可見光通訊(Li-Fi)被認為是一個未來發展潛力無限的技術，它可以有效解決射頻網路頻譜短缺的危機。與無線網路(Wi-Fi)相比，Li-Fi 使用的可見光頻譜不受監管，且是射頻頻譜寬度的 10,000 倍。然而，與 Wi-Fi 相比，Li-Fi 最不利的特性是其覆蓋範圍相對較小，這個先天性質驅使了研究人員構想出混合式 Li-Fi 與 Wi-Fi 網路，目的在同時擁有個別單項技術的優點，像是 Li-Fi 的高傳輸速度以及 Wi-Fi 的大覆蓋面積。

移動性管理是混合式 Li-Fi 與 Wi-Fi 網路中一個關鍵且無可避免的問題。未將用戶移動狀況納入考量的存取點選擇方法或負載平衡方案可能會導致頻繁的越區切換，從而降低系統性能。先前曾提出的處理此問題的相關研究通常會利用用戶的軌跡或移動速度等額外訊息以做出精確的決定。由於這類訊息在存取點處不易獲得，為了收集這些訊息會需要倚賴室內定位系統輔助，這無疑會消耗更多的資源和能源，但在準確度方面的提升卻相當有限。

本論文旨在提出一個將用戶移動狀況納入考慮但不使用額外訊息的方法，並以用戶的滿意度作為系統效能的主要評估目標，而非以往常見的系統總吞吐量。傳統方法往往會注重如何最大化系統總吞吐量，但從用戶的角度來看，用戶提出之需求是否能被滿足反倒是第一要務。

Light Fidelity (Li-Fi) is considered as a promising technology to stave off the spectrum crunch problem of the radio frequency (RF) networks. Compared to Wireless Fidelity (Wi-Fi), Li-Fi uses the visible light spectrum which is unregulated and 10,000 times larger than the RF spectrum width. However, the most disadvantageous characteristic of Li-Fi is its relatively small coverage area as compared to Wi-Fi, this intrinsic fact inspires researchers to conceive the idea of hybrid Li-Fi and Wi-Fi networks (HLWN), which aims at possessing the pros of individual technologies, such as the high transmission speed of Li-Fi and the large coverage area of Wi-Fi.

Mobility management is a critical and inevitable issue in an HLWN. An access point selection (APS) method or load balancing (LB) scheme without the consideration of user mobility might causes frequent handovers and thus deteriorate the system performance. Previous work proposed to deal with this issue usually make precise decision with the utilization of additional information like user’s trajectory or movement speed. As such information is not readily available at the access point (AP), to collect such information, an indoor positioning system is required and it certainly would consume more resources and power, but limited improvement in the aspect of accuracy.

In this thesis, the main goal is to develop a method which takes user mobility into consideration but uses no additional information, also, the objective of this work is not about the system throughput, but is users’ satisfactions. Traditional methods often aim to maximize the system throughput, but from users’ perspectives, the most important thing to users is if their requirements are fulfilled.

