High-speed rail communication secure transmission method based on active RIS assistance
By using an active RIS-assisted high-speed rail communication system, the channel model and reflection coefficient matrix are optimized, solving the problems of poor channel conditions and insufficient security in traditional high-speed rail communication systems under high-speed motion. This achieves efficient and reliable communication transmission and anti-eavesdropping capabilities, while reducing system energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHENGDU TECH UNIV
- Filing Date
- 2025-12-25
- Publication Date
- 2026-04-17
AI Technical Summary
Traditional high-speed rail communication systems suffer from poor channel conditions and limited transmission distances under high-speed motion, and lack effective security measures, resulting in low communication quality, poor reliability, high construction and maintenance costs, and inability to resist eavesdropping attacks.
The high-speed rail communication system with active RIS assistance constructs a channel model, defines the reflection coefficient matrix, optimizes the base station beamforming vector and the phase shift matrix of the active RIS, and uses an alternating optimization algorithm to minimize the base station transmit power, thereby enhancing signal transmission and anti-eavesdropping capabilities.
It significantly improves the safety and transmission efficiency of high-speed rail communication, enhances signal transmission distance and penetration, ensures seamless coverage, reduces system energy consumption, and meets the reliability requirements of high-speed operation.
Smart Images
Figure CN121888263A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of high-speed rail communication security technology, and more specifically, to a high-speed rail communication security transmission method based on active RIS assistance. Background Technology
[0002] With the continuous advancement of high-speed rail construction, the high-speed rail communication system, as a key infrastructure to ensure train operation safety and passenger travel comfort, is becoming increasingly important. The high-speed rail communication system needs to provide stable, efficient, and secure voice, video, and data transmission services for passengers and staff on trains to meet the growing communication demands.
[0003] Traditional high-speed rail communication systems typically employ the deployment of base stations along the line, utilizing direct-scan channels between these base stations and mobile relays on the train for wireless communication. However, this traditional approach has several inherent drawbacks. First, due to the high-speed movement of high-speed trains, direct-scan channel conditions are extremely harsh, exhibiting issues such as Doppler shift and rapid fading, resulting in low communication quality and reliability. Second, the transmission distance of direct-scan channels is limited, requiring dense deployment of base stations to achieve seamless coverage, leading to high construction and maintenance costs. Third, traditional methods lack effective security measures, making them unable to withstand potential eavesdropping attacks, and communication security cannot be guaranteed.
[0004] In view of this, the present invention proposes a high-speed rail communication security transmission method based on active RIS assistance to solve the above problems. Summary of the Invention
[0005] To overcome the aforementioned deficiencies of the prior art and to achieve the above objectives, the present invention provides the following technical solution: a high-speed rail communication security transmission method based on active RIS assistance, comprising:
[0006] Step 1: Construct a high-speed rail communication system including base stations, active RIS, mobile relays, and eavesdroppers;
[0007] Step 2: Establish channel models between the base station and the active RIS, between the active RIS and the mobile relay, and between the active RIS and the eavesdropper.
[0008] Step 3: Define the reflection coefficient matrix of the active RIS; and derive the expressions for the received signals of the mobile relay and the eavesdropper.
[0009] Step 4: Calculate the signal-to-noise ratio at the mobile relay and the eavesdropper, and solve for the channel capacity at the mobile relay and the eavesdropper using Shannon's theorem;
[0010] Step 5: Establish an optimization problem with the goal of minimizing the base station's transmit power and set constraints; jointly optimize the base station's beamforming vector and the phase shift matrix of the active RIS, and solve the optimization problem through an alternating optimization algorithm to minimize the base station's transmit power.
[0011] Furthermore, the construction of the high-speed rail communication system includes a base station, an active RIS, a mobile relay, and an eavesdropper, comprising: a base station equipped with N antennas; an active RIS equipped with M reflective elements, each of which is equipped with a power amplifier; and a mobile relay and an eavesdropper each equipped with one antenna.
[0012] Furthermore, in the steps of establishing the channel model between the base station and the active RIS, the channel model between the active RIS and the mobile relay, and the channel model between the active RIS and the eavesdropper, all channels are Ricean channels.
[0013] The channel coefficient from the base station to the active RIS is:
[0014]
[0015] Where K represents the Rice factor. G LoS This represents the line-of-sight component, which is related to the link distance and remains stable within each time slot. G NLoS This represents the non-line-of-sight component, modeled as Rayleigh fading. G LoS and G NLoS They can be represented as:
[0016]
[0017] m∈{1,...,M},n∈{1,...,N},
[0018]
[0019] Where β0 = -61.3849 dB represents the path loss at a distance of 1 meter; d is the distance between the base station and the active RIS; α1 = 2.5 and α2 = 3.6 are the path loss exponents in line-of-sight and non-line-of-sight scenarios, respectively; θ m,n The phase is a randomly distributed phase with values ranging from [0, 2π); while G1 NLOS Each element is a complex, circularly symmetric, zero-mean, unit-variance random variable used to characterize small-scale fading. Similarly, the channel coefficients from the active RIS to the k-th mobile relay and from the active RIS to the eavesdropper can be obtained.
[0020] Furthermore, the reflection coefficient matrix of the active RIS is defined as follows:
[0021] In the formula, β m≥0 indicates the magnification factor of the m-th reflecting unit, θ m ∈[0,2π) represents the phase shift coefficient of the m-th reflecting unit.
[0022] Furthermore, the derived expressions for the received signals of mobile relays and eavesdroppers are as follows:
[0023]
[0024] Among them, y k and y e Let represent the received signals of the k-th mobile relay and the eavesdropper, respectively, and w represent the beamforming vector of the base station. and Let G represent the additive white Gaussian noise received by the k-th mobile relay and the eavesdropper, respectively. This indicates the thermal noise generated by the active RIS component.
[0025] Furthermore, the signal-to-noise ratio at the mobile relay is calculated as follows:
[0026]
[0027] The signal-to-noise ratio at the eavesdropper's location is calculated as follows:
[0028]
[0029] in, and These represent the noise power at the mobile relay and the eavesdropper, respectively.
[0030] Furthermore, the channel capacity of the mobile relay is calculated as follows:
[0031] R k =log2(1+γ) k );
[0032] The channel capacity of the eavesdropper is:
[0033] R e =log2(1+γ) e ).
[0034] Furthermore, the optimization problem aimed at minimizing the base station's transmit power includes:
[0035] With the minimum transmit power of the base station as the objective, an objective function is established, and multiple constraints are set to construct an optimization problem. The constraints include active RIS transmit power constraints, active RIS phase shift matrix constraints, minimum rate requirement constraints for the k-th mobile relay, and maximum tolerable eavesdropping capacity constraints.
[0036] Represented as:
[0037]
[0038] The beamforming vector of the base station and the phase shift matrix at the active RIS are jointly optimized, and the optimization problem is solved by an alternating optimization algorithm.
[0039] The technical effects and advantages of the high-speed rail communication security transmission method based on active RIS assistance of the present invention are as follows:
[0040] This invention significantly enhances the security and anti-eavesdropping capabilities of high-speed rail communication systems. Through a meticulously designed optimization algorithm, it maximizes the signal reception quality for legitimate users (mobile relays) while effectively suppressing the signal reception capabilities of potential eavesdroppers. Secondly, it greatly improves the transmission efficiency and reliability of high-speed rail communication systems. Introducing an active RIS as an auxiliary unit not only provides additional spatial degrees of freedom but also actively amplifies and adjusts the phase of the signal, thereby significantly enhancing the transmission distance and penetration capability, ensuring seamless coverage and stable connection during high-speed train operation, and meeting the high reliability requirements of high-speed rail communication. Furthermore, it enables green energy saving in high-speed rail communication systems. By establishing an optimization model targeting the minimum transmission power of the base station and employing an efficient alternating optimization algorithm, the transmission power of the base station can be minimized while meeting the minimum rate requirements of mobile relays, fundamentally reducing the system's energy consumption. Attached Figure Description
[0041] Figure 1 This is a schematic diagram of a high-speed rail communication security transmission method based on active RIS assistance according to the present invention;
[0042] Figure 2 This is a graph showing the relationship between the transmit power of the present invention and the system multicast rate requirement;
[0043] Figure 3 This is a schematic diagram of a high-speed rail communication security transmission system based on active RIS assistance according to the present invention. Detailed Implementation
[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0045] Example 1
[0046] Please see Figure 1 As shown in this embodiment, a high-speed rail communication security transmission method based on active RIS assistance includes:
[0047] Step 1: Construct a high-speed rail communication system that includes base stations, active RIS, mobile relays, and eavesdroppers; for example, base stations and active RIS are deployed along the high-speed rail line, mobile relays are installed on the high-speed rail carriages, and eavesdroppers may be potential malicious users.
[0048] Step 2: Establish channel models between the base station and the active RIS, between the active RIS and the mobile relay, and between the active RIS and the eavesdropper.
[0049] Step 3: Define the reflection coefficient matrix of the active RIS; and derive the expressions for the received signals of the mobile relay and the eavesdropper.
[0050] Step 4: Calculate the signal-to-noise ratio at the mobile relay and the eavesdropper, and solve for the channel capacity at the mobile relay and the eavesdropper using Shannon's theorem;
[0051] Step 5: Establish an optimization problem with the goal of minimizing the base station's transmit power and set constraints; jointly optimize the base station's beamforming vector and the phase shift matrix of the active RIS, and solve the optimization problem through an alternating optimization algorithm to minimize the base station's transmit power.
[0052] Traditional high-speed rail communication systems typically employ direct-fire links or simple relay transmission methods. Direct-fire links are severely affected by the obstruction of the high-speed rail body, leading to a decline in signal quality. Relay transmission links are susceptible to Doppler shift and multipath effects in high-speed moving environments, reducing signal reliability.
[0053] Construct a high-speed rail communication system including a base station, an active RIS, a mobile relay, and an eavesdropper. The base station is equipped with N antennas; the active RIS is equipped with M reflector units, each of which is equipped with a power amplifier; the mobile relay and the eavesdropper are each equipped with one antenna.
[0054] In the steps of establishing the channel model between the base station and the active RIS, the channel model between the active RIS and the mobile relay, and the channel model between the active RIS and the eavesdropper, all channels are Ricean channels.
[0055] The channel coefficient from the base station to the active RIS is:
[0056]
[0057] Where K represents the Rice factor. G LoS This represents the line-of-sight component, which is related to the link distance and remains stable within each time slot. G NLoS This represents the non-line-of-sight component, modeled as Rayleigh fading. G LoS and G NLoS They can be represented as:
[0058]
[0059] m∈{1,...,M},n∈{1,...,N},
[0060]
[0061] Where β0 = -61.3849 dB represents the path loss at a distance of 1 meter; d is the distance between the base station and the active RIS; α1 = 2.5 and α2 = 3.6 are the path loss exponents in line-of-sight and non-line-of-sight scenarios, respectively; θ m,n The phase is a randomly distributed phase with values ranging from [0, 2π); while G1 NLOS Each element is a complex, circularly symmetric, zero-mean, unit-variance random variable used to characterize small-scale fading. Similarly, the channel coefficients from the active RIS to the k-th mobile relay and from the active RIS to the eavesdropper can be obtained.
[0062] The Ricean channel model more closely reflects the actual wireless propagation environment. It comprehensively considers multipath propagation and shadowing effects, thus more realistically describing the wireless channel characteristics in high-speed rail communication scenarios. The high-speed rail operating environment is complex, with factors such as train body obstruction and high-speed movement leading to multipath effects and shadowing fading during wireless signal propagation. The Ricean channel model can effectively capture these effects.
[0063] The reflection coefficient matrix of an active RIS is defined as follows:
[0064] In the formula, β m ≥0 indicates the magnification factor of the m-th reflecting unit, θ m ∈[0,2π) represents the phase shift coefficient of the m-th reflecting unit. It needs to be explained that when the incident signal reaches the reflecting unit, it will go through the following two main processes: power amplification and phase adjustment.
[0065] The power amplification process is as follows: Each power amplifier in the reflecting unit has a corresponding amplification factor, which is used to amplify the power of the incident signal; the value range of the amplification factor is usually [0, τ]. m ], where τ m This is the maximum amplification factor of the power amplifier, determined by the hardware circuit design and operating state; when it equals 0, it indicates that the reflecting unit is in the off state and will not reflect any signal; when it equals τ... m When the amplification factor of each reflector is adjusted, the overall amplification factor of the active RIS on the incident signal can be controlled, thereby affecting the power intensity of the reflected signal.
