Security transmission method for relay selection based cooperative non-orthogonal multiple access system

Abstract

The application discloses a security transmission method of a relay selection based cooperative non-orthogonal multiple access system, which is composed of the following steps: constructing a transmission signal model, constructing a channel error model, selecting an optimal relay, determining a connection interruption probability and determining a security interruption probability. Since the application adopts the relay selection based cooperative non-orthogonal multiple access system, a reasonable transmission signal model is established, a relay selection method is provided, and the security transmission performance of the system is ensured by using limited spectrum resources. Compared with the prior art, the security interruption probability of near users and far users in the system is effectively reduced. The application has the advantages of simple transmission method, easy implementation, reasonable relay selection, good security performance and the like.

Description

Technical Field

[0001] This invention belongs to the field of communication security technology, specifically relating to the secure information transmission of relay selection and jammer systems. Background Technology

[0002] Relay cooperative communication has proven to be an effective solution for extending transmission range, allowing one or more relays to be configured between the source and destination nodes. With the help of relays, network coverage can be expanded, and cell capacity can be increased to ensure channel capacity and link reliability.

[0003] Due to the broadcast nature of wireless channels, secure information transmission becomes particularly important. Compared to traditional encryption methods, physical layer security utilizes the physical characteristics of wireless channels, eliminating the need for traditional encryption algorithms and thus ensuring communication security. Even in the presence of eavesdroppers, physical layer security can maintain the confidentiality and security of communication through artificial noise-assisted transmission strategies.

[0004] However, most existing work assumes that the channel state information is perfect. In practical applications, channel uncertainty exists due to estimation errors and feedback delays. Currently, some research focuses on the secure transmission of information under imperfect channel state information and has proposed some excellent jamming strategies. However, the issues of relay selection and secure transmission of information in jammer systems supporting imperfect channel state information have not yet been studied.

[0005] In the field of relay selection and jammer system technology for imperfect channel state information, a pressing technical problem that needs to be solved is to provide a secure transmission method for cooperative non-orthogonal multiple access systems based on relay selection. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and to propose a secure transmission method for a cooperative nonorthogonal multiple access system based on relay selection that is simple to transmit, easy to implement, and has good confidentiality performance.

[0007] The technical solution adopted to solve the above technical problems consists of the following steps:

[0008] (1) Constructing the transmission signal model

[0009] The transmission signal model consists of one source node S and M relay nodes R. k The relay consists of one jammer node J, one near user node NU, one far user node FU, and one external eavesdropping node Eve, k∈{1,2,...,M}, where M represents the number of relay nodes, and M is a finite positive integer. The relays are located at the source node S and each relay node R... kA single antenna is set on the near user node NU, the far user node FU, and the external eavesdropping node Eve to form a transmission signal model;

[0010] (2) Constructing a channel error model

[0011] Determine the distance from source node S to relay node R according to formula (1). k Channel coefficients

[0012]

[0013] in, This is the channel estimation error coefficient, with a value ranging from 0 to 0.005. It is the distance from the source node S to the relay node R estimated before each time slot using the pilot-assisted method. k Channel coefficient, with values ​​of It is the source node S and the relay node R k The channel fading coefficient between them is set to 1. It is the source node S and the relay node R k The distance between them is 1m, and η is the path loss exponent, with a value of 2. This is the channel estimation error, with a value of 0.005.

[0014] The channel coefficient h of the channel from source node S to interfering node J is determined according to equation (2). SJ :

[0015]

[0016] Where, ε SJ This is the channel estimation error coefficient, with a value ranging from 0 to 0.005. These are the channel coefficients from the source node S to the interfering node J estimated before each time slot using the pilot-assisted method, and their values ​​are... λ SJ It is the channel fading coefficient between the source node S and the interfering node J, with a value of 1, d SJ This is the distance between the source node S and the jammer node J, with a value of 5m.

