Content-related energy efficiency analysis in cache-enabled device-to-device network

Cache-enabled device-to-device (D2D) communication is a promising technique to offload the core traffic and cache deployment is important in achieving the benefits brought by caching. While rare considered optimal caching deployment from the perspective of energy efficiency. In fact, cache deployment will certainly influence the distribution of active transmitters, network interference and power consumption, contributing to corresponding energy efficiency. In this paper, we first derive the accurate expression of content-related energy efficiency of cache-enabled D2D network as a function of cache deployment based on a proposed content-related interference model. And then optimization problem with respect to optimal caching probability to maximize the content-related energy efficiency is formulated. Due to the complicated function structure and highly coupled variables in objective function and constraints, we turn to three special cases to explore the approximately optimal solutions. It turns out that when the ratio of active intensity of request to cache is too large or too small, the optimization problem can reduce to a concave problem and the optimal caching deployment is achieved using KKT conditions. Numerical and simulation results validate the generality of proposed interference model and demonstrate the optimal caching deployment is related to transmit power and content popularity.