NOMA network covert communication method based on RIS and AmBC

Abstract

The invention discloses an NOMA network covert communication method based on RIS and AmBC. The method comprises the following steps: step 1, constructing an NOMA network communication model based on intelligent reflecting surface and environment backscatter communication; 2, establishing an effective concealment rate maximization problem under an imperfect CSI condition according to an NOMA network communication model; 3, solving an effective concealment rate maximization problem, and obtaining a corresponding optimal NOMA network communication model under the condition of the maximum effective concealment rate; and step 4, completing covert communication according to the optimal NOMA network communication model. The method can remarkably improve the spectrum efficiency, safety and concealment, reduces the energy consumption and operation cost, and can be widely applied to the scenes with higher communication safety requirements, such as government and finance.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and in particular to a NOMA network covert communication method based on RIS and AmBC. Background Art

[0002] With the rapid development of wireless communication technology, the commercialization of the fifth generation mobile communication system (5G) and the advent of the big data era, massive amounts of privacy data will be transmitted by wireless communication systems. The openness of wireless channels poses a challenge to the security of these data, especially in scenarios such as the transmission of privacy-sensitive information. It is necessary to ensure that the communication content cannot be detected and intercepted by unauthorized third parties.

[0003] Wireless covert communication came into being, which can ensure that the transmission of legitimate users is extremely unlikely to be detected by the monitor, thereby realizing the concealment of the information transmission process. As a potential multiple access technology, non-orthogonal multiple access technology (NOMA) actively introduces interference information, which can allow multiple users to communicate simultaneously in one time slot, subcarrier or extension code, improve spectrum efficiency, and expand the connection scale. Compared with traditional orthogonal multiple access technology, NOMA allows signals of different users to be superimposed and transmitted in the power domain, and uses successive interference cancellation (SIC) technology at the receiving end to separate and demodulate the signals of each user, thereby increasing the access capacity and spectrum utilization of the system, and providing more resource utilization space and signal hiding possibilities for covert communications.

[0004] At the same time, the Intelligent Reflecting Surface (IRS) technology has become a research hotspot in the field of wireless communications due to its advantages such as low cost and low power consumption. RIS is a planar array composed of a large number of low-cost, low-power passive reflective elements. The element can intelligently adjust the phase, amplitude and even polarization direction of the incident signal, thereby flexibly controlling the propagation environment of the wireless signal. By properly configuring the reflection coefficient of RIS, channel conditions conducive to communication can be created, such as enhancing signal strength, reducing interference, and achieving directional transmission of signals. In wireless covert communications, RIS can be used to cleverly manipulate the propagation path of the signal, so that the communication signal can be received by the intended recipient in a specific area, but difficult to be detected in other areas, thereby enhancing the concealment of the communication.

[0005] However, existing methods currently face problems such as high power consumption and difficulty in balancing the optimization configuration of RIS, signal detection and concealment performance. In addition, most existing studies aim to maximize energy efficiency, but do not involve maximizing the effective covert rate (ECR). Summary of the invention

[0006] In order to at least partially solve the problems of large power consumption, difficulty in balancing the optimization configuration of RIS, signal detection and concealment performance, and failure to maximize the effective concealment rate in the prior art, the present invention provides a NOMA network concealment communication method based on RIS and AmBC. The present invention constructs a NOMA network communication model based on intelligent reflecting surface (IRS) and ambient backscatter communication (AmBC), and establishes an effective concealment rate maximization problem under imperfect CSI conditions. The model is optimized according to the effective concealment rate maximization problem to obtain the optimal model, and the covert communication is completed according to the optimal model. The present invention considers incomplete interference elimination and the optimal division of the number of RIS elements, uses an alternating optimization scheme, combines the power factor and the number of reflective elements in each area, maximizes the effective concealment rate, significantly improves the transmission quality and concealment of the signal, expands the coverage, and reduces the risk of being discovered and power consumption.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] The present invention proposes a NOMA network covert communication method based on RIS and AmBC, comprising:

