Reconfigurable Intelligent Surfaces (RIS) Use Cases

We have looked at reconfigurable intelligent surfaces (RIS), also known as intelligent reflecting surfaces (IRS) in our posts earlier. While many research papers study how RIS can be used and optimized, few effort is devoted to analyzing the challenges to commercialize RIS and how RIS can be standardized. A new paper is looking to shed some light on RIS from an industrial viewpoint and provide a clear roadmap to make RIS industrially feasible. The following is from the paper:

RIS has a great potential for a wide range of applications as shown in Fig. 1, including unmanned aerial vehicles (UAV) communications, mmWave coverage extension, wireless information and power transfer, physical layer security, etc. For example, IRS can be either deployed on the ground to assist UAV communications with ground nodes or attached to UAVs to assist terrestrial communications via leveraging smart passive reflection from the sky. RISs are also expected to support the three main pillar use cases in current 5G networks, namely, enhanced mobile broadband (eMBB), ultra-reliable and low-latency communications (URLLC), and massive machine-type communications (mMTC). For example, RIS can be attached to improve coverage and establish high-capacity hot-spot, which is crucial for eMBB and mMTC applications in stadiums, smart factories, shopping centers, airports, etc. In particular, for mMTC scenarios where the devices may switch from active to inactive mode frequently, the device activity detection efficiency and accuracy can be effectively improved by exploiting the additional path provided by RIS. Furthermore, RIS can also be applied to effectively compensating the Doppler and delay spread effects, which are appealing for in URLLC applications such as smart transportation. Specifically, exploiting RISs to turn typically random wireless channels into more deterministic ones can effectively reduce retransmissions and minimize the latency. Therefore, RIS is a revolutionary technology to upgrade the current infrastructure, which is expected to boost a wide range of industries and eventually helps achieve the smart home and smart city in the future.

In this paper we mainly discuss the case of RIS being integrated into cellular networks. To clearly understand the way forward towards future commercial wireless networks with RIS as a key component, a view on the bigger picture of the whole standardization process is beneficial. The technologies embedded in commercial networks would first be studied by the academia thoroughly for a considerable period of time, with solutions to technical problems and use cases clearly developed and identified. In the meantime, the technology would pick up attention from the industry as a candidate for at least one major use case in some practical scenarios. As researchers from the industry proceed with the research, prototype development and testing, interacting with the academia by research collaborations, as is happening nowadays, the technology matures quickly. At this stage, early standardization process kicks off to further drive progress of the commercialization and industrialization of the particular technology. The standardization process usually begins with a SI in one or multiple regional SDOs or industrial forums and with the preliminary results available, a SI will later be established in international SDOs like the 3rd Generation Partnership Project (3GPP). What happens next is that a work item (WI) will succeed when the SI is completed and the conclusions favor a normative work where technical specifications will be defined and released, which is perceived as a sign that the technology is officially part of the global standards.

With heavy investments from the research institutes and businesses, surprisingly fast progress in terms of prototype building and testing is witnessed. As depicted in Fig. 3, corporations in the wireless industry have already started prototype building since the year of 2020 either independently or jointly with universities and those prototypes were tested in the 5G networks. The tests provide researchers and engineers with firsthand data on the performance of RIS in cellular networks and new problems emerge as well as advanced solutions.

In regional SDOs, the study on RIS is already under way. Those study or work items usually span for two years with technical reports or white papers as outcomes. Within the ITU, one critical milestone is the official release of the report for 6G trends which will be perceived as a guidebook for the next generation wireless networks. The discussion on the report started in February 2020 and the report is expected to be published in June 2022. It’s highly likely that RIS will be described as a critical component for 6G networks in the report. Since the ITU focuses on regulatory, spectrum and business aspects, it’s unlikely for RIS to be established as a focus group or a WI there. Further actions in the ITU will become clearer after 2023.

Currently focusing on completing Release 17 for 5G and starting further enhancements in Release 18, there is no formal plan on 6G by 3GPP. According to the past experience, each generation of wireless communication standards lasts for approximately a decade. The first 3GPP working group meeting for 5G started in April 2016, indicating that it’s reasonable to expect 6G related conceptual discussions on scenarios and requirements to take off after 2026. There are generally two possible ways to standardize RIS in 3GPP. One is to start a SI on scenarios and channel models in Release 18 and then a WI in Release 19 so that RIS can be deployed as a component of 5G advanced networks. The advantage of this approach is that RISs can be deployed in wireless networks in a massive scale soon which will help maturing this technology. What’s more, since RISs are part of 5G standards, they will be automatically included in 6G and when new features are defined for 6G networks, the combination between RIS and the new features will be possible. Another way is to standardize RISs as part of 6G together with other new features for 6G, which means the deployment of RISs may be delayed to the next generation and uncertainties might arise. Since RIS is a technology that can be seen as generic and band-agnostic, standardizing it as early as possible would enable opportunities for RIS to be combined with later technologies, contributing to greener, safer and more reliable wireless networks. On the other hand, there are still some challenging technical problems to be tackled which requires considerable amount of time. In this sense, the exact date to start studying RIS officially in 3GPP depends largely on the maturity of this technology. Since there was a first proposal submitted to 3GPP during its meeting in March 2021, the earliest possible time to start the SI is late 2021, paving the way to evolved wireless environment in near future.

The PDF is available here.

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