Half-duplex power beacon-assisted energy harvesting relaying networks: system performance analysis

In this work, the half-duplex (HF) power beacon-assisted (PB) energy harvesting (EH) relaying network, which consists of a source (S), Relay (R), destination (D) and a power beacon (PB) are introduced and investigated. Firstly, the analytical expressions of the system performance in term of outage probability (OP) and the system throughput (ST) are analyzed and derived in both amplify-and-forward (AF) and decode-and-forward (DF) modes. After that, we verify the correctness of the analytical analysis by using Monte-Carlo simulation in connection with the primary system parameters. From the numerical results, we can see that all the analytical and the simulation results are matched well with each other

Lower and upper bound intercept probability analysis in amplifier-and-forward time switching relaying half-duplex with impact the eavesdropper

In this paper, we proposed and investigated the amplifier-and-forward (AF) time switching relaying half-duplex with impact the eavesdropper. In this system model, the source (S) and the destination (D) communicate with each other via a helping of the relay (R) in the presence of the eavesdropper (E). The R harvests energy from the S and uses this energy for information transferring to the D. For deriving the system performance, the lower and upper bound system intercept probability (IP) is proposed and demonstrated. Furthermore, the Monte Carlo simulation is provided to justify the correctness of the mathematical, analytical expression of the lower and upper bound IP. The results show that the analytical and the simulation curves are the same in connection with the primary system parameters

Optimal finite horizon sensing for wirelessly powered devices

We are witnessing a significant advancements in the sensor technologies which has enabled a broad spectrum of applications. Often, the resolution of the produced data by the sensors significantly affects the output quality of an application. We study a sensing resolution optimization problem for a wireless powered device (WPD) that is powered by wireless power transfer (WPT) from an access point (AP). We study a class of harvest-first-transmit-later type of WPT policy, where an access point (AP) first employs RF power to recharge the WPD in the down-link, and then, collects the data from the WPD in the up-link. The WPD optimizes the sensing resolution, WPT duration and dynamic power control in the up-link to maximize an application dependant utility at the AP. The utility of a transmitted packet is only achieved if the data is delivered successfully within a finite time. Thus, we first study a finite horizon throughput maximization problem by jointly optimizing the WPT duration and power control. We prove that the optimal WPT duration obeys a time-dependent threshold form depending on the energy state of the WPD. In the subsequent data transmission stage, the optimal transmit power allocations for the WPD is shown to posses a channel-dependent fractional structure. Then, we optimize the sensing resolution of the WPD by using a Bayesian inference based multi armed bandit problem with fast convergence property to strike a balance between the quality of the sensed data and the probability of successfully delivering it

Wireless Powered Communication Networks

The limited life time of batteries is a crucial issue in energy-constrained wireless communications. Recently, the radio frequency (RF) wireless energy transfer (WET) technique has been developed as a new practical method to extend the life time of wireless communication networks. Inspired by this, wireless-powered communication network (WPCN) has attracted much attention. Therefore, in this thesis, we consider practical WET and wireless-powered information transmission in WPCNs. First we investigate a WPCN with two nodes, in which an access point (AP) exchanges information with a wireless-powered user. The user is assumed to have no embedded energy supply and needs to harvest energy from RF signals broadcast by the AP. Differing from existing work that focuses on the design of wireless-powered communication with one-way information flow, we deal with a more general scenario where both the AP and the user have information to transmit. Considering that the AP and user can work in either half-duplex or full-duplex mode as well as having two practical receiver architectures at the user side, we propose five elementary communication protocols for the considered system. Moreover, we define the concept of a throughput region to characterize the tradeoff between the uplink and downlink throughput in all proposed protocols. Numerical simulations are finally performed to compare the throughput regions of the proposed five elementary protocols. To further the study on WPCN, we investigate a wireless-powered two-way relay system, in which two wireless-powered sources exchange information through a multi-antenna relay. Both sources are assumed to have no embedded energy supply and thus first need to harvest energy from the radio frequency signals broadcast by the relay before exchanging their information via the relay. We aim to maximize the sum throughput of both sources by jointly optimizing the time switching duration, the energy beamforming vector and the precoding matrix at the relay. The formulated problem is non-convex and hard to solve in its original form. Motivated by this, we simplify the problem by reducing the number of variables and by decomposing the precoding matrix into a transmit vector and a receive vector. We then propose a bisection search, a 1-D search and an iterative algorithm to optimize each variable. Numerical results show that our proposed scheme can achieve higher throughput than the conventional scheme without optimization on the beamforming vector and precoding matrix at the relay. Due to the high attenuation of RF energy over a long distance, RF based wireless-powered communication is usually designed for low-power scenarios, e.g., wireless-powered sensor networks. Recently, magnetic induction (MI) based WET has been proposed to wirelessly transfer a large amount of energy. Inspired by this, we investigate MI based WET in WPCN. Specifically, we study a MI based wireless-powered relaying network, in which a MI source transmits information to a MI destination, with the help of a MI based wireless powered relay. We propose four active relaying schemes, which consider different relaying modes and different energy harvesting receiver architectures at the relay. We then aim to maximize the end-to-end throughput of each scheme by using a bisection search, a water-filling algorithm, a Lagrange multiplier, quasi-convex programming and an iterative algorithm. We compare the proposed active relaying schemes with passive relaying. Numerical results show that the proposed relaying schemes with a decode-and-forward relaying mode significantly improve the throughput over passive relaying

