Secure Communication Method and Device Combining Covert Sensing and Auxiliary Jamming

Abstract

The present invention provides a secure communication method and apparatus combining covert sensing and assisted jamming, which can be used in the field of communication technology. It receives the communication beamforming parameters and the communication and sensing beamforming parameters obtained by solving the optimization problem; predicts the current state information based on the historical state information of the eavesdropper; transmits the sensing signal and the current state information based on the communication and sensing beamforming parameters, so that the jammer jams the eavesdropper; communicates with the covert user terminal based on the communication beamforming parameters and the intelligent reflecting surface optimized by the optimal phase shift; when receiving the sensed echo signal, estimates the accurate state information of the eavesdropper and uses it as the historical state information. In this solution, the relevant parameters obtained by solving the optimization problem are received to optimize the transmit beamforming, then the state information of the sensing eavesdropper is tracked and sent to the jammer to prevent the eavesdropping of the eavesdropper. With the help of the intelligent reflecting surface with the optimized phase shift, the base station communicates with the covert user terminal, thereby achieving the purpose of improving the covert communication rate.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and particularly to a secure communication method and device combining covert sensing and assisted jamming. Background Art

[0002] With the rapid development of wireless communication technologies, people are increasingly relying on wireless networks for information transmission. However, a large amount of important and sensitive information, such as identity information, confidential documents, etc., is transmitted in open wireless networks, increasing the risk of being eavesdropped. Therefore, information security issues have attracted more and more attention.

[0003] To protect communication content from being detected by eavesdroppers, covert communication technologies have emerged. The purpose of covert communication is to achieve information transmission between a base station (such as Alice) and a covert user (such as Bob) without being detected by eavesdroppers (such as Willie). Covert communication technologies achieve the concealment of communication by utilizing the randomness and uncertainty of the channel, as well as the superposition and cover of signals. In a covert communication system, a covert user refers to a user whose information transmission needs to be carried out without being detected by eavesdroppers. At the same time, an open user refers to a user whose information transmission does not need to be hidden but is carried out normally.

[0004] In existing covert communication systems, a communication model assisted only by intelligent reflecting surfaces or the simplest three-node model is adopted. During the covert communication process, it is impossible to interfere with eavesdroppers, resulting in a low covert communication rate. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a secure communication method and device combining covert sensing and assisted jamming to achieve the purpose of improving the covert communication rate.

[0006] To achieve the above purpose, embodiments of the present invention provide the following technical solutions:

[0007] A first aspect of an embodiment of the present invention discloses a secure communication method combining covert sensing and assisted jamming, which is applied to a base station. The base station is communicatively connected to a jammer, an intelligent reflecting surface, and a central controller respectively. The method includes:

[0008] Receiving the communication beamforming parameters and the communication and sensing beamforming parameters obtained by the central controller solving an optimization problem. The optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal;

[0009] For each time slot in the service cycle of the eavesdropper, if the time slot is the first time slot, the initial state information of the known eavesdropper is used as the current state information. If the time slot is not the first time slot, the current state information is predicted based on the historical state information of the eavesdropper obtained in the previous time slot;

[0010] Based on the communication and sensing beamforming parameters, a first superimposed signal including a sensing signal and the current state information is transmitted, so that after receiving the current state information, the jammer sends a jamming signal to the eavesdropper;

[0011] Based on the communication beamforming parameters, a first message signal to be sent to the covert user terminal is sent to the intelligent reflecting surface, so that the intelligent reflecting surface sends the first message signal to the covert user terminal based on the optimal phase shift; the optimal phase shift is obtained by the central controller solving the optimization problem and sent to the intelligent reflecting surface;

[0012] When the sensing echo signal reflected by the eavesdropper from the sensing signal is received, the accurate state information of the eavesdropper is estimated based on the sensing echo signal, and the accurate state information is used as the historical state information for the next time slot.

[0013] Preferably, when receiving the sensing echo signal reflected by the eavesdropper from the sensing signal, estimating the accurate state information of the eavesdropper based on the sensing echo signal includes:

[0014] When receiving the sensing echo signal reflected by the eavesdropper from the sensing signal, relevant information of the eavesdropper is extracted from the sensing echo signal;

[0015] Using the relevant information and a tracking model constructed based on the extended Kalman filter technology, the accurate state information of the eavesdropper is obtained.

[0016] Preferably, the method further includes:

[0017] If the sensing echo signal is not received, the current state information is used as the historical state information for the next time slot.

[0018] Preferably, the method further includes:

[0019] If there is a first message signal to be sent to the covert user terminal and a second message signal to be sent to the public user terminal, based on the communication beamforming parameters, a second superimposed signal including the first message signal and the second message signal is sent to the intelligent reflecting surface, so that the intelligent reflecting surface sends the second superimposed signal to the covert user terminal and the public user terminal based on the optimal phase shift.

[0020] A second aspect of the embodiments of the present invention discloses a secure communication method combining covert sensing and assisted interference, which is applied to a central controller. The central controller is communicatively connected to a base station and an intelligent reflecting surface respectively. The method includes:

[0021] Construct a non-convex optimization problem according to multiple pre-analyzed constraints. The constraints include: communication covertness constraint, sensing covertness constraint, total power constraint, sensing capability constraint, radar detection constraint, and public user communication quality constraint. The optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal.

[0022] Decouple the optimization problem to obtain multiple sub-problems.

[0023] Use an alternating iterative optimization algorithm to solve each of the sub-problems to obtain communication beamforming parameters, communication and sensing beamforming parameters, and the optimal phase shift.

[0024] Send the communication beamforming parameters and the communication and sensing beamforming parameters to the base station, and send the optimal phase shift to the intelligent reflecting surface.

[0025] A third aspect of the embodiments of the present invention discloses a secure communication device combining covert sensing and assisted interference, which is applied to a base station. The base station is communicatively connected to a jammer, an intelligent reflecting surface, and a central controller respectively. The device includes:

[0026] A receiving unit, configured to receive the communication beamforming parameters and the communication and sensing beamforming parameters obtained by the central controller solving the optimization problem. The optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal.

[0027] A prediction unit, configured to, for each time slot in the eavesdropper's service period, if the time slot is the first time slot, use the known initial state information of the eavesdropper as the current state information, and if the time slot is not the first time slot, predict the current state information based on the historical state information of the eavesdropper obtained in the previous time slot.

[0028] A first transmitting unit, configured to transmit a first superimposed signal including a sensing signal and the current state information based on the communication and sensing beamforming parameters, so that after receiving the current state information, the jammer sends a jamming signal to the eavesdropper.

[0029] A second transmitting unit, configured to transmit a first message signal to be sent to the covert user terminal to the intelligent reflecting surface based on the communication beamforming parameters, so that the intelligent reflecting surface transmits the first message signal to the covert user terminal based on the optimal phase shift; the optimal phase shift is obtained by the central controller solving the optimization problem and sent to the intelligent reflecting surface;

[0030] A sensing unit, configured to estimate accurate state information of the eavesdropper based on the sensed echo signal when receiving the sensed echo signal reflected by the eavesdropper from the sensed signal, and use the accurate state information as historical state information for the next time slot.

[0031] Preferably, the sensing unit is specifically configured to:

[0032] When receiving the sensed echo signal reflected by the eavesdropper from the sensed signal, extract relevant information of the eavesdropper from the sensed echo signal;

[0033] Use the relevant information and a tracking model constructed based on the extended Kalman filtering technique to obtain the accurate state information of the eavesdropper.

[0034] Preferably, the sensing unit is further configured to:

[0035] If the sensed echo signal is not received, use the current state information as historical state information for the next time slot.

[0036] Preferably, the second transmitting unit is further configured to:

[0037] If there is a first message signal to be sent to the covert user terminal and a second message signal to be sent to the public user terminal, based on the communication beamforming parameters, send a second superimposed signal including the first message signal and the second message signal to the intelligent reflecting surface, so that the intelligent reflecting surface transmits the second superimposed signal to the covert user terminal and the public user terminal based on the optimal phase shift.

