RIS-enabled symbiotic scatter communication secure transmission beamforming design method

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a symbiotic scatter communication secure transmission beam forming design method capable of enabling a reconfigurable intelligent surface (RIS). According to the method, the electromagnetic amplitude and phase characteristics of the RIS are considered, so that an environment backscattering covert communication beam forming design scheme based on the multi-antenna technology is provided, the signal sending direction of reflection equipment is gathered on a legal receiver, the energy reaching a third-party user is minimum, and then the requirements of backscattering transmission concealment and reliability are met.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, specifically relating to a beamforming design method for secure transmission of co-occurring scattering communication enabled by a reconfigurable intelligent surface (RIS). Background Technology

[0002] Co-occurrence scattering (CAS) communication is an emerging technology that can significantly improve spectral and energy efficiency. In this technology, the secondary system utilizes the spectrum and radio frequency signals of the primary system to achieve backscatter communication. Simultaneously, the secondary system provides additional multipath components to the primary system, potentially enhancing its performance and enabling mutually beneficial transmission. In CAS, the strength of the reflection link is a key factor affecting the transmission performance of both the primary and secondary systems. RIS (Reflection Link Array) provides a solution for effectively enhancing the reflection link due to its passive beamforming capability. The RIS replaces traditional reflection communication units to transmit secondary system information and improves the transmission performance of the primary system through passive beamforming. RIS-enabled CAS has great application potential in IoT scenarios such as environmental monitoring, body health networks, and smart homes. For example, in a smart home scenario, the RIS connects to indoor sensors (such as humidity sensors) and is deployed on indoor windows. While assisting traditional cellular communication, the RIS modulates sensor information onto the cellular signal, and the mobile phone simultaneously recovers both the cellular signal and the RIS signal. In this scenario, RIS utilizes the already widely deployed cellular network to transmit information without requiring additional spectrum and energy resources. Therefore, RIS-enabled symbiotic scattering communication has great application potential in this scenario.

[0003] However, due to the openness of wireless channels and the characteristics of RIS-enhanced signals, RIS-enabled co-scatter communication is vulnerable to security threats. Therefore, improving the security and reliability of RIS-enabled co-scatter communication information transmission from the perspective of wireless transmission design is crucial. RIS's passive beamforming function enables directional information transmission; however, the beamforming design is affected by the electromagnetic amplitude and phase characteristics of the RIS. Summary of the Invention

[0004] To address the aforementioned issues, this invention considers the electromagnetic amplitude and phase characteristics of RIS and proposes a RIS-enabled co-scattering communication secure transmission beamforming design scheme, thereby reducing the probability of detection by third-party users and improving the transmission rate of the primary and secondary co-scattering communication systems.

[0005] This invention is based on Figure 1 Taking the model shown as an example, this paper illustrates a RIS-enabled co-occurrence scattering communication secure transmission beamforming design scheme. Figure 1As shown, the primary transmitter (PTx) uses active transmission technology to send its information to the primary receiver (PRx). The secondary transmitter (SRx), acting as the secondary transmitter (STx), periodically switches its antenna impedance based on its own bit information, modulating its information onto the radio frequency signal from the PTx and reflecting it back to the secondary receiver (SRx). An unauthorized third-party user, Willie, continuously listens to the channel to determine whether there is communication between the PTx and PRx, or between the RIS and SRx. Let... , , and These represent the numbers from PTx to PRx, SRx, and RIS, respectively. The channel response of each reflection unit and Willie, let , and They represent the RIS-1 The channel responses from each reflection unit to PRx, SRx, and Willie are considered. To improve the reliability of the subsystem transmission, the transmission symbol period of RIS is considered to be one-tenth of the symbol period of PTx. Times, RIS Each transmitted symbol can be represented as... PTx in the The transmission symbol corresponding to each position is represented as: ,in The received signal of PRx can be represented as

[0006] (1)

[0007] in, Indicates the PTx signal transmission power. , , , It is RIS The reflection coefficient of each reflecting unit. The received noise represents a cyclically symmetric complex Gaussian distribution, i.e. The received signal of SRx can be represented as...

[0008] (2)

[0009] in, The received noise at SRx follows a cyclically symmetric complex Gaussian distribution, i.e. Similarly, the received signal of receiver Willie can be expressed as...

