Research On User Association And Traffic Offloading In Satellite-terrestrial Integrated Networks

In order to cope with the problem of fast-growing traffic and meet the needs of users for communication regions,the satellite-terrestrial integrated networks(STIN)has become the focus of current research for the features of supporting large-scale service and the global seamless coverage.In STIN,the network capacity can be improved effectively and the local congestion can be prevented by offloading the traffic in the traffic intensive areas.However,the heterogeneity,topology time-varying characteristics and the diversity of network operators' bussiness strategies of STIN will affect the user access,which further affects the network performance and user experience.Therefore,this thesis studies the user association and traffic offloading strategies on the access side of STIN,including the following two aspects:1.In the research of user association strategy in STIN,aiming at the problem of the influence of resilient backhauling on user access,the user association strategy under the constraint of resilient backhauling is studied.Firstly,a STIN model is constructed with low earth orbit satellites and three types of base station,viz.macro base station,small cell base station and low earth orbit-based base station.On this basis,the optimization problem of maximizing the ratio of arrival rate to load rate is formulated by considering the constraints of user requirments,load situation and resilient backhauling.Then,the dynamic user association mechanism(DUA)is proposed to realize the load balance and find the best user association.In DUA,a dynamic cell range extension algorithm is developed to adjust the load of STIN in term of the resilient backhaul capacity,and a greedy-based user-centric user association with task classification algorithm is proposed to find the base station which has the maximum arrival rate and minimum load for each user,and to meet the requirements of user task processing.The simulation results show that the proposed DUA can not only balance the load of STIN,but also guarantee the task processing demand of users.2.In the research of the traffic offloading strategy in STIN,aiming at the impact of the heterogeneity of STIN and the diversity of the operator's business strategy on the user access,the traffic offloading strategy under the multiple constraints of cost,user mobility and user demands is studied.Firstly,a STIN model is constructed with low earth orbit satellite networks,cellular networks and WLAN.On this basis,an optimization problem aiming to minimize the difference between the offloading costs and gains is formulated.Then,considering user mobility and the demand of task processing delay,as well as the long propagation delay of satellite networks and the limited coverage of WLAN,an operator oriented greedy-based multi-constrained traffic offloading mechanism(GMTO)is proposed to find the best user offloading solution for operator.The simulation results show that the proposed GMTO can not only meet the requirements of offloading cost and offloading gain,but also guarantee the user experience in STIN.