[0038] A fourth aspect of the embodiments of the present invention discloses a secure communication device for joint covert sensing and assisted jamming, which is applied to a central controller. The central controller is communicatively connected to a base station and an intelligent reflecting surface respectively. The device includes:

[0039] A construction unit, configured to construct a non-convex optimization problem according to a plurality of pre-analyzed constraints; the constraints include: communication covert constraint, sensing covert constraint, total power constraint, sensing capability constraint, radar detection constraint, and public user communication quality constraint; the optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal;

[0040] A solution unit, configured to decouple the optimization problem into multiple sub-problems; and use an alternating iterative optimization algorithm to solve each of the sub-problems to obtain communication beamforming parameters, communication and sensing beamforming parameters, and an optimal phase shift.

[0041] A third transmitting unit, configured to send the communication beamforming parameters and the communication and sensing beamforming parameters to the base station, and send the optimal phase shift to the intelligent reflecting surface.

[0042] Based on the above-mentioned secure communication method and device for jointly performing covert sensing and assisting interference provided by an embodiment of the present invention, communication beamforming parameters and communication and sensing beamforming parameters obtained by a central controller solving an optimization problem are received; the optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal; for each time slot in the service cycle of the eavesdropper, if the time slot is the first time slot, the initial state information of the known eavesdropper is used as the current state information, and if the time slot is not the first time slot, the current state information is predicted based on the historical state information of the eavesdropper obtained in the previous time slot; a first superimposed signal including a sensing signal and the current state information is transmitted based on the communication and sensing beamforming parameters, so that after receiving the current state information, the jammer sends a jamming signal to the eavesdropper; based on the communication beamforming parameters, a first message signal to be sent to the covert user terminal is sent to the intelligent reflecting surface, so that the intelligent reflecting surface sends the first message signal to the covert user terminal based on the optimal phase shift; the optimal phase shift is obtained by the central controller solving the optimization problem and sent to the intelligent reflecting surface; when the sensing echo signal reflected by the eavesdropper from the sensing signal is received, the accurate state information of the eavesdropper is estimated based on the sensing echo signal, and the accurate state information is used as the historical state information for the next time slot. In this solution, the relevant parameters obtained by solving the optimization problem are received to optimize the transmit beamforming, and then the state information of the sensing eavesdropper is tracked and sent to the jammer to prevent the eavesdropping of the eavesdropper. With the help of the intelligent reflecting surface with the optimized phase shift, the base station communicates with the covert user terminal, thereby achieving the purpose of improving the covert communication rate. Description of the Drawings

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0044] Figure 1It is an architecture diagram of a covert communication system disclosed in an embodiment of the present invention;

[0045] Figure 2 It is a time slot division diagram disclosed in an embodiment of the present invention;

[0046] Figure 3 It is a flowchart of a secure communication method for joint covert sensing and assisted jamming disclosed in an embodiment of the present invention;

[0047] Figure 4 It is a flowchart of another secure communication method for joint covert sensing and assisted jamming disclosed in an embodiment of the present invention;

[0048] Figure 5 It is a schematic diagram of the convergence of the EKF method disclosed in an embodiment of the present invention;

[0049] Figure 6 It is a comparison diagram of the predicted trajectory and the true trajectory of the EKF method disclosed in an embodiment of the present invention;

[0050] Figure 7 It is a relationship curve diagram of the covert transmission rate and the number of iterations disclosed in an embodiment of the present invention;

[0051] Figure 8 It is a relationship curve diagram of the covert transmission rate and the total power disclosed in an embodiment of the present invention;

[0052] Figure 9 It is a relationship curve diagram of the covert transmission rate and the number of IRS units disclosed in an embodiment of the present invention;

[0053] Figure 10 It is a relationship curve diagram of the covert transmission rate and the covert tolerance value disclosed in an embodiment of the present invention;

[0054] Figure 11 It is a structural diagram of a secure communication device for joint covert sensing and assisted jamming disclosed in an embodiment of the present invention;

[0055] Figure 12 It is a structural diagram of another secure communication device for joint covert sensing and assisted jamming disclosed in an embodiment of the present invention. Detailed implementation manners

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0057] In this application, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0058] As can be seen from the background art, in the existing covert communication system, a communication model assisted only by an intelligent reflecting surface or the simplest three-node model is adopted. During the covert communication process, it is impossible to interfere with eavesdroppers, resulting in a low covert communication rate.

[0059] Therefore, the embodiments of the present invention disclose a secure communication method and device for joint covert sensing and assisted interference. In this solution, the relevant parameters obtained by solving the optimization problem are received to optimize the transmit beamforming. Then, the state information of the eavesdropper is tracked and sensed and sent to the jammer to prevent the eavesdropping of the eavesdropper. With the help of the intelligent reflecting surface with optimized phase shift, the base station communicates with the covert user terminal, thereby achieving the purpose of improving the covert communication rate.

[0060] As Figure 1 shown, it is an architecture diagram of a covert communication system disclosed in the embodiments of the present invention. The covert communication system includes: base station Alice, intelligent reflecting surface IRS, jammer Jammer, central controller, covert user terminal Bob and public user terminal Grace.

[0061] In the covert communication system, the base station with optimized transmit beamforming first predicts the state information of the eavesdropper Willie and sends it to the jammer to counter the eavesdropper. Subsequently, with the interference assistance of the jammer, the base station uses the intelligent reflecting surface optimized with the best phase shift to communicate with the covert user terminal and the public user terminal.

[0062] Specifically, the central controller constructs a non-convex optimization problem according to multiple constraints obtained by pre-analysis; decouples the optimization problem into multiple sub-problems; uses the alternating iterative optimization algorithm to solve each sub-problem to obtain the communication beamforming parameters, the communication and sensing beamforming parameters, and the best phase shift; sends the communication beamforming parameters and the communication and sensing beamforming parameters to the base station, and sends the best phase shift to the intelligent reflecting surface.

[0063] The constraints include: communication covert constraint, sensing covert constraint, total power constraint, sensing ability constraint, radar detection constraint and public user communication quality constraint; the optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal.

[0064] The base station receives the communication beamforming parameters and the communication-sensing beamforming parameters obtained by the central controller solving the optimization problem.

[0065] For each time slot in the eavesdropper's service period, if the time slot is the first time slot, the base station uses the known initial state information of the eavesdropper as the current state information. If the time slot is not the first time slot, the base station predicts the current state information based on the historical state information of the eavesdropper obtained in the previous time slot.

[0066] The base station uses the communication beamforming parameters and the communication-sensing beamforming parameters to optimize the transmit beamforming, and transmits the superimposed signal of the current state information and the sensing signal based on the communication-sensing beamforming parameters, so that the jammer sends a jamming signal to the eavesdropper.

[0067] With the assistance of the jammer, the base station sends a superimposed signal (including the message to be sent to the covert user terminal and the message to be sent to the public user terminal) to the intelligent reflecting surface based on the communication beamforming parameters.

[0068] The intelligent reflecting surface receives the optimal phase shift and performs optimization, so that when receiving the superimposed signal sent by the base station, it forwards it to the covert user terminal and the public user terminal based on the optimal phase shift.

[0069] When the base station receives the sensing echo signal generated by the eavesdropper reflecting the sensing signal, it estimates the accurate state information of the eavesdropper based on the sensing echo signal, and uses the accurate state information as the historical state information for the next time slot.

[0070] Among them, the eavesdropper can be a drone with eavesdropping capabilities; the covert user terminal, the public user terminal, and the jammer are all equipped with single antennas.

[0071] The base station is equipped with a uniform linear array antenna of M. For the convenience of implementation and separate deployment, all the antennas of the base station are divided into two groups, namely M1 and M2, where M1 + M2 = M. M1 is used for the communication-sensing stage, and M2 is used for the pure communication stage.

