Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/7440
標題: 一種使用互補碼的多載波分碼多工系統架構
A Multi-Carrier CDMA Architecture Based on Complementary Codes for Future Wideband Mobile Communications
作者: 葉浚峰
Yeh, Jeng-Feng
關鍵字: complete complementary code;完全互補碼;multi-carrier CDMA system;MAI-free;多載波分碼多工系統
出版社: 電機工程學系
摘要: 
本論文主要在探討使用完全互補碼(complete complementary code)的多載波分碼多工系統的可行性。由數個正交矩陣而產生的完全互補碼,是由數個自互補碼組所構成,而自互補碼組之間彼此為互互補碼的關係。而完全互補碼最大的特點在於碼組之間擁有完美的相關性。
在本論文中,我們依據完全互補碼的特性,設計了可以發揮其特性的通訊系統架構,主要是以多載波分碼多工為基礎,另外我們在展頻的方式上也有所改變,不同於以往的直接序列展頻分碼多工,我們所採用的展頻方式是將每一個bit展頻之後,並將每個bit之間的間隔縮短至1個chip後再將所有訊號疊加起來。如此一來,在傳輸速率上可以獲得相當大的好處。再者,由於我們所用的展頻碼為完全互補碼,其自相關函數及互相關函數是完美的,即使每個bit都與其它的bit重疊,然而bit之間並不會相互干擾,而用戶與用戶之間也沒有相互干擾的問題存在。然而,這樣的系統最大的問題在多路徑通道的干擾,由於我們的訊號在展頻之後相互的疊加,以致於遭遇到多路徑通道的環境時無法有夠好的表現,即使加上一般CDMA常用的RAKE接收機也無法解決多路徑通道所產生的干擾。
因此我們使用領航訊號來偵測通道,並利用偵測得來的通道參數對用戶訊號做處理,以期能完整的得回用戶的訊息。我們採用的接收機,利用領航訊號測得的通道參數,對用戶的訊號做處理,進而提高系統在多路徑通道下的性能。
實驗結果也顯示,我們所提出的遞回濾波器能夠使領航訊號測得較精確的通道參數,並且利用這些參數對用戶訊號做處理,能順利的得到用戶的訊息。

In this thesis, the feasibility of complete complementary code based multi-carrier CDMA system is studied. The complete complementary code is composed of several sets of auto-complementary codes, any two of which are cross-complementary codes. The perfect correlation between code sets is the distinguishing feature of complete complementary code. In this thesis, we designed a new multi-carrier CDMA system architecture according the property of complete complementary code. The most obvious characteristic is that the bit stream in the new system is no longer aligned one bit after another in time. Instead, a new bit will start only after one chip delay relative to the previous bit, which is spread by an element code of complete complementary code. The proposed new CDMA architecture can offer an MAI-free operation in both down-link (synchronous channel) and up-link (asynchronous channel) transmission under the AWGN channel, because of the use of the CC-codes. The performance of the proposed CDMA system under multi-path channels is extremely awful. It can be shown that the use of a RAKE receiver in the proposed CDMA system will still cause an unacceptable BER (with three identically strong paths). Therefore, the pilot signal was used for channel estimation. Then, we can coherently combine signals in different paths to yield a boosted-up decision variable before the decision device. The proposed CDMA system with a recursive filter could be work in multi-path channels environment. The obtained results shows that the complete complementary code based multi-carrier CDMA system with a recursive filter under multi-path channel could work very well.
URI: http://hdl.handle.net/11455/7440
Appears in Collections:電機工程學系所

Show full item record
 

Google ScholarTM

Check


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.