Non-orthogonal multiple access concealed communication method and cellular network system

Abstract

Disclosed are a non-orthogonal multiple access (NOMA) communication method and a cellular network system. The method comprises: a transmitting end sending multiple communication signals to multiple receiving ends; an interfering end cooperating with the transmitting end to send an interference signal; and enabling at least one of the multiple receiving ends to obtain a corresponding communication signal from the multiple communication signals and the interference signal via a reconfigurable smart surface (RIS). The communication scheme of the present invention utilizes the uncertainty of the amplitude and phase shift of the RIS in combination with the interference signal to improve the concealment of information transmission. At the same time, the uncertainty brought by the RIS can reduce the transmission power requirement of the existing interference signal, thereby reducing the overall power consumption and improving the overall communication rate of the cellular cell.

Description

Technical Field

[0001] The present disclosure relates to the field of wireless communications, and in particular to a non-orthogonal multiple access concealed communication method and a cellular network system. Background Art

[0002] In the upcoming sixth-generation wireless communication network (6G) era, it is foreseeable that massive amounts of data will be transmitted via wireless communications. This means that greater connectivity needs to be achieved within limited spectrum resources. One solution to improve spectrum utilization is non-orthogonal multiple access (NOMA), which can support multiple users on the same spectrum resource block through technologies such as power allocation, superposition coding, and successive interference cancellation (SIC).

[0003] With the increasing transmission of large amounts of private data over open wireless environments, network security has become increasingly important, leading to the development of physical layer security technologies. Physical layer security technologies can mitigate the risk of information leakage by exploiting the inherent randomness of noisy and fading channels. However, using existing physical layer security technologies solely to protect the content of communications is insufficient, as sometimes the communications themselves need to be hidden.

[0004] Therefore, a solution is needed to covertly transmit communication information from a legitimate sender to a legitimate receiver. Summary of the Invention

[0005] The technical problem addressed by this disclosure is to provide a non-orthogonal multiple access (NOMA) covert communication scheme that incorporates a reconfigurable smart surface (RIS). This communication scheme leverages the uncertainty of the amplitude and phase shift of the RIS in combination with interference signals to enhance the stealth of information transmission. Furthermore, the uncertainty introduced by the RIS reduces the transmit power requirement of existing interference signals, thereby reducing overall power consumption and increasing the overall communication rate of the cellular cell.

[0006] According to a first aspect of the present disclosure, a non-orthogonal multiple access (NOMA) covert communication method is provided, comprising: a transmitting end sending multiple communication signals to multiple receiving ends; an interfering end cooperating with the transmitting end to send an interference signal; and enabling at least one of the multiple receiving ends to obtain a corresponding communication signal from the multiple communication signals and the interference signal via a reconfigurable smart surface (RIS).

[0007] Optionally, the transmitting end sending multiple communication signals to multiple receiving ends includes: the transmitting end sending multiple communication signals with different powers on the same subcarrier, so that the multiple receiving ends each extract a corresponding communication signal from the received communication signal.

[0008] Optionally, when the at least one receiving end receives a signal via the reconfigurable smart surface, the interference signal transmission power of the interfering end is reduced.

[0009] Optionally, the interfering end and the transmitting end cooperate to send an interference signal, including: when the transmitting end sends multiple communication signals, the interfering end sends the interference signal with interference power, wherein the value of the interference power varies randomly within a threshold interference power range.

[0010] Optionally, when the at least one receiving end receives a signal via the reconfigurable smart surface, the interfering end sends the interference signal with reduced interference power, including: enabling the reconfigurable smart surface to construct an optimized channel for the at least one receiving end; and reducing the total transmission power of the transmitting end and the interfering end.

[0011] Optionally, the transmitting end is a cellular base station, the interfering end is a fixedly installed base station cooperative interferer, the reconfigurable smart surface is a fixedly installed base station cooperative reconfigurable smart surface within the coverage area of ​​the cellular base station, the receiving end is a cellular user, and the communication signal is a cellular communication signal.

[0012] Optionally, the transmitting end sends multiple communication signals to multiple receiving ends, and the interfering end cooperates with the transmitting end to send interference signals, including: the cellular base station obtains the distribution information of each of the multiple cellular users and determines whether each cellular user needs to receive cellular signals via the base station cooperative reconfigurable intelligent surface; and reduces the signal transmission power and interference transmission power for cellular users who receive cellular signals via the base station cooperative reconfigurable intelligent surface.

[0013] Optionally, reducing the interference signal transmission power of the interfering end includes: determining a reduction amount of the interference signal transmission power based on amplitude and phase shift changes of the base station cooperative reconfigurable smart surface.

[0014] Optionally, the method further includes: determining the relationship between the signal transmission power of the cellular base station and the interference power of the base station cooperative interference end based on the positions of the multiple cellular users, the amplitude and phase shift changes of the base station cooperative reconfigurable smart surface, so as to optimize the total communication rate of the multiple cellular users.

[0015] Optionally, the relationship between the cellular signal transmission power of the cellular base station and the interference power of the base station cooperative interference end for optimizing the total communication rate of the multiple cellular users is obtained based on reinforcement learning.

