Mobility management for D4D in HetNet

Nowadays, cellular operators are facing new challenges to satisfy the future demand of their clients. In addition, user's mobility among multi-tier networks leads to dropping ongoing calls in the system. The introductions of low power nodes and Device-to-Device (D2D) communication into Macro cells are regarded as promising technologies to provide a high data rate. A new design known as Device-for-Device (D4D) has appeared to satisfy the minimum requirement with seamless mobility among multi-tier Heterogeneous networks (HetNet). In this paper, we propose a new scheme to address mobility problems by deferring the handoff call using a user as relay until a target tier gets the minimum quality of service requirement. Our proposed scheme intends to keep the user connected to a small cell through D4D communication while moving among cells in a smooth way until obtaining sufficient resources. Simulation results show that our proposed scheme can significantly increase the number of admitted users and throughput in the system while reducing the blocking probability.