Dissertation Resource Allocation for Wireless Powered IoT Network 무선전력 IoT 네트워크를 위한 자원할당 최적화 기법 Graduate School, Myongji University Department of Electronics Engineering Nguyen Tien Tung Dissertation Advisor Yong-Hwa Kim February, 2021 Resource Allocation for Wireless Powered IoT Network Submitted in partial fulfillment of the requirements for the Ph. degree in Electronics Engineering February, 2021 Graduate School, Myongji University Department of Electronics Engineering Nguyen Tien Tung Resource Allocation for Wireless Powered IoT Network Graduate School, Myongji University Department of Electronics Engineering Nguyen Tien Tung We hereby recommend that the dissertation by the above candidate for the Ph. degree in Electronics Engineering be accepted. Chair, Evaluation Committee Prof.
JungKuk Kim Name Signature Member, Evaluation Committee Prof. JaeMin Kim Name Signature Member, Evaluation Committee Prof. Yong-Hwa Kim Name Signature Member, Evaluation Committee Prof. Jong-Ho Lee Name Signature Member, Evaluation Committee Prof.
SeongWook Lee Name Signature February, 2021 (별표 2-4) 인준서 Dissertation Title(22∼26p) Acknowledgement First and foremost, I would like to express my sincere gratitude to my advisor, Professor Yong-Hwa Kim, for guiding, supporting and valuable advice during my study. I was very fortunate and happy to have such a great advisor and mentor for my Ph. I have obtained a great deal of experiences from my advisor. I would also like to extend my appreciation to the rest of my dissertation committee members, including Prof.
JungKuk Kim, Prof JaeMin Kim, Prof. Jong-Ho Lee, Prof. SeongWook Lee for their encouragement and valuable comments. The valuable comments and feedbacks helped me to improve my dissertation.
I would like to thank all Professors at the Department of Electronics Engineering, Myongji University who taught and helped me to complete this dissertation. I would also like to thank Dr. Nguyen Van Dinh, Dr. Pham Quoc Viet for their very kind support.
Special thanks to all my colleagues at the ICT Information Technology Convergence Technology for supporting and sharing everything. Last but not the least, I would like to dedicate this dissertation and show my deepest gratitude and appreciation to my family, my beloved wife, Nguyen Thi Nhu Quynh and my two lovely daughters, Nguyen Ngoc Dan Khue, Nguyen Ngoc Hoa Nhien. Table of Contents List of Figures. iv List of Tables.
Sum Rate Maximization for Multi-user Wireless Powered IoT Network with Non-linear Energy Harvester: Time and Power Allocation .2 Description of the System Model and Energy Harvesting Models .2 Energy Harvesting Model .3 TDMA-enabled WPCN .4 OFDMA-enable WPCN.3 Joint Energy Harvesting Time and Power Allocation for TDMA-enable WPCN .4 Joint Energy Harvesting Time, Subcarrier Allocation and Power Allocation for OFDMA-enabled WPCN. Resource Allocation for Energy Efficiency in OFDMA-Enabled WPCN .2 System Model and Power Consumption Model .2 Power Consumption Model .3 Solution to Energy Efficiency of OFDMA-enabled WPCN. Resource Allocation for AF Relaying Wireless-Powered Networks with Nonlinear Energy Harvester.2 System Model and Problem Description. Summary and Conclusions.
79 Abstract in Korean. 86 iii List of Figures Fig.2 (a) Frame structure of TDMA-enabled WPCN. (b) Frame structure of OFDMA- enabled WPCN.3 Convergence behavior of the proposed algorithms.4 Average sum-rate versus the transmit power of the PB for different numbers of antennas at the AP.5 Average sum-rate versus the distance between the PB and AP.6 EH time versus the distance between the AP and PB. 7 Performance comparison between the proposed algorithms and the equal time allocation (ETA) algorithm.8 Performance comparison between the proposed algorithms and the fixed EH time- based algorithm.9 Performance comparison between the proposed algorithms and the fixed EH time- based algorithm.10 EH time versus the transmit power of the PB.11 Average sum-rate versus the number of users.12 Average sum-rate versus the energy conversion efficiency.13 Average sum-rate versus the EH time.2 Convergence of the proposed algorithm with different number of antennas at the AP.3 Energy efficiency for all schemes and EH durations of the proposed scheme versus PS's transmit power.4 Energy efficiency versus number of users.
