隨著現代網際網路發達，智慧型裝置的運用與開發也有著蓬勃的發展，而這也暗示著人們對於寬頻資料傳輸的極大需求，因此如何以簡單、快速並且符合經濟效益的方式處理訊號成了現代通訊技術發展的重要課題。
無論是在傳統同軸電纜或是大氣中高頻訊號都會受到相當大的傳輸損耗，導致傳輸容量與距離受到限制。因此將正交分頻多工技術(OFDM)應用於被動式光纖網路(PON)上被視為是極具潛力的選項之一，此方法可以提供足夠的頻寬並且解決傳輸損耗的問題。不過標準的OFDM-PON系統存在著一個不利於成本控制的缺點：需要接收冗餘的訊號，也就是說標準的OFDM-PON系統需要昂貴的高速轉換器才能解調訊號。在先前的研究中已提出了延時分複用正交分頻多工被動式光纖網路(DDM OFDM-PON)技術克服了以上的缺點。然而，由於DDM OFDM-PON技術尚未開發出可動態分配虛擬群組之資料容量，因此對於現行網路架構之可適性不佳，且尚無可用於此系統中的訊號品質改善技術。
本論文以固定取樣率之DDM OFDM-PON為基礎提出了可以容納不同取樣率的虛擬群組，同時提出了可用於DDM技術的預加重(pre-emphasis)和位元負載(Bit-loading)技術以提升訊號品質，並且開發出適用於次奈奎斯特取樣(sub-Nyquist sampling)的通道響應評估技術使得本系統之性能大幅提升。

Due to development of modern Internet, the applications of smart devices also have a thriving development, implying a great demand for broadband data transmission. Therefore, how to process signals in a simple, fast and cost-effective manner is the focus of modern communications.
High-frequency signals in either the traditional coaxial cable or the atmosphere are subject to considerable transmission loss, resulting in limited transmission capacity and distance. Therefore, the application of Orthogonal Frequency Division Multiplexing (OFDM) technology to Passive Optical Network (PON) is considered as one of the most promising candidate to provide enough bandwidth and solve the problem of transmission loss. However, the standard OFDM-PON system suffers from the disadvantage of being cost-prohibitive because it needs to receive redundant signals. Thus, a standard OFDM-PON system needs an expensive high-speed converter to demodulate signals. In previous works, Delay Division (DDM) Multiplexing OFDM-PON technology has been proposed to overcome the above shortcomings. However, the DDM OFDM-PON technology can only assign the same data capacity to all virtual groups, limiting the flexibility and adaptability to the current network architectures. Besides, there is no available technology to improve the performance of this system.
This thesis proposes a new method that can accommodate virtual groups with different sampling rates and capacities, thereby increasing the flexibility. In addition, this work proposes novel techniques to improve the performance of the DDM system, including pre-emphasis, bit-loading, and channel response estimation. The channel estimation technique is particularly central in an APD-based DDM system.

Acknowledgements i
摘要 iii
Abstract iv
Content vi
List of Figure ix
Chapter 1 Introduction 1
1.1 Background 1
1.2 Motivation 3
Chapter 2 Delay-Division-Multiplexing Orthogonal Frequency Division Multiplexing Te-chnology 6
2.1 Preface 6
2.2 OFDM-PON 7
2.2.1 Why PON 7
2.2.2 Orthogonal Frequency-division Multiplexing 8
2.2.4 The characteristics of OFDMA-PON 13
2.3 Delay Division Multiplexing OFDM-PON 14
2.3.1 Sub-Nyquist sampling 14
2.3.2 Relationship between time domain and frequency domain 17
2.3.3 Concept of DDM OFDM-PON 18
2.3.4 Mathematical description of the pre-processing 21
2.3.4.1 Transmission channel analysis 21
2.3.4.2 Pre-processing and sampling instant 25
2.3.5 The advantage of DDM OFDM-PON 30
2.4 Objective and problem statement 31
Chapter 3 DDM OFDM-PON for Hybrid Sampling Rate of ONUs and Quality Opti-mization 32
3.1 Preface 32
3.2 DDM OFDM-PON for hybrid sampling rate of ONUs 33
3.2.1 Introduction of hybrid-sampling-rate DDM OFDM-PON 33
3.2.2 Pre-processing 35
3.2.3 Arrangement for sampling delays 38
3.2.4 Additional consideration in IM/DD systems 40
3.3 Estimate channel response with Sub-Nyquist sampling 43
3.3.1 Localized method 43
3.3.2 Interleaved method 45
3.3.3 Whole-band method 48
3.4 Improving quality of received signal in DDM OFDM-PON scheme 53
3.4.1 Pre-emphasis 53
3.4.2 Bit-loading 57
Chapter 4 Experiment Demonstration of the Proposed EML System 59
4.1 Preface 59
4.2 Experimental setup for PON system 59
4.3 Experimental results of the PON system 61
4.3.1 SNR/BER results with fixed sampling rate of ONUs 61
4.3.2 SNR/BER results with different fiber length versus receiver type 62
4.3.3 SNR/BER results with hybrid sampling rate of ONUs 64
4.3.4 SNR/BER results with each channel estimation method 67
Chapter 5 Conclusion 75
Reference 77

