Secure transmission method of cooperative non-orthogonal multiple access system based on relay selection

Abstract

The invention discloses a secure transmission method of a cooperative non-orthogonal multiple access system based on relay selection. The secure transmission method comprises the steps of constructing a transmission signal model, constructing a channel error model, selecting an optimal relay, determining a connection interruption probability and determining a confidential interruption probability. Due to the fact that the cooperative non-orthogonal multiple access system of relay selection is adopted, a reasonable transmission signal model is established, a relay selection method is provided, limited spectrum resources are utilized, and the safe transmission performance of the system is guaranteed, compared with the prior art, the confidential interruption probability of near users and far users in the system is effectively reduced. The method has the advantages of being simple in transmission method, easy to implement, reasonable in relay selection, good in secrecy performance and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of communication security, and particularly relates to the secure transmission of information in a relay selection and jammer system. Background Art

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

[0003] Due to the broadcast nature of the wireless channel, the secure transmission of information becomes particularly important. Compared with traditional encryption methods, physical layer security utilizes the physical characteristics of the wireless channel and does not require traditional encryption algorithms, thus ensuring the security of communication. Even in the presence of eavesdroppers, physical layer security can ensure the confidentiality and security of communication through artificial noise assisted transmission strategies.

[0004] However, most existing works assume that the channel state information is perfect. In practical applications, due to the influence of estimation errors and feedback delays, the channel is uncertain. At present, some research is dedicated to studying the problem of secure information transmission under imperfect channel state information, and some excellent interference strategies have also been proposed, but the problem of secure information transmission in a relay selection and jammer system that supports imperfect channel state information has not been studied.

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

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned disadvantages of the prior art and propose a secure transmission method for a cooperative non-orthogonal multiple access system based on relay selection, which has a simple transmission method, is easy to implement, and has good confidentiality performance.

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

[0008] (1) Construct a transmission signal model

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

[0010] (2) Construct a channel error model

[0011] Determine the channel coefficient of the channel from the source node S to the relay node R according to Equation (1) k The channel coefficient of the channel

[0012]

[0013] Among them, is the channel estimation error coefficient, with a value range of 0 to 0.005, is the channel coefficient of the channel from the source node S to the relay node R estimated before each time slot according to the pilot-assisted method k The channel coefficient, with a value range of is the channel fading coefficient between the source node S and the relay node R k with a value of 1, is the distance between the source node S and the relay node R k with a value of 1m, η is the path loss exponent, with a value of 2, is the channel estimation error, with a value of 0.005;

[0014] Determine the channel coefficient h of the channel from the source node S to the jammer node J according to Equation (2) SJ :

[0015]

[0016] Among them, ε SJ is the channel estimation error coefficient, with a value range of 0 to 0.005, is the channel coefficient of the channel from the source node S to the jammer node J estimated before each time slot according to the pilot-assisted method, with a value of λ SJ is the channel fading coefficient between the source node S and the jammer node J, with a value of 1, d SJ is the distance between the source node S and the jammer node J, with a value of 5m;

[0017] Determine the channel coefficient of the channel from the relay node R k to the far user node FU according to Equation (3)

[0018]

[0019] Among them, is the channel estimation error coefficient, with a value range of 0 to 0.005, is the relay node R estimated before each time slot according to the pilot-assisted methodk Channel coefficient from the relay node R to the far user node FU, with a value of is the relay node R k Channel fading coefficient between the relay node R and the far user node FU, with a value of 1, is the relay node R k Distance between the relay node R and the far user node FU, with a value of 2m;

[0020] Determine the relay node R according to Equation (4) k Channel coefficient of the channel from the relay node R to the near user node NU

[0021]

[0022] where is the channel estimation error coefficient, with a value range of 0 to 0.005, is the channel coefficient of the channel from the relay node R to the near user node NU estimated by the pilot-assisted method before each time slot, with a value of k Channel coefficient from the relay node R to the near user node NU, with a value of is the relay node R k Channel fading coefficient between the relay node R and the near user node NU, with a value of 1, is the relay node R k Distance between the relay node R and the near user node NU, with a value of 1m;

[0023] Determine the relay node R according to Equation (5) k Channel coefficient of the channel from the relay node R to the external eavesdropping node Eve

[0024]

[0025] where is the channel estimation error coefficient, with a value range of 0 to 0.005, is the channel coefficient of the channel from the relay node R to the external eavesdropping node Eve estimated by the pilot-assisted method before each time slot, with a value of k Channel coefficient from the relay node R to the external eavesdropping node Eve, with a value of is the relay node R k Channel fading coefficient between the relay node R and the external eavesdropping node Eve, with a value of 1, is the relay node R k Distance between the relay node R and the external eavesdropping node Eve, with a value of 1m;

[0026] Determine the channel coefficient h of the channel from the jammer node J to the external eavesdropping node Eve according to Equation (6) JE :

[0027]

[0028] where εJE is the channel estimation error coefficient, with a value range of 0 to 0.005, is the channel coefficient from the jammer node J to the external eavesdropping node Eve estimated before each time slot according to the pilot-assisted method, with a value range of λ JE is the channel fading coefficient between the jammer node J and the external eavesdropping node Eve, with a value of 1, d JE is the distance between the 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 Equation (7) k* :[[]]END]]

[0031]

[0032] where Δ = {1, 2,..., M};

[0033] (4) Determine the connection outage probability

[0034] Determine the connection outage probability of the far user node FU according to Equation (8)

[0035]

[0036] where, is the relay node The received signal-to-noise ratio when decoding the signal x2 sent by the far user node FU, γ F,2 is the received signal-to-noise ratio when the far user node FU decodes x2, ρ s is the transmit signal-to-noise ratio of the source node S, with a value range of 0 to 50dB, ρ r is the optimal relay R k* The transmit signal-to-noise ratio of, with a value range of 0 to 50dB, is the relay node R k* The signal-to-noise ratio threshold for decoding x2, with a value range of 0 to 3dB, is the signal-to-noise ratio threshold for the far user node FU to decode x2, with a value range of 0 to 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;

[0037] (5) Determine the secrecy outage probability

[0038] Determine the secrecy outage probability of the far user node FU according to Equation (11)

[0039]

[0040] Among them, is the signal-to-noise ratio threshold for the external eavesdropping node Eve to decode x2, with a value ranging from 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 ε SJ , ε JE are channel estimation error coefficients, ε SJ , ε JE with values ranging from 0 to 0.005.

[0042] In equation (7) of step (3) of the present invention, M is the number of relay nodes, and M takes values from 1 to 6. is the selected optimal relay node, and k * takes values 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 a value of 0.76, and a1 is the power allocation factor of the near user node NU, where a1 takes a value of 0.24; is the received signal-to-noise ratio when the relay node decodes the signal x2 sent by the far user node FU, γ F,2 is the received signal-to-noise ratio when the far user node FU decodes x2; ρ s is the transmit signal-to-noise ratio of the source node S, with a value ranging from 0 to 50 dB, ρ r is the transmit signal-to-noise ratio of the optimal relay R k* , with a value ranging from 0 to 50 dB, is the signal-to-noise ratio threshold for the relay node to decode x2, with a value ranging from 0 to 3 dB; in equation (10), the is the signal-to-noise ratio threshold for the far user node FU to decode x2, with a value ranging from 0 to 3 dB.

