A Multi-User MISO Visible Light Communication Transmission Method Based on Liquid Crystal RIS

Abstract

The present invention discloses a multi-user MISO visible light communication transmission method based on liquid crystal RIS, comprising the following steps: (1) optimizing the parameters of LC-RIS through an artificial fish swarm algorithm; (2) calculating the signal transmitted by the LED transmitter according to the ZF precoding matrix that maximizes the channel capacity obtained in step 1; (3) calculating the signal received by the receiver according to steps 1 and 2. The present invention maximizes the system sum rate in the case of insufficient LED optical power and too high incident light loss rate of a traditional visible light receiver.

Description

Technical Field

[0001] The present invention relates to the technical field of optical wireless communication, and particularly relates to a multi-user MISO visible light communication transmission method based on liquid crystal RIS. Background Art

[0002] The beam propagation direction of traditional VLC systems is usually fixed, with limited coverage. And in visible light receivers, convex lenses are used to focus the incident light on the surface of the photodetector, which causes loss of the intensity of the incident light. However, with the gradual in-depth research on light RIS of mirror arrays and the rapid development of metamaterials, LC-RIS-assisted VLC systems have gradually come into the research vision of scholars. Different from the research on mirror array-based light RIS deployed on walls, LC-RIS is mainly deployed in VLC receivers for beam steering and light intensity amplification.

[0003] At present, the research on LC-RIS-based VLC systems mainly focuses on single-user VLC systems, and it has been found that the system has significant improvements in data rate and energy efficiency performance. However, the situation of multiple LC-RIS-assisted VLC receivers in the multi-user case has not been deeply explored. Compared with the single-user scenario, the optimization problem in the multi-light source-multi-user environment is more complex, and multiple factors need to be considered comprehensively. How to obtain the channel state information of each user in real time and how to optimize multiple LC-RIS simultaneously to maximize the system capacity are currently unsolved problems. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a multi-user MISO visible light communication transmission method based on liquid crystal RIS to solve the problems of low LED optical power and too high incident light loss rate of traditional visible light receivers.

[0005] Technical Solution: A multi-user MISO visible light communication transmission method based on liquid crystal RIS according to the present invention includes the following steps:

[0006] (1) The multi-user MISO visible light communication system based on liquid crystal RIS optimizes the parameters of LC-RIS through the artificial fish swarm algorithm;

[0007] (2) Calculate the signal sent by the LED transmitter according to the ZF precoding matrix that maximizes the channel capacity obtained in step (1);

[0008] (3) Calculate the signal received by the receiver.

[0009] Further, in step (1), the multi-user MISO visible light communication system based on liquid crystal RIS is as follows: L LEDs are distributed indoors as the transmitting end, and there are K users at the receiving end. Each receiving end consists of a single photodetector based on LC-RIS.

[0010] Further, step (1) includes the following steps:

[0011] (11) Set the parameters of the artificial fish swarm algorithm: Let the step size of each step , the crowding factor , the maximum number of attempts , the sensing range , the maximum number of iterations , the initial optimal solution , the refractive index vectors of multiple LC-RISs to be optimized are represented as , where are the initial values of N refractive index vectors of LC-RIS randomly generated;

[0012] (12) When the refractive index vector of LC-RIS is , the sum rate of users is calculated by the following method: Let the angular reflectivity of the optical signal transmitted by the l-th LED transmitter when it reaches the top interface of the k-th LC-RIS be represented as ;

[0013] Among them, is the relative refractive index of the k-th LC-RIS, is the air medium, the refractive index of the k-th LC-RIS, is the incident angle of the l-th LED transmitter to the top interface of the k-th LC-RIS, Then the angular transmittance of the light when it reaches the top interface of the LC-RIS is , similarly, the angular reflectivity of the optical signal when it leaves the LC-RIS is:

[0014] ;

[0015] Among them, Then the angular transmittance of the light when it leaves the LC-RIS is , the transmission coefficient of the k-th LC-RIS , the amplification gain coefficient of the k-th LC-RIS ,