[0010] (3)

[0011] in, The received noise at Willie's location follows a cyclically symmetric complex Gaussian distribution, i.e. .

[0012] Due to practical hardware limitations, the amplitude and phase characteristics of RIS electromagnetic reflection are extremely complex. RIS directly reflects the incident signal into electromagnetic space without needing to receive the incoming electromagnetic signal; therefore, RIS reflection occurs at the boundary between free space and the reflecting unit. Using the transmission line model, the impedance generated in free space is... According to antenna scattering theory, the reflecting device... The reflection coefficient of the root antenna It can be represented as:

[0013] (4)

[0014] in, Indicates the first The equivalent circuit load impedance at each reflecting unit. According to the above formula, the reflection coefficient of RIS is related to the equivalent load impedance of the reflecting unit. The RIS reflecting unit controls its bias voltage through the DC feed line to change the capacitance value of the varactor diode, thereby changing the equivalent load impedance and dynamically adjusting the reflection coefficient. Figure 2 This paper presents an RLC equivalent circuit structure based on transmission line theory, when the carrier frequency is... And the equivalent capacitance of the varactor diode is hour, This indicates the number of capacitance values ​​that the varactor diode can take, the first value being... Equivalent load impedance of each reflection unit for:

[0015] (5)

[0016] in, The inductance value of the bottom metal plate is determined by the thickness of the substrate. The inductance value of the top metal patch is related to its geometry and size. This represents the equivalent resistance caused by energy loss.

[0017] Since PTx uses active communication technology to transmit information, the average power of its transmitted symbols must be less than a given threshold. Therefore, the main system's transmitted symbols must satisfy the average power constraint. According to information theory, under the average power constraint, the mutual information of information transmission reaches its maximum when the transmitted signal follows a Gaussian distribution. Therefore, PTx transmits Gaussian signals, i.e. At this point, when the RIS transmission information is known, the channel capacity of the main system is:

[0018] (6)

[0019] Because RIS uses a passive backscatter mode to transmit information, the amplitude power of its transmitted signal is less than or equal to 1. Under this amplitude power constraint, the optimal distribution of RIS transmitted symbols is no longer a Gaussian distribution, but rather the amplitude follows a discrete distribution, and the phase follows a... The mutual information is uniformly distributed. However, the expression for mutual information under this optimal distribution is complex. Therefore, this invention uses its asymptotic result to characterize the channel capacity of the subsystem, namely:

[0020] (7)

[0021] RIS-enabled co-occurrence scattering communication involves two types of transmissions. For the third-party user Willie, it is necessary to determine not only whether PTx and PRx are communicating, but also whether RIS and SRx are communicating. This problem is a ternary assumption problem, and this invention uses... This indicates that neither the primary nor secondary systems in the RIS-enabled symbiotic scattering communication system communicated. This indicates that PTx and PRx are communicating, and RIS is assisting the main system in transmission. This indicates that PTx and PRx are communicating, and RIS is transmitting information to SRx while assisting the main system's transmission. Therefore, in a time slot of a received signal, this ternary hypothesis problem can be expressed as:

[0022] (8)

[0023] Assume a third-party user, Willie, determines whether the primary and secondary systems transmit information. For primary system transmission, Willie has two types of detection probabilities: false alarm probability and false negative probability. A false alarm probability indicates that PTx and PRx did not communicate, but Willie determines that they transmitted information. A false negative probability indicates that PTx and PRx communicated but were not detected by Willie. It is worth noting that in the ternary hypothesis problem... and Both indicate that the main system is communicating. This invention considers a third-party user, Willie, using energy detection to determine whether PTx and PRx are communicating. Specifically, the test statistic for Willie's energy detection can be written as:

[0024] (9)

[0025] in This represents the number of Willie sampling points measured using the RIS symbol period metric. For the scenario... In terms of test statistic It can be approximated by a Gaussian distribution, with a mean of 1 / 2. The variance is .for In terms of test statistic It can be approximated by a Gaussian distribution, with a mean of 1 / 2. The variance is .for In terms of test statistic It can also be approximated by a Gaussian distribution, with a mean of 1 / 2. The variance is .

