Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: A General MIMO Framework for NOMA Downlink and Uplink Transmission Based
  on Signal Alignment
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol