大气信道对空-地光通信的影响分析

大气随机信道对激光传输性能的影响是制约空-地激光通信的重要因素之一，因此开展对大气信道的研究对实现空-地激光通信具有非常重要的意义。对激光在大气中传输特性的研究，有助于了解激光通过大气信道传输时所产生变化的特征、规律和在空-地激光通信系统设计中寻找到合理的解决方案并很好地修正、补偿其对通信链路的影响。本文对激光在大气信道中的基本传输特性及大气随机信道对激光通信的影响进行了研究，同时提出了一些相应的解决途径。     

激光通信

研究了星间激光通信中不同波长光放大器的应用方案,提出并分析了对应的应用技术难点。对激光在大气中传输特性的研究,有助于了解激光通过大气信道传输时所产生变化的特征、规律和在空一地激光通信系统设计中寻找到合理的解决方案并很好地修正、补偿其对通信链路的影响。对激光在大气信道中的基本     

大气信道对红外激光通信系统性能影响的实验研究

针对近地面、准水平红外激光大气通信系统的应用,利用微脉冲激光雷达、大口径激光闪烁仪在济南市区进行了为期一周的昼夜连续观测,获得了影响红外激光通信系统性能的关键大气参量的信息.着重分析了大气衰减信道、大气湍流信道对一公里通信链路系统性能的影响,考查了通信设备在复杂大气条件下应用的可行性及可靠性.最后就减弱大气信道对通信性能影响的方法进行了总结和探讨.     

大气信道对红外激光通信系统性能影响的实验研究

针对近地面、准水平红外激光大气通信系统的应用,利用微脉冲激光雷达、大口径激光闪烁仪在济南市区进行了为期一周的昼夜连续观测,获得了影响红外激光通信系统性能的关键大气参量的信息.着重分析了大气衰减信道、大气湍流信道对一公里通信链路系统性能的影响,考查了通信设备在复杂大气条件下应用的可行性及可靠性.最后就减弱大气信道对通信性能影响的方法进行了总结和探讨.     

激光在雨中传输的分析与计算

本文通过分析雨滴其对激光的散射和吸收作用,研究激光在大气中传输时受雨滴作用的影响,计算不同雨滴对激光光强的影响,在不同降雨下,测试激光光强的变化,并通过软件仿真实时显示光斑的闪烁、漂移,为进一步优化激光通信系统性能设计、最终实现全天候超视距的大气激光通信做有意义的探索。     

基于退偏振比探测的大气激光通信

针对大气激光通信中多径散射效应产生的通信链路码间串扰问题,提出了一种基于退偏振比探测的大气激光通信传输方案。利用光子追迹和Stokes矢量变换进行了Monte Carlo仿真;通过设置不同的云层物理厚度和消光系数,得到接收光退偏振比与云层光学厚度的一一对应关系;基于Stotts公式,得到接收光退偏振比与平均脉冲时间展宽的对应关系。提出了在多径效应影响下的最佳通信传输速率方案,该方案在激光通信系统接收端直接进行退偏振比探测,可有效评估大气信道环境的多径强度,进而在保证激光通信传输质量的同时实现最大的通信传输速率。该研究在星地激光通信以及自适应激光通信的通信链路优化领域具有理论指导意义和应用价值。     

空间激光通信中湍流信道光束传输仿真

对大气光信道特性的研究是空间激光通信研究的重要组成部分。首先以大气湍流理论为基础,阐述了激光在大气中传输时受到的大气湍流的影响和分析方法。接着重点对近年来应用日益广泛的空间激光通信的数值仿真方法进行了综述。不仅介绍了基本传输方程及其求解方法,还对采用数值方法模拟光波在随机介质中传播的若干关键技术进行了分析。最后结合现有的研究成果,说明了数值方法在空间激光通信中的应用。     

雾对大气激光通信系统的影响及克服方法

分析了雾产生的原因、相关数学模型及其对大气激光通信系统的影响.为了克服雾对无线光通信链路的影响,将LDPC码作为信道编码应用到大气激光通信系统中,并结合置信传播迭代译码算法和副载波PSK强度调制方案,在有雾的大气信道中进行了仿真.仿真结果表明：LDPC码具有优越的纠错能力,并获得了较大的编码增益,该方案可以满足大气激光通信系统的需要.     

