臺灣博碩士論文加值系統

數據傳輸在智慧型行動裝置的使用已是一項不可或缺的技術，檔案傳送與多媒體串流服務的需求越益增加，促使無線通訊功能不斷精進。伴隨著無線通訊裝置的普遍性以及其相機的廣泛使用，使得可見光通訊技術 (Visible Light Communication, VLC) 在手機上的運用，成為熱烈討論的話題。其設計概念是考慮在照明燈具上賦予通訊功能，隨著不同的可見光特性與運用被提出，已出現涉及通訊安全、增加傳輸頻寬等相關議題，也開始深入探討利用可見光通訊來補足藍芽(Bluetooth)、RFID NFC (Radio Frequency Identification Near-Field Communication) 等無線近場通訊技術。此篇將考量以現有智慧型手機的硬體元件，建構可見光通訊系統以彌補現有無線電波傳輸的不足，其挑戰除了需整合現有的軟硬體資源，也必須克服傳輸時背景雜訊與本身陣列光源互相干擾。
本篇建立了一個可用於近場多重輸入多重輸出 (Near-Field Multiple Input Multiple Output, MIMO) 可見光通訊的成像取樣模型，包含了兩支智慧型手機並搭配超寬視角的魚眼鏡頭，並採用影像處理技術 (Sobel Edge Detector) 進行訊號處理，形成了一個完整的光通訊系統。緊湊的魚眼鏡頭投影平面、小尺寸像素和高角度分集，也意味著與緊湊平面接收器陣列的集成是可行的，使用智慧型手機的相機進行傳輸，除了可獲得實際傳輸通道的光強度外，也可以更貼近一般的生活。本文中所採用的Sobel edge detection 技術，可以針對可見光訊號在干擾的環境中不能直接應用無線電波通信所使用的 MIMO 技術的問題，必須調整MIMO系統等化器設計，來正確擷取訊號位置與強度以完成解調，我們設計的 MIMO VLC 系統可以有效地支持調光/亮度控制和其它可見光學特定要求。實驗結果顯示，本篇提出的MIMO VLC光學系統，可以成功的配合Sobel影像處理技術，解碼出所傳送的訊息。本系統在近場環境時，傳送與接收手機的距離分別為9cm、6cm與4cm時，分別有28.7%、24.6%與21.03% Symbol Error Rate (SER) 的傳輸效能。
本論文使用智慧行動裝置之螢幕與相機作為傳輸系統，以無線可見光為基礎，考量可見光的特性建構 MIMO VLC 系統，會採用魚眼鏡頭的角度分集特性，以提升傳輸的可靠度，除可發揮現有行動裝置的潛力，亦可彌補電磁波傳輸系統不足之處，未來更可以配合等化器與預編碼器的設計，進行最佳化，也可採用錯誤更正碼來提升傳輸效率。
　　關鍵詞：可見光通訊、光學多重輸入多重輸出收發器設計、亮度控制、成像接收器、魚眼鏡頭、Sobel edge detection、SER

Recently, the mobile phone plays an important role in our life. The camera embedded in mobile phone is pervasive and frequently used not only for capturing images, but also for communication. Moreover, users could download a digital file by using camera to capture the images (or video) in the screen of a desktop PC or even a smartphone. This paper realized a Near-Field Multiple-Input Multiple-Output (NF MIMO) Visible Light Communications (VLC) system. This system consists of a transmitter (one smart phone with a display monitor) to show images as sending signals, and a receiver (the other smart phone with a camera and a fisheye lens) to capture images as receiving signals. To reconstruct the data in the receiver, Sobel edge detection (a digital signal process technique) is applied to allocate the valid region and demodulate the received signal.
This paper considers applying the MIMO VLC system to the near field applications. In order to explore the spatial diversity in MIMO system, the potentials of high-resolution display and the camera have been exploited in the last decades. In addition, the fisheye lens combined with the ordinary lens (or an ultra-wide field-of-view lens) is adopted in the proposed system to provide high angular diversity. Based on Sobel edge detection, the signal demodulation would be realized in two steps. First, we use Sobel edge detection to find the boundary of smartphone’s display. Second, Sobel edge detection can segment the valid region of signal and estimate the signal energy by averaging the grayscale of pixels in segmented region. In our experience, the symbol error rates (SERs) of the implemented optical MIMO VLC system at distances 9cm, 6cm, and 4cm between two smartphones are 28.7%, 24.6%, and 21.03%, respectively.
In the future, the improvements may consider the optimization of pre-coder/equalizer, and applying error correction codes.

Key words： Visible light communications, optical MIMO transceiver design, brightness control, imaging receiver, fisheye lens, Sobel edge detection, SER

ACKNOWLEDGMENTS II
中文摘要 III
ABSTRACT V
TABLE OF CONTENTS VI
LIST OF FIGURES VIII
LIST OF TABLES XII
CH1 INTRODUCTION 9
CH2 RELEVANT RESEARCH 14
2.1 Visible Light Communication 14
2.2 The Multiple-input Multiple-output Technologies 17
2.3 Imaging Optical MIMO System 18
2.4 Optimum Solution 23
CH3 CONSTRUCTION OF MIMO VLC SYSTEM USING SMARTPHONES 27
3.1 Near-Field MIMO VLC System 27
3.1.1 Shorten the Transmission Distance of MIMO VLC System 28
3.2 Digital Signal Process for VLC Receiver 29
3.3 Design of MIMO VLC System 35
CH4 EXPERIMENTAL RESULT 44
4.1 Signal Modulation and Demodulation 44
CH5 CONCLUSION 50
REFERENCES 51
APPENDIX A 55

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