[0072] The intelligent reflecting surface is composed of N uniform array antennas, and the phase shift matrix of the intelligent reflecting surface can be expressed as: , where , the diag symbol represents a diagonal matrix, j is the imaginary symbol, and e is the natural logarithm.

[0073] The position coordinates of the base station are , the position coordinates of the covert user terminal are , the position coordinates of the jammer are , the position coordinates of the intelligent reflecting surface are .

[0074] Such as Figure 2As shown, it is a time slot division diagram disclosed in an embodiment of the present invention.

[0075] Among them, the eavesdropper's service time T is divided into I time slots, and the time of each time slot is T / I. The position coordinates of the eavesdropper in the i-th time slot are , and its speed is .

[0076] Then the state of the eavesdropper in the i-th time slot can be expressed as .

[0077] It should be noted that in order to consider a more realistic situation, the channel state information of the eavesdropper is unavailable and needs to be estimated and predicted by the base station. While the channel state information of all legitimate users is available.

[0078] An unmanned aerial vehicle (UAV) eavesdropper in high-altitude maneuver attempts to eavesdrop on the communication between the base station and the covert user terminal. Assume that the movement of the eavesdropper is a constant speed model. To ensure the security of communication, the base station predicts the prior state based on the posterior state .

[0079] As Figure 2 shown, each time slot is divided into 4 stages, which are in turn:

[0080] Prior state estimation stage: In this stage, the system predicts the current state information based on the previous information.

[0081] ISAC (Integrated Sensing and Communication) stage: In this stage, the system performs communication and sensing tasks simultaneously.

[0082] Communication Only stage: In this stage, the system only performs communication tasks and does not perform sensing.

[0083] Posterior state estimation stage: In this stage, the system updates the current state information based on the information received by sensing.

[0084] Specifically, for each time slot, in the prior state estimation stage, the base station predicts the current state information (i.e., the prior state of the current time slot) based on the state information of the eavesdropper estimated in the previous time slot (i.e., the posterior state of the previous time slot).

[0085] In the ISAC stage, the current state information and the sensing signal are superimposed and transmitted based on the communication and sensing beamforming parameters.

[0086] It should be noted that the initial state information of the eavesdropper in this application is known. In the first time slot, the base station will superimpose and transmit the initial state information as the current state information with the sensing signal.

[0087] It can be understood that the current state information received by the jammer includes at least the location information of the eavesdropper, so as to send interference signals to the eavesdropper.

[0088] In the pure communication stage, with the assistance of the jammer, the base station uses the communication beamforming parameters and the intelligent reflecting surface to communicate with the public user terminal and conduct covert communication with the covert user terminal.

[0089] In the posterior state estimation stage, new measurements can be made based on the sensing echo signal reflected by the eavesdropper to obtain the accurate state information of the eavesdropper, and this accurate state information is the posterior state of the current time slot.

[0090] The analysis of the channel model, communication model, and sensing model related to the above process is as follows:

[0091] 1. Channel model:

[0092] Assume that all the ground-air channels can be expressed as:

[0093] (1)

[0094] Among them, ρ is the reference power gain per meter, d ij represents the distance from user i to j, aw represents Alice and Willie, rw represents IRS and Willie, Jw represents Jammer and Willie, is the ground-air path loss exponent, and g ij represents the connection vector between user i and user j.

[0095] In the above embodiment of the present invention, the base station hopes to detect the existence of the eavesdropper while maintaining communication with the covert communication terminal. h ij is the channel gain between user i and user j (i.e., the channel model), and the first letter of the English abbreviation name of the user is used as the subscript. The English abbreviation names of each participating user in the covert communication system have been given above. For example, the channel model between the base station and the eavesdropper can be expressed as:

[0096] (2)

[0097] Among them, α aw is the reflectivity of the sensing target, and θ aw represents the angle of the base station with respect to the eavesdropper. The vector can be expressed as:

[0098] (3)

[0099] Among them, λ is the wavelength, and d aw is the spacing distance between two adjacent antennas of the radar. Generally, d aw = λ / 2.

[0100] 2. Communication model:

[0101] ISAC phase: In time slot i, in order to simultaneously achieve sensing and tracking of eavesdroppers and communication with the jammer, the base station transmits a superimposed signal x1 containing the current state information and sensing signal, which can be expressed as:

[0102] (4)

[0103] Among them, and represent the communication beamforming vector and sensing beamforming vector of the base station respectively, and are the communication signal with the jammer and the sensing signal for sensing eavesdroppers respectively. The communication rate between the base station and the jammer can be expressed as:

[0104] (5)

[0105] Among them, h aJ represents the channel gain from the jammer to the base station; represents the noise power or interference power generated by the jammer.

[0106] Pure communication phase: In time slot i, the jammer receives the current state information of the eavesdropper and transmits an interference signal with power P J to prevent the eavesdropping behavior of the eavesdropper. The base station sends the superimposed signal x2 to the two users. x2 is a non-orthogonal multiple access (NOMA) signal, which can be expressed as:

[0107] (6)

[0108] Among them, represents the NOMA communication symbol that satisfies , and are the information signals of the covert user terminal and the public user terminal respectively. is the NOMA communication beamforming matrix, and are respectively and beamforming vectors. The signal received by the NOMA user can be expressed as:

[0109] (7)

[0110] where is the Gaussian white noise at node k, and h ak represents the channel gain from user k to the base station, and h rk represents the channel gain from the IRS to user k, and h ar represents the channel gain from the base station to the IRS, and h Jr represents the channel gain from the jammer to the IRS, and h ar represents the channel gain from the base station to the IRS, and P J represents power. Assume that the covert user terminal and the legitimate user terminal are the near user and the far user respectively. To ensure the success of successive interference cancellation (SIC), the base station allocates more transmit power to send rather than , that is .

[0111] In this application, assume that there is perfect SIC at the covert user terminal and the legitimate user terminal, and the interference of receiving the signal of the other party between the two users does not need to be considered.

[0112] According to the NOMA principle, the covert user terminal detects and removes the corresponding interference by using SIC, and then detects its own signal . The legitimate user terminal detects by treating the signal related to as noise. The rates at which the covert user terminal detects signals and can be expressed as: and , where the signal-to-noise ratio can be expressed as: and . In addition, the communication rate at the legitimate user terminal can be expressed as:

[0113] (8)

[0114] where h ab represents the channel gain from the covert user terminal to the base station, h rb represents the channel gain from the IRS to the covert user terminal, h Jr represents the channel gain from the IRS to the jammer, h Jb represents the channel gain from the covert user terminal to the jammer, h ar represents the channel gain from the base station to the IRS, represents the channel gain from the legitimate user terminal to the jammer, Denote the channel gain from the legitimate user terminal to the base station, Denote the channel gain from the legitimate user terminal to the IRS, P J Denote the power, Denote the interference power at the covert user terminal.

[0115] It should be noted that, to make SIC feasible on the NOMA receiver, the achievable rate for the legitimate user terminal to detect its own message should not exceed the achievable rate for the covert user terminal to detect. Thus, we have (i.e., the radar detection constraint of the optimization problem). Meanwhile, to ensure the communication quality of the legitimate user terminal, we need (i.e., the communication quality constraint of the legitimate user for the optimization problem).

[0116] 3. Sensing model:

[0117] It should be noted that this application aims to use the sensing signal of the base station to track the eavesdropper and send its current status information to the jammer, and the jammer performs noise jamming on it, thereby improving the system's concealment. To achieve effective jamming, the base station needs to estimate the accurate current status information of the eavesdropper, so as to construct a channel related to the eavesdropper.

[0118] It should be noted that the eavesdropper is generally an airborne target and usually moves at a high speed. To improve the covert transmission performance, this application adopts a tracking model based on the Extended Kalman Filter (EKF) to track and predict the position of the enemy target according to the estimated speed information. The details of the target tracking based on EKF are as follows:

[0119] This application only considers the direct link with the eavesdropper. Then the echo signal received by the base station can be expressed as:

[0120]

[0121] where is the noise signal at the base station. Then the signal-to-noise ratio of the sensed echo signal received by the base station can be expressed as:

[0122] (9)

[0123] In addition, once the base station receives the sensed echo signal, it can obtain relevant information about the eavesdropper from it. This application uses the mutual information between h aw and the sensed echo signal as an index of the radar target detection performance, because the mutual information can characterize how much information the base station can learn from . It is given by .

[0124] In each time slot, the base station first predicts the current state information according to the state information of the eavesdropper estimated in the previous time slot, and sends the current state information to the jammer. With the assistance of the jammer's interference, the waveform of the NOMA signal (including the messages to be sent to the covert user terminal and the public user terminal) is designed. Subsequently, new measurements can be made based on the sensed echo signal, so that the new state of the eavesdropper can be estimated or predicted.

[0125] Specifically, considering that the speed of the eavesdropper is almost the same in two consecutive time slots, i.e., the constant velocity motion model. The state evolution prediction equation of the eavesdropper can be expressed as:

[0126] (10)

[0127] where is the state transition matrix. I3 and 03 are the 3×3 identity matrix and zero matrix respectively. is the state evolution noise, is the state evolution covariance matrix. Therefore, the current accurate state information of the eavesdropper in time slot i can be expressed as , and the prediction covariance matrix can be expressed as:

[0128] (11)

[0129] where is 's covariance matrix.

[0130] Assume the measurement parameter as , and the parameter measurement model can be expressed as:

[0131] (12)

[0132] where is the measurement function, is the measurement Gaussian noise. By linearizing the measurement model around the prediction model, the measurement model is transformed into:

[0133] (13)

[0134] where represents 's Jacobian matrix with respect to . The accurate state information prediction equation (tracking model) of the eavesdropper in time slot i can be expressed as:

[0135] (14)

[0136] where is the Kalman gain matrix, which is given by:

[0137] (15)

[0138] Among them, is the state evolution covariance matrix when the parameter is .

[0139] Based on the covert communication system disclosed in the above embodiments of the present invention, as Figure 3 shown, it is a flowchart of a secure communication method for joint covert sensing and assisted interference disclosed in the embodiments of the present invention, which is applied to a base station. The method includes the following steps:

[0140] Step S101: Receive the communication beamforming parameters and the communication and sensing beamforming parameters obtained by the central controller solving the optimization problem.

[0141] Among them, the optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal.

[0142] For the specific process of the central controller solving the optimization problem, please refer to Figure 4 the corresponding embodiments of the present invention.

[0143] Step S102: For each time slot in the eavesdropper service period, if the time slot is the first time slot, use the known initial state information of the eavesdropper as the current state information. If the time slot is not the first time slot, predict the current state information based on the historical state information of the eavesdropper obtained in the previous time slot.

[0144] Among them, the eavesdropper can be a drone, and the eavesdropper service period is the time period when the drone operates in the air and conducts eavesdropping.

[0145] Specifically, for each time slot, in the prior state estimation stage, the base station predicts its current state information (i.e., the prior state of the current time slot) according to the state information of the eavesdropper estimated in the previous time slot (i.e., the posterior state of the previous time slot).

[0146] It should be noted that the initial state information of the eavesdropper is known (it can be obtained in advance by other methods). In the first time slot, the base station will use the initial state information as the current state information and superimpose it on the sensing signal for transmission.

[0147] Step S103: Transmit a first superimposed signal including a sensing signal and the current state information based on the communication and sensing beamforming parameters, so that after the jammer receives the current state information, it sends a jamming signal to the eavesdropper.

[0148] In step S103, the base station is equipped with an M-element uniform linear array antenna. For the convenience of implementation with separate deployment, all the antennas of the base station are divided into two groups, namely M1 and M2, where M1 + M2 = M. M1 is used for the communication-sensing phase, and M2 is used for the pure communication phase.

[0149] In the specific implementation process of step S103, M1 is utilized to transmit a first superimposed signal containing the sensing signal and the current state information based on the communication-sensing beamforming parameters.

[0150] Among them, the process of superimposing the sensing signal and the current state information has been introduced in the analysis of the above communication model.

[0151] It can be understood that the current state information includes the location information of the eavesdropper, that is, the coordinate information. Therefore, when the jammer receives the current state information, it can send interference signals according to the location of the eavesdropper.

[0152] Step S104: Based on the communication beamforming parameters, the first message signal to be sent to the covert user terminal is sent to the intelligent reflecting surface, so that the intelligent reflecting surface sends the first message signal to the covert user terminal based on the optimal phase shift.

[0153] Among them, the optimal phase shift is obtained by the central controller solving the optimization problem and sent to the intelligent reflecting surface.

[0154] The intelligent reflecting surface is a wireless communication technology. By deploying a plane composed of a large number of low-cost passive reflecting units in the communication environment, it can intelligently adjust the phase, amplitude, and polarization of the reflected signal, thereby reconstructing the wireless propagation environment and significantly improving the performance of the wireless communication network.

[0155] In the embodiment of the present invention, the role of the intelligent reflecting surface is to act as a relay between the base station and two users (Bob and Grace). It solves the problem that there is no direct path between the base station and the two users due to geographical environment barriers, resulting in the inability to communicate.

[0156] In one embodiment, if there is a first message signal to be sent to the covert user terminal and a second message signal to be sent to the public user terminal, then based on the communication beamforming parameters, a second superimposed signal containing the first message signal and the second message signal is sent to the intelligent reflecting surface, so that the intelligent reflecting surface sends the second superimposed signal to the covert user terminal and the public user terminal based on the optimal phase shift.

[0157] Specifically, M2 in the two groups of antennas of the base station and the communication beamforming parameters are used to send the second superimposed signal containing the first message signal and the second message signal to the intelligent reflecting surface. The specific superimposing process has been introduced in the above communication model.

[0158] Step S105: When the sensed echo signal generated by the eavesdropper's reflected sensing signal is received, estimate the accurate state information of the eavesdropper based on the sensed echo signal, and use the accurate state information as the historical state information for the next time slot.

[0159] In the specific implementation process of step S105, when the sensed echo signal generated by the eavesdropper's reflected sensing signal is received, extract the relevant information of the eavesdropper from the sensed echo signal. The relevant information includes: the location information, speed information, etc. of the eavesdropper.

[0160] Then, use the relevant information and the tracking model constructed based on the extended Kalman filtering technology to obtain the accurate state information of the eavesdropper. For specific explanations, please refer to the sensing model part introduced in the above embodiments of the present invention.

[0161] Based on the secure communication method of jointly hidden sensing and assisted jamming disclosed in the above embodiments of the present invention, in this solution, the relevant parameters obtained by solving the optimization problem are received to realize the optimization of the transmit beamforming. Then, the state information of the eavesdropper is tracked and sensed and sent to the jammer to prevent the eavesdropping of the eavesdropper. With the help of the intelligent reflecting surface with optimized phase shifts, the base station communicates with the hidden user terminal. The core innovation lies in introducing a dual hidden mechanism for communication and sensing behaviors, tracking and predicting the trajectory of the mobile eavesdropper with real-time sensing capabilities, and realizing active defense through collaborative jamming and IRS phase optimization, thereby achieving the purpose of improving the hidden communication rate.

[0162] As Figure 4 shown, it is a flowchart of another secure communication method of jointly hidden sensing and assisted jamming disclosed in the embodiments of the present invention. This method is applied to a central controller and includes the following steps:

[0163] Step S201: Construct a non-convex optimization problem according to multiple constraints obtained by prior analysis.

[0164] In step S201, the constraints include: communication hiding constraint, sensing hiding constraint, total power constraint, sensing ability constraint, radar detection constraint, and public user communication quality constraint; the optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the hidden communication rate between the base station and the hidden user terminal.

