Cooperative non-orthogonal multiple access communication system-based covert transmission method

Abstract

The application discloses a covert transmission method based on a cooperative non-orthogonal multiple access communication system, and proposes a scheme for covert communication of a far user, which comprises two time slots, and the first time slot comprises: a base station transmits two-user superposition signals or only transmits near-user signals; if the two-user superposition signals are transmitted, the near user decodes the far user signals and the own signals in sequence, and the far user directly decodes the own signals; and the second time slot: the near user selects to forward the far user signals or to transmit artificial interference signals through the received signals. In the whole process, a monitoring end judges whether the base station has transmitted the covert signals of the far user through signal detection. The application improves the covert throughput of the system through noise uncertainty of each receiving node and the artificial interference signals, realizes reliable transmission of the far user information and the near user information while ensuring the covert performance of the communication system, and realizes maximization of the covert throughput of the system through optimization of a power coefficient ratio under the constraints of reliability and concealment.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication network technology, and particularly relates to a covert transmission scheme for wireless communication networks using user cooperative transmission and non-orthogonal multiple access technology. Background Technology

[0002] With the rapid development of key technologies such as channel coding, massive MIMO, and millimeter waves, the ultra-high speed of 5G networks and the widespread adoption of smart devices have accelerated the development of the Internet of Things. However, due to the openness and broadcast nature of wireless channels, secure information transmission is severely threatened in scenarios with malicious eavesdroppers, and security remains a major problem to be solved in wireless networks. There are two commonly used secure transmission technologies. The first is upper-layer encryption, where two users share a key to achieve secure information transmission. Unauthorized eavesdroppers, without the key, need powerful computing capabilities to crack it and obtain information. The other technology is physical layer security. Physical layer security relies on the complex spatiotemporal characteristics of the physical layer main channel and the eavesdropping channel, such as randomness and time-varying nature, and uses signal processing techniques to achieve secure information transmission. However, physical layer security fails when eavesdroppers have better decoding capabilities. To avoid exposing communication activities, the academic community has proposed a more secure technology: covert wireless communication technology, also known as low-probability detection technology. In cooperative communication systems, multiple nodes cooperate with each other to improve communication efficiency and coverage. In cooperative non-orthogonal multiple access systems, simultaneous communication between multiple users is achieved through non-orthogonal means, thereby improving the capacity and throughput of the communication system. The introduction of covert communication technology can maintain the high performance of the system while enhancing the security of the communication system.

[0003] As attached Figure 1 As shown, Alice is the source, Bob is the receiver, and Willie is the receiver. Alice and Bob transmit information wirelessly, and Willie eavesdrops to determine whether Alice is communicating (or whether a transmitter is communicating). Alice's goals include ensuring the quality of Bob's received signal and preventing Willie from making a correct judgment. Willie can use binary hypothesis testing to determine whether Alice is transmitting information to Bob, and the received signal is represented as:

[0004]

[0005] Where x(i), n w (i) represent the signal and noise received by Willie during the i-th symbol time, respectively, P a h is Alice's transmission power. aw For Alice-Willie's channel gain, This indicates that Alice did not communicate. This indicates that Alice has communicated. Since Willie only needs to make a binary decision, while Bob needs to determine which of the many possible codewords Alice sent, covert communication is difficult to achieve without prior information advantage. Therefore, Alice and Bob usually need to share a certain length of key in advance, so as to agree on a secret communication time and codebook, the latter referring to the legal codeword set and the correspondence between codewords and message symbols.

[0006] Willie determines the optimal decision rule for detecting eavesdroppers based on the received signals, using the Fisher-Neyman criterion and likelihood ratio test. The expression is as follows:

[0007]

[0008] Among them, T w This is the average power received by Willie, expressed as τ is the detection threshold predetermined by Willie, and n is the length of the transmitted information code. This indicates that no communication activity was detected. This indicates that communication activity has been detected. During the detection process, Willie may make two types of errors: false alarms and false negatives. A false alarm occurs when Willie mistakenly determines that Alice has transmitted information, with a probability denoted by P. FA =Pr(D1|H0) represents a missed detection; a missed detection means that Alice transmitted information but Willie mistakenly judged that she did not, and the probability is denoted by P. MD =Pr(D0|H1) means that when Alice's prior transmission probabilities are equal, Willie's detection error probability can be expressed as P. E =P FA +P MD This is used to measure the stealth performance of communication. P E The larger the size, the better the concealment; conversely, the smaller the size, the better the concealment. E The smaller the value, the worse the concealment, and the easier it is for Willie to detect the information transmission, resulting in low security. To ensure the concealment of communication, it is necessary to ensure that regardless of the scheme Willie uses, for any given very small constant ε, P always holds. E ≥1-ε.

