中上型衰落通道內相關性信號分集合成後之LCR與AFD效能研究

A Performance study for Average LCR and AFD of Dual MRC and SC Diversity over Correlated Nakagami Environment

朱有光(Yu Kuang Chu)

指導教授 ： 劉宗平 ； 楊耀波

元智大學/工程學院/電機工程學系/碩士(2003年)

摘要

在行動無線通信的環境中，因多重路徑傳播所造成的信號衰落現象，會顯著地降低系統的性能。評估通信系統性能的指標相當多，其中以平均準位跨越率(level crossing rate； LCR)與平均衰落時距(average fade duration； AFD)受到廣泛的運用。這兩項指標是包線振幅大小變化的二階型統計量，因而它們是非常重要的指標。
中上型通道模式已經證明為非常適合用來描述都會區或室內的無線通信環境。以往在討論無線通信的信號傳播時，大多假設多重路徑信號彼此間呈現統計性獨立。然而在真實的環境中，此種假設可能過於理想化，在此論文中，我們採用中上型通道模式，來探討二信號間的相關性，推導出LCR與AFD的相關數學式。並且利用數值計算的方法進行分析，比較其性能。
在此研究中，數值分析結果顯示，因多重路徑傳播的影響，若以最大比率及選擇性方式來合成接收信號時，則其所呈現LCR與AFD會明顯的受到信號間相關性之影響。當相關性較強時，接收系統的效能較差，相關性較弱時，則其效能較佳，此一研究所獲得之結果，可望提供給相關的研究工作參考。

關鍵字

衰落 ； 準位跨越率 ； 平均衰落時距

並列摘要

The signal fading phenomena caused by multi-path propagation in wireless system will significantly degrade the performance of communication systems. Due to the signal envelope fluctuations, there are a lot of criteria for evaluating performance of wireless communication systems. The level crossing rate (LCR) and average fading duration(AFD) are two of the most important parameters. Both of them characterize some aspects of the second-order statistical behavior of envelopes fluctuations.
Although there exist a lot of distributions that well characterized the statistics of the mobile radio signal; however, empirical results as well as physical reasoning have shown the fact that the Nakagami-m distribution is a more versatile model for variety of fading environment such as urban, suburban radio multi-path channels and even for indoor propagation. In this thesis , Nakagami fading channel were utilized to study the correlated signals and its related mathematical expressions are derived with LCR and AFD.
In this study , a dual-branch receiver with maximal ratio combining (MRC) and selection combining (SC) techniques over Nakagami-m fading channel was analyzed with numerical calculations. Signals in the two diversity branches are assumed to be correlated with Nakagami-m fading. The Results indicate that average level crossing rate(LCR) and average fade duration (AFD) are significant affected by the correlation between branches with MRC and SC schemes.

並列關鍵字

fading ； level crossing rate ； average fade duration

參考文獻

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