IEEE Communications Magazine - June 2017 - page 184

IEEE Communications Magazine • June 2017
182
0163-6804/17/$25.00 © 2017 IEEE
A
bstract
Recent significant advances in self-interference
cancellation techniques pave the way for the
deployment of full-duplex wireless transceivers
capable of concurrent transmission and reception
on the same channel. Despite the promise to the-
oretically double the spectrum efficiency, full-du-
plex prototyping in off-the-shelf chips of mobile
devices is still in its infancy, mainly because of the
challenges in mitigating self-interference to a tol-
erable level and the strict hardware constraints.
In this article, we argue in favor of embedding
full-duplex radios in onboard units of future vehi-
cles. Unlike the majority of mobile devices, vehic-
ular onboard units are good candidates to host
complex full-duplex transceivers because of their
virtually unlimited power supply and processing
capacity. Taking into account the effect of imper-
fect self-interference cancellation, we investigate
the design implications of full-duplex devices
at the higher-layer protocols of next-generation
vehicular networks and highlight the benefits they
could bring with respect to half-duplex devices in
some representative use cases. Early results are
also provided that give insight into the impact of
self-interference cancellation on vehicle-to-road-
side communications, and showcase the benefits
of FD-enhanced medium access control protocols
for vehicle-to-vehicle communications supporting
crucial road safety applications.
I
ntroduction
Making vehicles more connected and autono-
mous places unprecedented challenges in front
of stakeholders in the automotive and commu-
nication fields to refine technologies that meet
the ultra-low latency requirements while coping
with the reliability and scalability issues of IEEE
802.11,
1
the de facto standard for vehicular com-
munications.
Lately, full-duplex (FD) communication has
gained attention in the context of advanced
physical (PHY) layer design for fifth-generation
(5G) and beyond networks with the promise of
nearly doubling the system spectral efficiency [1,
2]. Although studies on the application of FD in
classic infrastructured IEEE 802.11 networks have
been conducted, the implications of FD adoption
in future vehicles have not been fully investigat-
ed yet. On one hand, there are concerns about
the technical feasibility of FD technologies in the
harsh channel propagation environment typical
of vehicular ad hoc networks (VANETs). On the
other hand, the availability of high-end transceiv-
ers that could be installed aboard the vehicles
promise to overcome the hardware complexity
limitations that delayed the practical realization of
FD technologies in other wireless systems.
Very few preliminary works have focused
on FD in cellular-based VANETs [3, 4]. While
acknowledging the importance of these works,
we believe that many more opportunities could
be disclosed if FD solutions carefully consider:
• The IEEE 802.11 standard technology
• The requirements and patterns of emerging
vehicular applications such as cooperative
and semi-autonomous driving
This is actually the aim and main contribution
of this article, the organization of which can be
summarized as follows. After introducing the FD
concept from the perspective of the PHY and
medium access control (MAC) layers, we discuss
why FD deployment in vehicular onboard units
(OBUs) has fewer concerns than in other mobile
devices like smartphones or laptops, and highlight
the challenges for FD protocol design in VANETs.
Then we focus on the most representative vehicu-
lar use cases in which FD concepts could be suc-
cessfully applied to improve their performance
by rethinking the MAC and/or higher-layer data
exchange protocols; and we complement our
discussion by early simulation results. Finally, we
debate open issues and future research perspec-
tives on the deployment of FD technologies in
VANETs.
FD: A
n
O
verview
A PHY layer perspective.
In theory, in-band
FD systems can double the system capacity by
allowing simultaneous transmission and recep-
tion over the same center frequency. In practice,
however, the increase in capacity is limited by the
self-interference (SI) that is unavoidably generat-
ed when the transmitted signal couples back to
the receiver in the in-band FD transceiver. Even
though the transmitted signal is perfectly known
in the digital baseband, eliminating the generat-
ed SI at the receiver has been considered for a
long time as a difficult, if not impossible, task. The
reasons essentially come from the considerable
power difference between the transmitted and
received signals,
2
and the multiple causes of ana-
log signal distortions (nonlinearities, I/Q imbal-
Full-Duplex Radios for
Vehicular Communications
Claudia Campolo, Antonella Molinaro, Antoine O. Berthet, and Alexey Vinel
A
utomotive
N
etworking
and
A
pplications
The authors argue in
favor of embedding FD
radios in onboard units of
future vehicles. Unlike the
majority of mobile devic-
es, vehicular onboard
units are good candidates
to host complex full-du-
plex transceivers because
of their virtually unlimited
power supply and pro-
cessing capacity.
Claudia Campolo and Antonella Molinaro are with Università Mediterranea di Reggio Calabria;
Antoine O. Berthet is with the Laboratory of Signals and Systems, CNRS-CentraleSupélec-Université Paris-Sud; Alexey Vinel is with Halmstad University.
1
The amendment for vehicu-
lar communications, formerly
known as IEEE 802.11p, is
now part of the IEEE 802.11-
2012 standard.
2
The direct SI signal is typi-
cally 100 dB more powerful
than the intended received
signal in Wi-Fi systems.
Digital Object Identifier:
10.1109/MCOM.2017.1600391
1...,174,175,176,177,178,179,180,181,182,183 185,186,187,188,189,190,191,192,193,194,...228
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