MFSK浅海远程通信多径抑制的频率分组编码方法

多频移键控调制技术（MFSK）对信道衰落有良好的适应性，是远程水声通信的重要技术。但是，用于浅海远程水声通信时，由于多径传播的影响，导致严重的码间干扰（ISI），使得远程微弱信号的频率估计产生较大偏差，误码率显著增加。本文针对远程水下信道和MFSK调制的特点，提出了一种新的频率分组编码（FGC）方法。该方法改变了传统MFSK的数据帧格式，相邻符号采用不同组的频率进行编码映射，有效抑制了多径干扰。在深入研究新方法统计特性的基础上进行了湖试验证，结果表明，采用FGC新方法的通信系统，多径抑制有效，性能稳健，更适合于80-100km水声远程通信。

Frequency group coding method to restrain the multipaths in MFSK long-range acoustic communications

Multi-frequency shift keying (MFSK) modulation, which is suitable to fading channels, is an important technique in long-range acoustic communications. But in the case of long-range acoustic communications in shallow water it is disturbed by severe multipaths whid produce increased inter-symbol interference (ISI). So the error of frequency estimation for the week signals is bigger and the BER becomes larger. Based on the characters of long rang underwater acoustic channels and MFSK modulation, a new Frequency Group Coding (FGC) method is proposed in this paper. This method is different from the traditional MFSK frame in that its neighboring MFSK symbols are mapped to different frequency group to restrain the severe multipaths effectively. After the statistical characteristics study by simulation in experiments on the new method in a lake were carried out. The results show the effectiveness and robustness of the new method in eliminating the multipath interference in long range shallow water acoustic communication up to the range of 80~100km.