Device-to-Device Content Delivery in Cellular Networks: Multicast or Unicast

Considering that the future cellular networks are more content-centric and content sharing among user equipments is more universal, device-to-device (D2D) technique attracts attention on supplying a feasible way for content delivery among proximal users without deploying additional infrastructure. Whereas some problems are still not clear such as the limitation on D2D communication for content delivery and which transmission mode (unicast or multicast) is more efficient. In this paper, the performance of content delivery is analyzed for D2D unicast and multicast, respectively. Several metrics such as the number of caching users, the number of request users, and the serving time of a content request are quantified with the consideration of user deployment and interference environment. These analyses provide an insight into D2D content delivery and deep understanding of D2D unicast and multicast on content delivery. To further distinguish appropriate conditions of employing unicast and multicast, energy efficiency is also investigated for two transmission modes. Extensive evaluations show that a better transmission mode can be selected based on the work presented in this paper. It is also verified that the efficiency of content delivery in cellular networks can be improved by this mode selection.