Energy-Efficient Two-Way Transmission in
Regenerative Full-Duplex Relaying Systems
Qimei Cui, Zhichun Shangguan, Yuhao Zhang and Baoling Liu
School of Information and Communication Engineering,
Beijing University of Posts and Telecommunications, Beijing, 100876, China
Email: {cuiqimei}@bupt.edu.cn
Abstract—In this paper, considering non-ideal power ampli-
fier (PA) and circuit power, we optimize the energy efficiency (EE)
of two-way full-duplex relaying (FDR) systems with decode-and-
forward (DF) protocol. With higher cooperative gain, the direct
link (DL) of the regenerative FDR is decoded at the receiver and
can contribute to the useful signal rather than the interference,
which can further improve the system performance significantly.
With this mechanism, the joint transmit power and duration
optimization problem is formulated to maximize the EE of the
FDR system, which is proved to be non-convex and cannot be
resolved by the standard convex methods. Therefore, a two-
step optimization algorithm (TSOA) is proposed to solve the
original non-convex problem, where the optimality of the solution
is ensured due to the rigorously proved convexity. Simulations
are carried out to verify the EE performance of our proposed
scheme, compared with the existing schemes. It is also revealed
that the FDR systems are basically comparable to the half-duplex
relaying (HDR) counterparts in terms of EE if the residual self-
interference (RSI) is below a certain level, and have the ability
to achieve higher data rate demand.
I. INTRODUCTION
Energy-efficient (EE) communication has been proposed
and drawn extensive interest in the exiting literatures under
the background of limited energy resource and environmental-
friendly transmission behaviors [1] [2]. It is reported that 2%
to 10% of the global energy consumption and 2% of the
greenhouse gases are generated by information and commu-
nication technologies (ICT), which is predicted to be further
sustained sharp growth in the future. On the other hand, mobile
devices in wireless networks have limited power supply so
that it is critical to extend their lifetime by EE maximization.
Relay operating either half-duplex (HD) or full-duplex (FD)
mode with cooperation is one of effective methods to improve
performance and potentially save energy [3]. By allowing relay
to simultaneously transmit and receive on the same time, the
FD transmission can overcome the spectral efficiency (SE)
loss caused by in HD transmission inherently, however, at the
cost of introducing the residual self-interference (RSI) [4].
Fortunately, due to significant advances on self-cancellation
techniques in full-duplex relaying (FDR) system recently [5],
[6], the RSI can be achieved to 80 dB, comprising 40 dB from
passive suppression and 40 dB from active cancellation [5],
[6], which provides the FD transmission with a good chance
to be used widely.
It is known that many studies have been carried out to
improve the EE of FDR systems. In [7], EE optimization
of decode-and-forward (DF) FDR systems were taken under
asymmetric multipath fading channels and shadowing con-
ditions. In [8], a low complexity EE-orientated optimization
algorithm in FD DF relay-assisted 60 GHz multiuser indoor
networks was proposed, by which the transmit power, sub-
carriers and throughput were allocated jointly across multiple
users. In [9], a DF protocol was proposed to selectively activate
the relay for FD cooperation based on the outage states of the
different links, which offered additional power savings while
keeping the same outage performance. In [5], the combination
of opportunistic mode selection was proposed, which switched
opportunistically between FD and HD dual-hop amplify-and-
forward (AF) systems, and transmit power adaptation for
maximizing EE .
As far as we are concerned, most exiting works on EE of
FDR systems have neglected the direct link (DL) or regarded it
as the noise at the receiver [5], [7], [8], [10]. However, due to
the greater transmit power in high-rate wireless transmission
and the randomness of channel gain, DL is truely worth to
be considered for cooperative diversity to improve the data
rate and EE effectively. In addition, negligible circuit power
and ideal power amplifiers (PAs) assumed previously may be
inaccurate since PAs consume dozens of watts and account for
up to 70% of the total energy budge and typically are non-
ideal with the output transmit power. Moreover, the non-ideal
PAs introduce an non-convex structures for EE optimization,
which is hard to deal with [11].
In this paper, focusing on regenerative FDR systems, where
the RSI is inevitable and the DL can be also used for data
transmission, we maximize the EE by joint transmit power
and duration optimization with the consideration of non-
ideal PAs and circuit power. Since the original formulated
optimization problem is non-convex, a two-step optimization
algorithm (TSOA) scheme is proposed to transform this prob-
lem into a convex one by solving the two divided subproblems
with rigorously proved convexity. Simulation results show that
the TSOA scheme provide higher EE and achievable larger
system capacity than the state-of-the-art schemes. Moreover,
It is revealed that the FDR systems are basically comparable
to the HD relaying (HDR) systems in terms of EE if the RSI is
below a certain level, and have the ability to satisfy the larger
data demand.
The remainder of this paper is organized as follows, Sec-
tion II presents system model, and Section III and Section IV
2018 IEEE Wireless Communications and Networking Conference (WCNC)
978-1-5386-1734-2/18/$31.00 ©2018 IEEE