Multi-user transmission method and device based on reconfigurable refractive metasurface antenna

Abstract

The application discloses a multi-user transmission method and device based on a reconfigurable refractive metasurface antenna, which comprises the following steps: modeling an optimization problem according to a digital beamforming matrix V D , the relationship between the phase shift of each radiation unit and the overall rate R of data sent by a base station to each user s, solving the optimization problem, obtaining an optimal digital beamforming matrix and an optimal phase shift, setting the phase shift of the reconfigurable refractive metasurface to the optimal phase shift, encoding the data stream x S of each user by using the optimal digital beamforming matrix, sending the encoding result through each feed source, and receiving the encoding result after the channel transmission by the user. The application can reduce interference, enhance useful signals and realize the simultaneous signal transmission to multiple users based on the reconfigurable refractive metasurface with multiple feed sources and the digital beamforming of the front end. The system sum rate can be maximized by optimizing the phase matrix and the digital beamforming matrix.

Description

Technical Field

[0001] This invention relates to the field of electronics, specifically to a multi-user transmission method and apparatus based on a reconfigurable refractive metasurface antenna. Background Technology

[0002] Massive MIMO is a crucial component of future wireless communication. Existing massive MIMO systems utilize traditional phased array antennas to achieve beamforming. However, traditional phased arrays suffer from high power consumption and high cost. To address this issue, reconfigurable reflective metasurface antennas have recently been proposed.

[0003] However, this antenna has the following drawback: because the feed source can block the reflected waves, its radiation efficiency is not high. To address this, reconfigurable refractive metasurface antennas have been proposed. Since reconfigurable refractive metasurfaces do not have the problem of feed source blocking, their radiation efficiency is higher than that of traditional reconfigurable reflective metasurface antennas. However, existing research on reconfigurable refractive metasurface antennas mainly focuses on how to design the antenna to optimize antenna-related parameters such as bandwidth and loss, without considering how to implement transmission in multi-user systems based on reconfigurable refractive metasurface antennas. Furthermore, existing research mainly focuses on reconfigurable refractive metasurface antennas with only a single feed source, making them unsuitable for multi-user systems.

[0004] Existing literature (B.Di.Et.al., "Hybrid Beamforming for Reconfigurable Intelligent Surface based Multi-user Communications: Achievable Rates with Limited Discrete Phase Shifts", IEEE Journal on Selected Areas in Communications (Volume:38, Issue:8, Aug.2020)) investigated how to simultaneously transmit data to multiple users in a reflective metasurface-assisted multi-user MIMO wireless communication system. However, the literature uses a reflective metasurface, and the base station's transmit antennas (feeds) are located in the far field of the metasurface. Therefore, the multi-user communication method mentioned in that literature cannot be directly used to implement the multi-user communication scenario we are considering.

[0005] Existing literature (Zhendong Li, Wen Chen, Senior Member, IEEE, and Huanqing Cao, "Beamforming Design and Power Allocation for Transmissive RMS-based Transmitter Architectures", https: / / arxiv.org / pdf / 2107.11013.pdf) proposes a transmitter based on a refractive metasurface and suggests a scheme to enable the transmitter to send data to multiple users simultaneously. However, the refractive metasurface in that literature performs both beamforming and digital carrier modulation functions, while the refractive metasurface in this paper only performs beamforming. Furthermore, the paper uses only one feed source, which transmits a single-frequency signal without data. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a multi-user transmission method and apparatus based on a reconfigurable refractive metasurface antenna, which, based on digital beamforming, enables multiple feed sources to simultaneously transmit data to multiple users.

[0007] The technical content of this invention includes:

[0008] A multi-user transmission method based on a reconfigurable refractive metasurface antenna includes the following steps:

[0009] 1) Based on the digital beamforming matrix V D Phase shift of each radiating element The relationship between the base station and the overall rate R of data transmission to each user s is modeled as an optimization problem, where m is the row number of the radiating element and n is the column number of the radiating element.

