Correlated Blocking in mmWave Cellular Networks: Macrodiversity, Outage, and Interference

In this paper, we provide a comprehensive analysis of macrodiversity for millimeter wave (mmWave) cellular networks. The key issue with mmWave networks is that signals are prone to blocking by objects in the environment, which causes paths to go from line-of-sight (LOS) to non-LOS (NLOS). We identify macrodiversity as an important strategy for mitigating blocking, as with macrodiversity the user will attempt to connect with two or more base stations. Diversity is achieved because if the closest base station is blocked, then the next base station might still be unblocked. However, since it is possible for a single blockage to simultaneously block the paths to two base stations, the issue of correlated blocking must be taken into account by the analysis. Our analysis characterizes the macrodiverity gain in the presence of correlated random blocking and interference. To do so, we develop a framework to determine distributions for the LOS probability, Signal to Noise Ratio (SNR), and Signal to Interference and Noise Ratio (SINR) by taking into account correlated blocking. We validate our framework by comparing our analysis, which models blockages using a random point process, with an analysis that uses real-world data to account for blockage. We consider a cellular uplink with both diversity combining and selection combining schemes. We also study the impact of blockage size and blockage density along with the effect of co-channel interference arising from other cells. We show that the assumption of independent blocking can lead to an incorrect evaluation of macrodiversity gain, as the correlation tends to decrease macrodiversity gain

Analysis of Millimeter-Wave Networks: Blockage, Antenna Directivity, Macrodiversity, and Interference

Due to its potential to support high data rates at low latency with reasonable interference isolation because of signal blockage at these frequencies, millimeter-wave (mmWave) communications has emerged as a promising solution for next-generation wireless networks. MmWave systems are characterized by the use of highly directional antennas and susceptibility to signal blockage by buildings and other obstructions, which significantly alter the propagation environment. The received power of each transmission depends on the direction the corresponding antennas point and whether the signal’s path is line-of-sight (LOS), non-LOS (i.e., partially blocked), or completely blocked. A key challenge in modeling blocking in mmWave networks is that, in actual networks, the blocking might be correlated. Such correlation arises, for example, when single transmitter tries to broadcast to pair of receivers that are close to each other, or more generally when they have a similar angle to the transmitter. In this situation, if the first receiver is blocked, it is likely that the second one is blocked, too. This dissertation explores four related but distinct issues associated with mmWave networks: 1) Analytical modeling of networks consisting of user devices and blockages with fixed or random, but independent, locations, 2) The careful characterization of correlated blocking and analysis of its impact on the performance of mmWave networks, 3) The proposed use of macrodiversity as an important strategy to mitigating correlated blocking in mmWave networks and the corresponding analysis, and 4) The proposed use of networks of unmanned aerial vehicles (UAVs) to provide connectivity in urban deployments. This work provides insight into the performance of variety of applications of mmWave communications, ranging from wireless personal area networks (WPAN), device-to-device networks, traditional terrestrial, cellular networks, and the UAV-based networks where the UAVs act as the cellular base stations. A common thread throughout this dissertation is the development of new tools based on stochastic geometry and their application to modeling and analysis. The analysis presented in this dissertation is general enough to find application beyond mmWave networks, for instance the results may also be applicable to systems that use free-space optical (FSO) signaling technologies

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

Effect of correlated building blockages on the ergodic capacity of mmWave systems in urban scenarios

The millimeter waves (mmWave) bands, considered to support the forthcoming generation of mobile communications technologies, have a well-known vulnerability to blockages. Recentworks in the literature analyze the blockage probability considering independence or correlation among the blocking elements of the different links. In this letter, we characterize the effect of blockages and their correlation on the ergodic capacity. We carry out the analysis for urban scenarios, where the considered blocking elements are buildings that are primarily parallel to the streets.We also present numerical simulations based on actual building features of the city of Chicago to validate the obtained expressions.This work was supported by Agencia Estatal De Investigación, Ministerio De Ciencia e Innovación, MCIN / AEI / 10.13039/501100011033 through the Project ROUTE56 - PID2019-104945GB-I00.Peer ReviewedPostprint (author's final draft

Robust cell-free mmWave/sub-THz access using minimal coordination and coarse synchronization

This study investigates simpler alternatives to coherent joint transmission for supporting robust connectivity against signal blockage in mmWave/sub-THz access networks. By taking an information-theoretic viewpoint, we demonstrate analytically that with a careful design, full macrodiversity gains and significant SNR gains can be achieved through canonical receivers and minimal coordination and synchronization requirements at the infrastructure side. Our proposed scheme extends non-coherent joint transmission by employing a special form of diversity to counteract artificially induced deep fades that would otherwise make this technique often compare unfavorably against standard transmitter selection schemes. Additionally, the inclusion of an Alamouti-like space-time coding layer is shown to recover a significant fraction of the optimal performance. Our conclusions are based on an insightful multi-point intermittent block fading channel model that enables rigorous ergodic and outage rate analysis, while also considering timing offsets due to imperfect delay compensation. Although simplified, our approach captures the essential features of modern mmWave/sub-THz communications, thereby providing practical design guidelines for realistic systems