[0066] The phase adjustment process is as follows: each phase shifter in the reflective unit has a corresponding phase shift coefficient, which is used to adjust the phase of the reflected signal; the value range of the phase shift coefficient is [0, 2π), which means that the amount of phase adjustment can be continuously changed between 0 and 2π; by precisely controlling the phase shift coefficient of each reflective unit, the phase of the reflected signal can be reconstructed, thereby realizing functions such as beamforming and signal focusing.
[0067] The expressions for the received signals of mobile relays and eavesdroppers are derived as follows:
[0068]
[0069]
[0070] Among them, y k and y e Let represent the received signals of the k-th mobile relay and the eavesdropper, respectively, and w represent the beamforming vector of the base station. and Let G represent the additive white Gaussian noise received by the k-th mobile relay and the eavesdropper, respectively. This indicates the thermal noise generated by the active RIS component.
[0071] The signal-to-noise ratio at the mobile relay point is calculated as follows:
[0072]
[0073] The signal-to-noise ratio at the eavesdropper's location is calculated as follows:
[0074]
[0075] in, and These represent the noise power at the mobile relay and the eavesdropper, respectively.
[0076] The channel capacity of a mobile relay is calculated as follows:
[0077] R k =log2(1+γ) k );
[0078] The channel capacity of the eavesdropper is:
[0079] R e =log2(1+γ) e );
[0080] The optimization problem is established with the goal of minimizing the base station's transmit power, including:
[0081] With the minimum transmit power of the base station as the objective, an objective function is established, and multiple constraints are set to construct an optimization problem. The constraints include active RIS transmit power constraints, active RIS phase shift matrix constraints, minimum rate requirements of the k-th mobile relay, and maximum tolerable eavesdropping capacity constraints.
[0082] The maximum tolerable eavesdropping capacity constraint is designed to ensure communication security by limiting the amount of information an eavesdropper can obtain to no more than a certain threshold. In high-speed rail communication systems, there are potential eavesdroppers attempting to steal information from legitimate users (mobile relays). Therefore, it is necessary to limit the channel capacity of eavesdroppers to ensure the confidentiality of communication.
[0083] The minimum rate requirement constraint for mobile relays is to ensure that legitimate users (mobile relays) receive sufficient quality of service to meet their minimum communication rate requirements.
[0084] The objective function is expressed as:
[0085]
[0086] The beamforming vector of the base station and the phase shift matrix at the active RIS are jointly optimized, and the optimization problem is solved by an alternating optimization algorithm.
[0087] Specifically, because the optimization variables w and Θ are coupled and the constraints are non-convex, this optimization problem is a non-convex optimization problem. Definition S = diag(1 1×M )(diag(1 1×M )) H ,Φ=diag((Gw) T )(diag((Gw) T )) H The optimization problem can then be transformed into:
[0088]
[0089] Introducing auxiliary variable μ k If η = 2, then the optimization problem can be further transformed into:
[0090]
[0091] The optimal values of w and Θ under the conditions of fixed active RIS phase shift matrix Θ and fixed beamforming vector w are obtained by using the continuous convex approximation method. Then, the optimization problem is solved by the alternating iterative optimization algorithm to minimize the base station transmit power.
[0092] The key to the continuous convex approximation method lies in constructing a convex infimum function, which approximates the original non-convex constraint with a series of convex constraints. By alternately optimizing the optimal value, a local optimum solution to the original problem can be obtained; the non-convex optimization problem is transformed into a series of convex optimization subproblems, which can then be solved efficiently using mature convex optimization theory and algorithms.
[0093] The alternating iterative optimization algorithm decomposes the original joint optimization problem into two subproblems, optimizes them separately, and alternates between them in each iteration until convergence.
[0094] In this embodiment of the invention, a simulation is set up, and the simulation is as follows:
[0095] Train configuration: The high-speed train consists of 8 carriages, each carriage is 200 meters long; 6 MRs are evenly deployed on the roof of the train, and each carriage is equipped with 0-1 mobile relays; a single Eve is randomly deployed on the roof of the train.
[0096] Communication link establishment: A secure communication link is established by deploying an active RIS between the base station and the MR.
[0097] Equipment parameters: The base station is equipped with 6 antennas, and the active RIS is equipped with 30 reflector units.
