高速無線光通訊的研究與應用

Research of High-Speed Optical Wireless Communication and Application

魏良育(Liang-Yu Wei)

指導教授 ： 鄒志偉

國立交通大學/電機學院/光電工程系所/博士(2019年)

摘要

2019年被視為第5代行動通訊(5G)元年，意味著行動通訊將邁入下一個里程碑。除了提供超高數據容量外，新型設施勢必要具備高層級的安全保護、幾乎零的延遲、大量設施的連通性及高比率能源節省的特性。由於射頻頻譜的壅塞及其費用、頻寬、規則、干擾的限制，已無法滿足未來高流量5G服務的需求。與射頻頻譜相比，光無線傳輸為主的系統能提供高容量的傳輸係因其無需執照的頻譜和較大的頻寬。然而，於光無線通訊的範疇使用可見光頻段即為眾所皆知的可見光通訊。可見光通訊的應用端包含了智慧家居、物聯網(IoT)、高精準度定位、水下通訊及機器與機器間(M2M)通訊。思科(Cisco)指出於2022年時，全球行動數據流量在機器與機間連結部份將達到52%的年均複合增長率(CAGR)，這也顯示了機器間通訊在未來生活中俱有極重要的地位。本論文中，我們發展了雙向可見光通訊系統，來達成高速的機器間傳輸。因此，可見光通訊被視為一具有潛力的方案，來減輕未來巨量連結5G網路中，射頻為主系統的負擔。
第2章節中，包含了開關鍵控(OOK)、四階脈衝振幅(PAM-4)及正交振幅調變格式的基礎介紹。且運用不同的技術來了解如何於光無線通訊系統中增加傳輸速率。第3章節中，我們首先提出並示範；利用單一垂直空腔面射型雷射(VCSEL)配合一聲光調制器(AOM)，可達到10.6 Gbit/s的正交分頻多工(OFDM)的下載速率與2 Mbit/s之再調制開關鍵控上傳速率。雙向系統中，上傳與下載的傳輸距離則均為3公尺。接著，引入預失真技術來增加上傳的速率到將近2.8倍，數值模擬則用來證明其通道頻寬的限制。值得一提的是，上傳的速率係因聲光調制器3-dB頻寬的限制。若是提高3-dB頻寬再引入預失真的技術，則能提供一高速雙向可見光通訊系統並用於機器與機器間的連結。
第4章節中，我們提出了一20.231 Gbit/s速率之紅/綠/藍雙向可見光通訊系統。此外，我們也利用了偏振多工的技巧來示範了一40.665 Gbit/s速率之紅/綠/藍雷射二極體為主的可見光通訊系統。此二系統均有能力提供機器間的高速傳輸，並應用於電腦伺服器室與數據中心之類的場所。第5章節中，2.898 Gbit/s速率之白光雷射同時提供了照明與通訊，我們也研究了x軸與y軸所能容忍的偏移範圍特性分析。接著，我們提出並示範了總速率為2.2333 Tbit/s之光無線傳輸為主的虛擬光纖-光接取網路，並用來提供給室內的白光可見光通訊使用。最後，我們也示範了傳輸距離1.5公尺下，6.915 Gbit/s的可見光通訊系統。
本論文提出了幾個可見光與紅外-自由空間光學的架構，及其應用於光無線傳輸領域。透過本論文，我們期待光無線通訊為主的系統應用，能在未來5G的網路中，幫忙卸載射頻為主系統的負擔。

