無線正交分頻多工系統中連續波干擾下之IQ不平衡效應的分析與評估

Abstract

OFDM系統會遭受IQ不平衡（I/Q Mismatch）、載波頻率位移（CFO）、取樣時間位移（SCO）以及直流位移（DC offset）等等許多前端的理想效應。而且，由於許多不同系統可免費使用不用執照的頻帶，因此OFDM系統也會受到來自於其他系統窄頻訊號的干擾，例如連續波干擾。此篇論文將會提出一些方法去解決IQ不平衡（I/Q Mismatch），且是在有連續波干擾情況下。另外，利用影子拒絕率(IRR)來判斷這些方法的效能。此篇論文有兩個主要的貢獻，第一，在有遵循802.11n標準下，提出的演算法只需要一次不複雜的計算就可以估計出IQ不平衡（I/Q Mismatch）係數。第二，透過影子拒絕率(IRR)進行模擬的時間可以降低很多。當訊號與干擾波比例等於-10dB時，理論分析以及模擬結果將證明提出的演算法可以改善系統效能。

OFDM systems suffer from the front-end non-ideal effects, such as IQ mismatch (IQM), carrier frequency offset (CFO), sampling clock offset (SCO), DC offset. Furthermore, due to unlicensed frequency bands shared by many different systems, OFDM systems are also interfered with narrowband interference, such as continuous wave (CW) jamming. In this paper, some methods on baseband are proposed to solve I/Q mismatch (IQM) under CW jamming in MIMO-OFDM systems. Through image-rejection-ratio (IRR), the efficiency of these methods is judged. There are two main contributions in this paper. First, by following the 802.11n standard, the proposed algorithm only needs one shoot calculation without too complicated computations. Second, the simulation time can be reduced significantly by IRR. A theoretical analysis and simulation results demonstrate the algorithms can improves the performance while signal-to-jamming ratio (SJR) equals to -10 dB.