基于导频的OFDM水下通信信道估计

Pilot based channel estimation for OFDM underwater communication

信道估计是OFDM水下通信相干解调的必要步骤.通过插入位置已知的导频信息,OFDM接收机可以知道水声信道在导频位置的频率响应.根据插入导频位置的不同,信道估计的性能也有很大的差异.块状、梳状和分散型3种导频分布方式被证明分别适用于不同的水声信道环境.水声信道可以看做是一个梳状滤波器,通过信道估计可以得到试验信道的通带和阻带.阻带的信道估计错误往往要大于通带,尤其是当信道的相干带宽较小时,这种现象则更为明显.子载波间干扰会对信道估计性能造成很大影响,利用改进的变换域滤波器导频降噪方法可以有效地降低这种影响.

Channel estimation is a compulsory task for coherent OFDM underwater communication. Channel frequency response can be estimated by pilots that are already known to the receiver. BER performance can vary a lot according to different type of pilot pattern. Three kinds of pilot distributions （block, comb and scatter） are analyzed, each of which is proved to work well in some certain underwater environment. Underwater channel is demonstrated to be a comb filter. With channel estimation, stopband and passband of the experiment channel are found and analyzed. Channel estimation error is more likely to occur in stopband than in passband, especially when the channel coherence bandwidth is small. Interchannel interference can cause large estimation error by increasing its noise level. An improved transform domain filter can reduce the estimation SNR significantly,