關鍵字

無線光通訊 ； 可見光通訊 ； 正交分頻多工 ； 第五代行動通訊 ； 虛擬光纖-光接取網路

並列摘要

This year (2019) is regarded as the first year of fifth-generation (5G) mobile communication, which means that mobile communication will step to the next milestone. Apart from offering ultra-high data capacity, newer infrastructures must possess the characteristic of high-level security protection, near-zero latency, massive facilities connectivity, and high-ratio energy saving. Due to radio frequency (RF) spectrum is congested and has its limitation of expense, bandwidth, regulation, and interference, it’s insufficient to fulfil the requirement of future high traffic 5G services. Compare with RF spectrum, OWC-based system can provide high-capacity transmission on account of the unlicensed spectrum and wider bandwidth. However, using visible light band in OWC field is the well-known technique called visible light communication (VLC). VLC has numerous applications in smart-home, internet-of-things (IoT), high precision positioning, underwater transmission, and machine-to-machine (M2M) communication. Cisco indicates that connection of M2M has CAGR of 52% in global mobile data traffic by 2022, which means that M2M communication has a crucial position in our future lives. In this dissertation, we developed bi-directional VLC system to realize high-speed M2M transmission. Hence, VLC has considered as a potential solution to mitigate the loading of RF-based system in future massive connective 5G network.
In chapter 2, basic introduction for modulation format of OOK, PAM-4 and QAM is included. Different techniques are applied to understand how to increase the data rate for OWC system. In chapter 3, using a single VCSEL with an AOM to reach 10.6 Gbit/s OFDM downstream and 2 Mbit/s remodulated OOK upstream is first propsed and demonstrated. Transmission distance of downstream and upstream for this bi-directional system is both 3 m. Then, pre-distortion technique is introduced to enhance the upstream remodulated data rate until ~2.8 times, numerical simulations are also performed to prove its limitations. It’s worth to said that the upstream data rate is limited by 3-dB bandwidth of AOM. If the 3-dB bandwidth is increased then introducing the technique of pre-distortion, it can supply high-speed bi-directional VLC system for M2M connection.
In chapter 4, we proposed a 20.231-Gbit/s tricolor bi-directional R/G/B VLC system. Moreover, a 40.665 Gbit/s tricolor R/G/B LD-based VLC system with technique of polarization-multiplexed is also demonstrated. Both of two systems are able to support high data rate for M2M connection in computer sever room or data center. In chapter 5, 2.898 Gbit/s phosphor-based white-light LD provides both illumination and communication, the performance tolerance offset ranges in both x and y-directions are also studied. Then, a 2.233 Tbit/s virtual-fiber optical-access-network OWC-based system is proposed and demonstrated for supporting indoor white-light VLC. Finally, a 6.915 Gbit/s white-light VLC system is also demonstrated at the transmission distance of 1.5 m.
This dissertation proposed several VLC and IR-FSO architectures with their applications in optical wireless communication. Through this research, we expect that the applications of OWC-based system could offload the loading of RF-based system in the future 5G network.

並列關鍵字

Optical Wireless Communication ； Visible Light Communication ； Orthogonal Frequency Division Multiplexing ； 5th Generation Mobile Communication ； Virtual Fiber Optical Access Network ； Free-Space Optics

參考文獻

[1(1)] Mansoor Shafi, Andreas F. Molisch, Peter J. Smith, Thomas Haustein, Peiying Zhu, Prasan De Silva, Fredirk Tufvessonn, Anass benjebbour, Gerhard Wunder, “5G: A Tutorial Overview of Standards, Trials, Challenges, Dployment, and Practice,” IEEE J. Sel. Areas Commun., vol. 35, no.6, pp. 1201-1221, Jun. 2017.

[1(2)] L. Hanzo, H. Haas, S. Imre, D. O’Brien, M. Rupp, and L. Gyongyosi, ‘‘Wireless myths, realities, and futures: From 3G/4G to optical and quantum wireless,’’ Proc. IEEE, vol. 100, pp. 1853-1888, May 2012.

[1(3)] http://www.itu.int/en/mediacentre/backgrounders/Pages/5G-fifth-generation-of-mobile-technologies.aspx

[1(4)] H. Elgala, R. Mesleh, and H. Haas, ‘‘Indoor optical wireless communication: Potential and state-of-the-art,’’ IEEE Com. Mag., vol. 49, no.9, pp. 56-62, Sep. 2011.

[1(5)] H. Chen, H. P. A. van den Boom, E. Tangdiongga, and T. Koonen, ‘’30-Gb/s bidirectional transparent optical transmission with an MMF access and an indoor optical wireless link,’’ IEEE Photon, Technol. Lett., vol. 24, no. 7, pp. 572-574, Apr. 1, 2012.