[0009] Step 1: Build a NOMA network communication model based on smart reflective surfaces and environmental backscattering communication to facilitate covert communication;

[0010] Step 2: According to the NOMA network communication model, the effective concealment rate maximization problem is established under the condition of imperfect CSI, which is convenient for optimizing the NOMA network communication model;

[0011] Step 3: Solve the problem of maximizing the effective concealment rate, and obtain the corresponding optimal NOMA network communication model under the condition of maximum effective concealment rate;

[0012] Step 4: Complete covert communication based on the optimal NOMA network communication model.

[0013] Furthermore, the NOMA network communication model includes a base station S, a smart reflection surface, a hidden user W and two public users U 1 and U 2 ;

[0014] The intelligent reflective surface includes a backscattering device area and an enhanced main signal area;

[0015] The backscattering device area includes R reflective elements, and the enhanced main signal area includes N reflective elements; wherein R+N=G, G is the number of reflective elements of the smart reflective surface, R is the number of reflective elements in the backscattering device area, and N is the number of reflective elements in the enhanced main signal area.

[0016] Furthermore, the NOMA network communication model is expressed by the following formula:

[0017]

[0018]

[0019] Among them, s is the superposition information of the base station, s 1 and 2 The base station sends the following to the public user U: 1 and U 2 Information, j is the interference signal, satisfying P 1 =a 1 P s and P 2 =a 2 P s To send to public user U 1 and U 2 Power, P s is the total transmission power of the base station, P j =a 3 P s is the transmission power of interference information, a 1 、a 2 and a 3 are the corresponding power factors respectively, and set a 1 +a 2 +a 3 =1, and a 2 ≥a 1 , and have mean zero and variance respectively. and Gaussian white noise, y 1 and 2 Public user U 1 and public user U 2 The received signal, φ r and φ n are the phase shift of the rth reflective element in the backscattering device area and the phase shift of the nth reflective element in the enhanced main signal area, respectively. h sb is the transmission channel from the base station to the backscatter device area, From the backscatter device area to the public user U 1 The transmission channel, h se is the transmission channel from the base station S to the enhanced main signal area, To enhance the main signal area to the public user U 2 Transmission channel, c is the signal of the backscattering device area, and Base station to public user U 1 and U 2 The transmission channel, For the backscatter device area, c(n) is not sent. The backscatter device area sends c(n), c(n) is the signal, v w is the Gaussian white noise of the secret user, β is the reflection coefficient of normalized c, the range is greater than 0 and less than 1, y w is the signal received by the hidden user, h bw is the transmission channel from the backscatter device area to the hidden user, h hw is the transmission channel from the backscatter device area to the hidden user W, h sw is the transmission channel from the base station to the hidden user, h ew It is the transmission channel from the enhanced main signal area to the hidden user.

[0020] Furthermore, the problem of maximizing the effective concealment rate under the condition of imperfect CSI is expressed by the following formula:

[0021]

[0022] stξ * ≥1-ε

[0023]

[0024] R+N=G

[0025] in, For public users 1 The probability of outage when decoding the signal in the backscatter device area, R 1 For base S and public user U 1 The link's preset transmission rate, ξ * is the minimum detection error probability, ε is the hidden constraint threshold, For public users 2 The probability of interruption when decoding the base station sending to itself, For public users 1 The interruption probability when decoding the base station sends to itself, δth1 and δ th2 are reliability constraint thresholds, ξ * =P FA +P MD , and are the false alarm probability and missed detection probability, respectively, 0 and D 1 are the binary decisions of hidden users, respectively.

