This edition first published 2020
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To my wife Hyeeun,
daughter Naul,
son Hanul
and
mother Hyungsuk
From 1G to 4G cellular networks, the main target of development was system capacity improvement. Thus, the current cellular systems have very efficient system architectures in terms of system capacity. However, it is not an optimal solution in terms of other system parameters (latency, energy efficiency, connection density, etc.). 5G systems have ambitious goals, and 5G applications cover various areas such as eHealth, factory automation, automated vehicles, critical communication, and so on. In recent mobile communications and networks events, leading mobile phone vendors and network equipment vendors have exhibited more than smartphones and networks. Connected and automated vehicles, smart cities, drones, and factory automations were highlighted, and they are highly related to latency, energy efficiency, mobility, and connection density. Thus, 5G systems no longer focus on system capacity only. Many other system parameters should be improved significantly. 5G applications can be classified into (i) enhanced mobile broadband communication (eMBB), (ii) ultra‐reliable and low latency communication (URLLC), and (iii) massive machine type communication (mMTC). Their target system parameters are different in accordance with use cases. The key metrics of eMBB, URLL, and mMTC are system capacity, latency, and connection density, respectively. They also have different system requirements and architectures. In this book, we analyze and design 5G communication and network systems from a different perspective. We introduce mathematical tools and find an optimal, suboptimal or tradeoff point to meet the system requirements.
There is a big gap between theoretical design and practical implementation. Countless papers are published every year to optimize wireless communication systems in academia, but their practical use is very limited in industry. The reasons why they have a big gap can be summarized as simple system models, limited target parameters, and lack of a holistic design. First, optimization algorithms are applied under simple system models. The simple system models sometimes include unrealistic system parameters such as perfect channel state information, limited numbers of users, no interferences, and so on. They allow optimization algorithms to solve the problem nicely, but they are far from practical solutions. Secondly, each optimization algorithm targets only one system parameter (for example, energy efficiency) while other system parameters (for example, system throughput, latency, complexity, and so on.) are not close to an optimal solution, and are sometimes even worse. Thirdly, one optimization algorithm is applied to a small part or component of a communication architecture and it finds an optimal solution. From a holistic point of view, the solution is not optimal. For example, although we design an energy‐efficient multicarrier modulation scheme and achieve significant energy savings, the other parameters might be worse and bring a higher energy consumption to another component. The architecture design is highly related to many other components of communications and networks. Sometimes there is a trade‐off relationship and sometime there is no optimal point. One decision in one design step is highly related to another decision in the next design step. It is very difficult to optimize many metrics such as complexity, system capacity, latency, energy efficiency, connection density, and flexibility. Thus, a wireless communication system designer makes a decision subjectively and empirically. It is a big challenge to reduce the gap between theoretical design and practical implementation.
This book introduces mathematical methods and optimization algorithms for wireless communications and networks and helps audiences find an optimal, suboptimal or tradeoff solution for each communication problem using the optimization algorithms. By this approach, audiences can understand how to obtain a solution under specific conditions and realize the limit of the solution.
This book is not a math book, and we skip the proofs of mathematical formulae and algorithms. This book focuses on design and optimization for 5G communication systems including eMBB, URLLC, and mMTC. The organization of the book is as follows: in Part I, mathematical methods and optimization algorithms for wireless communications are introduced. It will provide audiences with a mathematical background including approximation theory, LS estimation, MMSE estimation, ML and MAP estimation, matrix factorization, linear programming, convex optimization, gradient descent method, supervised and unsupervised learning, reinforcement learning, and so on. In Part II, 5G communication systems are designed and optimized using the mathematical methods and optimization algorithms. For example, the key metric of URLLC is latency. The latency is highly related to many PHY/MAC/network layer parameters such as frame size, transmit time interval, hybrid automatic repeat request (HARQ) processing time, round trip time, discontinuous reception, and so on. We look into them to minimize the latency. In addition, we design some key components using the optimization algorithms. It covers 5G NR, multiple input multiple output (MIMO), 5G waveforms (OFDMA, FBMC, GFDM, and UFMC), low‐density parity‐check (LDPC), short packet transmission theory, latency analysis of 4G and 5G networks, MEC optimizations, robust optimization, power control and management, wireless sensor networks, and so on. The main purpose of this book is to introduce mathematical methods and optimization algorithms and design 5G communication systems (eMBB, URLLC, mMTC) with a different perspective.
I am pleased to acknowledge the support of the VTT Technical Research Centre of Finland and John Wiley & Sons, and also the valuable discussion of my colleagues and experts in EU projects Flex5Gware, 5G‐Enhance, and 5G‐HEART. I am grateful for the support of my family and friends.
Haesik Kim
VTT Oulu, Finland