【作者】 王锋；

【导师】 胡贵军；

【作者基本信息】 吉林大学 ， 通信与信息系统， 2021， 博士

【摘要】 空间激光通信是利用光载波在自由空间进行信息传递的一种通信技术,具有频带宽、指向性好、抗电磁干扰和传输速率高等优点,逐渐成为光通信领域的研究重点,并被广泛应用于卫星通信、地面通信和军事领域。但是空间激光通信的通信链路难以中继,想要充分发挥其高速大容量优势,要求调制格式兼具高频谱效率和高功率效率特性。因此,研究适合空间激光通信的调制技术是一件重要的工作。此外,大气湍流会导致传播光束强度和相位的随机起伏,从而造成接收信号的深度衰落,导致空间激光通信系统性能下降,所以研究能够克服大气湍流影响的接收技术也具有重要的应用价值与意义。本文紧紧围绕空间激光通信系统,分别对调制技术和接收技术展开研究。在深入分析不同调制格式特性的基础上,对混合调制的性能进行了实验研究并设计了一种高灵敏度的四维调制格式;在分析了少模光纤高效的空间光接收能力基础上,分别对少模外差探测接收技术和模式分集接收技术进行了深入研究。本文的工作内容及创新点具体包括以下三个方面:1.面向空间激光通信对高谱效率、高功率效率调制格式的需求,研究并分析了混合调制的空间激光通信性能,提出了一种高性能的四维调制格式。首先,介绍并分析了光载波不同维度调制格式的原理、特点和接收性能。然后,搭建实验平台,实现了不同湍流强度下10Gbps mPPM-QPSK混合调制信号传输,研究了大气湍流强度对混合调制信号误码率的影响。最后,基于四维空间选取的星座点坐标和Gallager映射,提出了一种四维调制格式4D-nMD,研究其在不同湍流条件下的性能表现,与已知的几种同谱效率调制格式相比具有更高的功率效率。2.针对基于单模光纤接收的外差探测受大气湍流影响严重问题,提出了一种具有湍流补偿能力的少模外差探测接收技术。建立了基于少模光纤混频的少模外差探测数学模型,通过数值仿真,分析了不同湍流条件下少模外差接收的性能。采用Kramers-Kronig探测方法,搭建了基于少模外差探测的空间激光通信系统,测量了大气湍流信道下少模光纤与单模光纤的耦合特性,并实现了4Gbps QPSK信息传输,测量了系统的平均误码率与中断概率。实验结果表明:在中等和强湍流条件下,误码率达到前向纠错阈值时,少模外差探测比传统单模外差探测提升了约5dB的性能,所设计系统可以很好地补偿大气湍流效应。3.模式分集是一种新兴的利用少模光纤补偿大气湍流效应的接收技术,但是系统的电域结构十分复杂且实现成本较高。针对这一问题,提出并实现了一种基于非模式选择型光子灯笼+等增益合并(EGC)的模式分集接收系统,具有较高性能增益和较低复杂度。首先对基于模式分集接收的空间激光通信系统进行了数学建模,然后利用模式选择型光子灯笼和非模式选择型光子灯笼,分别搭建了基于模式分集接收的空间激光通信系统,并对两种光子灯笼输出端的功率分布特性进行测量与分析。最后,实现了4Gbps QPSK信号的模式分集接收,测量了系统的平均误码率与中断概率。实验结果显示:非模式选择型光子灯笼+EGC的方案在弱、中和强湍流条件下与性能上限的差异在1dB以内。更多还原

