A secure transmission method for a semi-authorization-free system assisted by non-orthogonal multiple access

Abstract

This invention discloses a full transmission method for a semi-unlicensed system with non-orthogonal multiple access assisted transmission. The transmission system includes a source node, one licensed user, one eavesdropping user, and multiple unlicensed users. In this invention, the entire communication process is completed in five steps: 1) The base station sends a training sequence; 2) Each user estimates its own channel state information; 3) The licensed user feeds back its transmit signal-to-noise ratio, target rate, and channel state information to the base station; 4) The base station calculates the decoding threshold for the licensed user and broadcasts the effective receive signal-to-noise ratio and threshold value for the licensed user; 5) The transmission rate of the unlicensed user is calculated using sequencing theory, and the unlicensed user with the maximum reachable rate is scheduled to access the resource block of the licensed user and transmit signals. The maximum reachable rate scheduling strategy can effectively reduce the number of unlicensed users accessing the resource block of the licensed user and improve the security performance of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communication networks, and in particular to a semi-authorized wireless communication network assisted by non-orthogonal multiple access technology. The present invention belongs to the field of physical layer security. Background Art

[0002] In the 5G era, the explosive growth of mobile data brought about by the popularization of smart terminals has put forward higher requirements for the speed, latency, signal coverage, etc. of wireless communication networks. So far, in order to meet the ever-increasing social needs, mobile communication technology has always maintained a high-speed iteration. The first generation of mobile communication technology is an analog communication technology that uses analog frequency modulation and frequency division multiple access. It is mainly based on the cellular networking structure to overcome the problems of low capacity and limited activity range of the large area system and realize voice functions; in order to improve the channel capacity and anti-interference ability of communication and reduce the investment cost of communication, the second generation of narrowband digital communication technology using time division multiple access technology and voice and SMS services is proposed; the third generation of multimedia mobile communication system, using code division multiple access technology, not only requires a large system capacity, but also supports the effective transmission of multiple services such as voice, data, images, multimedia, etc.; the fourth generation of mobile communication technology is also called wideband access and distribution network. It uses orthogonal frequency division multiple access technology, representing mobile multimedia, global mobile solutions, integrated wireless and customized services. At present, we are in the era of commercial use of the fifth generation of mobile communication technology, and are about to enter the convenient era of the Internet of Everything.

[0003] Non-orthogonal multiple access technology: As a promising multiple access technology, it is widely regarded as a technology for effectively utilizing spectrum resources in 5G wireless networks. The basic idea of ​​non-orthogonal multiple access technology is to use superposition coding technology at the transmitting end, actively introduce interference information, and achieve correct demodulation at the receiving end through serial interference cancellation technology. Non-orthogonal multiple access is mainly divided into power domain non-orthogonal multiple access, code domain non-orthogonal multiple access and space domain non-orthogonal multiple access technology. Unless otherwise specified below, non-orthogonal multiple access refers to power domain non-orthogonal multiple access. Power domain non-orthogonal multiple access refers to a communication technology that superimposes signals with different powers on the same time-frequency resources and performs interference cancellation at the receiving end.

[0004] As large-scale devices will access limited spectrum, two major scenarios in the Internet of Things: ultra-reliable low-latency communication (URLLC) and massive machine type communication (mMTC), have stricter requirements on latency and signaling overhead, that is, lower latency and signaling overhead.

[0005] Semi-unlicensed strategy: It is a combination of unlicensed scheme for machine-type users with small data packets and delay-tolerant traffic and authorized scheme for some users with large data packets and delay-sensitive traffic. It is a strategy to control the number of unlicensed users accessing spectrum resources. In order to alleviate conflicts over resources and obtain large-scale connectivity, this strategy allows unlicensed users (delay-tolerant devices) to share the spectrum resources of licensed users without affecting the exclusive channels of licensed users to communicate with base stations. It also solves the problem that a large number of users cannot successfully decode user information due to exceeding the non-orthogonal multiple access capacity.

[0006] Physical layer security technology: Physical layer security does not require a key. It uses the time-varying nature of wireless channels to encrypt communication systems, which can theoretically achieve absolute security in information transmission. As the computing power of terminals gradually increases, the ability of eavesdroppers to crack information is also gradually improving. Traditional cryptography is facing increasing pressure in the field of information encryption. Physical layer security is based on information theory and achieves information security at the physical layer. It is a very promising encryption method in the field of communications.

