启用NOMA的认知无线电网络中物理层的保密性分析
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The Secrecy Analysis over Physical Layer in
NOMA-enabled Cognitive Radio Networks
Luwei Wei, Tao Jing, Xin Fan, Yingkun Wen, Yan Huo
∗
School of Electronics and Information Engineering, Beijing Jiaotong University, Beijing, China
E-mail:
{16120139, tjing, fanxin, 16111024, yhuo}@bjtu.edu.cn
Abstract—An underlay cognitive radio network (CRN) with
non-orthogonal multiple access (NOMA) is a promising multiple
access scheme to solve the problem of scarce spectrum. This novel
NOMA-enabled underlay CRN can also enhance the transmission
secrecy via employing the deliberately introduced interference.
In this paper, we intend to investigate the secrecy capacity of a
pair of primary users (PUs) and randomly deployed secondary
users (SUs) in the NOMA-enabled underlay CRN. Considering
an existing eavesdropper in the network, we derive a closed-form
expression of the secrecy sum rate (SSR) of all SUs. Then, we
further formulate an SSR optimization problem for both PUs
and SUs and design a simulated annealing algorithm to find the
optimal power allocation. Simulation results demonstrate that the
secrecy performance of all NOMA-enabled SUs is higher than
that of SUs with frequency division multiple access (FDMA). In
other words, the use of the NOMA technology can improve the
secrecy performance of the cognitive radio system.
Index Terms—Underlay cognitive radio networks, non-
orthogonal multiple access, secrecy sum rate, power allocation.
I. INTRODUCTION
With the proliferation of smart mobile devices and the
corresponding apps in the Internet of Things (IoT), the radio
spectrum has fast become a scarce and expensive resource
[1]. Efficient spectrum allocation strategies are significant for
responding to scarce spectrum resources in widely distributed
wireless networks [2]. Two kinds of novel technologies are
studies to satisfy demands of spectrum resources. One is the
cognitive radio (CR) technology that can dynamically select
channels without inter-user interference (overlay CR) or under
certain interference temperature (underlay CR). The other is an
attractive solution, non-orthogonal multiple access (NOMA),
which allows multiple users to transmit signals using the same
time slot and the same carrier.
The above technologies to improve spectral efficiency based
on spectrum sharing may lead to a secure issue during commu-
nications [3]. For example, although an secondary user (SU) in
cognitive radio networks (CRNs) can access to a spectrum of
a primary user (PU), it may also wiretap legitimate signals
due to without appropriate spectrum management policies.
Accordingly, several models to ensure the optimal secure
transmission quality of primary systems in cognitive radio
networks (CRNs) have been investigated [4]–[6]. These works
designed a series of schemes to improve secrecy capacity
based on the cooperative jamming technology. In particular, Li
∗
Yan Huo is the corresponding author.
et al. explored strategies to improve the spectrum efficiency for
multiple-input multiple-output (MIMO) cooperative CRNs and
analyzed the secrecy capacity based on cooperative jamming
schemes in [4]. The authors of [5] studied cooperative secure
communications for a four-node cognitive radio network and
derived the achievable rate of an SU. Moreover, assuming that
SUs do not interfere with PUs’ transmission, [6] designed
a secure cooperative transmission mechanism for both PUs
and SUs. Yet, it is clear that the data rate of SUs with
poor channel states may be small although they obtain some
spectrum resources. As a result, the spectrum efficiency for
CRNs with conventional multiple access methods is low since
an SU with its sensing spectrum cannot be accessed by others.
Fortunately, the NOMA technology is proposed to guarantee
the transmit quality of the users with poor channel [7], [8] and
allow more users to access into one spectrum resource block
at the same time [9]. In [10], Ding et al. analyzed different
receiving qualities of two NOMA systems (i.e., NOMA with
fixed power allocation and CR-inspired NOMA). They proved
that the CR-inspired NOMA could strictly guarantee the
channel quality of a user with a poor channel condition. Com-
pared with the fixed-power-allocation NOMA, the CR-inspired
NOMA can achieve better fairness on spectrum allocation. In
addition, the authors of [11] developed the power allocation for
two SUs in the NOMA-enabled underlay CRN to improve the
spectral efficiency by using interference cancellation. Thus, it
is natural to introduce NOMA into underlay CRNs with power
constraints to greatly improve the spectrum utilization.
Recent studies have paid more attention to development
of efficient spectrum allocation strategies for NOMA-enabled
underlay CRNs. Taking wiretapping issues in wireless com-
munications into consideration, researchers intend to employ
cooperative jamming to achieve secure transmission over
physical layer in the NOMA-enabled underlay CRN [12]. The
authors in [13] analyzed secrecy performance of NOMA-based
networks by new exact and asymptotic expressions for the
security outage probability of one user. For a single-input
single-output (SISO) NOMA system, Zhang et al. presented
an optimal power allocation algorithm to maximize the secrecy
sum rate (SSR) in [14]. In [15], the authors derived new
closed-form expressions of the outage probability and ana-
lyzed the transmission performance in a large-scale NOMA-
enabled underlay CRN with randomly deployed users.
Although the above studies shed the light on their fields,
the solution of secure transmission for the NOMA protocol is
978-1-5386-3180-5/18/$31.00 ©2018 IEEE
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