OFDM-LED可見光通訊的特性與多重存取應用

Abstract

可見光通訊VLC是建立在發光二極體LED照明的普及度上，希望再賦予LED不同的應用，並結合主流調變格式，以提升產品的競爭力。VLC是在照明時能同時傳輸資料，整合了照明與無線通訊的一項技術。 本論文主要專注在室內的單工VLC系統搭配OFDM調變格式的討論，前部分將簡介VLC系統的應用實例，並討論OFDM的理論部分，論文後半的實驗部分會討論OFDM-VLC系統的兩個延伸。 首先是改變OFDM自身的等化方式，藉由適當地調整grid-type的pilot來達成和一般的training symbol作等化的方式一樣的可靠性並且能得到些許的傳輸量提升，整個實驗皆是以實際傳輸數據來作示範，同時也探討了OFDM的同步技術，是屬於一種基本性質探討的實驗。 接著是對於OFDM此格式的一種實際應用，利用OFDM來產生一個穩定的多重存取環境，並且維持空間中傳輸量盡量均衡的使用環境，實驗中將先使用實際的物理規格數據來建立我們希望的模型，並以模擬的方式來表達概念，並且呈現了多重存取的模擬結果後，實驗的後半部再以一維的疊加和干擾實驗的方式驗證此模型的可行性，並且討論了未來可行的工作。

White-light light emitting diode (LED) is gradually replacing the traditional lamps for lighting applications. The combination of the LED lamp with visible light communication (VLC) can provide lighting and communication simultaneously. The LED VLC provides many transmission advantages, such as license free and electromagnetic-interference (EMI) free, it is regarded as one of the promising access solutions in the future. Orthogonal frequency division multiplexing (OFDM) is one of the promising modulation formats for VLC; however, precise channel estimation is required for synchronization and equalization. In the first part of the thesis, we propose and demonstrate using a specific and adaptive arrangement of grid-type pilot scheme to estimate the VLC channel response. Experimental results show that our scheme can achieve same transmission performance and with some transmission capacity enhancement when compared with the method using training-symbol scheme (also called block-type pilot scheme). Then, in the second part of the thesis, a novel orthogonal frequency-division multiplexing access (OFDMA) based flexible optical-wireless network (FOWN) is proposed. Each user at different locations insidethe VLC system can have nearly equal transmission capacity in the proposed FOWN by using discrete multi-tone (DMT) frequency band sharing mechanism. Smooth mobile communication is thus satisfied. Simulation and experiments are performed to verify the feasibility of our proposed FOWN.