[0009] Cooperative non-orthogonal multiple access (COMA) is a novel wireless communication technology designed to improve the spectral efficiency and system capacity of multi-user systems. In traditional multiple access technologies, users communicate using orthogonal channels, but this can lead to wasted spectrum resources in high-density user scenarios. Cooperative COMA improves spectral efficiency by allowing the superposition of non-orthogonal signals between users and by employing interference cancellation and multi-user cooperation techniques. One architecture is the user cooperative COMA, such as... Figure 2As shown in the diagram, U1 and U2 represent the near user and the far user, respectively. In the first time slot, the base station transmits the signals of the two users superimposed at different powers. Since U1 is the near user, its channel conditions are better than those of the far user U2, so the power allocated to U1 is less than that of the far user U2. During decoding, serial interference cancellation is performed. U2's signal is first treated as interference, and then decoded. U2's signal is removed from the superimposed signal, and then U2's own signal is decoded. U2 is a weak user in the non-orthogonal multiple access system. During decoding, U1's signal is treated as interference, and U2's own signal is decoded. Since U1 has already decoded U2's information in the first time slot, U1 can forward U2's signal in the second time slot. Cooperative non-orthogonal multiple access technology not only improves the coverage of the communication system but also makes full use of prior information to remove interference, realizes parallel transmission of the communication link, and further improves spectrum efficiency. Summary of the Invention

[0010] For cooperative non-orthogonal multiple access communication systems, while pursuing higher system spectral efficiency, more serious information exposure may occur. This invention improves the system's covert throughput by addressing the noise uncertainty of each receiving node and artificial interference signals. It ensures the covert performance of the communication system while achieving reliable transmission of information from both distant and nearby users. Under the constraints of reliability and covertness, it maximizes the system's covert throughput by optimizing the power factor ratio.

[0011] In view of this, the technical solution adopted by the present invention is: a covert transmission method based on a cooperative non-orthogonal multiple access communication system, comprising the following steps:

[0012] Step S1: In the first time slot, channel state information within the communication network is estimated by sending pilot sequences, including channel state information between the base station and the near user link and between the near user and the far user link. Based on the channel state, the base station sends a signal, which is a superposition of the far user signal and the near user signal or only the near user signal. In the second time slot, the near user sends a message based on the received information.

[0013] Step S2: The malicious detection node performs binary detection based on the received signal, compares the collected average power with a judgment threshold. If it is higher than the threshold, it is determined that the system is transmitting hidden information; if it is lower than the threshold, it is determined that the system is not transmitting hidden information.

[0014] Step S3: Analyze the detection performance of malicious detection nodes and the probability of system outage to obtain the system's stealth performance and reliability. Under the constraints of the system's stealth performance and reliability, maximize the system's stealth throughput by optimizing the power allocation coefficient ratio k.

[0015] The present invention also provides a covert transmission system based on a cooperative non-orthogonal multiple access communication system, including...

[0016] A base station is used to transmit signals, which may be a superposition of distant user signals and near user signals or only the near user signal.

[0017] The near-user node is used to receive signals sent by the base station and decode the signals. Depending on whether it contains the hidden information of the distant user, it can choose to forward the hidden information or send artificial interference signals in the second time slot.

[0018] Remote user nodes are used to decode received hidden information;

[0019] The detection node is used to receive information from the wireless channel and determine whether there is any covert information being transmitted.

[0020] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described covert transmission method based on a cooperative non-orthogonal multiple access communication system.

[0021] The main advantages of this invention are: it proposes a novel cooperative non-orthogonal multiple access covert transmission method that integrates four technologies: user cooperative transmission, non-orthogonal multiple access, noise uncertainty, and covert communication. This method ensures the high-spectral characteristics of the system while improving the system's covert performance through cooperative transmission strategies, and utilizes artificial interference technology to achieve covert transmission while ensuring the system's reliability.

