A hybrid FSO / RF secure transmission method based on imperfect csi

Abstract

The application discloses a kind of hybrid FSO / RF security transmission methods based on imperfect CSI, belong to wireless communication technical field.The method includes: the communication system model of space-ground integration network based on unmanned aerial vehicle relay is constructed, wherein the first eavesdropper exists in FSO link, and the second eavesdropper exists in RF link;Under the condition of imperfect CSI, the transmission channel model of FSO link and RF link is established;The probability density function and the cumulative distribution function of end-to-end instantaneous signal-to-noise ratio are obtained based on the channel model;According to the probability density function and the cumulative distribution function, the closed expression of secret outage probability is obtained, and the secret outage probability value is calculated under given parameters to evaluate the physical layer security performance of system.The application simultaneously considers double-link eavesdropper and non-ideal channel state information, and realizes the quantitative evaluation of the security performance of hybrid FSO / RF system.

Description

Technical Field

[0001] This application belongs to the field of wireless communication technology, and in particular relates to a hybrid FSO / RF secure transmission method based on imperfect CSI. Background Technology

[0002] With the rapid development of 6G communication and the low-altitude economy, the Space-Air-Ground Integrated Network (SAGIN) integrates satellite, aviation, and terrestrial network resources to build a globally covered, high-speed, and secure communication network. In practical deployments, drones or high-altitude platforms are often used as relay nodes to mitigate the effects of atmospheric attenuation. However, traditional radio frequency (RF) technology faces problems such as low transmission rates, limited spectrum, and poor anti-interference capabilities, making it difficult to meet the high-speed and secure transmission requirements of future satellite internet.

[0003] Free-space optical (FSO) communication is considered an effective solution for high-speed data relay between satellites and high-altitude nodes due to its advantages such as ultra-high bandwidth, large capacity, resistance to electromagnetic interference, and high security, which can compensate for the shortcomings of RF technology. However, FSO communication is highly sensitive to the environment; atmospheric turbulence and severe weather can cause severe attenuation and flicker of the optical signal, affecting link stability. Therefore, hybrid communication systems that combine FSO and RF links have attracted widespread attention because they can leverage the complementary advantages of both.

[0004] However, existing research still has significant shortcomings: First, most studies only consider the presence of eavesdroppers on a single link, lacking security analysis when both FSO and RF links are simultaneously eavesdropped on; second, non-ideal Channel State Information (CSI) exists in real-world systems, but existing studies mostly assume perfect CSI, leading to significant discrepancies between theoretical and practical results; third, the security performance limits of systems under high signal-to-noise ratio conditions lack theoretical discussion, making it difficult to reveal the fundamental limitations brought about by non-ideal CSI and failing to provide accurate guidance for system design. Summary of the Invention

[0005] This application addresses the technical problem that the physical layer security performance of hybrid FSO / RF communication systems in existing integrated air-space-ground networks is difficult to quantify under non-ideal channel conditions, and provides a hybrid FSO / RF secure transmission method based on imperfect CSI.

[0006] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application provides a hybrid FSO / RF secure transmission method based on imperfect CSI, comprising the following steps: A communication system model for an integrated air-space-ground network based on UAV relay is constructed; wherein, the link between the low-Earth orbit satellite and the UAV relay is an FSO link, and the link between the UAV relay and the ground user is an RF link; the FSO link is susceptible to a first eavesdropper, and the RF link is susceptible to a second eavesdropper. In the case of imperfect CSI, the transmission channel model of the FSO link and the transmission channel model of the RF link are established based on the communication system model respectively. Based on the transmission channel model of the FSO link and the transmission channel model of the RF link, the corresponding probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio of the communication system model are obtained respectively. Based on the corresponding probability density function and cumulative distribution function, a closed-form expression for the confidentiality interruption probability of the communication system model is obtained. Under given parameters, the confidentiality interruption probability value is obtained based on the closed-form expression as the evaluation result, thus completing the evaluation of the physical layer security performance of the communication system model.

[0007] Furthermore, The formula for establishing the transmission channel model of the FSO link is as follows:

[0008] In the formula, Indicates precise channel gain. This represents the correlation coefficient of FSO link information. This represents a random variable with a Gaussian distribution having zero mean and unit variance; The formula for establishing the transmission channel model of the RF link is as follows:

[0009] In the formula, Indicates precise channel gain. Indicates and Radio frequency channel model random variables with the same variables, Represents the correlation coefficient. .