[0007] The general uplink non-orthogonal multiple access communication network model is as follows Figure 1 As shown in the figure, S is the source node, U 1 and U 2 The source node uses serial interference cancellation technology. In the uplink non-orthogonal multiple access communication system, there are two main ways for the base station to decode the user's information: 1. Decode the user's information based on the user's channel state information (CSI), that is, the base station first decodes the user U with a stronger CSI. 1 The information of the near user is then removed by serial interference cancellation technology, and then the user U with weak CSI is decoded. 2 (distant user) information, because the base station first receives U 1 The received signal can be decoded and deleted, and then the received signal can be decoded; 2. Decode the user's information according to the user's quality of service (QoS), that is, to ensure that the user U 1 The service quality of the user is decoded first, and then the user U 2 Information, because U 1 It may be a delay-sensitive device with a higher priority. This paper mainly considers the user's service quality.

[0008] Semi-licensed communication technology can not only improve spectrum efficiency but also reduce signaling overhead. At the same time, combined with non-orthogonal multiple access technology, it can solve the collision problem when multiple users compete for the same resource block, and can also significantly improve system performance. The combination of semi-licensed communication and non-orthogonal multiple access technology can further improve the performance of non-orthogonal multiple access communication systems. Figure 2As shown in the figure, BS is the base station, U B and U k are delay-sensitive and delay-tolerant users, respectively. Under the condition of ensuring the service quality of authorized users, is the power gain of unlicensed users greater than the decoding threshold value τ(|g B | 2 ), all unlicensed users are divided into two groups: the channel gain of users in group 1 is greater than the threshold value, that is, the base station cannot directly and correctly decode the information of the licensed users, and can only decode the information of the unlicensed users in the first stage of serial interference cancellation. The channel gain of all users in group 2 is less than the threshold value. Therefore, the information of the unlicensed users in this group can be decoded in the first stage of serial interference cancellation, and can also be decoded in the second stage. By comparing the achievable rates of the unlicensed users in the two stages, the maximum achievable rate can be obtained by decoding the information of the GF users in the second stage.

[0009] Physical layer security is a security theory based on information theory. It uses the time-varying nature of wireless channels and combines channel coding and encryption technology to ensure that information cannot be deciphered by eavesdroppers. In 1945, CE Shannon proved in a classic paper (see [1]: Shannon CE. Communication theory of secrecy systems [J]. The Bell System Technical Journal, 1949, 28 (4): 656-715.) from the perspective of information theory that in order to achieve absolute security of messages, the communication process must use a "one-time, one-pad" encryption method, that is, one bit of data should have one bit of key. This condition is too strict and difficult to apply in the engineering field. In 1975, A. Wyner first established a noisy eavesdropping channel model based on Shannon's research (see [2]: Wyner AD. The wire-tap channel [J]. The Bell System Technical Journal, 1975, 54 (8): 1355-1387.), as shown in the attached figure. Figure 3As shown in the figure, the eavesdropping model is an improvement on the Shannon model. In this model, Wyner proved that: when the channel condition of the main channel is better than that of the eavesdropping channel, when the source and the legitimate receiver transmit information, there must be a coding method that can make the probability of information transmission errors arbitrarily small. At this time, the eavesdropper cannot obtain any useful information, and the system is absolutely secure. From the perspective of information theory, the physical layer security is defined using the source entropy. After decades of development, the physical layer security theory has gradually matured. The use of physical layer security to achieve secure transmission of wireless communication systems has become a hot topic in academia and industry. The main indicators for measuring the physical layer security of the system include ergodic confidentiality capacity and security interruption probability. The security interruption probability refers to the probability that the instantaneous security capacity of the system is less than a given threshold value. The mathematical expression is:

[0010]

[0011] Among them, γ D and γ E Indicates the signal-to-noise ratio between the destination and the eavesdropping end. R s represents the safety rate threshold, F D (x) represents the cumulative distribution function of the main channel signal-to-noise ratio. f(γ E ) represents γ E The probability density function of .

[0012] The uplink communication system built based on non-orthogonal multiple access, semi-authorization-free and physical layer security theory will be widely used in low-latency, high-spectrum-efficiency, multi-connection ultra-reliable low-latency communications and ultra-multi-machine type communication systems. Summary of the invention

[0013] In view of the system security problem that there may be eavesdroppers in the transmission of the semi-unauthorized system assisted by uplink non-orthogonal multiple access, the present invention takes the security of the system into consideration and adopts a given user scheduling strategy (such as the maximum achievable rate of the user) to further improve the secure transmission of the non-orthogonal multiple access system on the basis of ensuring the service quality of authorized users.

