Implementation method of star-ris assisted dual micro base station communication

Abstract

The application discloses an implementation method of STAR-RIS assisted dual micro base station communication, which realizes the bidirectional communication between two micro base stations and the simultaneous communication between the two micro base stations and respective destination nodes. On the basis of meeting the minimum communication rate of the two micro base stations, the transmission phase shift matrix and amplitude coefficient of the STAR-RIS are optimized to maximize the minimum reachable rate of the two destination nodes. The simulation part analyzes the reachable rate of the system and the influence of the capability of the self-interference cancellation technology on the system performance. The advantage of the application is that the advantages of the STAR-RIS can be fully utilized, and the signal coverage range can be significantly improved and better network performance can be realized in the indoor scene of 5G / 6G.

Description

Technical Field

[0001] This invention relates to a method for implementing STAR-RIS-assisted dual micro base station communication, belonging to the field of communication technology. Background Technology

[0002] Currently, mobile communication is developing rapidly, with the fifth-generation mobile communication system (5G) entering the commercial stage, and research on the sixth-generation mobile communication system (6G) has also begun. The high-frequency bands used in 5G / 6G have advantages such as wide channel bandwidth, fast transmission speed, and low latency. However, high-frequency bands also have limitations: weak obstacle avoidance and penetration capabilities, and susceptibility to interference over long distances. Therefore, due to building obstruction, the signal from outdoor macro base stations attenuates significantly indoors, creating indoor 5G signal blind spots. Micro base stations, with their low power consumption and miniaturization, can be deployed effectively in areas inaccessible to macro base stations, providing deep coverage in densely populated areas and effectively solving the problem of indoor 5G / 6G signal blind spots. In practical applications, the combined use of micro base stations and macro base stations can achieve wider coverage and better network performance.

[0003] Meanwhile, STAR-RIS, with its reflection and transmission capabilities, offers a new approach to 5G / 6G deployment. STAR-RIS is composed of numerous low-cost, passive reflection and transmission elements. Each unit can independently reflect and transmit incident signals and adjust their amplitude and phase, enabling the reconstruction of the communication channel. Compared to traditional RIS which only provides half-plane coverage, STAR-RIS can utilize its transmission and reflection functions to provide services to users on both sides of the RIS, achieving 360° full-space coverage. Therefore, STAR-RIS can support and provide greater flexibility in signal transmission. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings and deficiencies of the existing technology by proposing a STAR-RIS-assisted dual micro base station communication method. In this method, both micro base stations operate in full-duplex mode, enabling them to exchange information while simultaneously sending information to their respective terminals, thereby improving system capacity. Furthermore, this invention provides a fast, reliable, and low-complexity transmission method.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for implementing STAR-RIS-assisted dual micro base station communication, which specifically includes the following steps:

[0006] Step 1: Assume that due to long distances and obstructions, there is no direct communication channel between the micro base stations (S1, S2) and the terminal nodes (D1, D2), and they can only communicate via STAR-RIS. S1 sends superimposed signal s1 to S2 and D1, while S2 simultaneously sends superimposed signal s2 to S1 and D2. For S1, S2 and D1 are a pair of NOMA users it serves, and for S2, S1 and D2 are a pair of NOMA users it serves.

[0007] Step 2: The signal from S1 is partially reflected by STAR-RIS to S2 and partially transmitted to D1. Simultaneously, the signal from S2 is also partially reflected by STAR-RIS to S1 and partially transmitted to D2, thus achieving bidirectional communication between S1 and S2, as well as simultaneous communication between S1 and D1, and between S2 and D2. Assuming complete knowledge of the channel state information, the reflection phase shift matrix of STAR-RIS can be determined based on the phase shift matrices of the S1-STAR-RIS link (H1) and the STAR-RIS-S2 link (H2). Considering far-field communication, H1 and H2 can be considered reciprocal channels, so the forward and backward channels between S1 and S2 are identical. Therefore, the determined reflection phase shift matrix aligns H1 and H2, achieving the maximum signal-to-noise ratio for bidirectional communication between S1 and S2. The transmission phase shift matrix of STAR-RIS is used to simultaneously assist communication between S1 and D1, and between S2 and D2, and is determined by maximizing the minimum rate between D1 and D2. These functions are made possible by the fact that the STAR-RIS reflection phase shift matrix and transmission phase shift matrix can be adjusted independently.

