電力線通訊中遞迴式通道估測與脈衝式雜訊消除演算法

Abstract

電力線通訊中，電力迴路不但存有多重路徑(Multipath)效應，且還受到脈衝式雜訊(Impulsive noise)干擾之影響。這兩種效應會使得接收端之通道估測準確度下降與資料錯誤率提升，嚴重影響整個系統之資料傳輸效能，因此提升通道估測之性能與消除脈衝式雜訊為提升電力線通訊品質之關鍵。 本論文參考IEEE P1901規格中的快速傅立葉轉換(Fast Fourier Transform) 之正交多工(Orthogonal Frequency-Division Multiplexing, OFDM)收發機技術 (FFT-based OFDM)為平台，提出一遞迴式接收機架構。本論文所提出之遞迴式通道估測與脈衝式雜訊消除演算法會在接收端的FFT方塊之前先進行前處理，以消除較強的脈衝式雜訊；在FFT方塊之後進行後處理，已消除殘餘的脈衝式雜訊同時進行通道估測。前處理方塊會先計算接收信號之峰度(Kurtosis)，以估計其強度，作為是否啟動零化法之依據，此外，零化法臨界值會根據離群值(Outlier)理論來設定。後處理會採用遞迴式的方法持續估計殘餘的脈衝式雜訊以及進行通道估測，這種結構將使得通道估測以及殘餘脈衝式雜訊消除處於互利互助之狀態。 電腦模擬結果顯示，傳統的零化法(Nulling)雖可消除部分脈衝式雜訊，但其效果不佳。然而，我們提出之遞迴式通道估測與脈衝式雜訊消除演算法不僅可提升通道估測之效能，同時也可有效消除脈衝式雜訊，因此使得整體系統性能大幅提升。

The multipath effect and impulsive noise (IN) of a power-line channel may affect the performance of power-line communications. Specifically, these two impairments reduce the accuracy of the channel estimation and increase the bit error rate (BER). In this thesis, we focus on the Fast Fourier Transform –based orthogonal frequency-division multiplexing (FFT-based OFDM) receiver, which is defined in IEEE P1901 standard and propose an iterative receiver architecture. Moreover, we devise an associated iterative channel estimation and IN cancellation algorithm for this receiver. Prior to the FFT operation, we pre-mitigate the IN by a nulling device to cancel the strong part of the IN sources. Furthermore, we mathematically derive the threshold of this nulling device according to the outlier detection theory. In addition, we propose using the value of the Kurtosis to decide whether to enable the pre-mitigation block or not. On the other hand, after the FFT operation, we iteratively post-mitigate the residual IN. The post-IN mitigation block iteratively cancel the residual IN and estimate the channel information, so that the channel estimation and IN mitigation are in a mutually beneficial status. Simulation results show that the proposed iterative receiver not only increases the accuracy of the channel estimator, but also effectively cancel IN sources.