[0010] 2) Solve this optimization problem to obtain the optimal digital beamforming matrix. With optimal phase shift Where t is the number of iterations;

[0011] 3) Set the phase shift of the reconfigurable refractive metasurface to the optimal phase shift. Using the optimal digital beamforming matrix For the data stream x sent to each user S Encode;

[0012] 4) The encoding results are sent through each feed source and are received by the user after being transmitted through the channel.

[0013] Furthermore, the optimal digital beamforming matrix is ​​obtained through the following steps. With optimal phase shift

[0014] 1) Digital beamforming matrix Keeping the current constant, we solve the optimization problem to obtain the maximum rate R. t and the corresponding optimal phase shift

[0015] 2) Optimal phase shift Keeping the current constant, we solve the optimization problem to obtain the maximum rate R′. t and the corresponding optimal digital beamforming matrix

[0016] 3) When the speed R t With speed R (t+1) When the difference is less than a preset threshold, the optimal digital beamforming matrix is ​​obtained. With optimal phase shift

[0017] Furthermore, the optimal digital beamforming matrix is ​​obtained through the following steps. With optimal phase shift

[0018] 1) Optimal phase shift Keeping the current constant, we solve the optimization problem to obtain the maximum rate R. t and the corresponding optimal digital beamforming matrix

[0019] 2) Digital beamforming matrix Keeping the current constant, we solve the optimization problem to obtain the maximum rate R′. t and the corresponding optimal phase shift

[0020] 3) When R t With speed R (t+1) When the difference is less than a preset threshold, the optimal digital beamforming matrix is ​​obtained. With optimal phase shift

[0021] Furthermore, the rate R = ∑ s R s The rate at which the base station sends data to user s Represents the optimal digital beamforming matrix The element in the k-th row and s-th column, σ 2 h represents the variance of the additive white Gaussian noise in the signal received by user s. (s,k) K represents the channel from feed k to user s. tThis represents the number of feed sources for the reconfigurable refractive metasurface antennas equipped in the base station.

[0022] Furthermore, the channel between user s and feed k in Indicates road damage. Γ represents the small-scale fading coefficient. m,n This represents the refractive index of the radiating element (m,n).

[0023] Furthermore, road damage Where λ represents the wavelength corresponding to the carrier frequency. This represents the product of the antenna gains of the transmitting antenna k and the receiving antenna of user s in the direction of the radiating element (m,n). This represents the distance from the feed source k to the radiating element (m,n). α represents the distance from user s to the radiation unit (m,n), and α represents the path loss factor.

[0024] Furthermore, the refractive index Where A m,n This indicates the amplitude of refraction.

[0025] Furthermore, each user s receives the signal of the encoded result. in Represents the optimal digital beamforming matrix The element in the k-th row and s-th column, n S This represents additive white Gaussian noise.

[0026] A storage medium storing a computer program, wherein the computer program is configured to execute the method described above at runtime.

[0027] An electronic device includes a memory and a processor, wherein the memory stores a program for performing the methods described above.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. Multiple feeders can be used to send signals to multiple users simultaneously, and the signals transmitted by the feeders carry data.

[0030] 2. Combined with front-end digital beamforming, interference can be better eliminated, maximizing system performance and speed. Attached Figure Description

[0031] Figure 1 Reconfigurable refractive metasurface antenna.

[0032] Figure 2 The method flowchart of the present invention.

[0033] Figure 3 A narrowband downlink network according to an embodiment of the present invention.

[0034] Figure 4 The hybrid beamforming process of the present invention. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only specific embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] A reconfigurable refractive metasurface antenna consists of multiple feed sources and a refractive metasurface. For example... Figure 1 As shown, the refractive metasurface is an array of multiple subwavelength elements. Each element has a PIN diode, which can be switched between ON and OFF by adjusting the bias voltage across it. When a signal is incident on each element, it undergoes refraction. By adjusting the state of the diodes on the elements, the phase of the refracted wave can be changed. The beamforming process of this antenna includes: the signal emitted by the feed is refracted when it is incident on each element; during this refraction, the metasurface elements apply a certain phase shift to the signal. By adjusting the bias voltage on the diodes, the refraction phase shift of the elements is appropriately set, thereby achieving beamforming.

