自我組織模糊類神經網路應用於非線性時變通道決策回授等化器; Self-Organizing Fuzzy Neural Network Applied to Decision Feedback Equalizers of Nonlinear Time-varying Channels

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Title:	自我組織模糊類神經網路應用於非線性時變通道決策回授等化器;Self-Organizing Fuzzy Neural Network Applied to Decision Feedback Equalizers of Nonlinear Time-varying Channels
Authors:	林德成;Te-cheng Lin
Contributors:	通訊工程研究所
Keywords:	自我組織;模糊類神經網路;時變通道;self organizing;fuzzy neural network;time varying channel
Date:	2009-06-26
Issue Date:	2009-09-22 11:23:11 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	傳統上，一些模糊類神經網路系統都使用倒傳遞演算法(Back propagation, BP)調整其系統參數，但是不良的初始值往往會導致演算法收斂到局部最佳解（Local Minimum）。故，好的初始值是很重要的。而在模糊類神經網路系統結構的設計上，模糊規則數量會直接影響到系統的效能，在系統學習期間，若該數量保持不變，則可能導致模糊規則數不適當之情形產生。為了解決BP法收斂到局部最佳解以及模糊類神經網路系統的結構設計問題，我們提出一種新型自我組織模糊類神經網路系統，它可根據輸入資訊自動建立系統結構以及設計初始值，再用BP訓練系統參數以達最佳效果。最後，我們將提出的演算法，應用在非線性時變通道決策回授等化器上，並和傳統模糊類神經網路系統架構下的等化器做比較。從模擬結果可看出其有效降低位元錯誤率(Bit Error Rate, BER)及均方誤差收斂值(Mean Square Error, MSE)。 Conventionally, a fuzzy neural network (FNN) system may adopt back-propagation (BP) learning algorithm to adjust parameters. An improper initial value in BP may lead to local minimum. Therefore, initial value selection is very important for BP. Furthermore, on structure design of FNN, the fuzzy rule numbers may affect the performance. Specially, if the number of fuzzy rules keeps unchanged during learning, which is prone to bring a deficiency or redundancy of fuzzy rules. To overcome the local minimum problem and structure design of a FNN system, we propose a novel self-organizing fuzzy neural network (SOFNN) system, which establishes the structure and obtain the initial values of the system automatically. Then the BP is used to optimize the parameters of a FNN system. Finally, the proposed algorithm is applied to decision feedback equalizer (DFE) of nonlinear time-varying channels for comparison with the conventional FNN. The simulation results show that SOFFN-based DFE can reduce both the BER and MSE effectively.
Appears in Collections:	[Graduate Institute of Communication Engineering] Electronic Thesis & Dissertation

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