Concealed communication method based on simultaneous transmission and reflection reconfigurable intelligent surface

Abstract

The invention discloses a covert communication method based on a simultaneous transmission and reflection reconfigurable intelligent surface, and the method comprises the following steps: in a system, a base station sends an NOMA signal to a first communication user through a direct connection link and an ASTAR-RIS reflection link, and sends a signal to a second communication user through an ASTAR-RIS transmission link, the first communication user is used as an energy collection node to perform energy collection and signal decoding by using the SWIPT technology; and when the second communication user fails to decode successfully, the first communication user forwards a signal of the second communication user by using the collected energy, and the second communication user sends interference to the monitor at the same time to weaken the detection performance of the monitor. According to the method, ASTAR-RIS, NOMA and SWIPT technologies are combined, the communication spectrum efficiency and the energy utilization rate can be improved, meanwhile, the detection performance of a monitor is effectively reduced, and the reliability and the practical value of a covert communication system are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wireless communication and covert communication, and particularly relates to a covert communication method based on a simultaneous transmission and reflection reconfigurable intelligent surface. BACKGROUND

[0002] With the rapid development of wireless communication, covert communication has attracted more and more attention in the fields of military and privacy protection. Although the traditional intelligent surface (RIS) can regulate the channel through passive reflection, its power is limited, and it is difficult to meet the needs of long-distance transmission or high-security communication.

[0003] In recent years, the proposed simultaneous transmission and reflection reconfigurable intelligent surface (ASTAR-RIS) can simultaneously support intelligent regulation of reflection and transmission signals, and has an active amplification function, overcoming the double-path loss attenuation problem of traditional RIS, and providing a new idea for improving the performance of covert communication.

[0004] On the other hand, the non-orthogonal multiple access (NOMA) protocol improves the spectrum utilization through power domain superposition, and the simultaneous wireless information and power transfer (SWIPT) technology enables the receiving end to simultaneously perform energy harvesting and information decoding, providing an implementation condition for cooperative covert communication.

[0005] However, in cooperative covert communication, the monitor may detect the covert signal through energy detection. Therefore, how to reduce the detection performance of the monitor while ensuring reliable communication of the legitimate user has become a key problem. SUMMARY

[0006] To solve the above problems, the application provides a covert communication method based on a simultaneous transmission and reflection reconfigurable intelligent surface, which effectively reduces the detection performance of the monitor by combining NOMA and SWIPT technologies, and realizes the balance between concealment and reliability.

[0007] The technical scheme adopted by the application is as follows: a covert communication method based on a simultaneous transmission and reflection reconfigurable intelligent surface, comprising the following steps:

[0008] S1, constructing a system architecture: the system includes a base station, an ASTAR-RIS, a first communication user, a second communication user and a monitor, and the communication is divided into two stages:

[0009] The first stage: the base station sends NOMA signals to the first communication user through the direct link and the ASTAR-RIS reflection link, and sends signals to the second communication user through the ASTAR-RIS transmission link; the first communication user is an energy collection node, which collects energy and decodes signals by using the simultaneous energy collection and information transmission technology; if the second communication user successfully decodes, the communication ends; if it is not successfully decoded, the second stage is entered;

[0010] The second stage: the first communication user forwards the signal of the second communication user by using the collected energy, and the second communication user and the monitor can receive the forwarded signal, and at the same time, the second communication user sends interference to the monitor to weaken the detection ability of the monitor to the covert signal;

[0011] S2, covert communication detection method: assuming that the channel is quasi-static Rayleigh fading, the channel coefficient is complex Gaussian distribution; the monitor performs energy detection on the received signal power under the assumption of no covert information and the assumption of having covert information, and determines the false alarm probability, the missed detection probability and the detection error probability according to the energy detection, and further calculates the average minimum detection error probability;

[0012] S3, interruption probability analysis: the first communication user decodes the signal of the second communication user and the signal of itself in turn according to NOMA, and calculates the interruption probability of the first communication user; the second communication user performs interruption probability analysis in the first stage and the second stage respectively, wherein in the second stage, the signal is forwarded by the first communication user and the detection performance of the monitor is reduced in combination with the interference.

[0013] Further, in step S2, the covert communication detection comprises:

[0014] In the first stage based on the quasi-static Rayleigh fading channel model, A and B are the active gains of the transmission path and the reflection path respectively, And denote the reflection coefficient and transmission coefficient matrix of the ASTAR-RIS respectively; , denote the amplitude and phase shift of the kth ASTAR-RIS element respectively; the channel coefficients of the links , , , ; the false alarm probability and the missed detection probability are derived by using the received power;

[0015] The false alarm probability is:

[0016]

[0017] Wherein, denotes the sum of noise at the eavesdropper and the noise generated by the active RIS, d is the distance corresponding to the channel, is the channel fading factor, B denotes the transmission gain, denotes the part of the NOMA signal transmitted by the base station allocated to the first communication user, is the number of projection units in the ASTAR-RIS, is the detection threshold of the first-stage eavesdropper;

[0018] The missed detection probability is:

[0019]

[0020] wherein denotes the part of the NOMA signal transmitted by the base station allocated to the second communication user;

[0021] The detection error probability is obtained according to the false alarm probability and the missed detection probability:

[0022] .

