適用於窄頻電力線通訊之循環穩態脈衝雜訊消除

Abstract

電力線原始設計為傳輸電力，並非用於信息傳輸，而電力線通道內含有許多電力設備，其內部具有切換式功能之電子零件，運作時會產生高能量的脈衝雜訊(impulsive noise)，若作為通訊媒介使用，脈衝雜訊將嚴重影響整個系統的資料傳輸效能。根據研究，具有循環穩態(cyclostationary)特性的週期性脈衝雜訊是窄頻電力線通道中最具威脅性的干擾，而且其能量通常是背景雜訊的數十倍以上。 本論文參考IEEE P1901.2標準之實體層規範為模擬平台，提出一強健性接收機架構，使用頻移濾波器(frequency shift filter, FRESH filter)估計循環穩態脈衝雜訊並將其消除，並且利用正交分頻多工(orthogonal frequency-division multiplexing, OFDM)訊號具有循環字首(cyclic prefix, CP)所導致的循環穩態特性，將受到脈衝雜訊干擾的接收訊號重建回來。然而，在脈衝雜訊的循環頻率(cyclic frequency)並非已知且固定情況下，循環頻率誤差將使頻移濾波器之效能大幅降低，故本論文也針對此問題提出一具循環頻率誤差補償之可適性頻移濾波演算法。軟體模擬結果顯示，本論文提出之演算法可有效估計循環頻率的變異並加以補償，再藉由消除循環穩態脈衝雜訊，使系統效能大幅改善。

The power line is originally designed for power transmission instead of communication. The power line channel contains many power devices. The electronic components with switching functions can easily introduce high energy impulsive noise. Used as a communication system, such impulsive noise can seriously degrade the data transmission efficiency of the entire system. According to the research, the periodic impulsive noise with cyclostationary characteristic is the most threatening interference in narrowband power line channel, and its energy is usually dozens of times higher than background noise. In this thesis, we refer to the physical layer specification of IEEE P1901.2 standard as the simulation platform and propose a robust receiver architecture for narrowband power line communication. The frequency shift filter (FRESH filter) is used to estimate the cyclostationary impulsive noise and eliminate it. The fact that an orthogonal frequency-division multiplexing (OFDM) signal has cyclostationary characteristics due to the cyclic prefix (CP) can be used to reconstruct the received signal interfered by the impulsive noise. However, the cyclic frequency of impulsive noise is not a constant, and such cyclic frequency error can greatly degrade the performance of the FRESH filter. Therefore, we also propose an adaptive FRESH filter algorithm for cyclic frequency error compensation in this thesis. The simulation results show that the algorithm proposed by us can effectively estimate and compensate the cyclic frequency error, eliminate the cyclostationary impulsive noise, and hence improve the system performance.