Research On Cooperation-Based Space Information Transmission Mechanisms

With the increasingly obvious trend of integeration for satellite communications and traditional terrestrial communications,especially the emergence of inter-satellite links and the enhancement of on-board processing capabilities,the interconnection of space nodes becomes the development trend and inevitable requirement of future space communications,and it is imperative to study and construct spatial information Internet based on cooperative transmission.The future spatial information Internet will be a communication network that acquires,transmits and processes spatial information in real time by using the space platform as the main carrier.By means of spatial nodes with different orbits,types and performances connected by inter-satellite and satellite-ground links,it cannot only support the high-dynamic,broadband and real-time transmssion of earth observation downwards,but also support the ultra-long-range,large-delay and reliable transmission of deep space exploration upwards.Its network architecture will have the multi-layer and three-dimensional characteristics,which will make future space communications show obvious characteristics of integrated cooperative transmission.However,the existence of such problems as long communication distance,large transmission delay and loss,limited network resources and frequent switching of transmission links makes the transmission capacity of spatial information limited and the network adaptability poor.The effective solution of these problems requires the emergence of fast,reliable,flexible and stable new technologies for cooperative transmission of spatial information.At present,some literatures have studied cooperation-based space information transmission technologies.However,whether traditional amplify-and-forward and decode-and-forward cooperative mode or network coding-based cooperative transmission mode,the existing research literature is less,and lack of systematic research.Especially in the future complex and changeable multi-layer space communication network new architecture and various new technologies background,there are still many problems to be solved.Therefore,it is very important to study the cooperation-based space information transmission mechanisms by considering intrinsic characteristics of future space communications,such as complex network structure,dynamic topology,long transmission distance and unstable link quality.Meanwhile,it can provide theoretical and technical support for improving the reliability,stability and effectiveness of space information transmission.Aiming at the above problems and challenges,this paper focuses on four aspects:cooperative space information transmission based on spatial diversity and network coding,cooperative space information transmission based on network coding and contact graph,cooperative space information transmission based on contact plan design and intelligent optimization,cooperative space information transmission based on contact plan design and adaptive intelligent optimization.The cooperation-based space information transmission mechanisms are studied.The main contributions and innovations in this dissertation are summarized as follows:(1)The second chapter addresses the influence of spatial diversity and network coding on spatial information transmission,and proposes a space information transmission scheme with the joint optimization of spatial diversity and system random linear network coding based on the two-state channel model.First,the satellite node based space cooperative communication model is adopted to realize long-distance information transmission among ground nodes.Then,the fading characteristics of spatial information transmission links between ground nodes and satellite nodes are analyzed and studied,and a two-state satellite-ground link transmission channel model is established.Next,based on the established system model and channel model,the spatial diversity and network coding are introduced to jointly optimize the performance of spatial information transmission.The performance differences of system outage probability and bit error rate are analyzed when different transmission schemes are adopted.Finally,theoretical analysis and simulation results prove that the proposed transmission scheme has better performance in term of transmission reliability.(2)The third chapter addresses the influence of network coding and contact graph on spatial information transmission,and proposes a space information transmission scheme with the joint optimization of network coding and contact graph routing based on destination.First,considering the discontinuity of inter-satellite link connectivity and time-varying network topology caused by the mobility of satellite nodes,the characteristics of link and network are described by "contact" and "contact graph".Then,the capacity constraints of inter-satellite links in space information transmission are analyzed,and network coding is introduced to improve network throughput and efficiency of space information transmission.The residual capacity of each "contact" is calculated and compared to determine whether to encode data of satellite nodes and a cooperative transmission scheme of spatial information is proposed based on joint optimization of network coding and contact graph.Finally,both theoretical analysis and simulation results prove that the proposed transmission scheme has better performance in term of transmission efficiency.(3)The fourth chapter addresses the influence of contact plan design and intelligent optimization on spatial information transmission,and proposes a space information transmission scheme with the joint optimization of contact plan design and intelligent optimization based on time-expanded graph with the limited capacity.First,in order to realize low-delay and high-reliability spatial information transmission between ground nodes and spatial nodes,the transmission characteristics of different space platforms between satellites and ground are analyzed,high-altitude platforms and unmanned aerial vehicles are introduced as space cooperative relay transmission nodes for satellite-ground transmissions,and a space-air-ground cooperative communication model based on nodes of satellite,high-altitude platforms and unmanned aerial vehicles is proposed.Then,to solve the problems of dynamic topology and limited resources in the multi-layer spatial information transmission network,the time-expanded graph is used to transform the dynamic network topology into a series of static network topologies,and the time-expanded graph with the limited capacity is constructed.Next,in order to achieve efficient transmission of spatial information under resource-constrained conditions,different intelligent optimization algorithms are introduced to optimize the scheduling of transmission link resources for inter-layer and intra-layer "contact" based on the given system model and the static topology diagrams,and different contact planning schemes are designed and proposed respectively.Finally,through theoretical analysis and simulation,it is proved that the proposed transmission schemes have better data transmission efficiency and can support real-time,efficient,and mass space information transmissions in future multi-layer space communication networks.(4)The fifth chapter addresses the influence of contact plan design and adaptive optimization on spatial information transmissions,and proposes a space information transmission scheme with the joint optimization of contact plan design and adaptive intelligent optimization based on the space-time graph.First,in order to improve the adaptability of space information transmissions,quasi-stationary high-altitude-platform nodes are introduced between satellite nodes and ground nodes as cooperative relay nodes for space information transmissions,and a space-air-earth cooperative communication model based on nodes of satellite and high-altitude platforms is constructed.Next,considering that spatial information transmissions will be affected not only by shadow effect and multipath effect,but also by atmospheric propagation and spatial transmission loss,especially for spatial information in Ka band,different weather conditions and different rainfall levels will have a greater impact on information transmissions.Therefore,an adaptive transmission scheme of spatial information is proposed,which enables spatial nodes to adopt different transmission strategies according to diferent weather conditions,so as to maximize the transmission efficiency and improve the transmission reliability.After that,based on the proposed adaptive transmission scheme,with the goal of minimizing data delivery time,different intelligent optimization algorithms are introduced to optimize the scheduling of "contact" in the system,and two contact planning schemes are designed and proposed.Finally,through theoretical analysis and simulation,it is proved that the proposed transmission schemes can not only achieve efficient transmissions with minimum delivery time,but also achieve load balancing among satellite nodes.In order to verify and evaluate the performances of the proposed transmission schemes,joint simulation experiments are carried out by using MATLAB and STK simulation software.Simulation results demonstrate that the proposed transmission schemes in this dissertation have significant advantages in improving the reliability and effectiveness of spatial information transmission compared with the existing research works.In addition,the research achievements in this dissertation are able to provide theoretical references and technical support for the future development and construction of space-air-ground cooperative communication networks.