[0026] Furthermore, the public user U 2 The interruption probability when decoding the base station to send to itself is expressed as follows:

[0027]

[0028] in, For public users 2 The signal-to-interference-to-noise ratio when decoding the information sent by the base station to itself, K and I are the complexity-accuracy trade-off parameters, δ i To calculate the intermediate value, γ is the gamma function, a 2 is the power factor, a′ is the calculated intermediate value, ψ 1 To calculate the median value, b 2 is the middle value, ψ 2 To calculate the intermediate value, Γ is the gamma function, γ 2T is the middle value, From base station to public user U 1 The variance of the transmission channel, R 2 are preset parameters.

[0029] Furthermore, the public user U 1 The interruption probability when decoding the base station to send to itself is expressed as follows:

[0030]

[0031] in, For public users 1 The decoded base station sends the data to the public user U 2 The signal-to-interference-to-noise ratio of information, γ 1T is the middle value, R 1 For base S and public user U 1 The link's preset transmission rate, For public users 1The signal-to-interference-and-noise ratio when decoding information sent by the base station to itself.

[0032] Furthermore, the public user U 1 The probability of outage when decoding a signal in the backscatter device area is given by the following formula:

[0033]

[0034] in, For public users 1 The decoded base station sends the data to the public user U 2 The signal-to-interference-noise ratio of the information, γ bT To calculate the intermediate value, R bd are preset parameters.

[0035] Furthermore, the step three specifically includes:

[0036] The effective concealment rate maximization problem is divided into the first sub-problem and the second sub-problem to facilitate the derivation of the optimal result;

[0037] Alternately solve the first subproblem and the second subproblem until the iteration difference is less than the set value or the maximum number of iterations is reached, and output the optimization result value;

[0038] The first sub-problem involves optimizing the number of reflective elements in the backscatter device area for a given power factor, as expressed by the following formula:

[0039]

[0040] R+N=G,

[0041] in, For public users 1 The probability of outage when decoding the signal in the backscatter device area, R 1 For base S and public user U 1 The link's preset transmission rate, δ th1 and δ th2 are reliability constraint thresholds, For public users 2 The probability of interruption when decoding the base station sending to itself, For public users 1 The outage probability when decoding a base station sending to itself.

[0042] The second sub-problem involves optimizing the power factor given the number of reflective elements in the optimal backscatter device area, as expressed by the following formula:

[0043]

[0044] stξ * ≥1-ε,

[0045] Among them, ξ * is the minimum detection error probability, and ε is the hidden constraint threshold.

[0046] Beneficial effects of the present invention:

[0047] The present invention uses RIS for signal redirection and combines AmBC to achieve directional beamforming, enhances the signal strength of the legitimate receiving end, and uses an alternating optimization scheme to jointly optimize the power factor and the number of reflective elements in the backscattering device area to maximize the model ECR. Compared with the traditional NOMA network, the present invention can significantly improve spectrum efficiency, security and concealment, reduce energy consumption and operating costs, and can be widely used in scenarios with high communication security requirements such as government and finance. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of a NOMA network covert communication model based on RIS and AmBC provided in an embodiment of the present invention.

[0049] Figure 2 A flowchart of a NOMA network covert communication method based on RIS and AmBC provided in an embodiment of the present invention.

[0050] Figure 3 The maximum ECR and P provided by the embodiment of the present invention max Schematic diagram of the relationship.

[0051] Figure 4 Different P provided by the embodiment of the present invention max , schematic diagram of the model energy efficiency comparison under G and α. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] Example 1

[0054] like Figure 1 and Figure 2 As shown, a NOMA network covert communication method based on RIS and AmBC includes:

[0055] S101: Construct a NOMA network communication model based on smart reflective surfaces and environmental backscatter communication.

[0056] Specifically, the NOMA network communication model includes a base station S, an intelligent reflecting surface (IRS), a hidden user W and two public users U. 1 and U 2 .

[0057] The intelligent reflective surface is divided into two areas, namely the backscatter device (BD) area and the enhanced main (EP) signal area, to assist the base station S with the hidden user W and the public user U. 1 and U 2 For communication, the RIS includes G reflective elements, and the BD and EP areas are equipped with R and N reflective elements respectively, satisfying R+N=G.

