Analysis on Caching Strategy for Device-to-Device Communication with Multiple Helpers

In order to alleviate the traffic burden, there has been researching on helper equipments (HEs) in wireless networks. In this paper, a novel caching scheme with HEs in Device-to-Device (D2D) communication is studied. The cost of the system is formulated to find the optimal number of HEs in D2D communication, in which the impact of mobility, cache size, number of devices are all taken into account. Due to the fact that with the increase of the number of HEs, the D2D transmission coverage and the system cost increases accordingly, we model the cost function and prove that it is a convex problem. By minimizing the cost, the optimal number of HEs is found out. We apply the optimal number of HEs to existing caching strategies, then can prove that the system performance will become better. Finally, the simulation shows that the mobility of HEs can extend D2D transmission coverage and especially improve the offloading performance. In addition, by applying the optimal number of HEs, different caching strategies can achieve higher cache hit rate at the minimum cost.