[0014] The present invention is based on physical layer security technology and considers the security of unlicensed users in an uplink non-orthogonal multiple access assisted semi-licensed system. A secure transmission scheduling strategy for a semi-licensed system assisted by non-orthogonal multiple access is disclosed. The core of the strategy is based on physical layer security technology and selects users with the maximum achievable rate. Specifically, the strategy includes the following steps:

[0015] Step S1: System initialization; sending a training series in a plurality of unlicensed user uplink non-orthogonal multiple access systems, and each user estimates the channel state information of each channel through a channel estimation algorithm.

[0016] Step S2: The authorized user sets its transmission signal-to-noise ratio and target rate R B and channel state information g B Feedback to the base station.

[0017] Step S3: The base station calculates the decoding threshold of the authorized user where τ(|g B | 2 )Depend on Get, P F is the transmission power of the unlicensed user, P B is the transmit power of the authorized user, R B is the rate threshold and |h k | 2 It represents the channel gain of the unlicensed user and broadcasts the effective received signal-to-noise ratio P of the authorized user. B |g B | 2 and τ(|g B | 2 ).

[0018] Step S4: The unlicensed user calculates its own transmission rate, and determines whether the power gain of the unlicensed user is greater than the decoding threshold value τ(|g B | 2 ), all unauthorized users are divided into two groups.

[0019] Step S5: According to step S4, the maximum achievable rate obtained by user k is in and They represent the signal rates of unlicensed users decoded by the base station in the first and second stages of serial interference cancellation, S 1 Indicates the group where the power gain of unlicensed users is less than the decoding threshold.

[0020] Step S6: Through distributed contention, the unlicensed user with the maximum achievable rate will be connected to the resource block of the licensed user.

[0021] The beneficial effects of the present invention are mainly as follows: considering the correlation of the channel gains of multiple unlicensed users, while ensuring the service quality of authorized users, the probability of successfully decoding users is increased through user scheduling strategies, the security interruption probability and signaling overhead of the semi-unlicensed system assisted by non-orthogonal multiple access are effectively reduced, and the system security performance is improved.

[0022] The beneficial effects of the present invention specifically come from the following three aspects:

[0023] (1) Using semi-grant-free non-orthogonal multiple access technology to communicate. Since the authorized user will generate high signaling overhead during the authorization process and the use of grant-free technology will cause collisions when the unauthorized users compete for the same resource block, in order to solve these two problems, semi-grant-free non-orthogonal multiple access technology came into being. Non-orthogonal multiple access technology can accommodate multiple users in the same resource block, but a large number of devices accessing the network will overflow the capacity of non-orthogonal multiple access technology. Semi-grant-free technology adopts a distributed competition method (see related literature [5] Z. Ding, R. Schober, P. Fan, and H. V. Poor, "Simple semi-grant-free transmission strategies assisted by non-orthogonal multiple access," IEEE Trans. Commun., vol. 67, no. 6, pp. 4464-4478, Jun. 2019. This article will not repeat it.) It can not only solve the high signaling overhead generated, but also solve the capacity overflow problem of non-orthogonal multiple access technology. Therefore, this technology can generate lower signaling overhead and improve spectrum efficiency and system performance.

[0024] (2) Adopt user scheduling strategy. User scheduling strategy can improve spectrum efficiency while ensuring low signaling overhead. In addition, unlike the semi-unlicensed non-orthogonal multiple access technology that does not adopt user scheduling strategy, the present invention considers that unlicensed users can schedule unlicensed users with the maximum achievable rate through distributed competition resources while ensuring the service quality of authorized users. The impact of the number of authorized users on system security is shown in the attached figure. Figure 5 This strategy can not only prevent users accessing the same resource block from overflowing the capacity of the non-orthogonal multiple access technology, but also enhance the security of the system.

