Abstract
Reconfigurable intelligent surfaces (RISs) have the potential of realizing the emerging concept of smart radio environments by leveraging the unique properties of metamaterials and large arrays of inexpensive antennas. In this article, we discuss the potential applications of RISs in wireless networks that operate at high-frequency bands, e.g., millimeter wave (30-100 GHz) and sub-millimeter wave (greater than 100 GHz) frequencies. When used in wireless networks, RISs may operate in a manner similar to relays. The present paper, therefore, elaborates on the key differences and similarities between RISs that are configured to operate as anomalous reflectors and relays. In particular, we illustrate numerical results that highlight the spectral efficiency gains of RISs when their size is sufficiently large as compared with the wavelength of the radio waves. In addition, we discuss key open issues that need to be addressed for unlocking the potential benefits of RISs for application to wireless communications and networks.
Highlights
NUMERICAL RESULTS we report some numerical illustrations in order to quantitatively compare Reconfigurable intelligent surfaces (RISs) and relays
We have discussed the differences and similarities between relays and RISs that are configured to operate as anomalous reflectors
This article complements the numerical study performed in [20], where the authors compare the power consumption and the energy efficiency of DF relays against RISs that operate as focusing lenses, and in [27], where the authors compare the energy efficiency of AF multi-antenna relays against RISs that are designed for optimal passive beamforming
Summary
B Y 2022, it is expected that the global mobile data traffic will reach a monthly run of 77 exabytes, which corresponds to a 7-fold growth compared with the monthly run of 2017. Such demands may not be accommodated by current cellular standards that utilize only sub-6 GHz frequency bands. Extensive measurements have been conducted at the millimeter wave band and, more recently, the sub-millimeter wave band. These have demonstrated that the use of highly directional steerable antennas enables mobile communication at such high frequencies [1]. Millimeter- and sub-millimeter wave signals may be severely attenuated by the presence of small-size objects, e.g., human bodies and foliage
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