[0026] Since formula (8) is a ternary hypothesis problem, there are three test thresholds. , and ,in express and Threshold between, express and Threshold between, express and The threshold between [variables]. Because in the ternary assumption problem, and Both indicate that the main system is communicating, therefore Willie's false alarm probability is... It can be represented as:

[0027] (10)

[0028] in, The reason why formula (10) holds true is that In this scenario, the mean and variance of the test statistic are minimized. Because... and Both indicate that the main system is communicating, therefore, there are two situations where PTx and PRx communication is missed: one is... False negative probability in the scenario Another one is False negative probability in the scenario , respectively represented as:

[0029]

[0030] In summary, the average detection error probability of the third-party user Willie in detecting the main system's transmission can be expressed as:

[0031] (11)

[0032] in This represents the prior probability that PTx sends a signal and RIS does not send a signal. This represents the prior probability that PTx transmits a signal and RIS transmits a signal. A higher Willie error probability indicates better stealth performance of the main system's transmission. At this time, Willie can know for sure whether the main system transmission has occurred, and the system's stealth is at its worst.

[0033] For subsystem transmissions, Willie also has two types of detection probabilities: false alarm probability and false negative probability. A false alarm probability indicates that the RIS did not transmit information, but Willie determined that it transmitted information. A false negative probability indicates that the RIS transmitted information but was not detected by Willie. Because... and Both indicate that the RIS did not transmit information; therefore, the false alarm probability regarding RIS transmission is divided into two categories: one is... False alarm probability in the scenario Another one is False alarm probability in the scenario It is worth noting that and The magnitude of the mean of the scenario test statistic and Relevant, therefore The probability of a false alarm in a given scenario. Specifically, the probability of a false alarm in the two scenarios is expressed as follows:

[0034] (12)

[0035] in, Indicates an indicator function, if but ,otherwise The probability of missing RIS and SRx communication can also be divided into two categories, namely... In the scenario, the judgment was made as and being sentenced as Therefore, the probability of missed detection It can be represented as

[0036] (13)

[0037] In summary, the average detection error probability of the secondary system transmission detected by the third-party user Willie can be expressed as:

[0038] (14)

[0039] A higher Willie error detection probability indicates better transmission concealment. as well as At this time, Willie can know for sure whether communication between the primary and secondary systems has occurred, and the system's transmission is least covert at this point.

[0040] This invention uses the maximization of Williede's minimum average detection error probability as an example to illustrate the passive beamforming variable for secure transmission based on RIS electromagnetic radiation characteristics. The design criteria and its optimization model are as follows:

[0041] (15)

[0042] In optimizing the problem In the context, constraint one represents the RIS-1... The values ​​of the reflection coefficient of each reflecting unit, and The weights that describe the probability of errors in the primary system transmission and the secondary system transmission detected by Willie are: .

[0043] The beneficial effects of this invention are as follows: This invention designs an environmental backscatter covert communication beamforming design scheme based on multi-antenna technology, which focuses the direction of the signal sent by the reflecting device on the legitimate receiver and minimizes the energy reaching the third-party user, thereby meeting the requirements of covertness and reliability of backscatter transmission. Attached Figure Description

[0044] Figure 1 This invention illustrates a RIS-enabled symbiotic scattering communication covert transmission system model.

[0045] Figure 2 The equivalent circuit model of the reflection unit based on transmission line theory in this invention is shown.

[0046] Figure 3 The relationship between the channel capacity of the primary and secondary systems and the transmitted signal-to-noise ratio is shown.

[0047] Figure 4 The relationship between the error probability of the primary and secondary system transmissions detected by Willie and the transmission signal-to-noise ratio is shown. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings.

[0049] Figure 1This invention illustrates a RIS-enabled symbiotic scattering communication covert transmission system model. PTx uses active transmission technology to send its information to PRx. RIS, acting as STx, periodically switches its antenna impedance based on its own bit information, modulating its information onto the RF signal from PTx and reflecting it to SRx. An unauthorized third-party user, Willie, continuously listens to the channel to determine whether there is communication between PTx and PRx or between RIS and SRx. Let... , , and These represent the numbers from PTx to PRx, SRx, and RIS, respectively. The channel response of each reflection unit and Willie, let , and Indicates the respective RIS number The channel responses from each reflection unit to PRx, SRx, and Willie are considered. To improve the reliability of the subsystem transmission, the transmission symbol period of RIS is considered to be one-tenth of the symbol period of PTx. Times, RIS Each transmitted symbol can be represented as... PTx in the The transmission symbol corresponding to each position is represented as: ,in The received signal of PRx can be represented as

[0050] (16)

[0051] in, Indicates the PTx signal transmission power. , , , It is RIS The reflection coefficient of each reflecting unit. The received noise represents a cyclically symmetric complex Gaussian distribution, i.e. The received signal of SRx can be represented as...

