【作者】 姜义君；

【导师】 马晶；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2010， 博士

【摘要】 相对于传统的微波通信方式而言,卫星光通信具有通信容量大、保密性好、抗电磁干扰能力强、不需要无线电频率使用许可、设备体积小、重量轻和功耗低等优点,因此该技术受到了国际上的广泛重视。目前对卫星光通信技术的研究已经成为了一个热门研究领域,在该研究领域中处于领先地位的日本、美国和欧洲等国家和地区已经相继进行了空间实验,成功实现了星间和星地的高速激光通信,在空间实验获得成功的基础上,这些国家和地区正积极准备将卫星光通信技术推向实用化。在可预见的未来,以激光作为信息载体的新一代卫星通信网络即将出现。在卫星与地面进行激光通信的过程中,作为信息载体的激光光束将通过地球表面的大气层,当光束在大气中传输时,大气湍流引起的折射率起伏将影响光束的传输质量,破坏光场的相干性,从而产生光强起伏、到达角起伏、光束漂移以及光束扩展等一系列光学效应。差错性能是衡量系统通信性能的重要指标,差错性能的优劣能够直接反映通信质量的好坏。一般来说,OOK系统的差错性能是用误码率来衡量的,而PPM和DPIM系统的差错性能是用误包率来衡量的。对于星地激光链路而言,大气湍流引起的上述光学效应将对链路的通信性能造成影响,从而增加信息传输过程中的差错概率,因此,本文对大气湍流影响下,星地激光链路的通信性能进行了研究。本文对国内外卫星光通信技术的研究进展进行了概述,对大气湍流的性质、大气光传输的基本理论以及大气湍流引起的光学效应对星地激光链路的影响进行了必要的阐述,同时对星地激光链路中通信系统的基本组成及工作原理进行了简要的介绍。研究了大气湍流引起的光束漂移效应对上行星地激光通信系统的影响,基于高斯光束上行传输的光束漂移和光强闪烁模型,给出了这两种效应共同作用下,接收光强概率密度的表达式;分别对不考虑探测器噪声和考虑探测器噪声情况下的系统误码率进行了分析,并在误码率分析的基础上,对系统的最佳束散角和最佳发射口径进行了研究。对采用OOK,PPM和DPIM调制方式的星地激光链路的通信性能进行了研究。给出了DPIM系统最佳判决阈值的计算公式。分别分析了OOK和DPIM系统在阈值检测情况下的系统误包率以及PPM系统在最优检测情况下的系统误包率。与此同时,在考虑湍流效应的情况下,基于上行和下行激光链路模型,对采用上述三种调制方式的星地激光通信系统的误包率进行了比较。进行了城市链路11.8km激光大气传输实验,对大气湍流影响下激光链路的光场传输特性进行了长期的实验观测。通过该实验对高斯光束在大气中的远场光强分布、接收光强闪烁指数、接收光强概率密度、光强衰落概率、光强起伏功率谱等湍流大气导致的接收光强统计性质进行了分析,并给出了闪烁指数和折射率结构常数的日变化规律。利用两个光学终端在距离为11.16km的城市链路上进行了星地激光通信地面模拟实验。实验对不同调制速率的两条激光链路的误码率以及接收光强闪烁指数进行了长期的测量,研究了接收光强闪烁指数和链路两端温度差的关系,给出了接收光强闪烁方差与系统误码率关系的实验结果,同时分别研究了不同调制速率两条链路的误码率与链路两端温度差的关系,并且利用该实验链路进行了长距离视频传输实验。本文的研究工作为星地激光链路的通信性能分析以及调制方式选择提供了理论基础,为星地激光链路的系统设计提供了实验依据。更多还原

【Abstract】 Comparing to the traditional microwave communication system, satellite laser communication systems have many potential advantages, such as higher data rate, low probability of intercept, no restriction for frequency use, less volume, less mass, less power consumption and so on. Recently, satellite laser communication has been concerned by many countries in the world and it has turned to be a hot topic in the field of satellite communication research. Space experiments have been performed in some countries or area, which have advanced technology on satellite laser communication, such as Japan, American and Europe. Intersatellite and ground-to-satellite laser communications have been realized in these experiments. Based on the achievements of the space experiments, these countries are preparing to promote this technology to real utility. In the near future, a new generation of the satellite communication network, which use laser as the carrier of the information, will appear.In ground-to-satellite laser communications, laser beam, as the information carrier, will propagates through the aerosphere of the earth. In this process, the refractive index fluctuation caused by atmospheric turbulence will influence the propagation of the laser beam, destroy the coherence of the optical field and result in a series of optical effects on the laser beam, such as intensity fluctuation, angle of arrival fluctuation, beam wander and spread, etc.Error performance is a importance parameter to indicate the communication performance of the system. The level of the error performance can be directly used to judge the quality of the communication system. Generally, error performance of a OOK system is indicated by bit error rate and error performances of PPM and DPIM systems are indicated by packet error rates.In a ground-to-satellite laser link, atmospheric turbulence introduced optical effects will influence the communication performance and increase the error probability of the information transmission. So with consideration of the turbulence effects, this dissertation is concerned with the researh on the communication performance of the ground-to-satellite laser link.First of all, the research status of ground-to-satellite laser communication is summarized. The characteristic of the atmospheric turbulence is described. Basic theory of laser propagation in turbulence and influeces of turbulence effects on the system are represented. The main configuration and principle of the ground-to-satellite laser communication system are introduced. Based on weak fluctuation theory and the beam-wander model, considering the combined effect of scintillation and beam wander, the probability density of the received intensity for uplink is derived. Bit error rate for uplink is analyzed, in comparison with the condition in which beam wander is not taken into account. Based on the bit error analysis, optimum divergence angle and transmitter beam radius for a communication system are researched.Packet error rates of OOK, DPIM and PPM modulation schemes are researched for ground-to-satellite laser links. Optimum threshold for DPIM system is deduced. Analysis process is based on threshold detection for OOK and DPIM, and optimal detection for PPM. Packet error rates of these three modulation schemes are compared for both uplink and downlink, with consideration of the turbulence effects in the ground-to-satellite laser link, and numerical results are given.An 11.8km urban laser link is established to perform the long term examination of the laser beam propagation characteristics through atmospheric turbulence. Far field distribution of Gaussian beam, scintillation index of the received intensity, probability density function, fade statistic, and high-frequency spectrum are researched based on the analysis of the experimental data. Besides, daily variation curve of scintillation index is given, compared with the variation of refractive-index structure parameter.An 11.16km bi-directional urban laser link is established by two satellite laser communication terminal, to perform the simulated experiment of the ground-to-satellite laser communication. Relations between scintillation index and the differences of temperature and humidity at two ends of the link are researched. Bit error rates are measured for two channels with different modulation rates and the results are given, with consideration of scintillation index. Relations between bit error rate and the differences of temperature and humidity at two ends of the link are also researched. In addition, long distance video transmission is performed and pictures of the transmitted video are presented.This dissertation can benefit the error perpormance analysis and modulation scheme choice for the ground-to-satellite laser communication system, and provide experimental foundation for the system design.更多还原