx, where Rx receives the superimposed signal from Tx and IRS. B (t)=h AB s A (t)+h IB Φh AI s A (t)+n B The noise n received by receiver Rx B It has a mean of 0 and a variance of Gaussian random variables; (3b) Receiver Rx selection As a filter coefficient, from r B The QPSK modulated signal waveform is obtained from (t), and Rx uses the QPSK signal to demodulate and recover the desired data bit string d(t).

5. A communication system that applies the distributed secure transmission method based on a smart reflective surface as described in any one of claims 1 to 4.

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