Sustainable Wireless Networks via Reconfigurable Intelligent Surfaces (RISs): Overview of the ETSI ISG RIS

TL;DR

The paper surveys the ETSI ISG RIS program, outlining the problem of standardizing and deploying Reconfigurable Intelligent Surfaces for 6G networks. It synthesizes deployment scenarios, RIS modeling frameworks, reference architectures, and ongoing standardization work, including near-field considerations and signaling implications. Key contributions include defining RIS-enabled channel models, AoI/BoI metrics, and practical architecture options, as well as detailing four ongoing Working Items (hardware, diversity/multiplexing, MF-RIS, and near-field modeling). The work highlights the potential of RIS to enhance energy efficiency and coverage, and it discusses how standardization bodies (ITU, 3GPP) and field trials are shaping the integration of RIS into future networks.

Abstract

Reconfigurable Intelligent Surfaces (RISs) are a novel form of ultra-low power devices that are capable to increase the communication data rates as well as the cell coverage in a cost- and energy-efficient way. This is attributed to their programmable operation that enables them to dynamically manipulate the wireless propagation environment, a feature that has lately inspired numerous research investigations and applications. To pave the way to the formal standardization of RISs, the European Telecommunications Standards Institute (ETSI) launched the Industry Specification Group (ISG) on the RIS technology in September 2021. This article provides a comprehensive overview of the status of the work conducted by the ETSI ISG RIS, covering typical deployment scenarios of reconfigurable metasurfaces, use cases and operating applications, requirements, emerging hardware architectures and operating modes, as well as the latest insights regarding future directions of RISs and the resulting smart wireless environments.

Figures (5)

• Figure 1: Illustration of the promising key use cases of RISs as identified in GR $001$GR_001.
• Figure 2: The Area of Influence (AoI) of an RIS is defined as the geographical area for which a quality-of-service threshold is satisfied with the aid of an RIS, i.e., ${\rm AoI} \triangleq \{ \mathcal{S}|m(\mathcal{S})\geq q_{\rm th} \}$ with $m(\cdot)$ denoting the desired performance metric, $\mathcal{S}$ is the geographical space, and $q_{\rm th}$ is the performance threshold ABoI_EURASIP. The AoI depends on the physical characteristics of the RIS, and given those characteristics, it can be dynamically adjusted.
• Figure 3: Let $\Gamma(f,x)$ denote the reflection coefficient of an RIS unit cell, given its working configuration $x$ and the operating frequency $f$, applied to an impinging wave $s(f)$. To characterize the Bandwidth of Influence (BoI) of an RIS consisting of multiple identical unit cells around a targeted central frequency $f_0$, the maximum contrast among all different states $x$ of a single unit cell, defined as: $C(f)\triangleq \max_{\forall x,x\neq x^{'}} |\Gamma(f,x)-\Gamma(f,x^{'}) |$, has been lately used ABoI_EURASIP, as shown the right graph. The BoI is defined as the set of frequencies where the maximum contrast is above a threshold value $C_{\rm min}$. If the maximum difference between any two different states tends to zero, the RIS offers no reconfigurability and acts as a dummy reflector with fixed frequency characteristics depending on the material used and the angle of incidence.
• Figure 4: A reference deployment architecture for RIS-assisted cellular networks. The RIS extends the coverage area of the BS when optimized to focus wireless propagation in the intended UE position.
• Figure 5: A timing advance example in a wireless network comprising one BS and two UEs, with all profiting from the deployment of a single RIS. The timing information can be used from the system to distinguish the RIS utilization between the two UEs.