Resource Trading for a Small-Cell Caching System: A Contract-Theory Based Approach

Evidences indicate that wireless video traffic has played an important role in cellular networks. Caching mechanisms which store popular contents into local small-cell base stations (SBSs) in cellular networks are proposed to further reduce transmission delay and release the traffic pressure over backhaul channels. In this paper, we consider a commercialized small-cell caching system consisting of a network service provider (NSP), several video retailers (VRs) and multiple mobile users (MUs). The NSP as a network facility monopoly releases its resources to the VRs in order to maximize its own profits. The distribution of VR's type is known to the NSP, while the actual type of a given VR is not known. We research on such an information asymmetric market within the framework of contract theory, formulated as an adverse selection problem. The MUs and SBSs are modeled as two independent Poisson point processes, and the directly downloading probability from the adjacent SBS is derived via stohastic geometry theory. Based on the probability, we formulate the utility functions of the NSP and the VRs. Then, the optimal contract problem is constructed. Also, we provide the feasibility of the contract, and the optimal contract is proposed when VR's popularity parameter γ takes different values. Numerical results are provided to show the optimal quality and the optimal price designed for each VR.