[0058] Secondly, artificial noise is injected at the base station S (keeping incomplete interference elimination), and the superposition information at the base station S can be expressed as:

[0059]

[0060] Among them, s is the superposition information of the base station, s 1 and 2 The base station sends the following to the public user U: 1 and U 2 Information, j is the interference signal, satisfying P 1 =a 1 P s and P 2 =a 2 P s To send to public user U 1 and U 2 Power, P s is the total transmission power of the base station, P j =a 3 P s is the transmission power of interference information, a 1 、a 2 and a 3 are the corresponding power factors respectively, and set a 1 +a 2 +a 3 =1, and a 2 ≥a 1 .

[0061] Secondly, the elements in the BD area of ​​RIS backscatter the signal c of RIS through the signal sent by the base station S, and the elements in the EP area only need to reflect the signal from the base station S. For the EP area, it is assumed that all elements can completely reflect the signal from S. Therefore, in U 1 and U 2 The signals received at are written as:

[0062]

[0063] in, and have mean zero and variance respectively. and Gaussian white noise, y 1 and 2 Public user U 1 and public user U 2 The received signal, φ r and φ n are the phase shift of the rth reflective element in the backscattering device area and the phase shift of the nth reflective element in the enhanced main signal area, respectively. h sb is the transmission channel from the base station to the backscatter device area, From the backscatter device area to the public user U 1 The transmission channel, h se is the transmission channel from the base station S to the enhanced main signal area, To enhance the main signal area to the public user U 2 Transmission channel, c is the signal of the backscattering device area, and Base station to public user U 1 and U 2 transmission channel.

[0064] Finally, the signals received by hidden user W are:

[0065]

[0066] in, For the backscatter device area, c(n) is not sent. The backscatter device area sends c(n), c(n) is the signal, v w is the Gaussian white noise of the secret user, β is the reflection coefficient of normalized c, the range is greater than 0 and less than 1, y w is the signal received by the hidden user, h bw is the transmission channel from the backscatter device area to the hidden user, h hw is the transmission channel from the backscatter device area to the hidden user W, h swis the transmission channel from the base station to the hidden user, h ew It is the transmission channel from the enhanced main signal area to the hidden user.

[0067] S102: Based on the NOMA network communication model, the effective concealment rate maximization problem is established under imperfect CSI conditions.

[0068] S103: Solve the problem of maximizing the effective concealment rate, and obtain the corresponding optimal NOMA network communication model under the condition of maximum effective concealment rate.

[0069] S104: Complete covert communication according to the optimal NOMA network communication model.

[0070] The present invention constructs a NOMA network communication model based on RIS and AmBC, and establishes an effective concealment rate maximization problem under imperfect CSI conditions. The model is optimized according to the effective concealment rate maximization problem to obtain the optimal model. The present invention can balance the optimization configuration, signal detection and concealment performance of RIS, significantly improve spectrum efficiency, security and concealment, reduce energy consumption and operating costs, and can be widely used in scenarios with high communication security requirements such as government and finance.

[0071] Example 2

[0072] Based on the above embodiments, the present invention proposes an expression for establishing the effective concealment rate maximization problem under imperfect CSI conditions, specifically including:

[0073]

[0074] stξ * ≥1-ε

[0075]

[0076] R+N=G

[0077] in, For public users 1 The probability of outage when decoding the signal in the backscatter device area, R 1 For base S and public user U 1 The link's preset transmission rate, ξ * is the minimum detection error probability, ε is the hidden constraint threshold, For public users 2 The probability of interruption when decoding the base station sending to itself, For public users 1 The probability of interruption when decoding the base station sends to itself, δ th1 and δ th2 are reliability constraint thresholds, ξ * =PFA +P MD , and are the false alarm probability and missed detection probability, respectively, 0 and D 1 are the binary decisions of hidden users, respectively.