[0016] According to a second aspect of the present disclosure, a cellular network system is provided, comprising: a cellular base station for transmitting multiple cellular communication signals to multiple receiving terminals using non-orthogonal multiple access (NOMA) communication; an interferer for transmitting interference signals in coordination with the cellular base station; and a reconfigurable smart surface for reconstructing and forwarding the cellular communication signal of at least one cellular user among a plurality of cellular users.

[0017] Optionally, when the at least one receiving end obtains a corresponding communication signal from a specific subcarrier via a reconfigurable smart surface (RIS), the interferer reduces the transmission power of the interference signal for the specific subcarrier.

[0018] According to a third aspect of the present disclosure, a computing device is provided, comprising: a processor; and a memory on which executable code is stored, and when the executable code is executed by the processor, the processor executes the method described in the first aspect above.

[0019] According to a fourth aspect of the present disclosure, a non-transitory machine-readable storage medium is provided, on which executable code is stored. When the executable code is executed by a processor of an electronic device, the processor executes the method described in the first aspect above.

[0020] Thus, the communication scheme of the present invention utilizes both the uncertainty of RIS and interference power to improve concealment performance. Furthermore, the communication scheme of the present invention can also optimize the power relationship between normal signal power and interference signal power (e.g., power allocation when the total value is determined), thereby ensuring or even improving the communication performance of users within the cellular network. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure with reference to the accompanying drawings, wherein like reference numerals generally represent like components in the exemplary embodiments of the present disclosure.

[0022] Figure 1 A simplified diagram of the principles of OFDM and NOMA is shown.

[0023] Figure 2 The typical application of RIS in wireless cellular networks is shown.

[0024] Figure 3 A schematic flow chart of a non-orthogonal multiple access communication method according to an embodiment of the present invention is shown.

[0025] Figure 4 Schematic diagrams of cellular cell communication are shown with and without multiple RIS deployed.

[0026] Figure 5The figure shows a schematic diagram of the composition of a cellular network capable of implementing the covert communication solution of the present invention.

[0027] Figure 6 An example of implementing the present invention to perform covert communication based on NOMA and RIS is shown.

[0028] Figure 7 The figure shows a schematic diagram of the structure of a computing device that can be used to implement the above-mentioned non-orthogonal multiple access concealed communication method according to one embodiment of the present invention. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0030] To achieve greater connectivity with limited spectrum resources, the Non-Orthogonal Multiple Access (NOMA) scheme has been proposed to improve spectrum utilization. NOMA can be seen as a technology developed based on Orthogonal Frequency Division Multiplexing (OFDM).

[0031] Figure 1 The figure shows the principle diagram of OFDM and NOMA. OFDM divides the available frequency band into multiple subcarriers (for example, the minimum unit in the frequency domain is a subcarrier with a bandwidth of 15KHz). The subcarriers are orthogonal to each other and do not interfere with each other. Each subcarrier is then used to send information to one user in a predetermined time slice (for example, the minimum unit is a time of 1 / 14ms, corresponding to an OFDM symbol). Figure 1 As shown on the left, the three subcarriers sc1, sc2, and sc3 are used to transmit information for users U1, U2, and U3 (white, light gray, and dark gray, respectively). In terms of power, the user power carried on the frequency and time domain resource planes is the same. That is, the three mutually orthogonal subcarriers sc1, sc2, and sc3 each transmit communication information at the same power.

[0032] In contrast, non-orthogonal multiple access (NOMA) technology changes the power domain from being exclusive to a single user to being shared by multiple users, thereby increasing the total amount of wireless access. In the time domain, NOMA technology can still use OFDM symbols as the smallest unit, and insert CP (Cyclic Prefix) between symbols to prevent inter-symbol interference. In the frequency domain, subcarriers can still be used as the smallest unit, and OFDM technology is used between each subcarrier (i.e., each subchannel) to keep the subcarriers orthogonal to each other and non-interfering with each other. Unlike OFDM technology, the power corresponding to each subcarrier and OFDM symbol is no longer allocated to only one user, but is shared by multiple users. The signal power of different users on the same subchannel and OFDM symbol is non-orthogonal. In other words, NOMA technology uses the same resource unit corresponding to the same subcarrier and the same OFDM symbol for multiple users according to different signal powers, thereby achieving the purpose of multiple access. This is also the origin of the name "non-orthogonal multiple access".

