Research On Key Technologies Of Dynamic And Continuable Space-terrestrial Integrated Communication

With the rapid development of wireless mobile communication technology,the service capability of communication networks in various fields has been continuously enhanced,but the coverage area of terrestrial networks is still limited.In remote areas such as villages,valleys,and islands,network infrastructure construction and maintaining are expensive so that the network coverage is low,making the contradiction between the growing demand for network services and network capacity with the increasing terminal number.In order to enhance the data service capability in remote areas,the deep integration of satellite-based space network and ground network to build SpaceTerrestrial Integrated Communication Networks(STIN)for an integrated communication system with full coverage,high dynamics,low latency and high reliability is an important vision of future network.Currently,STIN is a paradigm for future seamless global communication system,which has received much attention from academia and industry.With the improvement of Low-Earth-Orbit(LEO)satellite technology,the use of multiple LEO satellites to build a high-capacity,full-coverage,and low-latency space network to provide fast and continuous data services for accessing terminals is more favored in terms of economy and efficiency.LEO constellation is becoming an important part of the STIN construction.The 3rd Generation Partnership Project(3GPP)standardization work has started to study the architecture and solutions of LEO-based STIN since Release 15.Meanwhile,the industry is committed to promoting the construction of various LEO constellations to obtain LEO communication resources.In STIN,high-speed data transmission between any two regions on Earth can be achieved by establishing ground-satellite links(GSL)and inter-satellite links(ISL).However,compared with ground communications,longer space propagation delay,limited network transmission resources,and high-speed relative motion of LEO satellites make data transmission in STIN more complex.Time-varying network topology and transmission resources bring new requirements on variability and continuity for transmission link deployment and transmission strategy making in STIN.That is,it not only need to ensure seamless link deployment and handover under dynamic network conditions,but also need to ensure a stable and continuable data transmission performance during service duration to ensure the Quality of Experience(QoE)of users.In order to enhance the variability and continuity of LEO constellation based STIN data transmission,this dissertation studies key technologies of dynamic and continuable communication for STIN,from four aspects as STIN transmission control architecture design,LEO satellite network topology optimization technology,dynamic space routing optimization technology,and GSL handover optimization technology.Among them,research I provides architecture support for research II,III and IV,research II focuses on STIN dynamic topology optimization,research III focuses on ISL selection optimization,and research IV focuses on GSL handover optimization.The specific research contents are expressed as follows:1.Propose a transmission control architecture for STIN based on global information awareness.Firstly,we design a fine-grained LEO satellite gateway service sensing and resource allocation framework for different types of user requirements.We take terminal transmission requirements as the guiding basis for onboard resource allocation to achieve reasonable allocation and utilization of satellite resources.Further,we establish a timevarying graph model to describe the dynamic transmission resources of STIN and based on the Software Defined Networking global control logic,combining the global coverage capability of Geosynchronous-Earth-Orbit satellites and the computational capability of ground center to deploy the control layer of STIN.The designed global control architecture enhances the network transmission control capability through real-time network state sensing and resource allocation to support the study of satellite networking strategy,space routing strategy,and GSL handover optimization strategy.2.Propose a dynamic network topology optimization method for user QoE guarantee.We firstly propose a user-density-based STIN division algorithm,which divides all network nodes into different size of blocks based on user distribution for distributed networking to improve transmission response and data transmission efficiency.We then propose a STIN networking algorithm based on the minimum coverage vertex set theory to deploy backbone satellites and accessing satellites in each block to achieve efficient transmission services.Further,we derive the backbone satellite update mechanism based on the time-varying network model to achieve sustainable data services.Simulation results show that the proposed STIN topology optimization scheme can effectively reduce the average data transmission delay and network load pressure under different network conditions,and improve the STIN transmission stability during service duration.3.Propose a fuzzy-CNN based space routing optimization method.Considering the dynamic motion and different data transmission capabilities of satellite nodes in STIN,we design a multi-task space routing strategy based on the proposed STIN control framework,artificial intelligence techniques,and fuzzy logic.The global load information is collected and made into a multidimensional information matrix,which is used to train and update the convolutional neural network(CNN)models.The GEO satellite uses the CNN model to make routing decisions and publishes flow tables to the LEO constellation for data forwarding.Further,we analyze the situation that only the CNN-based routing may contradict user QoE,and add the user QoE evaluation module based on fuzzy logic into the output stage of CNN to improve the CNN selection,so as to achieve a user-friendly space routing strategy.Simulation results show that compared with traditional schemes,the proposed intelligent space routing strategy performs better in terms of network throughput and network congestion control,and the route adjustment based on fuzzy logic effectively improves user QoE.4.Propose a GSL handover optimization method with service continuity enhancement.In STIN,satellites can be regarded as high-speed mobile base stations in the space,connected to user terminals through GSL.When the accessing satellite flies over the terminal area and cannot provide reliable data service,the GSL needs to be handed over(HO)to the next satellite.The handover process has a significant impact on the transmission quality and network service continuity.We firstly propose a HO optimization strategy for GSLs based on the conditional handover(CHO)mechanism.A reward function is designed related to link service time and service capacity to modify the target link evaluation.The optimal target satellite selection algorithm is propsoed.Then,we predict the potential CHO combinations during service period by constructing a service continuity performance graph(SCG)model to dynamically adjust the HO sequence of GSLs to improve the network service continuity when the LEO satellite sequence flies over the accessing terminal.Simulation results show that the proposed GSL handover optimization scheme can significantly reduce the HO rate and improve the transmission stability and continuity during the service duration.