ETSI Publishes Use-Cases for RIS, But Significant Development is Ahead

After the launch of the European Telecommunications Standards Institute’s (ETSI) Industry Specification Group on Reconfigurable Intelligent Surfaces (ISG RIS) in October 2021, the group started to develop global standardization for RIS technology. After a gap of one and a half years, ETSI announced the first report (ETSI GR RIS-001) on RIS identifying use cases, deployment scenarios, and requirements to accelerate its interoperability with current and upcoming wireless technologies. The report describes eleven interesting use cases for RIS deployment to enhance network Key Performance Indicators (KPIs) including coverage, capacity, security, positioning, sustainability, and support for sensing, wireless power transfer, and ambient backscattering capabilities. The major use cases identified covers topics related to coverage enhancement, spectral efficiency, beam management, physical layer security, localization accuracy, sensing capabilities, energy efficiency, and link management. Moreover, the report pointed out several deployment scenarios including operating environment (e.g., Indoor, Outdoor and Hybrid models), RIS deployment (e.g., Static, Nomadic), and RIS control plane (e.g., centralized/distributed management, autonomous, User Equipment (UE)-controlled RIS). Last, but not least, requirements were defined such as hardware cost, reconfigurability, interoperability, deployment, maintenance, and, most importantly, the regulatory requirements.

RIS claimed to provide performance enhancement for KPIs such as coverage, capacity, positioning, security, and energy efficiency, as well as extended support for current and future wireless technology applications. RIS does not require high-cost active components (e.g., power amplifiers) which makes it more inexpensive and energy efficient. RIS comes in different flavors of circuit designs ranging from meta-surfaces that are electronically tunable using integrated surfaces like PIN diodes, liquid crystals, and varactor diodes to support Active, Passive, and Hybrid RIS hardware designs. Another interesting feature of RIS is the mode of operation that can be adopted depending on the use-case, including reflection, refraction, absorption, backscattering, transmitting, and receiving modes. RIS can be operated in Frequency Ranges (FR) FR1 (Sub-6GHz band), FR2 (mmWave band), Terahertz band, and unlicensed bands (with multiple channel access mechanisms). In theory, the benefits of RIS look very promising and align with current KPI requirements for next-generation wireless networks but its success depends on practical deployments.

The recent report from ETSI related to RIS use cases, development scenarios, and requirements is a step forward towards RIS development but there are still questions about its interoperability, integration, standardization, and regulations requirements. ETSI, along with supporting organizations, is focusing and advancing on other work items related to: (1) Technological challenges, architecture, and impact on standardization; (2) Implementation and practical considerations; and (3) Communication and channel models, channel estimation, and evaluation methodology. ETSI has plans to release more specifications related to above mentioned work items in the next couple of months. However, its full specification may still take considerable amount of time until its full integration and interoperability testing.

The individual benefits of RIS are clear but its actual utilization in wireless communication depends on its standardization, commercialization, and interoperability. The synergistic integration of RIS with emerging technologies such as massive Multiple Input Multiple Output (MIMO), small-cells Visible Light Communications (VLC), millimeter-wave (mmW), Terahertz (THz) communication, drone-aided communication, and energy harvesting needs to be investigated to claim full benefits of RIS in wireless communications systems. So far, there are continuous attempts from academia to develop implementation testbeds and field trials to confirm its viability in wireless networks, but they seem insufficient to prove its potential in commercial operating environment. It is still unclear who will develop RIS and when its early deployment will begin.

RIS development is at a very early stage, while initial efforts were being made by several vendors (ZTE, Huawei, VIVO), operators (China Unicom, China Telecom, NTT, DOCOMO), Standard Development Organizations (SDOs) (ETSI), and research institutions. However, the industry is quite far from commercial deployments. Similar, inorganic ways to deploy cellular networks have been discussed in the past, but none of them materialized. These have included LTE relays and repeaters, but RIS presents a unique approach, and, in the passive case, these elements do not even require power. It is thus necessary for the industry to work together to progress the understanding and implications of RIS, especially in the network modeling aspect, to understand how the whole network will behave, the tangible benefits of these reflectors, and the Total Cost of Operation (TCO) and Return on Investment (ROI) aspect. These are questions that will be answered in the few years to come, but RIS will likely only be used in extreme cases where coverage is absolutely necessary in situations where other, more traditional ways to improve coverage are not applicable. Moreover, the operating modes of RIS are use-case dependent, making it equally important to understand each mode of operation and its practical implications in wireless networks.