时变水声信道中基于BEM的迭代信道估计技术

水声信道的多径时延扩展和时变特性对信道估计和均衡技术的研究带来了很大的挑战,同时也决定了水声信道是一种时频双扩展信道,提出一种水声OFDM通信系统中基于软信息的迭代信道估计技术,利用基于复指数基扩展模型(CE-BEM)进行信道估计。OFDM系统本身可以消除由于多径引起的符号间干扰(ISI)。基于导频的BEM信道估计,可以实现对时变信道的估计,结合基于软信息迭代的迭代均衡模块,将每次迭代生成的符号软判决信息作为辅助导频用于信道估计。同时,为了防止由于信道时变引起的信道子载波间干扰(ICI)对导频符号的影响,采用基于保护间隔的导频插入法插入导频。仿真结果显示基于BEM的软信息迭代信道估计性能较非迭代信道估计时明显提升。

Iterative channel estimation based on BEM in time varying underwater acoustic channels

The multi-path delay spread and time-varying characteristics of underwater acoustic channel bring a great challenge to the research of channel estimation and equalization technology. In this paper, an iterative channel estimation technique based on soft information is proposed. Channel estimator based on complex exponential basis expansion model (BEM) is used. The underwater acoustic channel is a typical double selection channel, and the OFDM system can eliminate inter-symbol interference (ISI) caused by multipath. The BEM channel estimator, combined with the iterative equalizer based on soft information iteration, is used to get the channel state information. Soft decision symbols are not only fed back to the equalizer to cancel the intersymbol interference (ISI), but also used as training signals in the channel estimator to update the estimated channel state information (CSI). At the same time, the guard interval based pilot insertion method is used to prevent the influence of channel subcarrier interference (ICI) on pilot symbols. The simulation results show that the system performance of the iterative channel estimation is significantly improved.