[0098] Coordinate settings: The spatial coordinates of each device are defined as follows: The base station is located at (-30, 20, 15)m, MR1, MR2, MR3, MR4, MR5 and MR6 are located at (-10, 5, 2.5)m, (-10, 10, 2.5)m, (-10, 15, 2.5)m, (-10, 20, 2.5)m, (-10, 25, 2.5)m and (-10, 30, 2.5)m respectively, and Eve is located at (-10, 40, 2.5)m.
[0099] Benchmark Scheme: To verify the effectiveness of this scheme, two comparison benchmark schemes are set up:
[0100] 1) Passive RIS solution;
[0101] 2) Random phase shift scheme.
[0102] like Figure 2 The graph shows the relationship between transmit power and system multicast rate requirements. As can be seen, the transmit power of the proposed scheme, the passive RIS scheme, and the random phase-shift scheme all increase with increasing multicast rate. The core reason is that higher multicast rate requirements necessitate increasing base station transmit power. Furthermore, the proposed scheme demonstrates significantly better performance than the latter two. Specifically, compared to the passive RIS scheme, the proposed scheme employs an active RIS, which effectively mitigates the impact of double fading; and compared to the random phase-shift scheme, its advantages fully demonstrate the necessity of phase-shift optimization design.
[0103] This embodiment significantly enhances the security and anti-eavesdropping capabilities of the high-speed rail communication system. Through a carefully designed optimization algorithm, it maximizes the signal reception quality for legitimate users (mobile relays) while effectively suppressing the signal reception capabilities of potential eavesdroppers. Secondly, it greatly improves the transmission efficiency and reliability of the high-speed rail communication system. Introducing an active RIS as an auxiliary unit not only provides additional spatial degrees of freedom but also actively amplifies and adjusts the phase of the signal, thereby significantly enhancing the transmission distance and penetration capability, ensuring seamless coverage and stable connection during high-speed train operation, and meeting the high reliability requirements of high-speed rail communication. Furthermore, it achieves green energy saving for the high-speed rail communication system. By establishing an optimization model targeting the minimum transmission power of the base station and employing an efficient alternating optimization algorithm, the transmission power of the base station can be minimized while meeting the minimum rate requirements of the mobile relay, fundamentally reducing the system's energy consumption.
[0104] Example 2
[0105] Please see Figure 3 As shown, for parts not described in detail in this embodiment, please refer to the description in Embodiment 1. A high-speed rail communication security transmission system based on active RIS assistance is provided, comprising:
[0106] The system building module is used to construct a high-speed rail communication system that includes base stations, active RIS, mobile relays, and eavesdroppers.
[0107] The channel model module is used to establish channel models between the base station and the active RIS, between the active RIS and the mobile relay, and between the active RIS and the eavesdropper.
[0108] The integrated calculation module is used to define the reflection coefficient matrix of the active RIS and derive the expressions for the received signals of mobile relays and eavesdroppers.
[0109] The capacity calculation module is used to calculate the signal-to-noise ratio at the mobile relay and the eavesdropper, and to solve for the channel capacity of the mobile relay and the eavesdropper according to Shannon's theorem.
[0110] The integrated optimization module is used to establish an optimization problem with the goal of minimizing the base station's transmit power and set constraints; it jointly optimizes the base station's beamforming vector and the phase shift matrix of the active RIS, and solves the optimization problem through an alternating optimization algorithm to minimize the base station's transmit power; the modules are connected to each other via wired and / or wireless means to realize data transmission between the modules.
[0111] Example 3
[0112] This embodiment discloses an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the operation mode of the high-speed rail communication security transmission method based on active RIS assistance described above.
[0113] Since the electronic device described in this embodiment is used to implement the high-speed rail communication security transmission method based on active RIS assisted in the embodiments of this application, those skilled in the art can understand the specific implementation methods and various variations of the electronic device in this embodiment based on the high-speed rail communication security transmission method based on active RIS assisted in the embodiments of this application. Therefore, how the electronic device implements the method in the embodiments of this application will not be described in detail here. Any electronic device used by those skilled in the art to implement the high-speed rail communication security transmission method based on active RIS assisted in the embodiments of this application falls within the scope of protection of this application.
[0114] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters and thresholds in the formulas are set by those skilled in the art according to the actual situation.
[0115] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for users of ordinary technical skills, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.
