臺灣博碩士論文加值系統

隨著行動裝置的普及與物聯網之快速發展，網路存取的使用量大增，第五代行動通訊系統便以處理大量服務需求與兼容異質網路環境為目標，針對彈性的架構與動態的資源分配技術廣泛地討論。例如雲端無線存取網路將傳統基地台的基頻單元佈建在雲端，使基地台間可共享運算資源，以達到最佳化分配。而軟體定義網路則是透過網路管理架構的軟體化與控制模組的中心化，動態且彈性地即時管理網路服務。

在此種集中管理的網路架構下，現有的聯結管理機制並無法受益於此。此外，當裝置數量爆炸性成長，但無線資源仍相當有限的狀況時，在單一基地台底下，大量的聯結建立請求將導致嚴重的碰撞問題，降低資料傳輸的成功率，造成不必要的電力浪費。在多個基地台間，則需更全面性的負載平衡演算法，計算出最佳的聯結關係，提升整體的傳輸量，並避免基地台邊緣的乒乓效應造成的大量且不必要的交遞。因此，在採用雲端無存取網路和軟體定義網路的5G架構下，如何更有效率地控制與分配裝置與基地台之聯結，並處理大量的請求，需要進一步的研究探討。

本論文針對裝置數量超越基地台所能負荷的物理限制情境下，提出將裝置分組的核心想法，以組為單位設計聯結機制，並延遲部分請求，來提升整體網路的效率。在單一基地台底下，針對不移動的機器間通訊，將裝置依地域分組，並由群組組長協調組內的請求排序，來減緩基地台的隨機存取碰撞。在多基地台間，則針對使用者攜帶的移動裝置，透過集中的網路管理架構來取得更全面的資訊以達到負載平衡，在群組移動後，計算出各個基地台最佳的覆蓋範圍，以提升吞吐量。最後在基地台邊緣延遲交遞來減少乒乓效應的發生。

針對上述三種狀況：碰撞、負載平衡以及乒乓效應，論文中透過數學模型分析與模擬實驗來觀察成效，結果顯示在資源供不應求的狀況下，本論文提出之機制皆可透過增加使用者些許的延遲，換取整體網路更好的使用效率。此結果可提供電信業者在使用者需求超出網路硬體限制、資源不足時使用，適用於5G佈建早期的方案。

With the popularity of mobile devices and the advance of Internet of Things, the fifth generation mobile network (5G) requires to meet large amount of service requests in the heterogeneous networks. For this purpose, flexible network architectures with dynamic resource management, such as Cloud Radio Access Network (C-RAN) and Software-Defined Networking (SDN), are widely studied in recent years.

In C-RAN, a novel mobile network architecture, Baseband Units (BBUs) are centralized, virtualized and shared among Remote Radio Units (RRUs) to optimize the resources utilization of base stations. Compared to the traditional networks, SDN separates control plane and data plane to provide a more flexible and programmable network architecture. In this centralized architecture, services can be optimally managed in a global view.

However, existing association control schemes are not designed for the centralized network architecture. Besides, performance issues occur when the amount of devices increase significantly with limited wireless resources. With the large amount of devices, severe collisions occur under one base station, and load imbalance among base stations happens without a centralized association control. At the edge between cells, ping-pong effect may cause unnecessary handovers and signal overload. Therefore, how to design an efficient association control scheme under 5G centralized network architecture to handle the overloaded demands is required to be studied.

The idea of grouping devices is proposed in this dissertation to reduce the computation from the number of devices to the number of group in the association schemes. The collisions at a base station can be reduced by the scheduling in the group. When groups of devices move among base stations, SDN provide global view to find optimal coverages of base stations to increase throughput. At the edge of cell, the execution of handovers are postponed to avoid unnecessary handovers.

This dissertation proposes three schemes to handle the issues mentioned above: collisions, load balancing and ping-pong effect. Mathematical analysis and simulation experiments are conducted to evaluate the performances of these proposed schemes. The results show that the impacts of the issues are reduced with little delay when the demands are significantly higher than the resources that system can supply. The contribution of this dissertation is to provide some suggestions to operators at the early stage of 5G deployment.

摘要 i
Abstract iii
Acknowledgements v
Contents vi
List of Tables ix
List of Figures x
1 Introduction 1
1.1 The 5G Network 1
1.1.1 Software-Defined Networking and Network-Function Virtualization 4
1.1.2 Cloud Radio Access Networks 7
1.2 Studied Issues 11
1.2.1 Collision 12
1.2.2 Load Balancing 14
1.2.3 Ping-pong Effect 14
1.3 Organization of the Dissertation 15
2 Gateway-assisted Two-stage Radio Access Scheme 16
2.1 Introduction to Collision Issue 16
2.2 GATS Scheme 24
2.3 Analytical Model 27
2.3.1 Analytic Model for Basic Scheme 28
2.3.2 Analytic Model for GATS Scheme 30
2.4 Performance Evaluation 35
2.4.1 Effects of Nd on φ and E[Q] 35
2.4.2 Effects of λ and Ng on RA-slot Utilization 38
2.4.3 Effects of λ and Ng on Access Success Probability 39
2.4.4 Effects of λ and Ng on Average Message Delay 40
2.4.5 Discussion about Power Consumption 42
2.5 Summary 43
3 Adaptive Load balancing Scheme 45
3.1 Introduction to Load Balancing Issue 45
3.2 ALB Scheme 48
3.2.1 System Model 48
3.2.2 Flowcharts 51
3.2.3 Load Balancing Algorithm 56
3.3 Performance Evaluation 59
3.3.1 Simulation Model 59
3.3.2 Performance of APs 61
3.3.3 Effects on Users 65
3.4 Summary 69
4 Delay Handover Scheme 71
4.1 Introduction to Ping-pong Effect 71
4.2 DHO Scheme 74
4.2.1 Scenarios 74
4.2.2 Finite State Machine 76
4.3 Analytical Model 78
4.3.1 Timing Diagrams 79
4.3.2 Derivation of E[H(0)] 83
4.3.3 Derivation of E[H(d)] 84
4.3.4 Validation of R(d) 88
4.4 Performance Evaluation 93
4.4.1 Estimation of Simulation Parameters 93
4.4.2 Configuration of Delay Timer Dt 95
4.4.3 Effects of UE Mobility Model 99
4.4.4 Comparisons with Related Works 102
4.5 Summary 106
5 Conclusions and Future Work 107
References 109
Curriculum Vitae 121
Publication List 122

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