Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Frequency Synchronization for Uplink Massive MIMO Systems   In this paper, we propose a frequency synchronization scheme for multiuser
orthogonal frequency division multiplexing (OFDM) uplink with a large-scale
uniform linear array (ULA) at base station (BS) by exploiting the angle
information of users. Considering that the incident signal at BS from each user
can be restricted within a certain angular spread, the proposed scheme could
perform carrier frequency offset (CFO) estimation for each user individually
through a \textit{joint spatial-frequency alignment} procedure and can be
completed efficiently with the aided of fast Fourier transform (FFT). A
multi-branch receive beamforming is further designed to yield an equivalent
single user transmission model for which the conventional single-user channel
estimation and data detection can be carried out. To make the study complete,
the theoretical performance analysis of the CFO estimation is also conducted.
We further develop a user grouping scheme to deal with the unexpected scenarios
that some users may not be separated well from the spatial domain. Finally,
various numerical results are provided to verify the proposed studies.

12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn