| Space laser communication system is considered as an important and promising technology in the future communication of space-earth-ocean.has several apparent advantages like:1)Large information capacity and high transmission rate;2)good concealment and strong anti-interference ability;3)small system consumption,small volume and light-weighted.Laser transmitter is the key part of a space laser communication system.The application of conventional single laser source transmitter in free space optical communication system is confined due to it is lack of transmitting power and incapable to compensate atmospheric turbulence.In order to achieve longer communication range and improvement of communication rate,it is urgent to make technological breakthrough in output power and technical skills like adaptive optics to compensate atmospheric turbulence.In this dissertation,the research on coherent detection space laser communication system based on fiber laser phased array transmitter is carried out.We design and propose a feasible system scheme.With tools like Matlab,we set up a simulation platform to verify whether the system scheme is valid.We first conduct research of basics mechanism of atmospheric turbulence and theory of numeric stimulation of phase screen.And next we conduct exploration of key technologies involved in laser coherent combination communication system.We conduct analysis of problems including the design of fiber laser phased array transmitter,compensation of atmospheric turbulence and implementation of coherent detection.Moreover,we design a valid and practicable simulation platform in the hope to compare the performance between phased array transmitter and single aperture transmitter under atmospheric turbulence.The main research work and achievements are listing as follows:(1)We designed a stepped phase screen based on von Karman turbulence model,which is used to simulate the atmospheric channel of space laser communication system.We carried out an investigation on statistical models of atmospheric turbulence.We discuss the advantages and disadvantages between different ways to generate turbulence phase screen.The influence of atmospheric turbulence on laser communication is analyzed.The spectrum inversion method with more applicability is selected to generate the phase screen.(2)We designed a high noise margin phase compensation Viterbi-Viterbi algorithm based on the feedforward.We carried out an investigation and design on signal damage compensation algorithm.The spatial phase fluctuation of the transmitted light field in the atmosphere leads to wavefront distortion.The influence of phase fluctuations in the atmospheric channel on the space laser communication system is explored.According to the characteristics that the fluctuation of the fluctuation field changes faster with time and the amplitude is larger,the design is made.The feasibility of the algorithm is verified on the simulation platform.(3)We designed a 37-aperture laser phase-control array transmitter and carried out an investigation on laser phased array beam coherent combination and key technologies.The advantages and disadvantages and usage scenarios of different aperture filling techniques and multi-beam integrated control techniques are analyzed.According to the split-coherence coherent synthesis technique,the SPGD(Stochastic Parallel Gradient Descent)optimization algorithm is used to control the phase and tilt of the coherent synthetic laser.(4)Designed and built a simulation platform using Matlab as a tool.The light field of the far field of the phased array transmitter after turbulent atmosphere is simulated by the platform,and the BER(Bit Error Rate)performance of the communication system is analyzed.For comparison,the far field spot formed by the transmission of the single aperture transmitter is theoretically combined.The light field is compared and the conclusion that the phased array transmitter has better power budget performance is obtained. |
PDF Full Text Request