초고밀도밀리미터웨이브셀룰러네트워크에서이중연결기반핸드오버기법

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2019. 2. 박세웅최성현심병효.밀리미터 웨이브를 사용하는 초고밀도 셀룰러 네트워크에서 이동하는 단말은 기존의 네트워크보다 더 많은 핸드 오버를 경험할 것이며, 이는 서비스 중단 시간의 증가와 그로 인한 성능저하를 야기할 것이다. 이런 문제점을 해결하기 위한 솔루 션으로서 다중연결성은 밀리미터 웨이브의 통신 범위를 향상시키고 링크를 보다 견고하게 할 수 있다는 점에서 현재 많이 각광 받고 있는 기법 중 하나이다. 본 논 문에서는 한 개의 단말이 기존의 LTE 셀과의 연결을 유지하면서 두 개의 밀리미터 웨이브 셀과 동시에 연결하는 새로운 네트워크 구조를 제안하며, 이러한 연결성에 의존하는 단말의 이동성을 보장하며 핸드오버의 수를 감소시키기 위하여 이중연결 기반 핸드오버 기법을 제시하였다. 또한 논문에서는 제시한 이중연결기법 기반의 핸드오버 기법과 기존의 단일 연결 기반의 핸드오버 기법을 ns-3 시뮬레이션을 통 해 구현하고 비교하였다. 시뮬레이션 결과는 제안 된 기법이 핸드 오버 비율, 전송 실패율 및 전송 지연 시간을 크게 감소시킨다는 것을 보여주었다. 따라서 본 논문은 이중 연결 기반 핸드 오버 기법이 네트워크의 부담을 줄여주고 더 안정적인 전송을 보장하며 보다 나은 서비스 품질을 제공 할 것이라고 주장한다.Mobile UEs in ultra-dense millimeter-wave cellular networks will experience handover events more frequently than in conventional networks, which will cause increased service interruption time and performance degradation. To resolve this, leveraging multi-connectivity becomes a promising solution in that it can improve the coverage of millimeter-wave communications and support link robustness. In this paper, we propose a dual-connection based handover scheme for mobile UEs in an environment where they are connected simultaneously with two millimeter-wave cells to overcome frequent handover problems, keeping a legacy LTE connection. We compare our dual-connection based scheme with a conventional single-connection based one through ns-3 simulation. The simulation results show that the proposed scheme significantly reduces handover rate, transmission failure ratio and delay. Therefore, we argue that the dual-connection based handover scheme will decrease network controlling overheads, guarantee more reliable transmission and provide better quality-of-service.1 Introduction 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Related Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Contributions and Outline . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Background and System Model 5 2.1 LTE-MmWave Dual Connectivity and Small Cell Handover . . . . . . 5 2.2 Network Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Channel and Propagation Model . . . . . . . . . . . . . . . . . . . . 8 3 Secondary Cell Handover Design for Multi-Connectivity 9 3.1 MmWave-MmWave Dual Connectivity . . . . . . . . . . . . . . . . . 9 3.2 Secondary Cell Handover Scheme . . . . . . . . . . . . . . . . . . . 11 4 Implementation and Performance Evaluation 15 4.1 ns-3 Simulator Implementation . . . . . . . . . . . . . . . . . . . . . 15 4.2 Simulation Setting and Scenario . . . . . . . . . . . . . . . . . . . . 16 4.3 Simulation Results and Discussion . . . . . . . . . . . . . . . . . . . 18 4.3.1 File download completion time . . . . . . . . . . . . . . . . 18 4.3.2 Radio resource usage in user-plane . . . . . . . . . . . . . . . 20 4.3.3 Handover rate and file download failure ratio . . . . . . . . . 20 4.3.4 TCP performance . . . . . . . . . . . . . . . . . . . . . . . . 23 5 Conclusion 25Maste

Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks

Soaring capacity and coverage demands dictate that future cellular networks need to soon migrate towards ultra-dense networks. However, network densification comes with a host of challenges that include compromised energy efficiency, complex interference management, cumbersome mobility management, burdensome signaling overheads and higher backhaul costs. Interestingly, most of the problems, that beleaguer network densification, stem from legacy networks' one common feature i.e., tight coupling between the control and data planes regardless of their degree of heterogeneity and cell density. Consequently, in wake of 5G, control and data planes separation architecture (SARC) has recently been conceived as a promising paradigm that has potential to address most of aforementioned challenges. In this article, we review various proposals that have been presented in literature so far to enable SARC. More specifically, we analyze how and to what degree various SARC proposals address the four main challenges in network densification namely: energy efficiency, system level capacity maximization, interference management and mobility management. We then focus on two salient features of future cellular networks that have not yet been adapted in legacy networks at wide scale and thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and device-to-device (D2D) communications. After providing necessary background on CoMP and D2D, we analyze how SARC can particularly act as a major enabler for CoMP and D2D in context of 5G. This article thus serves as both a tutorial as well as an up to date survey on SARC, CoMP and D2D. Most importantly, the article provides an extensive outlook of challenges and opportunities that lie at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201

Improved Handover Through Dual Connectivity in 5G mmWave Mobile Networks

The millimeter wave (mmWave) bands offer the possibility of orders of magnitude greater throughput for fifth generation (5G) cellular systems. However, since mmWave signals are highly susceptible to blockage, channel quality on any one mmWave link can be extremely intermittent. This paper implements a novel dual connectivity protocol that enables mobile user equipment (UE) devices to maintain physical layer connections to 4G and 5G cells simultaneously. A novel uplink control signaling system combined with a local coordinator enables rapid path switching in the event of failures on any one link. This paper provides the first comprehensive end-to-end evaluation of handover mechanisms in mmWave cellular systems. The simulation framework includes detailed measurement-based channel models to realistically capture spatial dynamics of blocking events, as well as the full details of MAC, RLC and transport protocols. Compared to conventional handover mechanisms, the study reveals significant benefits of the proposed method under several metrics.Comment: 16 pages, 13 figures, to appear on the 2017 IEEE JSAC Special Issue on Millimeter Wave Communications for Future Mobile Network

End-to-End Simulation of 5G mmWave Networks

Due to its potential for multi-gigabit and low latency wireless links, millimeter wave (mmWave) technology is expected to play a central role in 5th generation cellular systems. While there has been considerable progress in understanding the mmWave physical layer, innovations will be required at all layers of the protocol stack, in both the access and the core network. Discrete-event network simulation is essential for end-to-end, cross-layer research and development. This paper provides a tutorial on a recently developed full-stack mmWave module integrated into the widely used open-source ns--3 simulator. The module includes a number of detailed statistical channel models as well as the ability to incorporate real measurements or ray-tracing data. The Physical (PHY) and Medium Access Control (MAC) layers are modular and highly customizable, making it easy to integrate algorithms or compare Orthogonal Frequency Division Multiplexing (OFDM) numerologies, for example. The module is interfaced with the core network of the ns--3 Long Term Evolution (LTE) module for full-stack simulations of end-to-end connectivity, and advanced architectural features, such as dual-connectivity, are also available. To facilitate the understanding of the module, and verify its correct functioning, we provide several examples that show the performance of the custom mmWave stack as well as custom congestion control algorithms designed specifically for efficient utilization of the mmWave channel.Comment: 25 pages, 16 figures, submitted to IEEE Communications Surveys and Tutorials (revised Jan. 2018

