3,577 research outputs found
무μ μ λ ₯ ν΅μ λ€νΈμν¬μμ ν©ν΅μ λ μ΅λν κΈ°λ° μμ ν λΉ κΈ°λ²
νμλ
Όλ¬Έ (λ°μ¬) -- μμΈλνκ΅ λνμ : 곡과λν μ κΈ°Β·μ 보곡νλΆ, 2020. 8. μ΄μ μ°.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.무μ ν΅μ μ΄ νμ¬λ μ€λ§νΈ κΈ°κΈ°μ νλ°μ μΈ μ±μ₯μΌλ‘, μ¬λ¬Ό μΈν°λ· λ€νΈμν¬μ κ°μ μ°¨μΈλ ν΅μ λ€νΈμν¬μμ μꡬνλ μ±λ₯μ μΆ©μ‘±νκΈ° μνμ¬ ν΄κ²°ν΄μΌ ν μ¬λ¬ λ¬Έμ κ° λ°μνμλ€. μ£Όμ λ¬Έμ μ€ νλλ κΈ°κΈ°μ νμ λ λ°°ν°λ¦¬ μ©λμΌλ‘ λ€νΈμν¬κ° μ νλ μκ° λμμλ§ λμν μ μλ κ²μ 극볡νλ κ²μ΄λ€. 무μ μ λ ₯ μ μ‘μ μ΄μ κ°μ΄ μλμ§κ° μ νλ λ€νΈμν¬μ μκΈ° μ§μμ±μ λΆμ¬ν μ μλ ν΄κ²° λ°©λ²μΌλ‘ κ³ λ €λκ³ μλ€. μ¬μ©μλ€μ 무μ μ λ ₯ μ μ‘μ ν΅νμ¬ μ μ© μλμ§μμ μν΄ μ μ‘λλ 무μ μ£Όνμ μ νΈλ‘λΆν° μλμ§λ₯Ό μμ§νκ³ λ°°ν°λ¦¬λ₯Ό μΆ©μ μν¬ μ μλ€. 무μ μ λ ₯ μ μ‘μ΄ κ°λ₯ν 무μ λ€νΈμν¬λ₯Ό μ€κ³νκΈ° μν 체κ³λ‘μ 무μ μ λ ₯ ν΅μ λ€νΈμν¬(Wireless powered communication network, WPCN)κ° μ μλμλ€. WPCNμ κΈ°μ§κ΅κ³Ό μ μ© μλμ§μμ μν μ κ°μ΄ νλ hybrid access-point (H-AP)μ μ¬λ¬ μ¬μ©μλ‘ κ΅¬μ±λλ€. WPCNμμ μ¬μ©μλ€μ νν₯λ§ν¬λ₯Ό ν΅νμ¬ λ¬΄μ μ λ ₯ μ μ‘μΌλ‘ λ°°ν°λ¦¬λ₯Ό μΆ©μ μν€κ³ , μν₯λ§ν¬λ₯Ό ν΅νμ¬ ν΄λΉ μλμ§λ‘ μ 보λ₯Ό μ μ‘νλ€. μ΄ λ, μμμ΄ λΆμ‘±νλ―λ‘ WPCNμ μμ€ν
μ νμ©νκΈ° μν΄μλ ν¨μ¨μ μΈ μ€κ³κ° νμμ μ΄λ€. μ΄λ₯Ό μνμ¬, λ³Έ λ
Όλ¬Έμμλ WPCNμ μν μμ€ν
μ€κ³μ μμ ν λΉμ λνμ¬, νΉν ν΅μ λ κ΄μ μμ νꡬνκ³ μ νλ€. λν, WPCNμ νΉμ§μΈ μ΄μ€ 근거리 λ¬Έμ μμ λΉλ‘―λ λμ μ¬μ©μκ° μ μ‘ μλ 격차λ₯Ό μννκ³ μ νλ€.
