隨著過去數十年移動裝置產業持續地成長，目前使用的射頻波段逐漸無法支撐大量的流量。可見光網路(Li-Fi)被視為是一種具發展潛力的技術，它可以有效解決射頻網路頻譜吃緊的危機。可見光網路的優勢在於可見光頻譜是射頻頻譜的1300倍，而且具備較佳的安全性。然而，承繼自光無法穿透牆壁和柱子等不透明物體的特性，可見光網路仍有其與生俱來的限制，像是易受障礙物影響以及覆蓋範圍相對射頻網路(Wi-Fi)來的小。於是研究人員提出整合射頻網路與可見光網路技術作為室內無線通訊的新作法，我們稱之為混合式無線網路。此無線網路不僅能互相彌補彼此先天上特性所造成的缺點，還能同時使用兩塊不重疊的頻譜，因此混合式無線網路被認定為室內通訊的有利的選擇。
在混合式無線網路中，負載平衡是一個至為關鍵的問題，目前已有許多探討此議題的研究。然而，既有的研究目標主要著重在吞吐量或是公平性的最大化，使用者滿意度並未得到太多的重視。因此本論文提出兩個旨在最小化滿意度變異數之動態資源配置演算法。最後，模擬結果顯示我們提出的方法在滿意度變異數以及平均滿意度上都有所改善。

As the industry of mobile devices has been steadily growing for the past few decades, the current radio frequency (RF) spectrum is getting insufficient to support the huge traffic demand. Light Fidelity (Li-Fi) is deemed to be a promising technology to resolve RF spectrum crisis. Li-Fi possesses several virtues over Wi-Fi, including 1300 times wider visible light spectrum and superior security. However, inherited from the characteristic that light would fail to penetrate through opaque objects like walls and pillars, Li-Fi has intrinsic limitations, such as sensitivity to object blockage and smaller coverage area relative to Wi-Fi. Then, researchers came up with the idea of integrating both Li-Fi and Wi-Fi technologies as a new approach to indoor wireless communications, which is referred to as hybrid Li-Fi and Wi-Fi networks (HLWNets). HLWNets not only complement the innate characteristics of Li-Fi and Wi-Fi but also simultaneously exploit two non-overlapping spectra. Therefore, HLWNets are considered as a favorable choice for indoor communications.
Load balancing (LB) is a critical issue in HLWNets and a great amount of research has been devoted to dealing with it. Most of them focused on maximization of system throughput or fairness, but user satisfaction did not grab much attention in previous literature. Therefore, we propose two methods aiming at minimization of the variance of user satisfaction. Simulation results show that both of our methods outperform the algorithm proposed in previous literature in terms of variance of satisfaction and average satisfaction.

[1] “Substantial Licensed Spectrum Deficit (2015-2019): Updating the FCC’s Mobile Data Demand Projections,” The Brattle Group, Tech. Rep., Jun. 2015.
[2] I. Stefan, H. Burchardt, and H. Haas, “Area Spectral Efficiency Performance Comparison Between VLC and RF Femtocell Networks,” IEEE International Conference on Communications (ICC) (2013), pp. 3825–3829.
[3] C. Lee et al., “26 Gbit/s LiFi System with Laser-Based White Light Transmitter,” Journal of Lightwave Technology, vol. 40, no. 5, pp. 1432-1439, 1 Mar.1, 2022.
[4] The LiFi Neon Indoor System. https://lifi-neon.de/product/
[5] M. B. Rahaim, A. M. Vegni, and T. D. C. Little, “A Hybrid Radio Frequency and Broadcast Visible Light Communication System,” IEEE GLOBECOM Workshops (GC Wkshps), Dec. 2011, pp. 792–796
[6] S. Shao et al., “An Indoor Hybrid Wi-Fi-VLC Internet Access System,” IEEE 11th Int. Conf. Mobile Ad Hoc Sensor Syst., Oct. 2014, pp. 569–574.
[7] X. Li, R. Zhang and L. Hanzo, “Cooperative Load Balancing in Hybrid Visible Light Communications and Wi-Fi,” IEEE Transactions on Communications, vol. 63, no. 4, pp. 1319-1329, Apr. 2015.
[8] F. Jin, R. Zhang, and L. Hanzo, “Resource Allocation under Delay-Guarantee Constraints for Heterogeneous Visible-Light and RF Femtocell,” IEEE Trans. Wireless Commun., vol. 14, no. 2, pp. 1020–1034, Feb. 2015.
[9] D. A. Basnayaka and H. Haas, “Hybrid RF and VLC Systems: Improving User Data Rate Performance of VLC Systems,” IEEE 81st Veh. Technol. Conf. (VTC Spring), Glasgow, U.K., May 2015, pp. 1–5.
[10] S. Dimitrov and H. Haas, Principles of LED Light Communications: Towards Networked Li-Fi. Cambridge, U.K.: Cambridge Univ., 2015.