[0165] Among them, the analysis processes of the radar detection constraint and the public user communication quality constraint have been introduced in the above embodiments of the present invention. The analysis processes of the communication hiding constraint and the sensing hiding constraint are as follows:

[0166] First of all, it should be noted that eavesdroppers attempt to monitor whether there is communication behavior at the base station and determine its location. In an actual scenario, if either the sensing signal or the communication signal is detected by an eavesdropper, it will pose a risk of exposing the sending node. Therefore, different from the prior art, this application takes into account both the sensing concealment constraint and the communication concealment constraint in one time slot.

[0167] 1. ISAC Phase

[0168] To determine whether a signal is transmitted, an eavesdropper will perform a binary hypothesis test on the base station. Specifically, the null hypothesis indicates that the base station is not transmitting signals or performing sensing and tracking, while the alternative hypothesis indicates that there is signal transmission or sensing and tracking at the base station. Therefore, under this hypothesis test, the signal received by the eavesdropper can be expressed as:

[0169] (16)

[0170] where is the Gaussian white noise at the eavesdropper.

[0171] When the null hypothesis holds, the received signal at the eavesdropper is only additive noise. When the alternative hypothesis holds, the eavesdropper receives the signal from the base station. Their probability density functions can be expressed as:

[0172] (17)

[0173] (18)

[0174] where , .

[0175] This application uses the misjudgment probability to measure the detection performance of the eavesdropper, defined as , where is the false alarm probability, is the miss detection probability. D = 0 indicates that the detection decision result of the eavesdropper is , D = 1 indicates that the decision result is . The optimal detection method of the eavesdropper is likelihood ratio detection, expressed as:

[0176] (19)

[0177] To limit the detection performance of the eavesdropper, its misjudgment probability is restricted within a certain range, expressed as:

[0178] (20)

[0179] Among them, denotes the concealment tolerance value, the smaller it is, the higher the concealment of the system.

[0180] The exact value of the likelihood ratio detection is difficult to calculate directly. By using the method of scaling, the detection performance of the eavesdropper can be limited within a preset range. The probability of misjudgment of the eavesdropper is higher than its lower bound, which can be expressed as:

[0181] (21)

[0182] where is the total variation distance. According to Pinsker's inequality, it can be known that:

[0183] (22)

[0184] where denotes the KL divergence, and further it can be obtained that:

[0185] (23)

[0186] Therefore, as long as holds, it can ensure that the detection performance of the eavesdropper is limited within the preset range. Next, the KL divergence at the eavesdropper in the ISAC phase is solved.

[0187] According to formula (17) and formula (18), the expression of the KL divergence can be obtained as:

[0188] (24)

[0189] where n is the transmission packet length.

[0190] Theorem 1: Corresponding to , the average concealment constraint (i.e., the sensing concealment constraint) in the ISAC phase is expressed as:

[0191] (25)

[0192] where .

[0193] Proof: Given , then it can be obtained that:

[0194] (26)

[0195] Considering that the channel coefficient is a random variable, calculate the average concealment constraint:

[0196] (27)

[0197] As long as it satisfies , then , Theorem 1 is proved.

[0198] 2. Simple communication stage

[0199] In this stage, the jammer sends a jamming signal to the eavesdropper with power to prevent the eavesdropper from eavesdropping. The eavesdropper also performs a binary hypothesis test. Specifically, the null hypothesis means that the base station does not transmit signals to the covert user terminal, while the alternative hypothesis means that there is signal transmission between the base station and the covert user terminal. Therefore, under this hypothesis test, the signal received by the eavesdropper can be expressed as:

[0200] (28)

[0201] where is the jamming power of the jammer, is the Gaussian white noise at the eavesdropper, h Jw is the channel gain from the eavesdropper to the jammer, h Jr is the channel gain from the IRS to the jammer, h rw is the channel gain from the eavesdropper to the IRS.

[0202] When the null hypothesis holds, the received signal at the eavesdropper only has additive noise and the jamming signal from the jammer. When the alternative hypothesis holds, the eavesdropper receives the signal from the base station. Their probability density functions can be expressed as:

[0203] (29)

[0204] (30)

[0205] where:

[0206]

[0207]

[0208] Similarly, the misjudgment probability is also used to measure the detection performance of the eavesdropper in the simple communication stage, defined as , where is the false alarm probability, is the miss detection probability. D = 1 means that the detection decision result of the eavesdropper is , D = 0 means that the decision result is . The optimal detection method of the eavesdropper is likelihood ratio detection, expressed as:

[0209] (31)

[0210] According to Theorem 1, the average covert constraint in the pure communication stage can be obtained as , which is the communication covert constraint.

[0211] where .

[0212] In the above embodiments of the present invention, the communication rate R between the base station and the jammer has been introduced c , obviously R c needs to be greater than or equal to the sensing rate R s to ensure the system performance. Then, there is a sensing ability constraint: R c ≥R s .

[0213] For the total power constraint and the sensing ability constraint, they are obtained according to the preset thresholds.

[0214] Specifically, the constructed non-convex optimization problem is as follows:

[0215] (32)

[0216] where R b is the covert communication rate, P is the total power threshold, and Γ is the minimum sensing threshold.

[0217] Step S202: Decouple the optimization problem into multiple sub-problems, and use the alternating iteration optimization algorithm to solve each sub-problem to obtain the communication beamforming parameters, the communication and sensing beamforming parameters, and the optimal phase shift.

[0218] In step S202, due to the high coupling of variables, it is difficult to directly solve the optimization problem. Therefore, the problem is decoupled into three sub-problems. Subsequently, the alternating iteration optimization algorithm is introduced to solve these sub-problems in turn. Due to the non-convexity of the problem, it is impossible to find the optimal solution. However, as a heuristic algorithm, the alternating iteration optimization algorithm can effectively solve the proposed problem.

[0219] The specific solution process is as follows:

[0220] 1) Optimize the phase shift: To simplify the problem, let:

[0221] (33)

[0222] where Q is , and a1 to a5 are used for equivalent substitution of the content after diag().

[0223] Meanwhile, , , , , , . Then, the optimization problem can be transformed into:

[0224] (34)

[0225] First, through simplification, we can obtain:

[0226] (35)

[0227] Then, introduce the auxiliary matrix:

[0228] (36)

[0229] Subsequently, substituting formula (36) into (35), we can get:

[0230] (37)

[0231] According to the properties of the matrix trace, we can obtain . To further simplify, let , then , where , .

[0232] Therefore, the optimization problem (34) is equivalent to:

[0233] (38)

[0234] Due to the existence of the non-convex objective function and the rank-one constraint, problem (38) is still a non-convex optimization problem. Then, using the semidefinite relaxation technique (Semidefinite Relaxation, SDR), first relax the rank-one constraint.

[0235] Therefore, the optimization problem (38) can be rewritten as:

[0236] (39)

[0237] For this fractional programming problem, use the Dinkelbach algorithm to solve the fractional programming problem. Let , .

[0238] Then, re-express (38) as:

[0239] (40)

[0240] where t is an auxiliary variable, and its iterative update formula is:

[0241] (41)

[0242] where \(k\) is the number of iterations. Since \(t\) is non-decreasing after each iteration, \(t\) is updated alternately according to (41) to solve for \(F\) in problem (40).

[0243] Generally speaking, \(F\) in problem (40) is not a rank-one matrix, that is , indicating that the optimal value of problem (40) only serves as an upper bound for problem (38). Therefore, based on the solution of problem (40), a Gaussian randomization method is used to construct an approximate solution to problem (38).

[0244] Specifically, first decompose \(F\), that is , where and are a unitary matrix and a diagonal matrix respectively. Then, a suboptimal solution can be obtained, where is an arbitrary vector that satisfies .

[0245] Among the independently generated Gaussian random vectors , select the best \(g\) as the optimal solution. Finally can be obtained through .

