由於聯網設備的爆炸性增長以及網絡服務的普及化，高效能高穩定性網絡的需求快速增長，無線電頻率逐漸面臨不敷使用的危機。可見光通訊網絡作為一個可能的解決方案被提出。
在室內可見光通訊網絡環境中，數據的傳輸可在可見光光譜上進行。LED燈泡做為發訊器，藉由強度調控的方式以人眼無法辨識的頻率進行訊號傳輸於可見光光譜，而接收端使用光電二極體即可以直接偵測的方式接收訊號。
由於可見光通訊網絡系統內發訊器和接收端分布十分密集，因此系統的表現極易小區間干擾的影響。用戶分群和資源分配的問題對於減少小區間干擾是關鍵。過往已有許多文獻探討這個問題。這些文獻的目的大多是最大化總流量、能源效益或是用戶公平性。在演算法計算複雜度和演算法準確度之間有著互償的關係。本論文提出一個啟發式資源配置演算法，其計算複雜度低且準確度可與非啟發式演算法抗衡。此外，本論文亦提出將分群重疊性列入考量的權重圖著色頻率複用演算法。

Due to the explosive growth of internet devices and plebeianization of internet services, the demand for fast and robust data transmition is higher than ever. The current radio requency (RF) spectrum on which cell phones and WiFi operate is gradually being outgrown by the demand. As a potential solution and relief to this spectrum crunch issue, visible light communications (VLC) has been proposed.
In a indoor VLC system, data transmission occurs on the visible light spectrum. The transmitter, which is an LED bulb, transmit data via intensity modulation (IM). The light intensity is modulated at frequencies out of the perceivable range of the human eye, while the receiving device, equipped with a photodiode (PD) as receiver, is able to receive data via direct detection.
Due to the dense deployment of access points (AP) and user equipments (UE), the performance of VLC systems is highly susceptible to the inter-cell interference (ICI). The user clustering and resource allocation problem of VLC systems is crucial to mitigating the ICI. Significant number of studies have been dedicated to tackle this issues. The goals of previous studies were largely aimed at maximizing throughput or energy effiency, or user fairness. There exists a trade-off relationship between the performance and the computational cost. In this paper, we proposed a heuristic resource allocation method that is low in computational cost and results in performance that is on par with non-heuristic algorithms. In conjunction, we proposed a weight graph-coloring based frequency reuse algorithm which takes overlapping severity into consideration.

[1] H. Haas, “LiFi is a paradigm-shifting 5G technology,”Reviews in Physics, vol. 3, pp. 26-31, Nov. 2018.
[2] H. Haas, L. Yin, Y. Wang and C. Chen, "What is LiFi?," Journal of Lightwave Technology, vol. 34, no. 6, pp. 1533-1544, 15 March15, 2016, doi: 10.1109/JLT.2015.2510021.
[3] Yan Chen, Anthony E. Kelly, and John H. Marsh, "Improvement of indoor VLC network downlink scheduling and resource allocation," Opt. Express, vol. 24, no. 23, pp. 26838-26850, 2016.
[4] D. Mohammed, D. K. D. Bourzig, M. Abdelkim and K. Mokhtar, "Digital data transmission via Visible Light Communication (VLC): Application to vehicle to vehicle communication," 2016 4th International Conference on Control Engineering & Information Technology (CEIT), Hammamet, 2016, pp. 1-5, doi: 10.1109/CEIT.2016.7929059.
[5] Y. Tanaka, S. Haruyama and M. Nakagawa, "Wireless optical transmissions with white colored LED for wireless home links," 11th IEEE International Symposium on Personal Indoor and Mobile Radio Communications. PIMRC 2000. Proceedings (Cat. No.00TH8525), London, UK, 2000, pp. 1325-1329 vol.2, doi: 10.1109/PIMRC.2000.881634.
[6] M. Ayyash et al., "Coexistence of WiFi and LiFi toward 5G: concepts, opportunities, and challenges," in IEEE Communications Magazine, vol. 54, no. 2, pp. 64-71, February 2016, doi: 10.1109/MCOM.2016.7402263.
[7] Y. Wang, X. Wu and H. Haas, "Resource Allocation in LiFi OFDMA Systems," GLOBECOM 2017 - 2017 IEEE Global Communications Conference, Singapore, 2017, pp. 1-6, doi: 10.1109/GLOCOM.2017.8254785.
[8] L. U. Khan, “Visible light communication: Applications, architecture, standardization and research challenges,” Digital Communications and Networks, vol. 3, no. 2, pp. 78-88, May 2017, doi: 10.1016/j.dcan.2016.07.004.
[9] H. Haas, “High-speed wireless networking using visible light,” Spie Newsroom, 2013, doi:10.1117/2.1201304.004773.