[0033] Figure 1 The right side of the diagram also shows three subcarriers sc1, sc2, and sc3. However, unlike the OFDM scheme on the left, in the NOMA scheme on the right, in the same subcarrier, the total subcarrier power can be divided into multiple different powers, each used for communication for different users. For example, the total transmission power of subcarrier sc1 is P1, and communication information needs to be sent to three users (U1-U3) at the same time. At this time, P1 can be divided into P according to the distance between the three users and the transmitter (according to the principle of fairness, the farther the distance, the greater the power required). 11 、P 12 and P 13 (where P 11 >P 13 >P 12 And P 11 +P 12 +P 13 =P1), and use P 11 Send U1 communication information, use P 12 Send U2 communication information, use P 13 Similarly, the total transmission power of subcarrier sc2 is P2, and communication information needs to be sent to two users (U4 and U5) at the same time. At this time, P2 can be divided into P and P according to the distance between the two users and the transmitting end (according to the principle of fairness, the farther the distance, the greater the power required). 24 and P 25 (where P 24 >P 25 And P 24 +P 25 =P2), and use P 24Send U4 communication information, use P 25 Send the communication information of U5. The total transmission power of subcarrier sc3 is, for example, P3, and communication information needs to be sent to three users (U1-U3) at the same time. At this time, P3 can be divided into P according to the distance between the three users and the transmitting end (according to the principle of fairness, the farther the distance, the greater the power required). 36 、P 37 and P 38 (where P 37 >P 36 >P 38 And P 36 +P 37 +P 38 =P1), and use P 36 Send U6 communication information, use P 37 Send U7 communication information, use P 38 The NOMA technology on the right can transmit information to more users within the same frequency band compared to OFDM on the left.

[0034] NOMA can use serial interference cancellation (SIC) technology to solve the problem of interference between the power of each user in the power domain. Specifically, at the transmitting end, NOMA uses power multiplexing (or power allocation) technology to allocate the signal power of different users on the same subcarrier according to the relevant algorithm, so that the signal power of each user reaching the receiving end is different. At the receiving end, NOMA uses SIC technology to cancel interference in a certain order according to the signal power of different users, thereby achieving the purpose of distinguishing different users.

[0035] In addition to encrypting communication content, underlying physical layer security technologies have been proposed to protect wireless network communications. Physical layer security technologies can reduce the risk of information leakage by exploiting the inherent randomness of noise and fading channels. However, in many scenarios, protecting communication content using existing physical layer security technologies alone is insufficient; the communication itself needs to be concealed. Therefore, the concept of covert communication has been proposed. Covert communication can be defined as the covert transmission of information from a legitimate sender to a legitimate receiver with negligible probability of detection by unauthorized eavesdroppers.

[0036] In the communication scheme of the present invention, in addition to utilizing the aforementioned NOMA technology, which improves spectral efficiency by assigning multiple users to a single resource block, to better achieve covert communication, reconfigurable smart surface (RIS) technology can also be introduced. RIS is a low-cost implementation solution that can improve the spectral efficiency of wireless communication networks. Compared to traditional communication-aiding technologies such as relays, RIS consumes less energy due to passive reflection and can operate in full-duplex (FD) mode without generating self-interference.

[0037] RIS is a planar array composed of a large number of low-cost passive reflective elements, each of which independently induces amplitude and / or phase variations in the incident signal, collaboratively achieving sophisticated three-dimensional (3D) reflective beamforming. Unlike existing transmitter / receiver wireless link adaptation technologies, RIS actively modifies the wireless channel between the transmitter and receiver through highly controllable and intelligent signal reflection. This opens new possibilities for further improving wireless link performance. By appropriately tuning the 3D passive beamforming, the signal reflected by the RIS can be constructively added with signals from other paths to enhance the desired signal power at the receiver, or destructively cancel undesired signals such as co-channel interference. Because RIS eliminates the need for a transmit RF chain and operates only over short distances, it can be densely deployed with scalable cost and low energy consumption, eliminating the need for complex interference management between passive RIS elements. RIS are typically fabricated with a low profile, lightweight, and conformal geometry, making them easily installed and removed from walls, ceilings, building facades, advertising panels, and other surfaces. Furthermore, because RIS is a complementary device, deploying it within existing wireless systems (such as cellular networks) in wireless networks does not require changing standards or hardware, requiring only necessary modifications to the communication protocols. Therefore, integrating RIS into wireless networks is transparent to users, providing high flexibility and superior compatibility with existing wireless systems.

[0038] Figure 2 Figure 1 shows a typical application of RIS in wireless cellular networks. Figure 2 As shown on the left side of the middle vertical line, the direct link between the user located in the dead zone and its serving base station is blocked by obstacles. In this case, deploying a RIS with clear links to the base station and the user helps to bypass the obstacles through intelligent signal reflection, thereby creating a virtual line of sight (LoS) link between them. This is particularly useful for coverage extension in mmWave communications that are susceptible to indoor blockages. Figure 2 As shown on the right side of the middle vertical line, for cell-edge users that suffer from both high signal attenuation from their serving base station (the base station on the left side of the figure) and severe co-channel interference from adjacent base stations (the base stations on the right side of the figure), RIS can be deployed at the cell edge. By properly designing its reflection beamforming, it not only helps to improve the desired signal power but also helps to suppress interference.

[0039] Therefore, the present invention proposes a non-orthogonal multiple access (NOMA) covert communication scheme that incorporates a reconfigurable smart surface (RIS). This scheme simultaneously leverages the uncertainty of the RIS's amplitude and phase shift (uncertainty for non-normal users) and interference power to improve the concealment performance of information transmission. The uncertainty introduced by the RIS reduces the existing interference power, enabling the base station to transmit communication information at a higher power when the total power is determined, thereby improving the overall communication rate of the network.

