STAR-RISs--Simultaneous Transmitting and Reflecting Reconfigurable Intelligent Surfaces

Date: 2024.03.18 10:50
Author: Joffrey LC

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STAR-RISs: Simultaneous Transmitting and Reflecting Reconfigurable Intelligent Surfaces. Jiaqi Xu et.al. IEEE Communications Letters, September 2021 (pdf) (Citations 171)

Quick Overview

• Full diversity order can be achieved on both sides.

• Far field and near field model

• ==The boundary between the near-field and the far-field is $2L_a^2/\lambda$，where$L_a$ is the largest dimension of the RIS aperture.==

Far field

• 反射和透射的RIS相移可 independently adjusted
• 反射和透射有个功率分配，因为是passive，所以应该满足能量守恒

Near field

根据Fresnel-Kirchhoff diffraction formula，应该建模为$M$个单元的求和：

$$g^\chi=\frac{1}{j \lambda} \iint_{(\Sigma)} U^\chi(Q) F\left(\theta^\chi\right) \frac{e^{2 j \pi d_m^\chi / \lambda}}{d^\chi} d \Sigma$$

$$g^\chi=\frac{A_e}{j \lambda} \sum_m \Phi_m^\chi h_m F\left(\theta_m^\chi\right) \frac{e^{2 j \pi d_m^\chi / \lambda}}{d_m^\chi}$$

$$\left|g^\chi\right|=\frac{A_e}{\lambda}\left|\sum_m \Phi_m^\chi h_m\left(1+\cos \theta_m^\chi\right) \frac{e^{2 j \pi d_m^\chi / \lambda}}{2 d_m^\chi}\right| .$$

Diversity Analysis

All elements of STAR-RIS share the same power ratio, i.e., $\beta^T_m=\beta^T,\beta^R_m=\beta^R,\forall m\in M$.

In fact, we can include the power ratios constrains of each element for further improving the performance.

定义diversity order：

红色是考虑leaning factor/rate，而蓝色是没有使用leaning rate$F(\theta)=1$的