[0010] Furthermore, FSO links follow the Gamma-Gamma fading model, while RF links follow the Rayleigh fading model.

[0011] Furthermore, based on the transmission channel model of the FSO link and the transmission channel model of the RF link, the corresponding probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio of the communication system model are obtained, specifically including: Based on the transmission channel model of the FSO link and the transmission channel model of the RF link, and combined with the decoding and forwarding protocol adopted by the UAV relay, the end-to-end signal-to-noise ratio is expressed as the minimum value of the signal-to-noise ratios of the FSO link and the RF link. The cumulative distribution function of the end-to-end signal-to-noise ratio is calculated using the cumulative distribution functions of the FSO link and the RF link.

[0012] Furthermore, based on the corresponding probability density function and cumulative distribution function, a closed-form expression for the security interruption probability of the communication system model is obtained. Given parameters, the security interruption probability value is obtained based on the closed-form expression as the evaluation result. The process of evaluating the physical layer security performance of the communication system model specifically includes: The instantaneous security capacity of the system is expressed as the minimum value between the security capacity of the FSO link and the security capacity of the RF link. The probability of security interruption is defined as the probability that the instantaneous security capacity is lower than the target security rate. A closed expression for the probability of security interruption is derived using the cumulative distribution function of the FSO link and the RF link. The probability of confidentiality interruption is calculated by substituting the given parameters into the closed expression and used as the evaluation result to complete the evaluation of the physical layer security performance of the communication system model.

[0013] Furthermore, it also includes: under high signal-to-noise ratio conditions, performing asymptotic analysis on the closed-loop expression of the confidentiality interruption probability to obtain an asymptotic expression of the confidentiality interruption probability, and determining the diversity order of the communication system model based on the asymptotic expression.

[0014] Furthermore, the given parameters include at least one of the following: FSO link correlation coefficient, RF link correlation coefficient, atmospheric turbulence intensity, pointing error, target security rate, channel state of the first eavesdropper, channel state of the second eavesdropper, number of antennas of the ground user, and number of antennas of the second eavesdropper.

[0015] Furthermore, it also includes: calculating the confidential throughput of the communication system model based on the closed-loop expression of the confidentiality interruption probability, and determining the optimal target confidentiality rate threshold that maximizes the confidentiality throughput based on the relationship between the confidentiality throughput and the target confidentiality rate.

[0016] Secondly, this application also provides a hybrid FSO / RF secure transmission system based on imperfect CSI, comprising: The system model building unit is used to build a communication system model of an integrated air-space-ground network based on UAV relay; wherein, the link between the low-orbit satellite and the UAV relay is an FSO link, the link between the UAV relay and the ground user is an RF link, the FSO link is subject to a first eavesdropper, and the RF link is subject to a second eavesdropper; The channel modeling unit is used to establish the transmission channel model of the FSO link and the transmission channel model of the RF link respectively based on the communication system model under the condition of imperfect CSI. The function acquisition unit is used to obtain the corresponding probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio of the communication system model based on the transmission channel model of the FSO link and the transmission channel model of the RF link, respectively. The evaluation unit is used to obtain a closed-form expression for the confidentiality interruption probability of the communication system model based on the corresponding probability density function and cumulative distribution function. Under given parameters, the unit obtains the confidentiality interruption probability value based on the closed-form expression as the evaluation result, thereby completing the evaluation of the physical layer security performance of the communication system model.

[0017] Thirdly, this application also provides a computer device, including: a processor and a computer-readable storage medium; A processor, adapted to execute computer programs; A computer-readable storage medium storing a computer program, which, when executed by the processor, implements the hybrid FSO / RF secure transmission method based on imperfect CSI.

[0018] Compared with the prior art, this application has the following beneficial effects: This application provides a hybrid FSO / RF secure transmission method based on imperfect CSI. Addressing the real-world scenario of a hybrid FSO / RF system in an integrated air-space-ground network with simultaneous dual-link eavesdroppers, a system model based on UAV relay is constructed. Under imperfect CSI conditions, transmission channel models for both the FSO and RF links are established separately. Based on this, the probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio are obtained, leading to a closed-form expression for the probability of security breach. The probability of security breach is then calculated under given parameters. This solution overcomes the problem of incomplete security performance assessments and significant deviations from reality caused by existing technologies that only consider a single-link eavesdropper and assume perfect CSI. It enables a quantitative assessment of the physical layer security performance of the system in dual-eavesdropper scenarios.

