Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: RIS-aided Massive MIMO: Achieving Large Multiplexing Gains with
  non-Large Arrays   This paper considers an antenna structure where a (non-large) array of
radiating elements is placed at short distance in front of a reconfigurable
intelligent surface (RIS). We propose a channel estimation procedure using
different configurations of the RIS elements and derive a closed-form
expression for an achievable downlink spectral efficiency by using the popular
hardening lower-bound. Next, we formulate an optimization problem, with respect
to the phase shifts of the RIS, aimed at minimizing the channels
cross-correlations while preserving the channels individual norms. The
numerical analysis shows that the proposed structure is capable of overcoming
the performance of a conventional massive MIMO system without the RIS.

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The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
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The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org