利用迭代式內插法結合改良式路徑估測法增強多輸入多輸出正交分頻多重存取系統之通道估測效能

本論文針對多輸入多輸出正交分頻多重存取(MIMO-OFDMA)系統之通道估測提出一改善方法，此改善方法的領航訊號使用梳型(Comb Type)編排方式。對於梳型編排方式之領航訊號，首先利用最小平方估測法(Least Square, LS)求出領航訊號的通道頻率響應，然後利用迭代式內插法(Iterative Interpolation Method, IIM)求出完整的通道頻率響應，之後再利用反傅利葉轉換(IFFT)得到通道的脈衝響應，接下來利用改良式路徑偵測估測法估測出較正確之通道路徑數，以求出最後之通道頻率響應。其作法為設定一門檻值(Threshold)來分離脈衝響應和雜訊，大於門檻值的脈衝響應留下來作為主要通道路徑，其餘脈衝響應視為雜訊並設為零，進而增加我們估測的準確性，使得估測的結果接近於實際通道頻率響應。由模擬結果顯示，本文所提出的改良式路徑估測法效能表現較IIM結合傳統LS估測法、FFT-based估測法、Hayashi’s估測法、路徑估測法(Path Detection, PD)及最小均方(Least Mean Square, LMS)等演算法佳。

關鍵字

多輸入多輸出；正交分頻多重存取；通道估測；迭代式內插法

並列摘要

In this thesis, we mainly study the performance improvement of channel estimation in MIMO-OFDMA systems. In order to improve the quality of the channel estimation of the comb type arrangement, we firstly use the least square (LS) algorithm to estimate the channel frequency response of pilots. Secondly, we use the iterative interpolation method (IIM) to interpolate the channel frequency response of data signals. Then, the channel impulse response is obtained by using the inverse fast Fourier transform (IFFT). To find the frequency response of the actual channel, we utilize the improved path detection (PD) method to estimate the accurate channel path. One threshold was set to separate the channel impulse response and noise in this PD method. If the magnitude of the channel impulse response is greater than the threshold, the corresponding channel can be regarded as main channel path. The others are regarded as noise and are set to zero to improve the accuracy of estimation, enabling the estimated results to close to the actual channel frequency response. Experimental results show that the proposed scheme obtains the best performance in terms of the bit error rate (BER) among the IIM scheme combined with the different methods, such as, the traditional LS, FFT-based, Hayashi, PD, and the least mean square (LMS) estimation methods.

並列關鍵字

Multiple-Input Multiple-Output (MIMO) ； Orthogonal Frequency Division Multiple Access (OFDMA) ； Channel Estimation ； Iterative Interpolation Method (IIM)

參考文獻

[1] K. Khurshid and I. A. Khokhar, “Comparison Survey of 4G Competitors (OFDMA, MC-CDMA, UWB, IDMA),” in Proc. IEEE International Conference on Aerospace Science & Engineering, pp. 1-7, 2013.

[5] S. Alamouti, “A Simple Transmit Diversity Technique for Wireless Communications,” IEEE Journal on Selected Areas in Communications, vol. 16, pp. 1451-1458, Oct.1998.

[6] T. S. Rappaport, Wireless Communications Principle and Practice, Second Edition, Prentice-Hall, 1996.

[7] R. R. Mosier and R. G. Clabaugh, “Kineplex, A Bandwidth Efficient Binary Transmission System,” American Institute of Electrical Engineers, vol. 76, pp. 723-728, Jan. 1958.

[11] ANSI, “Asymmetric Digital Subscriber Line (ADSL) Metallic Interface,” ANSI/TIEI/9J-007, Aug. 1997.

國際替代計量

利用迭代式內插法結合改良式路徑估測法增強多輸入多輸出正交分頻多重存取系統之通道估測效能

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