[0246] Practice has shown that by using this method and performing sufficient randomization on \(r\), the optimal objective value of problem (40) can be guaranteed to be approximately the optimal solution.

[0247] Finally, an algorithm for solving (34) is designed.

[0248] 2) Optimize the beamforming \(w_2\): Given and \(w_1\), the optimization problem is still non-convex. So first transform the optimization problem into a semidefinite programming problem and solve it using an iterative optimization algorithm based on the penalty function method. For further simplification, let:

[0249] (42)

[0250] Then . According to the properties of the matrix trace, we can get . Similarly, we can get and . Then the optimization problem can be further transformed into:

[0251] (43)

[0252] For the penalty function method, the rank-one constraint is first transformed into an equality constraint, that is:

[0253] (44)

[0254] wherein and represent the nuclear norm and the spectral norm of the matrix, respectively. Then, the transformed constraint conditions are incorporated into the objective function as penalty terms to solve Problem (43), and the following optimization problem is obtained:

[0255] (45)

[0256] wherein denotes the penalty parameter for penalizing the violation of (44). According to the well-known fact that if the initialized value is small enough, the solution efficiency of Problem (45) will decrease. Therefore, an algorithm based on two-layer penalty will be adopted to solve Problem (45).

[0257] In the inner layer, it is noted that Problem (45) is still non-convex. Therefore, the first-order Taylor expansion at is applied, and the lower bound of is where is the eigenvector associated with the largest eigenvalue of the given in the n-th iteration of the Successive Convex Approximation (SCA) method. Thus, the optimization problem can be further rewritten as:

[0258] (46)

[0259] Problem (46) is a convex problem and can be efficiently solved using the existing CVX (Convex Optimization Toolbox) solver. In the outer layer, the penalty factor will be gradually updated to a small enough value as follows:

[0260] (47)

[0261] wherein represents a constant scaling factor.

[0262] 3) Optimize the beamforming w1: The optimization problem can be expressed as:

[0263] (48)

[0264] This problem can be directly solved using the CVX toolbox.

[0265] Step S203: Send the communication beamforming parameters and the communication-sensing beamforming parameters to the base station, and send the optimal phase shift to the intelligent reflecting surface.

[0266] Based on the secure communication method combining covert sensing and assisted jamming disclosed in the embodiments of the present invention above, by decomposing the non-convex joint optimization problem into three sub-problems: sensing beamforming, communication beamforming, and IRS phase shift, and solving it through an iterative optimization algorithm, where the semi-definite relaxation method and Gaussian randomization are used to solve the optimal phase shift of the intelligent reflecting surface, the penalty function method and Dinkelbach algorithm are used to solve the communication beamforming, and the cvx solver is used to solve the communication and sensing beamforming. In this solution, an iterative optimization algorithm is proposed to jointly optimize the intelligent reflecting surface phase shift matrix, communication and sensing beamforming, so as to optimize the transmitting beamforming of the intelligent reflecting surface and the base station respectively, achieving a higher covert transmission rate compared with the traditional solution.

[0267] The embodiments of the present invention also disclose a simulation method for a covert communication system, so as to verify the effectiveness of the covert communication system and method disclosed in the above embodiments of the present invention, and at the same time obtain the influence of communication beamforming parameters, communication and sensing beamforming parameters, and the optimal phase shift on the covert communication performance respectively.

[0268] As Figure 5 shown, it is a schematic diagram of the convergence of the EKF method disclosed in the embodiments of the present invention.

[0269] Figure 1 The accuracy of the EKF method for predicting the eavesdropper's trajectory is verified. To ensure the irregularity of the eavesdropper's trajectory in the real scenario, the embodiments of the present invention assume that the heading angles of each time slot in the motion model are randomly generated, so as to generate a more random trajectory. By comparing the real trajectory with the predicted trajectory, the EKF method reduces the mean square error from 100 to 10 in 30 iterations with the help of real-time sensing feedback. This dynamic tracking ability ensures that the system can actively adjust the beamforming and IRS configuration, overcoming the limitations of the static eavesdropping assumption in existing research.

[0270] As Figure 6 shown, it is a comparison diagram of the predicted trajectory and the real trajectory of the EKF method disclosed in the embodiments of the present invention.

[0271] Among them, the real trajectory of the airborne eavesdropper and the predicted trajectory using the EKF method are shown. Figure 6 The cross points in

[0272] In the embodiments of the present invention, three benchmark schemes are also set, namely random IRS ISAC, IRS pure communication scheme, and random IRS pure communication scheme, so as to focus on analyzing the synergistic advantages among the ISAC technology, intelligent IRS optimization, and NOMA-enabled resource allocation strategies in a dynamic environment. The details of the three benchmark schemes are as follows:

[0273] Random IRS ISAC Scheme: This scheme adopts a traditional ISAC system and randomly configures the IRS phase shifts, retaining the dual functions of sensing and communication but without optimizing the IRS reflection coefficients, that is, only optimizing the sensing beamforming and communication beamforming of the base station. By comparing this scheme with the benchmark scheme, the performance gains of dynamic IRS phase optimization and joint sensing-communication resource allocation in enhancing concealment and spectral efficiency can be explored.

[0274] IRS Pure Communication Scheme: This scheme optimizes the IRS phase shifts specifically for communication tasks, decoupling the sensing function from the ISAC framework, that is, only optimizing the phase shifts of the intelligent reflecting surface and the communication beamforming of the base station. The goal of this scheme is to quantify the security and throughput improvements achieved through the collaborative integration of sensing and communication in the covert communication system and method disclosed in the embodiments of the present invention, especially for dynamic environments with mobile eavesdroppers.

[0275] Random IRS Pure Communication Scheme: This scheme combines random IRS phase shifts with pure communication operations, which can separate the contributions of IRS optimization and ISAC dual functions, that is, only optimizing the communication beamforming of the base station. This scheme highlights the limitations of static resource allocation and non-cooperative sensing-communication design, thus corroborating the necessity of the joint beamforming and trajectory sensing IRS configuration proposed in this paper.

[0276] As Figure 7 shown, it is a relationship curve graph of the covert transmission rate and the number of iterations disclosed in the embodiments of the present invention.

[0277] Figure 7 It shows the convergence characteristics of the covert transmission rate. The covert transmission rate rapidly rises from 0.6 bps / Hz to 5.1 bps / Hz within 10 iterations and then stabilizes.

[0278] It can be seen that the covert communication system and method disclosed in the embodiments of the present invention not only have a faster convergence speed but also significantly outperform the random IRS ISAC, IRS pure communication, and random IRS pure communication schemes in terms of performance. Combining the alternating optimization framework of semidefinite relaxation, penalty function method, and Dinkelbach algorithm, fast convergence is achieved by decoupling non-convex subproblems, which reflects the high efficiency of the decomposition technology in the covert communication system and method disclosed in the embodiments of the present invention, ensuring the practical application value of the scheme in resource-constrained and eavesdropping scenarios.

[0279] As Figure 8 shown, it is a relationship curve graph of the covert transmission rate and the total power disclosed in the embodiments of the present invention.

[0280] Figure 8 It shows the influence of the total power budget on the covert transmission rate under different schemes. Figure 8The covert transmission rate increases as the total power budget increases. This phenomenon is in line with the theoretical expectation because increasing the total power budget can expand the feasible region of beamforming optimization, thus enhancing the flexibility of the solution.

[0281] It should be noted that the covert communication system and method proposed in the above embodiments of the present invention are superior to the other three benchmark schemes under any total power budget. This superiority stems from the joint optimization of sensing-communication beamforming and IRS phase shift, which can dynamically control the interference at the eavesdropper and maximize the resource utilization rate. Specifically, the random IRS pure communication scheme has a 55.8% performance loss compared with the proposed scheme, highlighting the key role of IRS phase optimization and ISAC dual function in power-constrained scenarios. In addition, the covert transmission rate of the IRS pure communication scheme without sensing integration is 22.8% lower than that of the proposed scheme, and this gap verifies the necessity of using the ISAC dual function signal synchronization to improve sensing accuracy and communication security.