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

[0045] Since the present invention adopts a relay selection and jammer system, a reasonable transmission signal model is established, and an information security transmission method is proposed, which utilizes limited spectrum resources and reduces the secrecy outage probability. Compared with the prior art, at the relay node Rk When the number M is 3 and the signal-to-noise ratio is 10 - 50 dB, the connection interruption probability of the far user FU node is reduced by 0.080708 - 0.1005581, and the secrecy interruption probability of the far user FU node is reduced by 0.0016 - 0.2599. As the number of relays or the transmit signal-to-noise ratio increases, the connection interruption probability of the system decreases; as the transmit signal-to-noise ratio increases, the secrecy interruption probability also decreases. The present invention has the advantages of simple transmission method, easy implementation, good secrecy performance, etc., and can be used in the field of communication security technology. Description of the Drawings

[0046] Figure 1 It is the process flow chart of Embodiment 1 of the present invention.

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

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

[0049] Embodiment 1

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

[0051] (1) Construct a transmission signal model

[0052] The transmission signal model consists of 1 source node S, M relay nodes R k , 1 jammer node J, 1 near user node NU, 1 far user node FU, and 1 external eavesdropping node Eve. k ∈ {1, 2,..., M}, M represents the number of relay nodes, and M is a finite positive integer. In this embodiment, M takes the value of 3. Single antennas are set on the source node S, each relay node R k , the near user node NU, the far user node FU, and the external eavesdropping node Eve to form a transmission signal model;

[0053] (2) Construct a channel error model

[0054] Determine the channel coefficient of the channel from the source node S to the relay node R according to Equation (1) k channel coefficient

[0055]

[0056] where is the channel estimation error coefficient, and its value ranges from 0 to 0.005. In this embodiment, the value is 0.005. is the channel coefficient from the source node S to the relay node R estimated before each time slot according to the pilot-assisted method k and its value is the channel fading coefficient between the source node S and the relay node R k with a value of 1, the distance between the source node S and the relay node R k with a value of 1 m, η is the path loss exponent with a value of 2, is the channel estimation error with a value of 0.005;

[0057] Determine the channel coefficient h of the channel from the source node S to the jammer node J according to Equation (2) SJ :

[0058]

[0059] where ε SJ is the channel estimation error coefficient with a value ranging from 0 to 0.005. In this embodiment, the value of ε SJ is 0.005, is the channel coefficient of the channel from the source node S to the jammer node J estimated before each time slot according to the pilot-assisted method, and its value is λ SJ is the channel fading coefficient between the source node S and the jammer node J with a value of 1, and d SJ is the distance between the source node S and the jammer node J with a value of 5 m;

[0060] Determine the channel coefficient of the channel from the relay node R k to the far user node FU according to Equation (3)

[0061]

[0062] where is the channel estimation error coefficient with a value ranging from 0 to 0.005. In this embodiment, its value is 0.005, is the channel coefficient of the channel from the relay node R k to the far user node FU estimated before each time slot according to the pilot-assisted method, and its value is is the channel fading coefficient between the relay node R k and the far user node FU with a value of 1, is the distance between the relay node R k and the far user node FU with a value of 2 m;

[0063] Determine the channel coefficient of the channel from the relay node R k to the near user node NU according to Equation (4)

[0064]

[0065] Among them, is the channel estimation error coefficient, with a value range of 0 to 0.005. In this embodiment, takes the value of 0.005. is the channel coefficient of the relay node R k to the near user node NU estimated before each time slot according to the pilot-assisted method, with a value of is the relay node R k to the channel fading coefficient between the near user node NU, with a value of 1. is the relay node R k to the distance between the near user node NU, with a value of 1 m;

[0066] Determine the channel coefficient of the relay node R k to the external eavesdropping node Eve channel according to Equation (5)

[0067]

[0068] Among them, is the channel estimation error coefficient, with a value range of 0 to 0.005. In this embodiment, takes the value of 0.005. is the channel coefficient of the relay node R k to the external eavesdropping node Eve estimated before each time slot according to the pilot-assisted method, with a value of is the relay node R k to the channel fading coefficient between the external eavesdropping node Eve, with a value of 1. is the relay node R k to the distance between the external eavesdropping node Eve, with a value of 1 m;