[0040] Figure 3 A schematic flow chart of a non-orthogonal multiple access communication method according to an embodiment of the present invention is shown. The method can be implemented by any wireless communication system that uses NOMA for communication and needs to conceal the communication content.

[0041] In step S310, the transmitting end sends multiple communication signals to multiple receiving ends. The transmitting end can use NOMA technology to send multiple communication signals to multiple receiving ends. Specifically, the transmitting end can Figure 1 As shown on the right, communication information is sent using orthogonal subcarriers (subchannels), and different powers can be used on the same subcarrier to send signals to different receiving ends.

[0042] In step S320, the interfering end cooperates with the transmitting end to transmit an interference signal. Here, the interfering end can be a friendly interfering end, which is used to transmit the interference signal under the control of the transmitting end or in cooperation with the transmitting end. For example, when the transmitting end transmits multiple communication signals, the interfering end transmits the interference signal at an interference power. When the transmitting end transmits signals using multiple subcarriers, the interfering end can also transmit the interference signal using multiple subcarriers. Since the interference signal is transmitted simultaneously and the content of the interference signal is known to the receiving end (or can be eliminated by the receiving end), the interference signal itself can interfere with the eavesdropper's judgment of whether the transmitting end is transmitting a signal to the receiving end.

[0043] Furthermore, in order to improve the interference resistance, the transmission power of the interference signal needs to be randomly changed. Specifically, the interference power P J Considered as a random variable, uniformly distributed in In this way, uncertainty (against the eavesdropper) is generated. It can be regarded as a pre-defined threshold interference power, or an upper limit of random variation of interference power.

[0044] In step S330, at least one of the multiple receiving ends can be enabled to obtain a corresponding communication signal from the multiple communication signals and the interference signal via a reconfigurable smart surface (RIS). Specifically, by appropriately arranging the RIS or selecting receiving ends based on the distribution of receiving ends, the multiple receiving ends can include a receiving end that receives signals via the RIS. In the implementation of a cellular cell, multiple RIS can be reasonably arranged within the cellular cell to ensure a high probability that legitimate users within the cell communicate using the RIS. As mentioned above, the RIS is a plane composed of a large number of passive reflective elements, each of which can independently induce amplitude and / or phase changes in the incident signal. The amplitude and / or phase changes can be known by the receiving end, but are unknown to eavesdroppers. Therefore, the signal transmitted through the RIS will further introduce uncertainty in amplitude and phase for non-normal users (e.g., eavesdroppers), thereby further enhancing the concealment of the communication from the sender to the receiver from eavesdroppers.

[0045] In one embodiment, Figure 3 The method shown can be regarded as a covert communication method for a specific subcarrier within the communication frequency band. In this case, the transmitting end sending multiple communication signals to multiple receiving ends may include: the transmitting end sending multiple communication signals at different powers on the same subcarrier, so that each of the multiple receiving ends can extract the corresponding communication signal from the received communication signal. Figure 1 For example, the transmitter can use P on subcarrier sc1. 11 Send U1's communication information to P 12 Send U2 communication information to P 13 Send the communication information of U3, U1, U2 and U3 can each receive the three messages on subcarrier sc1 and parse the required information according to the transmission power; 24 Send U4 communication information to P 25 Send U5 communication information, U4 and U5 can each receive these two messages on subcarrier sc2, and parse out the information they need based on the transmission power; can receive the two messages on subcarrier sc3 with P 36 Send U6 communication information to P 37 Send U7 communication information to P 38 When sending the communication information of U8, U6, U7 and U8 can each receive the three messages on subcarrier sc3 and parse out the required information according to the transmission power.

[0046] Correspondingly, the interfering end may also send an interference signal on each subcarrier. For example, the interfering end may also send an interference signal on three subcarriers sc1, sc2 and sc3 with interference power P J1 、P J2 and PJ3 To transmit the interference signal, at this time, P J1 、P J2 and P J3 Each can be an independently changing random variable and uniformly distributed in middle.

[0047] Here, since the purpose of introducing the interference end is to prevent the eavesdropper from knowing whether there is a legitimate signal transmission on the current subcarrier through the uncertainty of the interference power transmitted by the interference end, the transmission through the RIS will bring further uncertainty because each element of the RIS can independently induce the amplitude and / or phase change of the incident signal. Therefore, when the at least one receiving end receives the signal via the reconfigurable smart surface, the interference end can reduce the transmission power of the interference signal, that is, reduce the upper limit of the interference power. The above-mentioned reduction in the transmission power of the interference signal can be a reduction in the distribution range of the interference power. At this time, when at least one of the multiple receiving ends obtains the corresponding communication signal based on the reconfigurable smart surface, reducing the interference signal transmission power of the interference end may include: when it is determined that there is at least one receiving end that obtains the corresponding communication signal based on the reconfigurable smart surface, causing the value of the interference power to randomly change within a second threshold interference power range, and the value of the second threshold interference power is less than the threshold interference power.

