Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hybrid Precoding for mmWave V2X Doubly-Selective Multiuser MIMO Systems   Millimeter wave (mmWave) is a practical solution to provide high data rate
for the vehicle-to-everything (V2X) communications. This enables the future
autonomous vehicles to exchange big data with the base stations (BSs) such as
the velocity and the location to improve the awareness of the advanced driving
assistance system (ADAS). In this context, we consider a single-cell multiuser
doubly-selective system wherein the BS simultaneously serves multiple vehicles.
To accomplish this requirement, the BS is implemented in hybrid architecture to
support multiple spatial streams while the vehicles have analog-only
structures. In this work, we develop a low-complexity hybrid precoding
algorithm wherein the design of the hybrid precoder at the BS and the analog
combiner at the vehicles require small training and feedback overhead. We
propose a two-stage hybrid precoding algorithm wherein the first stage designs
the analog beamformers as in single user scenario while the second stage
designs the multiuser digital precoder at the BS. In the second stage, we
derive closed-form digital precoders such as Maximum Ratio Transmission (MRT),
Zero-Forcing (ZF) and Minimum Mean Square Error (MMSE) as a first variant while
we propose iterative digital precoder as a second variant. The design of the
digital precoders for the two variants requires the limited feedback sent from
the vehicles to BS. We refer to the random vector quantization (RVQ) and the
beamsteering codebooks to quantize the feedbacks for variants I and II,
respectively, since the perfect feedback requires long overhead and large
training. We evaluate the rate loss incurred by the quantization of the digital
and analog codebooks against the perfect channel state information at the
transmitter (CSIT).

33
The categories of this paper are: plasm-ph
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
17
The categories of this paper are: q-fin
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas