基于LDPC与PPM的水下高速光通信系统设计
文献类型：学位论文
| 作者 | 米乐 |
| 文献子类 | 硕士 |
| 导师 | 陈卫标 |
| 关键词 | 水下光通信 underwater optical communication LDPC编码 low-density parity check codes PPM调制 pulse position modulation 蒙特卡洛 Monte Carlo method |
| 其他题名 | Design of High speed Underwater Optical Communication System Based on LDPC and PPM |
| 英文摘要 | 水下通信中蓝绿光通信方式具有通信速率高、保密性好、抗干扰能力强等优点。相较于大气光通信，水下光通信中光脉冲在海水传输过程中会受到吸收和散射的双重影响，光信号在传输过程中发生时域和空域的展宽以及能量的衰减，导致水下光通信系统的误码率升高，通信性能急剧下降。 论文首先介绍了光通信系统的基本构成，分析了光脉冲在海水中的传输特性，阐述了吸收与散射对水下光通信的不同影响。对水下信道的主要研究方法-蒙特卡洛仿真法进行详细的介绍。 其次针对水下光通信中常用的几种调制方式做出了比较分析，分析结果表明，针对水下光通信系统中发射端功率受限的特点，选取恰当的调制方式可以节省发射端平均功率，提高通信系统的传输速率。比较分析水下光通信中常用的信道编码方式，综合考虑硬件实现复杂度与编码性能，选择LDPC码作为系统的信道编码。之后详细阐述了LDPC的快速编码原理，对不同译码方式和迭代次数对系统性能的影响进行了仿真分析。详细说明了将LDPC编码与PPM调制相结合的迭代译码算法，仿真结果表明，将LDPC与PPM调制相结合的系统可以充分利用接收端接收到的软信息，可以获得约3dB的编码增益。采用LDPC与PPM相结合的系统可以在相同发射端能量条件下实现更远距离的通信。也可以在同样的通信距离下获得更低的误码率，系统的通信性能会得到提升。 接着根据MC仿真结果，设计了一套基于蓝光激光二极管与光电二极管的水下光通信系统。重点介绍了适用于硬件实现的LDPC编码方式，并且基于现场可编程逻辑器件（FPGA）实现了不同码率的LDPC编码器与PPM调制器的构造。在实验室环境中对设计的高速光通信系统进行了功能验证。系统最终可获得的最大通信速率为155.93kbps。 最后为了验证更远距离下LDPC编码与PPM调制方式相结合的系统的纠错性能，利用实验室已有水下激光通信试验系统，将PPM调制和LDPC编码进行了移植，并在大型水池的环境下进行了试验验证，试验结果表明，随着传输距离的增加，信噪比急剧下降，在水池环境下达到最远通信距离130m，统计试验测得的误码率情况可知，LDPC编码码率越低，系统的误码率越低，通信性能越好，在相同误码率的情况下LDPC编码与PPM调制相结合的通信系统可获得2.34dB的编码增益。; Underwater optical communication has the advantages of high speed, good secrecy, and good anti-interference ability. Compared with the free space optical communication, laser pulses are affected by absorption and scattering during the transmission of seawater. In the process of optical signal transmission, laser pulses will be stretched with the increase of communication distance, and the amplitude of received signals will be reduced. Consequently, the BER performance of underwater laser communication will be drastically reduced. Firstly, the paper introduces the basic structure of the optical communication system. Analyzes the transmission characteristics of light pulses in seawater, explains the different effects of absorption and scattering. The detailed analysis of the simulation process of the Monte Carlo Simulation Method. Secondly, a comparative analysis was made on several modulation methods commonly used in underwater optical communications. The results indicated that due to the limited power of underwater optical communication systems, selecting a proper modulation method could save the average power of the transmitter and improve the transmission rate of the communication system. Then the thesis introduces the basic knowledge of channel coding methods in underwater optical communication. Considering the hardware implementation complexity and coding performance, we selected the LDPC code as the channel coding finally. The principle of fast coding of LDPC in detail was also introduced. And then simulation analysis was performed on the system performance of different decoding methods and iteration times. The iterative decoding algorithm combining LDPC and PPM was described in detail. The simulation results show that the system based on LDPC and PPM can make full use of the received soft information and obtained 3dB coding gain. The system based on LDPC and PPM can achieve longer distance communication at the same transmitter energy and the communication performance of the system will be improved. Then we designed an underwater optical communication system based on MC results, which used a blue laser diode as the transmitter and a photodiode as the receiver. The LDPC encoding method which is suitable for hardware implementation was introduced in detail, and the construction of LDPC with different code rates encoders and PPM modulators was implemented based on field programmable logic devices. The design of a high-speed optical communication system was verified in a laboratory environment. The maximum communication rates of the system was 155.93 kbps. Finally, pool experiments were carried out to verify the performance of the system based on LDPC coding and PPM modulation by using an existing underwater laser communication system. The experimental results demonstrated that the designed system with LDPC and PPM obtained 2.34dB coding gain in JerlovⅡ water. The lower the LDPC encoding bit rate, the lower the bit error rate of the system and the better the communication performance. The maximum communication distance was about 130 meters. |
| 学科主题 | 光学工程 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31042]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 米乐. 基于LDPC与PPM的水下高速光通信系统设计[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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