雾对大气激光通信系统的影响及克服方法

分析了雾产生的原因、相关数学模型及其对大气激光通信系统的影响.为了克服雾对无线光通信链路的影响,将LDPC码作为信道编码应用到大气激光通信系统中,并结合置信传播迭代译码算法和副载波PSK强度调制方案,在有雾的大气信道中进行了仿真.仿真结果表明:LDPC码具有优越的纠错能力,并获得了较大的编码增益,该方案可以满足大气激光通信系统的需要.     

大气激光通信非对称限幅光正交频分复用技术

将一种新的正交频分复用调制技术运用到大气激光通信系统中,分析了采用这种非对称限幅光正交频分复用调制技术的大气激光通信系统在大气湍流信道下的性能.在此基础上,把非对称限幅光正交频分复用调制方案与传统的开关键控及直流偏置光正交频分复用调制方案进行了比较,并在大气湍流信道中进行了仿真.仿真结果表明:非对称限幅光正交频分复用调制技术增强了系统对大气湍流的抗干扰能力,该方案可以满足大气激光通信系统的需要.     

Some limitations on optical communication reliability through Kolmogorov and non-Kolmogorov turbulence

In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received signal, affecting link performance.Influence of Kolmogorov and non-Kolmogorov turbulence statistics on laser communication links are analyzed for different propagation scenarios, and effects of different turbulence spectrum models on optical communication links are presented. Statistical estimates of the communication parameters such as the probability of fade (miss) exceeding a threshold dB level, the mean number of fades, and BER are derived and examples provided. The presented quantitative data suggest that the non-Kolmogorov turbulence effects on lasercom channels are more severe in many situations and need to be taken into account in wireless optical communication. Non-Kolmogorov turbulence is especially important for elevations above the boundary layer as well as for even low elevation paths over water.     

Capacity of wander and spread beams in log-normal distribution non-Kolmogorov turbulence optical links

We model the average channel capacity of optical wireless communication systems in weak turbulence horizontal channels, using the log-normal distribution models. The effects of beam wander and spread, pointing errors, turbulence inner scale, turbulence outer scale and the spectral index of non-Kolmogorov turbulence on system's performance are included. The model can evaluate the influence of the atmospheric turbulence conditions in the performance of a ground-to-train optical wireless communication system.     

大气激光通信非对称限幅光正交频分复用技术

将一种新的正交频分复用调制技术运用到大气激光通信系统中,分析了采用这种非对称限幅光正交频分复用调制技术的大气激光通信系统在大气湍流信道下的性能.在此基础上,把非对称限幅光正交频分复用调制方案与传统的开关键控及直流偏置光正交频分复用调制方案进行了比较,并在大气湍流信道中进行了仿真.仿真结果表明:非对称限幅光正交频分复用调...     

自由空间宽谱部分相干光通信系统

大气湍流对自由空间光通信系统所造成的影响是不可忽略的，为了减弱湍流对空间光通信系统带来的影响，实验搭建了一套通信距离为900 m的真实大气信道宽谱部分相干光通信系统。系统采用皮秒脉冲泵浦高非线性光纤产生超连续谱并滤波得到部分相干宽谱脉冲，对其调制后完成通信。在测试过程中，实验专门设置了一条参考链路，保证了测试环境的一致性。实验结果表明，在中等湍流条件下，系统光强闪烁指数为0.035 8，相比窄线宽通信系统提升了23%，最低探测灵敏度达到了-23.35 dBm，相比窄线宽通信系统提升了42%。与窄线宽激光通信系统相比，宽谱部分相干光通信系统可以明显降低湍流引起的光功率抖动，并提升自由空间光通信系统通信性能。     

Investigation on the influence of intensity scintillation and beam wander in space optical uplink DWDM communication system

Abstract

Dense wavelength division multiplexing (DWDM) has been widely applied in ground optical communication. However, the technology of DWDM is still not mature enough in the space optical communication system. In order to further advance the use of DWDM into space optical communication, the probability density function (PDF) and the bit-error rate (BER) performance of DWDM is investigated in uplink communications under the influence of atmospheric turbulence, consisting of intensity scintillation and beam wander caused by atmospheric turbulence. Numerical results show that the atmospheric turbulence has a great impact on BER and PDF, and wavelength, divergence angel, and other relevant parameters should be carefully considered in this DWDM system. This work can be conducive for improving DWDM design of space optical uplink communication systems.     

