Redundant Caching And Resource Allocation For D2D Communication In Heterogeneous Cellular Networks

With the development of mobile multimedia services, the demand for multimedia content of mobile users is increasing, leading to the load of core network increased. Heterogeneous cellular network can effectively improve the capacity of wireless network by configuring low power base station in the coverage area of traditional macrocell base station, which is a key technology of mobile communication system in the future.In order to reduce the load of the core network, the traditional way is to cache files in the macro base station (MBS) in advance, and then the MBS provide content service for the mobile users in the coverage of it.The concept of distributed cache has been extended to wireless communication area. In heterogeneous cellular networks, popular content on servers subject to frequent demand for delivery is cached in MBS,low-power base stations (SBSs) and mobile terminals, and provide services for mobile users together. Benefit from the substantial increase in mobile terminal storage capacity, it is possible to cache files in the mobile terminal and then provide services for nearby users by D2D communication. Caching files in the mobile terminal can divert the load of the base station, alleviate the congestion of the core network, realize the short range transmission, reduce the power consumption, shorten the delay of transmission.For the download of the requested files, in order to improve the cache hit ratio of requesters, which achieve content from the local system,a SBSs and mobile terminals combined cache strategy based on the distributed cache technology is proposed in this paper. Firstly,a algorithm based on PageRank to select the optimized D2D helpers by analyzing the link quality and requests among users is proposed. Then,combination with the file popularity and physical domain to select appropriate content to cache, and determine where is cached. Simulation results show that the proposed scheme can effectively improve the file cache hit ratio, reduce the total power consumption and total time delay.For the failure coded fragment repair, a resource allocation scheme based on erasure coding and D2D communication technique is proposed.We consider the users' physical domain and social domain, based on the matching theory to manage the wireless resource, improving the success probability of repairing the failure coded fragment. Further, considering the Gaussian white noise and channel fading, and combining the adaptive modulation technique to optimize the correct probability of repairing the failure coded fragment. The simulation results show that the combination of resource allocation and adaptive modulation not only improves the repair correctness of the failure coded fragment, but also improves the system throughput.