Access And Handover Technologies For Multi-layer Space Network

With the development of terrestrial communication network,the space communication networks composed of satellite and high-altitude platforms also develops rapidly and becomes of recent research hotspot.GEO satellite covers a wide area that three GEO satellites can achieve global coverage.LEO satellite has low-height earth orbit and the transmission delay is small.LEO satellite constellation can also achieve global coverage.High-altitude platform has many advantages such as easy to deploy,easy to recover,low cost,small delay,but they are not stable enough because they are exposed to the air,and easily affected by the wind,heat and so on.Multi-layer space network can combine the advantages of each layer to improve system stability,and is the future research direction of space network.The thesis first analyzes the access and handover strategy in LEO satellite network,proposes a channel reservation strategy based on queuing time.At the same time,we consider the ordinary users and advanced users.Predict the time of handover through the location information and ensure the system performance especially for advanced user handover performance through channel reservation and queuing.Then the relationship between the number of beams and the handover performance in LEO satellite network is analyzed,and the optimal number of beams is obtained with best handover performance.Studies on multi-layer networks of high-altitude platforms and satellites are not much currently.The balloon is the easily affected by the wind power.So this thesis simulates and analyzes access and handover performance of double-layer networks composed of balloons and LEO satellites.The simulation results show that the double layer network has better performance than the single layer network.Finally,the access control strategy in GEO / LEO double-layer satellite network is studied.Considering the simultaneous presence of ordinary users and advanced users,a LEO satellite-preferred direct access strategy is given,but the approach does not make reasonable use of the GEO satellite channel,and the frequent handover due to access to LEO satellites will increase pressure of the system.So this thesis puts forward an improved strategy based on the channel occupancy rate.Advanced users adopt the LEO direct access strategy and for ordinary users adopt a new strategy by setting the access threshold.Through the simulation analysis,the improved strategy gets better utilization efficiency,with better access and handover performance and ensures the communication quality of the advanced users.