[0025] (3) The impact of rate pairs. The rate composed of the interruption rate threshold and the safety rate threshold has a great impact on the safety of the system. Whether the product of the rate pairs is greater than 1 affects the safety interruption probability of the system as shown in the attached figure. Figure 6 Attached Figure 6 The Monte Carlo simulation results in show that when the product of the rate pairs is less than 1, the system security can be significantly enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a model of a general uplink non-orthogonal multiple access system;

[0027] Figure 2 A semi-unlicensed system model assisted by non-orthogonal multiple access;

[0028] Figure 3 It is the Wyner eavesdropping channel model;

[0029] Figure 4 A security system model assisted by non-orthogonal multiple access;

[0030] Figure 5 The impact of the number of unlicensed users on the security outage probability of non-orthogonal multiple access assisted systems;

[0031] Figure 6 The impact of rate on the probability of system safety interruption;

[0032] Figure 7 Implementation process of secure transmission scheme for semi-unlicensed system assisted by non-orthogonal multiple access. DETAILED DESCRIPTION

[0033] like Figure 4 As shown, the present invention considers the security of a system assisted by non-orthogonal multiple access, wherein BS represents a base station, U B and U k are delay-sensitive and delay-tolerant users, respectively, and E is an eavesdropping end. The communication system described in the embodiment of the present invention includes a base station BS, an authorized user U B , an eavesdropping node E and K unauthorized users U F , and the base station and all users are equipped with a single antenna. The channel power gain of the authorized user is |g B | 2 The channel power gain of the unlicensed user is expressed as |g k | 2 Indicates that after sorting, it is |h 1 2 ≤…≤|h K | 2 ,in and Assume that all channels obey independent and identically distributed Rayleigh fading. Therefore, after the channels are sorted, |h i | 2 and |h j | 2 The probability density function and cumulative distribution function of (1≤i<j≤K) can be expressed as:

[0034]

[0035]

[0036] in, φ 2 =K-j+n+1 and φ 3=m+jin. i, j represent the i-th user and the j-th user respectively; m, n represent the m+1-th user and the n+1-th user respectively; x, y represent the channel gain variable |h| 2 The lower and upper bounds of |h i | 2 ,|h j | 2 represent the channel gains of user i and user j respectively.

[0037] The embodiment of the present invention is based on physical layer security technology and considers the security of unlicensed users in an uplink non-orthogonal multiple access assisted semi-licensed system. A secure transmission scheduling strategy for a semi-licensed system assisted by non-orthogonal multiple access is disclosed. The core of the strategy is to select users with the maximum achievable rate based on physical layer security technology. The specific implementation process of the present invention is as follows: Figure 7 As shown, it is mainly divided into three stages. The first stage mainly includes: the base station sends a training sequence, each user estimates its own channel state information, the authorized user feeds back its own transmission signal-to-noise ratio, rate threshold and channel state information to the base station, and the base station calculates and broadcasts the decoding threshold and effective receiving power gain of the authorized user; in the second stage, the unauthorized users are grouped according to the decoding threshold of the authorized user; the third stage is mainly to schedule the unauthorized users who meet the requirements to access the resource blocks of the authorized users according to the scheduling strategy. The specific implementation process is divided into six steps:

[0038] Step S1: The base station broadcasts a training sequence. This step has two purposes: (1) estimating the channel state information of the authorized user and the unauthorized user, i.e., BS-U B and BS-U k ,k∈[1:K]; (2) Estimate the channel state information of the eavesdropped channel. That is, the channel state information of the BS-E channel. The acquisition of the channel state information of each link can be achieved by monitoring the transmission of each port or using some complex channel estimation algorithms. The specific method (see reference [3] Zou Y, Zhu J, Wang X, et al. Improving physical-layer security in wireless communications using diversity techniques [J]. IEEE Network, 2015, 29 (1): 42-48.) will not be repeated in this paper.

[0039] Step S2: The authorized user sets its transmission signal-to-noise ratio and target rate R B and channel state information g BFeedback to the base station (see reference [4]: ​​Z. Ding, R. Schober, and HV Poor, "A new QoS-guarantee strategy for NOMA assisted semi-grant-free Transmission," IEEE Trans. Commun, vol. 69, no. 11, pp. 7489-7503, Nov 2021.).

[0040] Step S3: The base station calculates the decoding threshold of the authorized user in Get, P F is the transmission power of the unlicensed user, P B , R B and |h k | 2 They represent the power sent by the authorized user, the rate threshold, and the channel gain of the unauthorized user, and broadcast the effective receiving power gain P of the authorized user. B |g B | 2 and τ(|g B | 2 ).