[0017] Determine the relay node R according to formula (3). k Channel coefficients of the channel to the far user node (FU)

[0018]

[0019] in, This is the channel estimation error coefficient, with a value ranging from 0 to 0.005. The relay node R is estimated before each time slot using the pilot-assisted method.k The channel coefficients to the far user node FU are set to a value of It is relay node R k The channel fading coefficient between the user node (FU) and the remote user node (FU) is set to 1. It is relay node R k The distance to the remote user node FU is set to 2m;

[0020] Determine the relay node R according to formula (4). k Channel coefficients of the NU channel to the nearest user node

[0021]

[0022] in, This is the channel estimation error coefficient, with a value ranging from 0 to 0.005. The relay node R is estimated before each time slot using the pilot-assisted method. k The channel coefficients to the nearest user node (NU) are set to a value of It is relay node R k The channel fading coefficient to the nearest user node (NU) is set to 1. It is relay node R k The distance to the nearest user node (NU) is set to 1m.

[0023] Determine the relay node R according to formula (5). k Channel coefficients of the channel to the external eavesdropping node Eve

[0024]

[0025] in, This is the channel estimation error coefficient, with a value ranging from 0 to 0.005. The relay node R is estimated before each time slot using the pilot-assisted method. k The channel coefficient of Eve to the external eavesdropping node is set to a value of It is relay node R k The channel fading coefficient between Eve and the external eavesdropping node is set to 1. It is relay node R k The distance to the external eavesdropping node Eve is set to 1m.

[0026] The channel coefficient h of the channel from jammer node J to external eavesdropping node Eve is determined according to equation (6). JE :

[0027]

[0028] Where, εJE This is the channel estimation error coefficient, with a value ranging from 0 to 0.005. These are the channel coefficients from jammer node J to external eavesdropping node Eve, estimated before each time slot using the pilot-assisted method, with values ​​ranging from 1 to 2. λ JE This is the channel fading coefficient between jammer node J and external eavesdropping node Eve, with a value of 1, d JE This is the distance between jammer node J and the external eavesdropping node Eve, with a value of 2m.

[0029] (3) Select the optimal relay

[0030] Select the optimal relay R according to formula (7). k* :

[0031]

[0032] Where Δ = {1, 2, ..., M};

[0033] (4) Determine the probability of connection interruption

[0034] The connection interruption probability of the remote user node FU is determined according to equation (8).

[0035]

[0036] in, It is a relay node The received signal-to-noise ratio (SNR) when decoding the signal transmitted by the remote user node FU x2, γ F,2 It is the received signal-to-noise ratio (SNR) when the remote user node performs FU decoding x2, ρ s ρ is the transmit signal-to-noise ratio of the source node S, with a value ranging from 0 to 50 dB. r It is the optimal relay R k* The transmit signal-to-noise ratio is set to 0–50 dB. It is relay node R k* The signal-to-noise ratio threshold for decoding x2 ranges from 0 to 3 dB. a1 is the signal-to-noise ratio threshold for decoding x2 at the far user node FU, with a value of 0 to 3 dB; a2 is the power allocation factor of the far user node FU, with a value of 0.76; a1 is the power allocation factor of the near user node NU, with a value of 0.24.

[0037] (5) Determine the probability of security breach

[0038] The probability of confidentiality interruption of the remote user node FU is determined according to equation (11).

[0039]

[0040] in, α is the signal-to-noise ratio threshold of the external eavesdropping node Eve decoder x2, with a value of 0 to 1 dB; α is the transmission time allocation factor, with a value of 0.5; and β is the energy conversion efficiency, with a value of 0.8.

[0041] In step (2) of the present invention, the said ε SJ , ε JE It is the channel estimation error coefficient. ε SJ , ε JE The value ranges from 0 to 0.005.

[0042] In formula (7) of step (3) of the present invention, M is the number of relay nodes, and M takes a value of 1 to 6. For the selected optimal relay node, k * The value ranges from 1 to 6.

[0043] In equation (9) of step (4) of the present invention, a2 is the power allocation factor of the far user node FU, where a2 takes the value of 0.76, and a1 is the power allocation factor of the near user node NU, where a1 takes the value of 0.24. It is a relay node The received signal-to-noise ratio (SNR) when decoding the signal transmitted by the remote user node FU x2, γ F,2 It is the received signal-to-noise ratio when the remote user node performs FU decoding x2; ρ s ρ is the transmit signal-to-noise ratio of the source node S, with a value ranging from 0 to 50 dB. r It is the optimal relay R k* The transmit signal-to-noise ratio is set to 0–50 dB. It is a relay node The signal-to-noise ratio threshold for decoding x2 is 0 to 3 dB; in equation (10), the aforementioned It is the signal-to-noise ratio threshold for FU decoding x2 at the remote user node, with a value ranging from 0 to 3dB.