1 Illustration of an RWPCN.2 Convergence of the proposed algorithm with different numbers of antennas at the BS and different power levels at the PS.3 The e2e sum throughput of the system for different schemes versus the transmit power of the BS. 4 The e2e sum throughput versus the number of users. 5 End-to-end sum throughput versus the number of antennas at the BS. 75 v List of Tables Table 2.2 Complexity analysis for different schemes .1 Complexity analyses for different schemes .2 Evaluation of user fairness issue.
76 vi Resource Allocation for Wireless Powered Communication Networks Nguyen Tien Tung Department of Electronics Engineering Graduate School, Myongji University Directed by Professor Kim Yong Hwa Our first work aims to maximize the sum rate (SR) of a wireless powered communication network (WPCN), where an energy-constrained access point (AP) harvests energy from the radio-frequency signals transmitted by a power beacon (PB) for assisting user data transmission. In the wireless information transfer (WIT) phase, AP employs the harvested energy to convey independent signals to multiple users through either time- division multiple access (TDMA) or orthogonal frequency-division multiple access (OFDMA). We jointly optimize the energy harvesting (EH) time and the AP power allocation, considering both the conventional linear and practical nonlinear EH models at the AP. The optimization problems of both TDMA- and OFDMA-enabled WPCNs are formulated as nonconvex programs, which are challenging to solve globally.
To achieve an efficient optimal solution to the problem of TDMA-enabled WPCN, we first decompose the original nonconvex problem into three convex subproblems, and then propose a low- complexity iterative algorithm for its solution. For the OFDMA-enabled WPCN, the problem belongs to a difficult class of mixed-integer nonconvex programming due to the vii involvement of binary variables for subcarrier allocation. To overcome this issue, we convert the problem to a quasi-convex problem and then employ a bisection search to obtain the optimal solution. Simulation results are provided to confirm the benefit of jointly optimizing the EH time and the AP power allocation compared to baseline schemes.
The performance of the proposed TDMA-enabled WPCN is shown to be superior to that of the proposed OFDMA-enabled WPCN in terms of SR when the transmit power of PB and the number of antennas of AP are relatively large. The second work considers a wireless powered communication network (WPCN), where an energy-constrained device directly uses harvested energy from a power transfer source to transmit independent signals to multiple Internet of Thing (IoT) users using orthogonal frequency division multiple access (OFDMA). Our goal is to maximize the system energy efficiency (EE) by jointly optimizing the duration of energy harvesting (EH), subcarrier and power allocation. The formulated problem is a mixed integer nonlinear programming (MINLP) problem due to the presence of binary assignment variables, and thus it is very challenging to solve it directly.
By leveraging Dinkelbach method, a very efficient iterative algorithm with closed-form solutions in each iteration is developed, where its convergence is guaranteed. Numerical results show that the proposed algorithm obtains a fast convergence and outperforms baseline algorithms. Notably, they also reveal that the power source should transmit its maximum allowable power to obtain the optimal EE performance. The third work considers a relay-based wireless-powered communication network to assist wireless communication between a source and multiple users.
In particular, the relay adopts a nonlinear energy model to harvest energy from a power beacon and subsequently uses it for information transmission over time division multiple access. Aiming at the viii maximization of end-to-end (e2e) sum throughput, we formulate a novel optimization problem that jointly optimizes the power and time fraction for energy and information transmission. For a simple yet efficient solution for the nonconvex problem, we first convert it to a more computationally tractable problem and then develop an iterative algorithm, in which closed-form solutions are obtained at each iteration. The effectiveness of our proposed approach is verified and demonstrated through simulation results.
