Intelligent Omni-Surfaces: Simultaneous Refraction and Reflection for Full-Dimensional Wireless Communications

Abstract

The development of metasurfaces has unlocked various use cases in wireless communication networks to improve performance by manipulating the propagation environment. Intelligent omni-surface (IOS), an innovative technique in this category, is proposed for coverage extension. In contrast to the widely studied reflective metasurfaces, i.e., intelligent reflecting surfaces (IRSs), which can only serve receivers located on the same side of the transmitter, the IOS can achieve full-dimensional wireless communications by enabling the simultaneous reflection and refraction of the surface, and thus users on both sides can be served. In this paper, we provide a comprehensive overview of the state-of-the-art in IOS from the perspective of wireless communications, with the emphasis on their design principles, channel modeling, beamforming design, experimental implementation and measurements, as well as possible applications in future cellular networks. We first describe the basic concepts of metasurfaces, and introduce the corresponding design principles for different types of metasurfaces. Moreover, we elaborate on the reflective-refractive model for each IOS element and the channel model for IOS-aided wireless communication systems. Furthermore, we show how to achieve full-dimensional wireless communications with the IOS for three different scenarios.In particular, we present the implementation of an IOS-aided wireless communication prototype and report its experimental measurement results. Finally, we outline some potential future directions and challenges in this area.

Rate Splitting in MIMO RIS-Assisted Systems With Hardware Impairments and Improper Signaling

“…To address this issue, another technology for intelligent metasurfaces is proposed that can allow transmission and reflection at the same time, which in known as simultaneously transmit and reflect (STAR) RIS [25]. Note that STAR-RIS is also known as intelligent omni-surfaces since it can provide an omnidirectional coverage [25], [26]. The superiority of STAR-RIS over regular RIS has been investigated in [16], [27]- [31] by taking into account different scenarios.…”

Reconfigurable Intelligent Surfaces 2.0: Beyond Diagonal Phase Shift Matrices

“…2) Hybrid Mode: In this mode, signals impinging on one side of the RIS can be partially reflected toward the same side and partially transmitted toward the opposite side, yielding a whole space coverage. The RIS with hybrid mode is also known as simultaneous transmitting and reflecting RIS (STAR-RIS) or intelligent omni-surface (IOS) [8]. To support the hybrid mode, each two antennas with uni-directional radiation pattern are back to back placed to form one cell, and are connected to a 2-port fully-connected reconfigurable impedance network [9] as shown in Fig.…”

A Dynamic Grouping Strategy for Beyond Diagonal Reconfigurable Intelligent Surfaces With Hybrid Transmitting and Reflecting Mode

“…Existing BD-RIS works focus on modeling [3], beamforming design [4], [5], and mode/architecture design [6]- [10]. BD-RIS was first modeled in [3] using the scattering parameters, where single-, group-, and fully-connected architectures are introduced based on the circuit topology of the network of tunable RIS impedances.…”

“…The corresponding beamforming designs are studied in [4] and [5]. Inspired by the intelligent omni surface with enlarged coverage compared to conventional RIS [6] and thanks to the structural flexibility introduced by the more general scattering matrices of BD-RIS, BD-RIS with hybrid [7] and multi-sector modes [8] are proposed, which achieve full-space coverage with enhanced performance. On the other hand, to explore the best performance-complexity trade-off provided by BD-RIS, other special architectures, Manuscript received; H. Li and M. Nerini are with the Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, U.K. (email:{c.li21, m.nerini20}@imperial.ac.uk).…”