次世代有線與無線整合光網路之研究

Abstract

根據Edholm’s law，有線與無線服務的傳輸速率將逐漸趨於一致。近來，智慧型裝置的普及更是大幅地推動了次世代無線網路的發展。對於次世代無線網路的推動，許多技術與經濟相關的問題仍待克服。這篇論文著重於研究這些問題，並希望能提供多面向的解決方案。

在這篇論文中，兩種用於解決鋪設次世代無線網路所需高Capex (Capital expenditure)與Opex (Operational expenditure)的方案被提出並研究。次世代無線網路所需的新無線服務站預示著大量Capex跟Opex的投入。然而，在新網路發展的初期，這些資本的投入與回收時程難以估計。因此，我們提出mobile-over-PON (Passive optical network)的架構：利用已經布建於PONs的ODNs (Optical distribution networks)作為次世代無線網路的backhaul或fronthaul，進行無線資料的傳輸。這舒緩了針對次世代無線網路，鋪設大量新光纖的需求；針對基於CPRI (Common public radio interface) fronthaul的頻寬與延遲問題，我們研究使用AoF (Analog-over-fiber) FTTA (Fiber-to-the-antenna)技術的fronthaul系統，並提出一種名為MASK-MQAM-OFDM (M-ary amplitude-shift keying- M-ary quadrature amplitude modulation orthogonal frequency-division multiplexing)的新型調變格式，以在AoF-FTTA架構下，有效傳輸CoMP (Coordinated multi-point)的控制信號。除了重複使用PONs的ODNs來舒緩鋪設大量光纖的成本外，我們也提出基礎建設共享的架構：每個新無線服務站都由多個運營商所共享，藉由分攤基礎建設的布建與維護成本，運營商可以進一步節省Capex和Opex的投入。由於我們提出的方案可以有效減少運應商在資本的投入，它將在次世代無線網路發展上，為運營商提供極大的優勢。

在這篇論文中，我們也針對長期的網路發展，提出網路無縫升級的方案。過去被布建的ODNs主要採用能量耦合器，由於預期基於AWGs (Arrayed waveguide gratings)的ODNs可以提供更佳的系統效能，我們規劃三個階段的網路升級過程，以平順地將使用能量耦合器的ODNs轉變成使用AWGs的ODNs。

在這篇論文中，我們也研究應用於次世代無線網路的可見光-照明整合系統。LEDs (Light-emitting diodes)具有成為未來主流照明源的潛力。藉由LEDs的高調變頻寬特性，我們有機會在照明系統中，附加高速可見光通訊的應用。因此，可見光通訊可以在射頻通訊外，提供額外的通訊資源，其在次世代無線網路具有高度的價值。在這篇論文中，三個可見光-照明整合系統的相關問題被重點研究。我們提出使用dimming-DMT (Dimming-discrete-multi-tone)和R/G/B LEDs同時實現顏色調控與可見光通訊。我們也研究基於螢光粉白光LEDs的傳輸系統。我們探討了常應用於此種可見光通訊系統的藍光濾波器之必要性。我們也提出了一種新的FAWN (Flexible access wireless network)架構，有效整合多個可見光通訊服務站，以彈性擴充光網路的服務範圍。

在這篇論文中，我們也提出增加頻寬使用效率的架構，以在有限的可用波長下，增加服務的終端節點數。我們提出利用OFDM進行backhaul信號的傳輸，以提供每個波長更高的傳輸速率。我們也提出特殊的波長配置計畫，以更有效率地進行RoF-FTTA fronthaul的信號傳輸。我們並針對未來FTTH (Fiber-to-the-home)的架構，提出使用MASK-MQAM-OFDM技術，以有效同時傳輸PON信號與可見光通訊信號。

Edholm’s law has predicted the convergence in capacity between the wireline and wireless systems. Popularity of smart devices is pushing the development of the next-generation (NG) wireless networks. In the system evolution processes, many technical and economic issues should be overcome. This dissertation is aiming for providing multi-aspect plans for solving these issues.

In this dissertation, two solutions which can be simultaneously adopted to relieve the capital expenditure (Capex) and operational expenditure (Opex) of the NG wireless systems are proposed and studied. In order to solve the explosively increasing requirements for new backhauls or fronthauls for the corresponding number of cells, mobile-over-passive optical network (PON) architectures are proposed. We propose re-using the optical distribution networks (ODNs) of legacy PONs as the backhauls or fronthauls to transport the mobile data. This can relieve the burden of deploying massive new optical fibers. In order to solve the potential bandwidth and latency issues of the common public radio interface (CPRI) based fronthaul systems, we also propose and study the fronthaul systems using analog-over-fiber (AoF) fiber-to-the-antenna (FTTA) techniques. A novel coding technique, M-ary amplitude-shift keying- M-ary quadrature amplitude modulation orthogonal frequency-division multiplexing (MASK-MQAM-OFDM), is proposed to efficiently transport the control signals in the AoF-FTTA fronthauls for coordinated multi-point (CoMP) applications. Besides re-suing the ODNs of PONs, we also propose an infrastructure sharing architecture to further reduce the Capex and Opex for the operators. In our proposed architecture, each cell can be shared by different operators, so that the building and managing cost are also shared by different operators. Hence, operators save their expenditure. Since it is still uncertain that how the newly deployed cells will balance the budget, our proposed architectures will provide the operators a cost-effective and practical manner to implement their new systems in the early stage of developing the NG wireless systems.

A migration plan to seamlessly upgrade our proposed architectures is also proposed in this dissertation. The legacy ODNs of PONs are mainly built using power splitters. In order to improve the system performance by using arrayed waveguide grating (AWG)-based ODNs, we propose a three-phase migration plan to smoothly transform the power-splitter-based ODNs into AWG-based ODNs.

Visible light communication (VLC)-lighting integrated systems for the NG wireless networks are also studied in this dissertation. Light-emitting diodes (LEDs) are potential choices for the future lighting systems. High-speed VLC may be implemented exploiting LEDs featuring higher modulation bandwidth. Since VLC can be used as a complementary resource to the RF wireless systems, it is highly valuable for the NG wireless systems. In this dissertation, three issues for the VLC-lighting systems are studied. We propose using dimming-discrete-multi-tone (dimming-DMT) and R/G/B LEDs to enable the VLC-lighting systems functioning simultaneous color control and VLC. We also study the transmission systems using phosphor-based white-light LEDs (WLEDs). The necessity of the commonly used blue filters in the VLC systems is examined. A flexible access wireless network (FAWN) is also proposed to flexibly extend the VLC systems by combing multiple cells.

Bandwidth-efficient transmission architectures are also proposed in this dissertation to serve for more nodes. We propose and demonstrate using OFDM based backhaul systems to increase the capacity of the systems. We also propose special wavelength allocation plans to more efficiently transport the RoF-FTTA fronthaul signals. For the future fiber-to-the-home (FTTH) systems, MASK-MQAM-OFDM is also proposed to simultaneously transport the PON and VLC signals.