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

[0023] (1) Ensure the covert throughput of the cooperative non-orthogonal multiple access system. By introducing appropriate noise uncertainty and selecting a suitable power coefficient ratio, the covert throughput of the system can be effectively improved. Figure 3 Monte Carlo simulation results show that the present invention can enhance the covert throughput of the system when the power coefficient ratio is large, compared with the ideal case, that is, when there is no noise uncertainty at the receiving node.

[0024] (2) Adopt a cooperative interference strategy. When the base station only sends near user information, the near user sends interference signals in the second time slot to confuse the detection end. Otherwise, the low power collection will arouse suspicion from the monitoring end.

[0025] (3) Using noise uncertainty to increase system concealment. In practical applications, background noise sources include thermal noise, quantization noise, and imperfect filters. Due to temperature changes, environmental noise variations, and calibration errors, noise uncertainty is almost unavoidable. Legitimate users can also intentionally generate interference signals to increase the randomness of the received signal power at the detection end, thereby achieving the purpose of covert communication. Attached Figure Description

[0026] Figure 1 This is a classic covert communication model;

[0027] Figure 2 A user-collaborative non-orthogonal multiple access system model;

[0028] Figure 3 This represents the impact of the power factor ratio on the system's hidden throughput. Detailed Implementation

[0029] like Figure 2 As shown, this invention considers a cooperative non-orthogonal multiple access covert communication system, comprising a base station Alice, a near user Bob, a far user Carlo, and a malicious detection node Willie. Alice broadcasts signals to both users, where Carlo's signal (private data, etc.) needs to be hidden. To enhance the diversity gain of the covert signal, utilizing the characteristics of a CNOMA system, the near user Bob will use a DF strategy to forward Carlo's signal, while Willie will detect whether Alice is transmitting covert information to Carlo throughout the communication process. For ease of explanation, h ij Let $\frac{i}{b}$ represent the channel coefficients from node $i$ to node $j$, $i \in {a, b}$, $j \in {b, c, w}$, where $a$, $b$, $c$, and $w$ represent Alice, Bob, Carlo, and Willie, respectively. All channel distributions follow a quasi-static Rayleigh distribution, and their mean is expressed as $\frac{ ... It means that d ij Let h represent the distance between the two nodes, and v represent the path loss exponent. Assume Bob knows h. ab Carlo knows the channel state information, h ac and h bc Willie knows all the channel state information associated with Bob, while Bob knows all the related channel state information. Willie's detection capability is strongest when he knows all the related channel state information, making the design of a cooperative non-orthogonal multiple access covert communication system more meaningful and challenging. All nodes use a single antenna and employ half-duplex communication mode; therefore, Bob cannot simultaneously receive and forward signals. Thus, each round of communication is divided into two time slots, and each transmission time slot is equal and continuous.

[0030] The overall implementation process of user-cooperative non-orthogonal multiple access transmission is mainly divided into two time slots. The first time slot mainly includes: base station Alice transmitting signals, which are then decoded by nearby user Bob and distant user Carlo respectively. The second time slot includes: nearby user Bob forwarding his covert information to Carlo. If Alice does not transmit covert information in the first time slot, Bob transmits artificial interference noise in the second time slot. Throughout the process, Willie collects power through signal detection, which plays a role in detecting Alice's transmission behavior.

[0031] This invention relates to the application of wireless covert transmission technology in cooperative non-orthogonal multiple access systems, and the specific steps are as follows:

[0032] Step S1: Estimate the channel state information in the communication network by sending pilot sequences (Reference [1]: L.Lv, H.Jiang, ZGDing, L.Yang, J.Chen.Secrecy-enhancing design for cooperative downlink and uplink NOMA with an untrusted relay[J].IEEE Transactions on Communications, 2020, 68(3):1698-1715.) Specifically, the channel state information of the link between the base station and the near user and the link between the near user and the far user.