[0048] Specifically, the reduction of the threshold interference power can be performed for subcarriers with RIS forwarding. For example, in the example where the three subcarriers sc1, sc2 and sc3 send communication signals to U1-U8, if U5 operating on subcarrier sc2 and U7 operating on subcarrier sc3 receive signals via RIS, the P can be reduced respectively. J2 and P J3 The value distribution range of J2 and P J3 is evenly distributed in A random variable in which The value is less than It can be regarded as a reduced upper limit of interference power.

[0049] The NOMA covert communication scheme introduced by the present invention using RIS can be applied to various application scenarios where NOMA can be used for wireless communication, and can particularly be implemented as a cellular communication scheme. To this end, in a preferred embodiment of the present invention, the transmitting end is a cellular base station, the interfering end is a fixed base station cooperative jammer, the reconfigurable smart surface is a fixed reconfigurable smart surface installed within the coverage area of ​​the cellular base station, the receiving end is a cellular user, and the communication signal is a cellular communication signal.

[0050] In cellular network implementations, cellular base stations, base station cooperative jammers, and RISs are relatively fixedly positioned at optimized locations, and the building structure within the cellular network remains relatively constant. Therefore, cellular base stations have knowledge of the jammer locations, RIS locations, and building distribution within their own cells. The present invention ensures a high probability that legitimate users within a cell will communicate using the RISs by deploying multiple RISs within the cell. Figure 4 Schematic diagrams of cellular cell communication are shown with and without multiple RIS deployed.

[0051] like Figure 4 As shown in the left figure, there are several legal receivers and illegal eavesdroppers in the cell, and some legal receivers cannot receive services because they are too far away and outside the coverage area of ​​the cell.

[0052] The legitimate sender (base station) currently has several channels available, but since the number of available channels is less than the number of users, NOMA is needed for channel multiplexing. Under a certain NOMA channel allocation scheme, all receivers are assigned to these channels. In the conventional jammer-assisted covert communication shown in the left figure, the jammer sends an interference signal, making it impossible for illegal eavesdroppers to accurately determine whether there is a legitimate transmission in a certain channel. However, in order to achieve covert communication, the power of the interference signal sent by the jammer needs to reach a certain intensity, which increases the difficulty for the legitimate receiver to recover its own signal from the normally transmitted signal, and makes the power overhead of covert communication too large.

[0053] The introduction of RIS can, on the one hand, enhance the communication quality of users within the RIS coverage area, and on the other hand, enable legitimate users who are unable to receive services to receive signals. In terms of concealment, illegal eavesdroppers within its coverage area will be more unable to accurately determine the existence of legitimate transmissions due to greater uncertainty (from the uncertainty of RIS amplitude and phase). In addition, since RIS has low cost and energy consumption, it can be used in actual operation. Figure 4 As shown in the figure on the right, by deploying multiple RISs to cover most of the cell area, any legitimate user communicating within the cell will likely complete communication through the RIS. This improves user communication quality, reduces the transmission power of interference signals, and reduces the probability of successful detection of illegal eavesdroppers, thereby improving network security.

[0054] Based on this knowledge, the cellular base station can determine in real time which subcarriers to use to transmit cellular communication signals to which cellular users, thereby optimizing the effectiveness of covert communication. To this end, a transmitting end transmits multiple communication signals to multiple receiving ends, and the interfering end cooperates with the transmitting end to transmit interference signals, including: the cellular base station obtains the distribution information of each of the multiple cellular users and determines whether each cellular user needs to receive cellular signals via the base station-cooperative reconfigurable smart surface; and reduces the signal transmission power and interference transmission power for cellular users receiving cellular signals via the base station-cooperative reconfigurable smart surface. Thus, through the reasonable arrangement of RIS within the cellular cell, the subcarriers used are likely to include the uncertainty introduced by the RIS (uncertainty for eavesdroppers), thereby reducing the overall interference signal transmission power of the jammer. When the total transmission power of the base station and the jammer is limited, reducing the jammer's transmission power means increasing the base station's transmission power, thereby improving the overall communication rate of the cellular network. Alternatively, the jammer's transmission power can be simply reduced without adjusting the base station's transmission power, thereby reducing power consumption.

[0055] Furthermore, the reduction in the interference signal transmission power can be calculated based on the amplitude and phase shift changes of the base station cooperative reconfigurable smart surface. Furthermore, based on the locations of the multiple cellular users and the amplitude and phase shift changes of the base station cooperative reconfigurable smart surface, the relationship between the signal transmission power of the cellular base station and the interference power of the base station cooperative interference end can be determined to optimize the total communication rate of the multiple cellular users. In a preferred embodiment, the relationship between the cellular signal transmission power of the cellular base station and the interference power of the base station cooperative interference end can be calculated based on reinforcement learning to optimize the total communication rate of the multiple cellular users.

[0056] According to another aspect of the present invention, it can also be implemented as a cellular network system. Figure 5 A schematic diagram of a cellular network capable of implementing the covert communication solution of the present invention is shown. As shown, the cellular network may include a base station 510, a jammer 520, and multiple strategically placed RISs 530, such as RISs located at the edge of the cellular network or to avoid obstruction by buildings.

