双选择衰落信道下OFDM系统基于梳状导频的变换域频率分集式信道估计

Frequency Diversity Transform Domain Channel Estimation Based on Comb Pilots over Double Selective Fading Channels

由于高速铁路无线信道表现出频率选择性和时间选择性衰落(双选择性衰落),正交频分复用(OFDM)在该信道上传输,需要实时跟踪估计信道变化,降低估计噪声。由于离散傅里叶变换具有快速算法IFFT/FFT,基于变换域的信道估计技术逐渐受到关注。通常,OFDM系统的梳状导频数多于信道冲击响应长度,导致变换域信道估计方法降噪比较困难。本文提出一种梳状导频变换域频率分集式信道估计方法,它通过联合若干分组的变换域信道估计,明显降低估计噪声,从而降低信道估计的均方误差(MSE)和系统的误码率(BER)。理论分析和仿真结果表明,在时不变信道中,当分集数为L,该方法对MSE的增益是10lg(L);在时变信道中,该方法出现"错误平底",但相对于传统变换域信道估计方法,性能仍有改善。

Orthogonal frequency division multiplexing（OFDM） should estimate and track the wireless channels in double selective fading.Due to the lower implementation complexity,transform domain channel estimation becomes increasingly attractive recently.Generally,the comb-pilot number is more than the wireless channel order,which makes noise suppression difficult.In this paper,a novel frequency diversity channel estimation method via pilot groups combining is proposed,which can reduce noises and improve the performance of the Mean Square Error（MSE） and Bit Error Rate（BER）.Through analysis and simulation,it is proved that when the method is employed in time invariant channels,the diversity gain of MSE is 10lg（L） dB with the diversity order being L and when it is imployed in time varying channels,there exists the error floor,however,its performance still remains improved in comparison with the conventional transform domain channel estimation methods.