인프라가 없는 환경에서의 재난 통신망을 위한 동기화 및 그룹 형성 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2016. 8. 이광복.A public safety network (PSN) has been developed as a special class of wireless communication network that aims to save lives and prevent property damage. PSNs have evolved separately from commercial wireless networks satisfying various requirements and regulatory issues associated with them. With growing needs for the transmission of multimedia data, existing voice-centric PSN technologies are facing hurdles in fulllfilling the demand for high capacity and different types of services. Mission-critical requirements for PSNs include the guaranteed dissemination of emergency information such as alarm texts, images, and videos of disasters even in the absence (or destruction) of cellular infrastructure. Many research projects have been launched to meet the mission-critical requirement of PSN, e.g., Aerial Base Station with Opportunistic Links for Unexpected & TEmporary events (ABSOLUTE), Alert for All (Alert4All), Mobile Alert InformAtion system using satellites (MAIA), and so on. The research projects include the emergency communications using satellite communications, aerial eNodeBs, and terrestrial radio access technologies. The approaches take advantages of inherent broadcasting and resilience with respect to Earth damages for disseminations of alert messages. In this dissertation, we limit our interests to terrestrial radio access technologies, e.g., LTE, TETRA, TETRAPOL, and DMR, because PSNs should be operational even in the low-class user equipments (UEs) that are lack of satellite communication functionalities. In Chapter 2 of this dissertation, we propose a distributed synchronization algorithm for infrastructure-less public safety networks. The proposed algorithm aims to minimize the number of out-of-sync user equipments by efficiently forming synchronization groups and selecting synchronization reference UEs in a distributed manner. For the purpose, we introduce a novel affinity propagation technique which enables an autonomous decision at each UE based on local message-passing among neighboring UEs. Our simulation results show that the proposed algorithm reduces the number of out-of-sync UEs by up to 40% compared to the conventional scan-and-select strategy. In Chapter 3 of this dissertation, we study an infrastructure-less public safety network where energy efficiency and reliability are critical requirements in the absence of cellular infrastructure, i.e., base stations and wired backbone lines. We formulate the IPSN group formation as a clustering problem. A subset of user equipments, called group owners (GOs), are chosen to serve as virtual base stations, and each non-GO UE, referred to as group member, is associated with a GO as its member. We propose a novel clustering algorithm in the framework of affinity propagation, which is a state- of-the-art message-passing technique with a graphical model approach developed in the machine learning field. Unlike conventional clustering approaches, the proposed clustering algorithm minimizes the total energy consumption while guaranteeing link reliability by adjusting the number of GOs. Simulation results verify that the IPSN optimized by the proposed clustering algorithm reduces the total energy consumption of the network by up to 31% compared to the conventional clustering approaches.Chapter 1 INTRODUCTION 1 1.1 Distributed Synchronization Algorithm for Infrastructure-less Public Safety Networks 2 1.2 Reliable Low-Energy Group Formation for Infrastructure-less Public Safety Networks 3 1.3 Outline of Dissertation 8 1.4 Notations 8 Chapter 2 Distributed Synchronization Algorithm for Infrastructure-less Public Safety Networks 10 2.1 System Model and Problem Formulation 10 2.2 Distributed Synchronization Algorithm based on Message-passing 17 2.2.1 Preliminaries: affinity propagation 17 2.2.2 Distributed Synchronization Algorithm 19 2.3 Distributed Synchronization Procedures 20 2.4 Simulation Results 25 Chapter 3 Reliable Low-Energy Group Formation for Infrastructure-less Public Safety Networks 42 3.1 System Model and Problem Formulation 42 3.1.1 Channel Model and Network Structure 42 3.1.2 ProblemFormulation 44 3.2 Constrained Clustering Algorithm for IPSN 47 3.2.1 Similarity Modeling 47 3.2.2 Proposed Clustering Algorithm 47 3.3 Determination of initial point 51 3.4 Simulation Results 56 Chapter 4 Conclusion and Future Work 72 4.1 Conclusion 72 4.2 Future Work 73 Bibliography 74 Abstract (In Korean) 82Docto

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