[0044] In equation (11) of step (5) of the present invention, α is the transmission time allocation factor, where α takes the value of 0.5, and β is the energy conversion efficiency, where β takes the value of 0.8. It is the signal-to-noise ratio threshold of the external eavesdropping node Eve decoder x2, with a value ranging from 0 to 1 dB.

[0045] Because this invention employs a relay selection and jammer system, establishes a reasonable transmission signal model, and proposes an information security transmission method, it reduces the probability of security interruption by utilizing limited spectrum resources. Compared with existing technologies, at relay node R...k When the number of relays M is 3 and the signal-to-noise ratio (SNR) is 10–50 dB, the connection interruption probability of the remote user FU node decreases by 0.080708–0.1005581, and the security interruption probability of the remote user FU node decreases by 0.0016–0.2599. As the number of relays or the transmit SNR increases, the system connection interruption probability decreases; as the transmit SNR increases, the security interruption probability also decreases. This invention has advantages such as simple transmission method, ease of implementation, and good security performance, and can be used in the field of communication security technology. Attached Figure Description

[0046] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention.

[0047] Figure 2 This is the simulation curve of Embodiment 1 of the present invention. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments.

[0049] Example 1

[0050] exist Figure 1 In this embodiment, the secure transmission method for a cooperative non-orthogonal multiple access system based on relay selection consists of the following steps:

[0051] (1) Constructing the transmission signal model

[0052] The transmission signal model consists of one source node S and M relay nodes R. k The relay consists of one jammer node J, one near user node NU, one far user node FU, and one external eavesdropping node Eve, k∈{1,2,...,M}, where M represents the number of relay nodes. M is a finite positive integer, and in this embodiment, M is 3. The relays are located at the source node S and each relay node R... k A single antenna is set on the near user node NU, the far user node FU, and the external eavesdropping node Eve to form a transmission signal model;

[0053] (2) Constructing a channel error model

[0054] Determine the distance from source node S to relay node R according to formula (1). k Channel coefficients

[0055]

[0056] in, This is the channel estimation error coefficient, with a value ranging from 0 to 0.005, as used in this embodiment. The value is 0.005. It is the distance from the source node S to the relay node R estimated before each time slot using the pilot-assisted method. k Channel coefficient, with values ​​of It is the source node S and the relay node R k The channel fading coefficient between them is set to 1. It is the source node S and the relay node R k The distance between them is 1m, and η is the path loss exponent, with a value of 2. This is the channel estimation error, with a value of 0.005.

[0057] The channel coefficient h of the channel from source node S to interfering node J is determined according to equation (2). SJ :

[0058]

[0059] Where, ε SJ This is the channel estimation error coefficient, with a value ranging from 0 to 0.005. In this embodiment, ε SJ The value is 0.005. These are the channel coefficients from the source node S to the interfering node J estimated before each time slot using the pilot-assisted method, and their values ​​are... λ SJ It is the channel fading coefficient between the source node S and the interfering node J, with a value of 1, d SJ This is the distance between the source node S and the jammer node J, with a value of 5m.

[0060] Determine the relay node R according to formula (3). k Channel coefficients of the channel to the far user node (FU)

[0061]

[0062] in, This is the channel estimation error coefficient, with a value ranging from 0 to 0.005, as used in this embodiment. The value is 0.005. The relay node R is estimated before each time slot using the pilot-assisted method. k The channel coefficients to the far user node FU are set to a value of It is relay node R k The channel fading coefficient between the user node (FU) and the remote user node (FU) is set to 1. It is relay node R k The distance to the remote user node FU is set to 2m;

[0063] Determine the relay node R according to formula (4). k Channel coefficients of the NU channel to the nearest user node

[0064]

[0065] in, This is the channel estimation error coefficient, with a value ranging from 0 to 0.005, as used in this embodiment. The value is 0.005. The relay node R is estimated before each time slot using the pilot-assisted method. k The channel coefficients to the nearest user node (NU) are set to a value of It is relay node R k The channel fading coefficient to the nearest user node (NU) is set to 1. It is relay node R k The distance to the nearest user node (NU) is set to 1m.