[0019] This application further specifies that the FSO link follows a Gamma-Gamma fading model, and the RF link follows a Rayleigh fading model. Through this system modeling, the channel model more closely reflects the actual transmission environment. Simulation results show that increasing the correlation coefficient of either the FSO link or the RF link can significantly reduce the probability of system security interruption, and the theoretical results are completely consistent with Monte Carlo simulations.

[0020] This application also reveals the theoretical conclusion that imperfect CSI leads to a zero system diversity order through asymptotic analysis of the closed-loop expression for the security outage probability under high signal-to-noise ratio conditions. Specifically, the system security outage probability converges to a constant determined by the correlation coefficient of the FSO link channel. Furthermore, by calculating the security throughput and determining the optimal target security rate threshold, a quantitative basis for system parameter configuration is provided. Simulation results show that increasing the number of ground user antennas and employing maximum ratio combining technology can significantly improve security performance, and there exists an optimal target security rate threshold that maximizes the security throughput. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a hybrid FSO / RF secure transmission method based on imperfect CSI, provided as an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of a hybrid FSO / RF communication system model based on UAV relay in an integrated air-space-ground network provided in an embodiment of the present invention.

[0024] Figure 3 The graph showing the relationship between the system security interruption probability and the average signal-to-noise ratio under different FSO link correlation coefficients is provided for embodiments of the present invention.

[0025] Figure 4 The graph showing the relationship between the system security interruption probability and the average signal-to-noise ratio under different RF link correlation coefficients is provided for embodiments of the present invention.

[0026] Figure 5 The graph showing the relationship between the system security interruption probability and the average signal-to-noise ratio under different numbers of ground user antennas and second eavesdropper antennas provided in this embodiment of the invention.

[0027] Figure 6The graph showing the relationship between the system security interruption probability and the average signal-to-noise ratio under different target security levels is provided for embodiments of the present invention.

[0028] Figure 7 The graph showing the relationship between the confidential throughput and the target confidentiality rate under different eavesdropper channel states is provided for embodiments of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] See Figure 1 This application provides a hybrid FSO / RF secure transmission method based on imperfect CSI, comprising the following steps: S1, Construct a communication system model for an integrated air-space-ground network based on UAV relay; wherein, the link between the low-orbit satellite and the UAV relay is an FSO link, the link between the UAV relay and the ground user is an RF link, the FSO link is subject to a first eavesdropper, and the RF link is subject to a second eavesdropper; In a more specific embodiment provided in this application, such as Figure 2 As shown, the low-Earth orbit satellite S and the UAV relay R are connected via an FSO link, while the UAV relay R and the ground user D are connected via an RF link. Due to long-distance transmission and obstacles, there is no direct link between the low-Earth orbit satellite S and the ground user D.

[0031] The FSO link has a first eavesdropper E1, which is used to eavesdrop on the optical signal transmission between the low-orbit satellite and the UAV relay; the RF link has a second eavesdropper E2, which is used to eavesdrop on the radio frequency signal transmission between the UAV relay and the ground user.

[0032] In this embodiment, the low-Earth orbit satellite S node is equipped with a transmitting aperture, the UAV relay R node is equipped with an optical receiving aperture and an RF transmitting antenna, the first eavesdropper E1 is equipped with a single receiving aperture, and the ground user D and the second eavesdropper E2 are respectively equipped with... and Root receiving antenna.

[0033] Furthermore, the ground user D is equipped with multiple receiving antennas, the second eavesdropper E2 is equipped with multiple receiving antennas, and both the ground user D and the second eavesdropper E2 use maximum ratio combining technology to process the received signals.

[0034] S2, In the case of imperfect CSI, establish the transmission channel model of the FSO link and the transmission channel model of the RF link based on the communication system model respectively; Specifically, the low-Earth orbit satellite S transmits optical signals using intensity modulation and direct detection (IM / DD) technology. The signals received at the UAV relay R and the first eavesdropper E1 can be represented as:

[0035] in, .