[0037] The multi-user transmission method of the present invention, such as Figure 2 As shown, it includes:

[0038] 1. Based on the digital beamforming matrix V D Phase shift of each radiating element The relationship between the base station and the overall rate R of data transmission to each user s is modeled as an optimization problem, where m is the row number of the radiating element and n is the column number of the radiating element.

[0039] 2. Solve this optimization problem to obtain the optimal digital beamforming matrix. With optimal phase shift Where t is the number of iterations;

[0040] 3. Set the phase shift of the reconfigurable refractive metasurface as the optimal phase shift. Using the optimal digital beamforming matrix For the data stream x sent to each user S Encode;

[0041] 4. Encoding results transmitted by each feed source;

[0042] 5. The encoded result is received by the user after being transmitted through the channel.

[0043] Specifically, consider a narrowband downlink network, such as... Figure 3 As shown, the network comprises multiple users and one base station; the number of users is denoted as S. For beamforming, the base station employs a reconfigurable refractive metasurface antenna to effectively serve users within a 120-degree sector directly opposite the antenna. To enable simultaneous data transmission to multiple users, the reconfigurable refractive metasurface antenna is equipped with K... t One feed source.

[0044] Assume the refractive metasurface contains M*N units, each unit having a size of l. M ×l N Let A denote the refraction amplitude and phase shift of the (m,n)th element. m,n and The refractive index of this unit can then be written as Where the refraction amplitude A m,n It can be modeled as This represents the angle of incidence from the feed source to the element (m,n). We also assume that regardless of the angle of incidence, the phase shift of the element can vary within the range (0,2π) when the state of the element changes.

[0045] Suppose the channel from base station feed k to user s consists of M×N metasurface-based channels, where the (m,n)th channel represents the channel from the feed k through the (m,n)th metasurface unit to the user. We model the (m,n)th metasurface-based channel as the product of path loss, fast fading, and the response of the refractive metasurface, i.e.:

[0046]

[0047] in, Represents road damage; This represents the small-scale fading coefficient, with a mean of 0 and a variance of 1, and it is assumed that the small-scale fading of each cell is independent. Here, further modeling of path loss is performed:

[0048]

[0049] λ represents the wavelength corresponding to the carrier frequency. This represents the product of the antenna gains of the feed k and the receiving antenna of the user s in the direction of the radiating element (m,n), and α represents the path loss factor. and G represents the distance from the feed k to the single radiating element (m,n) and the distance from the user s to the element (m,n), respectively. I This represents the antenna gain of a single radiating element.

[0050] In summary, the channel from the feeder to the user can be written as follows:

[0051]

[0052] To ensure the beam projected by the refractive metasurface is aligned with each user, we propose a hybrid beamforming scheme. In this scheme, the base station performs digital beamforming, while the refractive metasurface performs analog beamforming. Specifically, the base station first utilizes the digital beamforming matrix V... D The data stream x sent to each user is encoded to achieve digital beamforming. The encoded signal is then up-converted and transmitted through each feed source. The signals transmitted by each feed source can be written as follows:

[0053] e = V D x

[0054] When a signal transmitted by the antenna is incident on the individual elements of the refractive metasurface, it undergoes refraction. Simultaneously, the refractive metasurface applies a phase shift and amplitude change to the signal. By adjusting the state of the elements, this phase shift can be altered, thereby changing the beam shape and achieving analog beamforming. After passing through the refractive metasurface and the surrounding environment, the signal is received by the user. The received signal of user s can be written as...

[0055]

[0056] in Represents the element in the k-th row and s-th column of the digital beamforming matrix, n s This represents the additive white Gaussian noise in the signal received by user s, with a mean of 0 and a variance of σ. 2 Let s′ represent the ID of a user other than user s. From this, we can obtain the data transmission rate from the base station to user s.

[0057]

[0058] To maximize system performance and rate, we jointly optimize the digital beamforming matrix V. D and the phase of each unit cell of the refracting metasurface As shown below

[0059]

[0060] stTr(V D H V D)≤P T ,

[0061]

[0062] Where P T This represents the maximum transmission power of the base station. This represents the i-th possible value of the refraction phase of element (m,n), Tr() represents the trace of the matrix, and st represents the value that makes . We solve the above hybrid beamforming problem in the following way, as follows: Figure 4 As shown:

[0063] 1) Keep the digital beamforming matrix unchanged and optimize the phase shift of the refractive metasurface using mathematical methods;

[0064] 2) Keep the phase of the refractive metasurface unchanged and optimize the digital beamforming matrix using mathematical methods;

[0065] 3) Repeat step 1) until the difference between the sum rate of two adjacent iterations is less than the preset threshold.

[0066] It is easily understood that the present invention can also keep the phase of the refractive metasurface unchanged and solve the hybrid beamforming problem.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-user transmission method based on a reconfigurable refractive metasurface antenna, comprising the following steps: 1) Based on digital beamforming matrix Refraction phase shift of each radiating element With base stations to each user Overall data transmission rate The relationship between them, modeling to maximize the overall rate The optimization problem in which The row number is the radiating element. The column number of the radiating element; 2) Solve this optimization problem to obtain the optimal digital beamforming matrix. With optimal refractive phase shift ,in The constraint for solving this optimization problem, given the number of iterations, is to use the optimal digital beamforming matrix. The transmitted power does not exceed the base station's maximum transmit power, and the optimal refractive phase shift is achieved. In the set of refraction phase values ​​for the (m,n)th radiation element; 3) Set the refractive phase shift of the reconfigurable refractive metasurface as the optimal refractive phase shift. and using the optimal digital beamforming matrix Data streams sent to each user Encode; 4) Through each feed source The encoded result is sent, and the encoded result is received by the user after being transmitted through the channel; wherein, the feed source To the radiation unit The spacing is .

2. The method as described in claim 1, characterized in that, Overall rate The base station provides users with Data transmission rate , Represents the optimal digital beamforming matrix The Line number Column elements, The variance of the additive white Gaussian noise in the signal received by user s is represented by . This represents the channel from feed k to user s. The number of feed sources representing the reconfigurable refractive metasurface antennas equipped in the base station. This represents the ID of a user other than user s.

3. The method as described in claim 1, characterized in that, user With feed Channel between ,in Indicates road damage. This represents the small-scale fading coefficient. Represents a radiating unit The refractive index.

4. The method as described in claim 1, characterized in that, Road damage ,in This represents the wavelength corresponding to the carrier frequency. This represents the transmitting antenna. and users The receiving antenna in the radiating element Antenna gain product in the direction, On behalf of users To the radiation unit The spacing, Represents the road loss factor. This represents the antenna gain of a single radiating element.

5. The method as described in claim 4, characterized in that, refractive index ,in This indicates the amplitude of refraction.

6. The method as described in claim 1, characterized in that, Each user Receive the signal of the encoded result ,in Represents the optimal digital beamforming matrix The Line number Column elements, Represents additive white Gaussian noise. This indicates the number of feed sources equipped in a reconfigurable refractive metasurface antenna. This represents the ID of a user other than user s. Indicates from the feed source To users The channel, Indicates sending to the user Data flow, Indicates sending to the user The data stream.

7. A storage medium storing a computer program, wherein, The computer program is configured to execute the method of any one of claims 1-6 at runtime.

8. An electronic device comprising a memory and a processor, the memory storing a computer program, the processor being configured to run the computer program to perform the method as claimed in any one of claims 1-6.

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