[0041] Step S4: The unlicensed user calculates its own transmission rate, and determines whether the power gain of the unlicensed user is greater than the decoding threshold value τ(|g B | 2 ), all unlicensed users are divided into two groups: Group 1 has a user channel gain greater than the threshold value, i.e., P F |h m | 2 >τ(|g B | 2 ), where P F To avoid unauthorized users from transmitting, there is That is, the base station cannot directly decode the information of the authorized user correctly, and can only decode the information of the unauthorized user in the first stage of serial interference elimination. The channel gain of all users in group 2 is less than the threshold value, that is, P F |h k | 2 <τ(|g B | 2 ). Therefore, the information of the unlicensed users in this group can be decoded in the first stage of serial interference cancellation or in the second stage. The achievable rate when decoded in the first stage is The achievable rate in the second stage of decoding is log 2 (1+P F |h k |2 ). Obviously, decoding the information of GF users in the second stage can achieve the maximum achievable rate;

[0042] Step S5: According to step S4, the maximum achievable rate obtained by user K is in and |S 1 | represents the group when the channel gain of the unlicensed user is less than the decoding threshold. Under the condition of ensuring the service quality of the authorized user, |S 1 |=K means that all unauthorized users are decoded in the first stage; |S 1 |=0 means that all unauthorized users are decrypted in the second stage; |S 1 |=k means that the unauthorized user can decode in both the first stage and the second stage.

[0043] Step S6: Through distributed competition, the unlicensed user with the maximum rate will be connected to the resource block of the licensed user. At this time, the expression of the signal received by the base station is Where P i and g i , i∈{B,F} represents user U i The transmission power and channel gain, x i For U i The unit power signal sent is n means the mean is 0 and the variance is σ 2 Additive white Gaussian noise.

[0044] The security performance of the system of the embodiment of the present invention is analyzed below. Based on step S5, the probability density function and cumulative distribution function of the relevant variables are derived using probability theory and sorting theory, and the security interruption probability of the system is derived. According to the expression of the security interruption probability and some algebraic operations, the kth unauthorized user U can be obtained. k The probability of safe interruption when sending a signal is:

[0045]

[0046] Among them, R th Indicates the safe rate threshold. ε B =θ B -1, and They represent the safe achievable rates when all unauthorized users are in group 1, all in group 2, and both in group 1 and group 2, respectively. out,1 Indicates that when the authorized user is interrupted, the unauthorized user U kThe other three represent the security interruption probability of the unauthorized user U when the authorized user is not interrupted. k The probability of safety interruption.

[0047] The closed-form expression of the safety interruption probability in the above formula is:

[0048] When the product of the interrupt rate threshold and the safety interrupt rate threshold is less than 1:

[0049]

[0050] When the product of the interrupt rate threshold and the safety interrupt rate threshold is greater than 1:

[0051]

[0052] Among them, a, b, and c below correspond to the variables of the corresponding functions in the above formula. is the exponential integral function, ε 1 =α B θ th , ε 4 =ε 3 +(iP B α th +1)α B , ε B =θ B -1, ε th =θ th -1, λ 1 =P B θ th ,λ 2 =P B α th +1,λ 3 =θ th +1,η 1 =KP B θ th , η 2 =KP B α th +1,η 3 =Kθ th +1,η 4 =C 0 P B θ th , A0 =m+1,B 0 =Kkn-1,C 0 =n+1,W 0 =Kk, x 2 =W i i th +1, you 1 =W i P B i th ,v 1 =u 1 P F e 1 , l 1 =u 1 e 1 +P F x 3 e 1 +ξ 2 , x 5 =(B i +W i )i th +1, v 2 =u 1 P F e 1 ,l 2 =u 1 e 1 +ξ 6 P F e 1 +ξ 5 , g 2 =q j i th +1, g 5 =(b j +q j )i th +1, you 2 =q j P B i th ,v 3 =u 2 P F e 1 ,v 4 =u 2 P F e 1 ,l 3 =u2 ε 1 +ζ 3 P F ε 1 +ζ 2 , l 4 =u 2 ε 1 +ζ 6 P F ε 1 +ζ 5 .

