FSO通信系统中基于LDPC码的编码多级调制技术研究

发布时间：2018-03-12 09:31

本文选题：自由空间光通信　切入点：大气湍流信道　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：自由空间光通信(Free Space Optical,FSO),光通信技术的一种,是指利用调制激光束通过自由空间传输信息的光学无线通信技术,又称为无线光通信。FSO系统具有大通信容量、高速传输、高带宽、部署快速便携、安全保密性强、低功耗以及低成本等优点,在频谱资源日益匮乏的今天,光波频段的通信具有极大的潜力。FSO系统作为无线通信网络的有效补充,可以用来解决Internet“最后一公里”问题,是下一代超高速无线通信网络的重要组成部分。FSO通信主要是以大气作为传输媒质进行信息的传递,FSO系统的性能主要受大气湍流的影响,如何降低大气湍流对FSO系统的干扰并提高系统性能是当前FSO领域重点研究的目标之一。近年来研究者们提出了混合的调制方式,能够很大程度上提高系统性能。而传统的编码技术与混合调制技术的联合方式能有效地提高FSO系统的带宽利用效率并降低误码率。中继协作传输技术应用在FSO系统中能够进一步抑制大气湍流的不良影响并提升FSO系统的性能。本文联合低密度奇偶校验码(Low-Density Parity-Check,LDPC)、脉冲位置调制(Pulse Position Modulation,PPM)和二进制相移键控调制(Binary Phase Shift Keying,BPSK)提出了PPM-BPSK-LDPC编码多级调制方式。针对PPM-BPSK-LDPC编码多级调制方式,设计了FSO通信系统发射端及接收端模型;在对数正态分布的大气湍流信道中,通过该系统模型推导出PPM-BPSK-LDPC编码多级调制方式的编译码公式和带宽利用率表达式;理论分析并仿真验证了该编码多级调制方式的带宽利用率和系统误码率性能。结果表明,与传统的PPM调制和LDPC编码结合的方式相比,所提的PPM-BPSK-LDPC编码多级调制方式带宽利用率更高,误码率更低。因此PPM-BPSK-LDPC编码多级调制方式在FSO系统中具有一定的应用空间。由于大气湍流的影响,当发射端和接收端距离较远时,采用单跳FSO链路时不能满足FSO系统的误码率要求。为了进一步改善系统性能,本文提出了中继协作的PPM-BPSK-LDPC编码多级调制方式。该方式是在PPM-BPSK-LDPC编码多级调制方式的基础上,利用中继节点进行协作通信。通过解码转发中继方式的三点中继协作系统模型,在Gamma-Gamma大气湍流信道中对FSO系统的误码率进行仿真分析。仿真结果表明,中继协作的PPM-BPSK-LDPC编码多级调制方式相较于无中继协作的PPM-BPSK-LDPC编码多级调制方式误码率性能更好。该方式结合了中继协作以及PPM-BPSK-LDPC编码多级调制方式的优点,适用于发射端和接收端距离较远的FSO通信系统,能够有效地改善系统性能。
[Abstract]:Free Space Optical Communication (FSO), a kind of optical communication technology, refers to optical wireless communication technology which uses modulated laser beam to transmit information through free space. It is also called wireless optical communication. FSO system has large communication capacity, high speed transmission and high bandwidth. With the advantages of fast and portable deployment, strong security, low power consumption and low cost, the communication in optical frequency band has great potential as an effective supplement to wireless communication network. It can be used to solve the "last kilometer" problem of Internet. It is an important component of the next generation ultra-high speed wireless communication network. The performance of Internet system is mainly affected by atmospheric turbulence. How to reduce the disturbance of atmospheric turbulence to FSO system and improve the system performance is one of the important research targets in the field of FSO. In recent years, researchers have proposed a mixed modulation method. The combination of traditional coding technology and hybrid modulation technology can effectively improve the bandwidth utilization efficiency and reduce the bit error rate of FSO system. The relay cooperative transmission technology is applied in FSO system. The system can further suppress the adverse effects of atmospheric turbulence and improve the performance of FSO system. In this paper, we propose a PPM-BPSK-LDPC editor with Low-Density Parity-CheckPPC codes, Pulse Position Modulation (PPMs) and binary Phase shift keying Modulation (PPMs), which are based on low density parity Parity-Checkcheck codes (LDPCs) and binary Phase shift keying Modulation (BPSK). Code multilevel modulation. For PPM-BPSK-LDPC coded multilevel modulation, In this paper, the transmitter and receiver models of FSO communication system are designed, and the encoding and decoding formulas and bandwidth utilization expressions of PPM-BPSK-LDPC coded multilevel modulation are derived in the logarithmic normal distribution atmospheric turbulent channel. The bandwidth utilization and bit error rate (BER) performance of the coded multilevel modulation scheme are theoretically analyzed and simulated. The results show that, compared with the traditional PPM modulation and LDPC coding, the proposed scheme is more efficient than the traditional one. The proposed PPM-BPSK-LDPC coding multilevel modulation scheme has higher bandwidth utilization and lower bit error rate. Therefore, the PPM-BPSK-LDPC coded multilevel modulation scheme has a certain application space in FSO systems. Because of the influence of atmospheric turbulence, when the distance between the transmitter and the receiver is longer, In order to improve the performance of FSO system, a relaying cooperative multilevel modulation scheme for PPM-BPSK-LDPC coding is proposed in this paper, which is based on the PPM-BPSK-LDPC coded multilevel modulation scheme. Through decoding and forwarding the three-point relay cooperative system model, the BER of FSO system in Gamma-Gamma atmospheric turbulent channel is simulated and analyzed. The relaying cooperative PPM-BPSK-LDPC coding multilevel modulation has better BER performance than the PPM-BPSK-LDPC coding multilevel modulation scheme without intermediate and secondary cooperation. This scheme combines the advantages of relay cooperation and PPM-BPSK-LDPC coding multilevel modulation. It is suitable for FSO communication system with long distance between transmitter and receiver, and can improve system performance effectively.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1;TN911.22

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