A Survey of Scheduling in 5G URLLC and Outlook for Emerging 6G Systems

Future wireless communication is expected to be a paradigm shift from three basic service requirements of 5th Generation (5G) including enhanced Mobile Broadband (eMBB), Ultra Reliable and Low Latency communication (URLLC) and the massive Machine Type Communication (mMTC). Integration of the three heterogeneous services into a single system is a challenging task. The integration includes several design issues including scheduling network resources with various services. Specially, scheduling the URLLC packets with eMBB and mMTC packets need more attention as it is a promising service of 5G and beyond systems. It needs to meet stringent Quality of Service (QoS) requirements and is used in time-critical applications. Thus through understanding of packet scheduling issues in existing system and potential future challenges is necessary. This paper surveys the potential works that addresses the packet scheduling algorithms for 5G and beyond systems in recent years. It provides state of the art review covering three main perspectives such as decentralised, centralised and joint scheduling techniques. The conventional decentralised algorithms are discussed first followed by the centralised algorithms with specific focus on single and multi-connected network perspective. Joint scheduling algorithms are also discussed in details. In order to provide an in-depth understanding of the key scheduling approaches, the performances of some prominent scheduling algorithms are evaluated and analysed. This paper also provides an insight into the potential challenges and future research directions from the scheduling perspective

Mobile and Wireless Communications

Mobile and Wireless Communications have been one of the major revolutions of the late twentieth century. We are witnessing a very fast growth in these technologies where mobile and wireless communications have become so ubiquitous in our society and indispensable for our daily lives. The relentless demand for higher data rates with better quality of services to comply with state-of-the art applications has revolutionized the wireless communication field and led to the emergence of new technologies such as Bluetooth, WiFi, Wimax, Ultra wideband, OFDMA. Moreover, the market tendency confirms that this revolution is not ready to stop in the foreseen future. Mobile and wireless communications applications cover diverse areas including entertainment, industrialist, biomedical, medicine, safety and security, and others, which definitely are improving our daily life. Wireless communication network is a multidisciplinary field addressing different aspects raging from theoretical analysis, system architecture design, and hardware and software implementations. While different new applications are requiring higher data rates and better quality of service and prolonging the mobile battery life, new development and advanced research studies and systems and circuits designs are necessary to keep pace with the market requirements. This book covers the most advanced research and development topics in mobile and wireless communication networks. It is divided into two parts with a total of thirty-four stand-alone chapters covering various areas of wireless communications of special topics including: physical layer and network layer, access methods and scheduling, techniques and technologies, antenna and amplifier design, integrated circuit design, applications and systems. These chapters present advanced novel and cutting-edge results and development related to wireless communication offering the readers the opportunity to enrich their knowledge in specific topics as well as to explore the whole field of rapidly emerging mobile and wireless networks. We hope that this book will be useful for students, researchers and practitioners in their research studies