[1]“Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2016–2021,” Cisco White Paper, 2017.
[2] T. Koonen, “Fiber to the Home/Fiber to the Premises: What, Where, and When?” Proceedings of the IEEE, Volume: 94, Issue: 5, p. 911 – 934, May 2006.
[3] C. C. Wei, H. C. Liu, C. T. Lin, “Novel Delay-Division-Multiplexing OFDMA Passive Optical Networks Enabling Low-Sampling-Rate ADC,” Optical Fiber Communication Conference, Los Angeles, California United States, paper M3J.1, 2015.
[4] C. C. Wei, H. C. Liu, C. T. Lin, “Analog-to-Digital Conversion Using Sub-Nyquist Sampling Rate in Flexible Delay-Division Multiplexing OFDMA PONs,” Journal of Lightwave Technology, Volume: 34, Issue: 10, p. 2381 – 2390, May15, 15 2016.
[5] J. H. Hsu, M. Yu, C. C. Wei, … “Novel DDM-OFDM-PON with Hybrid Sub-Nyquist Sampling Rates Featuring Heterogeneous ONUs with Different Capacities” propose in Optical Fiber Communication Conference, San Diego United States, 2018.
[6] P. P. Iannone and K. C. Reichmann, “Optical access beyond 10 Gb/s PON”, in European Conference and Exhibition on Optical Communication (ECOC), paper Tu.3. B.1, 2010.
[7] K. Grobe and J.-P Elbers, “PON in Adolescence: From TDMA to WDM-PON,” IEEE Commun. Mag., vol. 46, p. 26 – 34, Jan. 2008.
[8] R. P. Leon, “Brief prsentation of telecom fundamentals for non technical people”, website https://www.slideshare.net/, Engineering, 2014.
[9] J. Armstrong, “OFDM for optical communications,” Journal of Lightwave Technology, Volume: 27, Issue: 3, p. 189 – 204, Feb.1, 2009.
[10] N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency-division multiplexing,” IEEE Communications Magazine, Volume: 48, Issue: 7, p. 70 – 77, Jul. 2010.
[11] The IEEE 802.16 Working Group on Broadband Wireless Access Standards, http://www.ieee802.org/16/
[12] J. Kani, F. Bourgart, A. Cui, A. Rafel, M. Campbell, R. Davey, and S. Rodrigues, “Next-generation PON-Part I: Technology roadmap and general requirements,” IEEE Communications Magazine, Volume: 47, Issue: 11, p. 43 – 49, Nov. 2009.
[13] K. Grobe and J. P. Elbers, “PON in adolescence: From TDMA to WDM-PON,” IEEE Communications Magazine, Volume: 46, Issue: 1, p. 26 – 34, Jan. 2008.
[14] F. T. An, K. S. Kim, D. Gutierrez, S. Yam, E. Hu, K. Shrikhande, and L. G. Kazovsky, “SUCCESS: A nextgeneration hybrid WDM/TDM optical access network architecture,” Journal of Lightwave Technology, Volume: 22, Issue: 11, p. 2557 – 2569, Nov. 2004.
[15] A. V. Oppenheim, A. S. Willsky, S. H. Nawab “Signals & systems (2nd ed.),” Prentice-Hall, Inc. Upper Saddle River, NJ, USA ,1996