在本篇論文中，我們利用了一項調變技術，稱之為直流偏置光正交分頻多工 (DCO-OFDM)應用於可見光通訊(Visible Light Communication)來達到100(百萬位元/秒)的高速數據傳輸。
根據上述目標，與工研院(ITRI)共同制定下，我們選用最適合的參數以符合標準。在40百萬赫茲(MHz)的頻寬下，直流偏置光正交分頻多工(DCO-OFDM)的系統設計有一些特點: 第一點、採用了16正交振幅調變(QAM)的調變與以流水線式(Pipeline)的單延遲反饋(Single Delay Feedback)架構為基礎的1024點快速傅立葉轉換(Fast Fourier Transform)。第二點、我們使用了39062赫茲(Hz)的子載波頻寬與1/8符元長度的循環字首(Cyclic Prefix)來克服頻率選擇性衰減通道(Frequency Selective Fading Channel)。第三點、利用了國際電機電子工程學會(IEEE) 802.11a的前置符元(Preamble)在park演算法的基礎下來做時間同步。第四點、領航符元(Pilot Symbols)被用來解決因為取樣頻率偏移(Sampling Clock Offset)所造成在頻域的相位旋轉，然而容忍度可以達到正負100百萬分率(ppm)。第五點、提出了座標旋轉數字計算方法(Coordinate Rotation Digital Computer)來達成三角函數功能以及代替除法器。最後階段，在訊號雜訊比(SNR)為21分貝(dB)的情況下，已經可以達到10-4的位元錯誤率(BER)。此外，我們也已經完成運用VLC多媒體播放器(VLC Media Player)來播放影片以及達到斷線後可以立即重新連線的功能。雖然整體測試過後，因為類比數位轉換器與數位類比轉換器(ADC/DAC)的取樣頻率限制的關係，能夠達成的傳輸速率會比較低，不過我們的直流偏置光正交分頻多工(DCO-OFDM)收發機在硬體實現下，已經用封包產生器測試過，事實上確認是可以達到至少100(百萬位元/秒)的速率的。

In the thesis, we exploit a modulation technology called DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) applied in visible light communication (VLC) to achieve high-speed 100 Mbps data transmission.

According to the above objectives, set up with Industrial Technology Research Institute (ITRI), we choose the best parameter to meet the standards. In 40 MHz bandwidth, there are some features for DCO-OFDM system design: First, 16 quadrature amplitude modulation (QAM) and 1024 points fast fourier transform (FFT) based on pipeline single delay feedback (SDF) architecture are selected. Second, 39062 Hz subcarrier bandwidth and cyclic prefix (CP) which takes 1/8 lengths of symbols are used to overcome frequency selective fading channel. Third, IEEE 802.11a preamble is exploited to do timing synchronization based on park algorithm. Fourth, pilot symbols are used to solve phase rotation caused by sampling clock offset (SCO) in frequency domain which the tolerance can be up to $
m\ 100 \rm{ppm}$. Fifth, coordinate rotation digital computer (CORDIC) is proposed to achieve trigonometric functions and replace divider. In the final stage, based on the condition of 21 dB signal-to-noise ratio (SNR), bit error rate (BER) has been achieved $10^{-3}$. In addition, we also have completed the function of displaying movie with VLC media player and reconnecting immediately when disconnection. Although the high-speed data transmission cannot be reached due to the restriction of the sampling frequency of the analog-to-digital converter/digital-to-analog converter (ADC/DAC) after testing. However, in hardware implementation, our DCO-OFDM transceiver has been tested with the packet generator, confirming that the data rate was in fact reached at least 100 Mbps.

Abstract
1 Introduction 1
1.1 Background................................................1
1.1.1 Visible Light Communication (VLC) Systems...........2
1.1.2 Orthogonal Frequency Division Multiplexing (OFDM)...2
1.1.3 Applications of OFDM in VLC Systems.................5
1.2 Motivation................................................6
1.3 Main Contributions........................................7
1.4 Organization..............................................7
2 System Description and Comparison for Indoor VLC Systems 9
2.1 Indoor VLC Systems........................................9
2.2 Optoelectronic Devices....................................10
2.2.1 Electro-optic Conversion Devices....................10
2.2.2 Photoelectric Conversion Devices....................11
2.3 VLC Transmitter Structure Analysis........................12
2.4 VLC Transmitter Modulation Technologies...................13
2.4.1 On-off Keying (OOK).................................13
2.4.2 Pulse Amplitude Modulation (PAM)....................15
2.4.3 Pulse Width Modulation (PWM)........................16
2.4.4 Pulse Position Modulation (PPM).....................17
2.4.5 Variable Pulse Position Modulation (VPPM)...........17
2.4.6 Asymmetrically Clipped Optical OFDM (ACO-OFDM)......19
2.4.7 DC-biased Optical OFDM (DCO-OFDM)...................21
2.5 Comparison of Light Fidelity (Li-Fi) Products for Indoor VLC
Systems...................................................22
3 System Design and Performance Analysis 25
3.1 Introduction..............................................25
3.2 System Specification......................................25
3.3 Design and Verification Flow..............................26
3.4 DCO-OFDM System Model.....................................27
3.4.1 Modulation..........................................30
3.4.2 Subcarrier Allocation...............................30
3.4.3 Inverse Fast Fourier Transform (IFFT) and Fast Fourier
Transform (FFT).....................................35
3.4.4 Cyclic Prefix.......................................36
3.4.5 Preamble............................................36
3.4.6 Synchronization.....................................39
3.5 System Performance........................................47
3.5.1 Without Timing Synchronization vs. With Timing
Synchronization.....................................48
3.5.2 Without Sampling Clock Offset Synchronization vs. With
Sampling Clock Offset Synchronization...............49
4 Architecture Design 53
4.1 Modulation................................................55
4.2 Subcarrier Allocation.....................................55
4.3 Timing Synchronization....................................56
4.4 Sampling Clock Offset Estimation and Compensation.........56
4.5 Channel Estimation........................................61
4.6 Performance Verification..................................63
5 Implementation Results 65
5.1 Sampling Clock Offset Estimation and Compensation.........65
5.2 Signal-to-noise ratio (SNR) Measurement...................70
5.3 Resource Utilization......................................71
5.4 Performance Verification..................................72
5.5 Data Rate for System Model................................72
6 Conclusions and Future Works 77
6.1 Conclusions...............................................77
6.2 Future Works..............................................78

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