标题: | 正交分频多工系统中Clipping Noise之消除 Clipping noise mitigation for OFDM systems |
作者: | 林钧陶 tow 吴文榕 Wen-Rong Wu 电信工程研究所 |
关键字: | 正交分频多工;讯号峰值;截波;OFDM;PAPR;Clipping |
公开日期: | 2003 |
摘要: | 由于在正交分频多工(OFDM)系统中,过高的时域讯号峰值会造成传送讯号直流偏压过高,使其增加传送功率之消耗.我们采以限制讯号振幅的方式来达到降低讯号峰值之目的.但这会引进额外的杂讯(Clipping Noise),进而严重影响系统的表现.我们考虑以下三种消除此杂讯的方法.分别为在传送端利用超频取样加上低通滤波器的方式来降低杂讯;以及在接收端利用decision-aided reconstruction(DAR)或clipping noise estimation and cancellation(CNEC)两种演算法来还原讯号.一般而言, DAR与CNEC在演算过程中我们均假设Clipping Ratio(CR)为已知.但此假设未必适用于所有的应用.因此我们亦提出一个可以在接收端准确估计CR的方法.此外,我们也探讨为了减少接收机中类比数位转换器的位元数或是动态范围所等效造成Clipping的效应,我们可将DAR与CNEC稍作修改以符合需求.另外,我们建议在处理接收端产生的Clipping Noise时,使用递回方式估计通道来以达到提升DAR与CNEC的效果.最后透过模拟结果显示以上提出之方法均能有效压抑Clipping Noise对系统的影响以及正确估计出我们需要的参数. Orthogonal Frequency Division Multiplexing (OFDM) signals exhibit a large peak to average power ratio (PAPR), which leads to a high amplifier power consumption. Signal clipping is known to be the simplest method to solve the problem. However, clipping will introduce clipping noise and this will adversely affect the system performance. In this thesis, we first study clipping noise mitigation methods. We consider three methods, namely, filtering oversampled clipping noise, decision-aided reconstruction (DAR), and clipping noise estimation and cancellation (CNEC). Conventionally, the clipping ratio, an important parameter for DAR and CNEC, is assumed to be known. However, this may not be possible for all applications. We then propose a new clipping ratio estimation method for DAR and CNEC. In addition to signal clipping at transmitter, we also consider the clipping in the receiver. The advantage of receiver clipping is that the number of required analog to digital conversion (ADC) bits can be reduced. We modify the DAR and CNEC algorithms such that they can be operated in this scenario. To further enhance the performance, we suggest an iterative channel estimation scheme for DAR and CNEC. Simulations show that clipping noise can be effectively reduced using proposed algorithms. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT009113549 http://hdl.handle.net/11536/46368 |
显示于类别: | Thesis |
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