水声通信中基于信道辨识的盲turbo均衡方法

水声信道多途效应明显,造成接收信号存在严重的码间干扰(ISI,Intersymbol interference)。基于最小均方误差(MMSE,Minimum mean square error)准则的turbo均衡器级联了均衡和信道译码,能够有效去除ISI,并获得优良的性能。由于水声信道的时变性,传统MMSE-turbo均衡需要周期性的训练序列,以实现连续可靠的通信。训练序列虽然提高了通信的可靠性,但降低了信息的有效传输速率。因此,为提高通信效率,本文提出了一种盲turbo均衡方法,该方法通过引入新的盲信道辨识器来同时获得信道估计响应和已去除部分ISI的初步均衡输出信号,并为turbo均衡提供初始的响应参数和比特软信息。与水声通信中应用较多的盲判决反馈均衡器(DFE,Decision feedback equalizer)相比,海上实验结果证明本文提出的盲turbo均衡方法抗信道多途衰落的能力较强,并且与传统MMSE-turbo均衡相比无需训练序列,因此提高了信息的有效传输速率。

Blind turbo equalization based on channel identification for underwater acoustic communications

Underwater acoustic channels usually suffer from the extended multipath propagation which causes intersymbol interference (ISI). Turbo equalization is an iterative equalization and decoding technique that can remove ISI and achieve impressive performance. Since underwater channels are time-varying, turbo equalization needs periodic transmission of training sequences to keep continuous communication. Although the training sequence improves communication reliability, it decreases the effective bit rate. We therefore propose a blind turbo equalizer, which includes a blind channel identifier and a turbo equalizer. The estimated channel impulse response is used to get initial response of the turbo equalizer. Sea test results show that the new blind turbo equalizer can perform better than the blind decision feedback equalizer (DFE), and it increases the effective bit rate, comparing with the conventional turbo equalizer.