  As the demand of mobile devices (MDs) for data services is explosively
increasing, traditional offloading in the cellular networks is facing the
contradiction of energy efficiency and quality of service. Device-to-device
(D2D) communication is considered as an effective solution. This work
investigates a scenario where the MDs have the same demand for common content
and they cooperate to deliver it using multicast multihop relaying. We focus on
the problem of total power minimization by grouping the MDs in multihop D2D
networks, while maintaining the minimum rate requirement of each MD. As the
problem is shown to be NP-complete and the optimal solution can not be found
efficiently, two greedy algorithms are proposed to solve this problem in
polynomial time. Simulation results demonstrate that lots of power can be saved
in the content delivery situation using multihop D2D communication, and the
proposed algorithms are suitable for different situations with different
advantages.
