多用戶正交分頻多工系統之單區塊子載波平均盲蔽通道估測演算法

Capon提出的傳統式最小變異無失真響應（Minimum Variance Distortionless Response, MVDR）演算法用於盲蔽式波束成型與抵達方向（Direction-of-Arrival, DOA）之估測，以及Schmidt提出的多重訊號源分類（Multiple Signals Classification, MUSIC）演算法用於DOA的估測，已被廣泛地用於陣列訊號處理領域。這兩個演算法所做的基本假設為所有未知的訊號源皆為廣義穩態（Wide-sense Stationary）且彼此之間在統計上是互相獨立的。波束成型被考慮在多用戶正交分頻多工（Orthogonal Frequency Division Multiplexing, OFDM）系統的上傳模式（Uplink）中，而上述的假設只對前置快速傅立葉轉換波束成型架構（Pre-FFT Beamforming Structure）是成立的，然而由於缺乏路徑分集（Path Diversity），不管是MVDR演算法或是MUSIC演算法所得到的波束成型效能都會受到限制。對於多用戶OFDM系統的上傳模式之後置快速傅立葉轉換波束成型架構（Post-FFT Beamforming Structure），適當地建立離散時間多輸入多輸出訊號模型，再以子載波平均取代統計平均用於估測訊號的相關矩陣，MVDR與MUSIC演算法可以被證明是可應用的（也就是上述的基本假設能夠解除）。本論文提出一個針對多用戶OFDM系統的單區塊盲蔽通道估測演算法。假設通道在一個信號區塊時間內通道是固定的，在一個備有多天線陣列的接收端（基地台）以及單一天線發射端（移動物體）的環境下，所提出的演算法利用子載波平均可以在一個正交分頻多工的區塊時間內估計出所有的通道參數（DOA，抵達時間，通道震幅）。最後，呈現一些模擬結果以驗證所提出的盲蔽通道估測演算法的功效不錯，即使子載波的數量不大。

關鍵字

通道估測；正交分頻；子載波平均；後置快速傅立葉轉換波束成型架構

並列摘要

In this thesis, a block-by-block blind channel estimation algorithm is proposed for a multiuser orthogonal frequency division multiplexing (OFDM) system with a uniform linear antenna array at the base station and a single antenna at each mobile unit. Provided that the channel is static within an OFDM block (i.e., block fading channel), based on the subcarrier averaging, the proposed channel estimation algorithm can estimate all the channel parameters (directions of arrival, time delays and multipath gains of all the users) within only one OFDM block. Some simulation results are provided to justify the efficacy of the proposed channel estimation algorithm even when the total number of subcarriers is not very large.

並列關鍵字

Channel estimation ； OFDM ； Subcarrier averaging ； post-FFT beamforming structure

參考文獻

M. Budsabathon, Y. Hara, and S. Hara, ``Optimum beamforming for pre-FFT OFDM adaptive antenna array," IEEE Trans. Vehicular Technology, vol. 53, pp. 945-955, July 2004.

M. Okada and S. Komaki, ``Pre-DFT combining space diversity assisted COFDM," IEEE Trans. Vehicular Technology, vol. 50, pp. 487-496, Mar. 2001.

D. Bartolome and A. I. Perez-Neira, ``MMSE techniques for space diversity receivers in OFDM-based wireless LANs," IEEE Journal on Selected Areas in Communications, vol. 21, pp. 151-160, Feb. 2003.

H. Matsuoka and H. Shoki, ``Comparison of pre-FFT and post-FFT processing adaptive arrays for OFDM systems in the presence of co-channel interference," Proc. IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, vol. 2, Beijing, China, Sept. 7-10, 2003, pp. 1603-1607.

Z. Lei and F.P.S. Chin, ``Post and pre-FFT beamforming in an OFDM system," Proc. IEEE 59th Vehicular Technology Conference, vol. 1, Milan, Italy, May 17-19, 2004, pp. 39-43.

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多用戶正交分頻多工系統之單區塊子載波平均盲蔽通道估測演算法

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