[0016] Among them, is the wavelength of the incident light, E is the applied electric field, is the electro-optic coefficient, and the gain of the signal transmitted by the k-th LED transmitter after passing through the l-th LC-RIS is ;

[0017] where is the LOS channel gain from the l-th LED transmitter to the k-th receiver, d is the depth of the LC-RIS, and the channel gain at the k-th photodetector is expressed as , and the total channel gain of the VLC system is , and the ZF precoding based on the pseudo-inverse is , where , is the equal channel gain of the parallel sub-channels. Considering that the ZF precoding based on the pseudo-inverse completely eliminates MUI, the signal-to-interference-plus-noise ratio at the k-th user is expressed as , where is the covariance of the pulse amplitude modulation symbol transmitted to the k-th user, is the variance of the noise, and the achievable rate at user k is , and the sum rate of the system users is ;

[0018] (13) Calculate the number m of the initial values of the refractive index vector whose Euclidean distance from is less than , and find the refractive index vector at the center position of the initial values of the refractive index vector. Substitute into operation (12) to obtain the sum rate of the users as ,

[0019] If , then is updated to ,

[0020] where is a random number between [0, 1]. When , randomly select a new refractive index vector within the sensing range of . Substitute into operation (12) to obtain the sum rate of the users as . If , then takes a step forward in the direction, that is . If after attempts, it still does not satisfy , then remains unchanged;

[0021] (14) Calculate the number of refractive index vectors whose Euclidean distance from is less than The number m of initial values of the refractive index vector, and find the refractive index vector that maximizes the user sum rate among the initial values of the refractive index vector , substitute into operation (12) to obtain the user sum rate as , if , then is updated to , otherwise perform the operation in the above operation (13) when ;

[0022] (15) Compare the user sum rates after performing operation (13) and operation (14), and select the LC-RIS refractive index when the user sum rate is the largest as the optimal solution. Define the LC-RIS refractive index vector at this time as , and obtain the user sum rate as according to operation (12);

[0023] (16) When , update the value of Y to , and the optimal solution of this iteration is , when , then the optimal solution of this iteration is the optimal solution obtained in the previous iteration.

[0024] Further, step (2) is specifically as follows: According to the optimization algorithm in step (1), obtain the ZF precoding matrix that maximizes the user sum rate , then the signal vector transmitted by multiple LEDs is expressed as ;

[0025] Among them, represents the pulse amplitude modulation symbols transmitted to all users, is the DC bias added to the signal, and the signal transmitted by the l-th LED is expressed as , is the element in the l-th row and k-th column of

[0026] Further, step (3) is specifically as follows: The signal received at the k-th user is expressed as ,

[0027] where m is the k-th column of , and

[0028] A multi-user MISO visible light communication transmission system based on liquid crystal RIS according to the present invention includes:

[0029] Fish school module: Used to optimize the parameters of LC-RIS in a multi-user MISO visible light communication system based on liquid crystal RIS through an artificial fish school algorithm;

[0030] Calculation module: Used to calculate the signal transmitted by the LED transmitter according to the ZF precoding matrix that maximizes the channel capacity obtained in the fish school module;

[0031] Receiving module: Used to calculate the signal received by the receiver.

[0032] Furthermore, in the fish school module, the multi-user MISO visible light communication system based on liquid crystal RIS is specifically as follows: There are L LEDs as the transmitting end distributed indoors, and there are K users at the receiving end. Each receiving end consists of a single photodetector based on LC-RIS.

[0033] Furthermore, the fish school module is specifically as follows:

[0034] (a) Set the parameters of the artificial fish school algorithm: Let the step size per step , crowding factor , maximum number of attempts , sensing range , maximum number of iterations , initial optimal solution , the refractive index vectors of multiple LC-RISs to be optimized are represented as , where are the initial values of N refractive index vectors of LC-RIS randomly generated;

[0035] (b) When the refractive index vector of LC-RIS is , the sum rate of users is calculated by the following method: Let the angular reflectivity when the optical signal transmitted by the l-th LED transmitter reaches the top interface of the k-th LC-RIS be represented as ;

