Wireless Information and Power Transfer in
Full-Duplex Two-Way Massive MIMO AF Relay
Systems
Junjuan Feng
1
, Shaodan Ma
1
, Guanghua Yang
2
,andBinXia
3
1
Department of Electrical and Computer Engineering, University of Macau, Macao
2
Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong
3
Department of Electronic Engineering, Shanghai Jiao Tong University, China
Abstract—In this paper, we investigate wireless information
and power transfer in full-duplex (FD) two-way massive MIMO
amplify-and-forward (AF) relaying network. In the considered
network, the relay is an energy demander and applies time
switching scheme to harvest energy from the users for amplifying
and forwarding the users’ signals. Different from prior studies,
MIMO users and antenna correlation are considered. Achievable
sum-rate is analyzed and the impact of antenna correlations is
discovered. It is revealed from the analysis that the transmission
power at the MIMO users can be cut down proportionally to
1/𝑀
𝑟
and/or the transmission power at the relay can be scaled
down proportionally to 1/𝑀
2
𝑟
to maintain a constant sum-rate,
when massive antennas are equipped at the relay. Here 𝑀
𝑟
denotes the number of antennas at the relay. Moreover, the
optimal time switching ratio for energy harvesting at the relay
is found to maximize the sum-rate. Finally, the analytical results
are validated by computer simulations.
Index Terms—Energy harvesting, time switching relay, power
scaling law, zero-forcing, deterministic result, asymptotic sum-
rate.
I. INTRODUCTION
Lately, wireless information and power transfer (WIPT) has
attracted lots of attention due to its convenience and high
capability to extend the lifetime of energy constrained wireless
networks [1] [2]. It utilizes the fact that the radio-frequency
(RF) signal can carry information and energy simultaneously
and provides one promising solution for charging wireless
devices. Another promising technique which has been widely
discussed is relaying [3] [4]. It can increase spectral efficiency
and extend the coverage for signal transmission with the aid of
a relay node [5]. When combining these techniques together,
notable s pectral efficiency improvement can be realized with
high convenience to wireless users. WIPT in relay systems
thus has attracted considerable research interest in recent years
[6]–[9].
Some analytical results on WIPT in relay systems have
been reported in the literature. Particularly, [7] [8] and [9]
investigate WIPT in two-way/multi-way half-duplex relay sys-
tems. Since all the nodes in the relay systems are operated in
half duplex mode, multiple phases are needed to achieve the
information exchange among users. To reduce the number of
phases and improve spectral efficiency, full duplex is adopted
and a full duplex one-way relay network is investigated
in [6]. In the network, the relay can transmit and receive
signals simultaneously and self-loop interference due to the
leakage of the transmitted signal back to the node itself
is unavoidable. Achievable throughput is analyzed and it is
demonstrated that significant spectral efficiency improvement
can be achieved in full duplex relay networks even with self-
loop interference. In most of the prior analyses, single antenna
users are considered. Since multiple antenna technique can
further boost spectral and energy efficiency, it is desirable
to investigate the performance of WIPT in full duplex relay
systems with multiple input multiple output (MIMO) users.
When multiple antennas are equipped in the users and the
relay, spatial antenna correlation may occur due to the limited
spacing among the antennas and this may affect the system
performance which hasn’t been analyzed before in full duplex
WIPT systems.
In this paper, we investigate the WIPT in full duplex two-
way MIMO relay networks. Massive MIMO relay is applied
to exploit the benefits of spectral efficiency improvement and
energy saving from massive antenna deployment [9]. Different
from prior analyses, MIMO users and antenna correlations at
both the users and the relay are considered. In the considered
network, two MIMO users are energy sources and would like
to exchange information with the aid of the energy demanding
massive MIMO relay. Time switching energy harvesting at
the relay is particularly considered and achievable sum-rate
is analyzed. It is revealed that with massive antennas at the
relay, the transmission power at the two users can be scaled
down proportionally to 1/𝑀
𝑟
and/or the transmission power
at the relay can be scaled down proportionally to 1/𝑀
2
𝑟
to
maintain a constant sum-rate, where 𝑀
𝑟
denotes the number
of antennas at the relay. Impact of antenna correlation on
the sum-rate is also discovered. Moreover, with the analytical
results, the optimal time switching ratio for energy harvesting
can be found to maximize the sum-rate.
II. SYSTEM MODEL
In this paper, a full-duplex (FD) two-way massive MIMO
amplify-and-forward (AF) relay network with two MIMO
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