  Future mobile networks are supposed to serve high data rates required by
users. To accommodate the high data rates, a direct communication between
nearby mobile terminals (MTs), known as Device-to-device (D2D) communication,
can be exploited. Furthermore, a communication in high frequency bands, such
as, visible light communication (VLC), is also foreseen as an enabler for the
high data rates. In conventional D2D communication, pairs of the MTs should
reuse the same frequencies to keep a high spectral efficiency of the system.
However, this implies either interference among the D2D pairs or utilization of
complex and advanced resource allocation algorithms. In this paper, we propose
a new concept for D2D communication combining VLC and RF technologies in order
to maximize capacity of the system. This paper provides an analysis of the
operational limits for the proposed concept and investigates capacity gains
introduced by the combined usage of RF and VLC bands for D2D. Moreover, we
discuss several practical issues related to the proposed RF-VLC D2D concept.
Performed analyses show that the RF--VLC D2D is able to improve the capacity in
an indoor scenario by a factor of 4.1 and 1.5 when compared to stand-alone RF
D2D and VLC D2D, respectively.