[0069] Determine the channel coefficient h of the jammer node J to the external eavesdropping node Eve channel according to Equation (6) JE :

[0070]

[0071] Among them, ε JE is the channel estimation error coefficient, with a value range of 0 to 0.005. In this embodiment, ε JE takes the value of 0.005. is the channel coefficient of the jammer node J to the external eavesdropping node Eve estimated before each time slot according to the pilot-assisted method, with a value of λ JEis the channel fading coefficient between the jammer node J and the external eavesdropping node Eve, with a value of 1, d JE is the distance between the 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 Equation (7)

[0074]

[0075] where Δ = {1, 2,..., M};

[0076] (4) Determine the connection outage probability

[0077] Determine the connection outage probability of the far user node FU according to Equation (8)

[0078]

[0079] where, is the relay node is the received signal-to-noise ratio when the relay node decodes the signal x2 sent by the far user node FU, γ F,2 is the received signal-to-noise ratio when the far user node FU decodes x2, ρ s is the transmit signal-to-noise ratio of the source node S, with a value ranging from 0 to 50dB, ρ r is the optimal relay is the transmit signal-to-noise ratio of, with a value ranging from 0 to 50dB, is the relay node is the signal-to-noise ratio threshold for decoding x2, with a value ranging from 0 to 3dB, in this embodiment has a value of 3dB, is the signal-to-noise ratio threshold for the far user node FU to decode x2, with a value ranging from 0 to 3dB, in this embodiment has a value of 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 secrecy outage probability

[0081] Determine the secrecy outage probability of the far user node FU according to Equation (11)

[0082]

[0083] where, is the signal-to-noise ratio threshold for the external eavesdropping node Eve to decode x2, with a value ranging from 0 to 1dB, in this embodiment The value is 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.

[0084] Embodiment 2

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

[0086] (1) Construct a transmission signal model

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

[0088] (2) Construct a channel error model

[0089] This step is the same as that in Embodiment 1.

[0090] (3) Select the optimal relay

[0091] This step is the same as that in Embodiment 1.

[0092] (4) Determine the connection outage probability

[0093] Determine the connection outage probability of the far user node FU according to Equation (8)

[0094]

[0095] Where is the received signal-to-noise ratio when the relay node R k* decodes the signal x2 sent by the far user node FU, γ F,2 is the received signal-to-noise ratio when the far user node FU decodes x2, ρ s is the transmit signal-to-noise ratio of the source node S, with a value range of 0 - 50 dB, ρ r is the transmit signal-to-noise ratio of the optimal relay with a value range of 0 - 50 dB, is the signal-to-noise ratio threshold for the relay node to decode x2, with a value range of 0 - 3 dB. In this embodiment, is taken as 2 dB, is the signal-to-noise ratio threshold for the far user node FU to decode x2, with a value ranging from 0 to 3 dB. In this embodiment, the value is 2 dB. 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 secrecy outage probability

[0097] Determine the secrecy outage probability of the far user node FU according to Equation (11)

[0098]

[0099] where is the signal-to-noise ratio threshold for the external eavesdropping node Eve to decode x2, with a value ranging from 0 to 1 dB. In this embodiment, the value is 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 0.7.

[0100] Embodiment 3

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

[0102] (1) Construct a transmission signal model

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

[0104] (2) Construct a channel error model

[0105] This step is the same as that in Embodiment 1.

[0106] (3) Select the optimal relay

[0107] This step is the same as that in Embodiment 1.

[0108] (4) Determine the connection outage probability

[0109] Determine the connection outage probability of the far user node FU according to Equation (8)

[0110]

[0111] Among them, is the relay node is the received signal-to-noise ratio when the relay node decodes the signal x2 sent by the far user node FU, γ F,2 is the received signal-to-noise ratio when the far user node FU decodes x2, ρ s is the transmit signal-to-noise ratio of the source node S, with a value range of 0 to 50 dB, ρ r is the optimal relay 's transmit signal-to-noise ratio, with a value range of 0 to 50 dB, is the relay node 's signal-to-noise ratio threshold for decoding x2, with a value range of 0 to 3 dB. In this embodiment, the value is 1 dB, is the signal-to-noise ratio threshold for the far user node FU to decode x2, with a value range of 0 to 3 dB. In this embodiment, the value is 1 dB, 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 secrecy outage probability

[0113] Determine the secrecy outage probability of the far user node FU according to Equation (11)

[0114]

[0115] Among them, is the signal-to-noise ratio threshold for the external eavesdropping node Eve to decode x2, with a value range of 0 to 1 dB. In this embodiment, the value is 0.5 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 0.6.

[0116] To verify the beneficial effects of the present invention, the inventor conducted a comparative simulation experiment using the secure transmission method of the cooperative non-orthogonal multiple access system based on relay selection in Embodiment 1 of the present invention (hereinafter referred to as the method of Embodiment 1) and the method without cooperative interference (hereinafter referred to as the comparative experiment method). The experimental results are shown in Figure 2 . Figure 2 is the influence of different transmission signal-to-noise ratios on the secrecy outage probability . It can be seen from Figure 2 that compared with the comparative experiment method, when the signal-to-noise ratio is 10 to 50 dB, the secrecy outage probability of the far user node FU is reduced by 0.0016 to 0.2599 respectively.

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) Construct a transmission signal model The transmission signal model consists of 1 source node S and M relay nodes R k , 1 jammer node J, 1 near user node NU, 1 far user node FU, and 1 external eavesdropping node Eve. Let k ∈ {1, 2,..., M}, where M represents the number of relay nodes and M is a finite positive integer. At the source node S, each relay node R k , near user node NU, far user node FU, and external eavesdropping node Eve, single antennas are set up to form the transmission signal model; (2) Construct a channel error model Determine the channel coefficient of the channel from the source node S to the relay node R according to Equation (1). k Channel coefficient of the channel Among them, is the channel estimation error coefficient, with a value range of 0 to 0.005, is the channel coefficient from the source node S to the relay node R estimated before each time slot according to the pilot-assisted method k with a value range of is the channel fading coefficient between the source node S and the relay node R k with a value of 1, is the distance between the source node S and the relay node R k with a value of 1 m, η is the path loss exponent with a value of 2, is the channel estimation error with a value of 0.005; Determine the channel coefficient \(h\) of the channel from the source node \(S\) to the jammer node \(J\) according to Equation (2). SJ : Among them, ε SJ is the channel estimation error coefficient, with a value range of 0 to 0.005, is the channel coefficient from the source node S to the jammer node J estimated before each time slot according to the pilot-assisted method, with a value of λ SJ is the channel fading coefficient between the source node S and the jammer node J, with a value of 1, d SJ is the distance between the source node S and the jammer node J, with a value of 5m; Determine the relay node R according to Equation (3) k Channel coefficient of the channel to the far user node FU Among them, is the channel estimation error coefficient, with a value ranging from 0 to 0.005, is the channel coefficient from relay node R k to the far user node FU estimated before each time slot according to the pilot-assisted method, and the value is is relay node R k the channel fading coefficient between it and the far user node FU, with a value of 1, is the distance between relay node R k and the far user node FU, with a value of 2m; Determine the relay node R according to Equation (4) k Channel coefficient of the channel to the nearby user node NU Among them, is the channel estimation error coefficient, with a value ranging from 0 to 0.005, is the channel coefficient from relay node R k to the near user node NU estimated before each time slot according to the pilot-assisted method, and the value is is relay node R k the channel fading coefficient between relay node R and the near user node NU, with a value of 1, k is the distance between relay node R and the near user node NU, with a value of 1 m; Determine the relay node R according to Equation (5) k Channel coefficient of the channel to the external eavesdropping node Eve Among them, is the channel estimation error coefficient, with a value ranging from 0 to 0.005, is the channel coefficient from the relay node R k to the external eavesdropping node Eve estimated before each time slot according to the pilot-assisted method, and the value is is the relay node R k the channel fading coefficient between the relay node R to the external eavesdropping node Eve, with a value of 1, k is the distance between the relay node R k to the external eavesdropping node Eve, with a value of 1m; Determine the channel coefficient \(h\) of the channel from the jammer node \(J\) to the external eavesdropping node Eve according to Equation (6). JE : Among them, ε JE is the channel estimation error coefficient, with a value range of 0 to 0.005, is the channel coefficient from the jammer node J to the external eavesdropping node Eve estimated before each time slot according to the pilot-assisted method, with a value of λ JE is the channel fading coefficient between the jammer node J and the external eavesdropping node Eve, with a value of 1, d JE is the distance between the jammer node J and the external eavesdropping node Eve, with a value of 2m; (3) Select the optimal relay Select the optimal relay according to Equation (7) where, Δ = {1, 2,..., M}; (4) Determine the connection outage probability Determine the connection interruption probability of the far user node FU according to Equation (8). Among them, is the relay node is the received signal-to-noise ratio, γ, when the relay node decodes the signal x2 sent by the far user node FU F,2 is the received signal-to-noise ratio, ρ, when the far user node FU decodes x2 s is the transmit signal-to-noise ratio of the source node S, with a value range of 0 to 50 dB, ρ r is the optimal relay with a transmit signal-to-noise ratio, with a value range of 0 to 50 dB, is the relay node is the signal-to-noise ratio threshold for decoding x2, with a value range of 0 to 3 dB, is the signal-to-noise ratio threshold for the far user node FU to decode x2, with a value range of 0 to 3 dB, 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; (5) Determine the secrecy outage probability Determine the secrecy outage probability of the far user node FU according to Equation (11). Among them, is the signal-to-noise ratio threshold for the external eavesdropping node Eve to decode x2, with a value ranging from 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.

2. The secure transmission method of the relay selection-based cooperative non-orthogonal multiple access system according to claim 1, characterized in that: In step (2), the ε SJ , ε JE are channel estimation error coefficients, ε SJ , ε JE take values from 0 to 0.

005.

3. The secure transmission method of the relay selection-based cooperative non-orthogonal multiple access system according to claim 1, characterized in that: In formula (7) of step (3), M is the number of relay nodes, and the value of M ranges from 1 to 6. is the selected optimal relay node, k * ranges from 1 to 6.

4. The secure transmission method of the relay selection-based cooperative non-orthogonal multiple access system according to claim 1, characterized in that: In formula (9) of step (4), a2 is the power allocation factor of the far user node FU, where the value of a2 is 0.76, and a1 is the power allocation factor of the near user node NU, where the value of a1 is 0.24; is the relay node R k * The received signal-to-noise ratio when decoding the signal x2 sent by the far user node FU, γ F,2 is the received signal-to-noise ratio when the far user node FU decodes x2; ρ s is the transmit signal-to-noise ratio of the source node S, with a value range of 0 to 50 dB, ρ r is the optimal relay R k* 's transmit signal-to-noise ratio, with a value range of 0 to 50 dB, is the relay node R k* The signal-to-noise ratio threshold for decoding x2, with a value range of 0 to 3 dB; In formula (10), the is the signal-to-noise ratio threshold for the far user node FU to decode x2, with a value range of 0 to 3 dB.

5. The secure transmission method of the relay selection-based cooperative non-orthogonal multiple access system according to claim 1, characterized in that: In formula (11) of step (5), the α is the transmission time allocation factor, where α takes a value of 0.5, and β is the energy conversion efficiency, where β takes a value of 0.

8. is the signal-to-noise ratio threshold for the external eavesdropping node Eve to decode x2, and its value ranges from 0 to 1 dB.

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