[0282] As Figure 9 shown, it is a curve graph showing the relationship between the covert transmission rate and the number of IRS units disclosed in the embodiments of the present invention.

[0283] Figure 9 It shows the influence of the number of IRS units on the covert communication rate. When the number of IRS units increases from 15 to 45, the covert performance is significantly improved, verifying the key role of IRS in enhancing security and throughput. This improvement stems from the expansion of the degrees of freedom (DoF), which enables more accurate beamforming for the covert user terminal.

[0284] Although increasing the number of IRS units can improve the covert communication rate by providing additional DoF, practical constraints such as hardware cost, lightweight design, and deployment portability need to be weighed. When the number of IRS units is 45, the performance of the covert communication system and method proposed in the above embodiments of the present invention is 53% and 14% better than that of the random IRS ISAC and random IRS pure communication schemes respectively. This gap indicates that it is necessary to jointly optimize the IRS phase and sensing-communication beamforming to fully release the potential of IRS. In contrast, the IRS pure communication scheme without sensing integration only achieves 4.4 bps / Hz, highlighting the dual function advantage of ISAC in balancing covertness and resource efficiency.

[0285] As Figure 10 shown, it is a curve graph showing the relationship between the covert transmission rate and the covert tolerance value disclosed in the embodiments of the present invention.

[0286] Figure 10It shows the relationship between the covert tolerance and the covert transmission rate. When the covert tolerance is relaxed from 0.05 to 0.35, the covert transmission rate of the covert communication system and method proposed in the above embodiments of the present invention increases from 2.4 bps / Hz to 4.9 bps / Hz. The other three benchmark schemes show lower rates under each covert tolerance.

[0287] This difference stems from the fact that the covert communication system and method proposed in the above embodiments of the present invention can dynamically adjust the power allocation and IRS phase shift based on real-time sensing feedback, while maximizing the legitimate channel gain and adaptively suppressing Willie's detection ability.

[0288] Under strict covert constraints, the curve slope is large; as the constraints are relaxed, the growth rate of each scheme gradually slows down, mainly due to hardware limitations and interference cancellation gain saturation. This phenomenon is easy to understand: when the covert tolerance is low, the base station can allocate more power to the covert signal, promoting the improvement of the covert transmission rate; but as the constraints are further relaxed, the limited energy budget becomes the main factor restricting the growth of the covert rate. This non-linear characteristic highlights the necessity of joint trajectory prediction and resource optimization to maintain performance gain under dynamic security requirements.

[0289] From the above simulation process, it can be seen that the covert communication system and method disclosed in the above embodiments of the present invention innovatively introduce a dual covert mechanism for communication and sensing behaviors to ensure security in a resource-constrained environment. By decomposing the non-convex joint optimization problem into three sub-problems: sensing beamforming, communication beamforming, and IRS phase shift, an alternating optimization algorithm integrating semi-definite relaxation, penalty function method, and Dinkelbach transformation is developed, achieving a higher covert transmission rate compared to traditional schemes. Different from existing research that relies on unrealistic static assumptions, the core innovation of the present invention lies in integrating real-time sensing capabilities to track and predict the trajectory of the mobile eavesdropper, and achieving active defense through cooperative interference and IRS phase optimization. The simulation results verify the superiority of the covert communication system and method disclosed in the above embodiments of the present invention in terms of information security performance compared to the benchmark schemes.

[0290] As Figure 11 shown, it is the structural diagram of a secure communication device for joint covert sensing and assisted interference disclosed in an embodiment of the present invention. This device is applied to a base station and includes:

[0291] A receiving unit 111, configured to receive the communication beamforming parameters and the communication and sensing beamforming parameters obtained by the central controller solving the optimization problem. The optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal.

[0292] A prediction unit 112 is configured to, for each time slot in the eavesdropper service cycle, if the time slot is the first time slot, use the initial state information of the known eavesdropper as the current state information, and if the time slot is not the first time slot, predict the current state information based on the historical state information of the eavesdropper obtained in the previous time slot.

[0293] A first transmission unit 113 is configured to transmit a first superimposed signal including a sensing signal and the current state information based on the communication and sensing beamforming parameters, so that after receiving the current state information, the jammer transmits a jamming signal to the eavesdropper.

[0294] A second transmission unit 114 is configured to transmit a first message signal to be sent to the covert user terminal to the intelligent reflecting surface based on the communication beamforming parameters, so that the intelligent reflecting surface transmits the first message signal to the covert user terminal based on the optimal phase shift; the optimal phase shift is obtained by the central controller solving an optimization problem and sent to the intelligent reflecting surface.

[0295] In one embodiment, the second transmission unit 114 is specifically configured to:

[0296] If there is a first message signal to be sent to the covert user terminal and a second message signal to be sent to the public user terminal, a second superimposed signal including the first message signal and the second message signal is transmitted to the intelligent reflecting surface based on the communication beamforming parameters, so that the intelligent reflecting surface transmits the second superimposed signal to the covert user terminal and the public user terminal based on the optimal phase shift.

[0297] A sensing unit 115 is configured to, when receiving a sensed echo signal generated by the eavesdropper reflecting the sensing signal, estimate the accurate state information of the eavesdropper based on the sensed echo signal, and use the accurate state information as the historical state information for the next time slot.

[0298] In one embodiment, the sensing unit 115 is specifically configured to:

[0299] When receiving a sensed echo signal generated by the eavesdropper reflecting the sensing signal, extract relevant information of the eavesdropper from the sensed echo signal; use the relevant information and a tracking model constructed based on the extended Kalman filtering technique to obtain the accurate state information of the eavesdropper.

[0300] In one embodiment, the sensing unit 115 is further configured to:

[0301] If the sensed echo signal is not received, use the current state information as the historical state information for the next time slot.

[0302] Based on the secure communication device for joint covert sensing and assisted jamming disclosed in the above embodiments of the present invention, in this solution, the relevant parameters obtained by receiving and solving the optimization problem are used to optimize the transmit beamforming. Then, the state information of the eavesdropper is tracked and sensed and sent to the jammer to prevent the eavesdropping of the eavesdropper. With the help of the intelligent reflecting surface with optimized phase shifts, the base station communicates with the covert user terminal. The core innovation lies in introducing a dual covert mechanism for communication and sensing behaviors, tracking and predicting the trajectory of the mobile eavesdropper with real-time sensing capabilities, and achieving active defense through collaborative jamming and IRS phase optimization, thereby achieving the purpose of improving the covert communication rate.

[0303] As Figure 12 shown, it is a structural diagram of another secure communication device for joint covert sensing and assisted jamming disclosed in the embodiments of the present invention, applied to a central controller, including:

[0304] A construction unit 121, configured to construct a non-convex optimization problem according to multiple constraints obtained by pre-analysis.

[0305] Among them, the constraints include: communication covert constraint, sensing covert constraint, total power constraint, sensing capability constraint, radar detection constraint, and public user communication quality constraint; the optimization problem is used to optimize the transmit beamforming of the base station and the phase shifts of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal.

[0306] A solving unit 122, configured to decouple the optimization problem into multiple sub-problems; use an alternating iterative optimization algorithm to solve each sub-problem to obtain communication beamforming parameters, communication and sensing beamforming parameters, and the optimal phase shifts.

[0307] A third transmitting unit 123, configured to send the communication beamforming parameters and the communication and sensing beamforming parameters to the base station, and send the optimal phase shifts to the intelligent reflecting surface.

