基于多元LDPC码水声扩频通信系统仿真

发布时间：2018-01-17 16:27

本文关键词：基于多元LDPC码水声扩频通信系统仿真　出处：《昆明理工大学》2017年硕士论文　论文类型：学位论文

更多相关文章： 水声通信 LDPC 扩频 多载波 纠错编码

【摘要】：随着人口膨胀性的增长,而可供开采的陆地资源逐步枯竭。由于70%的地球表面都是海洋,其蕴藏着丰富的海洋资源,各国纷纷加快对海洋的探索和开发步伐。集海洋学科、信息学科为一体的水声技术作为海洋开发的主导技术之一越来越受到各国的重视,但水下信道是一个极其复杂的时-空-频变参多径衰落信道,极大的制约了水声信号在高速率,远距离,低误码的传输。当前,信道纠错编码技术对于无论是相干调制,还是非相干调制方式下的水声通信系统都是不可缺少的关键技术。针对水声信道的特征,将LDPC码应用到扩频水声通信系统中,可以提高系统的频带利用率和可靠性。低密度奇偶校验(LDPC)码具有:结构简单、编码增益高、在高斯信道下接近香农限的性能和强大的纠错能力;抗突发性差错的特性,不需加入交织器,避免可能带来的时延且在频率选择性衰落信道中具有良好的性能;译码是并行的,延时远远小于传统Turbo码的串行迭代译码算法。LDPC码可降低在水声信道传输时的信号失真,展现出良好的应用前景。水声信道的多径干扰会对信号产生严重的衰落,是现代水声通信发展的瓶颈之一。扩频技术、均衡技术、分集技术等是目前发展较为成熟的抗多径干扰技术。扩频技术既能有效的抗多径干扰,又有很好的多址性能,也是构建水下通信网络的关键技术。论文首先介绍包括传播损失、信道噪声、多径干扰、多普勒效应等水声信道的基本特征,并对频率选择性衰落、时间选择性衰落、瑞利信道衰落特性进行定量的描述,建立了时变的水声信道模型;其次,提出一种V型结构的QC-LDPC码校验矩阵的构造方法,通过迭代编码来实现线性编码,降低编码的复杂度,并对LLRBP译码算法进行改进,提供准确的译码信息;在基于扩频的基础上,加入LDPC码信道纠错编码技术,设置仿真参数,验证分析不同阶域的LDPC码的纠错性能以及LDPC码结合扩频技术应用在水声通信中的优势;最后,介绍了包括MC-CDMA、MC-DS-CDMA、MT-CDMA的多载波扩频理论,并比较其优缺点,最终提出LDPC码MT-CDMA多载波扩频水声通信系统,设置仿真参数,在不同码长、不同调制方式下进行仿真,对比RS码下系统的误码率,证明本文提出的系统优化具有一定的合理性和实用性。
[Abstract]:With the increase of population expansion, the land resources available for exploitation are gradually depleted. Because 70% of the earth's surface is full of oceans, it is rich in marine resources. Many countries have accelerated the exploration and development of the ocean. As one of the leading technologies of marine development, underwater acoustic technology, which integrates ocean science and information science, has been paid more and more attention by many countries. But underwater channel is an extremely complex time-space-frequency variable-parameter multipath fading channel, which greatly restricts the transmission of underwater acoustic signal at high speed, long distance and low error code. Channel error correction coding technology is an indispensable key technology for underwater acoustic communication system, whether coherent modulation or non-coherent modulation mode, aiming at the characteristics of underwater acoustic channel. The application of LDPC code to the spread spectrum underwater acoustic communication system can improve the bandwidth efficiency and reliability of the system. The low density parity check (LDPC) code has simple structure and high coding gain. Under Gao Si channel, the performance of approaching Shannon limit and strong error correction ability; In order to avoid the possible delay and have good performance in frequency-selective fading channel, no interleaver is needed to resist sudden error. The decoding is parallel, and the delay is much less than the conventional serial iterative decoding algorithm. LDPC-code can reduce the signal distortion in underwater acoustic channel transmission. The multipath interference of underwater acoustic channel will cause serious fading of the signal, which is one of the bottlenecks of the development of modern underwater acoustic communication: spread spectrum technology, equalization technology. Diversity technology is a mature anti-multipath interference technology. Spread spectrum technology not only can resist multi-path interference effectively, but also has good multi-access performance. It is also the key technology to construct underwater communication network. Firstly, this paper introduces the basic characteristics of underwater acoustic channel, including propagation loss, channel noise, multipath interference, Doppler effect, and frequency selective fading. The time-selective fading and Rayleigh channel fading characteristics are quantitatively described and the time-varying underwater acoustic channel model is established. Secondly, a method of constructing V-type QC-LDPC code check matrix is proposed. The linear coding is realized by iterative coding, and the complexity of coding is reduced, and the LLRBP decoding algorithm is improved. Providing accurate decoding information; On the basis of spread spectrum, the LDPC code channel error correction coding technology is added to set the simulation parameters. Verify and analyze the error-correcting performance of LDPC codes in different order domains and the advantages of LDPC codes combined with spread spectrum technology in underwater acoustic communication. Finally, the multi-carrier spread spectrum theory including MC-CDMA-MC-DS-CDMA-MT-CDMA is introduced, and its advantages and disadvantages are compared. Finally, the LDPC code MT-CDMA multi-carrier spread spectrum underwater acoustic communication system is put forward. The simulation parameters are set up, and the simulation is carried out under different code length and modulation mode, and the bit error rate of the system under RS code is compared. It is proved that the system optimization proposed in this paper is reasonable and practical.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.3

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