The effect of turbulence on NLOS underwater wireless optical communication channels [Invited]

Conventional line-of-sight underwater wireless optical communication(UWOC) links suffer from huge signal fading in the presence of oceanic turbulence due to misalignment, which is caused by variations in the refractive index in the water. Non-line-of-sight(NLOS) communication, a novel underwater communication configuration,which has eased the requirements on the alignment, is supposed to enhance the robustness of the UWOC links in the presence of such turbulence. This Letter experimentally and statistically studies the impact of turbulence that arises from temperature gradient variations and the presence of different air bubble populations on NLOS optical channels. The results suggest that temperature gradient-induced turbulence causes negligible signal fading to the NLOS link. Furthermore, the presence of air bubbles with different populations and sizes can enhance the received signal power by seizing the scattering phenomena from an ultraviolet 377 nm laser diode.     

基于自适应光学补偿的自由空间光通信系统性能研究

自由空间光通信在未来全球通信网中具有潜在的应用价值,然而自由空间光通信的性能易受大气湍流影响,而自适应光学能够解决大气湍流问题.在gamma-gamma分布大气湍流中,用自适应光学技术对自由空间光通信系统进行补偿,进行通信系统误码率的分析,给出了上行链路和下行链路的模拟结果.结果表明:自适应光学误差补偿技术能够很好地提高自由空间光通信的性能,并且低阶自适应光学补偿就能达到很好的校正效果.     

Wander of a Gaussian-Beam Wave Propagated Through a Non-Kolmogorov Turbulent Atmosphere

Both increasing experimental evidence and some results of theoretical investigation have shown that there exist two kinds of turbulence in the aerosphere, Kolmogorov and non-Kolmogorov turbulence. Thus, it is necessary to improve the theory of optical wave propagation through atmospheric turbulence, namely, study the laser-beam propagation in non-Kolmogorov turbulence, before analyzing the joint influence of the Kolmogorov turbulence and non-Kolmogorov one on satellite laser communication. The beam wander will lead to the performance degradation of satellite laser communication systems and exert an influence on the achievement and stability of its links. In this paper, we consider a theoretical power spectrum of refractive-index fluctuations with a generalized power law in order to derive the variance of Gaussian-beam wave wander in weak turbulence for a horizonal path and analyze the influence of spectral power-law variations on the beam wander. We show that the expression for the beam-wander variance is of concise closed form and independent of the optical wavelength.     

孔径平均效应对采用相位补偿技术的空间相干光通信系统误码率的影响

基于大气湍流影响下的空间相干光通信系统模型和孔径平均效应的平面波模型,通过数值模拟研究了弱光强波动条件下孔径平均效应以及大气湍流内外尺度对相干光通信系统误码率和接收孔径直径最优值的影响。研究结果表明:孔径平均效应能够有效减小相干光通信系统的误码率,改善系统性能;原始信噪比越高,传输距离越短,波长越长,相位补偿模式的J值越大,接收孔径直径越接近最优值,孔径平均效应对误码率的改善效果越明显;孔径平均效应会影响接收孔径直径的最优值,相位补偿模式的J值越大,影响越明显;系统误码率和接收孔径直径最优值会随着大气湍流内尺度的增大而相应增大,随着大气湍流外尺度的减小而相应减小。研究结果将为空间相干光通信系统设计提供必要的理论依据。     

Air turbulence effects on performance of optical wireless communication with crosstalk in server backplane

Free space optical interconnections(FSOIs) are anticipated to become a prevalent technology for short-range high-speed communication. FSOIs use lasers in board-to-board and rack-to-rack communication to achieve improved performance in next generation servers and are expected to help meet the growing demand for massive amounts of inter-card data communication. An array of transmitters and receivers arranged to create an optical bus for inter-card and card-to-backplane communication could be the solution. However, both chip heating and cooling fans produce temperature gradients and hot air flow that results in air turbulence inside the server, which induces signal fading and, hence, influences the communication performance. In addition, the proximity between neighboring transmitters and receivers in the array leads to crosstalk in the received signal, which further contributes to signal degradation. In this Letter, the primary objective is to experimentally examine the off-axis crosstalk between links in the presence of turbulence inside a server chassis. The effects of geometrical and inter-chassis turbulence characteristics are investigated and first-and second-order statistics are derived.