Caching Optimization for D2D-Assisted Heterogeneous Wireless Networks

5G networks are required to provide ultra reliable low latency communications while dealing with the permanent growth of data traffic. In Heterogeneous Networks (Hetnets) assisted with Device-to-Device (D2D) communications, traffic can be offloaded to small base stations or to devices in order to improve the transmission delays even with small caching. In this paper, we aim at reducing the average content delivery delay by optimizing the caching placement strategy in the context of D2D-assisted Hetnets. First, we analytically derive an upper bound on the average content delivery delay. Then, we formulate the problem of minimizing this upper bound through caching placement. The optimal solution is obtained for a single file, then used to propose a low-complex heuristic solution for multiple files. Numerical results illustrate the efficiency of our solution compared to other strategies.