[0308] Based on the secure communication device for joint covert sensing and assisted jamming disclosed in the above embodiments of the present invention, by decomposing the non-convex joint optimization problem into three sub-problems: sensing beamforming, communication beamforming, and IRS phase shift, and solving them through an iterative optimization algorithm, where the semi-definite relaxation method and Gaussian randomization are used to solve the optimal phase shifts of the intelligent reflecting surface, the penalty function method and the Dinkelbach algorithm are used to solve the communication beamforming, and the cvx solver is used to solve the communication and sensing beamforming. In this solution, an iterative optimization algorithm is proposed to jointly optimize the phase shift matrix of the intelligent reflecting surface, the communication and sensing beamforming, and the communication beamforming to optimize the transmit beamforming of the intelligent reflecting surface and the base station respectively, achieving a higher covert transmission rate compared with the traditional solution.

[0309] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for a system or system embodiment, since it is basically similar to a method embodiment, the description is relatively simple. For the relevant parts, reference can be made to the description of the method embodiment. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative work.

[0310] Those skilled in the art can further realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Skilled professionals can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0311] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A secure communication method combining stealth perception and assisted interference, characterized in that Applied to a base station, the base station is communicatively connected to a jammer, an intelligent reflecting surface, and a central controller respectively. The method includes: Receiving the communication beamforming parameters and the communication and sensing beamforming parameters obtained by the central controller solving an optimization problem. The constraints of the optimization problem include: communication secrecy constraint, sensing secrecy constraint, total power constraint, sensing capability constraint, radar detection constraint, and communication quality constraint of public users. The optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the secrecy communication rate between the base station and the covert user terminal. For each time slot in the service cycle of the eavesdropper, if the time slot is the first time slot, use the initial state information of the known eavesdropper as the current state information. If the time slot is not the first time slot, predict the current state information based on the historical state information of the eavesdropper obtained in the previous time slot. Based on the communication and sensing beamforming parameters, transmit a first superimposed signal including a sensing signal and the current state information, so that after receiving the current state information, the jammer sends a jamming signal to the eavesdropper. Based on the communication beamforming parameters, send a first message signal to be sent to the covert user terminal to the intelligent reflecting surface, so that the intelligent reflecting surface sends the first message signal to the covert user terminal based on the optimal phase shift. The optimal phase shift is obtained by the central controller solving the optimization problem and sent to the intelligent reflecting surface. When receiving the sensing echo signal reflected by the eavesdropper from the sensing signal, estimate the accurate state information of the eavesdropper based on the sensing echo signal, and use the accurate state information as the historical state information for the next time slot.

2. The method according to claim 1, wherein The step of when receiving the sensing echo signal reflected by the eavesdropper from the sensing signal and estimating the accurate state information of the eavesdropper based on the sensing echo signal includes: When receiving the sensing echo signal reflected by the eavesdropper from the sensing signal, extract the relevant information of the eavesdropper from the sensing echo signal. Using the relevant information and a tracking model constructed based on the extended Kalman filtering technique to obtain the accurate state information of the eavesdropper.

3. The method according to claim 1, characterized in that The method further includes: If the sensing echo signal is not received, use the current state information as the historical state information for the next time slot.

4. The method according to any one of claims 1 to 3, characterized in that, The method further includes: If there is a first message signal to be sent to the covert user terminal and a second message signal to be sent to the public user terminal, based on the communication beamforming parameters, send a second superimposed signal including the first message signal and the second message signal to the intelligent reflecting surface, so that the intelligent reflecting surface sends the second superimposed signal to the covert user terminal and the public user terminal based on the optimal phase shift.

5. A secure communication method combining covert perception and assisted interference, characterized in that, Applied to a central controller, the central controller is communicatively connected to a base station and an intelligent reflecting surface respectively. The method includes: Construct a non-convex optimization problem according to multiple constraints obtained from pre-analysis; the constraints include: communication secrecy constraint, sensing secrecy constraint, total power constraint, sensing ability constraint, radar detection constraint, and public user communication quality constraint; the optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the secrecy communication rate between the base station and the covert user terminal; Decouple the optimization problem to obtain multiple sub-problems; Use the alternating iteration optimization algorithm to solve each of the sub-problems to obtain communication beamforming parameters, communication and sensing beamforming parameters, and the optimal phase shift; Send the communication beamforming parameters and the communication and sensing beamforming parameters to the base station, and send the optimal phase shift to the intelligent reflecting surface; the base station transmits a first superimposed signal containing a sensing signal and current state information based on the communication and sensing beamforming parameters, so that the jammer sends a jamming signal to the eavesdropper after receiving the current state information.

6. A secure communication device that combines stealth perception and auxiliary interference, characterized in that Applied to a base station, the base station is communicatively connected to a jammer, an intelligent reflecting surface, and a central controller respectively, and the device includes: A receiving unit, configured to receive the communication beamforming parameters and the communication and sensing beamforming parameters obtained by the central controller solving the optimization problem; the constraints of the optimization problem include: communication secrecy constraint, sensing secrecy constraint, total power constraint, sensing ability constraint, radar detection constraint, and public user communication quality constraint; the optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the secrecy communication rate between the base station and the covert user terminal; A prediction unit, configured to, for each time slot in the service period of the eavesdropper, if the time slot is the first time slot, use the known initial state information of the eavesdropper as the current state information, and if the time slot is not the first time slot, predict the current state information based on the historical state information of the eavesdropper obtained in the previous time slot; A first transmitting unit, configured to transmit a first superimposed signal containing a sensing signal and the current state information based on the communication and sensing beamforming parameters, so that the jammer sends a jamming signal to the eavesdropper after receiving the current state information; A second transmitting unit, configured to transmit a first message signal to be sent to the covert user terminal to the intelligent reflecting surface based on the communication beamforming parameters, so that the intelligent reflecting surface sends the first message signal to the covert user terminal based on the optimal phase shift; the optimal phase shift is obtained by the central controller solving the optimization problem and sent to the intelligent reflecting surface; A sensing unit, configured to, when receiving the sensing echo signal reflected by the eavesdropper from the sensing signal, estimate the accurate state information of the eavesdropper based on the sensing echo signal, and use the accurate state information as the historical state information of the next time slot.

7. The device according to claim 6, characterized in that, The sensing unit is specifically configured to: When receiving the sensing echo signal reflected by the eavesdropper from the sensing signal, extract the relevant information of the eavesdropper from the sensing echo signal; Use the relevant information and a tracking model constructed based on the extended Kalman filtering technique to obtain the accurate state information of the eavesdropper.

8. The device according to claim 6, characterized in that, The sensing unit is further configured to: If the sensing echo signal is not received, use the current state information as the historical state information for the next time slot.

9. The device according to any one of claims 6 to 8, characterized in that The second transmitting unit is further configured to: If there is a first message signal to be sent to the covert user terminal and a second message signal to be sent to the public user terminal, based on the communication beamforming parameters, send a second superimposed signal including the first message signal and the second message signal to the intelligent reflecting surface, so that the intelligent reflecting surface sends the second superimposed signal to the covert user terminal and the public user terminal based on the optimal phase shift.

10. A secure communication device combining stealth perception and auxiliary interference, characterized in that, Applied to a central controller, the central controller is communicatively connected to a base station and an intelligent reflecting surface respectively, and the device includes: A construction unit for constructing a non-convex optimization problem according to a plurality of pre-analyzed constraints; the constraints include: communication concealment constraint, sensing concealment constraint, total power constraint, sensing ability constraint, radar detection constraint, and public user communication quality constraint; the optimization problem is used to optimize the transmit beamforming of the base station and the phase shift of the intelligent reflecting surface to maximize the covert communication rate between the base station and the covert user terminal; A solving unit for decoupling the optimization problem into a plurality of sub-problems; using an alternating iterative optimization algorithm to solve each of the sub-problems to obtain communication beamforming parameters, communication and sensing beamforming parameters, and an optimal phase shift; A third transmitting unit for sending the communication beamforming parameters and the communication and sensing beamforming parameters to the base station, and sending the optimal phase shift to the intelligent reflecting surface; the base station transmits a first superimposed signal including a sensing signal and current state information based on the communication and sensing beamforming parameters, so that the jammer sends a jamming signal to the eavesdropper after receiving the current state information.

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