超奈奎斯特速率传输的高谱效水声通信研究

With the opening up of ocean power and smart ocean strategies, there is a wide requirements for high-speed and reliable underwater acoustic communication technology. Currently, there are two key problems in underwater acoustic communications. One is how to realize high-speed communication with low signal-to-noise ratio and limited bandwidth. The other is how to obtain reliable communication under time-frequency doubly-spread wideband underwater acoustic channels. As an extension of ordinary linear modulation, Faster-Than-Nyquist signaling simply sends the usual data bearing pulses faster. Although it will results in intersymbol interference (ISI) or/and intercarrier interference (ICI), this innovation can transmit up to twice the bits as ordinary modulation at the same bit energy, spectrum, and error rate, and comes into view nowadays. In this subject, we will research FTN signaling technology under the time-frequency doubly-spread wideband underwater acoustic channels, and realize the high-speed and reliable underwater acoustic communication under the more serious ISI or/and ICI conditions, in order to realize an innovative solution to the high-speed underwater acoustic communication. This project consist of the following main research topics. The first one is to establish the prototype filter that can match the time-frequency doubly-spread wideband underwater acoustic channels and the fast implementation of the FTN signaling modulation and demodulation. The second one is shortening equalization for the ISI/ICI caused by FTN itself. The third one is to research bidirectional iterative reception algorithms based on hybrid time-frequency domain equalization. The research group has been engaged in the research of underwater acoustic communications for years, and has build solid basic work for this project.

海洋强国与智慧海洋战略的开启，对高速可靠水声通信存在广泛需求。当前水声通信亟待解决两个关键问题：一是如何在低信噪比与有限带宽下实现高速通信，另一个是如何在时频双扩展信道下实现可靠传输。超奈奎斯特传输技术(Faster-Than-Nyquist，FTN)在一定的ISI/ICI代价下，可以以接近2倍的Nyquist速率传输码元且不影响误码性能，将通信速率提高近1倍，正受到通信界的极大关注。本项目拟在恶劣的水声信道中研究FTN技术，在更加严重的ISI和ICI条件下实现高速可靠水声通信，以在高速可靠水声通信关键技术上实现创新的解决方案。研究内容主要包括FTN水声通信原型滤波器的设计与调制解调的快速实现，FTN所引入的ISI与ICI的缩短均衡，以及时频域联合双向迭代高性能均衡算法的研究。申请人及项目组一直从事水声通信研究，已有较好积累，承担单位建有相关的国家级科研基地，完全有能力保障项目的顺利执行。

针对水声信道带宽极其有限的特点，本项目提出采用超奈奎斯特速率传输方案来实现高谱效的水声通信。但水声信道还具有严重的时变多径双扩展特性，再加上超奈奎斯特传输自身引入的严重的码间干扰，使得研究超奈奎斯特传输的可靠接收算法具有非常重要的实际意义。本项目主要关注超奈奎斯特传输的高性能接收算法。针对水声信道时变快等特点，本项目设计了双向帧结构，与传统的单向均衡算法相比，双向均衡算法得益于两个均衡器的分集增益，能够有效地抑制错误传播，提高符号检测性能。在此帧结构基础上，本项目分别开展了基于信道估计的均衡、直接自适应均衡(DA-EQ)以及两者的结合三种接收方案的研究，并结合Turbo迭代、接收分集和最小误码率自适应滤波器系数更新准则。此外，也采用时间反转、后验软符号信息传递等技术更一步提高接收性能。湖试结果表明在超奈奎斯特传输中在加速因子为0.75时(即频谱效率提高33.3%)系统的误比特率可以降到10的-4次方量级以下。项目还研究了索引调制与非正交多址两个高谱效调制方案以及一些水声网络协议。在工程实现上，项目研制了基于多核处理器的水声MIMO通信机，项目研究的算法与方案已经部分在该水声通信机上得到实现。同时研究了水声网络协议栈实验平台以进行水声网络仿真与实验验证。