可見光通訊（Light Fidelity, Li-Fi）被認為是室內無線通訊中具有高度發展潛力的技術之一。相較於傳統無線網路（Wireless Fidelity, Wi-Fi），Li-Fi 可利用可見光頻譜進行資料傳輸，具備高速傳輸、高空間重複使用率以及降低射頻頻譜壅塞等優勢。然而，Li-Fi 的覆蓋範圍相對較小，且其傳輸品質容易受到使用者移動、遮蔽以及 line-of-sight 中斷的影響。為了同時結合 Li-Fi 的高傳輸速率與 Wi-Fi 的大範圍覆蓋特性，混合式 Li-Fi/Wi-Fi 網路逐漸成為室內無線通訊的重要研究方向。
在混合式 Li-Fi/Wi-Fi 網路中，移動性管理與換手決策是關鍵且不可避免的問題。若存取點選擇僅依據瞬時訊號品質，可能導致使用者在不同存取點之間頻繁切換，進而產生乒乓換手與額外換手成本。此外，若未將存取點負載納入考量，使用者可能集中連接至少數訊號品質較佳的存取點，造成負載不均與服務品質下降。因此，混合式 Li-Fi/Wi-Fi 網路中的換手決策不應只考慮訊號品質，也應同時納入存取點負載、使用者移動狀態、訊號變化趨勢與換手穩定性。
本論文旨在提出一種兼顧負載平衡與換手穩定性的存取點選擇方法。所提出的方法透過模糊邏輯整合 SINR、使用者速度、SINR 變化量、存取點負載與網路類型等決策因素，並針對 Li-Fi 與 Wi-Fi 不同的傳輸特性分別設計模糊規則庫，使系統能根據不同網路條件給予候選存取點適當的優先分數。此外，本論文加入基於分數差距的遲滯機制與最小停留時間限制，使使用者只有在候選存取點具有足夠優勢且滿足穩定性條件時才執行換手。整體而言，本研究期望在混合式 Li-Fi/Wi-Fi 網路中，提供一個能同時考量使用者服務品質、存取點負載分布與換手穩定性的決策機制。

Light Fidelity (Li-Fi) is considered one of the promising technologies for indoor wireless communication. Compared with traditional Wireless Fidelity (Wi-Fi), Li-Fi uses the visible light spectrum for data transmission and has the advantages of high data rate, high spatial reuse, and reduced radio-frequency spectrum congestion. However, Li-Fi has a relatively small coverage area, and its transmission quality is easily affected by user mobility, blockage, and the interruption of line-of-sight transmission paths. To combine the high data rate of Li-Fi and the wide coverage of Wi-Fi, hybrid Li-Fi/Wi-Fi networks have gradually become an important research direction for indoor wireless communication.
In hybrid Li-Fi/Wi-Fi networks, mobility management and handover decision-making are critical and unavoidable issues. If access point selection is based only on instantaneous signal quality, users may frequently switch between different access points, resulting in ping-pong handovers and additional handover costs. In addition, if access point load is not considered, users may concentrate on a small number of access points with better signal quality, leading to load imbalance and degraded service quality. Therefore, handover decisions in hybrid Li-Fi/Wi-Fi networks should not only consider signal quality, but also take access point load, user mobility, signal variation, and handover stability into account.
This thesis aims to propose an access point selection method that considers both load balancing and handover stability. The proposed method uses fuzzy logic to integrate several decision factors, including SINR, user speed, SINR variation, access point load, and network type. In addition, separate fuzzy rule bases are designed for Li-Fi and Wi-Fi according to their different transmission characteristics, so that the system can assign appropriate priority scores to candidate access points under different network conditions. Furthermore, this thesis introduces a score-based hysteresis mechanism and a minimum dwell time constraint, so that a handover is performed only when the candidate access point has a sufficient advantage and the stability condition is satisfied. Overall, this study aims to provide a decision-making mechanism for hybrid Li-Fi/Wi-Fi networks that jointly considers user service quality, access point load distribution, and handover stability.

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