[0052] (17)

[0053] in, The received noise at SRx follows a cyclically symmetric complex Gaussian distribution, i.e. Similarly, the received signal of receiver Willie can be expressed as...

[0054] (18)

[0055] in, The received noise at Willie's location follows a cyclically symmetric complex Gaussian distribution, i.e. .

[0056] Due to practical hardware limitations, the amplitude and phase characteristics of RIS electromagnetic reflection are extremely complex. RIS directly reflects the incident signal into electromagnetic space without needing to receive the incoming electromagnetic signal; therefore, RIS reflection occurs at the boundary between free space and the reflecting unit. Using the transmission line model, the impedance generated in free space is... According to antenna scattering theory, the reflecting device... The reflection coefficient of the root antenna It can be represented as:

[0057] (19)

[0058] in, Indicates the first The equivalent circuit load impedance at each reflecting unit. According to the above formula, the reflection coefficient of RIS is related to the equivalent load impedance of the reflecting unit. The RIS reflecting unit controls its bias voltage through the DC feed line to change the capacitance value of the varactor diode, thereby changing the equivalent load impedance and dynamically adjusting the reflection coefficient.

[0059] Figure 2 This invention illustrates the equivalent circuit model of the reflection unit based on transmission line theory, when the carrier frequency is... And the equivalent capacitance of the varactor diode is At that time, the first Equivalent load impedance of each reflection unit for:

[0060] (20)

[0061] in, The inductance value of the bottom metal plate is determined by the thickness of the substrate. The inductance value of the top metal patch is related to its geometry and size. This represents the equivalent resistance caused by energy loss.

[0062] Since PTx uses active communication technology to transmit information, the average power of its transmitted symbols must be less than a given threshold. Therefore, the main system's transmitted symbols must satisfy the average power constraint. According to information theory, under the average power constraint, the mutual information of information transmission reaches its maximum when the transmitted signal follows a Gaussian distribution. Therefore, PTx transmits Gaussian signals, i.e. At this point, when the RIS transmission information is known, the channel capacity of the main system is:

[0063] (twenty one)

[0064] Because RIS uses a passive backscatter mode to transmit information, the amplitude power of its transmitted signal is less than or equal to 1. Under this amplitude power constraint, the optimal distribution of RIS transmitted symbols is no longer a Gaussian distribution, but rather the amplitude follows a discrete distribution, and the phase follows a... The mutual information is uniformly distributed. However, the expression for mutual information under this optimal distribution is complex. Therefore, this invention uses its asymptotic result to characterize the channel capacity of the subsystem, namely:

[0065] (twenty two)

[0066] RIS-enabled co-occurrence scattering communication involves two types of transmissions. For the third-party user Willie, it is necessary to determine not only whether PTx and PRx are communicating, but also whether RIS and SRx are communicating. This problem is a ternary assumption problem, and this invention uses... This indicates that neither the primary nor secondary systems in the RIS-enabled symbiotic scattering communication system communicated. This indicates that PTx and PRx are communicating, and RIS is assisting the main system in transmission. This indicates that PTx and PRx are communicating, and RIS is transmitting information to SRx while assisting the main system's transmission. Therefore, in a time slot of a received signal, this ternary hypothesis problem can be expressed as:

[0067] (twenty three)

[0068] Assume a third-party user, Willie, determines whether the primary and secondary systems are transmitting information. For primary system transmission, Willie has two types of detection probabilities: false alarm probability and false negative probability. A false alarm probability indicates that PTx and PRx are not communicating, but Willie determines they are transmitting information. A false negative probability indicates that PTx and PRx are communicating, but Willie fails to detect it. This invention considers that the third-party user Willie uses energy detection to determine whether PTx and PRx are communicating. Willie's false alarm probability... It can be represented as:

[0069] (twenty four)

[0070] in, .because and Both indicate that the main system is communicating, therefore, there are two situations where PTx and PRx communication is missed: one is... False negative probability in the scenario Another one is False negative probability in the scenario , respectively represented as:

[0071]

[0072] In summary, the average detection error probability of the third-party user Willie in detecting the main system's transmission can be expressed as:

[0073] (25)

[0074] in This represents the prior probability that PTx sends a signal and RIS does not send a signal. This represents the prior probability that PTx sends a signal and RIS sends a signal.

[0075] For subsystem transmissions, Willie also has two types of detection probabilities: false alarm probability and false negative probability. A false alarm probability indicates that the RIS did not transmit information, but Willie determined that it transmitted information. A false negative probability indicates that the RIS transmitted information but was not detected by Willie. Because... and Both indicate that the RIS did not transmit information; therefore, the false alarm probability regarding RIS transmission is divided into two categories: one is... False alarm probability in the scenario Another one is False alarm probability in the scenario It is worth noting that and The magnitude of the mean of the scenario test statistic and Relevant, therefore The probability of a false alarm in a given scenario. Specifically, the probability of a false alarm in the two scenarios is expressed as follows:

[0076] (26)

[0077] in, Indicates an indicator function, if but ,otherwise The probability of missing RIS and SRx communication can also be divided into two categories, namely... In the scenario, the judgment was made as and being sentenced as Therefore, the probability of missed detection It can be represented as

[0078] (27)

[0079] In summary, the average detection error probability of the secondary system transmission detected by the third-party user Willie can be expressed as:

[0080] (28)

[0081] A higher Willie error detection probability indicates better transmission concealment. as well as At this time, Willie can know for sure whether communication between the primary and secondary systems has occurred, and the system's transmission is least covert at this point.

[0082] This invention uses the maximization of Williede's minimum average detection error probability as an example to illustrate the passive beamforming variable for secure transmission based on RIS electromagnetic radiation characteristics. The design criteria and its optimization model are as follows:

[0083] (29)

[0084] In optimizing the problem In the context, constraint one represents the RIS-1... The values ​​of the reflection coefficient of each reflecting unit, and The weights that describe the probability of errors in the primary system transmission and the secondary system transmission detected by Willie are: By analyzing the optimization problem It can be seen that, The range of values ​​for is non-convex; therefore, the optimization problem... Non-convex. This invention employs a one-dimensional search method to iteratively search for the optimal value corresponding to each reflection coefficient. The reflection coefficient is obtained. Then, the optimal detection threshold of Willie is obtained through one-dimensional search, and the reflection coefficient and detection threshold are solved iteratively until the algorithm converges.

[0085] The beneficial effects of this invention will be verified through simulation below. The simulation parameters are set as follows: assuming the channel follows Rayleigh fading, the variance of the direct link channel is 1, the ratio of the average intensity of the direct link to the average intensity of the reflected link corresponding to each RIS reflection unit is 20 dB, and the Willie sampling symbol number is... The number of RIS reflection units is 128. , , , And varactor diodes The range of values ​​is .

[0086] Figure 3 This demonstrates the design of passive beamforming variables with the objective of maximizing Willie's minimum average detection error probability. The primary and secondary system channel capacities are shown below. It can be seen that with the transmission signal-to-noise ratio... With the increase in the transmission signal-to-noise ratio (SNR), the channel capacity of both the primary and secondary systems is improved. However, the rate of increase in the primary system's channel capacity with respect to the transmission SNR is greater than that of the secondary system. This is because the secondary system's transmission period is longer than that of the primary system, meaning the secondary system can only obtain SNR gain and not diversity gain.

[0087] Figure 4 The figure illustrates the relationship between the error probability of Willie detection of primary and secondary system transmissions and the transmit signal-to-noise ratio. Two schemes are compared: RIS without assisting the primary system transmission and RIS only assisting the primary system transmission. Specifically, RIS without assisting the primary system transmission means the RIS is not operational, and the primary system only uses the direct link channel to transmit information; RIS only assisting the primary system transmission means the RIS is operational but does not transmit secondary system information. As can be seen from the figure, for the primary system, RIS only assisting the primary system transmission provides the best stealth performance, while RIS without assistance provides the worst stealth performance. This is because the RIS can manipulate the electromagnetic wave propagation environment, making... In this scenario, Willie receives reduced signal energy, thus improving its stealth transmission performance. Simultaneously, Willie has the highest probability of detecting errors in secondary system transmissions because... and The two scenarios are difficult to distinguish, which leads to a higher probability of errors for Willie. Therefore, the covert transmission of the subsystem has the best performance.

Claims

1. A RIS-enabled co-occurrence scattering communication secure transmission beamforming design method, wherein the co-occurrence scattering communication system includes a master system transmitter (PTx), a master system receiver (PRx), a reconfigurable smart surface (RIS), a secondary system receiver (SRx), and a third-party user (Willie), wherein PTx uses active transmission technology to send its information to PRx, RIS, as a secondary system transmitter (STx), periodically switches its antenna impedance according to its own bit information, modulates the information onto the radio frequency signal from PTx and reflects it to SRx, and Willie continuously listens to the channel to determine whether there is communication between PTx and PRx or between RIS and SRx; characterized in that, The method includes: The RIS transmit symbol period is set to PTx symbols. Times, RIS Each transmitted symbol is represented as PTx in the The transmission symbol corresponding to each position is represented as: , PRx received signal for: ， in, Indicates the PTx signal transmission power. This represents the channel response from PTx to PRx. , Indicates RIS Channel response from each reflecting unit to PRx , It is the number of reflection units in the RIS. , Indicates the number of PTx to RIS Channel response of each reflecting unit , It is RIS The reflection coefficient of each reflecting unit. The received noise represents a cyclically symmetric complex Gaussian distribution, i.e. ; SRx received signal Represented as: ， in, This represents the channel response from PTx to SRx. , Indicates RIS The channel response from each reflecting unit to SRx, The received noise at SRx follows a cyclically symmetric complex Gaussian distribution, i.e. ; Willie's received signal Represented as: ， in, This represents the channel response from PTx to Willie. , Indicates RIS The channel response from each reflecting unit to Willie, The received noise at Willie's location follows a cyclically symmetric complex Gaussian distribution, i.e. ; Since Willie needs to determine not only whether PTx and PRx communicate, but also whether RIS and SRx communicate, he establishes the following ternary hypothesis problem: ， in, This indicates that neither the primary nor secondary systems of the RIS-enabled symbiotic scattering communication system communicated. This indicates that PTx and PRx are communicating, and RIS is assisting the main system in transmission; This indicates that PTx and PRx are communicating, and that RIS is transmitting information to SRx while assisting the main system in transmitting data. Willie is configured with two types of detection probabilities: false alarm probability and false negative probability, thereby setting the average detection error probability transmitted by the Willie detection main system. Represented as: ， in, This represents the prior probability that PTx sends a signal and RIS does not send a signal. yes False negative probability of PTx and PRx communication in the scenario , yes The probability of missed detection in PTx and PRx communication under the given scenario. This represents the prior probability that PTx transmits a signal and RIS transmits a signal. The false alarm probability of PTx and PRx communication: ， in, It is the test statistic for the Willie energy test. This indicates the number of Willie sampling points measured using the RIS symbol period criterion. , express and Threshold between, express and Threshold between, express and Threshold between; Willie detects the average detection error probability transmitted by the secondary system. Represented as: ， in, express The false alarm probability of RIS and SRx communication in the scenario. express The false alarm probability of RIS and SRx communication in the scenario. Indicates the false negative probability of RIS and SRx communication: ， ， in, Indicates an indicator function, if but ,otherwise ; Depend on and Get, when as well as At this time, the system's transmission security is at its worst, thus the minimum average detection error probability that maximizes Williede's is used as the passive beamforming variable for IRS secure transmission. Design principles, establishing optimization problems : ， in, It is RIS The reflection coefficient of the root antenna, It is RIS The equivalent load impedance of each reflection unit It is the equivalent capacitance of the varactor diode in the RIS reflector device. , This indicates the number of capacitance values ​​that the varactor diode can take. It is the impedance generated in free space. and The weights represent the probabilities of errors in the primary and secondary system transmissions detected by Willie. ; By solving optimization problems The optimal reflection coefficient of RIS is obtained.

2. The RIS-enabled co-occurrence scattering communication secure transmission beamforming design method according to claim 1, characterized in that, Solving optimization problems The specific method is: For nonconvex optimization problems A one-dimensional search method is used to iteratively search for the optimal value corresponding to each reflection coefficient. The reflection coefficient is obtained. Then, the optimal detection threshold of Willie is obtained through one-dimensional search. The reflection coefficient and detection threshold are solved iteratively until the algorithm converges, and the optimal reflection coefficient of RIS is obtained.

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