Research On Key Technologies Of Deep Space Optical Communication Networks

Deep space is a new activity and development area for human after the sea,land and air.Deep space communication technology provides the support and guarantee for deep exploration,which is the information transmission channel between human and deep space probes.Therefore,deep space communication plays an important role in deep space exploration missions.Nowadays,satellite communication is the key and hub to achieve seamless global coverage,but it can not meet the society’s ever growing demand for bandwidth with the characteristics of low frequency and limited modulation rate.In order to alleviate the pressure of information flows in communication networks,the number of satellites around the world is increasing.Crosstalk between satellite microwave links will inevitably increase.Compared with microwave communication,laser communication has the advantages of good confidentiality,low power consumption,small device volume,strong anti electromagnetic interference ability,and so on.Thus,as a new generation communication technology,deep space optical communication(DSOC)network will become one of the hot topics with the significant prospects of academics and industrialization.At present,some available literatures have researched the key technologies of ground space optical network and satellite optical network,but most of these researches relay on their own network architectures and service characteristics,which can not be directly applied to the DSOC network.Therefore,the key technologies for DSOC network much be researched,and its inherent features such as long transmission distance,unfixed network infrastructure,discontinuous transmission connection,long transmission delay and limited node energy,should be considered.In recent years,USA,Japan and ESA have invested a lot of manpower,material and financial resources to conduct in-depth research DSOC.However,the existing studies on DSOC mostly concentrated in point to point signal transmission.Obviously,the research on DSOC is still in its infancy,many key issues need to be addressed.Accordingly,the research on the key technologies of DSOC networks has the considerably academic and industrial significance.The contributions and innovations in this dissertation are summarized as follows:(1)The second chapter addresses the influence of atmospheric channel on signal transmission for space to ground optical communication.First,considering the influence of atmospheric random channel on signal transmission is one of the important factors for space to ground optical communication.This paper generally analyzes the vertical distribution and composition of atmosphere,and the absorption effect,the absorption effect,attenuation effect,scattering effect and atmosphere turbulence are also discussed in detail.In addition,the fog,rain,and sand particle characteristics in atmosphere are theoretical researched.Next,the transmittance,scattering intensity and atmospheric attenuation are simulated with different atmosphere conditions,which can be used to measure the atmosphere attenuation situation.Finally,this paper has built the space to ground optical communication system,and the simulation of this system with different weather conditions has been conducted.According to above researches,this paper also has put forward the corresponding solutions for the atmosphere effect on space to ground optical communication,including the wavelength selection with different weather conditions,the height setting of optical ground station and angle selection of transmitter for optical ground station.(2)The third chapter addresses the link design of DSOC and OAM(Orbital Angular Momentum,OAM)modulation technology.First,according to the different communication channels,the DSOC links can be divided into space to ground link and space to space link,i.e.space to ground optical link and inter-satellite optical link.Considering the long communication distance,strict link budget and many influencing factors,this paper separately designs and simulates the space to ground optical link and inter-satellite optical link.Then,considering the multiplexing technology can greatly increase the system capacity,which can be an effective way to improve the communication rate.This paper sets up the PDM(Polarization Division Multiplexing,PDM)system model and WDM(Wavelength Division Multiplexing,WDM)system model,and tests the performance of the two system models.Finally,related researches show that OAM multiplexing technology can further improve the information transmission rate and create a new degree of freedom and the thin air or even vacuum deep space environment provide the feasibility for OAM multiplexing technology.Therefore,this paper researches the OAM modulation technology in DSOC.(3)The fourth chapter addresses the MAC(Media Access Control,MAC)access technology and routing design for DSOC backbone network.First,the structure of DSOC backbone network is designed,and a flat wireless Mesh structure for DSOC backbone network is also proposed.Each backbone node acts as the relay station of interstellar communication,and Lagrange equilibrium system for each planet is built with the Sun as the center,so as to realize the multi-hop transmission.Then,due to the sensitive characteristics of angle and position for laser communication,this paper designs the node model with multiple interfaces,which can make full use of the space resources.Based on the above design,the DMAC(Directional Media Access Control,DMAC)protocol is proposed for DSON backbone network.Compared with NDMAC(NON-DMAC,NDMAC),DMAC protocol can effectively improve the performance of network.Finally,considering DSOC has the characteristics of the long distance and line of sight transmission,due to obstacles,background noise and node transmission ability,a large number of unidirectional links will arise.In addition,the node energy is also limited,thus,this paper presents the RA-ACA(Routing Algorithm based on Ant Colony Algorithm,RA-ACA)algorithm.Compared with TACA(Traditional Ant Colony Algorithm,TACA)algorithm,RA-ACA algorithm can effectively reduce the transmission delay,and prolong the network survival time.(4)The fifth chapter addresses routing algorithm of DSOC network.First,previous researches of routing algorithms for deep space communication network were mostly based on radio frequency communication,which was different from laser communication.Therefore,related routing algorithms can not be directly applied to the DSOC network.Then,considering the challenges of routing design for DSOC network,due to the sensitive characteristics of angle and position for laser communication,this paper presents DFRA(Directional Flooding Routing Algorithm,DFRA)algorithm based on multiple interfaces design.So the spatial multiplexing and frequency division multiplexing can be availably combined.Compared with TFRA(Traditional Flooding Routing Algorithm,TFRA)algorithm,DFRA algorithm can avoid the non-directional and blind transmission,and save more energy.Finally,considering the technical advantages of wireless sensor network,related researches proposed that wireless sensor network could be applied to deep space exploration.But the specific routing algorithm research is still in the blank stage.Thus,this paper proposes the DSODD(Deep Space Optical Directed Diffusion,DSODD)algorithm.Compared with DD(Directed Diffusion,DD)algorithm,DSODD algorithm is better than the DD algorithm,and performance of DSODD algorithm is much better after path reinforce.To determine and evaluate the performance of the proposed protocol and algorithms,this thesis builds a simulation platform based on OPTISYSTEM,MATLAB and NS2 simulation software.Simulation results demonstrate that the proposed protocol and algorithms in this dissertation gain significant advantages in increasing network throughput,reducing network transmission delay and saving node energy.In addition,the research achievements in this dissertation are able to provide the abundant theoretical foundation and technical guarantee for the development of future deep space optical communication networks.