Advanced D2D
band overhead reduction is also available from the
well-confined spectrum. Sophisticated receiver algorithms
including channel estimation and equalization
can further mitigate the multi-path fading
channel impact without the CP.
With FQAM, the statistical distribution of ICI is likely
to be non-Gaussian, especially for cell-edge users.
As a result, the transmission rates for the cell-edge
users can be significantly improved.
The statistics of ICI and the performance enhancement
possibility have been proven by practical
implementation of a system which uses FQAM.
FQAM system environment for cellular downlink
OFDMA networks is shown in Figure 23 and 24.
Our experimental results show that the transmission
rates for interference-limited users in FQAM-based
OFDMA networks are around 300% higher than
those in QAM-based OFDMA networks [23][24].
Advanced D2D communication is an attractive
technology that enhances spectral efficiency and
reduces end-to-end latency for 5G. Not entirely depending
on the cellular network, D2D devices can
communicate directly with one another when they
are in close proximity. Hence, D2D communication
will be used for offloading data from network so that
the cost of processing those data and related signaling
is minimized. Moreover, enhanced version of
D2D communication was suggested lately for being
used as special purpose such as Mission Critical
Push-To-Talk (MCPTT) communication and Vehicleto-
Anything (V2X) communication.
In advanced D2D communication, a single radio
resource can be reused among multiple groups
which want to communicate with each other if the
interference incurred between groups is tolerable.
Hence, we can increase the spectral efficiency and
the number of the simultaneous connection by utilizing
D2D communication in 5G. Moreover, since the
data is directly transmitted and not going through
the core network, the end-to-end latency can be
considerably reduced. Therefore, advanced D2D
communication is quite well aligned with IoT services
as shown in Figure 25. The cars can communicate
with each other to exchange the information for
safety alarm and infotainment without cellular base
station. The home appliances communicate with
each other for home automation service. Many objects
in proximity region can be connected to each
other so that IoT services can be accomplished.