[0008] Step 3: S1, S2, D1, and D2 decode their respective signals. S1 and D2 receive the superimposed signal from S2. Assuming S1's channel conditions are better than D2's, and it is a strong user in the NOMA user pair allocated less power, according to the basic principles of NOMA, S1 first decodes D2's information and uses SiC to subtract it from the received signal before decoding its own information. D2, the weak user allocated more power, directly decodes its own information, treating the received information from S1, the interference signal from S2, and the additive Gaussian noise as interference noise. Similarly, S2 and D1 receive the superimposed signal from S1. Assuming S2 is a strong user and D1 is a weak user, S2 needs to use SiC to decode its own information, while D2 treats the received information from S2, the interference signal from S1, and the additive Gaussian noise as interference noise and directly decodes its own information.

[0009] Beneficial effects:

[0010] 1. The present invention provides a reconfigurable smart surface capable of simultaneous transmission and reflection, enabling dual micro base station communication and significantly improving signal coverage and network performance.

[0011] 2. This invention enables bidirectional communication between two micro base stations and simultaneous communication between them and their respective destination nodes. While satisfying the minimum communication rate of the two micro base stations, the transmission phase shift matrix and amplitude coefficient of STAR-RIS are optimized with the goal of maximizing the achievable rate of the two destination nodes.

[0012] 3. This invention can fully utilize the advantages of STAR-RIS, and can significantly improve signal coverage and achieve better network performance in 5G / 6G indoor scenarios. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the system model of the STAR-RIS-based dual micro base station communication scheme of the present invention.

[0014] Figure 2 This is a graph showing the variation of the transmit signal-to-noise ratio with respect to the achievable speeds of the present invention, including S1, S2, D1, D2, and the system.

[0015] Figure 3 This is a graph showing the total achievable rate as a function of transmit signal-to-noise ratio for different numbers of STAR-RIS units in this invention.

[0016] Figure 4 This is a graph showing the achievable speed of the system of the present invention as a function of the self-interference elimination coefficient. Detailed Implementation

[0017] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes.

[0018] The system of this invention includes one STAR-RIS, two micro base stations, and two users. The system employs a NOMA scheme, simultaneously serving two NOMA user pairs. For S1, S2, and D1, it serves one pair of NOMA users; for S2, S1, and D2, it serves another pair of NOMA users. This enables bidirectional communication between S1 and S2, as well as simultaneous communication between S1 and D1, and between S2 and D2.

[0019] I. System Model

[0020] like Figure 1 As shown, the two full-duplex micro base stations S1 and S2 of this invention communicate bidirectionally via a STAR-RIS consisting of N elements and simultaneously communicate with their respective single-antenna target nodes D1 and D2. S1 and S2 are located on one side of the STAR-RIS, and D1 and D2 are located on the other side. It is assumed that there are no direct communication channels between S1 and S2, between S1 and D1, and between S2 and D2 due to obstacles.

[0021] Let H i =(h i,1 h i,2 ,L,h i,N ) T ∈? N×1 and G i =(g i,1 g i,2 ,L,g i,N ) T ∈? N×1 Let i ∈ {1,2}, representing the Rayleigh fading channels from Si to STAR-RIS and from STAR-RIS to Di, respectively. Assuming all elements on STAR-RIS have the same amplitude coefficient, the reflection and transmission factor matrices are:

[0022]

[0023] Among them, the amplitude satisfies And β t +β r =1; phase shift satisfies θ k,n ∈[0,2π), n∈N={1,2,LN}.

[0024] In a NOMA-assisted communication system, two micro base stations simultaneously transmit superimposed signals from two users. S1 transmits a superimposed signal containing information from S2 and D1. Simultaneously, S2 sends a superimposed signal containing information from S1 and D2. Where x1, x2, z1, and z2 are the information of S1, S2, D1, and D2 respectively, and α1, β1 and α2, β2 are two pairs of NOMA allocation coefficients, satisfying α1 + β1 = 1 and α2 + β2 = 1. Therefore, the received signals of S1 and S2 can be expressed as:

[0025]

[0026] in, C0 represents the path loss at a reference distance of 1 meter, d H1 and d H2 Let S1 and S2 represent the distances to STAR-RIS, respectively, and α be the path loss exponent; i ∈ {1, 2}, if i = 1 then P i S represents the emitter power of Si. i This represents the transmitted signal of Si; due to self-interference caused by Si operating in full-duplex mode, h I,i k represents the self-interference channel of Si. i Characterizing the ability of Si self-interference cancellation technology, k i =0 represents perfect self-interference cancellation, ki =1 indicates that no self-interference cancellation was performed; n Si The additive white Gaussian noise at Si has a power of σ.