[0023] Further, the first communication user uses the simultaneous energy harvesting and information transmission technology to collect energy, and the collected energy is used to forward the signal of the second communication user in the second stage;

[0024] The power used by the first communication user for forwarding is:

[0025]

[0026] The energy used for forwarding is:

[0027]

[0028] And it is equal to the product of the power and the time in the second stage Therefore, the information power of the second communication user transmitted is:

[0029]

[0030] wherein, is the part used for information decoding in the SWPIT of the first communication user, is the energy conversion efficiency, is the time interval of the first stage, is the interval of the second stage.

[0031] Further, the second communication user sends an interference signal in the second stage to weaken the detection performance of the monitor;

[0032] The false alarm probability is:

[0033]

[0034] wherein, is the detection threshold of the second-stage eavesdropper; is the maximum value of the interference power transmitted by the second communication user;

[0035] The missed detection probability is:

[0036]

[0037] wherein, , , , , ,

[0038] The detection error probability is obtained from the obtained missed detection and false alarm probabilities, and then the average minimum detection error probability is obtained.

[0039] Further, the first-stage outage probability calculation comprises:

[0040] According to the NOMA protocol, the first communication user first decodes the signal of the second communication user, then removes it from the received signal, and detects its own signal:

[0041]

[0042]

[0043] wherein, denotes the signal-to-interference-and-noise ratio of the first user decoding the signal of the second user first; is the signal-to-interference-and-noise ratio of decoding its own signal;

[0044] The outage probability expression of the first communication user is:

[0045]

[0046] wherein, ,

[0047] Finally, the outage probability of the first communication user is obtained as:

[0048]

[0049] wherein,

[0050] The outage probability expression of the second communication user is:

[0051] ​​​​

[0052] wherein, .

[0053] Further, the second stage interruption probability calculation comprises:

[0054] On the basis of receiving the direct link signal and the ASTAR-RIS transmission link signal, combined with the second stage forwarding signal, an interruption probability expression is obtained;

[0055] After the first communication user forwards the information, the signal-to-noise ratio of the second communication user is:

[0056]

[0057] The interruption probability expression of the second communication user is:

[0058]

[0059] wherein, , is the second kind of modified Bessel function.

[0060] The beneficial effects generated by the present application are: the present application realizes the joint regulation of transmission and reflection through ASTAR-RIS, expands the communication coverage; combined with NOMA and SWIPT technology, improves the spectrum efficiency and energy utilization rate; through user cooperation forwarding and interference design, the detection performance of the monitor is significantly reduced, and the balance between concealment and reliability is realized. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is the system model diagram in the embodiment of the present application;

[0062] Figure 2 is the flowchart of the present application. DETAILED DESCRIPTION

[0063] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the description, and obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other embodiments can also be obtained according to these drawings without creative labor. In order to facilitate the understanding of the present application, the present application will be described in more detail in combination with the drawings and specific embodiments.

[0064] The following is an embodiment of the present application, in which the present application is a concealment communication method based on simultaneous transmission and reflection reconfigurable intelligent surface, as shown in Figure 2 The method comprises the following steps:

[0065] S1, construct a system architecture: as Figure 1As shown, the system includes a base station Alice, an ASTAR-RIS, a first communication user Bob, a second communication user Carol, and a monitor Willie. PA is the signal power sent by Alice, and are the average powers of x1(n) and x2(n) respectively. A and B are the active gains of the transmission path and the reflection path respectively, and represent the reflection coefficient and transmission coefficient matrices of the ASTAR-RIS respectively. , represent the amplitude and phase shift of the kth ASTAR-RIS element respectively. The link channel coefficients , , , ;

[0066] First stage: Alice sends NOMA signals to Bob through a direct link and an ASTAR-RIS reflection link, and sends signals to Carol through an ASTAR-RIS transmission link; Bob is an energy harvesting node that collects energy and decodes signals using SWIPT technology; if Carol successfully decodes, the communication ends; if it is not successfully decoded, it enters the second stage.

[0067] Second stage: Bob forwards Carol's signal using the collected energy, and Carol and Willie can receive the forwarded signal, while Carol sends interference to Willie to weaken its detection ability.