[0057] A cellular base station 510 transmits multiple cellular communication signals to multiple receiving terminals using non-orthogonal multiple access (NOMA) communication. An interferer 520 is configured to coordinate with the cellular base station to transmit interference signals. A RIS 530 is configured to reconstruct and forward the cellular communication signal of at least one cellular user among the multiple cellular users.

[0058] As previously described, when at least one cellular user obtains a corresponding communication signal from a specific subcarrier via a reconfigurable intelligent surface (RIS), the jammer 520 reduces the power of the interference signal transmitted on the specific subcarrier. Preferably, the cellular base station 510 can perform real-time subcarrier allocation for users within the cell based on the user's location relative to the RIS, so that each subcarrier in use includes a cellular user that needs to receive signals via the RIS, thereby reducing the interference power of the jammer on each subcarrier.

[0059] The above describes a communication scheme that simultaneously utilizes the uncertainty of RIS and interference power to improve concealment performance. Furthermore, the communication scheme of the present invention can also optimize the power relationship between normal signal power and interference signal power (e.g., power allocation when the total value is determined), thereby ensuring or even improving the communication performance of users within the cellular network.

[0060] Application Examples

[0061] In order to further illustrate the principle of the present invention, the following Figure 5 An application example of the present invention is described. Figure 6 An example of implementing the present invention to perform covert communication based on NOMA and RIS is shown.

[0062] A. System Model

[0063] like Figure 6 As shown, consider a system consisting of a legitimate sender (A), a pair of NOMA legitimate receivers (B1 and B2), a RIS and a friendly jammer (J). Specifically, A is a cellular cell base station and J is a cooperative jammer. B2 is a cell center user that can communicate directly with A, while B1 is a cell edge user. Since there is no direct link between A and B1 due to the long distance and blocking objects, a RIS is needed to assist the communication between A and B1. An illegal eavesdropper (W) aims to detect whether A is sending a message to B2. By exploiting the properties of NOMA, the existence of this transmission is hidden from W. That is, in this example, it is necessary to implement covert transmission of A-B2, and assume that the A-B1 transmission is public. J is controlled by A to reduce the probability that the A-B2 transmission is detected by W. In this system, it is assumed that all nodes have one antenna.

[0064] RIS has N reflection units, and its reflection coefficient matrix is ​​recorded as Θ = diag (β1e jθ1 ,β2e jθ2 ,...,β N e jθN ), where β n ∈[0,1] and θ n∈[0,2π) are the amplitude reflection coefficient and phase shift variable of the nth reflection unit respectively.

[0065] 1) Channel model: It is necessary to consider both path loss and small-scale fading. The small-scale fading vectors between A / J / B1 / W and RIS are denoted as h AR / h JR / h RB / h RW , the space of these vectors is N×1. The small-scale fading between A / J and B2 is represented by h AB / h JB The small-scale fading between A / J and W is represented by h AW / h JW In addition, all channels experience path loss where d χ is the distance, α χ is the path loss coefficient.

[0066] 2) Signal model: A transmission signal sequence, Among them, P A is the transmission power of A, s1(k) and s2(k) are the signals transmitted to B1 and B2 respectively, and α1 and α2 represent the power allocation coefficients of B1 and B2 respectively (α1+α2=1). First, assume that the power allocation between the two users is fixed and set α1>α2 to achieve user fairness. On the other hand, J sends an interference signal sequence Among them, P J is the interference power, s J (k) is the interference signal that confuses W. Interference power P J is a random variable uniformly distributed over , thus generating uncertainty. Its probability density function (PDF) is:

[0067]

[0068] The received signals at B1 and B2 are as follows:

[0069]

[0070]

[0071] in,

[0072] At the B1 end, its signal is directly decoded and the B2 signal is regarded as interference. Its signal-to-noise ratio is:

[0073]

[0074] in Is the self-interference elimination coefficient. At B2, the signal of B1 is first detected, and the corresponding signal-to-noise ratio is:

[0075]

[0076] After achieving continuous interference cancellation, the signal of B2 is decoded and the corresponding signal-to-noise ratio is;

[0077]

[0078] On the other hand, W attempts to W (k), k=1,2,...,K, and use the Neyman-Pearson test to determine whether A is sending a message to B2. Therefore, W actually faces a binary detection problem:

[0079] 1) The null hypothesis H0 states that A does not transmit information to B2. 2) The alternative hypothesis H1 states that information is continuously transmitted from A to B2. The received signals observed by W under the two hypotheses are as follows:

[0080]

[0081]

[0082] in, L5=L(d JW ),L6=L(d RW )L(d JR ),L7=L(d AW ),L8=L(d RW )L(d AR ).

[0083] Based on (7) and (8), W is detected using a radiometer for binary detection. By monitoring the average received power of W, The decision rules are as follows:

[0084]

[0085] Where τ>0 is the detection threshold of W, and D0 and D1 are the decision results in favor of H0 and H1, respectively. It can be assumed that W uses an infinite number of signal samples for binary detection, that is, K→∞. Therefore, the uncertainty of the transmitted signal and the received noise does not exist, and the average received power of W is:

[0086]

[0087] in,

[0088] B. Performance Indicators

[0089] The performance indicators can be set as detection error probability (DEP) and ergodicity, which are used for power optimization problems.