[0066] Determine the relay node R according to formula (5). k Channel coefficients of the channel to the external eavesdropping node Eve

[0067]

[0068] in, This is the channel estimation error coefficient, with a value ranging from 0 to 0.005, as used in this embodiment. The value is 0.005. The relay node R is estimated before each time slot using the pilot-assisted method. k The channel coefficient of Eve to the external eavesdropping node is set to a value of It is relay node R k The channel fading coefficient between Eve and the external eavesdropping node is set to 1. It is relay node R k The distance to the external eavesdropping node Eve is set to 1m.

[0069] The channel coefficient h of the channel from jammer node J to external eavesdropping node Eve is determined according to equation (6). JE :

[0070]

[0071] Where, ε JE This is the channel estimation error coefficient, with a value ranging from 0 to 0.005. In this embodiment, ε JE The value is 0.005. These are the channel coefficients from jammer node J to external eavesdropping node Eve, estimated before each time slot using the pilot-assisted method, with values ​​ranging from 1 to 2. λ JEThis is the channel fading coefficient between jammer node J and external eavesdropping node Eve, with a value of 1, d JE This is the distance between jammer node J and the external eavesdropping node Eve, with a value of 2m.

[0072] (3) Select the optimal relay

[0073] Select the optimal relay according to formula (7).

[0074]

[0075] Where Δ = {1, 2, ..., M};

[0076] (4) Determine the probability of connection interruption

[0077] The connection interruption probability of the remote user node FU is determined according to equation (8).

[0078]

[0079] in, It is a relay node The received signal-to-noise ratio (SNR) when decoding the signal transmitted by the remote user node FU x2, γ F,2 It is the received signal-to-noise ratio (SNR) when the remote user node performs FU decoding x2, ρ s ρ is the transmit signal-to-noise ratio of the source node S, with a value ranging from 0 to 50 dB. r It is the optimal relay The transmit signal-to-noise ratio is set to 0–50 dB. It is a relay node The signal-to-noise ratio threshold for decoding x2 ranges from 0 to 3 dB. This embodiment... The value is 3dB. This is the signal-to-noise ratio threshold for the remote user node FU decoding x2, with a value ranging from 0 to 3 dB. (This is the value used in this embodiment.) The value is 3dB, a2 is the power allocation factor of the far user node FU with a value of 0.76, and a1 is the power allocation factor of the near user node NU with a value of 0.24.

[0080] (5) Determine the probability of security breach

[0081] The probability of confidentiality interruption of the remote user node FU is determined according to equation (11).

[0082]

[0083] in, This is the signal-to-noise ratio threshold value of the external eavesdropping node Eve decoder x2, with a value ranging from 0 to 1 dB. (This is the value used in this embodiment.) The value is 1dB, α is the transmission time allocation factor with a value of 0.5, and β is the energy conversion efficiency with a value of 0.8.

[0084] Example 2

[0085] The secure transmission method for a cooperative non-orthogonal multiple access system based on relay selection in this embodiment consists of the following steps:

[0086] (1) Constructing the transmission signal model

[0087] The transmission signal model consists of one source node S and M relay nodes R. k The system consists of one jammer node J, one near user node NU, one far user node FU, and one external eavesdropping node Eve, where k∈{1,2,...,M}, and M represents the number of relay nodes. M is a finite positive integer, and in this embodiment, M is 4. The relay nodes are located at the source node S and each relay node R... k A single antenna is set on the near user node NU, the far user node FU, and the external eavesdropping node Eve to form a transmission signal model;

[0088] (2) Constructing a channel error model

[0089] The steps are the same as in Example 1.

[0090] (3) Select the optimal relay

[0091] The steps are the same as in Example 1.

[0092] (4) Determine the probability of connection interruption

[0093] The connection interruption probability of the remote user node FU is determined according to equation (8).

[0094]

[0095] in, It is relay node R k* The received signal-to-noise ratio (SNR) when decoding the signal transmitted by the remote user node FU x2, γ F,2 It is the received signal-to-noise ratio (SNR) when the remote user node performs FU decoding x2, ρ s ρ is the transmit signal-to-noise ratio of the source node S, with a value ranging from 0 to 50 dB. r It is the optimal relay The transmit signal-to-noise ratio is set to 0–50 dB. It is a relay node The signal-to-noise ratio threshold for decoding x2 ranges from 0 to 3 dB. This embodiment... The value is 2dB. This is the signal-to-noise ratio threshold for the remote user node FU decoding x2, with a value ranging from 0 to 3 dB. (This is the value used in this embodiment.) The value is 2dB, a2 is the power allocation factor of the far user node FU with a value of 0.76, and a1 is the power allocation factor of the near user node NU with a value of 0.24.

