As a revolutionary paradigm for intelligently controlling wireless channels,
intelligent reflecting surface (IRS) has emerged as a promising technology for
future sixth-generation (6G) wireless communications. While IRS-aided
communication systems can achieve attractive high channel gains, existing
schemes require plenty of IRS elements to mitigate the «multiplicative
fading» effect in cascaded channels, leading to high complexity for real-time
beamforming and high signaling overhead for channel estimation. In this paper,
the concept of sustainable intelligent element-grouping IRS (IEG-IRS) is
proposed to overcome those fundamental bottlenecks. Specifically, based on the
statistical channel state information (S-CSI), the proposed grouping strategy
intelligently pre-divide the IEG-IRS elements into multiple groups based on the
beam-domain grouping method, with each group sharing the common reflection
coefficient and being optimized in real time using the instantaneous channel
state information (I-CSI). Then, we further analyze the asymptotic performance
of the IEG-IRS to reveal the substantial capacity gain in an extremely
large-scale IRS (XL-IRS) aided single-user single-input single-output (SU-SISO)
system. In particular, when a line-of-sight (LoS) component exists, it
demonstrates that the combined cascaded link can be considered as a
«deterministic virtual LoS» channel, resulting in a sustainable squared array
gain achieved by the IEG-IRS. Finally, we formulate a weighted-sum-rate (WSR)
maximization problem for an IEG-IRS-aided multiuser multiple-input
single-output (MU-MISO) system and a two-stage algorithm for optimizing the
beam-domain grouping strategy and the multi-user active-passive beamforming is
proposed.

Este artículo explora los viajes en el tiempo y sus implicaciones.

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