[0090] 1) Detection Error Probability: The concealment performance can be measured by DEP, which is the probability of W making an error, mathematically defined as:

[0091]

[0092] in, is the false alarm probability, represents the probability of missed detection, ξ∈[0,1].

[0093] 2) Ergodic rate: The transmission between A and B1 is public, and its ergodic rate is:

[0094]

[0095] Where B is the bandwidth, which is set to 1 without loss of generality. The data rate of B2 in covert communication is called the covert rate. Its ergodic covert rate is:

[0096]

[0097] C. Power Allocation Optimization

[0098] In order to improve the performance of the covert RIS-NOMA communication system, the goal can be set to optimize the transmission power (P A ) and the upper limit of the interference power of J Therefore, the optimization problem can be formulated as

[0099]

[0100] Limited by

[0101]

[0102] in is the average minimum DEP (AMDEP). Specifically, (14a) maximizes the sum of the ergodic rates of B1 and B2, (14b) is the transmit power constraint, and (14c) is the concealment performance constraint, where ε is the predefined concealment performance requirement.

[0103] In other words, the transmit power (P A ) and the upper limit of the interference power of J The optimization relationship between B1 and B2 is to maximize the overall communication rate of B1 and B2.

[0104] Various methods can be used to find the optimal solution to the above optimization problem. In one embodiment, reinforcement learning (RL) can be used to find how to optimize the transmission power (P) of A for different cellular terminal locations when a specific base station and RIS are arranged. A ) and the upper limit of the interference power of J To maximize the overall communication rate of cellular users.

[0105] Reinforcement learning (RL) is a learning process in which an agent takes actions in an environment to maximize its reward. RL has a set of states and a set of actions. At each time step t, the agent observes the state s t And perform action a t Then, the state changes from s t Transfer to s t+1 , the agent receives a reward r t . The state transition follows a Markov decision process. The goal of RL is to learn a mapping from states and actions to long-term reward values. Therefore, RL can be used to optimize power allocation to maximize, for example Figure 6 The sum rate of two users B1 and B2 is shown.

[0106] In practical applications, since the locations of base stations, jammers, RIS and building distribution in each cell are relatively fixed, it is possible to determine how to allocate subcarriers to different users and how to allocate the transmission power (P) of A to the user under various user distribution conditions in the cell. A ) and the upper limit of the interference power of J Power is distributed among the users so as to improve the overall communication rate of the users and / or reduce the overall power consumption while ensuring covert communication.

[0107] Figure 7 The figure shows a schematic diagram of the structure of a computing device that can be used to implement the above-mentioned non-orthogonal multiple access concealed communication method according to one embodiment of the present invention.

[0108] See also Figure 7 The computing device 700 includes a memory 710 and a processor 720. The computing device can be implemented as a control device of a base station or an interfering terminal.

[0109] The processor 720 may be a multi-core processor or may include multiple processors. In some embodiments, the processor 720 may include a general-purpose main processor and one or more special coprocessors, such as a graphics processing unit (GPU) or a digital signal processor (DSP). In some embodiments, the processor 720 may be implemented using customized circuits, such as application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs).

[0110] The memory 710 may include various types of storage units, such as system memory, read-only memory (ROM), and permanent storage devices. ROM may store static data or instructions required by the processor 720 or other modules of the computer. The permanent storage device may be a readable and writable storage device. The permanent storage device may be a non-volatile storage device that retains stored instructions and data even when the computer is powered off. In some embodiments, the permanent storage device uses a large-capacity storage device (such as a magnetic or optical disk, flash memory) as the permanent storage device. In other embodiments, the permanent storage device may be a removable storage device (such as a floppy disk, optical drive). The system memory may be a readable and writable storage device or a volatile readable and writable storage device, such as dynamic random access memory. The system memory may store some or all instructions and data required by the processor during operation. In addition, the memory 710 may include any combination of computer-readable storage media, including various types of semiconductor memory chips (DRAM, SRAM, SDRAM, flash memory, programmable read-only memory), and magnetic disks and / or optical disks may also be used. In some embodiments, the memory 710 may include a readable and / or writable removable storage device, such as a compact disc (CD), a read-only digital versatile disc (e.g., DVD-ROM, dual-layer DVD-ROM), a read-only Blu-ray disc, an ultra-density optical disc, a flash memory card (e.g., SD card, mini SD card, Micro-SD card, etc.), a magnetic floppy disk, etc. Computer-readable storage media do not include carrier waves and transient electronic signals transmitted wirelessly or wired.

[0111] The memory 710 stores executable codes. When the executable codes are processed by the processor 720, the processor 720 can execute the non-orthogonal multiple access concealed communication method described above.

[0112] The non-orthogonal multiple access covert communication method and corresponding cellular network system according to the present invention have been described in detail with reference to the accompanying drawings. The communication scheme of the present invention utilizes both the uncertainty of RIS and interference power to improve covert performance. Furthermore, the communication scheme of the present invention can optimize the power relationship between normal signal power and interference signal power (e.g., power allocation when the total value is determined), thereby ensuring or even improving communication performance for users within the cellular network.

