I. Introduction
Ubiquitous mobile users holding smart phones and tablets have triggered an explosive demand for video/audio streaming, which significantly increases network load. However, it is observed that the increased load is mostly caused by duplicate downloading of popular content [1]. A solution to relieve overload is to cache popular content locally at intermediate nodes, such as cellular base stations (BSs) and personal devices in distributed device-to-device (D2D) networks. In order to make efficient utilization of limited storage resource in D2D integrated cellular networks, the development of cooperative caching becomes imperative.