[0068] S2, covert communication detection analysis: under the quasi-static Rayleigh fading channel, assuming that Willie performs energy detection on the received power under the conditions of no covert information H0 and with covert information H1; by analyzing the received power of Willie, the detection error probability is calculated by calculating the false alarm probability and the missed detection probability, and the average minimum detection error probability is further obtained; the specific steps are as follows:

[0069] S21, first stage detection error probability: based on the quasi-static Rayleigh fading channel model in the first stage, the false alarm probability and the missed detection probability are derived using the received power; the signal received by Willie is divided into no covert information sent hypothesis H0 and sent hypothesis H1, and the power is:

[0070]

[0071] wherein, represents the active noise generated by the RIS, represents the noise generated at willie, d is the distance of the corresponding channel, is the channel fading factor.

[0072] The false alarm probability is:

[0073]

[0074] The false alarm probability and the missed detection probability are respectively:

[0075]

[0076]

[0077] According to the above two formulas, the detection error probability is given by:

[0078]

[0079] S22, the second stage detection error probability: the first communication user uses the simultaneous energy collection and information transmission technology to collect energy, and the collected energy is used to forward the signal of the second communication user in the second stage, that is, Bob forwards information to Carol, and the power used by Bob to forward is:

[0080]

[0081] The energy used for forwarding is:

[0082]

[0083] And it is equal to the product of the power and time of the second stage So the power of the information sent to Carol is:

[0084]

[0085] Among them, is the part used for information decoding in the SWPIT for Bob, is the energy conversion efficiency, is the first stage time interval, is the second stage interval.

[0086] Carol sends an interference signal , which is subject to uniform distribution Under a certain interference power, as long as Bob forwards the information, Willie will receive additional power and directly mark it as covert transmission. Therefore, in order to reduce the detection performance of Willie, define as random; The power of the signal received by Willie is:

[0087]

[0088] The false alarm probability is:

[0089]

[0090] The false alarm probability is:

[0091]

[0092] where, is the detection threshold of the second stage willie; is the maximum value of the interference power emitted by Carol; .

[0093] Similarly, the missed detection probability is:

[0094]

[0095] Simplify as follows:

[0096]

[0097] where, , , , , .

[0098] When two parameter different exponential variables are added, the sum is no longer an exponential distribution, but a double exponential convolution (a special case of double gamma distribution), and its PDF (probability density function) is:

[0099]

[0100] This is a standard result, commonly used in wireless communication theory to calculate expectations or probabilities.

[0101]

[0102] Because the three are independent, they can be written as a triple integral:

[0103]

[0104]

[0105] Since they are independent probability density functions, such variable integral is legal and reasonable; the final expression of the missed detection probability can be obtained by step-by-step integral calculation of the above formula:

[0106]

[0107] wherein, , , , , .

[0108] The detection error probability is obtained from the obtained missed detection and false alarm probability, and then the average minimum detection error probability is obtained.

[0109] S3, interruption probability analysis; Bob decodes Carol's signal after receiving the signal, and then detects his own signal to obtain the interruption probability; Carol calculates the interruption probability in the first stage and the second stage respectively, wherein the second stage combines the signal forwarded by Bob for judgment; the specific steps are:

[0110] S31, first stage interruption probability analysis of Bob and Carol: Bob's received power, according to the NOMA protocol, Bob first decodes Carol's signal, then removes it from the received signal, and detects his own signal; the relevant signal-to-interference noise ratio is:

[0111]

[0112]

[0113] wherein, Bob decodes Carol's signal first. is the signal-to-interference noise ratio for decoding his own signal.

[0114] Then the interruption probability of Bob is:

[0115]

[0116] Let , ; then the interruption probability expression of Bob is simplified as:

[0117]

[0118] wherein, .

[0119] Carol's received power and signal-to-interference noise ratio:

[0120]

[0121]

[0122] The interruption probability expression of Carol is:

[0123]

[0124] set up Ultimately, Carol's interruption probability expression simplifies to:

[0125]

[0126] S32, Second Stage Carol Outage Probability Analysis: Based on the received direct link signal and the ASTAR-RIS transmitted link signal, combined with the second stage forwarded signal, the outage probability expression is obtained; after Bob forwards the information, Carol's signal-to-noise ratio is:

[0127]

[0128] Carol's interruption probability expression is:

[0129]

[0130] set up The specific expression for Carol's interruption probability is:

[0131]

[0132] in It is a modified Bessel function of the second kind (first order), which needs to be calculated by numerical methods or by looking up tables.

