【作者】 田洋；

【导师】 钟杰； 康冬鹏；

【作者基本信息】 浙江大学 ， 工程硕士（专业学位）， 2020， 硕士

【摘要】 自由空间激光通信技术兼具光通信系统的高带宽和无线技术的灵活性,对于实现深空探索、卫星导航、地球观测以及5G+蜂窝网络升级需求支撑等都有着十分重要的意义。所以自由空间激光通信中的关键技术研究是一个极具研究价值和工程应用价值的课题。本论文聚焦远距离和超远距离激光通信链路,对相干激光通信测距一体化算法以及大气湍流信道衰落建模等技术进行研究。主要研究内容与创新工作如下:首先,针对高动态的超远、远距离激光通信链路,本文应用了高灵敏度的相干探测机制,设计了基于数字信号处理的相干激光通信与测距一体化算法,并在MATLAB仿真和FPGA硬件实现中对该算法进行了验证。其中,重点研究了异步时钟下基于定时同步算法的测距方法;对于动态频率偏移量小且具有足够稳定性的异步时钟源,在Gbps通信速率下将测距结果的精度提高到了毫米级精度。另外,针对动态多普勒频移与激光器稳定性不足带来的高速波长偏移,本文提出了光电混合的反馈零差检测方案,并设计了三路并行FFT频偏估计算法。在Gbps通信速率下,该算法可处理接收机中高达300 MHz/s的动态波长偏移,且跟踪残差满足接收机中后续相位噪声的处理要求,大幅改善了接收机的性能。其次,针对星地或地面激光链路,大气湍流会大大降低接收信号的质量。本文给出了仿真湍流大气的折射和衍射特性的分步传播方法,采用菲涅尔积分表征衍射作用,随机相位屏模拟大气折射特性,仿真得到了不同湍流强度下接收平面光信号强度和相位的衰落情况。而后通过计算仿真中接收信号的统计相干因子,证得分步传播方法可以有效地仿真光束传播。另外,大气湍流随机相位屏用子谐波低频补偿傅里叶变换法生成,并通过相位结构函数验证得到仿真产生的随机相位屏统计特性与相应大气湍流理论相符。该分步模型的建立可以帮助在实验室条件下基于前人的数据采集和统计模型进行仿真,定量分析大气湍流,对于自由空间激光通信系统可靠性的评估十分重要。更多还原

【Abstract】 Free-space laser communication technology combines large capacity of optical communication systems with the flexibility of wireless technologies,which is of great significance for deep space exploration,satellite navigation,earth observation,and applications supporting 5G+ cellular network upgrades.Therefore,the research on key technologies for free-space laser communication has great research value and engineering application value.This dissertation focuses on long-distance and ultra-long-distance laser communication links,comprehensively studying coherent laser integrated communication/ranging system and modeling of atmospheric turbulent channel fading.The contents of this dissertation are listed as follows:Firstly,for high-dynamic ultra-long-distance and long-distance laser communication links,coherent detection with high sensitivity is applied in this dissertation.An integrated communication/ranging algorithm with feedback-homodyne detection is proposed,which is based on digital signal processing.As demonstrated by the MATLAB simulation and real-time FPGA implementation,for asynchronous clock sources with subtle dynamic frequency offset and sufficient stability,the fractional symbol ranging algorithm based on timing offset compensation has been proven to improve the accuracy of ranging results to millimeter-level at Gbps communication rate.Meanwhile,the parallel FFT frequency offset estimation algorithm is proposed for tracking the highspeed wavelength shift caused by the dynamic Doppler frequency shift and insufficient laser stability.It’s verified that the algorithm can handle dynamic wavelength offsets up to 300 MHz/s at Gbps communication rate,and residual offset meets the processing requirements of subsequent phase noise compensation in the receiver,which greatly improves the performance of the receiver.Secondly,for satellite-to-ground or ground laser links,atmospheric turbulence will greatly affect the quality of received signals.This dissertation presents a step-by-step propagation method for simulating the refraction and diffraction characteristics of the turbulent atmosphere.The Fresnel integral is used to characterize the diffraction effect,while the random phase screen simulates the refraction characteristics of the atmosphere.The simulation results of fading irradiance and phase of the received signal under different turbulence intensities are obtained.Then,the statistical coherence factor of the simulated receiving signal is calculated,which proves the step-by-step propagation method can effectively simulate the beam propagation.In addition,the random phase screen simulating atmospheric turbulence is generated by the Fourier transform method with subharmonic low-frequency compensation.For verification,the statistical characteristics of the random phase screen generated by simulation is calculated,and the results are consistent with the corresponding theory.The establishment of this step-by-step propagation model can help simulation based on previous data collection and statistical models under laboratory conditions,helping quantitative analysis of atmospheric turbulence,which is of great importance for the reliability evaluation of Free-space laser communication systems.更多还原