실제 전파 환경을 반영한 이동통신 시스템의 최적화 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2016. 8. 김성철.The 4th generation cellular systems, such as LTE (Long-Term Evolution) or LTEAdvanced, significantly improve the speed and the quality of data service as compared to the previous generation systems. In this situation, many applications generating a huge amount of mobile traffic (e.g., high definition (HD) video streaming or cloudbased storage services) have been widely spread. For this reason, the amount of mobile data traffic keeps increasing and sometimes even exceeds the capacity of the system. In order to accommodate explosively increasing mobile data traffic, service providers try to enhance the spatial reuse of wireless resources by deploying more base stations (BSs). Furthermore, small-sized BSs, such as pico and femto BSs, draw much attention as an economical and easy to deploy solution for relieving the load of macro BSs. In this dissertation, I investigate several strategies for optimizing the utilization of cellular systems. Especially, load balancing algorithms, which forcibly redirect users associated with a congested BS thereby experiencing low service quality to nearby BSs, are proposed. As a first step, I propose methods for predicting the service quality (or equivalently the long-term average throughput) of each individual user when multiple users share the same BS. During developing these algorithms, the time-varying characteristic of wireless channel due to multi-path propagation environment is considered to reflect real propagation environments. To this end, the fluctuation phenomenon of the received signal strength is expressed by a random variable, and then, two types of user throughput estimation schemes are developed. The proposed algorithms can be easily implemented in a practical system, and prediction errors are less than 10% for almost every case. Based on the proposed throughput estimation methods, I deal with a user association problem in multi-cell environments. At first, a centralized user association algorithm is developed, where a central node collects all the channel information between every BS and every user and then assigns an optimal base station to each individual user. However, transferring a lot of information to the central node requires excessive uplink feedback and backhaul usage. In addition, such overheads are increased with the density of BSs. For this reason, I propose a decentralized version of user association algorithm, where users themselves choose an optimal BS by considering not only their service quality but also network-wide utilization. The proposed decentralized algorithm especially can be compatible with heterogeneous cellular networks, where there are abundant BSs in the vicinity of each user. Finally, I study an inter-tier interference management problem between macro and small cell BSs in heterogeneous cellular networks. As the name indicates, small cell BSs are designed to consume much less power as compared to conventional macro BSs. For this reason, users associated with small cell BSs experience severe interference from macro BSs. To mitigate inter-tier interference, the eICIC (enhanced Inter Cell Interference Coordination) method was proposed. In this scheme, macro BSs periodically mute data transmission in order to guarantee the signal quality of users at the small cell BSs. In this dissertation, I try to optimize both user association and inter-tier interference management problems. As a result, users change their association and the system alters data transmission strategies in order to optimize network-wide utilization.Chapter 1 INTRODUCTION 1 Chapter 2 USER THROUGHPUT ESTIMATION FOR THE PF SCHEDULING ALGORITHM 5 2.1 Motivation 5 2.2 System Model 6 2.3 Throughput Estimation for a Single Antenna Scenario under the Rayleigh Fading Environment 9 2.4 Throughput Estimation for General Cases 13 2.4.1 Single User MIMO Scheduling Scenario 13 2.4.2 Multiuser MIMO Scheduling Scenario 14 2.5 Implementation Issues 15 2.6 Performance Evaluation and Discussion 16 2.6.1 Simulation Setup 16 2.6.2 Single Antenna Scenario 17 2.6.3 Multiple Antenna Scenario 20 Chapter 3 DYNAMIC USER ASSOCIATION IN MULTI-CELL CELLULAR NETWORKS 24 3.1 Motivation 24 3.2 System Model 25 3.3 Problem Formulation 27 3.3.1 Objective and Optimal Algorithm 27 3.3.2 User Association Problem 29 3.4 Centralized Dynamic User Association Algorithm 31 3.5 Performance Evaluation and Discussion 34 3.5.1 Simulation Setup 34 3.5.2 Throughput Estimation Error in Multi-cell Environments 36 3.5.3 Load Balancing Effect 37 Chapter 4 DECENTRALIZED USER ASSOCIATION METHOD IN HETEROGENEOUS CELLULAR NETWORKS 40 4.1 Motivation 40 4.2 System Model 41 4.3 Problem Formulation 43 4.4 Decentralized User Association Algorithm 44 4.4.1 Overview 44 4.4.2 User Scheduling and Throughput Estimation 46 4.4.3 Broadcast Signal Design 46 4.5 Fully Decentralized Algorithm 52 4.6 Performance Evaluation and Discussion 53 4.6.1 Simulation Setup 53 4.6.2 Unbalanced Traffic Intensity 54 4.6.3 Equal Traffic Intensity 59 4.6.4 Dynamic Scenarios 64 Chapter 5 JOINT OPTIMIZATION OF USER ASSOCIATION & INTER-TIER INTERFERENCE MANAGEMENT IN HETEROGENEOUS CELLULAR NETWORKS 68 5.1 Motivation 68 5.2 System Model 69 5.3 Problem Formulation 70 5.4 Joint Optimization Algorithm 72 5.5 Performance Evaluation and Discussion 74 5.5.1 Simulation Setup 74 5.5.2 Simulation Results 74 Chapter 6 CONCLUSION 80 Appendix 82 Appendix A Proof of Proposition 5.1 82 Appendix B Proof of Proposition 5.3 83 Abstract (In Korean) 93Docto