[0113] In addition, the method according to the present invention may also be implemented as a computer program or a computer program product, which includes computer program code instructions for executing the above steps defined in the above method of the present invention.

[0114] Alternatively, the present invention can also be implemented as a non-transitory machine-readable storage medium (or computer-readable storage medium, or machine-readable storage medium) on which executable code (or computer program, or computer instruction code) is stored. When the executable code (or computer program, or computer instruction code) is executed by a processor of an electronic device (or computing device, server, etc.), the processor executes the various steps of the above-mentioned method according to the present invention.

[0115] Those skilled in the art will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both.

[0116] The flowcharts and block diagrams in the accompanying drawings show the possible implementation architecture, functions and operations of the systems and methods according to multiple embodiments of the present invention. In this regard, each box in the flowchart or block diagram can represent a module, program segment or part of code, and the part of the module, program segment or code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order than that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flowchart, and the combination of the boxes in the block diagram and / or flowchart, can be implemented with a dedicated hardware-based system that performs the specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0117] While various embodiments of the present invention have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to existing technologies, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A non-orthogonal multiple access (NOMA) covert communication method, comprising: The transmitting end sends multiple communication signals to multiple receiving ends; The interference end cooperates with the transmitting end to transmit an interference signal; as well as enabling at least one of the plurality of receiving ends to obtain a corresponding communication signal from the plurality of communication signals and the interference signal via a reconfigurable smart surface (RIS); When the at least one receiving end receives a signal via the reconfigurable smart surface, the interfering end transmits the interference signal with reduced interference power, where the amount of reduction in the interference power is determined based on amplitude and phase shift changes of the reconfigurable smart surface.

2. The method according to claim 1, wherein The transmitting end sends multiple communication signals to multiple receiving ends, including: The transmitting end transmits a plurality of communication signals at different powers on the same subcarrier, so that each of the plurality of receiving ends extracts a corresponding communication signal from the received plurality of communication signals.

3. The method according to claim 1, wherein The interfering end and the transmitting end cooperate to transmit the interference signal, including: When the transmitting end sends a plurality of communication signals, the interfering end sends an interference signal with an interference power, wherein the value of the interference power varies randomly within a threshold interference power range.

4. The method according to claim 1, wherein When the at least one receiving end receives a signal via the reconfigurable smart surface, the interfering end sending the interference signal with reduced interference power includes: enabling the reconfigurable smart surface to construct an optimized channel for the at least one receiving end; and The total transmission power of the transmitting end and the interfering end is reduced.

5. The method according to claim 1, wherein The transmitting end is a cellular base station, the interfering end is a fixedly installed base station cooperative jammer, the reconfigurable smart surface is a fixedly installed reconfigurable smart surface within the coverage area of ​​the cellular base station, the receiving end is a cellular user, and the communication signal is a cellular communication signal.

6. The method according to claim 5, wherein: The transmitting end sends multiple communication signals to multiple receiving ends, and the interfering end cooperates with the transmitting end to send the interference signal, including: The cellular base station obtains distribution information of each of the plurality of cellular users and determines whether each cellular user needs to receive a cellular signal via the base station in cooperation with the reconfigurable smart surface; and The signal transmission power and interference transmission power for cellular users receiving cellular signals via a base station in cooperation with a reconfigurable smart surface are reduced.

7. The method of claim 5, further comprising: Based on the positions of the plurality of cellular users, the amplitude and phase shift changes of the reconfigurable smart surface, the relationship between the signal transmission power of the cellular base station and the interference power of the interference end is determined to optimize the total communication rate of the plurality of cellular users.

8. The method of claim 7, wherein: Based on reinforcement learning, a relationship between the cellular signal transmission power of the cellular base station and the interference power of the interfering end is obtained to optimize the total communication rate of the plurality of cellular users.

9. A cellular network system comprising: A cellular base station transmits multiple cellular communication signals to multiple cellular users using non-orthogonal multiple access (NOMA) communication; an interference device, configured to cooperate with the cellular base station to transmit an interference signal; as well as A reconfigurable smart surface, configured to reconstruct and forward a cellular communication signal of at least one cellular user among a plurality of cellular users; When at least one cellular user obtains a corresponding communication signal from a specific subcarrier via a reconfigurable smart surface (RIS), the jammer reduces the transmission power of an interference signal for the specific subcarrier, and the amount of reduction in the transmission power is determined based on the amplitude and phase shift changes of the reconfigurable smart surface.

10. A computing device comprising: processor; as well as A memory having executable codes stored thereon, which, when executed by the processor, causes the processor to perform the method according to any one of claims 1 to 8.

11. A non-transitory machine-readable storage medium having executable codes stored thereon, which, when executed by a processor of an electronic device, causes the processor to perform the method according to any one of claims 1 to 8.

12. A computer program product having executable codes stored thereon, which, when executed by a processor of an electronic device, causes the processor to perform the method according to any one of claims 1 to 8.

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