[0036] Among them, is the relative refractive index of the k-th LC-RIS, is the air medium, the refractive index of the k-th LC-RIS, is the incident angle from the l-th LED transmitter to the top interface of the k-th LC-RIS, Then the angular transmittance when the light reaches the top interface of the LC-RIS is , similarly, the angular reflectivity when the optical signal leaves the LC-RIS is:

[0037] ;

[0038] Among them, Then the angular transmittance of light leaving the LC-RIS is , the transmission coefficient of the k-th LC-RIS , the amplification gain coefficient of the k-th LC-RIS ,

[0039] where, is the wavelength of the incident light, E is the applied electric field, is the electro-optic coefficient, and the gain after the signal transmitted by the k-th LED transmitter passes through the l-th LC-RIS is ;

[0040] where, is the LOS channel gain from the l-th LED transmitter to the k-th receiver, d is the depth of the LC-RIS, and the channel gain at the k-th photodetector is expressed as , the total channel gain of the VLC system is , the ZF precoding based on the pseudo-inverse is , where , is the equal channel gain of the parallel sub-channels. Considering that the ZF precoding based on the pseudo-inverse completely eliminates MUI, the signal-to-interference-plus-noise ratio at the k-th user is expressed as , where, is the covariance of the pulse amplitude modulation symbol transmitted to the k-th user, is the variance of the noise, and the achievable rate at user k is , and the sum rate of the system users is ;

[0041] (c) Calculate the number m of the initial values of the refractive index vector whose Euclidean distance from is less than , and find the refractive index vector at the center position of the initial values of the refractive index vector. Substitute into operation (b) to obtain the sum rate of the users as ,

[0042] If , then is updated to ,

[0043] where, is a random number between [0, 1]. When , randomly select a new refractive index vector within the sensing range of . Substitute into operation (b) to obtain the sum rate of the users as . If , then towards Advance one step in the direction, that is If an attempt is made times and still does not meet , then remain unchanged;

[0044] (d) Calculate the number m of the initial refractive index vectors whose Euclidean distance from is less than , and find the refractive index vector that maximizes the user sum rate among the initial refractive index vectors . Substitute into operation (b) to obtain the user sum rate as . If , then update to , otherwise perform the operation in (c) above when ;

[0045] e) Compare the user sum rates after performing operations (c) and (d), and select the LC-RIS refractive index when the user sum rate is the largest as the optimal solution. Define the LC-RIS refractive index vector at this time as . According to operation (b), the user sum rate is ;

[0046] f) When , update the value of Y to . The optimal solution for this iteration is . When , then the optimal solution for this iteration is the optimal solution obtained in the previous iteration.

[0047] Furthermore, in the calculation module, according to the optimization algorithm in the fish swarm module, obtain the ZF precoding matrix that maximizes the user sum rate. Then the signal vector transmitted by multiple LEDs is expressed as ;

[0048] Among them, represents the pulse amplitude modulation symbols transmitted to all users, is the DC bias added to the signal. The signal transmitted by the l-th LED is expressed as , is the element in the l-th row and k-th column.

[0049] Furthermore, in the receiving module, specifically as follows: The signal received at the k-th user is expressed as ,

[0050] where m is the k-th column of is the additive Gaussian noise composed of shot noise and thermal noise.

[0051] Advantageous effects: Compared with the prior art, the present invention has the following remarkable advantages: Based on the refractive index constraints of each LC-RIS, the artificial fish swarm optimization algorithm is used to simultaneously optimize the refractive index values of multiple LC-RISs, effectively improving the system capacity and fully exploiting the transmission potential of multi-user VLC based on LC-RIS. Description of the Drawings

[0052] Figure 1 is the system model of the present invention;

[0053] Figure 2 is the relationship between the sum rate and the transmitted optical power when the user positions are random in the present invention (670 nm);

[0054] Figure 3 is the relationship between the sum rate and the transmitted optical power when the user positions are fixed in the present invention;

[0055] Figure 4 is the user position and the LED position coordinates in the present invention;

[0056] Figure 5 is the relationship between the sum rate and the FOV when the user positions are fixed in the present invention (670 nm);

[0057] Figure 6 is the relationship between the sum rate and the FOV when the user positions are random in the present invention. Detailed Embodiments

[0058] The technical solution of the present invention will be further described below with reference to the drawings.

