多使用者偵測技術應用於基於OFDM之MC-CDMA系統在雷利通道下之效能分析

Performance Analysis of Multiuser Detections Applied to OFDM Based MC-CDMA System in Rayleigh Channel

謝坤穎(Kun-Ying Hsieh)

指導教授 ： 呂振森

國立臺北科技大學/電資學院/電機工程系研究所/碩士(2007年)

摘要

本論文主要是探討基於OFDM之MC-CDMA系統在雷利緩慢衰減通道下效能分析。OFDM是一種數位多載波調變系統，每個子載波傳送資料與一般調變一樣，如相位移調變, 正交相位調變等，如此每個子載波仍然可以維持和一般調變的資料率在相同的頻寬之下。在實務方面，正交分頻訊號從快速傅立葉轉換演算法產生。多載波分碼多工系統特性為利用互為正交之展頻碼做使用者資料區別。基於OFDM之MC-CDMA系統結合OFDM系統及MC-CDMA系統的優點，但在雷利緩慢衰減通道下，其不同使用者間的正交性會受到破壞，因此系統效能會受到影響，值得進一步深入探討。本論文將以理論分析此一系統，在雷利緩慢衰減通道下，單一使用者之位元錯誤率，並討論使用頻帶多寡對位元錯誤率之影響。同時，亦將討論在多個使用者共用相同頻寬下，分別使用複雜度低的平行干擾消除法、連續干擾消除法，及複雜度高的最小均方誤差法與機率資料連結多使用者偵測器，以理論和電腦模擬，分析此一系統在不同偵測器之效能。

關鍵字

正交分頻多工 ； 多載波分碼多工 ； 多使用者偵測

並列摘要

The thesis focused on the performance of OFDM based MC-CDMA systems in Rayleigh slow fading channel. OFDM is a digital multi-carrier modulation scheme, which uses a large number of closely-spaced orthogonal sub-carriers. Each sub-carrier is modulated with a conventional modulation scheme like phase-shift keying and quadrature amplitude modulation to maintain the similar data rates compared to the conventional single-carrier modulation schemes under the same bandwidth. In implementaion, the OFDM signals are generated from the Fast Fourier transform (FFT) algorithm. The MC-CDMA system utilizes mutually orthogonal spreading codes to distincguish user data. The OFDM based MC-CDMA system shares the benefits of both OFDM and MC-CDMA systems. However, in the Rayleigh fading channel the system performance is degraded by the disruption of the user orthogonality. In this thesis, we’ve derived the bit error rate formula of the single user detection for the above system in Rayleigh fading channel. For the multiuser case, we explored two complexity MUD schemes. One is the lower complexity MUD scheme such as PIC, SIC, and the other is the higher performance but higher complexity MUD scheme such as MMSE, PDA. To provide a reliable performance analysis of multi-user detectors in OFDM based MC-CDMA system, we compared the approximated bit-error-probability formulas with bit error rates simulated by computer.

並列關鍵字

OFDM ； MC-CDMA ； Rayleigh fading channel ； MUD

參考文獻

[20] 李正修，機率資料連結多使用者偵測器於分碼多工系統之效能分析及改善，碩士論文，國立臺北科技大學電機工程系碩士班，台北，2005。

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