[0096] (5) Determine the probability of security breach

[0097] The probability of confidentiality interruption of the remote user node FU is determined according to equation (11).

[0098]

[0099] in, This is the signal-to-noise ratio threshold value of the external eavesdropping node Eve decoder x2, with a value ranging from 0 to 1 dB. (This is the value used in this embodiment.) The value is 1dB, α is the transmission time allocation factor with a value of 0.5, and β is the energy conversion efficiency with a value of 0.7.

[0100] Example 3

[0101] The secure transmission method for a cooperative non-orthogonal multiple access system based on relay selection in this embodiment consists of the following steps:

[0102] (1) Constructing the transmission signal model

[0103] The transmission signal model consists of one source node S and M relay nodes R. k The system consists of one jammer node J, one near user node NU, one far user node FU, and one external eavesdropping node Eve, where k∈{1,2,...,M}, and M represents the number of relay nodes. M is a finite positive integer, and in this embodiment, M is 6. The relay nodes are located at the source node S and each relay node R... m A single antenna is set on the near user node NU, the far user node FU, and the external eavesdropping node Eve to form a transmission signal model;

[0104] (2) Constructing a channel error model

[0105] The steps are the same as in Example 1.

[0106] (3) Select the optimal relay

[0107] The steps are the same as in Example 1.

[0108] (4) Determine the probability of connection interruption

[0109] The connection interruption probability of the remote user node FU is determined according to equation (8).

[0110]

[0111] in, It is a relay node The received signal-to-noise ratio (SNR) when decoding the signal transmitted by the remote user node FU x2, γ F,2 It is the received signal-to-noise ratio (SNR) when the remote user node performs FU decoding x2, ρ s ρ is the transmit signal-to-noise ratio of the source node S, with a value ranging from 0 to 50 dB. r It is the optimal relay The transmit signal-to-noise ratio is set to 0–50 dB. It is a relay node The signal-to-noise ratio threshold for decoding x2 ranges from 0 to 3 dB. This embodiment... The value is 1dB. This is the signal-to-noise ratio threshold for the remote user node FU decoding x2, with a value ranging from 0 to 3 dB. (This is the value used in this embodiment.) The value is 1dB, a2 is the power allocation factor of the far user node FU with a value of 0.76, and a1 is the power allocation factor of the near user node NU with a value of 0.24.

[0112] (5) Determine the probability of security breach

[0113] The probability of confidentiality interruption of the remote user node FU is determined according to equation (11).

[0114]

[0115] in, This is the signal-to-noise ratio threshold value of the external eavesdropping node Eve decoder x2, with a value ranging from 0 to 1 dB. (This is the value used in this embodiment.) The value is 0.5dB, α is the transmission time allocation factor with a value of 0.5, and β is the energy conversion efficiency with a value of 0.6.

[0116] To verify the beneficial effects of the present invention, the inventors conducted a comparative simulation experiment using the secure transmission method for a cooperative non-orthogonal multiple access system based on relay selection according to Embodiment 1 of the present invention (hereinafter referred to as the Embodiment 1 method) and a method without cooperative interference (hereinafter referred to as the comparative experimental method). The experimental results are shown in […]. Figure 2 . Figure 2 The impact of different transmission signal-to-noise ratios on the probability of security breach. The impact. By Figure 2 As can be seen, compared with the comparative experimental method, the method in Example 1 reduced the probability of confidentiality interruption of the remote user node FU by 0.0016 to 0.2599 when the signal-to-noise ratio was 10 to 50 dB.

