Abstract
Owing to the envisioned new use-cases, such as immersive virtual reality and high-fidelity mobile hologram, and their potential challenging new requirements for future wireless networks, extensive research has already started on 6G and beyond wireless technologies. Despite the fact that several modern physical layer solutions have been introduced in the past decade, a level of saturation has been reached in terms of the available spectrum and adapted modulation/coding solutions, which accordingly limits the maximum capacity and reliability. Within this respective, reconfigurable intelligent surface (RIS)-empowered communication appears as a potential candidate to overcome the inherent drawbacks of legacy wireless systems. The core idea of RIS-assisted communication is the transformation of the random and uncontrollable wireless propagation environment into a reconfigurable communication system entity that plays an active role in conveying information and improving system performance. In this paper, the well-known multipath fading phenomenon is revisited in mobile wireless communication systems, and novel and unique solutions are introduced from the perspective of RISs. The feasibility of eliminating or mitigating the multipath fading effect stemming from the movement of mobile receivers is also investigated by utilizing RISs. It is shown that rapid fluctuations in the received signal strength due to the Doppler effect can be effectively reduced by using real-time tunable RISs. It is also proven that for a hypothetical propagation environment where all reflectors are coated with RISs, the multipath fading effect can be totally eliminated. Furthermore, we show that for more general propagation environments with several interacting objects, even a few real-time tunable RISs can remarkably reduce the Doppler spread and the deep fades in the received signal.
Highlights
Fifth generation (5G) wireless networks have three major use-cases with different user requirements, namely enhanced mobile broadband, ultra-reliable and low-latency communications (URRLC), and massive machine type communications
We focus on the same basic system model of subsection 2.1 (Figure 1), we consider that the interacting object (IO) creates a controllable reflection at this time, thanks to the reconfigurable intelligent surface (RIS) that is mounted on its facade with the purpose of manipulating the reflected signals
By following a bottom-up approach, first, we have investigated simple propagation scenarios with a single RIS and/or a plain IO
Summary
Fifth generation (5G) wireless networks have three major use-cases with different user requirements, namely enhanced mobile broadband (eMBB), ultra-reliable and low-latency communications (URRLC), and massive machine type communications (mMTC). A plethora of modern PHY solutions, including multi- and advantages: carrier modulation, adaptive modulation and coding, nonorthogonal multiple access, relaying, beamforming, massive MIMO, and reconfigurable antennas, have been considered to overcome these challenges in the several decades, the overall progress in terms of the PHY improvement has been still relatively slow This can be explained by the following undeniable fact in wireless systems: the propagation environment has been perceived as a randomly behaving entity until the start of the modern wireless communications era and it degrades the overall received signal quality and the communication QoS owing to (i) RISs do not require an energy source for RF signal processing thanks due their almost passive architecture;.
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