[0033] Step S2: In the first time slot, if base station Alice sends downlink superimposed signals for both users, i.e. Where, x b (t) is the signal from near user Bob, x c (t) is the signal of the remote user Carlo, P a It is the transmit power of base station Alice, α b With α c These are the power allocation coefficients of the two signals, satisfying α. b +α c =1, α b <α c , At this point, the expressions for the received signals by Bob and Carlo are:

[0034]

[0035]

[0036] In the formula, y b (t) represents Bob's received signal, y c (t) represents the received signal from Carlo, n b(t) and n c (t) represents the noise signal at Bob and Carlo, both of which follow a uniform distribution in the decibel domain. If Alice only transmits signals close to the user, then the expression for Bob's received signal is:

[0037] Step S3: If Alice sends downlink superimposed signals from both users, Bob and Carlo decode in the first time slot. According to serial interference cancellation technology, Bob first decodes x. c (t), therefore Bob decodes x in the first time slot c The signal-to-interference-plus-noise ratio (SIR) of (t) is:

[0038]

[0039] In the formula, Let x be the noise power at Bob's location. Bob then removes x from the two received signals. c (t), then decode its own signal x b (t), whose signal-to-noise ratio is:

[0040]

[0041] In the first time slot, Carlo directly decodes x from the received signal. c The signal-to-interference-plus-noise ratio at time (t) is:

[0042]

[0043] In the formula, Let be the noise power at Carlo.

[0044] Step S4: In the second time slot, Bob sends information based on the received signal. If Alice sends x... b (t) and x c (t), since Bob already knew x in the first time slot c (t) can act as a relay to forward x to Carlo. c (t), thereby enhancing the reception of concealed signals. Carlo's received signal at this time is represented as:

[0045]

[0046] If Alice only sends x b (t), In order to confuse Willie, Bob will simulate a normal cooperative non-orthogonal multiple access communication process and send artificial interference noise x in the second time slot. j (t). In either case, Willie will monitor the entire communication process because Willie cannot know x. cThe specific timing of sending (t).

[0047] Step S5: Willie performs binary detection. To obtain Willie's optimal decision threshold, hypothesis testing theory is generally used to analyze Willie's ability to detect legitimate communication behavior. Therefore, Willie's received signal is:

[0048]

[0049] In the formula, P b P is Bob's transmission power. j artificial interference signal x j The transmission power of (t), This represents the signal Willie received in the first time slot. The signal received by Willie in the second time slot is represented by nw(t), which is the noise signal at Willie's location. H0 and H1 represent the fact that Alice performed covert communication and did not perform covert communication, respectively.

[0050] Willie obtained the average power P for each time slot through energy detection. w Alice's communication behavior is judged by comparing it with a pre-set detection threshold τ. The specific detection rules are as follows: Where M represents the length of the covert information code, and D0 and D1 represent Willie's judgment on whether Alice performed covert transmission. When P w >τ, Willie determines that Alice has performed a covert transmission (D1), when P w <τ, Willie determines that Alice did not perform covert transmission (D0). Assuming the transmitted information code length is infinite, i.e., M→∞, then the average power detected by Willie is:

[0051]

[0052] In the formula, Z is the noise signal n at Willie. w The power of (t) has the following probability density function:

[0053]

[0054] In the formula, z2=ωσ 2 , σ 2 It is the estimated noise power, and ω (ω>1) is the noise uncertainty.

[0055] Step S6: Analyze the stealth performance of the system implemented in this invention. Willie's detection error probability is ξ = P. FA +P MD, where P FA =Pr(D1|H0) is the false alarm probability, representing the false alarm rate that was incorrectly predicted to have sent covert information even though no covert information was sent. P MD =Pr(D0|H1) represents the false alarm probability, indicating that a covert message was sent but was mistakenly judged not to have been sent. The specific expression for the false alarm probability is:

[0056] In formula (12), The expression for the probability of a missed detection is:

[0057]

[0058] In the formula, Since Δ2 > Δ1 and z2 > z1, Willie's false detection probability has two forms of expression.

[0059] 1) When Willie's false detection probability is:

[0060]

[0061] Taking the derivative of the above formula reveals that, in this case, the false detection probability first increases monotonically and then decreases monotonically, with the optimal detection threshold value being τ. * =Δ2+z1, at this time the minimum error detection probability is:

[0062]

[0063] 2) When Willie's false detection probability is:

[0064]

[0065] Clearly, the optimal detection threshold must be within the interval [Δ1+z2, Δ2+z1], at which point the minimum false detection probability is zero.

[0066] Step S8: Calculate the system interruption probability. The Alice-Carlo transmission interruption probability is calculated as follows:

[0067]

[0068] The probability of Alice-Bob's transmission being interrupted is:

[0069]

[0070] In the formula, The power coefficient ratio, R bR c xb(t) and xc(t) are the minimum transmission rates, respectively.