[11] X. Wu, M. D. Soltani, L. Zhou, M. Safari and H. Haas, “Hybrid LiFi and WiFi Networks: A Survey,” IEEE Communications Surveys & Tutorials, vol. 23, no. 2, pp. 1398-1420, Secondquarter 2021.
[12] Y. Wang, D. A. Basnayaka, X. Wu, and H. Haas, “Optimization of Load Balancing in Hybrid LiFi/RF Networks,” IEEE Trans. Commun., vol. 65, no. 4, pp. 1708–1720, Apr. 2017.
[13] X. Wu, D. C. O’Brien, X. Deng and J. -P. M. G. Linnartz, “Smart Handover for Hybrid LiFi and WiFi Networks,” IEEE Transactions on Wireless Communications, vol. 19, no. 12, pp. 8211-8219, 2020.
[14] Y. Wang, D. A. Basnayaka and H. Haas, “Dynamic Load Balancing for Hybrid Li-Fi and RF Indoor Networks,” 2015 IEEE International Conference on Communication Workshop (ICCW), 2015, pp. 1422-1427.
[15] X. Wu and H. Haas, “Mobility-Aware Load Balancing for Hybrid LiFi and WiFi Networks,” Journal of Optical Communications and Networking, vol. 11, no. 12, pp. 588-597, Dec. 2019.
[16] M. Kashef, M. Ismail, M. Abdallah, K. A. Qaraqe and E. Serpedin, “Energy Efficient Resource Allocation for Mixed RF/VLC Heterogeneous Wireless Networks,” IEEE Journal on Selected Areas in Communications, vol. 34, no. 4, pp. 883-893, Apr. 2016.
[17] 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, Jan. 2018.
[18] Leo Liberti, “Undecidability and hardness in mixed-integer nonlinear programming,” RAIRO- Operations Research, EDP Sciences, 2019, 53 (1), pp.81-109.
[19] Z. Zeng, M. Dehghani Soltani, Y. Wang, X. Wu and H. Haas, “Realistic Indoor Hybrid WiFi and OFDMA-Based LiFi Networks,” IEEE Transactions on Communications, vol. 68, no. 5, pp. 2978-2991, May 2020.
[20] Y. Wang, X. Wu, and H. Haas, “Load Balancing Game with Shadowing Effect for Indoor Hybrid LiFi/RF Networks,” IEEE Trans. Wireless Commun., vol. 16, no. 4, pp. 2366–2378, Apr. 2017.
[21] X. Wu, M. Safari, and H. Haas, “Access Point Selection for Hybrid Li-Fi and Wi-Fi networks,” IEEE Trans. Commun., vol. 65, no. 12, pp. 5375–5385, Dec. 2017.
[22] R. Ahmad, M. D. Soltani, M. Safari, A. Srivastava and A. Das, “Reinforcement Learning Based Load Balancing for Hybrid LiFi WiFi Networks,” IEEE Access, vol. 8, pp. 132273-132284, 2020.
[23] X. Wu and D. C. O’Brien, “A Novel Machine Learning-Based Handover Scheme for Hybrid LiFi and WiFi Networks,” 2020 IEEE Globecom Workshops (GC Wkshps, 2020, pp. 1-5.
[24] V. S. Rajput, D. R. Ashok and A. Chockalingam, “Joint NOMA Transmission in Indoor Multi-cell VLC Networks,” 2019 IEEE 30th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2019, pp. 1-6.
[25] 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, Mar. 2020.
[26] A. A. Purwita, M. D. Soltani, M. Safari, and H. Haas, “Terminal Orientation in OFDM-Based LiFi Systems,” IEEE Trans. Wireless Commun., vol. 18, no. 8, pp. 4003–4016, Aug. 2019.
[27] M. D. Soltani, A. A. Purwita, Z. Zeng, H. Haas and M. Safari, “Modeling the Random Orientation of Mobile Devices: Measurement, Analysis and LiFi Use Case,” IEEE Transactions on Communications, vol. 67, no. 3, pp. 2157-2172, Mar. 2019.
[28] H. Haas et al., “Introduction to indoor networking concepts and challenges in LiFi,” Journal of Optical Communications and Networking, vol. 12, no. 2, pp. A190-A203, Feb. 2020.
[29] H. Burchardt, S. Sinanovic, Z. Bharucha, and H. Haas, “Distributed and Autonomous Resource and Power Allocation for Wireless Networks,” IEEE Trans. Commun., vol. 61, no. 7, pp. 2758–2771, Jul. 2013.
[30] Y. Meng, J. Li, H. Li and P. Liu, “Graph-Based User Satisfaction-Aware Fair Resource Allocation in OFDMA Femtocell Networks,” IEEE Transactions on Vehicular Technology, vol. 64, no. 5, pp. 2165-2169, May 2015.