  Caching in wireless device-to-device (D2D) networks can be utilized to
offload data traffic during peak times. However, the design of incentive
mechanisms is challenging due to the heterogeneous preference and selfish
nature of user terminals (UTs). In this paper, we propose an incentive
mechanism in which the base station (BS) rewards those UTs that share contents
with others using D2D communication. We study the cost minimization problem for
the BS and the utility maximization problem for each UT. In particular, the BS
determines the rewarding policy to minimize his total cost, while each UT aims
to maximize his utility by choosing his caching policy. We formulate the
conflict among UTs and the tension between the BS and the UTs as a Stackelberg
game. We show the existence of the equilibrium and propose an iterative
gradient algorithm (IGA) to obtain the Stackelberg Equilibrium. Extensive
simulations are carried out to evaluate the performance of the proposed caching
scheme and comparisons are drawn with several baseline caching schemes with no
incentives. Numerical results show that the caching scheme under our incentive
mechanism outperforms other schemes in terms of the BS serving cost and the
utilities of the UTs.
