Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Few-Bit CSI Acquisition for Centralized Cell-Free Massive MIMO with
  Spatial Correlation   The availability and accuracy of Channel State Information (CSI) play a
crucial role for coherent detection in almost every communication system.
Particularly in the recently proposed cell-free massive MIMO system, in which a
large number of distributed Access Points (APs) is connected to a Central
processing Unit (CPU) for joint decoding, acquiring CSI at the CPU may improve
performance through the use of detection algorithms such as minimum mean square
error (MMSE) or zero forcing (ZF). There are also significant challenges,
especially the increase in fronthaul load arising from the transfer of high
precision CSI, with the resulting complexity and scalability issues. In this
paper, we address these CSI acquisition problems by utilizing vector
quantization with precision of only a few bits and we show that the accuracy of
the channel estimate at the CPU can be increased by exploiting the spatial
correlation subject to this limited fronthaul load. Further, we derive an
estimator for the simple \emph{Quantize-and-Estimate} (QE) strategy based on
the Bussgang theorem and compare its performance to
\emph{Estimate-and-Quantize} (EQ) in terms of Mean Squared Error (MSE). Our
simulation results indicate that the QE with few-bit vector quantization can
outperform EQ and individual scalar quantization at moderate SNR for small
numbers of bits per dimension.

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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: hep-th
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The categories of this paper are: hep-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-th
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The categories of this paper are: astro-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: hep-lat