[0078]

[0079] in, For public users 2 The signal-to-interference-to-noise ratio when decoding the information sent by the base station to itself, K and I are the complexity-accuracy trade-off parameters, δ i To calculate the intermediate value, γ is the gamma function, a 2 is the power factor, a′ is the calculated intermediate value, ψ 1 To calculate the median value, b 2 is the middle value, ψ 2 To calculate the intermediate value, Γ is the gamma function, γ 2T is the middle value, From base station to public user U 1 The variance of the transmission channel, R 2 is the preset parameter, For public users 1 The decoded base station sends the data to the public user U 2 The signal-to-interference-noise ratio of the information, R 1 For base S and public user U 1 The link's preset transmission rate, For public users 1 The signal-to-interference-to-noise ratio when decoding the information sent by the base station to itself, For public users 1 The decoded base station sends the data to the public user U 2 The signal-to-interference-noise ratio of the information, γ bT To calculate the intermediate value, R bd are preset parameters.

[0080] Example 3

[0081] On the basis of the above embodiments, the present invention proposes a process for obtaining the corresponding optimal NOMA network communication model under the condition of maximum effective concealment rate, which specifically includes:

[0082] The optimization problem is decomposed into the first sub-problem W1 and the second sub-problem W2. The block coordinate descent (BCD) alternating optimization scheme is used to solve the power factor and the number of reflective elements in the backscattering device area until convergence to determine the optimal solution of the NOMA network communication model, and the optimal power factor and the number of reflective elements in the backscattering device area are output to maximize the ECR.

[0083] The first sub-problem W1 is to optimize the number of reflective elements R in the backscattering device area given the power factor. The expression is as follows:

[0084]

[0085] R+N=G,

[0086] The second sub-problem W2 is to optimize the power factor given the number of reflective units in the optimal backscattering device area, which can be expressed as follows:

[0087]

[0088] stξ * ≥1-ε,

[0089] Then, the first subproblem and the second subproblem are solved alternately, the iteration value is updated, and the optimal power factor and the number of reflective elements in the backscattering device area are output to maximize the ECR of the model.

[0090] Among them, P FA The expression is as follows:

[0091]

[0092] P MD The expression is as follows:

[0093]

[0094] The expression of ξ can be expressed as:

[0095]

[0096]

[0097] μ 1 =Δ(a 2 +a 3 ) max

[0098] μ 2 =ΔP max

[0099] Among them, Δ is the calculated intermediate value, μ 1 To calculate the intermediate value, μ 1 =Δ(α 2 +α 3 ) max , μ 2 To calculate the intermediate value, μ 2 =ΔP max , v w The variance of τ is the detection threshold, P max is the maximum transmission power of base station S, Q 1 To calculate the median value,

[0100] In particular, the optimal detection threshold τ in the above formula * Not set in and when and When * As τ increases, it first decreases and then increases. Therefore, we can get When * =1-a 1 .

[0101] The closed expression for the outage probability is as follows:

[0102] The receiver at the receiving end uses the SIC scheme to decode the information, so the public user U at the receiving end 1 First decode the public user U 2 The public user U at the receiving end decodes the information of the signal in the backscattering device area. 2 , only the own information needs to be decoded.

[0103] U 1 The signal-to-interference plus noise ratio (SINR) when decoding the corresponding information can be shown as follows:

[0104] U 1 In decoding public user U 2 The SINR when receiving the information is as follows:

[0105] U 1 In decoding public user U 2 The SINR when receiving the information is as follows:

[0106]

[0107] where ρ∈[0, 1] is the imperfect interference cancellation coefficient, is the power split factor, Q 2 and Q 3 Calculate the intermediate values ​​for .

[0108] U 1 Signal-to-interference-and-noise ratio (SINR) when decoding own information It is expressed as follows:

[0109]

[0110] U 1 Signal-to-Interference-to-Noise Ratio (SINR) when decoding signal information in the backscatter device area It is expressed as follows:

[0111]

[0112] U 2 Signal-to-interference-and-noise ratio (SINR) when decoding the corresponding information It can be expressed as:

[0113]

[0114] In particular, to ensure that 1 and U 2 To successfully decode a message, the message transmission rate must exceed the respective threshold. If the message cannot be successfully decoded, an interruption occurs.