[0071] Step S9: Optimize the power coefficient ratio k under the constraints of concealment and reliability. This problem can be expressed as:

[0072]

[0073] η represents the system's hidden throughput; It is the interruption probability for user Bob. It is the interruption probability of the remote user's Carlo. The average minimum error detection probability is given by formula (15) for... Calculate the statistical average; δ represents the system reliability. Since Bob's interruption probability is greater than Carlo's, ... The constraints will be more stringent; ε represents the system's concealment.

[0074] For the hidden constraint, given any ε, we have k ≥ k2, where k2 is... The expression for k. Regarding the interrupt constraint, if Bob's minimum interrupt is greater than δ, then η is 0, so this case is not considered. Let k3 be... Since Bob's interruption probability first decreases and then increases, k3 generally has two values. The specific value needs to be determined by considering the trend of η and the value of ε. The optimal value of k can be divided into the following three cases.

[0075] 1) When 0 < k < k1, η increases continuously in this interval, while The power factor decreases continuously, therefore the optimal power factor allocation ratio is k. * =k1. Here, k1 is the... At that time, it made Minimum power factor allocation ratio.

[0076] 2) When Within this interval, η and All decrease continuously, at which point k * =max(k2,k3).

[0077] 3) When η decreases continuously within this interval, while The solution is continuously increasing. When k2 > k3, there is no solution to this problem; when k2 < k3, k... * =k2.

[0078] In summary, the optimal power allocation ratio k is as follows:

[0079]

[0080] Step S10: Determine the benchmark scheme and verify the superior performance of the proposed invention. The proposed solution suffers from noise uncertainty at all receiving nodes, while the benchmark scheme has no noise uncertainty at any receiving node.

[0081] Figure 3 It shows ω and P a right The influence of ω = 0. Where ω = 0 represents the ideal situation, i.e., there is no noise uncertainty at the receiver, P j =0 represents the case of no human interference. Clearly, the absence of noise uncertainty and human interference significantly reduces the difficulty of Willie's detection, and the system... All are lower than the proposed solution. It is easy to see that as ω increases, The ω increases accordingly, but gradually levels off. This means that a certain degree of noise uncertainty can be misleading for Willie, but excessively high ω can also affect legitimate communication, leading to communication interruptions, etc. This provides some reference for real-world situations and for interference activities at the monitoring end.

Claims

1. A covert transmission method based on a cooperative non-orthogonal multiple access communication system, characterized in that, Includes the following steps: Step S1: By sending pilot sequences, estimate the channel state information in the communication network, including the channel state information between the base station and the near user link and between the near user and the far user link. In the first time slot, according to the channel state, the base station sends a signal. The sent signal is a superimposed signal of the far user signal and the near user signal. The far user and the near user decode in the first time slot. In the second time slot, the user sends a message based on the received information. Step S2: The malicious detection node performs binary detection based on the received signal, compares the collected average power with a judgment threshold. If it is higher than the threshold, it is determined that the system is transmitting hidden information; if it is lower than the threshold, it is determined that the system is not transmitting hidden information. The signal received by the malicious detection node is: In the formula, x b (t) is the signal near the user, x c (t) is the signal from the remote user, P a It is the base station's transmit power, α b With α c These are the power allocation coefficients for the two signals, h ij P represents the channel coefficient from node i to node j, i∈{a,b}, j∈{b,c,w}, where a, b, c, and w represent the base station, the near user, the far user, and the malicious detection node, respectively. b To improve the user's transmission power, P j artificial interference signal x j The transmission power of (t), This represents the signal received by the malicious detection node in the first time slot. n represents the signal received by the malicious detection node in the second time slot. w (t) is the noise signal at the malicious detection node, where H0 and H1 represent the base station performing covert communication and not performing covert communication, respectively. The average power is compared with a judgment threshold τ, and the specific detection rule is as follows: Where M represents the length of the covert information code, and D0 and D1 represent the judgments of the malicious detection node on whether the base station has performed covert transmission; assuming the length of the transmitted information code is infinite, i.e., M→∞, then the average power detected by the malicious detection node is: In the formula, Z is the noise signal n at the malicious detection node. w The power of (t) has the following probability density function: In the formula, z2=ωσ 2 , σ 2 It is the estimated noise power, where ω (ω > 1) is the noise uncertainty; Step S3: Analyze the detection performance of malicious detection nodes and the probability of system outage to obtain the system's stealth performance and reliability. Under the constraints of the system's stealth performance and reliability, maximize the system's stealth throughput by optimizing the power allocation coefficient ratio k. When analyzing the system's stealth performance, it is necessary to calculate the false detection probability of malicious detection nodes. The false detection probability of malicious detection nodes is: 1) When The probability of a malicious detection node making a false detection is: Taking the derivative of the above formula reveals that, in this case, the false detection probability first increases monotonically and then decreases monotonically, with the optimal detection threshold value being τ. * =Δ2+z1, at this time the minimum error detection probability is: 2) When The probability of a malicious detection node making a false detection is: Clearly, the optimal detection threshold must be within the interval [Δ1+z2, Δ2+z1], and the minimum false detection probability is zero. The system outage probability includes: the base station-remote user transmission outage probability is: The probability of transmission interruption between the base station and the nearest user is: In the formula, The power coefficient ratio, R b R c x b (t) and x c (t) Minimum transmission rate; Considering the system's concealment performance and reliability constraints, the problem of optimizing the power allocation coefficient ratio k can be expressed as: η represents the system's hidden throughput; It is the interruption probability for user Bob. It is the interruption probability of the remote user's Carlo. δ represents the average minimum error detection probability; δ represents the system reliability; ε represents the system stealth. The optimal value of k can be divided into the following three cases: 1) When 0 < k < k1, η increases continuously in this interval, while The power factor decreases continuously, therefore the optimal power factor allocation ratio is k. * =k1; here k1 is when At that time, it made Minimum power factor allocation ratio; 2) When Within this interval, η and All decrease continuously, at which point k * =max(k2,k3); 3) When η decreases continuously within this interval, while The problem has no solution when k2 > k3, and when k2 < k3, k increases continuously. * =k2; In summary, the optimal power allocation ratio k is as follows:

2. The covert transmission method based on a cooperative non-orthogonal multiple access communication system according to claim 1, characterized in that: In the first time slot, if the base station sends the superimposed signals of two users, then it is... Where, x b (t) is the signal near the user, x c (t) is the signal from the remote user, P a It is the base station's transmit power, α b With α c These are the power allocation coefficients of the two signals, satisfying α. b +α c =1, α b <α c , At this time, the expressions for the received signals of the near user and the far user are: In the formula, y b (t) represents the received signal near the user, y c (t) represents the received signal from the remote user, n b (t) and n c (t) represents the noise signals at the near and far users; If the base station only transmits signals to the nearest user, then the expression for the received signal to the nearest user is: h ij Let represent the channel coefficients from node i to node j, i∈{a,b}, j∈{b,c,w}, where a, b, c, and w represent the base station, the near user, the far user, and the malicious detection node, respectively.

3. The covert transmission method based on a cooperative non-orthogonal multiple access communication system according to claim 2, characterized in that: In step S1, if the base station sends downlink superimposed signals for two users, the near user and the far user decode in the first time slot, with the near user decoding x first. c (t), first time slot near-user decoding x c The signal-to-interference-plus-noise ratio (SIR) of (t) is: In the formula, The noise power is located near the user; then the user cancels out x from the two received signals. c (t), then decode its own signal x b (t), whose signal-to-noise ratio is: In the first time slot, the distant user directly decodes x from the received signal. c The signal-to-interference-plus-noise ratio at time (t) is: In the formula, This represents the noise power at the remote user location.

4. The covert transmission method based on a cooperative non-orthogonal multiple access communication system according to claim 3, characterized in that: In the second time slot, the information sent by the user based on the received signal includes two cases: if the base station sends x b (t) and x c (t), where the nearest user acts as a relay to forward x to the distant user. c (t), where the received signal of the distant user is represented as: If the base station only sends x b (t), near the user sends artificial interference noise x j (t).

5. A covert transmission system based on a cooperative non-orthogonal multiple access communication system using the method described in any one of claims 1-4, characterized in that: include A base station is used to transmit signals, which are superimposed signals from distant and near users. The near-user node is used to receive signals sent by the base station and decode the signals. Depending on whether it contains the hidden information of the distant user, it can choose to forward the hidden information or send artificial interference signals in the second time slot. Remote user nodes are used to decode received hidden information; The detection node is used to receive information from the wireless channel and determine whether there is any covert information being transmitted.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements the steps of the covert transmission method based on a cooperative non-orthogonal multiple access communication system as described in any one of claims 1 to 4.

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