[0053] Figure 5 In order to avoid the impact of the number of authorized users on the security outage probability of the non-orthogonal multiple access assisted system, the parameters are set as follows: R th = 0.1 and R B =0.9 represents the safety rate threshold and the unsafe rate threshold respectively. Wherein "K" represents the number of unauthorized users proposed in the present invention, "Sim" represents the Monte Carlo simulation result, and "Analysis" represents the theoretical analysis result. This figure proves the correctness of the theoretical analysis by Monte Carlo simulation. Obviously, increasing the safety rate threshold will deteriorate the security performance of the wireless communication system. When the transmission power of the unauthorized user is relatively large, the user scheduling strategy proposed in the present invention can obviously enhance the security of the system. Figure 6 is the impact of the rate on the probability of system security interruption. The parameter is set as: K = 4 represents the number of unauthorized users. th =0.1,R B =0.9, R th =0.1,R B =1.5 and R th =0.9,R B =1.5 respectively indicates that the product of the rate pairs is less than 1 and greater than 1, and at the same time, the impact of each rate on the system can be compared. "Sim" represents the Monte Carlo simulation results, and "Analysis" represents the theoretical analysis results. This figure proves the correctness of the theoretical analysis by Monte Carlo simulation. Obviously, the product of the rate pairs is less than 1, which can enhance the safety performance of the system. In addition, the simulation results show that when the product of the rate pairs is less than 1, the smaller the unsafe rate, the smaller the SOP, that is, the smaller the unsafe rate, the better the safety of the system.

Claims

1. A method for secure transmission of a semi-authorized system assisted by non-orthogonal multiple access, characterized in that , including the following steps: Step S1: system initialization; sending a training series in a plurality of unlicensed user uplink non-orthogonal multiple access systems, and each user estimates the channel state information of each channel through a channel estimation algorithm; Step S2: The authorized user sets its transmission signal-to-noise ratio and target rate R B and channel state information g B Feedback to the base station; Step S3: The base station calculates the decoding threshold of the authorized user where τ(|g B | 2 )Depend on Get, P F is the transmission power of the unlicensed user, P B is the transmit power of the authorized user, R B is the rate threshold of the authorized user, |h k | 2 It represents the channel gain of the unlicensed user and broadcasts the effective received signal-to-noise ratio P of the authorized user. B |g B | 2 and τ(|g B | 2 ); Step S4: The unlicensed user calculates its own transmission rate, and determines whether the power gain of the unlicensed user is greater than the decoding threshold value τ(|g B | 2 ), all unlicensed users are divided into two groups, that is, the power gain is greater than the decoding threshold value is group 1 (|S1|), and the power gain is less than the decoding threshold value is group 2 (|S2|): The user channel gain in group 1 is greater than the threshold, that is, P F |h k | 2 >τ(|g B | 2 ), so there is That is, the base station cannot directly and correctly decode the information of the authorized user, and can only decode the information of the unauthorized user in the first stage of serial interference elimination; the channel gain of all users in group 2 is less than the threshold value, that is, P F |h k | 2 <τ(|g B | 2 ), the information of the unlicensed users in this group can be decoded in the first stage of serial interference cancellation or in the second stage. The achievable rate when decoded in the first stage is The achievable rate in the second stage of decoding is log2(1+P F |h k | 2 ), it is obvious that decoding the information of the unlicensed user in the second stage can achieve the maximum achievable rate; Step S5: According to step S4, the maximum achievable rate obtained by user k is in and They represent the signal rates of unlicensed users decoded by the base station in the first and second stages of serial interference cancellation, respectively. |S1| represents the group of unlicensed users whose power gain is less than the decoding threshold value. Under the condition of ensuring the service quality of authorized users, |S1|=0 means that all unauthorized users decode in the second stage; |S1|=K means that all unauthorized users decode in the first stage; |S1|=k means that unauthorized users can decode in both the first stage and the second stage; Step S6: Through distributed contention, the unlicensed user with the maximum achievable rate will be connected to the resource block of the licensed user.

2. According to claim 1, a non-orthogonal multiple access assisted semi-authorization-free system security transmission method is characterized by: In step S6, the expression of the signal received by the base station is: Where P i and g i , i∈{B,F} represents user U i The transmission power and channel gain, x i For U i The unit power signal sent is n means the mean is 0 and the variance is σ 2 Additive white Gaussian noise.

3. A method for secure transmission in a semi-authorized-free system assisted by non-orthogonal multiple access according to claim 1 or 2, characterized in that: The kth unauthorized user U k The probability of safe interruption when sending a signal is: in, ε B =θ B -1, and They represent the safe achievable rates when all unauthorized users are in group 1, all in group 2, and both in group 1 and group 2, respectively. out,1 Indicates that when the authorized user is interrupted, the unauthorized user U k The probability of safety interruption, P out,2 represents the security interruption probability when the unauthorized user is decoded in the second stage, P out,3 represents the security interruption probability when the unauthorized user is decoded in the first stage, P out,4 Indicates the security interruption probability when the unauthorized user is decoded in the first stage or the second stage.

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