[10] S. H. Ali, S. P, G. R. Embedded and M. J, "Design and Evaluation of LiFi Module for Audio Applications," 2018 15th IEEE India Council International Conference (INDICON), Coimbatore, India, 2018, pp. 1-5, doi: 10.1109/INDICON45594.2018.8987134.
[11] V. Aleksieva, H. Valchanov and D. Dinev, "Comparison Study of Prototypes based on LiFi Technology," 2019 International Conference on Biomedical Innovations and Applications (BIA), Varna, Bulgaria, 2019, pp. 1-4, doi: 10.1109/BIA48344.2019.8967478.
[12] J. M. Kahn and J. R. Barry, "Wireless infrared communications," in Proceedings of the IEEE, vol. 85, no. 2, pp. 265-298, Feb. 1997, doi: 10.1109/5.554222.
[13] J. Armstrong and A. J. Lowery, "Power efficient optical OFDM," in Electronics Letters, vol. 42, no. 6, pp. 370-372, 16 March 2006, doi: 10.1049/el:20063636.
[14] Qi Wang, Chen Qian, Xuhan Guo, Zhaocheng Wang, David G. Cunningham, and Ian H. White, "Layered ACO-OFDM for intensity-modulated direct-detection optical wireless transmission," Opt. Express, vol. 23, no. 9, pp. 12382-1239, 2015.
[15] Y. Saito, Y. Kishiyama, A. Benjebbour, T. Nakamura, A. Li and K. Higuchi, "Non-Orthogonal Multiple Access (NOMA) for Cellular Future Radio Access," 2013 IEEE 77th Vehicular Technology Conference (VTC Spring), Dresden, 2013, pp. 1-5, doi: 10.1109/VTCSpring.2013.6692652.
[16] L. Yin, X. Wu and H. Haas, "On the performance of non-orthogonal multiple access in visible light communication," 2015 IEEE 26th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), Hong Kong, 2015, pp. 1354-1359, doi: 10.1109/PIMRC.2015.7343509.
[17] M. Obeed, A. M. Salhab, S. A. Zummo and M. Alouini, "New Algorithms for Energy-Efficient VLC Networks With User-Centric Cell Formation," in IEEE Transactions on Green Communications and Networking, vol. 3, no. 1, pp. 108-121, March 2019, doi: 10.1109/TGCN.2018.2886605.
[18] X. Li, Y. Huo, R. Zhang and L. Hanzo, "User-Centric Visible Light Communications for Energy-Efficient Scalable Video Streaming," in IEEE Transactions on Green Communications and Networking, vol. 1, no. 1, pp. 59-73, March 2017, doi: 10.1109/TGCN.2016.2646820.
[19] X. Li, F. Jin, R. Zhang, J. Wang, Z. Xu and L. Hanzo, "Users First: User-Centric Cluster Formation for Interference-Mitigation in Visible-Light Networks," in IEEE Transactions on Wireless Communications, vol. 15, no. 1, pp. 39-53, Jan. 2016, doi: 10.1109/TWC.2015.2466539.
[20] S. Feng, R. Zhang, W. Xu and L. Hanzo, "Multiple Access Design for Ultra-Dense VLC Networks: Orthogonal vs Non-Orthogonal," IEEE Transactions on Communications, vol. 67, no. 3, pp. 2218-2232, March 2019, doi: 10.1109/TCOMM.2018.2884482.
[21] I. Moreno and C.-C. Sun, "Modeling the radiation pattern of LEDs," Opt. Express, vol. 16, no. 3, pp. 1808-1819, 2008.
[22] T. Komine and M. Nakagawa, "Fundamental analysis for visible-light communication system using LED lights," in IEEE Transactions on Consumer Electronics, vol. 50, no. 1, pp. 100-107, Feb. 2004, doi: 10.1109/TCE.2004.1277847.
[23] Kyongkuk Cho and Dongweon Yoon, "On the general BER expression of one- and two-dimensional amplitude modulations," in IEEE Transactions on Communications, vol. 50, no. 7, pp. 1074-1080, July 2002, doi: 10.1109/TCOMM.2002.800818.
[24] F. Yang, Y. Sun and J. Gao, "Adaptive LACO-OFDM With Variable Layer for Visible Light Communication," in IEEE Photonics Journal, vol. 9, no. 6, pp. 1-8, Dec. 2017, Art no. 7907908, doi: 10.1109/JPHOT.2017.2768435.
[25] X. Zhang, Q. Wang, R. Zhang, S. Chen and L. Hanzo, "Performance Analysis of Layered ACO-OFDM," in IEEE Access, vol. 5, pp. 18366-18381, 2017, doi: 10.1109/ACCESS.2017.2748057.
[26] A. Aldalbahi et al., "Extending ns3 to simulate visible light communication at network-level," 2016 23rd International Conference on Telecommunications (ICT), Thessaloniki, 2016, pp. 1-6, doi: 10.1109/ICT.2016.7500485.