A Survey on STAR-RIS: Use Cases, Recent Advances, and Future Research Challenges

Abstract

The recent development of metasurfaces, which may enable several use cases by modifying the propagation environment, is anticipated to have a substantial effect on the performance of 6G wireless communications. Metasurface elements can produce essentially passive sub-wavelength scattering to enable a smart radio environment. STAR-RIS, which refers to reconfigurable intelligent surfaces (RIS) that can transmit and reflect concurrently (STAR), is gaining popularity. In contrast to the widely studied RIS, which can only reflect the wireless signal and serve users on the same side as the transmitter, the STAR-RIS can both reflect and refract (transmit), enabling 360-degree wireless coverage, thus serving users on both sides of the transmitter. This paper presents a comprehensive review of the STAR-RIS, with a focus on the most recent schemes for diverse use cases in 6G networks, resource allocation, and performance evaluation. We begin by laying the foundation for RIS (passive, active, STAR-RIS), and then discuss the STAR-RIS protocols, advantages, and applications. In addition, we categorize the approaches within the domain of use scenarios, which includes increasing coverage, enhancing physical layer security (PLS), maximizing sum rate, improving energy efficiency (EE), and reducing interference. Next, we will discuss the various strategies for resource allocation and measures for performance evaluation. We aimed to elaborate, compare, and evaluate the literature in terms of setup, channel characteristics, methodology, and objectives. In conclusion, we examine the open research problems and potential future prospects in this field.

From 5G-Advanced to 6G in 2030: New Services, 3GPP Advances, and Enabling Technologies

“…RIS improves communication links and extends the coverage of wireless networks. Current RIS elements can passively modify their impedance by external stimuli, but new developments can also refract electromagnetic waves effectively, implementing the Simultaneously Transmitting And Reflecting RIS (STAR-RIS) [136].…”

Next-Hop Relay Selection for Ad Hoc Network-Assisted Train-to-Train Communications in the CBTC System

“…After selecting an action a t , a new state s t+1 is obtained, and the reward r t corresponding to this action is also computed. The goal of the agent is to find a policy π(s t , a t ), which maximizes the expected discounted cumulative reward E K−1 ∑ i=t γ i−t r i+1 [9]. Therefore, the action-state value function is used to calculate the expected discounted cumulative reward of each relay selection policy and then select the policy π with the largest reward.…”

“…In addition, the deployment of the terrestrial core network and base station are complex, which makes network construction and maintenance cost high. Therefore, new technologies such as reconfigurable intelligent surfaces [8,9] and wireless ad hoc networks have been proposed to improve T2T communication.…”

STAR-RIS-aided UAV NOMA Mobile Edge Computing Network with RF Energy Harvesting

“…By adjusting the configuration of these reflecting elements, RIS can control the reflection of signals, thereby enhancing wireless communication performance. Thus, STAR-RIS holds great potential to revolutionize wireless communication systems by enabling more efficient and flexible utilization of the wireless spectrum, improving coverage, and enhancing communication performance [8].…”