RIS auxiliary wireless communication system

Abstract

The invention provides an RIS (Radio Information System) auxiliary wireless communication system, which relates to the technical field of communication facilities and comprises a near-field or far-field RIS auxiliary system, a BS (Base Station) is provided with a single antenna, and the BS is provided with multiple antennas. Two different deployment schemes of an RIS auxiliary wireless system under near-field and far-field path loss channels are researched in the application. A simulation result shows that a deployment strategy close to a single antenna in a near field obtains higher capacity than a deployment strategy close to a multi-antenna. For a far field, a simulation result shows that the equivalent capacity can be obtained by deploying the RIS near the User or the BS no matter how the transmission power or the number of the deployed RIS units changes. The results enhance the flexibility of deploying the RIS and provide a valuable opinion for the design of an actual RIS auxiliary communication system.

Description

Technical Field

[0001] The present invention relates to the technical field of communication facilities, and in particular to a RIS-assisted wireless communication system. Background Art

[0002] With the rapid development of fifth-generation (5G) wireless communication technology, researchers have paid more and more attention to 5G-advanced (5G-a) and sixth-generation (6G) communication systems. To facilitate the realization of 6G wireless communication, reconfigurable smart surfaces (RIS) have recently emerged as one of the most promising technologies. RIS is a planar metasurface composed of many passive low-cost reflective units. Each unit can dynamically adjust its amplitude and phase to achieve adaptive control of the wireless environment and efficiently and economically address the service needs of large-scale wireless devices. In the existing literature, researchers have extensively studied various aspects related to RIS, including location deployment, channel estimation, beamforming design, and performance analysis. In practice, the deployment of RIS poses a key challenge with important theoretical and practical significance. Most of the current studies on RIS-assisted systems assume a predetermined RIS deployment. However, some recent studies have studied the issue of RIS deployment from the perspective of communication theory. For example, the deployment strategy of wireless relay systems enhanced by smart reflective surfaces focuses on the capacity scaling order associated with single and multiple RIS deployments under the line-of-sight channel model. In another example, a new joint deployment of BS and RIS is studied to enhance wireless network coverage by leveraging multiple RIS reflections. In addition, a new communication system in the prior art that integrates active smart reflective surfaces and passive smart reflective surfaces explores the impact of the deployment of the two transmission schemes on the achievable rate in the context of a line-of-sight channel model.

[0003] However, most of the research on RIS-assisted systems focuses on the plane wave model. As the transmission frequency band increases, such as the millimeter wave (mmWave) band, the Rayleigh distance will also decrease, which may require a shift from the traditional plane wave model to the spherical wave model, and the phase variation of the signals arriving at different RIS units cannot be ignored. Therefore, the near-field spherical wave model has become a key research for the deployment of RIS-assisted communication systems. For example, it is not clear whether the traditional strategy of deploying RIS near the BS or User is still the best strategy for deploying RIS communication systems at present, and whether it is still applicable to near-field communications. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the research on RIS auxiliary system in the prior art mainly focuses on the plane wave model, and there is no relevant research on the spherical wave model.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A RIS-assisted wireless communication system includes a near-field or far-field RIS-assisted system, wherein a BS is configured with a single antenna and a BS is configured with multiple antennas.

[0007] The direct link between BS and User is blocked, and the signal received by the user is expressed as

[0008]

[0009] in m=1,…,N and n=1,…,N are RIS reflection matrices, h RIS-User It is the channel from RIS to User. BS-RIS It is the channel from BS to RIS. t is the transmitting power, s is the transmitting signal, and n is the additive white Gaussian noise.

[0010] The normalized power radiation pattern is shown below

[0011]

[0012] in and Represent the normalized power radiation pattern of BS Normalized power radiation diagram of the user When ∈ = 1, it represents the normalized power radiation pattern of the RIS cell

[0013] In the first deployment, when the RIS is centered on the origin in the yz plane, the geometric center of the RIS is aligned with the origin of the coordinate system.

