Pareto-Optimal Power Allocation of
Device-to-Device Communication with Two-Way
Decode-and-Forward Helping Relay
Yiyang Ni
∗
, Shi Jin
†
, Hongbo Zhu
∗
, Shixiang Shao
∗
, and Kai-Kit Wong
‡
∗
Jiangsu Key Laboratory of Wireless Communications College of Telecommunications and Information Engineering,
Nanjing University of Posts and Telecommunications Nanjing 210003, China, Email: {cynthia
nyy}@163.com
†
National Mobile Communications Research Laboratory, Southeast University, Nanjing 210096, China
‡
Department of Electronic and Electrical Engineering, University College London, United Kingdom
Abstract—This paper considers a new strategy utilizing two-
way decode-and-forward (DF) relaying for device-to-device (D2D)
communications underlaying cellular networks. Assuming that all
the terminals have single antenna, we first derive the sum-rate
expressions for both the D2D and cellular links and then propose
a Pareto-optimal method to maximize the achievable sum-rate of
both D2D and cellular links. Simulation results demonstrate that
the sum-rate for the D2D link can be greatly enhanced without
compromising the performance of the cellular link.
I. INTRODUCTION
As an underlay approach to cellular networks, device-to-
device (D2D) communication has recently attracted consider-
able attention due to its much improved spectral efficiency [1].
In this case, D2D users communicate to each other directly
over a D2D link reusing the cellular network’s frequency
resource without the help of the base station (BS) [2, 3] to not
only increase the spectral efficiency but also enhance the cell
throughput. However, it poses new challenges to the network
to cope with this new interference scenarios [4].
To avoid the harmful inter-channel interference, an intuitive
approach is to ensure orthogonal resource allocation for both
cellular and D2D communication [5]. However, orthogonal re-
source allocation would mean that the spectrum efficiency will
be low. Hence, non-orthogonal frequency reuse mechanisms
were investigated recently to enhance the system performance
[4, 6, 7]. For this reason, interference management has become
a major issue. Considerable efforts were made on controlling
the interference between D2D and cellular users, see e.g., [8–
10]. In [11], according to the interference level, three reception
modes for the D2D users were discussed to improve the outage
probability. Nevertheless, the improved model in [11] requires
the participation of the BS in the decoding process as a
relay. In [12], beamforming and interference cancellation were
considered with a multi-antenna BS in the downlink (DL).
In cellular networks, relay-assisted communication has at-
tracted lots of interests due to its great potential in enhancing
the system performance [13–16]. Of increasing interest is the
two-way relay network. For instance, the achievable rates have
been studied for decode-and-forward (DF) relaying system in
[13, 17]. Recently, [18] investigated the performance for a two-
way DF relay network in the case of multiple interferers at
the source nodes. One-way multi-hop DF relaying for D2D
communication in the uplink (UL) was also addressed in
[19]. Power allocation schemes were proposed to improve the
achievable rate of amplify-and-forward (AF) relay channels in
[19], but without considering the cellular link. Another power
allocation scheme was proposed in [8] and [10] in which the
BS controlled the transmit power of D2D users to guarantee
reliable communication for the cellular users. However, the
performance of D2D link was not taken into account.
Motivated by the growing interest of two-way relaying,
this paper presents a new D2D communication strategy using
a two-way DF relay node in both UL and DL. Then we
derive the achievable sum-rate expressions for both D2D and
cellular users. We find that the achievable sum-rate of the D2D
communication can be improved without compromising the
performance of the cellular link. As a major contribution, we
present a Pareto-optimal power allocation scheme to maximize
the achievable sum-rate of both D2D and cellular links.
II. S
YSTEM MODEL
In this section, we consider two models for D2D communi-
cation. First we illustrate the traditional D2D communication
strategy. Then we propose a new D2D strategy aided by a two-
way DF relay node. To facilitate our discussion, we refer to
the case where the D2D link contains a relay node as MODE2
and the case without a relay node as MODE1. We consider an
isolated cell interference scenario including one cellular user
and a pair of D2D users (i.e., UEC, D
1
and D
2
). Note that
all the users are equipped with single antenna. In this paper,
we focus on the intra-cell interference caused by D2D users
sharing the same frequency bands with the cellular user.
A. MODE1–Traditional D2D Strategy
For the k-th UL phase, an interference scenario is described
in Fig. 1, where UEC transmits messages to the BS while D
1
sends messages to D
2
reusing the same frequency resources
as UEC. Thus, D2D and cellular users cause interference to
each other in the k-th time slot. Similarly, for the (k +1)-th
DL phase, the BS transmits messages to UEC, while D
2
sends
messages to D
1
via D2D link directly. As a consequence, the
received signal at user j (j = D
1
,D
2
,C,B,R) during the t-
th time slot (t = k, k +1)under MODEm (m =1, 2) can be
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