正交频分复用通信系统中的快变信道估计

信道的快速变化导致正交频分复用通信系统(OFDM)载波间的正交性遭到破坏,从而产生载波间的相互干扰(ICI),传统的信道估计方法(不可虑ICI影响)不再适用。为此,Choi等人提出了相应的快变信道估计方法,但该方法计算量较大,且需要信道的统计特性知识,而实际信道的统计特性往往无法精确得到。Linartz等人证明:在大多数应用条件下,信道在一个OFDM帧周期内的变化近似满足线性特性。对OFDM系统的ICI特性进行了时域和频域两方面分析,并利用信道变化的线性特性,提出了一种新的快变信道估计方法,该方法具有计算量小、且不需要信道的统计特性信息的优点。文章还得到如下结论:与慢变信道情形不同,在信道快速变化条件下,当OFDM系统中的训练序列应分成许多长度相同的组,且这些组在OFDM帧中等间隔分布时,信道估计误差最小。

Estimation of Time-varying Channels for OFDM Systems

Channels' rapid variations lead to the loss of orthogonality among subcarriers,resulting in inter -carrier interference(ICI )in orthogonal frequency division multiplexing(OFDM)systems.In this case,traditional channel estimation methods become inapplicable.Choi,etc.,have proposed an algorithm for fast-varying channel estimation,but it requires a high computational complexity and needs the channel statistical knowledge,which is usually not obtained accurately.LINARTZ,etc.,put forward that in the practice,Channel varies linearly during an OFDM block in the practice.This paper proposes a novel method for estimating channel parameters varying within an OFDM symbol,basing on time-and frequency-domain ICI analysis and the assumption that channel varies linearly during an OFDM block.This paper also considers the ICI effects and concludes that in time-varying scenarios,it should group pilot tones together into blocks equispaced onto the FFT grid,which is different with the result for time-invariant channels.