무선 전력 통신 네트워크에서 합통신량 최대화 기반 자원 할당 기법

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 이정우.With the explosive growth of smart devices equipped with wireless communication, there have been numerous challenges to untangle for supporting user demands in the next generation of communication networks such as Internet of Things networks. One of prime concerns is to overcome the finite lifespan of networks due to the limited battery capacity. Wireless power transfer (WPT) has been considered as a promising solution for providing self-sustainability to energy-constrained networks. WPT enables users to charge their batteries by collecting energy from a radio-frequency signal transmitted by a dedicated energy source. As a framework to the design of wireless networks with WPT, a wireless powered communication network (WPCN) consisting of a hybrid access-point (H-AP) and multiple users has emerged. A H-AP serves users in a WPCN as a base station as well as delivers energy to users as a dedicated energy source. In a WPCN, users charge their batteries by WPT via downlink, and use the energy for uplink transmission. Due to the scarcity of resources, an efficient design is crucial to exploit the system. To support this, I explore system design and resource allocation for WPCNs, especially in the perspective of throughput performance. In addition, I aim to mitigate severe rate disparity which originates from the doubly near-far problem, an inherent characteristic of a WPCN. To begin with, I discuss a cooperative WPCN, in which a user with good channel condition relays information of a user with bad channel condition to enhance user fairness. The sum-throughput is maximized in the considered network subject to a set of quality of service (QoS) requirements. By analyzing the optimal solution, the conditions under which the WPCN benefits from the cooperation are characterized. Based on the new findings, I propose a novel resource allocation algorithm for sum-throughput maximization, which is helpful to practical use of user cooperation. Secondly, I discuss a multi-antenna WPCN where non-orthogonal multiple access (NOMA) transmission is employed in the uplink. To address issues regarding adopting NOMA, user clustering exploiting the multi-antenna system is further applied so that the number of users in a single NOMA transmission is reduced. To deal with the difficulty of jointly optimizing cluster-specific beamforming and time/energy resources for sum-throughput maximization, the beamforming is determined first, and then the resources are optimized for given beamforming. A novel algorithm for cluster-specific beamforming design followed by the sum-throughput maximization algorithm is proposed. Lastly, I consider a WPCN assisted by intelligent reflecting surface (IRS) which has recently received significant attention for its potential of enhancing wireless communication experience. By employing an IRS in a WPCN,users harvest extra energy, and the signal strength of each user can be elevated. For the considered system model, beamforming at the IRS and resources are optimized to maximize sum-throughput. In particular, both NOMA and orthogonal multiple access are considered for uplink transmission, and the performance comparison between the two multiple access schemes are presented.