[0027] The received signals at points D1 and D2 can be represented as:

[0028]

[0029] in, d Gi This represents the distance between Di and STAR-RIS; n Di This represents the additive white Gaussian noise at point Di, with a power of σ.

[0030] II. Signal-to-noise ratio

[0031] According to the NOMA decoding rules, strong users need to decode the information of weak users first, then use SIC technology to delete it, and finally decode their own information, while weak users directly decode their own information. Assuming S1 and S2 are strong users in the two pairs of NOMA users in this invention, and they are allocated smaller powers (β1 > α1 and β2 > α2), then their SINR for decoding weak user information is:

[0032]

[0033] After decoding the weak user information, the SINR is subtracted from the received signal using SIC, and then the SINR of the decoded information is:

[0034]

[0035] in Let R be the emission signal-to-noise ratio of Si. Therefore, the achievable rate of Si is R. Si =log2(1+γ) Si ).

[0036] Weak users D1 and D2 treat the strong user's information as interference and directly decode their own information with the following SINR:

[0037]

[0038] Therefore, the achievable rate of Di is R. Di =log2(1+γ) Di ).

[0039] III. Design of Reflection and Transmission Phase Shift Matrices

[0040] By designing a reflection phase shift matrix to facilitate bidirectional communication between S1 and S2, and taking advantage of the fact that the forward and backward channels of communication between S1 and S2 are the same, we can easily obtain the optimal reflection phase shift as follows:

[0041]

[0042] This allows for the maximum signal-to-noise ratio at both S1 and S2.

[0043] To facilitate communication between S1 and D1, and between S2 and D2, a transmission phase shift matrix is ​​designed. Since simultaneous communication between two pairs of users is required, the optimal transmission phase shift cannot be directly calculated. Therefore, the following optimization problem is designed to obtain the transmission phase shift matrix. While ensuring the minimum communication rate requirements of S1 and S2, the goal is to maximize the minimum communication rate of D1 and D2, optimizing the amplitude coefficient and transmission phase shift matrix of STAR-RIS. The specific optimization problem is as follows:

[0044]

[0045] Where R 1,min and R 2,min These represent the minimum communication rate requirements for S1 and S2, respectively. The first and second constraints guarantee the QoS requirements of the communication rates of S1 and S2, while the third constraint is the STAR-RIS amplitude constraint. Note that this invention uses a fixed power allocation coefficient. Optimizing the power allocation coefficient can further improve system performance, but this is beyond the scope of this invention.

[0046] The following presents a feasible scheme to optimize the above optimization equations, in order to verify the performance of the STAR-RIS system.

[0047] The optimal phase shift for bidirectional communication between S1 and S2 is given by equation (7). Combining equations (5) and (7), the SINR of Si can be further expressed as:

[0048]

[0049] By R Si =log2(1+γ) Si Constraint 1 can be represented as follows: Simplifying, we get β r ≥Δ1, where Similarly, constraint two can be expressed as It can be simplified to β r ≥Δ2, where

[0050] In summary, to meet the minimum communication rate requirements of S1 and S2, β r ≥max{Δ1,Δ2}. Simultaneously, the minimum communication rate between D1 and D2 must be maximized, according to constraint three β. r +β t =1, therefore we can get

[0051]

[0052] Therefore, problem (8) can be further transformed into finding a transmission phase shift matrix that maximizes the minimum communication rate of D1 and D2, i.e.

[0053]

[0054] IV. Performance Analysis

[0055] This invention also analyzes the achievable rate of the system and the impact of the self-interference cancellation technology on system performance.

[0056] Superimposed signal containing S2 and D1 information The achievable rate at S1 is: (Sent from S1 to S2 and D1)

[0057] C S1 =E(log2(1+γ) S1 (12)

[0058] The achievable rate at point D1 is:

[0059] C D1 =E(log2(1+γ) D1 (13)

[0060] Superimposed signal containing both S1 and D2 information The achievable rates from S2 to S1 and D2 are respectively:

[0061] C S2 =E(log2(1+γ) S2 (14)

[0062] and

[0063] C D2 =E(log2(1+γ) D2 (15)

[0064] Therefore, the overall achievable rate C of this communication system is the sum of the achievable rates of each link, i.e., C = C0. S1 +C D1 +C S2 +C D2 .

[0065] The simulation scenario settings for the STAR-RIS-based dual micro base station communication scheme in this embodiment of the invention are as follows: Figure 1 As shown, the simulation area consists of two micro base stations, two single-antenna users, and one STAR-RIS. It is assumed that all links in this communication system follow Rayleigh fading, and the distances from B1 and B2 to STAR-RIS are both 2m, i.e., d h1 =dh2 =2, the distances of D1 and D2 from STAR-RIS are 5m and 8m respectively, i.e., d G1 =5,d G2 =8,

[0066] The path loss index α = 2, and the path loss C0 at a reference distance of 1 meter = 0 dB.

