氏学位名

何 吉名

博士（システム情報科学）

学 位 記 番 号

第４８号

学位授与年月日

令和２年９月１７日

学位論文題目

Secure Communication Protocol Design for Buffer-AidedRelaying Systems

論文審査委員

主査 姜 暁鴻副査 稲村 浩副査 藤野 雄一
副査 和田 雅昭

論文 要 旨With the rapid evolution of information and communication technologies, more
complicated network architectures and more advanced network topologies and accesstechniques are exploited to support the unprecedented growth of data traffic in the 5G
communication. This fact, therefore, leads to an enormous amount of sensitive andconfidential information transmitted via the wireless channels, e.g., financial data,
medical records, and customer files. How to guarantee information security has
attracted increasing concerns from both academia and industry recently. 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 an everlasting security guarantee and no need forcostly secret key distribution/management and complex encryption algorithms. This
thesis, therefore, focuses on the design of communication protocols with PHY security
techniques to secure a buffer-aided relaying system, where relay buffers are adopted tohelp the transmission of information.
We first investigate the secure communication in a two-hop cooperative wirelessnetwork, where a buffer-aided relay helps forward data from the source to destination,
and a passive eavesdropper attempts to intercept data transmission from both thesource and relay. To ensure the transmission security and communication quality of

service (QoS) of the system, we design the novel communication protocols for two casesthat the instantaneous channel state information is available or unavailable at thesource node. For the evaluation of system performance, we then derive the closed-form
expressions of end-to-end secrecy outage probability, system throughput and secrecy
throughput, respectively. Based on the theoretical performance analysis, we further
explore the performance optimization issues, revealing the insightful tradeoffs between
the transmission security and QoS. An iterative algorithm is developed to identify theoptimal setting of link selection parameters, which is helpful for the practicalconfiguration of link selection policies to satisfy various system performancerequirements. Finally, we conduct simulations to validate our theoretical performance
analysis, and also provide extensive numerical results to illustrate the efficiency of the
proposed communication protocols for ensuring secure communication in thebuffer-aided relaying system.
We then investigate the secure communication in a wireless relaying system
where the packet lifetime is limited, multiple buffer-aided relays help the source
forward packets to the destination, and a passive eavesdropper attempts to wiretap thetransmissions over both hops. To guarantee the end-to-end transmission security andtimeliness in the system, we design a novel security/delay-aware communication
protocol that grants transmission nodes different priorities for packet delivery based on
the wireless channel state, real-time buffer state, and packet delay requirement. To
evaluate the performance of the proposed protocol, we then develop a Markov
chain-based theoretical framework to fully characterize the packet occupancy process in
the relay buffers. With the help of this framework, we further derive under two typicalfading channel cases the closed-form expressions for three fundamental system
performance metrics, namely the reliable outage probability, packet discarding
probability and achievable secrecy throughput. Finally, we present extensive simulationand numerical results to validate our theoretical results, as well as to demonstrate theefficiency of the proposed protocol for ensuring secure and timely communication in thebuffer-aided relaying system. The results indicate that the proposed communication
protocol can be flexibly controlled according to different lifetime constraints to satisfy
different performance requirements of the system.

審査結果の要旨
This thesis focuses on the study of secure communication protocol design for buffer-aidedrelaying (BAR) systems. More specifically, this thesis conducts the studies on: 1) the design ofsecure communication protocol for BAR systems, 2) the design of security/delay-aware
communication for BAR systems. In the first study, this thesis proposes the secure communication
protocols for two transmission modes (i.e., adaptive-rate transmission and fixed-rate transmission),
respectively, to satisfy various quality of service (QoS) requirements (i. e., end-to-end secrecy
outage probability, throughput and secrecy throughput). In the second study, this thesis proposes anovel security/delay-aware communication protocol to ensure the security and timeliness of datatransmission for BAR system, and provides analysis on the reliable outage probability, packet
discarding probability and achievable secrecy throughput of the proposed protocol.
・論文の構成Chapter 1 Introduction
Chapter 2 Related Works
Chapter 3 Secure Communication Protocol for Buffer-Aided Relaying Systems
Chapter 4 Security/Delay-Aware Communication Protocol for Buffer-Aided Relaying Systems
Chapter 5 Conclusion
Appendices A, B
・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 explores the PHY security techniques of buffer-aided relaying (BAR) andcooperative jamming to design: 1) Secure communication protocol for BAR systems; 2)
Security/delay-aware communication protocol for BAR systems.
In the first work, we propose two communication protocols to secure the transmission in a
BAR system under adaptive-rate and fixed-rate transmission models. Despite some initial works on
this topic, how to conduct link selection to reconcile the transmission security with the considerationof communication quality of service (QoS) guarantee is still an open issue. As a step forward in thisdirection, this thesis investigates the important trade-off issue between transmission security andcommunication QoS, and designs the corresponding secure communication protocols. The
theoretical framework based on the optimization theory is also established for performance
optimization of the proposed communication protocols.
In the second work, we propose a novel security/delay-aware communication protocol for a
BAR system. It is worth noting that available works are based on the ideal assumption that thepacket lifetime is unlimited. However, to support the critical delay-sensitive applications, it is ofgreat importance to further investigate the protocol design and performance analysis for BAR
networks with the constraint of limited packet lifetime. Hence, we propose a communication
protocol to guarantee both the security and timeliness of packet transmission in a BAR network withlimited packet lifetime constraint. Furthermore, a Markov chain-based theoretical framework isdeveloped to fully characterize the packet occupancy process in buffers such that the overall
performance of the proposed protocol can be theoretically analyzed.
・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 valuable insights.
1. It is expected that the results in this study can shed new insights on the design ofcommunication protocol to achieve secure communication in wireless networks whilesatisfying the various QoS requirements.
2. The novel theoretical frameworks developed in this thesis could be helpful for exploring theperformance in other network scenarios as well.