[0059] As Figure 1 shown, an embodiment of the present invention provides a multi-user MISO visible light communication transmission method based on a liquid crystal RIS, including the following steps:

[0060] Step 1: A multi-user MISO visible light communication system based on a liquid crystal RIS has L LEDs distributed indoors as the transmitting end, and there are K users at the receiving end. Each receiving end consists of a single photodetector based on an LC-RIS. The fish swarm algorithm is used to calculate the parameters of the LC-RIS, which is specifically implemented through the following steps:

[0061] (11) Set the parameters of the artificial fish swarm algorithm: Let the step size per step , the crowding factor , the maximum number of attempts , the sensing range , maximum number of iterations , initial optimal solution , the refractive index vectors of multiple LC-RISs to be optimized are represented as , where are the initial values of N refractive index vectors of LC-RISs randomly generated;

[0062] (12) When the refractive index vector of the LC-RIS is , the sum rate of the user is calculated by the following method: Let the angular reflectance when the optical signal emitted by the l-th LED transmitter reaches the top interface of the k-th LC-RIS be represented as ;

[0063] where is the relative refractive index of the k-th LC-RIS, is the air medium, the refractive index of the k-th LC-RIS, is the incident angle of the l-th LED transmitter to the top interface of the k-th LC-RIS, Then the angular transmittance when the light reaches the top interface of the LC-RIS is , similarly, the angular reflectance when the optical signal leaves the LC-RIS is:

[0064] ;

[0065] where Then the angular transmittance when the light leaves the LC-RIS is , the transmission coefficient of the k-th LC-RIS , the amplification gain coefficient of the k-th LC-RIS ,

[0066] where is the wavelength of the incident light, E is the applied electric field, is the electro-optic coefficient, and the gain when the signal emitted by the k-th LED transmitter passes through the l-th LC-RIS is ;

[0067] where is the LOS channel gain from the l-th LED transmitter to the k-th receiver, d is the depth of the LC-RIS, and the channel gain at the k-th photodetector is represented as , the total channel gain of the VLC system is , the ZF precoding based on the pseudo-inverse is , where , For the channel gains such as parallel sub-channels, considering that the ZF precoding based on the pseudo-inverse completely eliminates MUI, the signal-to-interference-plus-noise ratio at the k-th user is expressed as , where is the covariance of the pulse amplitude modulation symbols transmitted to the k-th user, is the variance of the noise, and the achievable rate at user k is , and the sum rate of the system users is ;

[0068] (13) Calculate the number m of the initial values of the refractive index vectors whose Euclidean distance from is less than , and find the refractive index vector at the central position of the initial values of the refractive index vectors. Substitute into operation (12) to obtain the sum rate of the users as ,

[0069] If , then is updated to ,

[0070] where is a random number between [0, 1]. When , randomly select a new refractive index vector within the sensing range of . Substitute into operation (12) to obtain the sum rate of the users as . If , then take one step forward in the direction of , that is . If after trying times, it still does not satisfy , then remains unchanged;

[0071] (14) Calculate the number m of the initial values of the refractive index vectors whose Euclidean distance from is less than , and find the refractive index vector that maximizes the sum rate of the users among the initial values of the refractive index vectors. Substitute into operation (12) to obtain the sum rate of the users as, . If , then is updated to , otherwise perform the operation when in the above operation (13);

[0072] (15) Compare the user sum rate after performing operation (13) and operation (14), and select the LC-RIS refractive index when the user sum rate is the largest as the optimal solution. Define the LC-RIS refractive index vector at this time as , and obtain the user sum rate according to operation (12) as ;

[0073] (16) When , update the value of Y to , and the optimal solution of this iteration is . When , then the optimal solution of this iteration is the optimal solution obtained in the previous iteration.

[0074] Step 2: According to the optimization algorithm in Step 1, obtain the ZF precoding matrix that maximizes the user sum rate. According to the optimization algorithm in Step (1), obtain the ZF precoding matrix that maximizes the user sum rate , then the signal vector transmitted by multiple LEDs is expressed as ;

[0075] Among them, represents the pulse amplitude modulation symbols transmitted to all users, is the DC bias added to the signal. The signal transmitted by the l-th LED is expressed as , is in the element at the l-th row and k-th column.