[0115] U 2 In decoding S 2 The interruption probability can be expressed as:

[0116]

[0117] U 1 Decoding S 1 The outage probability can be expressed as:

[0118]

[0119] Further calculation, when hour, The expression is as follows:

[0120]

[0121] Among them, q 1 To calculate the median value, ω 1 To calculate the intermediate value ω 1 =α 2 -γ2T (α 1 +ρα 3 ), D v (z) represents the parabolic cylindrical function, which is an operational function, b 1 for λ su1 From base station S to U 1 The wireless channel has complex Gaussian fading, E is the calculated intermediate value,

[0122] when hour, The expression is as follows:

[0123]

[0124] U 1 The outage probability when decoding the signal in the backscatter device area can be expressed as:

[0125]

[0126] Further calculation, when hour, The expression is as follows:

[0127]

[0128] when hour, The expression is as follows:

[0129]

[0130] In particular, in the above formula

[0131] ω 1 =a 2 -γ 2T (a 1 +ρa 3 ),ω 2 =a 1 -γ 1T ρa 3 .

[0132] Furthermore, 1 to 7 The solution process is as follows:

[0133]

[0134] Further, among them D v(z) represents the parabolic cylindrical function, W a，b (·) is the Whittaker function, I and K represent different complexity-accuracy trade-off parameters, ψ 1 to 7 All are calculated intermediate values.

[0135] Preferably, if Figure 3 and Figure 4 As shown, the present invention also provides the maximum ECR and P of the NOMA network communication model max Relationship diagram and different P max , G and α are used to verify the effect of the present invention.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A NOMA network covert communication method based on RIS and AmBC, characterized in that: include: Step 1: Construct a NOMA network communication model based on smart reflective surfaces and environmental backscattering communication; Step 2: According to the NOMA network communication model, the effective concealment rate maximization problem is established under the condition of imperfect CSI; Step 3: Solve the problem of maximizing the effective concealment rate, and obtain the corresponding optimal NOMA network communication model under the condition of maximum effective concealment rate; Step 4: Complete covert communication based on the optimal NOMA network communication model.

2. According to claim 1, a NOMA network covert communication method based on RIS and AmBC is characterized in that: The NOMA network communication model includes a base station S, a smart reflective surface, a hidden user W and two public users U1 and U2; The intelligent reflective surface includes a backscattering device area and an enhanced main signal area; The backscattering device area includes R reflective elements, and the enhanced main signal area includes N reflective elements; wherein R+N=G, G is the number of reflective elements of the smart reflective surface, R is the number of reflective elements in the backscattering device area, and N is the number of reflective elements in the enhanced main signal area.

3. According to claim 2, a NOMA network covert communication method based on RIS and AmBC is characterized in that: The NOMA network communication model is expressed as follows: Among them, s is the superposition information of the base station, s1 and s2 are the information sent by the base station to public users U1 and U2 respectively, and s j is the interference signal, satisfying P1=a1P s and P2 = a2P s is the power sent to public users U1 and U2, P s is the total transmission power of the base station, P j =a3P s is the transmission power of the interference information, a1, a2 and a3 are the corresponding power factors, set a1+a2+a3=1, and a2≥a1, and have mean zero and variance respectively. and Gaussian white noise, y1 and y2 are the signals received by public user U1 and public user U2 respectively, φ r and φ n are the phase shift of the rth reflective element in the backscattering device area and the phase shift of the nth reflective element in the enhanced main signal area, respectively. h sb is the transmission channel from the base station to the backscatter device area, is the transmission channel from the backscatter device area to the public user U1, h se is the transmission channel from the base station S to the enhanced main signal area, is the transmission channel from the enhanced main signal area to the public user U2, c is the signal of the backscattering device area, and are the transmission channels from the base station to public users U1 and U2 respectively, For the backscatter device area, c(n) is not sent. The backscatter device area sends c(n), c(n) is the signal, v w is the Gaussian white noise of the secret user, β is the reflection coefficient of normalized c, the range is greater than 0 and less than 1, y w is the signal received by the hidden user, h bw is the transmission channel from the backscatter device area to the hidden user, h hw is the transmission channel from the backscatter device area to the hidden user W, h sw is the transmission channel from the base station to the hidden user, h ew It is the transmission channel from the enhanced main signal area to the hidden user.