Claims

1. A covert communication method based on a reconfigurable smart surface with simultaneous transmission and reflection, characterized in that, Includes the following steps: S1, System Architecture Construction: The system includes a base station, ASTAR-RIS, a first communication user, a second communication user, and a monitor. Communication is divided into two phases: Phase 1: The base station sends NOMA signals to the first communication user via a direct link and an ASTAR-RIS reflection link, and simultaneously sends signals to the second communication user via an ASTAR-RIS transmission link; the first communication user is an energy harvesting node that uses simultaneous energy harvesting and information transmission technology to harvest energy and decode the signal; if the second communication user successfully decodes the signal, the communication ends. If decoding fails, proceed to the second stage; Second stage: The first communication user uses the collected energy to forward the signal of the second communication user. Both the second communication user and the monitor can receive the forwarded signal. At the same time, the second communication user sends interference to the monitor to weaken the monitor's ability to detect concealed signals. S2, Covert Communication Detection Method: Assuming the channel is quasi-static Rayleigh fading and the channel coefficients are complex Gaussian distribution; Under the assumptions of no covert information and with covert information, the monitor performs energy detection on the received signal power and determines the false alarm probability, missed detection probability and detection error probability accordingly, and further calculates the average minimum detection error probability. S3, Interruption Probability Analysis: The first communication user sequentially decodes the second communication user's signal and its own signal according to NOMA, and calculates the interruption probability of the first communication user accordingly; the second communication user performs interruption probability analysis in the first stage and the second stage respectively, wherein in the second stage, the first communication user forwards the signal and combines it with interference to reduce the detection performance of the monitor.

2. The covert communication method based on a reconfigurable smart surface with simultaneous transmission and reflection according to claim 1, characterized in that, In step S2, the covert communication detection includes: In the first stage based on the quasi-static Rayleigh fading channel model, A and B are the active gains of the transmission path and the reflection path, respectively. and These represent the reflection coefficient and transmission coefficient matrices of ASTAR-RIS, respectively; , Represent the amplitude and phase shift of the k-th ASTAR-RIS element, respectively; and the channel coefficients of each link. , , , ; Derive the false alarm probability and the missed detection probability using the received power; The false alarm probability is: in, This represents the sum of the noise at the eavesdropper's location and the noise generated by the active RIS; d is the distance to the corresponding channel. Channel fading factor This refers to the portion of the NOMA signal transmitted by the base station allocated to the first communication user. The number of projection units in ASTAR-RIS The detection threshold for eavesdroppers in the first stage; The probability of a missed detection is: Here, it represents the portion of the NOMA signal transmitted by the base station allocated to the second communication user; Based on the false alarm probability and the false negative probability, the detection error probability is: 。 3. The covert communication method based on a reconfigurable smart surface with simultaneous transmission and reflection according to claim 1, characterized in that, The first communication user uses simultaneous energy harvesting and information transmission technology to harvest energy, and the harvested energy is used to forward the signal of the second communication user in the second stage; The power used by the first communication user for forwarding is: The energy used for forwarding is: And it is equal to the product of the power and time of the second stage. Therefore, the information power of the second communication user sent is: in, This is the part of the SWPIT used for information decoding in the first communication user. It is energy conversion efficiency. This is the first phase of the time interval. This is the second phase gap.

4. The covert communication method based on a reconfigurable smart surface with simultaneous transmission and reflection according to claim 1, characterized in that, The second communication user sends interference signals in the second phase to weaken the detector's performance; The false alarm probability is: in, The detection threshold for eavesdroppers in the second stage; This is the maximum value of the interference power transmitted by the second communication user; ; The probability of a missed detection is: in, , , , , , ; The probability of detection error is obtained from the probabilities of missed detection and false alarm, and then the average minimum probability of detection error is obtained.

5. The covert communication method based on a reconfigurable smart surface with simultaneous transmission and reflection according to claim 1, characterized in that, The first stage interruption probability calculation includes: According to the NOMA protocol, the first communication user first decodes the second communication user's signal, then removes it from the received signal, and detects its own signal: in, This indicates the signal-to-interference-plus-noise ratio (SIR) of the signal decoded by the first user before the second user's signal is decoded. To determine the signal-to-interference-plus-noise ratio (SIR) for decoding its own signal; The interruption probability expression for the first communication user is: in, , ; Finally, the interruption probability of the first communication user can be obtained as: in, ; The interruption probability expression for the second communication user is: in, .

6. The covert communication method based on a reconfigurable smart surface with simultaneous transmission and reflection according to claim 1, characterized in that, The second-stage interruption probability calculation includes: Based on the received direct link signal and the ASTAR-RIS transmitted link signal, combined with the second-stage forwarding signal, the interruption probability expression is obtained; After the first communication user forwards the information, the signal-to-noise ratio of the second communication user is: The interruption probability expression for the second communication user is: in, , It is a modified Bessel function of the second kind.

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