Moreover, the results reveal that the source should transmit with its maximum allowable power budget to obtain the optimal e2e sum throughput. Keyword Amplify-and-forward relay, nonconvex optimization, nonlinear energy harvester, IoT, Energy-efficiency, Wireless powered communication networks, TDMA, OFDMA, resource allocation, subcarrier assignment.1 Background With the exponential growth in the number of smart devices, it is predicted that there will be 28 billion connected devices in the globe by 2021 [1]. These devices are identified as Internet of Things (IoT) devices that perform tasks in a wide range of applications including industrial automation, smart home, connected vehicles, environmental monitoring, home intelligent machine, etc [2]. However, from another point of view, the demand of spectrum usage as well as energy consumption has increased dramatically.
Therefore, spectrum utilization and energy consumption management for any wireless communication network become the most critical issues that need to be extensive studied [3]. Moreover, because of the rapidly increase in energy costs and the tremendous carbon footprints of existing systems, an environment-friendly solution, which is radio frequency (RF) energy harvesting technology, for both maintain the network lifetime and enhance the communication quality is proposed [4]. Exploiting the characteristics of RF signals that carry both information and power, energy-constrained devices can be charged without replacing their batteries regularly. This technology has an alternative role for maintaining wireless communication networks, especially wireless IoT networks, deployed in the places with poor or unstable fixed power sources, while reducing costs or danger and -1- increasing convenience [5].
Relying on the technology, two main research directions, such as simultaneous wireless information and power transfer (SWIPT) and wireless powered communication network (WPCN) has been widely investigated. For SWIPT-based network, the two functions, i., information and energy transfer, are implemented in the same source. For WPCN-based network, the information transfer and energy transfer are separately deployed at the different sources. In addition, the performance of EH-based networks needs to be carefully evaluated in terms of resource usage, which is scarce when the number of devices soars., sum-rate, energy efficiency for EH-based networks is critical and has become a hot topic in recent years.
However, resource management in EH-based networks is completely different from convention systems without EH and more challenge in designing solutions. Because apart from the critical and popular issues related to multiple access, spectrum usage, coverage expansion, or energy efficiency have extensively studied in conventional non-EH systems. The time allocation for the EH and the information transmission durations arising in the EH-based networks should also be considered to design.2 Contributions This dissertation has contributed to address spectral and energy efficiency issues in the field of IoT WPCNs. We develop efficient solutions for resource allocation the such networks.
The key contributions are summarized as follows: • Sum rate maximization problem of a multi-users WPCN adopting time-division multiple access (TDMA) and orthogonal frequency-division multiple access -2- (OFDMA) is investigated. This work is the first attempt to design a solution by jointly optimizing the energy harvesting (EH) time and power allocation in transmission phase. The contributions have published in [6]. • Energy efficiency maximization of a multi-users WPCN adopting orthogonal frequency-division multiple access (OFDMA) is considered.
This work proposes an efficient iterative algorithm with closed-form solutions in each iteration to address this issue by leveraging Dinkelbach method. The contributions of this works have appeared in [7]. • Sum throughput maximization of a relay-based WPCN to assist wireless communication between a source and multiple users is evaluated. An efficient algorithm is proposed to determine the solution by jointly optimizing the power and time fraction for energy and information transmission.
The results of this work have published in [8].3 Dissertation Outline The rest of the thesis is organized as follows. In chapter 2, we study the sum rate maximization for multi-user wireless powered IoT network with non-linear energy harvester. In chapter 3, we turn our attention to the resource allocation for energy efficiency in OFDMA-enable WPCN. In chapter 4, we investigate the resource allocation for AF relaying wireless powered networks with non-linear energy harvester.
In chapter 5, a conclusion of this thesis is provided and some directions of research are drawn in the future.