Delay performance analysis of cooperative cell caching in future mobile networks

Due to the exponentially increasing demands for multimedia services over recent years, the growing network traffic load becomes a severe concern for the mobile network operators (MNOs). However, the wireless link capacity, the radio access networks, and MNOs´ backhaul networks cannot deal with the traffic load effectively. To solve this problem, content caching is regarded as an effective emerging technique to reduce the duplicated transmissions of the content downloads demanded by mobile users and improve users´ quality of service (QoS). Therefore, in this paper, we mainly focus on the cooperative cell caching for future mobile networks, where each cell (e.g., base station) can cache popular contents for improving QoS especially on the overall delay performance of users. The task is formulated as a problem of minimizing the expected overall user delay of accessing the demanded contents. Instead of rewriting it as a non-linear and non-convex problem based on an approximate transformation, we convert it to a linear programming problem by using a novel equivalent transformation. To solve the problem, rather than using the existing branchand-bound (BNB) method, which suffers from exponential-time and exponential-space complexity, we propose a new distributed suboptimal algorithm, which has polynomial-time and linearspace complexity. Numerical evaluation results demonstrate that our proposed cooperative cell caching framework can reduce the expected overall delay significantly.