摘要
在這個論文中, 我們提出兩種方法來改善非同調系統的效能. 一種是根據外在訊息轉換圖(EXIT chart), 而另一種則是使用碼自交錯放置法. 不規則低密度奇偶碼(irregular LDPC code) 已廣泛地被運來用最佳化各種通訊系統. 然而在某些情況下, 根據傳統外在訊息轉換圖的最佳化過程使用的高斯假設將失去它的準確性, 導致實際與預測的極限產生錯誤. 我們可以看到在使用訊息乘載前導符號和空間多工的分同調時空系統中, 軟質的機率密度函數和高斯函數有很大的區別. 我們因此設計一種有效的錯誤率最佳化方法. 使用我們提出的最佳話法比起傳統的最佳化法更能準確的預測極限及得到更好得效能. 對於碼交錯放置法, 它使用額外的前導符號來幫助解調及解碼, 隨著不同的碼字交錯器, 鄰近的碼字將收到不同的額外訊息因而造成不同的結果. 最後, 我們使用個別的外在訊息轉換圖來解釋它們造成的結果.

In this thesis, we propose using two methods to improve the performanceof a noncoherent system using information-bearing pilot and spacial multiplexing. The former is based on EXIT(extrinsic information transfer) chart and the latter is based on the codeword-interleaving strategy. It is known that irregular low-density parity-check (LDPC) code is widely used for optimizing performance in various communication systems. However, in some cases, the Gaussian approximation for the soft values used in the conventional
EXIT-chart-based optimization procedure may lose its accuracy, and result in a large prediction error for the convergence threshold. It can be shown that for a noncoherent space-time system using information-bearing pilots and spatial multiplexing, the probability density function of the soft values is far from Gaussian. We have therefore designed an efficient performance optimization method. Compared to the use of conventional optimization
method, using the proposed method provides a more accurate prediction of convergence threshold and better system performance. For the codewordinterleaved scheme, which uses extra pilots to help demap and decode, we introduce a method that can be used to extend it to our system. With a different codeword interleaver, the extra information being passed to the adjacent codeword may be different and, hence, produce different results.

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