[0076] Step 3: From Step 1 and Step 2, it can be obtained that the signal received at the k-th user is expressed as ,

[0077] where m is of the k-th column, is the additive Gaussian noise composed of shot noise and thermal noise.

[0078] As Figure 2 shows, after repeating this algorithm 100 times using the Monte Carlo simulation method, the relationship between the transmitted optical power and the system sum rate under different transmission schemes when the user positions are random is compared. When the transmitted optical power of the transmitter increases from 1W to 10W, the system sum rate after LC-RIS optimization is always greater than the system sum rate before LC-RIS optimization and the system sum rate using only ZF precoding. The experimental results show that placing LC-RIS in front of the receiver can not only amplify and steer the incident light beam, but also further verify the superiority of the artificial fish swarm optimization algorithm adopted in the present invention.

[0079] As Figure 3As shown, when the user's position is fixed, the influence of the beam wavelength on the system sum rate is very small under the condition of only using ZF precoding. However, after adding LC-RIS in front of the receiver, it can be clearly seen that when the beam wavelength is 510 nm, the system sum rate is significantly higher than that when the beam wavelength is 670 nm.

[0080] As Figure 4 shown, when using the user position parameters and the LED transmitter position parameters at a fixed position, that is Figure 3 and Figure 5 the position parameters used in

[0081] As Figure 5 shown, the maximum system sum rate is achieved at low FOV values because a smaller FOV leads to a higher concentrator gain, which effectively focuses the incident light and enhances the received signal strength. On the contrary, a higher FOV leads to a decrease in the concentrator gain, thus reducing the corresponding system sum rate.

[0082] As Figure 6 shown, under different FOV conditions, the system sum rate when the beam wavelength is 510 nm after LC-RIS optimization is always greater than that when the beam wavelength is 670 nm. While in the case of only using ZF precoding, when the FOV is between 50° and 60°, the system sum rate when the beam wavelength is 510 nm is higher than that when the beam wavelength is 670 nm. However, in the range of FOV from 60° to 90°, the system sum rate when the beam wavelength is 510 nm is lower than that when the beam wavelength is 670 nm.

Claims

1. A multi-user MISO visible light communication transmission method based on liquid crystal RIS, characterized in that, Including the following steps: (1) The multi-user MISO visible light communication system based on liquid crystal RIS optimizes the parameters of LC-RIS through the artificial fish swarm algorithm; among them, S1: calculate the number m of the initial values of the refractive index vector whose Euclidean distance from is less than , and find the refractive index vector at the center position of the initial values of the refractive index vector, substitute into the model established by the artificial fish swarm algorithm to obtain the user sum rate of , If , then update to , Among them, is a random number between [0, 1]. When occurs, randomly select a new refractive index vector within the perception range , substitute into the model established by the artificial fish swarm algorithm to obtain the user sum rate as . If , then take a step forward in the direction, that is . If after attempting times it still does not satisfy , then remains unchanged; S2: Calculate the number m of the initial values of the refractive index vectors whose Euclidean distance from is less than , and find the refractive index vector that maximizes the user sum rate among the initial values of the refractive index vectors . Substitute into the model established by the artificial fish swarm algorithm to obtain the user sum rate as . If , then is updated to , otherwise perform the operation in the above operation S2 when ; S3: Compare the sum rate of users after performing operations S1 and S2, and select the LC-RIS refractive index when the sum rate of users is the largest as the optimal solution. Define the LC-RIS refractive index vector at this time as , and the sum rate of users obtained according to the model established by the artificial fish swarm algorithm is ; S4: When occurs, update the value of Y to . The optimal solution for this iteration is . When occurs, the optimal solution for this iteration is the optimal solution obtained in the previous iteration; (2) Calculate the signal transmitted by the LED transmitter according to the ZF precoding matrix that maximizes the channel capacity obtained in step (1). (3) Calculate the signal received by the receiver.

