Delay-QoS-Driven Robust Power Allocation over
Full-Duplex Relay Multicarrier Secure System
Sui Liang
1
, Piming Ma
1
, Yanbo Ma
2
1
School of Information Science and Engineering, Shandong University, Jinan, China
2
School of Management Science and Engineering, Shandong University of Finance and Economics, Jinan, China
Email: 13606411933@163.com, mapiming@sdu.edu.cn, yanboma@sdufe.edu.cn
Abstract—In this paper, we investigate the power allocation
policy under channel uncertainties over the full-duplex (FD)
relay multicarrier secure communication system. Considering the
requirement of the statistical delay quality-of-service (QoS), an
optimization problem of maximizing the secure effective capacity
under the constrains of powers of both the whole system and
the residual loop-interference (LI) of FD relay is formulated to
study the robust power allocation via the worst case method.
Furthermore, after simplifying the original optimization problem
by Taylor approximation, we obtain the optimal solution by
using Lagrange dual method and Karush-Kuhn-Tucker (KKT)
conditions. Simulation results illustrate the advantages of the
proposed robust power allocation strategy and the trade-off
between the secure effective capacity and robustness can be
achieved.
Index Terms—quality-of-service (QoS); secure effective ca-
pacity; full-duplex (FD); secure communication; robust power
allocation.
I. I NTRODUCTION
The resource allocation of secure communication system
has been received a public concern with the secrecy rate
proposed by Wyner [1]. The technique of the full-duplex
(FD) relay with loop-interference (LI) cancelations [2] has
the better frequency spectrum utilization than the traditional
half-duplex (HD) relay [3]. Moreover, to overcome channel
frequency selectivity fading, the prevailing solution is orthog-
onal frequency-division multiplexing (OFDM) which is widely
used in HD relay communication system [4].
In addition, in the environment of delay-sensitive network,
the delay-tolerant guarantee as a kind of quality-of-service
(QoS) requirements plays a critically important role in the
secure transmission [5], [6]. [7] introduced the secure effective
capacity to depict the relationship between the capacity and the
statistical delay QoS requirement by building the relation of
physical layer transmission mechanism and the cache queries
of the link layer for secure communication.
However, the most of the existing researches are limited
on the perfect channel state information (CSI). In fact, it is
difficult to obtain the perfect CSI according to the channel
estimation. Hence, the worst-case approach assumes that the
actual channel lies in a uncertainty region is widely used to
trace the imperfect CSI [8], [9]. In this paper, the robust power
allocation policy is investigated for the uncertain channel gains
of residual LI of FD relay in the multicarrier secure system.
The aim is to maximize the secure effective capacity for certain
Fig. 1: System model for the FD relay secure communication
delay QoS guarantee under the constraints of the total power
and the residual LI of FD relay and we formulate the robust
optimization problem and solve it by Lagrange dual method
and Karush-Kuhn-Tucker (KKT)conditions [8]. Simulation
results show that the proposed robust power allocation policy
satisfied the statistical delay QoS requirement and can trace
the changes of the channel over the FD multicarrier secure
communication system.
II. S
YSTEM MODEL AND SECURE EFFECTIVE CAPACITY
Let us consider a point-to-point secure communication sys-
tem with an eavesdropper as shown in Fig.1. We assume there
is one source, one FD relay, one legitimate destination and
one eavesdropper which are equipped with a single antenna
except the FD relay.
Suppose the source is far away from the legitimate des-
tination, and there is no direct link. The source can send
confidential data to the legitimate destination by the FD
relay, which is equipped with two antennas and employs the
decode and forward (DF) mode to forward signals. Besides,
we assume that the LI cancellation is not perfect and there
exists the residual LI on the relay.
Meanwhile, the total bandwidth B is divided into N or-
thogonal subcarriers. Let g
(k)
SR
, g
(k)
RD
, g
(k)
LI
and g
(k)
RE
denote
the channel gains of the source-relay (SR) link, the relay-
destination (RD) link, the residual LI link and the relay-
eavesdropper (RE) link, respectively. Let p
(k)
S
and p
(k)
R
denote
the transmit power of the source and the FD relay over the
kth subcarrier, respectively. We assume all the noise terms
are complex Gaussian random variables with zero mean and
variance σ
2
=1.
Therefore, considering the DF full-duplex relay in the secure
system [3], the achievable secrecy rate over the kth subcarrier
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