2096 IEEE COMMUNICATIONS LETTERS, VOL. 17, NO. 11, NOVEMBER 2013
Robust Artificial Noise Aided Transmit Design for
MISO Wiretap Channels with Channel Uncertainty
Yanqun Tang, Jun Xiong, Dongtang Ma, and Xiaoying Zhang
Abstract—In this letter, we study the robust artificial noise
(AN) aided transmit design for a multiple-input single-output
(MISO) wiretap channel with a single-antenna eavesdropper. We
consider two uncertainty models for the imperfect channel state
information (CSI) on the main and eavesdropper’s channels at
the transmitter. For the deterministic uncertainty model, we solve
the worst-case secrecy rate maximization (WC-SRM) problem
via semidefinite program (SDP). For the stochastic uncertainty
model, we propose a suboptimal solution to the outage probability
constrained secrecy rate maximization (OP-SRM) problem based
on the robust design for the WC-SRM problem. The simulation
results demonstrate performance improvement of the proposed
worst case robust design as compared to that based on the worst
case method without usage of AN.
Index Terms—Physical layer security, wiretap channel, robust
design, artificial noise, channel uncertainty.
I. INTRODUCTION
R
ECENTLY, physical layer security has drawn much
attention, which exploits the randomness of wireless
propagation channels to enhance the security [1]–[3]. We study
the robust transmit design for multiple-input single-output
(MISO) wiretap channels in the presence of a single-antenna
eavesdropper. Assuming the channel state information (CSI)
at the transmitter is imperfect, we consider two uncertain ty
models for the errors on the main and eavesdropper’s channel,
i.e., the deterministic uncertainty model (DUM) [4]–[8] and
the stochastic uncertainty model (SUM) [6], [9], [10].
We first optimize the worst-case secrecy rate maximization
(WC-SRM) problem for the DUM. In [4], the authors ex-
ploited the saddle-point property to transform the WC-SRM
problem into a convex problem. In [5], the authors studied
the r obust design with the artificial noise (AN) for a MISO
wiretap channel with multiple single-antenna eavesdroppers.
The WC-SRM problem was solved by performing a one-
dimensional lin e search in which a series of semidefinite
programs (SDP) are involved. The work was later extended to
the multi-antenna case for the eavesdroppers in [6]. However,
in the aforementioned works, the CSI on the main channel
was all assumed to be perfect at the transmitter. Furthermore,
in [7] and [8], the authors studied the robust transmit designs
for the DUM on the main and eavesdropper’s channels. The
authors of [7] provided an explicit solution, and the authors of
Manuscript received July 22, 2013. The associate editor coordinating the
re view of this paper and approving it for publication was A. Rabbachin.
The authors are with the College of Electronic Science and
Engineering, National University of Defense Technology, Changsha,
410073, China (e-mail: {tangyanqun, xj8765, dongtangma}@nudt.edu.cn,
zxy
nudt@163.com).
This work was supported in part by the NSFC under Grants 61372099,
61101096 and 61302140.
Digital Object Identifier 10.1109/LCOMM.2013.100713.131673
[8] solved the WC-SRM problem by a SDP solution. However,
the usage of AN has not been considered in [7] and [8]. Thus,
we will fill up the gap in this letter and propose a robust AN
aided transmit design in terms of the input covariance matrices
for information-bearing signal and AN. Similar to [5], [6], [8],
we also solve the WC-SRM problem via SDP. The simulation
results show that our proposed design provides better secrecy
performance than the method in [7].
Then, we optimize the outage probability constrained se-
crecy rate maximization (OP-SRM) problem for the SUM. For
a MISO wiretap channel with multiple single-antenna eaves-
droppers, assuming that the transmitter knows perfect CSI
on the m ain channel and statistical information of the eaves-
dropper’s channel, the authors in [11] derived a closed-form
power allocation for m inimizing secrecy outage probability.
Considering the case o f imperfect CSI on the eavesdropper’s
channel, the authors of [9] presented the projection methods
to optimize the b eamforming schemes without/with usage of
AN, and the authors of [10] provided a safe approximation
method based on the Bernstein-type inequality. Later in [6],
the work was extended to the multi-antenna case for the
eavesdroppers. The mathematical relationship between the
SUM and the DUM derived in [12] was exploited to solve
the OP-SRM problem. However, all the works in [6], [9]–
[11] did not consider the case of imperfect CSI on the main
channel. Thus, we consider the SUM for the CSI errors on the
main and eavesdropper’s channels. Similar to [6], we adopt
the relationship to provide an approximation to the OP-SRM
problem and solve it based on the developed robust design for
the WC-SRM problem.
II. S
YSTEM MODEL
We consider a multiple-input single-output single-antenna
eavesdropper (MISOSE) system where a N
t
-antenna transmit-
ter (Alice) sends confidential messages to a legitimate receiver
(Bob) in the presence of an eavesdropper (Eve). The signals
received at Bob and Eve, respectively, are defined as
y
b
= h
H
x + n
b
,y
e
= g
H
x + n
e
, (1)
where h ∈ C
N
t
and g ∈ C
N
t
denote the channel vectors
for the main channel between Alice and Bob and the eaves-
dropper’s channel between Alice and Eve, respectively. The
scalars n
b
and n
e
denote the zero-mean unit-variance additive
white complex Gaussian noises at Bob and Eve, respectively.
The vector x ∈ C
N
t
denotes the signal transmitted at Alice
with x = s + z,wheres is the confidential message intended
for Bob with covariance matrix Q
s
∈ C
N
t
×N
t
,andz is the
AN created by Alice to confuse Eve with covariance matrix
Q
z
∈ C
N
t
×N
t
.
1089-7798/13$31.00
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2013 IEEE