2. The multi-user MISO visible light communication transmission method based on liquid crystal RIS according to claim 1, wherein, In step (1), the multi-user MISO visible light communication system based on liquid crystal RIS is as follows: There are L LEDs as the transmitting end distributed indoors, and there are K users at the receiving end. Each receiving end consists of a single photodetector based on LC-RIS.

3. A multi-user MISO visible light communication transmission method based on liquid crystal RIS according to claim 2, characterized in that, Step (1) also includes performing the following operations: (11) Set the parameters of the artificial fish swarm algorithm: Set the step size of each step , crowding factor , maximum number of attempts , sensing range , maximum number of iterations , initial optimal solution , the refractive index vectors of multiple LC-RISs to be optimized are represented as , where are the initial values of N randomly generated refractive index vectors of LC-RISs; (12) The refractive index vector of the LC-RIS is when the sum rate of the user is achieved by the following method: Let the angular reflectivity of the optical signal transmitted by the l-th LED transmitter when it reaches the top layer interface of the k-th LC-RIS be denoted as ； wherein, is the relative refractive index of the k-th LC-RIS, is the air medium, is the refractive index of the k-th LC-RIS, is the incident angle of the l-th LED transmitter to the top interface of the k-th LC-RIS, then the angular transmittance when the light reaches the top interface of the LC-RIS is , similarly, the angular reflectance when the optical signal leaves the LC-RIS is: ； Among them, the angular transmittance when light leaves the LC-RIS is , the transmission coefficient of the k-th LC-RIS , the amplification gain coefficient of the k-th LC-RIS , wherein, is the wavelength of the incident light, E is the applied electric field, is the electro-optic coefficient, and the gain of the signal transmitted by the k-th LED transmitter after passing through the l-th LC-RIS is ; wherein, is the LOS channel gain from the l-th LED transmitter to the k-th receiver, d is the depth of the LC-RIS, and the channel gain at the k-th photodetector is expressed as , and the total channel gain of the VLC system is , and the ZF precoding based on the pseudo-inverse is , where , is the equal channel gain of the parallel subchannels. Considering that the ZF precoding based on the pseudo-inverse completely eliminates MUI, the signal-to-interference-plus-noise ratio at the k-th user is expressed as , where is the covariance of the pulse amplitude modulation symbol transmitted to the k-th user, is the variance of the noise, and the achievable rate at user k is , and the sum rate of the system users is .

4. A multi-user MISO visible light communication transmission method based on liquid crystal RIS according to claim 3, characterized in that, Step (2) is specifically as follows: According to the optimized algorithm in step (1), the ZF precoding matrix that maximizes the user sum rate is obtained , then the signal vector transmitted by multiple LEDs is expressed as ; Among them, represents the pulse amplitude modulation symbol transmitted to all users, is the DC bias added to the signal, and the signal transmitted by the l-th LED is expressed as , is the element in the l-th row and k-th column.

5. A multi-user MISO visible light communication transmission method based on liquid crystal RIS according to claim 4, characterized in that, Step (3) is specifically as follows: The signal received at the k-th user is expressed as ， where m is the k-th column of is additive Gaussian noise composed of shot noise and thermal noise.

6. A multi-user MISO visible light communication transmission system based on liquid crystal RIS, characterized in that, Including: Fish swarm module: Used to optimize the parameters of LC-RIS through the artificial fish swarm algorithm for the multi-user MISO visible light communication system based on liquid crystal RIS; among them, the following operations are performed in the fish swarm module: (c) Calculate the number m of the initial values of the refractive index vectors whose Euclidean distance from is less than , and find the refractive index vector at the central position of the initial values of the refractive index vectors . Substitute into the model established by the artificial fish swarm algorithm to obtain the user sum rate of . If , then update to , Among them, is a random number between [0, 1]. When , randomly select a new refractive index vector within the perception range , and substitute into the model established by the artificial fish swarm algorithm to obtain the user sum rate as . If , then take a step forward in the direction, that is . If it tries times and still does not meet , then remains unchanged; (d) Calculate the number m of the initial values of the refractive index vectors whose Euclidean distance from is less than , and find the refractive index vector that maximizes the user sum rate among the initial values of the refractive index vectors . Substitute into the model established by the artificial fish swarm algorithm to obtain the user sum rate as . If , then is updated to , otherwise perform the operations in (c) above when ; (e) Compare the user sum rate magnitudes after performing operations (c) and (d), and select the LC-RIS refractive index when the user sum rate is the largest as the optimal solution. Define the LC-RIS refractive index vector at this time as , and the user sum rate obtained according to the model established by the artificial fish swarm algorithm is ; (f) When , update the value of Y to , and the optimal solution for this iteration is . When , then the optimal solution for this iteration is the optimal solution obtained in the previous iteration Calculation module: Used to calculate the signal transmitted by the LED transmitter according to the ZF precoding matrix that maximizes the channel capacity obtained in the fish swarm module. Receiving module: Used to calculate the signal received by the receiver.

