# Cooperative Caching and Resource Allocation in Integrated Satellite-Terrestrial Networks  
[PERSON]  
1 China Academy of Space Technology (Vi'an), Xi'an 710100, China; [EMAIL_ADDRESS] (Y.W. )1 China Academy of Space Technology (Vi'an), Xi'an 710100, China; wang.yl@stu. users, where caching servers are placed on LEO satellites. However, there are strictly limited on-board resources for satellite networks, which cannot meet with the service requirements of users when a large number of terminal users arrive [12; 13]. By combining the advantages of terrestrial and satellite networks, cooperative content caching in integrated satellite-terrestrial networks has been a promising approach to provide content services for terminal users on-demand in a flexible and efficient way [14; 15]. It should be noted that, different from terrestrial networks with relatively unchanged topologies and sufficient resources, the topologies of satellite networks with strictly limited on-board resources can also be time-varying [16]. Accordingly, it is a challenging issue to make the feasible strategies of cooperative caching and resource allocation in integrated satellite-terrestrial networks. Extensive research focuses on the issues of cooperative caching and resource allocation in integrated satellite-terrestrial networks [17; 18]. Some existing related works without inter-satellite communication are preliminarily studied based on the consideration of simplifying the problem complexity [19; 20], where the performance cannot be guaranteed due to the lack of inter-satellite cooperative caching. Furthermore, the inter-satellite communication capabilities for LEO satellite networks are considered to provide cooperative caching services for terminal users. The problems are also formulated to optimize the objectives, e.g., cache hit-rate [21], content access delay [22], net-gains [23], etc. However, little of the existing related work discusses the joint optimization problem of data routing, network bandwidth, and on-board storage resources for cooperative caching in integrated satellite-terrestrial networks. Moreover, as the number of satellites increases, the dimensional information concerning the spatial state will correspondingly increase, which can also bring a difficulty in the global resource management [24]. Therefore, the cooperative caching architectures of integrated satellite-terrestrial networks should also be investigated to reduce the system complexity of resource management and improve the real-time decision-making. In this paper, a cooperative caching and resource allocation problem in integrated satellite-terrestrial networks is discussed, where the inter-satellite and satellite-terrestrial cooperative caching is introduced to manage the satellite-terrestrial network resources in a more flexible and effective way. Each terminal user can retrieve the cache content just from the access satellite, the neighbors, or the ground data center to simplify the system complexity. Different content popularity and geographical distribution of terminal users are also considered for the system model. Then, the problem is formulated under multiple physical constraints, and the aim is to jointly minimize the total deployment costs of storage resource usage and network bandwidth consumption. To reduce the computation complexity while improving the real-time decision making, a cooperative caching and resource allocation (CCRA) algorithm is proposed by introducing a neighborhood search approach, where the content service can be provided for each user in the neighboring sub-network of the access satellite. Finally, the simulation experiments are conducted to evaluate the performance of the proposed CCRA algorithm in different application scenarios, as well as compared with the existing approaches of Greedy and breath-first search (BFS). The results show that the proposed CCRA algorithm outperforms Greedy and BFS in reducing the total deployment costs of storage resource usage and network bandwidth consumption.