Claims
1. A high-speed rail communication security transmission method based on active RIS assistance, characterized in that, include: Step 1: Construct a high-speed rail communication system including base stations, active RIS, mobile relays, and eavesdroppers; Step 2: Establish channel models between the base station and the active RIS, between the active RIS and the mobile relay, and between the active RIS and the eavesdropper; Step 3: Define the reflection coefficient matrix of the active RIS; and derive the expressions for the received signals of the mobile relay and the eavesdropper. Step 4: Calculate the signal-to-noise ratio at the mobile relay and the eavesdropper, and solve for the channel capacity at the mobile relay and the eavesdropper using Shannon's theorem; Step 5: Establish an optimization problem with the goal of minimizing the base station's transmit power, and set constraints; The beamforming vector of the base station and the phase shift matrix of the active RIS are jointly optimized, and the optimization problem is solved by an alternating optimization algorithm to minimize the base station transmit power.
2. The high-speed rail communication security transmission method based on active RIS assistance according to claim 1, characterized in that, The aforementioned high-speed rail communication system comprises a base station, an active RIS, a mobile relay, and an eavesdropper. The base station is equipped with N antennas; the active RIS is equipped with M reflective elements, each of which is equipped with a power amplifier; the mobile relay and the eavesdropper are each equipped with one antenna.
3. The high-speed rail communication security transmission method based on active RIS assistance according to claim 1, characterized in that, In the steps of establishing the channel model between the base station and the active RIS, the channel model between the active RIS and the mobile relay, and the channel model between the active RIS and the eavesdropper, all channels are Ricean channels. The channel coefficient from the base station to the active RIS is: Where K represents the Rice factor, and G LoS G represents the line-of-sight component; NLoS G represents the non-line-of-sight component. LoS and G NLoS They are represented as follows: m∈{1,...,M},n∈{1,...,N}, Where β0 represents the path loss at a distance of 1 meter; d is the distance between the base station and the active RIS; α1 and α2 are the path loss exponents in line-of-sight and non-line-of-sight scenarios, respectively; θ m,n The phase is a randomly distributed phase with values ranging from [0, 2π); while G1 NLOS Each element is a complex, circularly symmetric, zero-mean, unit-variance random variable, yielding the channel coefficients from the active RIS to the k-th mobile relay and from the active RIS to the eavesdropper.
4. The high-speed rail communication security transmission method based on active RIS assistance according to claim 1, characterized in that, The reflection coefficient matrix of the active RIS is defined as follows: In the formula, β m ≥0 indicates the magnification factor of the m-th reflecting unit, θ m ∈[0,2π) represents the phase shift coefficient of the m-th reflecting unit.
5. The high-speed rail communication security transmission method based on active RIS assistance according to claim 1, characterized in that, The derived expressions for the received signals of mobile relays and eavesdroppers are as follows: Among them, y k and y e Let represent the received signals of the k-th mobile relay and the eavesdropper, respectively, and w represent the beamforming vector of the base station. and Let G represent the additive white Gaussian noise received by the k-th mobile relay and the eavesdropper, respectively. This indicates the thermal noise generated by the active RIS component.
6. The high-speed rail communication security transmission method based on active RIS assistance according to claim 1, characterized in that, The signal-to-noise ratio at the mobile relay point is calculated as follows: The signal-to-noise ratio at the eavesdropper's location is calculated as follows: in, and These represent the noise power at the mobile relay and the eavesdropper, respectively.
7. A high-speed rail communication security transmission method based on active RIS assistance according to claim 1, characterized in that, The channel capacity of a mobile relay is calculated as follows: R k =log2(1+γ k ); The channel capacity of the eavesdropper is: R e =log2(1+γ e )。 8. A high-speed rail communication security transmission method based on active RIS assistance according to claim 1, characterized in that, The optimization problem established with the minimum transmit power of the base station as the objective includes: With the minimum transmit power of the base station as the objective, an objective function is established, and multiple constraints are set to construct an optimization problem. The constraints include active RIS transmit power constraints, active RIS phase shift matrix constraints, minimum rate requirement constraints for the k-th mobile relay, and maximum tolerable eavesdropping capacity constraints. Represented as: The beamforming vector of the base station and the phase shift matrix at the active RIS are jointly optimized, and the optimization problem is solved by an alternating optimization algorithm.