7. A multi-user MISO visible light communication transmission system based on liquid crystal RIS according to claim 6, characterized in that, In the fish swarm module, the multi-user MISO visible light communication system based on liquid crystal RIS is as follows: There are L LEDs as the transmitting end distributed indoors, and there are K users at the receiving end. Each receiving end consists of a single photodetector based on LC-RIS.

8. A multi-user MISO visible light communication transmission system based on liquid crystal RIS according to claim 7, characterized in that, The fish swarm module is also used to perform the following operations: (a) Set the parameters of the artificial fish swarm algorithm: set the step size per step , crowding factor , maximum number of attempts , perception range , maximum number of iterations , initial optimal solution , the refractive index vectors of multiple LC-RISs to be optimized are represented as , where are the initial values of N randomly generated refractive index vectors of LC-RISs; (b)When the refractive index vector of the LC-RIS is , the sum rate of the users is obtained . The implementation process is as follows: Let the angular reflectivity of the optical signal transmitted by the l-th LED transmitter when it reaches the top interface of the k-th LC-RIS be denoted as ； wherein, is the relative refractive index of the k-th LC-RIS, is the air medium, is the refractive index of the k-th LC-RIS, is the incident angle from the l-th LED transmitter to the top interface of the k-th LC-RIS, then the angular transmittance when the light reaches the top interface of the LC-RIS is , similarly, the angular reflectance when the optical signal leaves the LC-RIS is: ； Among them, the angular transmittance when light leaves the LC-RIS is , the transmission coefficient of the k-th LC-RIS , the amplification gain coefficient of the k-th LC-RIS , wherein, is the wavelength of the incident light, E is the externally applied electric field, is the electro-optic coefficient, and the gain of the signal emitted by the k-th LED transmitter after passing through the l-th LC-RIS is ; wherein, is the LOS channel gain from the l-th LED transmitter to the k-th receiver, d is the depth of the LC-RIS, and the channel gain at the k-th photodetector is expressed as , and the total channel gain of the VLC system is , and the ZF precoding based on the pseudo-inverse is , where , is the equal channel gain of the parallel subchannels. Considering that the ZF precoding based on the pseudo-inverse completely eliminates MUI, the signal-to-interference-plus-noise ratio at the k-th user is expressed as , where is the covariance of the pulse amplitude modulation symbol transmitted to the k-th user, is the variance of the noise, and the achievable rate at user k is , and the sum rate of the system users is .

9. A multi-user MISO visible light communication transmission system based on liquid crystal RIS according to claim 8, characterized in that, In the calculation module, according to the optimization algorithm in the fish swarm module, the ZF precoding matrix that maximizes the user sum rate is obtained. Then, the signal vector transmitted by multiple LEDs is expressed as ; Among them, represents the pulse amplitude modulation symbols transmitted to all users, is the DC bias added to the signal, and the signal transmitted by the l-th LED is expressed as , is the element in the l-th row and k-th column.

10. A multi-user MISO visible light communication transmission system based on liquid crystal RIS according to claim 9, characterized in that, In the receiving module, specifically as follows: The signal received at the k-th user is denoted as , where m is the k-th column of, is additive Gaussian noise composed of shot noise and thermal noise.

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