同調光纖通信技術已經受到世界各方的強烈關注，此種通訊技術可以實現高頻譜效率的傳輸系統。同調光纖通信技術和1980年代相比最大的不同是採用了數位信號處理（DSP）。在1980年代，若要採用零差檢測需要所謂的光鎖相迴路(OPLL)，而此種迴路是相當難以實現的。最新的同調光纖通信技術應用數位信號處理來取代光鎖相迴路來實現零差檢測，數位信號處理要比零差檢測來的容易實現的多。
實時的數位信號處理的實現現今仍是一個問題。對於實現高速通訊系統而言，數位信號處理採用的運算邏輯需要極端強大的計算能力。人們總是利用現場可編程邏輯陣列（FPGA）來實現實時的數位信號處理，但此種晶片的成本目前仍過於昂貴。
這個碩士論文打算利用搭載專門用於計算的圖型處理器的個人電腦（PC）來取代現場可編程邏輯陣列。若是可以成功開發此種接收器，可以顯著降低數位同調接收器的成本。此外，這種接收器是基於的是軟體而不是硬體。這意味著此種接收器功能更具備彈性並容易調整。

The coherent optical fiber communication technology is attracting significant attentions in the world, because it can realize the spectrally efficient transmission system.
One major difference between 1980’s and the latest coherent technology is the utilization of the digital signal processing (DSP). In 1980’s the optical phase locked loop (OPLL) was required to realize the homodyne detection, and it was significantly difficult to realize. The latest coherent technology utilizes the DSP in place of the OPLL to realize the homodyne detection, and it is much easier than the OPLL.
The real-time realization of the DSP is still a problem. Because the DSP uses software to process the signal, it needs an extreme calculation power for the high-speed communication system. People always utilize the field programmable gate array (FPGA) to realize the real-time DSP, but the cost of the FPGA is too expensive for the commercial system at this moment.
This master thesis intend to utilize commercially available personal computer (PC) contained a GPU calculation board to replace FPGA. It can reduce the cost of the coherent receiver. Also, this receiver is defined by the software rather than the hardware. It means that we can realize a flexible receiver defined by the software.

致謝 I
中文摘要 II
Abstract III
Contents V

1　Introduction 1
1.1　Optical Coherent Transmission Systems . . . . . . . . . . . . . . . . . . . . 1
1.2 Graphic Processing Unit based Digital Coherent Receiver . . . . . . . . .3
1.3　Motivation of this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Structure of this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2　Theory of QPSK digital coherent receiver 7
2.1　Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2　Coherent Detection of Phase-diversity Homodyne Receiver . . . . . . . . 8
2.2.1 Coherent detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
2.2.2 Homodynedetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
2.3　 Quadrature Phase Shift Keying Modulation . . . . . . . . . . . . . . . . . . . . 11
2.4 QPSK Demodulation Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3　GPU Calculation Technology 20
3.1　Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2　 CUDA parallel computing architecture . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.1　Processing flow . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.2　Grid, Block, and Thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2.3　Memories on GPU board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4 Experimental Study of QPSK Digital Coherent Receiver with Carrier 27
4.1　Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2.1 Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.2 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.3 Algorisms of DSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3.1 Phase Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3.2 Differential decoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.3.3 Adjustment for following the trajectory of physical phase . . . . . 40
4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Source Code of MATLAB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Acronyms 52

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