[0014] Let N be the number of regularly arranged elements in the rows and columns of the RIS array, let N be an odd number, and let the size of each cell along the y-axis and z-axis be d,

[0015] Assume E n,m represents the RIS element at the nth row and mth column. The coordinates of the RIS element are in E n,m The reflection coefficient is Here β n,m and α n,m represent the amplitude and phase shift of the RIS element respectively;

[0016] Use θ b , θ u and To represent the elevation and azimuth from the RIS center to the BS, and the elevation and azimuth from the RIS center to the user;

[0017] Use and Indicates E n,m Elevation and azimuth to BS, E n,m Elevation and azimuth to User;

[0018] Use and Indicates BS to cell E n,m Elevation and azimuth, User to cell E n,m The elevation and azimuth angles of the BS are as follows: the distance from BS to RIS is d1, and the distance from RIS to User is d2;

[0019] Then, the coordinates of BS are The coordinates of User are Therefore, the distance between BS and element En, and the distance m between User and element En can be expressed as and In a multi-antenna base station system, the distance between the base station and the RIS unit is The distance between the user and the RIS unit is The coordinates of BS are The symbols b and N b They represent the BS antenna spacing and the number of BS antennas respectively.

[0020] In the second deployment, when the BS is centered on the origin in the yz plane, the geometric center of the BS is aligned with the origin of the coordinate system; let N and N r =N 2 It represents the number of regularly arranged elements in the rows and columns of the RIS array and the total number of RIS units;

[0021] Assume E n,m represents the RIS element at the nth row and mth column. The coordinates of the RIS element are Where m∈[1,N], n∈[1,N], and D∈[0,100] represent the distance that the RIS moves from the vicinity of the BS to the vicinity of the User along a specific straight line; E n,m The reflection coefficient is Here β n,m and α n,m are the amplitude and phase shift of the RIS unit, respectively;

[0022] Assume that the fixed distance from BS to User is 100m and the coordinates of BS are r B =(0,0,0), the coordinate of User is r u =(0,100,0). Therefore, the distance between the BS and the RIS unit, and the distance between the User and the RIS unit can be expressed as and The distance between the RIS center and the BS is d b , the distance between the RIS center and the User is d u , the distance between the RIS center and the RIS element is In a multi-antenna base station system, the symbol N is used b To represent the number of BS antennas;

[0023] The coordinates of BS are b represents the spacing between BS antennas, where n b ∈[1,N b ]; In addition, the distance between BS and RIS unit is The distance between User and RIS unit is The distance between the RIS center and the BS is The distance between the RIS center and the User is d u,c , the distance between the RIS center and the RIS unit is

[0024] In this application, two different deployment schemes of RIS-assisted wireless systems under near-field and far-field path loss channels are studied. Simulation results show that in the near field, the single-antenna deployment strategy achieves higher capacity than the multi-antenna deployment strategy. For the far field, simulation results show that deploying RIS near the User or BS can achieve equivalent capacity regardless of the transmission power or the number of deployed RIS units. These results enhance the flexibility of deploying RIS and provide valuable insights for the design of practical RIS-assisted communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Two different deployment scenarios of the embodiments of the present invention;

[0026] Figure 2 This is a RIS-assisted system of a multi-antenna BS in the near field according to an embodiment of the present invention.

[0027] Figure 3 The first deployment scheme of the BS equipped with single antenna and multiple antennas in the near field or far field according to the embodiment of the present invention (a) Achievable capacity and distance. (b) Achievable capacity and number of RIS elements. (c) Achievable capacity and size of RIS elements.

[0028] Figure 4 Second deployment scheme of BS equipped with single antenna and multiple antennas in near field or far field according to the embodiment of the present invention (a) Achievable capacity and distance. (b) Achievable capacity and number of RIS elements. (c) Achievable capacity and size of RIS elements. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with specific embodiments.

[0030] A RIS-assisted wireless communication system includes a near-field or far-field RIS-assisted system, wherein a BS is configured with a single antenna and a BS is configured with multiple antennas.

[0031] In an implementation mode, the direct link between the BS and the User is blocked, see Figure 1 ,

[0032] The attached figure illustrates the signal propagation path in two cases where the RIS is close to the BS and the User. The propagation of near-field signals follows the spherical wave model, and the phase and amplitude of the signal vary with the distance and angle. When the RIS is close to the BS, the angle difference between the base station and the RIS results in relatively poor signal propagation characteristics. When the RIS is close to the user, the angle between the base station and the RIS tends to be vertical, the signal propagation characteristics are more uniform, and the angle from the RIS to the user is relatively favorable.

[0033] Therefore, the RIS close to the user can more effectively reflect the signal from the BS to the user, thereby improving the performance gain. In the far field, the propagation of the signal follows the plane wave mode, and the phase and amplitude of the signal change less than in the near field. Therefore, in the near field, the performance gain of the signal can be improved by adjusting the deployment of the RIS, while in the far field, due to the plane wave characteristics of signal propagation, the deployment of the RIS has a relatively small impact on the signal gain.

[0034] In one embodiment, the signal received at the user is represented as

[0035]

[0036] in m=1,…,N and n=1,…,N are RIS reflection matrices, h RIS-User It is the channel from RIS to User. BS-RIS It is the channel from BS to RIS. t is the transmitting power, s is the transmitting signal, and n is the additive white Gaussian noise.

[0037] BS uses normalized power radiation pattern The antenna with antenna gain Gt transmits a signal with power Pt to the RIS. The signal is reflected by the RIS and the normalized power radiation pattern received by the user is and antenna gain Gr. The normalized power radiation pattern is shown below

[0038]

[0039] in and Represent the normalized power radiation pattern of BS Normalized power radiation diagram of the user When ∈ = 1, it represents the normalized power radiation pattern of the RIS cell

[0040] The boundary distance between the near field and the far field is often called the Rayleigh distance and is defined as A is the maximum size of the antenna, is the wavelength. As the frequency increases, especially in the millimeter wave band, the probability that the BS and the User are within the Rayleigh distance increases.

[0041] In the first deployment scenario implemented, the RIS is centered on the origin in the yz plane, and the geometric center of the RIS is aligned with the origin of the coordinate system. Let N be the number of regularly arranged elements in the rows and columns of the RIS array, and let N be an odd number. The size of each cell along the y-axis and z-axis is d. Let E n，m represents the RIS element at the nth row and mth column. The coordinates of the RIS element are in

[0042] E n,m The reflection coefficient is Here β n,m and α n,m Respectively represent the amplitude and phase shift of the RIS element; respectively, θ b , θ u and To represent the elevation and azimuth from the RIS center to the BS, and the elevation and azimuth from the RIS center to the user; and Indicates E n,m Elevation and azimuth to BS, E n,m The elevation and azimuth to User; respectively and Indicates BS to cell E n,m Elevation and azimuth, User to cell E n,m The elevation and azimuth angles of the BS are as follows: the distance from BS to RIS is d1, and the distance from RIS to User is d2;

[0043] Then, the coordinates of BS are The coordinates of User are Therefore, the distance between the BS and the RIS unit, and the distance between the User and the RIS unit can be expressed as and In a multi-antenna base station system, the distance between the base station and the RIS unit is The distance between the user and the RIS unit is The coordinates of BS are The symbols b and N b They represent the BS antenna spacing and the number of BS antennas respectively.

[0044] In the second deployment scenario implemented, the BS is centered on the origin in the yz plane, and the geometric center of the BS is aligned with the origin of the coordinate system. Let N and N r =N 2 represents the number of regularly arranged elements in the rows and columns of the RIS array and the total number of RIS units. Let E n,m represents the RIS element at the nth row and mth column. The coordinates of the RIS element are Where m∈[1,N], n∈[1,N], and D∈[0,100] represent the distance that the RIS moves from the vicinity of the BS to the vicinity of the User along a specific straight line; E n,m The reflection coefficient is Here β n,m and α n,m are the amplitude and phase shift of the RIS unit respectively. The fixed distance from BS to User is 100m, and the coordinates of BS are r B =(0,0,0), the coordinate of User is r u =(0,100,0).