무선 통신이 탑재된 스마트 기기의 폭발적인 성장으로, 사물 인터넷 네트워크와 같은 차세대 통신 네트워크에서 요구하는 성능을 충족하기 위하여 해결해야 할 여러 문제가 발생하였다. 주요 문제 중 하나는 기기의 한정된 배터리 용량으로 네트워크가 제한된 시간 동안에만 동작할 수 있는 것을 극복하는 것이다. 무선 전력 전송은 이와 같이 에너지가 제한된 네트워크에 자기 지속성을 부여할 수 있는 해결 방법으로 고려되고 있다. 사용자들은 무선 전력 전송을 통하여 전용 에너지원에 의해 전송되는 무선 주파수 신호로부터 에너지를 수집하고 배터리를 충전시킬 수 있다. 무선 전력 전송이 가능한 무선 네트워크를 설계하기 위한 체계로서 무선 전력 통신 네트워크(Wireless powered communication network, WPCN)가 제안되었다. WPCN은 기지국과 전용 에너지원의 역할을 같이 하는 hybrid access-point (H-AP)와 여러 사용자로 구성된다. WPCN에서 사용자들은 하향링크를 통하여 무선 전력 전송으로 배터리를 충전시키고, 상향링크를 통하여 해당 에너지로 정보를 전송한다. 이 때, 자원이 부족하므로 WPCN의 시스템을 활용하기 위해서는 효율적인 설계가 필수적이다. 이를 위하여, 본 논문에서는 WPCN을 위한 시스템 설계와 자원 할당에 대하여, 특히 통신량 관점에서 탐구하고자 한다. 또한, WPCN의 특징인 이중 근거리 문제에서 비롯된 높은 사용자간 전송 속도 격차를 완화하고자 한다. 우선, 협력 무선 전력 통신 네트워크에 대해 논의한다. 해당 네트워크에서는 채널 상태가 좋은 사용자가 그렇지 않은 사용자의 정보를 중계하여 사용자 공정성을 향상시킨다. 고려하는 시스템 모델에서 합통신량을 최대화하는 데 각 사용자의 서비스 품질(Quality of service, QoS)을 보장하도록 한다. 위 문제의 최적해를 분석하여, WPCN이 사용자 협력 기법을 통하여 이득을 얻는 조건을 밝히고, 이를 기반으로 사용자 협력 기법을 실용적으로 활용할 수 있는 합통신량 최대화를 위한 새로운 자원 할당 알고리즘을 제안한다. 다음으로, 상향링크에서 비직교 다중 접속(Non-orthogonal multiple access, NOMA)이 적용된 다중 안테나 WPCN에 대하여 논의한다. NOMA를 활용하는 것과 관련된 여러 문제를 해결하기 위하여, 다중 안테나 시스템을 이용한 사용자 클러스터링 기법이 추가로 적용되고, 이에 단일 NOMA 전송의 사용자 수가 감소한다. 합통신량 최대화를 위하여 클러스터별 빔형성과 시간 및 에너지 자원을 공동으로 최적화하는 것이 어렵기 때문에, 먼저 빔형성을 설계한 다음, 해당 빔형성이 적용된 네트워크에 대하여 자원을 최적화한다. 이에, 클러스터별 빔형성 설계와 합통신량 최대화를 위한 새로운 알고리즘을 제안한다. 마지막으로, 무선 통신의 성능을 향상시킬 후보 기술 중 하나인 지능형 반사 표면(Intelligent reflecting surface, IRS)이 도입된 WPCN을 고려한다. IRS를 도입함으로써, 사용자들은 추가로 에너지를 얻을 수 있으며 신호 세기를 높일 수 있다. 고려된 시스템 모델의 합통신량을 최대화하도록 IRS의 빔형성과 자원을 최적화한다. 특히, 상향링크를 위하여 NOMA와 직교 다중 접속이 고려되고, 두 다중 접속 기법간의 성능 비교가 이루어진다.1 Introduction 1 1.1 Related Work 3 1.1.1 Wireless Powered Communication Networks 3 1.1.2 A NOMA-Based WPCN 4 1.2 Contributions and Organization 6 1.3 Notation 8 2 Wireless Powered Communication Networks with User Cooperation 9 2.1 Introduction 10 2.2 System model 14 2.3 Problem Formulation 18 2.4 Optimal Solution of QoS Constrained Sum-Throughput Maximization 21 2.4.1 Case (I): Positive z1, z21 and z22 25 2.4.2 Case (II): Positive z1 and z22, and undefinable z21 35 2.5 QoS Constrained Sum-Throughput Maximization Algorithm 40 2.5.1 Proposed Algorithm 41 2.5.2 Computational Complexity Comparison 42 2.6 Sum-Throughput Maximization with Processing Cost 46 2.7 Simulation Results 48 2.8 Conclusion 53 3 NOMA-Based Wireless Powered Communication Networks with User Clustering 56 3.1 Introduction 57 3.1.1 Throughput Maximization in WPCN 58 3.1.2 User Clustering in NOMA 59 3.1.3 Motivation and Contribution 60 3.2 System model 62 3.3 Optimal Beamforming And Resource Allocation 66 3.3.1 Beamforming Design 67 3.3.2 Sum-Throughput Maximization 69 3.3.3 TDMA-based WPCN with Cluster-specific Beamforming 76 3.4 Simulation Results 79 3.5 Conclusion 87 4 IRS-Assisted Wireless Powered Communication Networks: Comparison of NOMA and OMA 89 4.1 Introduction 90 4.2 System Model 91 4.2.1 NOMA-based WPCN 92 4.2.2 OMA-based WPCN 94 4.3 Sum-Throughput Maximization 94 4.3.1 NOMA-based WPCN with throughput constraints 95 4.3.2 OMA-based WPCN with throughput constraints 98 4.4 Simulation Results 99 4.5 Conclusion 102 5 Conclusion 106 5.1 Summary 106 5.2 Future directions 107 Abstract (In Korean) 117 감사의 글 119Docto