摘要：Cognitive radio is regarded as a key technique in the fifth generation communication system. We consider that the popular contents can be cached in cognitive mobile users who compose a cognitive Device-to-Device (D2D) network. Cached Contents in this network can be shared by cooperating with each other. Consequently, contents can be downloaded from local cache, cognitive D2D network or cellular network with different access cost. It has communication cost when accessing cellular networks, and time delay and cooperative cost when accessing cognitive D2D networks. To minimize the total cost of all the mobile users, we formulate an optimal content placement problem. This problem is hard to solve, and we proposed a suboptimal cache scheme, including cache placement and cache replacement. Our approach quantifies time delay cost by modeling the primary appearance as a continuous-time Markov chain. Numerical results show that our approach is lowcomplexity and implementable.
关键词：Cognitive radio ; cache ; cellular network ; Device-to-Device (D2D) communication
