Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Single-RF MIMO: From Spatial Modulation to Metasurface-Based Modulation   In multiple-input multiple-output (MIMO), multiple radio frequency (RF)
chains are usually required to simultaneously transmit multiple data streams.
As a special MIMO technology, spatial modulation (SM) activates one transmit
antenna with one RF chain and exploits the index of the active antenna for
information transfer at each time slot. Recently, reconfigurable metasurfaces
have emerged as a promising technology that is able to reconfigure the wireless
propagation environment by altering the amplitude and/or phase of the incident
signal. In this article, we aim for the implementation of single-RF MIMO by
shifting the focus from SM to metasurface-based modulation. Specifically, the
principles of SM and metasurfaces are first presented. After reviewing the
evolution of SM, we elaborate on the idea of metasurface-aided single-RF MIMO
and discuss some implementations for it in line with notable variants of SM. A
comparison between antenna-based and metasurface-based modulation is made to
highlight the advantages of using metasurfaces. We finally investigate the
research challenges and opportunities in the context of metasurface-based
modulation.

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The categories of this paper are: q-bio
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The categories of this paper are: cond-mat
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
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The categories of this paper are: nlin
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The categories of this paper are: nucl-ex
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The categories of this paper are: physics