[0067] Figure 2 This is a curve showing the achievable speed of the system of this invention, as well as the achievable speeds of S1, S2, D1, and D2, as a function of the transmit signal-to-noise ratio (SNR) of S1 or S2. The NOMA allocation coefficients are set to α1 = α2 = 0.2, β1 = β2 = 0.8, and the self-interference cancellation coefficients are set to k1 = k2 = 0.1. It is assumed that the transmit power at S1 and S2 is equal, i.e., P1 = P2, and the system transmit power P = P1 + P2. The number of units in the STAR-RIS is set to 6, and the minimum communication rates of S1 and S2 are R... 1,min =0.2 and R 2,min =0.1. For example... Figure 2 As shown, with the increase of the transmit signal-to-noise ratio of S1 or S2, the achievable rates of S1, S2, D1, and D2, as well as the system achievable rate, all increase. Meanwhile, when the transmit signal-to-noise ratio of S1 or S2 increases to a certain value, the achievable rates of S1, S2, D1, and D2, as well as the system achievable rate, tend to a constant value.

[0068] Figure 3 These are curves showing the achievable rate of the system of this invention as a function of the transmit signal-to-noise ratio (SNR) in S1 or S2 for different numbers of STAR-RIS cells. Besides the number of STAR-RIS cells, Figure 3 Simulation parameter settings and Figure 2 Consistent. By Figure 3 It can be seen that as the number of STAR-RIS cells increases in the low signal-to-noise ratio region, the achievable system speed increases significantly, while in the high signal-to-noise ratio region, the achievable system speed does not change significantly with the number of STAR-RIS cells.

[0069] Figure 4 This is a curve showing the achievable rate of the system as a function of the self-interference cancellation coefficient. In this simulation scenario, the number of STAR-RIS cells is set to 6. Observations show that when the transmit signal-to-noise ratios (SNRs) at both S1 and S2 are 20dB, 30dB, and 40dB, the achievable rate decreases as the self-interference cancellation coefficient increases. Furthermore, we find that the higher the SNR, the smaller the change in achievable rate with the self-interference cancellation coefficient. Also, the difference between the achievable rate at 30dB and 20dB is larger, while the difference at 40dB is smaller. This conclusion is consistent with... Figure 3 The results are consistent.