[0045] Therefore, the distance between the BS and the RIS unit, and the distance between the User and the RIS unit can be expressed as and The distance between the RIS center and the BS is d b , the distance between the RIS center and the User is d u , the distance between the RIS center and the RIS element is In a multi-antenna base station system, the symbol N is used b to represent the number of BS antennas; the coordinates of BS are b represents the spacing between BS antennas, where n b ∈[1,N b ]; In addition, the distance between BS and RIS unit is The distance between User and RIS unit is The distance between the RIS center and the BS is The distance between the RIS center and the User is d u,c , the distance between the RIS center and the RIS unit is

[0046] The following is a consideration of the RIS-assisted system in two different deployment scenarios in conjunction with specific embodiments. Specifically, a channel model is first proposed, and then the achievable capacity is described.

[0047] A. Performance of the first deployment scenario

[0048] 1) Near field Assume that f1 is a millimeter wave band. When f = f1, the BS and the User are located in the near field, and both the BS-RIS link and the RIS-User link use the spherical wave model for channel modeling. n,m The path loss between User and E n,m The path loss between can be expressed as

[0049]

[0050] Where I is the vertical unit vector, G t and G r are the antenna gains of BS and User respectively. and Represent the normalized power radiation patterns of BS and User antennas respectively.

[0051] The total channel coefficient matrix of the RIS-assisted communication system is h = (h RIS-User ) T Θh BS-RIS .

[0052] In this application, the weight coefficient matrix of the MRC algorithm is assumed to be The signal-to-noise ratio of the RIS-assisted system in the near field can be expressed as

[0053]

[0054] The achievable capacity of a single-antenna BS near-field system is C ns =log2(1+γ). Considering the optimal phase shift of RIS, the amplitude and phase of RIS array element are set to β in this application. 1,1 =β 1,2 =β n,m =1 and A single antenna BS can achieve a capacity of

[0055]

[0056] 2) Near field RIS-assisted system based on BS with multiple antennas in local area. n,m The path loss between User and E n,mThe path loss between can be expressed as

[0057]

[0058] Similarly, in this application, the weight coefficient matrix of the MRC algorithm is set to The signal-to-noise ratio can be expressed as

[0059]

[0060] The achievable capacity of a multi-antenna BS near-field system is C nm =log2(1+γ). Considering the optimal phase shift of RIS, the amplitude and phase of RIS array element are set to β in this application. 1,1 =β 1,2 =β n,m =1 and The achievable near-field capacity of a multi-antenna BS is expressed as

[0061]

[0062] 3) Far field Assume that f2 is a lower frequency band. When f = f2, the BS and the User are in the far field. The BS-RIS link and the RIS-User link both use the plane wave model for channel modeling. Similarly, in order to obtain the maximum value of each term, the weight coefficient matrix of the MRC algorithm is set in this application as The amplitude and phase of the RIS array element are β 1,1 =β 1,2 =β n,m =1 and α n,m =2πf2(d1+d2) / c. The capacity that a single-antenna BS can achieve in the far field is

[0063]

[0064] 4) Far field Similarly, in order to maximize each item, the weight coefficient matrix of the MRC algorithm is set as follows in this application: The amplitude and phase of the RIS array elements are set to the optimal value. The multi-antenna BS can achieve a capacity of

[0065]

[0066] B. Performance of the Second Deployment Scenario

[0067] 1) Near field Assume that f1 is a millimeter wave band. When f = f1, the BS and the User are both in the near field, and the BS-RIS link and the RIS-User link both use the spherical wave model for channel modeling.n,m Between BS and E n,m The path loss between can be expressed as (3). and It is expressed as:

[0068]

[0069] The total channel coefficient matrix of the RIS-assisted communication system is h = (h RIS-User ) T Θ hBS-RIS .