4. According to claim 2, a NOMA network covert communication method based on RIS and AmBC is characterized in that: The problem of maximizing the effective concealment rate under the condition of imperfect CSI is expressed as follows: in, is the interruption probability of public user U1 when decoding the signal in the backscattering device area, R1 is the preset transmission rate of the link between base S and public user U1, ξ * is the minimum detection error probability, ε is the hidden constraint threshold, The outage probability when the public user U2 decodes the base station's transmission to itself, is the outage probability of public user U1 when decoding the base station’s message to itself, δ th1 and δ th2 are reliability constraint thresholds, ξ * =P FA +P MD , and are the false alarm probability and missed detection probability respectively, and D0 and D1 are the binary decisions of the hidden users respectively.

5. According to claim 4, a NOMA network covert communication method based on RIS and AmBC is characterized in that: The interruption probability of the public user U2 when decoding the data sent by the base station to itself is expressed by the following formula: in, is the signal-to-interference-noise ratio when public user U2 decodes the information sent by the base station to itself, K and I are the complexity-accuracy trade-off parameters, δ i To calculate the intermediate value, γ is the gamma function, a2 is the power factor, a′ is the calculated intermediate value, ψ1 is the calculated intermediate value, b2 is the middle value, ψ2 is the calculated intermediate value, Γ is the gamma function, γ 2T is the middle value, is the variance of the transmission channel from the base station to the public user U1, and R2 is a preset parameter.

6. According to claim 5, a NOMA network covert communication method based on RIS and AmBC is characterized in that: The interruption probability of the public user U1 when decoding the data sent by the base station to itself is expressed by the following formula: in, is the signal-to-interference-noise ratio when public user U1 decodes the information sent by the base station to public user U2, γ 1T is the middle value, R1 is the preset transmission rate of the link between the base S and the public user U1. The signal to interference and noise ratio when public user U1 decodes the information sent by the base station to itself.

7. According to claim 6, a NOMA network covert communication method based on RIS and AmBC is characterized in that: The outage probability when public user U1 decodes the signal in the backscattering device area is expressed as follows: in, The signal-to-interference-noise ratio when public user U1 decodes the information sent by the base station to public user U2, γ bT To calculate the intermediate value, R bd are preset parameters.

8. According to claim 4, a NOMA network covert communication method based on RIS and AmBC is characterized in that: The step three specifically includes: The effective concealment rate maximization problem is divided into the first sub-problem and the second sub-problem; Alternately solve the first subproblem and the second subproblem until the iteration difference is less than the set value or the maximum number of iterations is reached, and output the optimization result value; The first sub-problem involves optimizing the number of reflective elements in the backscatter device area for a given power factor, as expressed by the following formula: R+N=G, in, is the interruption probability of public user U1 when decoding the signal in the backscattering device area, R1 is the preset transmission rate of the link between base S and public user U1, δ th1 and δ th2 are reliability constraint thresholds, The outage probability when the public user U2 decodes the base station's transmission to itself, The outage probability for public user U1 when decoding the base station sending to itself. The second sub-problem involves optimizing the power factor given the number of reflective elements in the optimal backscatter device area, as expressed by the following formula: stx * ≥1-e, Among them, ξ * is the minimum detection error probability, and ε is the hidden constraint threshold.

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