| Summary: | 博士 === 國立成功大學 === 電機工程學系碩博士班 === 95 === In recent years, Ethernet Passive Optical Networks (E-PONs) have emerged as the method of choice for providing broadband, high-speed services over the last (first) mile. This dissertation discusses the implementation of new spectral amplitude coding techniques based on Spectral Amplitude Coding Optical Code-Division Multiple-Access (SAC-OCDMA) schemes over Fiber-to-the-Home (FTTH) networks.
According to the geographic distribution of the Optical Network Unit (ONU) groups in the network, this dissertation classifies ONUs (i.e. subscribers) as either central-shared (e.g. a group of ONUs within an office or an apartment complex) or single (e.g. individual ONUs within a home). Various topologies are proposed to meet the differing requirements of the two ONU types for flexibility and confidentiality. For the single-type ONU, Fiber Bragg Grating-based encoder/decoders (FBG-based codecs) are configured using Walsh-Hadamard code as the signature address code, Conversely, for central-shared ONUs, Arrayed Waveguide Grating-based encoder/decoders (AWG-based codecs) are configured using maximum length sequence code (M-sequence code) as signature address code. The problems of Multiple Access Interference (MAI) and Phase-Induced Intensity Noise (PIIN) are investigated in the various FBG- and AWG-based codec schemes presented in this dissertation. Overall, the results show that the proposed schemes allow a significant increase in the number of simultaneous active users (i.e. ONUs) for a bit error rate (BER) of 10-9.
The proposed Spectral Polarization Coding (SPC) scheme is incorporated with polarization coding as the signature address code of the single type ONUs. Here, unipolar Walsh-Hadamard code is employed as the signature address to allocate each specified wavelength an individual vertical or horizontal State-of-Polarization (SOP). The numerical results demonstrate that the proposed approach achieves a better double spectral efficiency than conventional supercode.
We propose an enhanced hybrid Spectral Polarization and Amplitude Coding (hybrid SPC/SAC) scheme designed to improve the performance of the SPC scheme by further reducing the number of wavelength collisions. Compared to the SPC scheme, the distinguishing feature of the hybrid SPC/SAC scheme is its use of null wavelengths, which significantly reduces the number of wavelength collisions in the photo-detector, and hence reduces the PIIN noise.
For central-shared type ONUs, we present a Wavelength-Division Multiplexing and OCDMA (hybrid WDM/OCDMA) scheme for central-shared ONUs (subscribers). In the proposed approach, the periodic cyclic and Free-Spectral-Range (FSR) properties of AWG routers are exploited to partition the total ONU capacity in the network into different groups in accordance with the subscribers’ geographical locations. It is shown that while the number of AWGs in the proposed scheme is comparable to that of conventional WDM-EPON schemes, the hybrid WDM/OCDMA scheme has improved flexibility, confidentiality and scalability characteristics.
In order to enhance the confidentiality of AWG-based codecs for central-shared type ONUs, the dynamic reconfigurable coding/decoding scheme is implemented by using optical switches and simple electrical shift registers. In addition, a dynamic codeword modification policy is proposed which identifies the code matrix assignment which minimizes the Degree of Weighted Load Balance (DWLB). The evaluation results demonstrate that the reconfiguration policy outperforms one class of static policies both in terms of the DWLB and the number of register shifts required to reconfigure the code matrix assignment.
This dissertation proposes various SAC-OCDMA techniques over FTTH networks as alternatives to traditional Time-Division-Multiplexing (TDM-) and WDM-EPON methods. In general, the results show that the proposed schemes not only reduce the processing time and resolve the collision problem resulting from the simultaneous arrival of active packets at the optical line terminal (OLT) or ONUs, but also significantly improve the data confidentiality characteristics of FTTH networks.
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