浅海水声通信中非规则LDPC码的构造、优化和应用研究

Time-varying strong multipath interference is the major obstacle to a reliable data transfer in shallow water acoustic channels, which is also one of the key problems that should to be solved urgently in coherent underwater acoustic communications. The adaptive equalization for shallow water acoustic channels and the construction, optimization and implementation of irregular LDPC codes will be deeply investigated in this project. Moreover, the cascade and iterative computation of the equalization and the irregular LDPC codes will be investigated. The decoder threshold of LDPC codes will be analyzed and its optimal degree distribution for shallow water acoustic channels will be searched by using the density evolution algorithm. The corresponding irregular LDPC codes will be constructed by using progressive edge growth (PEG) method. The effects of structure of parity matrix H, decoder algorithm, cascade mode, code length, and parameters of channel adaptive equalization on the performances of the constructed irregular LDPC codes will be investigated. A Turbo-LDPC code will be constructed and its decoder performance in shallow water acoustic channels will be investigated. In addition, the new code will be compared with the conventional Turbo code and LDPC code. The real-time coding and decoding of the constructed irregular LDPC codes will be realized by the DSP software method. Furthermore, a DSP-based high-speed coherent underwater acoustic communication system will be developed. The system attempts to achieve the following communication performances: the communication distance is 5~8km, the data rate is 5kbits/s, and the bit error ratio is less than 10-5. The achievement of this project will provide a new high-tech support for marine research and production.

时变强多途干扰是浅海水声信道数据可靠传输的主要障碍，也是目前水声相干通信迫切需要解决的关键技术问题之一。针对该问题对浅海水声信道自适应均衡、非规则LDPC码的构造、优化和应用，以及两者的级连、迭代运算等展开深入研究；采用密度进化算法分析浅海水声信道中LDPC码的译码阈值，搜索最优度分布函数对，PEG方法构造相应非规则LDPC码；研究校验矩阵H的结构、译码算法、级连模式、码长和信道自适应参数等对所构造非规则LDPC码性能的影响机制；构建Turbo-LDPC码，分析其在浅海水声信道中的译码性能并将其与传统Turbo码、LDPC码进行比较；DSP软件方法实现LDPC码的实时编译码；基于DSP成功研制一套高速水声相干通信实验样机，实现通信距离5~8km，传输速率5kbits/s，系统误比特率小于10-5的通信性能。本项目的顺利实施有望为海洋方面的科研和生产活动提供一种高新技术支持。

水声通信在军事和民用领域都有重要应用价值，如海洋环境监测、海洋资源勘探、海洋科学研究和水下蛙人语音通信等。本项目针对水声通信关键技术之一的高效信道纠错编码，即LDPC码展开深入研究，不仅具有重要的科学意义，也有重大的应用价值。本项目建立了一种基于BELLHOP射线理论的时变浅海水声信道仿真模型。研究了发射/接收机相对运动、海面波浪传播等信道边界变化等对浅海水声信道冲击响应的影响机制。分析了声波频率、声速剖面、海底沉积物参数、海水声吸收和海面声反射等因素的影响。将LDPC译码输出反馈输入到自适应判决反馈均衡器（DFE），建立了一种适用于浅海多途水声信道，有很强抗码间干扰能力的DFE-LDPC迭代译码结构，导出了该结构中变量节点译码器和校验节点译码器的EXIT曲线，采用EXIT曲线匹配方法对LDPC码在多途浅海水声信道中的译码阈值进行了分析。提出了一种采用差分进化算法对LDPC码度分布对函数进行优化的新方法，给出了不同信道和不同码率的优化设计实例。基于TI公司TMS320 C6713 DSP成功研制了一套通信速率5.0kbps的实时水声通信系统。进行了水池和厦门港海浅海水声数据传输试验，取得了传输距离5km，误比特率小于10-5的良好通信效果。将该系统与WT2000声码器相结合，实现了一种具有较高语音质量的水下实时语音通信系统。本项目积累了大量的实验仿真和现场测试数据，所取得的研究成果有望为海洋科学研究和海洋环境监测等提供一种高新技术支持。