氏学位名

Zhang Yuanyu

名博士（システム情報科学）

学 位 記 番 号

第３４号

学位授与年月日

平成２９年３月２３日

学位論文題目

Physical Layer Security Performance Study for Wireless Networks
with Cooperative Jamming

論文審査委員

主査 姜 暁鴻副査 藤野 雄一
副査 稲村 浩副査 和田 雅昭論

文 要 旨

Due to the rapid development of wireless communication technology andwidespread proliferation of wireless user equipment, wireless networks become
indispensable for lots of applications in daily life. The broadcast nature of wirelessmedium makes information exchange in such networks vulnerable to eavesdropping
attacks from malicious eavesdroppers, resulting in network security one of the major
concerns for system designers. Physical layer (PHY) security has been proposed as one
promising technology to provide security guarantee for wireless communications, owing
to its unique advantages over traditional cryptography-based mechanisms, like aneverlasting

security

guarantee

andnoneedfor

costlysecretkey

distribution/management and complex encryption algorithms. This thesis therefore
focuses on the PHY security performance study for wireless networks with cooperative
jamming (a typical PHY security technique), where non-transmitting helper nodes
generate jamming signals to counteract eavesdropping attacks.
We first explore the PHY security performances of small-scale wireless networks
with non-colluding (i.e., independently-operating) eavesdroppers, for which we study
the eavesdropper-tolerance capability (ETC) of a two-hop wireless network with one
source-destination pair, multiple relays and multiple non-colluding eavesdroppers. We
consider two relay selection schemes to forward the packets from the source to thedestination, i.e., random relaying and opportunistic relaying. For both relaying schemes,we first derive the secrecy outage probability (SOP) and transmission outage probability(TOP) of the network by applying the classical Probability Theory. We then determine
the ETC of the network by solving an optimization problem that aims to maximize thenumber of eavesdroppers that can be tolerated under a certain SOP constraint and acertain TOP constraint. Finally, we present extensive simulation and numerical results
to demonstrate the validity of the theoretical analysis and also to illustrate ourtheoretical findings.
We then investigate the PHY security performances of small-scale wirelessnetworks with colluding (i.e., cooperatively-operating) eavesdroppers, for which westudy the SOP performance of a two-hop wireless network with one source-destination
pair, multiple relays and multiple colluding eavesdroppers. Based on the classical
Probability Theory, we first conduct analysis on the SOP of the simple non-colludingcase. For the SOP analysis of the more hazardous M-colluding scenario, where any M
eavesdroppers can combine their observations to decode the message, the techniques ofLaplace transform, keyhole contour integral, and Cauchy Integral Theorem are jointly
adopted to work around the highly cumbersome multifold convolution problem involvedin such analysis, such that the related signal-to-interference ratio modeling for all
colluding eavesdroppers can be conducted and thus the corresponding SOP can beanalytically determined. Finally, simulation and numerical results are provided todemonstrate the validity of the theoretical analysis also to illustrate our theoreticalfindings.
Finally, we examine the cooperative jamming design issue in large-scale wirelessnetworks. Towards this end, we propose a friendship-based cooperative jamming
scheme to ensure secure communications in a finite Poisson network with one source
destination pair, multiple legitimate nodes and multiple eavesdroppers distributed
according to two independent and homogeneous Poisson Point Processes (PPP),respectively. The jamming scheme consists of a Local Friendship Circle (LFC) and aLong-range Friendship Annulus (LFA), where all legitimate nodes in the LFC serve as
jammers, but the legitimate nodes in the LFA are selected as jammers through threelocation-based policies. To understand both the security and reliability performances ofthe proposed jamming scheme, we first model the sum interference at any location in
the network by deriving its Laplace transform under two typical path loss scenarios.
With the help of the interference Laplace transform results, we then derive the exact
expression for the TOP and determine both the upper and lower bounds on the SOP,
such that the overall outage performances of the proposed jamming scheme can bedepicted. Finally, we present extensive numerical results to validate the theoreticalanalysis of TOP and SOP and also to illustrate the impacts of the friendship-based
cooperative jamming on the network performances.

審査結果の要旨

This thesis focuses on the fundamental physical layer (PHY) security performance study for
wireless networks with the security technique of cooperative jamming. More specifically, this thesis
conducts the studies on: 1) the PHY security performance of small-scale wireless networks with
non-colluding eavesdroppers, 2) the PHY security performance of small-scale wireless networks
with colluding eavesdroppers, and 3) the cooperative jamming design for large-scale wirelessnetworks. In the first study, this thesis presents an attempt on the analysis of eavesdropper-tolerance
capability of two-hop wireless networks under two relaying schemes (i.e., random and opportunisticrelaying). In the second study, this thesis tackles the technical challenge of exactly modeling thedistribution of aggregate signal-to-interference ratio of colluding eavesdroppers and provides
analysis on the secrecy outage probability (SOP) of two-hop wireless networks with colluding
eavesdroppers. In the last study, this thesis proposes a friendship-based cooperative jamming scheme
for Poisson Networks and studies the related performances of SOP and transmission outageprobability.
・論文の構成Chapter 1 Introduction
Chapter 2 Related Works
Chapter 3 Physical Layer Security Performance Study of Small-Scale Wireless Networks withNon-Colluding Eavesdroppers
Chapter 4 Physical Layer Security Performance Study of Small-Scale Wireless Networks with
Colluding Eavesdroppers
Chapter 5 Cooperative Jamming Design in Large-Scale Wireless Networks
Chapter 6 Conclusion
Appendices A, B, C.1, C.2, C.3, C.4
・研究目的の妥当性，従来の手法との比較においての有意性，および理論・実験手法の新規性
This thesis studied the fundamental security performance of wireless networks with physicallayer (PHY) security technology. More specifically, this thesis focuses on the PHY security
technique of cooperative jamming and conducts the studies of: 1) the PHY security performance ofsmall-scale wireless networks with non-colluding eavesdroppers, 2) the PHY security performanceof small-scale wireless networks with colluding eavesdroppers, and 3) the cooperative jamming
design for large-scale wireless networks.
In the first work, we study the eavesdropper-tolerance capability (ETC) of two-hop wirelessnetworks. Despite much work has been done on this topic, the exact ETC of such networks remainsuninvestigated. This thesis represents a first attempt to address this issue. By applying the classical
Probability Theory, this thesis first provides the exact models for the transmission outage probability(TOP) and secrecy outage probability (TOP), then formulates the ETC as an optimization problem
under the constraints of SOP and TOP, and finally obtains the exact ETC result by solving theoptimization problem based on both the Stochastic Ordering theory and method of proof bycontradiction.
In the second work, we study the SOP performance of two-hop wireless networks withcolluding eavesdroppers. Despite much work on this topic, the SOP study with the consideration ofcooperative jamming technique remains an open problem due to the technical challenge of exactlymodeling the distribution of the aggregate signal-to-interference ratio of colluding eavesdroppers.
We conduct such a SOP study with the consideration of cooperative jamming and tackle the above
technical challenge by jointly applying the mathematical tools of Laplace transform, keyhole contour
integral and Cauchy Integral Theorem.
In the last work, we consider the cooperative jamming design issue with the consideration ofsocial relationships. Available works on this topic suffer from two main limitations: they usuallyadopt some over-simplified social relationship models (e.g., social trust and social tie) that fail tocapture the geometry-based social behaviors; and they usually consider some over-simplified
network scenarios with only one eavesdropper and several jammers (i.e., nodes that send jamming
signals to suppress eavesdroppers). To address these limitations, we consider a more general
friendship model and a large-scale wireless network with the Poisson Point Process. We propose afriendship-based cooperative jamming scheme that selects nodes that are friends of the transmitter as
jammers, and also propose three jammer selection policies based on the geometry properties of thenetwork. Based on the theory of Stochastic Geometry, we conduct studies on the TOP and SOP
performances of the concerned large scale networks with the proposed cooperative jamming scheme.
・得られた知見のシステム情報科学の分野における意義
The results of this thesis provide the following insights.
1. The studies conducted in this thesis will be helpful for the design of secure wireless networks.
The results in the ETC study illustrate the tradeoffs among security, reliability and ETC of awireless network, which can serve as a guideline for the design of wireless networks withvarious performance requirements.

2. The results in the SOP study under colluding eavesdroppers shop the impact of eavesdropper
collusion on network security, and thus shed light on the design of new PHY security
techniques to effectively counteract such more hazardous eavesdropping attacks.
3. The results in this thesis help us to understand the potentials of cooperative jamming tschniquein counteracting the eavesdropping attacks. In particular, the proposed friendship-based
cooperative jamming scheme could open a new approach for the design of more powerfulcooperative jamming schemes by fully exploring not only the social behavior but also otherinherent properties of wireless networks.