[1] Cisco, “Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2015-2020,” Cisco White Paper, 2016.
[2] D. C. Sicker and L. Blumensaadt, “The Wireless Spectrum Crunch: White Spaces for 5G?,” Fundamentals of 5G Mobile Networks, pp. 165-187, 2015.
[3] H. Haas, L. Yin, Y. Wang and C. Chen, “What is Li-Fi?,” Journal of Lightwave Technology, vol. 34, no. 6, pp. 1533-1544, 2016.
[4] R. Bian, I. Tavakkolnia, and H. Haas, “15.73 Gb/s Visible Light Communication with Off-the-Shelf Leds,” Journal of Lightwave Technology, vol. 37, no. 10, pp.2418–2424, 2019.
[5] H. Haas, “Visible Light Communication,” 2015 Optical Fiber Communications Conference and Exhibition, pp. 1-72, 2015
[6] M. B. Rahaim, A. M. Vegni and T. D. C. Little, “A Hybrid Radio Frequency and Broadcast Visible Light Communication System,” 2011 IEEE GLOBECOM Workshops, pp. 792-796, 2011.
[7] D. A. Basnayaka and H. Haas, “Hybrid RF and VLC Systems: Improving User Data Rate Performance of VLC Systems,” 2015 IEEE 81st Vehicular Technology Conference, pp. 1-5, 2015.
[8] Z. Zeng, M. Dehghani Soltani, Y. Wang, X. Wu and H. Haas, “Realistic Indoor Hybrid Wi-Fi and OFDMA-Based Li-Fi Networks,” IEEE Transactions on Communications, vol. 68, no. 5, pp. 2978-2991, 2020.
[9] X. Wu, D. C. O’Brien, X. Deng and J. -P. M. G. Linnartz, “Smart Handover for Hybrid Li-Fi and Wi-Fi Networks,” IEEE Transactions on Wireless Communications, vol. 19, no. 12, pp. 8211-8219, 2020.
[10] X. Wu, M. Safari and H. Haas, “Access Point Selection for Hybrid Li-Fi and Wi-Fi Networks,” IEEE Transactions on Communications, vol. 65, no. 12, pp. 5375-5385, 2017.
[11] X. Wu and H. Haas, “Mobility-Aware Load Balancing for Hybrid Li-Fi and Wi-Fi Networks,” IEEE/OSA Journal of Optical Communications and Networking, vol. 11, no. 12, pp. 588-597, 2019.
[12] M. Obeed, A. M. Salhab, S. A. Zummo and M. Alouini, “Joint Power Allocation and Cell Formation for Energy-Efficient VLC Networks,” 2018 IEEE International Conference on Communications, pp. 1-6, 2018.
[13] R. Jiang, Q. Wang, H. Haas and Z. Wang, “Joint User Association and Power Allocation for Cell-Free Visible Light Communication Networks,” IEEE Journal on Selected Areas in Communications, vol. 36, no. 1, pp. 136-148, 2018.
[14] M. A. Dastgheib, H. Beyranvand, J. A. Salehi and M. Maier, “Mobility-Aware Resource Allocation in VLC Networks Using T-Step Look-Ahead Policy,” Journal of Lightwave Technology, vol. 36, no. 23, pp. 5358-5370, 2018.
[15] L. Li, Y. Zhang, B. Fan and H. Tian, “Mobility-Aware Load Balancing Scheme in Hybrid VLC-LTE Networks,” IEEE Communications Letters, vol. 20, no. 11, pp. 2276-2279, 2016.
[16] A. Ibrahim, T. Ismail, K. F. Elsayed, M. S. Darweesh and J. Prat, “Resource Allocation and Interference Management Techniques for OFDM-Based VLC Atto-Cells,” IEEE Access, vol. 8, pp. 127431-127439, 2020.
[17] M. Obeed, A. M. Salhab, S. A. Zummo and M. Alouini, “Joint Optimization of Power Allocation and Load Balancing for Hybrid VLC/RF Networks,” IEEE/OSA Journal of Optical Communications and Networking, vol. 10, no. 5, pp. 553-562, 2018.
[18] X. Wu and D. O’Brien, “A Novel Handover Scheme for Hybrid Li-Fi and Wi-Fi Networks,” 2020 IEEE International Conference on Communications, pp. 1-5, 2020.
[19] ETSI, “LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RCC); Protocol Specification,” 3GPP Technical Specification 36.331 version 13.0.0 Release 13, 2016.
[20] X. Wu and H. Haas, “Load Balancing for Hybrid Li-Fi and Wi-Fi Networks: To Tackle User Mobility and Light-Path Blockage,” IEEE Transactions on Communications, vol. 68, no. 3, pp. 1675-1683, 2020.
[21] Y. Wang, S. Videv and H. Haas, “Dynamic Load Balancing with Handover in Hybrid Li-Fi and Wi-Fi Networks,” 2014 IEEE 25th Annual International Symposium on Personal, Indoor, and Mobile Radio Communication, pp. 575-579, 2014.
[22] J. Wang, Q. Hu, J. Wang, M. Chen and J. Wang, “Tight Bounds on Channel Capacity for Dimmable Visible Light Communications,” Journal of Lightwave Technology, vol. 31, no. 23, pp. 3771-3779, 2013.
[23] X. Wu, C. Chen and H. Haas, “Mobility Management for Hybrid Li-Fi and Wi-Fi Networks in the Presence of Light-Path Blockage,” 2018 IEEE 88th Vehicular Technology Conference, pp. 1-5, 2018.