Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 6G Massive Radio Access Networks: Key Issues, Technologies, and Future
  Challenges   Driven by the emerging use cases in massive access future networks, there is
a need for technological advancements and evolutions for wireless
communications beyond the fifth-generation (5G) networks. In particular, we
envisage the upcoming sixth-generation (6G) networks to consist of numerous
devices demanding extremely high-performance interconnections even under
strenuous scenarios such as diverse mobility, extreme density, and dynamic
environment. To cater for such a demand, investigation on flexible and
sustainable radio access network (RAN) techniques capable of supporting highly
diverse requirements and massive connectivity is of utmost importance. To this
end, this paper first outlines the key driving applications for 6G, including
smart city and factory, which trigger the transformation of existing RAN
techniques. We then examine and provide in-depth discussions on several
critical performance requirements (i.e., the level of flexibility, the support
for massive interconnectivity, and energy efficiency), issues, enabling
technologies, and challenges in designing 6G massive RANs. We conclude the
article by providing several artificial-intelligence-based approaches to
overcome future challenges.

11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
2
The categories of this paper are: math