[0070] Similarly, in this application, the weight coefficient matrix of the MRC algorithm is set to The signal-to-noise ratio can be expressed as (4), and the achievable capacity of the near-field system is C ns =log2(1+γ). Similarly, the amplitude and phase of the RIS array element are set to β 1,1 =β 1,2 =β n,m =1 and The achievable capacity of a single antenna BS near field is

[0071]

[0072] 2) Near field Assume that f1 is a millimeter wave band. When f = f1, the BS and User are both in the near field, and the BS-RIS link and the RIS-User link both use the spherical wave model for channel modeling. n,m The path loss between can be expressed as (6). and Expressed as

[0073]

[0074] The total channel coefficient matrix of the RIS-assisted communication system is h = (h RIS-User ) T Θh BS-RIS .

[0075] Similarly, in this application, the weight coefficient matrix of the MRC algorithm is assumed to be The signal-to-noise ratio of the RIS-assisted BS-RIS-User communication link in the near field can be expressed as (7), and the achievable capacity of the near-field system is C nm =log2(1+γ). Similarly, the amplitude and phase of the RIS array element are set to β 1,1 =β 1,2 =β n,m =1 and The achievable capacity of a near-field multi-antenna BS is

[0076]

[0077] 3) Far field According to the previous near-field analysis, the capacity that a single-antenna BS can achieve in the far field is

[0078]

[0079] in and

[0080] 4) Far field Similarly, based on the analysis of the near field, the multi-antenna BS can achieve a capacity of

[0081]

[0082] The theoretical results are verified by simulation in this application. The capacity performance of the RIS-assisted system with single-antenna and multi-antenna BS is compared through simulation results in two different scenarios: lower frequency band and millimeter wave. If not specified otherwise, the simulation parameters are set as follows. The frequencies f1 and f2 are set to 30 GHz and 3 GHz respectively. Other parameters are set to P t =20dBm.

[0083] Figure 3 Results showing the achievable capacity for the first deployment scenario. Figure 4 Results showing the achievable capacity for the second deployment scenario. Figure 3 (a) and Figure 4 (a) shows the functional relationship between the achievable capacity and the distance between the BS or the user. It can be seen that as the distance increases, the achievable capacity decreases significantly. Figure 3 (b) and Figure 4 (b) shows the relationship between the achievable capacity and the number of RIS elements. As the number of RIS elements increases, the achievable capacity also increases. Figure 3 (c) and Figure 4 (c) The achievable capacity is examined in relation to the RIS unit size. As the RIS element size increases, the achievable capacity also increases.

[0084] At the same time, from Figure 3 and Figure 4 It can be seen that for a near-field multi-antenna BS, deploying RIS near the user can achieve higher capacity than deploying it near the BS. However, for far-field multi-antenna BSs and near-field or far-field single-antenna BSs, deploying RIS near the user or BS can achieve comparable capacity. The reasons are as follows: Figure 2As shown in Figure 1, the propagation of near-field signals follows the spherical wave model, and the phase and amplitude of the signal vary with the distance and angle. When the RIS is close to the BS, the angle difference between the base station and the RIS results in relatively poor signal propagation characteristics. When the RIS is close to the user, the angle between the base station and the RIS tends to be vertical, the signal propagation characteristics are more uniform, and the angle from the RIS to the user is relatively favorable.

[0085] Therefore, the RIS close to the user can more effectively reflect the signal from the BS to the user, thereby improving the performance gain. In the far field, the propagation of the signal follows the plane wave mode, and the phase and amplitude of the signal change less than in the near field. Therefore, in the near field, the performance gain of the signal can be improved by adjusting the deployment of the RIS, while in the far field, due to the plane wave characteristics of signal propagation, the deployment of the RIS has a relatively small impact on the signal gain.

[0086] In summary, two different deployment schemes of RIS-assisted wireless systems under near-field and far-field path loss channels are studied in this application. Simulation results show that the near-field close to single antenna deployment strategy achieves higher capacity than the close to multiple antenna deployment strategy. For the far field, simulation results show that deploying RIS near the User or BS can achieve equivalent capacity regardless of the transmission power or the number of deployed RIS units. These results enhance the flexibility of deploying RIS and provide valuable insights for the design of practical RIS-assisted communication systems.

Claims

1. A RIS-assisted wireless communication system, characterized in that: It includes near-field or far-field RIS-assisted systems, where the BS is configured with a single antenna and the BS is configured with multiple antennas.

2. A RIS-assisted wireless communication system according to claim 1, characterized in that: The direct link between BS and User is blocked, and the signal received by the user is expressed as in m=1,…,N and n=1,…,N are RIS reflection matrices, h RIS-User It is the channel from RIS to User. BS-RIS It is the channel from BS to RIS. t is the transmitting power, s is the transmitting signal, and n is the additive white Gaussian noise.

3. A RIS-assisted wireless communication system according to claim 2, characterized in that: The normalized power radiation pattern is shown below in and Represent the normalized power radiation pattern of BS Normalized power radiation diagram of the user When ∈ = 1, it represents the normalized power radiation pattern of the RIS cell 4. A RIS-assisted wireless communication system according to claim 3, characterized in that: When the RIS is centered on the origin in the yz plane, the geometric center of the RIS is aligned with the origin of the coordinate system; Let N be the number of regularly arranged elements in the rows and columns of the RIS array, and let N be an odd number, and let the size of each cell along the y-axis and z-axis be d; Assume E n,m represents the RIS element at the nth row and mth column. The coordinates of the RIS element are in E n,m The reflection coefficient is Here β n,m and α n,m represent the amplitude and phase shift of the RIS element respectively; Let θ b , θ u and to represent the elevation angle and azimuth angle from the RIS center to the BS, and the elevation angle and azimuth angle from the RIS center to the User, respectively; make and Respectively represent E n,m Elevation and azimuth to BS, E n,m Elevation and azimuth to User; make and Respectively represent BS to cell E n,m Elevation and azimuth, User to cell E n,m The elevation and azimuth angles of the BS are as follows: the distance from BS to RIS is d1, and the distance from RIS to User is d2; Then, the coordinates of BS are The coordinates of User are Therefore, BS and element E n,m The distance between User and element E n,m The distance between them can be expressed as In a multi-antenna base station system, the distance between the base station and the RIS unit is The distance between the user and the RIS unit is The coordinates of BS are The symbols b and N b They represent the BS antenna spacing and the number of BS antennas respectively.

5. A RIS-assisted wireless communication system according to claim 3, characterized in that: When BS is centered at the origin on the yz plane, the geometric center of BS is aligned with the origin of the coordinate system; let N and N r =N 2 It represents the number of regularly arranged elements in the rows and columns of the RIS array and the total number of RIS units; Assume E n,m represents the RIS element at the nth row and mth column. The coordinates of the RIS element are Where m∈[1,N], n∈[1,N], and D∈[0,100] represent the distance that the RIS moves from the vicinity of the BS to the vicinity of the User along a specific straight line; E n,m The reflection coefficient is Here β n,m and α n,m Respectively represent the amplitude and phase of the RIS element; Assume that the fixed distance from BS to User is 100m and the coordinates of BS are r B =(0,0,0), the coordinate of User is r u =(0,100,0); therefore, the distance between the BS and the RIS unit, and the distance between the User and the RIS unit can be expressed as and The distance between the RIS center and the BS is d b , the distance between the RIS center and the User is d u , the distance between the RIS center and the RIS element is In a multi-antenna base station system, the symbol N is used b To represent the number of BS antennas; The coordinates of BS are b represents the spacing between BS antennas, where n b ∈[1,N b ]; In addition, the distance between BS and element is The distance between User and element is The distance between the RIS center and the BS is The distance between the RIS center and the User is d u,c , the distance between the RIS center and the RIS element is

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