【Abstract】 Space laser communication refers to the communication technology that uses optical carrier to transmit information in the free space,which has the advantages of strong directivity,anti-electromagnetic interference ability and rich frequency resources.So,it has gradually become the focus of research in the field of optical communication,and has been widely used in satellite-to-ground communication,ground communication and military fields.However,the communication link of space laser communication is difficult to relay.In order to give full play to its advantages of high speed and large capacity,the modulation format is required to have the characteristics of high frequency spectral efficiency and high power efficiency.Therefore,it is an important work to study the modulation technology suitable for space laser communication.In addition,atmospheric turbulence will lead to the random fluctuation of the intensity and phase of the propagating beam,resulting in the deep fading of the received signal and the degradation of the performance of the space laser communication system.Therefore,the research on the receiving technology that can overcome the influence of atmospheric turbulence also has important application value and significance.This paper focuses on the space laser communication system and investigates the modulation technology and reception technology,respectiviely.Based on the in-depth analysis of the impact of the modulation format on the performance of the communication system,a four-dimensional modulation format with high sensitivity is designed.Based on the analysis of the efficient free-space optical reception capability of few-mode fiber,the few-mode heterodyne detection technology and mode diversity reception technology are deeply studied and implemented,respectively.The main contributions and the innovation points of this dissertation are as follows:1.Aiming at the requirements of high spectral efficiency and high power efficiency modulation format for space laser communication,the performance of hybrid modulation for space laser communication is studied and analyzed,and a high-performance four-dimensional modulation format is proposed..Firstly,a space optical communication experimental platform in laboratory based on modified Von Karman model turbulence is built.Using this platform,the transmission of 10 Gbps mPPM-QPSK mixed modulation signals under different turbulence is realized.The effect of atmospheric turbulence intensity on the bit error rate of mixed modulation format is studied experimentally.Secondly,a four-dimensional modulation format4D-nMD is proposed to meet the demand of high frequency spectral efficiency.The modulation format selects constellation points in the four-dimensional space,and realizes the mapping from multiple bit labels to four-dimensional amplitude through Gallager mapping.Finally,the optical simulation software optisystem is used to build a space optical communication system,and the performance of the proposed modulation format and several modulation formats under the same spectral efficiency are verified and compared.2.In order to solve the problem that heterodyne detection based on single-mode optical fiber reception is seriously affected by atmospheric turbulence,a few-mode heterodyne detection and reception technique with turbulence compensation capability is proposed.Firstly,the mathematical model of few mode heterodyne detection based on few mode fiber mixing is established,and the performance of few mode heterodyne receiver under different turbulence conditions is analyzed by numerical simulation data.Then,aiming at the problem that heterodyne detection requires strict frequency and phase matching or locking between local oscillator light and signal light,a few mode heterodyne detection method based on Kramers Kronig relationship is proposed.Finally,a space optical communication system based on few mode heterodyne detection is built in the laboratory.On the one hand,the coupling characteristics of few mode fiber and single-mode fiber in atmospheric turbulence channel are measured;On the other hand,the few mode heterodyne detection reception of 4Gbps QPSK information is realized.The experimental results show that under medium and strong turbulence conditions,when the bit error rate reaches at forward error correction threshold,the performance of few mode heterodyne detection is about 5dB higher than that of heterodyne detection received with a single-mode fiber.The designed system can well compensate the medium and strong turbulence effect.3.Mode diversity is an emerging reception technique that uses few-mode fiber to compensate for the atmospheric turbulence effects,but has very complex electrical domain structure which leading to expensive cost in implement.Considering this problem,a mode diversity reception based on non-mode selective photon lantern and equal gain combining(EGC)is proposed and implemented,which has high performance gain and low complexity.Firstly,the space optical communication system based on mode diversity reception is mathematically modeled.For EGC method,an index to measure the difference between the mode diversity reception system and the theoretical performance upper limit is proposed and verified by experimental measurements.Then,the space optical communication system based on mode diversity reception in the laboratory is built with the mode-selective photon lantern and non-mode-selective photon lanterns.And the power distribution characteristics of mode diversity reception of different photon lanterns are measured and analyzed.Finally,the mode diversity reception of 4Gbps QPSK signal is realized,and the average bit error rate and interrupt probability of the system are measured.The experimental results show that the performance differenc between the scheme with the non-mode selective photon lantern and EGC and the upper performance bound is less than 1dB under weak to strong turbulence,and is 1.9dB better than the scheme of mode selective photon lantern with EGC.It is the best choice for mode diversity EGC scheme.更多还原