臺灣博碩士論文加值系統

多重輸入多重輸出-正交分頻多工(MIIMO-OFDM)系統是一種不耗費頻寬及必v且具有高速傳輸的系統。為了充分使用空間、時間及頻率的分集效應，採用本身具有內建穿插器(Interleaver)的低密度同位元檢查(LDPC)碼。在接收端我們利用次佳化的線性最小均方根誤差-軟性干擾消除(LMMSE-SIC)解映射演算法，減輕因為傳送天線個數多及星座圖(Constellation)太大時，造成系統的計算複雜度增加的問題。
在本篇論文提出結合LDPC解碼器的通道估計演算法，利用LDPC的軟性位元資訊與具有機率定義的均方根誤差(MMSE)演算法，避免低位元信賴度時，硬性決策造成高估計誤差的問題，並且在通道追蹤過程中不需利用任何的領航符元(Pilot Symbol)。最後，再提出兩個方法，利用時域相臨通道相關性的方法，增強通道值的精確度。
最後，由模擬的方式分析系統及所提出的演算法。結果顯示本演算法在正規化都卜勒(Doppler)頻率0.01的快退(Fast Fading)無線移動通道中，在封包錯誤率0.01全通道估計值相差0.12dB。

Multiple input multiple output- orthogonal frequency division multiplexing (MIMO-OFDM) that is a highly efficient data transmission system does not increase any transmission power or bandwidth to improve the channel capacity. For exploiting the space, time and frequency diversity, the low density parity-check (LDPC) is used as a channel coding with a built-in interleaver. We used suboptimal soft demapping algorithms, linear minimum mean square error- soft interference cancellation (LMMSE-SIC), to reduce computational complexity caused a large constellation size and a lot of transmission antennas in the receiver.

In this thesis a jointed LDPC decoder and channel estimator algorithm was proposed. The algorithms applied soft bits information of LDPC to avoid estimate errors in low bits reliability during the demapping process. Finally, we used time domain channel correlation to enhance the accuracy of estimates.

Computer simulations under fast fading conditions and normalized Doppler frequency 0.01 show that performance of the proposed channel estimation algorithms are
0.12 dB worse than perfect channel estimation algorithms as packet error rate is 0.01.

目 錄

圖目錄 3
第一章 簡 介 5
第二章 系統模型 8
2.1 MIMO-OFDM 介紹 8
2.1.1 OFDM 系統介紹 8
2.1.2循環字首與保護邊帶的觀念 10
2.1.3 MIMO介紹 12
2.2 LDPC 介紹 12
2.2.1線性區塊碼 13
2.2.2圖形表示法 13
2.3 無線傳輸系統通道特性 15
2.3.1 通道狀態的定義 16
2.3.2 通道架構 16
2.3.3 通道模型 18
2.3.4 模型應用 21
2.4 系統架構 24
第三章 接收機系統與通道估計演算法 28
3.1 軟性解映射 30
3.2 LDPC 解碼演算法 33
3.3 通道估計演算法 35
第四章 模擬結果與分析 41
第五章 結論與未來發展 45
參考資料 47
中英名詞對照表 51

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