Claims

1. A secure transmission method for a cooperative non-orthogonal multiple access system based on relay selection, characterized in that... It consists of the following steps: (1) Constructing a transmission signal model The transmission signal model consists of one source node S and... relay nodes 1 jammer node It consists of one near user node (NU), one far user node (FU), and one external eavesdropping node (Eve). , Indicates the number of relay nodes. Given a finite number of positive integers, in the source node S, each relay node... A single antenna is set on the near user node NU, the far user node FU, and the external eavesdropping node Eve to form a transmission signal model; (2) Constructing a channel error model Determine the distance from the source node S to the relay node according to formula (1). Channel coefficients : （1） in, This is the channel estimation error coefficient, with a value of [value missing]. , It is the source node S to relay node estimated before each time slot using the pilot-assisted method. Channel coefficient, with values ​​of , It is the source node S and the relay node The channel fading coefficient between them is set to 1. It is the source node S and the relay node The distance between them is 1m. The path loss exponent has a value of 2. This is the channel estimation error, with a value of 0.

005. Determine the distance from the source node S to the interfering node according to formula (2). Channel coefficients : （2） in, This is the channel estimation error coefficient, with a value of [value missing]. , The distance from the source node S to the jammer node is estimated before each time slot using the pilot-assisted method. Channel coefficient, with values ​​of , It is the source node S and the interfering node The channel fading coefficient between them is set to 1. It is the source node S and the interfering node The distance between them is 5m; Determine the relay node according to formula (3). Channel coefficients of the channel to the far user node (FU) : （3） in, This is the channel estimation error coefficient, with a value of [value missing]. , The relay node is estimated before each time slot using the pilot-assisted method. The channel coefficients to the far user node FU are set to a value of , It is a relay node The channel fading coefficient between the user node (FU) and the remote user node (FU) is set to 1. It is a relay node The distance to the remote user node FU is set to 2m; Determine the relay node according to formula (4). Channel coefficients of the NU channel to the nearest user node : （4） in, This is the channel estimation error coefficient, with a value of [value missing]. , The relay node is estimated before each time slot using the pilot-assisted method. The channel coefficients to the nearest user node (NU) are set to a value of , It is a relay node The channel fading coefficient to the nearest user node (NU) is set to 1. It is a relay node The distance to the nearest user node (NU) is set to 1m. Determine the relay node according to formula (5). Channel coefficients of the channel to the external eavesdropping node Eve : （5） in, This is the channel estimation error coefficient, with a value of [value missing]. , The relay node is estimated before each time slot using the pilot-assisted method. The channel coefficient of Eve to the external eavesdropping node is set to a value of , It is a relay node The channel fading coefficient between Eve and the external eavesdropping node is set to 1. It is a relay node The distance to the external eavesdropping node Eve is set to 1m. Determine the jammer node according to formula (6). Channel coefficients of the channel to the external eavesdropping node Eve : （6） in, This is the channel estimation error coefficient, with a value of [value missing]. , The jammer node is estimated before each time slot using the pilot-assisted method. The channel coefficient of Eve to the external eavesdropping node is set to a value of , It is an interfering node The channel fading coefficient between Eve and the external eavesdropping node is set to 1. It is an interfering node The distance to the external eavesdropping node Eve is set to 2m. (3) Select the optimal relay Select the optimal relay according to formula (7). : （7） in, , This indicates the selection of the independent variable that corresponds to the maximum value of the expression within the parentheses; (4) Determine the probability of connection interruption The connection interruption probability of the remote user node FU is determined according to equation (8). : （8） （9） （10） in, Indicates the probability of the event within the parentheses occurring. It is a relay node Decoding the signal sent by the remote user node FU The received signal-to-noise ratio at that time, It is a remote user node FU decoding The received signal-to-noise ratio at that time, It is the transmit signal-to-noise ratio of the source node S, and its value is... , It is the optimal relay The transmit signal-to-noise ratio is set to a value of , It is a relay node decoding The signal-to-noise ratio threshold value is set to a value of , It is a remote user node FU decoding The signal-to-noise ratio threshold value is set to a value of , This is the power allocation factor for the remote user node (FU), with a value of 0.

76. It is the power allocation factor for the nearest user node (NU), with a value of 0.24; (5) Determine the probability of security breach The probability of confidentiality interruption of the remote user node FU is determined according to equation (11). : （11） in, It is an external eavesdropping node, Eve, that decodes. The signal-to-noise ratio threshold value is set to a value of , This is the transmission time allocation factor, with a value of 0.

5. It is the energy conversion efficiency, with a value of 0.

8.

2. The secure transmission method for a cooperative non-orthogonal multiple access system based on relay selection according to claim 1, characterized in that: In step (3) of equation (7), the stated This represents the number of relay nodes. Values , The optimal relay node is selected. The value is .

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