[0036] The instantaneous signal-to-noise ratio (SNR) of an FSO link can be expressed as:

[0037] in, express The average signal-to-noise ratio of the link, express .

[0038] Due to the limitations of long-distance transmission and relay hardware, channel estimation errors can occur. This embodiment considers the imperfect CSI of the FSO link. Specifically, the imperfect channel state information is expressed through the imperfect channel gain. It can also be expressed as:

[0039] In the formula, Indicates precise channel gain. This represents the correlation coefficient of FSO link information. Let represent a random variable with a Gaussian distribution of zero mean and unit variance, which is related to... Irrelevant.

[0040] This embodiment models imperfect channel state information as represented by accurate channel state information and channel estimation error, using the FSO link information correlation coefficient. The control channel estimation accuracy solves the problem of inaccurate models caused by ignoring channel estimation errors in existing technologies.

[0041] The signal received by the UAV relay R is decoded and forwarded to ground user D via the RF link. The received signal at the nth antenna of ground user D and the second eavesdropper E2 can be expressed as:

[0042] In the formula, , This represents the transmit power at node R. express The decoded signal, This indicates that the mean is 0 and the variance is 0. Additive white Gaussian noise, This represents the outdated channel gain between the nth antenna from node R to t.

[0043] This embodiment considers outdated CSI of the RF link. The outdated channel state information is specifically expressed through the outdated channel gain. This can be represented as:

[0044] In the formula, Indicates precise channel gain. Indicates and Radio frequency channel model random variables with the same variables, Represents the correlation coefficient. .

[0045] The signals received by all antennas at ground user D and the second eavesdropper E2 are obtained using maximum ratio combining (MRC) technology. Therefore, the actual signal-to-noise ratio during data transmission can be expressed as:

[0046] This step addresses the discrepancy between theoretical analysis and practical application caused by existing technologies neglecting non-ideal channel characteristics by establishing channel models for imperfect and outdated CSI.

[0047] S3, based on the transmission channel model of the FSO link and the transmission channel model of the RF link, respectively obtain the corresponding probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio of the communication system model; The probability density function PDF and cumulative distribution function CDF of the instantaneous signal-to-noise ratio of the FSO link are constructed based on the Gamma-Gamma distribution and are expressed as follows:

[0048]

[0049] In the formula, , , This indicates the pointing error coefficient. and Parameters representing large-scale and small-scale irradiance fluctuations. Among them, and They are represented as follows:

[0050] and

[0051] The probability density function (PDF) and cumulative distribution function (CDF) of the instantaneous signal-to-noise ratio (SNR) of the RF link are constructed based on the Rayleigh distribution and are expressed as follows:

[0052]

[0053] In the formula, , This represents the average SNR of the RF link.

[0054] This step addresses the discrepancy between theoretical analysis and practical application caused by existing technologies neglecting non-ideal channel characteristics by establishing channel models for imperfect and outdated CSI.

[0055] Based on the transmission channel model of the FSO link and the transmission channel model of the RF link, and combined with the decoding and forwarding protocol adopted by the UAV relay, the end-to-end signal-to-noise ratio of the system is expressed as the minimum value between the signal-to-noise ratio of the FSO link and the signal-to-noise ratio of the RF link.

[0056] Using the cumulative distribution functions of the FSO link and the RF link, the cumulative distribution function of the system's end-to-end signal-to-noise ratio is calculated: therefore, The CDF can be represented as:

[0057] This step expresses the end-to-end signal-to-noise ratio as the minimum of the two link signal-to-noise ratios and derives the distribution characteristics of the system's end-to-end signal-to-noise ratio using the cumulative distribution function.

[0058] S4. Based on the corresponding probability density function and cumulative distribution function, obtain the closed-loop expression for the confidentiality interruption probability of the communication system model. Under given parameters, obtain the confidentiality interruption probability value based on the closed-loop expression as the evaluation result, and complete the evaluation of the physical layer security performance of the communication system model.

[0059] In a more specific embodiment provided in this application, the instantaneous security capacity of the system is represented as the minimum value between the FSO link security capacity and the RF link security capacity;

[0060] In the formula, and These represent the security capabilities of the FSO and RF links, respectively.

[0061] The probability of a security breach is defined as the instantaneous security capacity falling below the target security rate. The probability of:

[0062] Using the cumulative distribution functions of the FSO link and the RF link, a closed-form expression for the probability of security interruption is derived:

[0063]

[0064] In the formula, , This represents the average signal-to-noise ratio of the first eavesdropper's link. This represents the average signal-to-noise ratio of the second eavesdropper's link. This indicates the number of antennas for ground users. This indicates the number of antennas used by the second eavesdropper.

[0065] In a more specific embodiment provided in this application, the given parameters include at least one of the following: FSO link correlation coefficient, RF link correlation coefficient, atmospheric turbulence intensity, pointing error coefficient, target security rate, channel state of the first eavesdropper, channel state of the second eavesdropper, number of antennas of the ground user, and number of antennas of the second eavesdropper.

[0066] Substituting the given parameters into the above closed expression, the specific value of the probability of security breach is calculated and used as the evaluation result.

[0067] A lower probability of security breach indicates better physical layer security performance. By analyzing the quantitative impact of at least one of the above parameters on the probability of security breach, the physical layer security performance of the communication system model is evaluated.

[0068] This step defines the probability of security interruption and derives a closed-form expression by representing the instantaneous security capacity of the system as the minimum of the security capacities of the two links. This solves the problem that existing technologies cannot quantitatively evaluate the security performance of a system in a dual-eavesdropper scenario.

[0069] In a more specific embodiment of this application, under high signal-to-noise ratio conditions, when At that time, the closed-loop expression for the probability of the security interruption. Asymptotic analysis yields an asymptotic expression for the probability of security breach:

[0070]

[0071] use The security coding gain can be expressed as:

[0072] In high SNR regions tending towards 1- , which is represented as a constant. Therefore, the diversity order of the entire system is zero.

[0073] In this step, due to the existence of imperfect CSI, even if the transmit power is increased indefinitely, the probability of system security interruption cannot be reduced indefinitely, but rather converges to a constant determined by the imperfect CSI of the FSO link. This solves the problem of the lack of limit analysis of system security performance in existing technologies.

[0074] Furthermore, it also includes: calculating the secure throughput of the communication system model based on the closed-form expression of the secure interruption probability. Secure throughput represents the achievable rate of the system under the constraints of ensuring confidentiality and reliability, and can be expressed as:

[0075] Based on the confidential throughput and target confidentiality rate The relationship is used to determine the optimal target security rate threshold that maximizes the secure throughput.

[0076] To verify the effectiveness of the secure transmission method proposed in this application and the correctness of the theoretical analysis, this embodiment analyzes the physical layer security performance of the system through numerical simulation and verifies the theoretical derivation results using the Monte Carlo simulation method.

[0077] The simulation parameters are set as follows: the FSO link follows the Gamma-Gamma fading model, and the RF link follows the Rayleigh fading model. Atmospheric turbulence intensity is divided into two cases: moderate turbulence... When the flow is weakly turbulent Parameters such as pointing error coefficient, channel correlation coefficient, number of antennas, and target security rate are set according to different simulation scenarios.

[0078] In this embodiment, the impact of different correlation coefficients of the FSO link on the system security interruption probability SOP is analyzed through simulation.

[0079] like Figure 3 As shown, the results indicate that the probability of system security interruption decreases with the increase of the FSO link correlation coefficient. This is because a higher FSO link correlation coefficient indicates a smaller channel estimation error, thus improving the system's security performance.

[0080] when At that time, there are some minimum values ​​for SOP, because the channel correlation coefficient value is affected by... Value restrictions, that is The value will affect the value of SOP. The impact of different RF link correlation coefficients on system start-up cost (SOP) is analyzed through simulation. For example... Figure 4 As shown, the channel estimation error decreases with increasing RF link correlation coefficient values, significantly improving system security performance. However, under high signal-to-noise ratio conditions, the system security interruption probability values ​​under different RF link correlation coefficient values ​​merge into the same minimum value, indicating that system performance is determined by the FSO link.

[0081] like Figure 5 As shown, using multiple antennas and maximum ratio combining techniques can significantly improve the system's security performance. Simultaneously, increasing the number of antennas for ground users and reducing the number of antennas for second eavesdroppers can improve the performance against security breaches, as more receiver antennas can provide greater diversity gain.

[0082] like Figure 6 As shown, the probability of system security interruption increases with the target security level. The increase is due to the increase in the target's confidentiality level. This is because the higher the target's confidentiality level, the higher the confidentiality capacity the system needs to provide to meet secure transmission requirements, making confidentiality interruption events more likely to occur. Therefore, A smaller value can actually improve the system's security performance; however, due to the imperfect CSI, the SOP (Standard Operating Procedure) may vary. Time tends to be constant.

[0083] like Figure 7 As shown, with the increase of the target confidentiality rate, the confidentiality throughput value first increases and then decreases. There exists an optimal threshold that allows the system to achieve the best confidentiality throughput performance. Below this threshold, the confidentiality throughput is determined by the value of [value missing]; while above this threshold, the system's reliability and security are reduced, and the confidentiality throughput is determined by [value missing]. Decide.

[0084] In a more specific embodiment provided in this application, a hybrid FSO / RF secure transmission system based on imperfect CSI is described, the structure of which is shown below. Figure 2 The system includes: The system model building unit is used to build a communication system model of an integrated air-space-ground network based on UAV relay; wherein, the link between the low-orbit satellite and the UAV relay is an FSO link, the link between the UAV relay and the ground user is an RF link, the FSO link is subject to a first eavesdropper, and the RF link is subject to a second eavesdropper; The channel modeling unit is used to establish the transmission channel model of the FSO link and the transmission channel model of the RF link respectively based on the communication system model under the condition of imperfect CSI. The function acquisition unit is used to obtain the corresponding probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio of the communication system model based on the transmission channel model of the FSO link and the transmission channel model of the RF link, respectively. The evaluation unit is used to obtain a closed-form expression for the confidentiality interruption probability of the communication system model based on the corresponding probability density function and cumulative distribution function. Under given parameters, the unit obtains the confidentiality interruption probability value based on the closed-form expression as the evaluation result, thereby completing the evaluation of the physical layer security performance of the communication system model.

[0085] The specific implementation methods of the above units are described in steps S1 to S4 of Embodiment 1, and will not be repeated here.

[0086] In another embodiment provided in this application, a computer device is provided, including a processor and a computer-readable storage medium.

[0087] The processor is adapted to execute a computer program. The computer-readable storage medium stores a computer program that, when executed by the processor, implements the hybrid FSO / RF secure transmission method based on imperfect CSI as described above.

[0088] In another embodiment provided in this application, a computer-readable storage medium is provided, the computer-readable storage medium storing a computer program adapted to be loaded by a processor and executed as described in the hybrid FSO / RF secure transmission method based on imperfect CSI.

[0089] The computer-readable storage medium can be any tangible medium that contains or stores a program, such as a USB flash drive, portable hard drive, read-only memory, random access memory, magnetic disk, or optical disk.

[0090] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this application, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A hybrid FSO / RF secure transmission method based on imperfect CSI, characterized in that, Includes the following steps: A communication system model for an integrated air-space-ground network based on UAV relay is constructed; wherein, the link between the low-Earth orbit satellite and the UAV relay is an FSO link, and the link between the UAV relay and the ground user is an RF link; the FSO link is susceptible to a first eavesdropper, and the RF link is susceptible to a second eavesdropper. In the case of imperfect CSI, the transmission channel model of the FSO link and the transmission channel model of the RF link are established based on the communication system model respectively. Based on the transmission channel model of the FSO link and the transmission channel model of the RF link, the corresponding probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio of the communication system model are obtained respectively. Based on the corresponding probability density function and cumulative distribution function, a closed-form expression for the confidentiality interruption probability of the communication system model is obtained. Under given parameters, the confidentiality interruption probability value is obtained based on the closed-form expression as the evaluation result, thus completing the evaluation of the physical layer security performance of the communication system model.

2. The hybrid FSO / RF secure transmission method based on imperfect CSI according to claim 1, characterized in that, The formula for establishing the transmission channel model of the FSO link is as follows: In the formula, Indicates precise channel gain. This represents the correlation coefficient of FSO link information. Let represent a random variable with a Gaussian distribution having zero mean and unit variance; The formula for establishing the transmission channel model of the RF link is as follows: In the formula, Indicates precise channel gain. Indicates and Radio frequency channel model random variables with the same variables, Represents the correlation coefficient. .