μ°μ , νλ ₯ 무μ μ λ ₯ ν΅μ λ€νΈμν¬μ λν΄ λ
Όμνλ€. ν΄λΉ λ€νΈμν¬μμλ μ±λ μνκ° μ’μ μ¬μ©μκ° κ·Έλ μ§ μμ μ¬μ©μμ μ 보λ₯Ό μ€κ³νμ¬ μ¬μ©μ 곡μ μ±μ ν₯μμν¨λ€. κ³ λ €νλ μμ€ν
λͺ¨λΈμμ ν©ν΅μ λμ μ΅λννλ λ° κ° μ¬μ©μμ μλΉμ€ νμ§(Quality of service, QoS)μ 보μ₯νλλ‘ νλ€. μ λ¬Έμ μ μ΅μ ν΄λ₯Ό λΆμνμ¬, WPCNμ΄ μ¬μ©μ νλ ₯ κΈ°λ²μ ν΅νμ¬ μ΄λμ μ»λ 쑰건μ λ°νκ³ , μ΄λ₯Ό κΈ°λ°μΌλ‘ μ¬μ©μ νλ ₯ κΈ°λ²μ μ€μ©μ μΌλ‘ νμ©ν μ μλ ν©ν΅μ λ μ΅λνλ₯Ό μν μλ‘μ΄ μμ ν λΉ μκ³ λ¦¬μ¦μ μ μνλ€. λ€μμΌλ‘, μν₯λ§ν¬μμ λΉμ§κ΅ λ€μ€ μ μ(Non-orthogonal multiple access, NOMA)μ΄ μ μ©λ λ€μ€ μν
λ WPCNμ λνμ¬ λ
Όμνλ€. NOMAλ₯Ό νμ©νλ κ²κ³Ό κ΄λ ¨λ μ¬λ¬ λ¬Έμ λ₯Ό ν΄κ²°νκΈ° μνμ¬, λ€μ€ μν
λ μμ€ν
μ μ΄μ©ν μ¬μ©μ ν΄λ¬μ€ν°λ§ κΈ°λ²μ΄ μΆκ°λ‘ μ μ©λκ³ , μ΄μ λ¨μΌ NOMA μ μ‘μ μ¬μ©μ μκ° κ°μνλ€. ν©ν΅μ λ μ΅λνλ₯Ό μνμ¬ ν΄λ¬μ€ν°λ³ λΉνμ±κ³Ό μκ° λ° μλμ§ μμμ 곡λμΌλ‘ μ΅μ ννλ κ²μ΄ μ΄λ ΅κΈ° λλ¬Έμ, λ¨Όμ λΉνμ±μ μ€κ³ν λ€μ, ν΄λΉ λΉνμ±μ΄ μ μ©λ λ€νΈμν¬μ λνμ¬ μμμ μ΅μ ννλ€. μ΄μ, ν΄λ¬μ€ν°λ³ λΉνμ± μ€κ³μ ν©ν΅μ λ μ΅λνλ₯Ό μν μλ‘μ΄ μκ³ λ¦¬μ¦μ μ μνλ€. λ§μ§λ§μΌλ‘, 무μ ν΅μ μ μ±λ₯μ ν₯μμν¬ ν보 κΈ°μ μ€ νλμΈ μ§λ₯ν λ°μ¬ νλ©΄(Intelligent reflecting surface, IRS)μ΄ λμ
λ WPCNμ κ³ λ €νλ€. IRSλ₯Ό λμ
ν¨μΌλ‘μ¨, μ¬μ©μλ€μ μΆκ°λ‘ μλμ§λ₯Ό μ»μ μ μμΌλ©° μ νΈ μΈκΈ°λ₯Ό λμΌ μ μλ€. κ³ λ €λ μμ€ν
λͺ¨λΈμ ν©ν΅μ λμ μ΅λννλλ‘ IRSμ λΉνμ±κ³Ό μμμ μ΅μ ννλ€. νΉν, μν₯λ§ν¬λ₯Ό μνμ¬ NOMAμ μ§κ΅ λ€μ€ μ μμ΄ κ³ λ €λκ³ , λ λ€μ€ μ μ κΈ°λ²κ°μ μ±λ₯ λΉκ΅κ° μ΄λ£¨μ΄μ§λ€.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
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