사용자 중심의 밀리미터파 통신 시스템을 위한 이동성 인식 분석 프레임워크 및 네트워크 관리 기법

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2021. 2. 박세웅.Millimeter wave (mmWave) communication enables high rate transmission, but its network performance may be degraded significantly due to blockages between the transmitter and receiver. There have been two approaches to overcome the blockage effect and enhance link reliability: multi-connectivity and ultra-dense network (UDN). Particularly, multi-connectivity under a UDN environment facilitates user-centric communication. It requires dynamic configuration of serving base station groups so that each user experiences high quality services. This dissertation studies a mathematical framework and network manament schemes for user-centric mmWave communication systems. First, we models user mobility and mobility-aware performance in user-centric mmWave communication systems with multi-connectivity, and proposes a new analytical framework based on the stochastic geometry. To this end, we derive compact mathematical expressions for state transitions and probabilities of various events that each user experiences. Then we investigate mobility-aware performance in terms of network overhead and downlink throughput. This helps us to understand network operation in depth, and impacts of network density and multi-connection capability on the probability of handover related events. Numerical results verify the accuracy of our analysis and illustrate the correlation between mobility-aware performance and user speed. Next, we propose user-oriented configuration rules and price based association algorithms for user-centric mmWave networks with fully/partially wired backhauls. We develop a fair association algorithm by solving the optimization problem that we formulate for mmWave UDNs. The algorithm includes an access price based per-user request decision method and a price adjustment rule for load balancing. Based on insights from the algorithm, we develop path-aware access pricing policy for mmWave integrated access and backhaul networks. Numerical evaluations show that our proposed methods are superior to other comparative schemes. Our findings from analysis and optimization provide useful insights into the design of user-centric mmWave communication systems.밀리미터파 통신은 고속 전송을 가능하게 하지만 송신기와 수신기 사이의 장애물로 인해 네트워크 성능이 크게 저하될 수 있다. 장애물 효과를 극복하고 링크 안정성을 향상시키는 다중 연결 및 네트워크 초고밀화 두가지 접근법이 있다. 특히 각 사용자가 고품질의 서비스를 경험할 수 있도록 서빙 기지국 그룹의 동적 구성이 필요하므로 초고밀도 네트워크 환경에서 다중 연결은 사용자 중심 통신을 용이하게 한다. 본 논문은 사용자 중심의 밀리미터파 통신 시스템을 위한 수학적 프레임워크와 네트워크 관리 체계를 연구한다. 먼저 다중 연결을 사용하여 사용자 중심의 밀리미터파 통신 시스템에서 사용자 이동성과 이동성 인식 성능 지표를 모델링하고 확률기하분석을 기반으로 하는 새로운 분석 프레임워크를 제안한다. 이를 위해 각 사용자가 경험하는 다양한 이벤트의 상태 전이 확률에 대한 수학적 표현을 도출한다. 그런 다음 네트워크 오버헤드 및 다운 링크 수율 측면에서 이동성 인식 성능을 연구한다. 이를 통해 네트워크 운영에 대한 깊이있는 이해와 네트워크 밀도 및 다중 연결 기능이 핸드 오버와 관련된 이벤트의 확률에 미치는 영향을 이해할 수 있다. 시뮬레이션 결과는 분석의 정확성을 검증하고 이동성 인식 성능과 사용자 속도 간의 상관 관계를 보여준다. 다음으로 완전 또는 부분 유선 백홀이 있는 사용자 중심 밀리미터파 네트워크를 위한 사용자 중심 구성 규칙 및 접속 가격 기반 연결 알고리즘을 제안한다. 밀리미터파 초고밀도 네트워크에 대한 최적화 문제를 해결하여 공정한 연결 알고리즘을 개발한다. 이 알고리즘에는 접속 가격 기반 사용자 별 요청 결정 방법과 로드 밸런싱을 위한 가격 조정 규칙이 포함된다. 위 알고리즘 개발을 통해 얻은 통찰력을 기반으로 밀리미터파 통합 액세스 및 백홀 네트워크를 위한 경로 인식 접속 요금 정책을 개발한다. 수치 평가에 따르면 제안된 방법이 다른 비교 기법보다 우수하다. 분석 및 최적화 결과는 사용자 중심의 밀리미터파 통신 시스템 설계에 대한 유용한 통찰력을 제공할 것 이다.Abstract i Contents iii List of Tables vi List of Figures vii 1 Introduction 1 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Outline and Contributions . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Mobility-Aware Analysis of MillimeterWave Communication Systems with Blockages 5 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.1 Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.2 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.1 Network Model . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.2 Connectivity Model . . . . . . . . . . . . . . . . . . . . . . 10 2.2.3 Mobility Model . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.3 Mobility-Aware Analysis . . . . . . . . . . . . . . . . . . . . . . . . 13 2.3.1 Analytical Framework . . . . . . . . . . . . . . . . . . . . . 13 2.3.2 Urban Scenario with Ultra-Densely Deployed BSs . . . . . . 18 2.3.3 Handover Analysis for Macrodiversity . . . . . . . . . . . . . 22 2.3.4 Normalized Network Overhead and Mobility-Aware Downlink Throughput with Greedy User Association . . . . . . . . 24 2.4 Numerical Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3 Association Control for User-Centric Millimeter Wave Communication Systems 34 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 3.2 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.2.1 Network Model . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.2.2 Channel Model and Achievable Rate . . . . . . . . . . . . . . 39 3.2.3 User Centric mmWave Communication Framework . . . . . . 39 3.3 Traffic Load Management . . . . . . . . . . . . . . . . . . . . . . . . 44 3.3.1 Optimal Association and Admission Control . . . . . . . . . 45 3.3.2 Outage Analysis . . . . . . . . . . . . . . . . . . . . . . . . 51 3.4 Performance Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.4.1 Evaluation Environments . . . . . . . . . . . . . . . . . . . . 53 3.4.2 Performance Comparison . . . . . . . . . . . . . . . . . . . . 55 3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4 Path Selection and Path-Aware Access Pricing Policy in Millimeter Wave IAB Networks 60 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 4.2 System Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.2.1 Geographic and Pathloss Models . . . . . . . . . . . . . . . . 62 4.2.2 IAB Network Model . . . . . . . . . . . . . . . . . . . . . . 63 4.3 Path Selection Strategies . . . . . . . . . . . . . . . . . . . . . . . . 66 4.4 Path-Aware Access Pricing Policy . . . . . . . . . . . . . . . . . . . 69 4.5 Performance Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 72 4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5 Conclusion 80 5.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 5.2 Limitations and Future Work . . . . . . . . . . . . . . . . . . . . . . 82 Abstract (In Korean) 90Docto

Performance Comparison of Dual Connectivity and Hard Handover for LTE-5G Tight Integration in mmWave Cellular Networks

MmWave communications are expected to play a major role in the Fifth generation of mobile networks. They offer a potential multi-gigabit throughput and an ultra-low radio latency, but at the same time suffer from high isotropic pathloss, and a coverage area much smaller than the one of LTE macrocells. In order to address these issues, highly directional beamforming and a very high-density deployment of mmWave base stations were proposed. This Thesis aims to improve the reliability and performance of the 5G network by studying its tight and seamless integration with the current LTE cellular network. In particular, the LTE base stations can provide a coverage layer for 5G mobile terminals, because they operate on microWave frequencies, which are less sensitive to blockage and have a lower pathloss. This document is a copy of the Master's Thesis carried out by Mr. Michele Polese under the supervision of Dr. Marco Mezzavilla and Prof. Michele Zorzi. It will propose an LTE-5G tight integration architecture, based on mobile terminals' dual connectivity to LTE and 5G radio access networks, and will evaluate which are the new network procedures that will be needed to support it. Moreover, this new architecture will be implemented in the ns-3 simulator, and a thorough simulation campaign will be conducted in order to evaluate its performance, with respect to the baseline of handover between LTE and 5G.Comment: Master's Thesis carried out by Mr. Michele Polese under the supervision of Dr. Marco Mezzavilla and Prof. Michele Zorz

Design and Performance Analysis of Next Generation Heterogeneous Cellular Networks for the Internet of Things

The Internet of Things (IoT) is a system of inter-connected computing devices, objects and mechanical and digital machines, and the communications between these devices/objects and other Internet-enabled systems. Scalable, reliable, and energy-efficient IoT connectivity will bring huge benefits to the society, especially in transportation, connected self-driving vehicles, healthcare, education, smart cities, and smart industries. The objective of this dissertation is to model and analyze the performance of large-scale heterogeneous two-tier IoT cellular networks, and offer design insights to maximize their performance. Using stochastic geometry, we develop realistic yet tractable models to study the performance of such networks. In particular, we propose solutions to the following research problems: -We propose a novel analytical model to estimate the mean uplink device data rate utility function under both spectrum allocation schemes, full spectrum reuse (FSR) and orthogonal spectrum partition (OSP), for uplink two-hop IoT networks. We develop constraint gradient ascent optimization algorithms to obtain the optimal aggregator association bias (for the FSR scheme) and the optimal joint spectrum partition ratio and optimal aggregator association bias (for the OSP scheme). -We study the performance of two-tier IoT cellular networks in which one tier operates in the traditional sub-6GHz spectrum and the other, in the millimeter wave (mm-wave) spectrum. In particular, we characterize the meta distributions of the downlink signal-to-interference ratio (sub-6GHz spectrum), the signal-to-noise ratio (mm-wave spectrum) and the data rate of a typical device in such a hybrid spectrum network. Finally, we characterize the meta distributions of the SIR/SNR and data rate of a typical device by substituting the cumulative moment of the CSP of a user device into the Gil-Pelaez inversion theorem. -We propose to split the control plane (C-plane) and user plane (U-plane) as a potential solution to harvest densification gain in heterogeneous two-tier networks while minimizing the handover rate and network control overhead. We develop a tractable mobility-aware model for a two-tier downlink cellular network with high density small cells and a C-plane/U-plane split architecture. The developed model is then used to quantify effect of mobility on the foreseen densification gain with and without C-plane/U-plane splitting