Research On Ubiquitous Mobile Access Theory And Technology Based On Intelligent Caching

With the rapid development of the air-space-ground integrated information network,diversified access devices such as satellites,vehicles and unmanned aerial vehicles gradually establish a closer connection relationship with traditional cellular network access devices.They cooperate with each other to form a wide coverage,fully connected,diversified ubiquitous mobile communication network.Edge caching,a classic technology in the field of wireless communication,is favored by researchers because of its advantages in reducing energy consumption and delay.However,the traditional caching technology has been unable to meet the ubiquitous communication needs in the future due to the lack of mobility of edge devices.Therefore,it is an urgent challenge to develop innovative caching strategies for the diversified edge access devices with different mobile characteristics in the future.Based on the mobility of edge devices in the future ubiquitous networks,this thesis divided them into three categories:fixed position,regular motion and irregular motion.Furthermore,theories and methods related to internal caching strategies are analyzed successively.Firstly,for the problem of explosive traffic growth in fixed position nodes caused by streaming media represented by the on-line video,this thesis proposes an intelligent caching strategy based on machine learning theory.Secondly,for the regular motion access nodes represented by non-geostationary orbit(NGSO)satellites,the research scenarios are divided into intensive region and non-intensive region according to the gap between requests and available resources,furthermore,the multi-satellite cooperative caching strategy and the inter-satellite routing strategy are studied in this thesis,respectively.Finally,this thesis proposes an efficient caching strategy based on the theory of spreading dynamics for the question of traffic video distributing in Internet of vehicles(IoV),which is one of the most representative networks composed of nodes with irregular motion.Furthermore,the main research contents and innovations of this thesis are as follows:1.Research on intelligent caching strategy of edge nodes for the on-line videoFacing the problem of explosive growth of traffic data caused by streaming media such as on-line video in the fixed position access nodes,the idea of segment caching which divids the complete video into several segments and store separately has become an effective design of caching strategy for edge devices with the small cache space.However,the adoption of segment caching in edge networks will divide the simple video transmission process into two coupling stages because of separate data caching,which leads to more complicated resource allocation.In this thesis,this problem is discussed,and its mathematical model is established to minimize the energy consumption of video transmissions.By introducing an efficient prediction window of channel fading,an optimal dynamic scheduling algorithm based on Q-learning is proposed to minimize power consumption while ensuring smooth video streaming.The proposed Q-learning algorithm is simulated and the impacts of channel state,target video bit rate and large-scale channel parameter are evaluated.Simulation results show that the proposed method can effectively reduce the total power consumption while ensuring the smooth playback of video service,thanks to the fact that the proposed method is intelligent which can effectively utilize idle resources in favorable channel states.2.Research on the cooperative caching strategy in intensive region for NGSO satellite system.For NGSO satellites working in the region with intensive requests,the caching of high value data requested frequently can reduce the request delay and energy consumption,which is a practical system optimization scheme.However,as the NGSO satellites cached data leave the region,these advantages will disappear with them.This thesis is intended for the cache strategy in the NGSO satellite constellations and formulates an effective data sharing strategy between NGSO satellites for avoiding the invalidation of cached data.The density of cached data is a key indicator for the sharing strategy,because excessive sharing can increase the probability of cache hits at the expense of waste of resources and vice versa.Spreading dynamics is a physical model to describe the interaction of individuals in complex networks,which is helpful to predict the decisive threshold in the system.Therefore,this thesis identifies the relationship between satellite speed,constellation structure,data size and hit probability,calculating a decisive threshold for the effective data density based on spreading dynamics.Meanwhile,the ideas of water-filling algorithm and reinforcement learning algorithm have been improved and applied to the data sharing strategy limited by the satellite cache space.Finally,the proposed strategy is compared with the traditional strategy in a variety of scenarios,and the results verify the effectiveness of the proposed optimization strategy in terms of energy consumption and service delay.3.Research on the intersatellite routing strategy in non-intensive region for NGSO satellite system.In contrast to the case of intensive requests,NGSO satellite in non-intensive region receive fewer requests,causing valuable caching resources to be idle and thus wasted.On the other hand,NGSO satellites in intensive region are more likely to face the problem of insufficient cache resources.In this case,it is an effective idea to build a multi-hop route composed of inter-satellite link(ISL)between NGSO satellites in intensive regions and nonintensive regions.However,the relative motion between NGSO satellites is a major obstacle in the formulation of routing strategy.This thesis proposes a dynamic routing strategy based on multi-layer satellite architecture for unicast and multicast scenarios respectively.For the unicast,a routing strategy based on Q-learning is proposed to optimize bandwidth and delay simultaneously,and the effectiveness is verified by the comparison against the traditional routing strategy.For the multicast,an advanced Q-Iearning multicast routing algorithm based on spatial directionality is proposed to optimize the overall transmission success rate and resource cost,and the superiority of the proposed routing strategy are verified by simulation results.4.Research on caching strategy of traffic video for vehiclesIn the irregular motion nodes represented by IoV,the complexity and variability of node location is an important obstacle to fumulate the caching strategy in such networks.An example of the effective diffusion of cached traffic video within the IoV is presented here,the variability of vehicle locations,the timeliness of traffic videos,the scarcity of available resources,and the complexity of link quality all are great obstacles to effective diffusion of data within the network.In this thesis,we focus on abstracting the intrinsic relationship between the diffusion efficiency of the data and the topology of the IoV,and explore the criteria of topology optimization strategy to minimize the total delay for all nodes in the network.Specifically,the mathematical models of topology control,parallel transmission,and diffusion delay are established,respectively.In particular,the spreading index is quantified to formulate diffusion strategies accurately,which is an intuitive evaluation parameter using the model of spreading dynamics in complex networks.Its effectiveness and limitations are verified by simulation.Then,based on this index,an efficient topology control strategy and a hybrid diffusion strategy for delay reduction are proposed.Compared with the traditional content-centric network(CCN)and proactive diffusion strategy,the proposed strategy shows greater advantages in total delay optimization due to the performance improvement brought by more efficient topology.Extensive simulation results verify the effectiveness and the applicable scenarios are described.