Claims

1. A method for implementing STAR-RIS-assisted dual micro base station communication, characterized in that, The method includes the following steps: Step 1: Due to long distances and obstacles, there is no direct communication channel between micro base stations S1 and S2 and terminal nodes D1 and D2. They can only communicate via STAR-RIS. S1 sends superimposed signals. S2 also sends a superimposed signal to both S2 and D1. For S1 and D2, S1, S2, and D1 are a pair of NOMA users served by S1, and S2, S1, and D2 are a pair of NOMA users served by S2. The two full-duplex micro base stations S1 and S2 communicate bidirectionally via a STAR-RIS consisting of N elements and simultaneously communicate with their respective single-antenna destination nodes D1 and D2. S1 and S2 are located on one side of the STAR-RIS, and D1 and D2 are located on the other side. It is assumed that there are no direct channels between S1 and S2, between S1 and D1, and between S2 and D2 due to obstructions. Specifically: make and , Let and represent the Rayleigh fading channels from Si to STAR-RIS and from STAR-RIS to Di, respectively. Assuming all elements on STAR-RIS have the same amplitude coefficient, the reflection and transmission factor matrices are: ， ，(1) Among them, the amplitude satisfies and Phase shift satisfies , , In a NOMA-assisted communication system, two micro base stations simultaneously transmit superimposed signals from two users. S1 sends a superimposed signal containing information from S2 and D1. Simultaneously, S2 sends a superimposed signal containing information from S1 and D2. ,in , , , Information for S1, S2, D1, and D2 respectively. , and , For two pairs of NOMA allocation coefficients, satisfying and Therefore, the received signals of S1 and S2 can be expressed as: ，(2) in, , This represents the path loss at a reference distance of 1 meter. and These represent the distances from S1 and S2 to STAR-RIS, respectively. The path loss index; ,like but , ; Represents the emitter power of Si. This represents the transmitted signal of Si; due to self-interference caused by Si operating in full-duplex mode, This represents the self-interference channel of Si. Characterizes the ability of Si self-interference cancellation technology. This represents the achievement of perfect self-interference elimination. This indicates that self-interference cancellation was not performed; The additive white Gaussian noise at Si has a power of ; The received signals at points D1 and D2 can be represented as: (3) in, , , This represents the distance between Di and STAR-RIS; , ; This represents the additive white Gaussian noise at point Di, with a power of ; Step 2: The signal from S1 is partially reflected by STAR-RIS to S2 and partially transmitted to D1. Simultaneously, the signal from S2 is also partially reflected by STAR-RIS to S1 and partially transmitted to D2. This achieves bidirectional communication between S1 and S2, as well as simultaneous communication between S1 and D1, and between S2 and D2. Assuming the channel state information is completely known, the reflection phase shift matrix of STAR-RIS can be determined based on the S1-STAR-RIS link. and STAR-RIS-S2 link The phase shift matrix is ​​determined, taking far-field communication into account. and It can be considered a reciprocal channel, so the forward and backward channels between S1 and S2 are the same. Therefore, the determined reflection phase shift matrix can make... and Alignment is achieved to obtain the maximum signal-to-noise ratio for bidirectional communication between S1 and S2. The STAR-RIS transmission phase shift matrix is ​​used to simultaneously assist communication between S1 and D1, and between S2 and D2, and is determined by maximizing the minimum rate between D1 and D2. Step 2 determines the optimization problem by maximizing the minimum rate in D1 and D2, specifically including: By designing a reflection phase shift matrix to facilitate bidirectional communication between S1 and S2, and taking advantage that the forward and backward channels of communication between S1 and S2 are the same, the optimal reflection phase shift is obtained as follows: ，(7) This allows for a maximized signal-to-noise ratio at both S1 and S2. To facilitate communication between S1 and D1, and between S2 and D2, a transmission phase shift matrix is ​​designed. Since simultaneous communication between two pairs of users is required, the optimal transmission phase shift cannot be directly calculated. Therefore, the following optimization problem is designed to obtain the transmission phase shift matrix. Under the premise of ensuring the minimum communication rate requirement between S1 and S2, the goal is to maximize the minimum communication rate between D1 and D2. The amplitude coefficient and transmission phase shift matrix of STAR-RIS are optimized. The specific optimization problem is as follows: ，(8) in and These represent the minimum communication rate requirements for S1 and S2, respectively. The first and second constraints guarantee the QoS requirements of the communication rates of S1 and S2, while the third constraint is the amplitude constraint of STAR-RIS. The optimal phase shift for bidirectional communication between S1 and S2 is given by equation (7). Combining equations (5) and (7), the SINR of Si can be further expressed as: ，(9) Depend on Constraint 1 can be represented as follows: , Simplification yields ,in , ; Similarly, constraint two can be expressed as It can be simplified to ,in , ; In order to meet the minimum communication rate requirements of S1 and S2, At the same time, it is also necessary to maximize the minimum communication rate between D1 and D2, according to constraint three. We can obtain: (10) Therefore, the optimization problem can be further transformed into finding a transmission phase shift matrix that maximizes the minimum communication rate of D1 and D2: (11) Step 3: S1, S2, D1, and D2 each decode their signals. S1 and D2 receive the superimposed signal from S2. Assuming that S1's channel conditions are better than D2's, and that S1 is a strong user in the NOMA user pair but is allocated less power, according to the basic principles of NOMA, S1 first decodes D2's information and uses SiC to subtract it from the received signal before decoding its own information. Meanwhile, D2, the weak user allocated more power, directly decodes its own information. At the same time, the received information from S1, the interference signal from S2, and the additive Gaussian noise are all treated as interference noise. S2 and D1 receive the superimposed signal from S1. Assuming that S2 is a strong user and D1 is a weak user, S2 needs to use SiC to decode its own information, while D2 receives the information from S2, the interference signal from S1, and the additive Gaussian noise as interference noise and directly decodes its own information. The decoding process in step 3 specifically includes: According to the NOMA decoding rules, strong users need to decode the information of weak users first, then use SIC technology to delete it, and finally decode their own information. Weak users, on the other hand, directly decode their own information. Assuming S1 and S2 are strong users in two pairs of NOMA users, they are allocated smaller power, i.e. and Then their SINR for decoding weak user information is: ，(4) After decoding the weak user information, the SINR is subtracted from the received signal using SIC, and then the SINR of the decoded information is: ，(5) in Let be the emission signal-to-noise ratio of Si, therefore the achievable rate of Si is . ; Weak users D1 and D2 treat the strong user's information as interference and directly decode their own information with the following SINR: (6) Therefore, the achievable rate of Di is .

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