3. The hybrid FSO / RF secure transmission method based on imperfect CSI according to claim 1, characterized in that, FSO links follow the Gamma-Gamma fading model, while RF links follow the Rayleigh fading model.

4. The hybrid FSO / RF secure transmission method based on imperfect CSI according to claim 1, characterized in that, Based on the transmission channel model of the FSO link and the transmission channel model of the RF link, the corresponding probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio of the communication system model are obtained, specifically including: Based on the transmission channel model of the FSO link and the transmission channel model of the RF link, and combined with the decoding and forwarding protocol adopted by the UAV relay, the end-to-end signal-to-noise ratio is expressed as the minimum value of the signal-to-noise ratios of the FSO link and the RF link. The cumulative distribution function of the end-to-end signal-to-noise ratio is calculated using the cumulative distribution functions of the FSO link and the RF link.

5. The hybrid FSO / RF secure transmission method based on imperfect CSI according to claim 1, characterized in that, The closed-form expression for the security interruption probability of the communication system model is obtained based on the corresponding probability density function and cumulative distribution function. Given parameters, the security interruption probability value is obtained from the closed-form expression as the evaluation result. The process of evaluating the physical layer security performance of the communication system model specifically includes: The instantaneous security capacity of the system is expressed as the minimum value between the security capacity of the FSO link and the security capacity of the RF link. The probability of security interruption is defined as the probability that the instantaneous security capacity is lower than the target security rate. A closed expression for the probability of security interruption is derived using the cumulative distribution function of the FSO link and the RF link. The probability of confidentiality interruption is calculated by substituting the given parameters into the closed expression and used as the evaluation result to complete the evaluation of the physical layer security performance of the communication system model.

6. The hybrid FSO / RF secure transmission method based on imperfect CSI according to claim 4, characterized in that, Also includes: Under high signal-to-noise ratio conditions, an asymptotic analysis is performed on the closed-loop expression of the confidentiality interruption probability to obtain an asymptotic expression of the confidentiality interruption probability, and the diversity order of the communication system model is determined based on the asymptotic expression.

7. A hybrid FSO / RF secure transmission method based on imperfect CSI according to claim 5, characterized in that, The given parameters include at least one of the following: FSO link correlation coefficient, RF link correlation coefficient, atmospheric turbulence intensity, pointing error, target security rate, channel state of the first eavesdropper, channel state of the second eavesdropper, number of antennas of the ground user, and number of antennas of the second eavesdropper.

8. The hybrid FSO / RF secure transmission method based on imperfect CSI according to claim 1, characterized in that, Also includes: The confidential throughput of the communication system model is calculated based on the closed-form expression of the confidentiality interruption probability, and the optimal target confidentiality threshold that maximizes the confidentiality throughput is determined based on the relationship between the confidentiality throughput and the target confidentiality rate.

9. A hybrid FSO / RF secure transmission system based on imperfect CSI, characterized in that, include: The system model building unit is used to build a communication system model of an integrated air-space-ground network based on UAV relay; wherein, the link between the low-orbit satellite and the UAV relay is an FSO link, the link between the UAV relay and the ground user is an RF link, the FSO link is subject to a first eavesdropper, and the RF link is subject to a second eavesdropper; The channel modeling unit is used to establish the transmission channel model of the FSO link and the transmission channel model of the RF link respectively based on the communication system model under the condition of imperfect CSI. The function acquisition unit is used to obtain the corresponding probability density function and cumulative distribution function of the end-to-end instantaneous signal-to-noise ratio of the communication system model based on the transmission channel model of the FSO link and the transmission channel model of the RF link, respectively. The evaluation unit is used to obtain a closed-form expression for the confidentiality interruption probability of the communication system model based on the corresponding probability density function and cumulative distribution function. Under given parameters, the unit obtains the confidentiality interruption probability value based on the closed-form expression as the evaluation result, thereby completing the evaluation of the physical layer security performance of the communication system model.

10. A computer device, characterized in that, include: Processor and computer-readable storage media; A processor, adapted to execute computer programs; A computer-readable storage medium storing a computer program that, when executed by the processor, implements a hybrid FSO / RF secure transmission method based on imperfect CSI as described in any one of claims 1 to 8.

Images