Simultaneously Transmitting and Reflecting Surfaces for Ubiquitous Next Generation Multiple Access in 6G and Beyond

TL;DR

This survey presents STARS as a pivotal technology for realizing ubiquitous NGMA by enabling simultaneous transmission and reflection to create a full-space smart radio environment. It provides a rigorous treatment of the foundational physics, operating protocols, and category taxonomy, followed by performance analyses across rate, outage, and coverage metrics. The paper then surveys full-space beamforming designs (power-efficient, capacity-maximizing, and intelligent ML-based methods) and explores advanced STARS applications in UAVs, PLS, SWIPT, THz communications, and CoMP, along with the interplay with ISAC, MEC, NOMA, and NFC. By detailing practical prototypes, analytical results, and optimization strategies, the work highlights how STARS can overcome half-space limitations and enable flexible, high-capacity NGMA deployments with energy efficiency and security considerations. Overall, STARS emerge as a versatile, scalable platform for next-generation wireless networks, capable of integrating sensing, computation, and security with communication across diverse platforms and bands.

Abstract

The ultimate goal of next generation multiple access (NGMA) is to support massive terminals and facilitate multiple functionalities over the limited radio resources of wireless networks in the most efficient manner possible. However, the random and uncontrollable wireless radio environment is a major obstacle to realizing this NGMA vision. Given the prominent feature of achieving 360° smart radio environment, simultaneously transmitting and reflecting surfaces (STARS) are emerging as one key enabling technology among the family of reconfigurable intelligent surfaces for NGMA. This paper provides a comprehensive overview of the recent research progress of STARS, focusing on fundamentals, performance analysis, and full-space beamforming design, as well as promising employments of STARS in NGMA. In particular, we first introduce the basics of STARS by elaborating on the foundational principles and operating protocols as well as discussing different STARS categories and prototypes. Moreover, we systematically survey the existing performance analysis and beamforming design for STARS-aided wireless communications in terms of diverse objectives and different mathematical approaches. Given the superiority of STARS, we further discuss advanced STARS applications as well as the attractive interplay between STARS and other emerging techniques to motivate future works for realizing efficient NGMA.

Figures (18)

• Figure 1: Illustration of the concept of STARS and the facilitated 360° smart radio environment.
• Figure 2: Organization of the survey.
• Figure 3: Conceptual illustration of the equivalent circuit of STARS element.
• Figure 4: Three protocols for employing STARS.
• Figure 5: Signal models for STARS under dual-sided signal incidence.