Reconfigurable Intelligent Surface-Empowered MIMO Systems

Reconfigurable intelligent surface (RIS)-assisted communications appear as a promising candidate for future wireless systems due to its attractive advantages in terms of implementation cost and end-to-end system performance. In this paper, two new multiple-input multiple-output (MIMO) system designs using RISs are presented to enhance the performance and boost the spectral efficiency of state-of-the-art MIMO communication systems. Vertical Bell Labs layered space-time (VBLAST) and Alamouti's schemes have been considered in this study and RIS-based simple transceiver architectures are proposed. For the VBLAST-based new system, an RIS is used to enhance the performance of the nulling and canceling-based sub-optimal detection procedure as well as to noticeably boost the spectral efficiency by conveying extra bits through the adjustment of the phases of the RIS elements. In addition, RIS elements have been utilized in order to redesign Alamouti's scheme with a single radio frequency (RF) signal generator at the transmitter side and to enhance its bit error rate (BER) performance. Monte Carlo simulations are provided to show the effectiveness of our system designs and it has been shown that they outperform the reference schemes in terms of BER performance and spectral efficiency.Comment: To appear in IEEE SYSTEMS JOURNAL, 9 pages, 6 figures, and 1 tabl

Reconfigurable Intelligent Surface Assisted Railway Communications: A survey

The number of train passengers and the demand for high data rates to handle new technologies such as video streaming and IoT technologies are continuously increasing. Therefore the exploration of millimeter waves (mmWave) band is a key technology to meet this demand. However, the high penetration loss makes mmWave very sensitive to blocking, limiting its coverage area. One promising, efficient, and low-cost solution is the reconfigurable intelligent surface (RIS). This paper reviews the state of the art of RIS for railway communications in the mmWave context. First, we present the different types of RIS and review some optimization algorithms used in the literature to find the RIS phase shift. Then, we review recent works on RIS in the railway domain and provide future directions

A study on multi-RIS for multi-user distributed MIMO systems

This paper presents a preliminary analysis on the impact of Reconfigurable Intelligent Surfaces (RISs) for the realization of multi-user Distributed multiple input multiple output (DMIMO) systems, where the distributed units are actually RISs. Assuming no direct link between the multi-antenna Access Point (AP) and the users, we design the joint transmit beamforming from the AP to the set of RISs associated to each user, performed via RIS phase shift shaping. In order to comply with the semipassive nature of RISs, the phase shifts are computed via a Genetic Algorithm (GA), where the optimization is based on the Signal-to-Leakage-and-Noise-Ratio (SLNR) precoding scheme. Numerical results confirm that this GA implementation significantly outperforms the common Maximum Ratio Beamforming (MRB) approach in terms of interference suppression and sumrate, but at the price of a significant increase in computational complexity. Our solution justify the interest of a multi-RIS system for spatial multiplexing, and opens to several further research directions

Reconfigurable Intelligent Surfaces for Smart Cities: Research Challenges and Opportunities

The concept of Smart Cities has been introduced as a way to benefit from the digitization of various ecosystems at a city level. To support this concept, future communication networks need to be carefully designed with respect to the city infrastructure and utilization of resources. Recently, the idea of 'smart' environment, which takes advantage of the infrastructure for better performance of wireless networks, has been proposed. This idea is aligned with the recent advances in design of reconfigurable intelligent surfaces (RISs), which are planar structures with the capability to reflect impinging electromagnetic waves toward preferred directions. Thus, RISs are expected to provide the necessary flexibility for the design of the 'smart' communication environment, which can be optimally shaped to enable cost- and energy-efficient signal transmissions where needed. Upon deployment of RISs, the ecosystem of the Smart Cities would become even more controllable and adaptable, which would subsequently ease the implementation of future communication networks in urban areas and boost the interconnection among private households and public services. In this paper, we describe our vision of the application of RISs in future Smart Cities. In particular, the research challenges and opportunities are addressed. The contribution paves the road to a systematic design of RIS-assisted communication networks for Smart Cities in the years to come.Comment: Submitted for possible publication in IEEE Open Journal of the Communications Societ