STAR-RISs-- a Correlated T&R Phase-Shift Model and Practical Phase-Shift Configuration Strategies

Date: 2024.03.12 16:26
Author: Joffrey LC

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STAR-RISs: A Correlated T&R Phase-Shift Model and Practical Phase-Shift Configuration Strategies. Jiaqi Xu et.al. IEEE Journal of Selected Topics in Signal Processing, August 2022 (pdf) (Citations 37)

Quick Overview

• To realize a full-space smart radio environment, each STAR-RIS element has to dynamically impose two distinct tunable phase-shift values, one for the transmitted signal and one for the reflected signal.
• The phase shift can/cant be adjusted independently.

Phase shift model

Correlated adjustment

Independent adjustment

According to the Maxwell’s Equations, the phase shift of both transmitting and reflecting can be adjusted independently if the if the impedances $Z_e$and $Z_m$​ in (1) and (2) can take on arbitrary complex values, which means that the STAR-RIS required a active or lossy elements.

OMA v.s. NOMA

OMA

选择FDMA，且两个用户占用正交的、相同带宽的频带。则其可达速率为：

有意思的是，带宽变为1/2，因为两个用户各占一半，然后噪声功率也下降，因为用户带宽各占一半

NOMA

一个用户采用SIC（连续干扰消除）来消除干扰。为了成功实施SIC，给强信道弱功率，弱信道强功率

• 基于CSI的用户排序
• CSI强的用户先解码CSI弱的用户的信号
• 然后CSI强的通过SIC减去用户弱的，得到自己的信号
• 弱信道将强信道（弱功率）当做干扰

例如，R强，T弱，则有：

• 先R解T:

• 再R解R：

• 再T解T：

Three available optimization methods

Primary-Secondary Phase-Shift Configuration (PS-PSC) Strategy

step1: 先只考虑主要用户，而忽略其中的约束

step2: 再考虑次要用户，次要用户相移为主要用户的v调整（次要用户的相移为主要用户相移的$+\pi/2$ or $+3\pi/2$）

Diversity Preserving Phase-Shift Configuration (DP-PSC) Stratege

先计算二者的最优：

然后通过查表进行：

记误差：

$$\delta_m^\chi=\left|\phi_m^{\chi^*}-\Delta \phi_m^\chi\right|$$

有:

$$\delta_m^\chi\leq \pi/4$$

T/R-Group Phase-Shift Configuration (TR-PSC) Strategy

分组，分为透射和反射，分别用于不同用户