Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Novel 3D Space-Time-Frequency Non-Stationary Channel Model for 6G THz
  Indoor Communication Systems   Terahertz (THz) communication is now being considered as one of possible
technologies for the sixth generation (6G) communication systems. In this
paper, a novel three-dimensional (3D) space-time-frequency non-stationary
massive multiple-input multiple-output (MIMO) channel model for 6G THz indoor
communication systems is proposed. In this geometry-based stochastic model
(GBSM), the initialization and evolution of parameters in time, space, and
frequency domains are developed to generate the complete channel transfer
function (CTF). Based on the proposed model, the correlation functions
including time auto-correlation function (ACF), spatial crosscorrelation
function (CCF), and frequency correlation function (FCF) are investigated. The
results show that the statistical properties of the simulation model match well
with those of the theoretical model. The stationary intervals at different
frequencies are simulated. The non-stationarity in time, space, and frequency
domains is verified by theoretical derivations and simulations.

5
The categories of this paper are: gr-qc
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The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
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The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
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The categories of this paper are: astro-ph