Cooperative Transmission via Caching Helpers

This paper models the cooperative transmission via caching helpers (cache-based joint transmission), which cache one of the K most popular files, in wireless cellular networks and analyzes its performance in terms of the file transmission success probability in the stochastic geometry framework. For given caching placement, the caching helpers can either provide a file diversity gain by serving different files or a cooperative gain by jointly transmitting the same files. In order to account for the tradeoff between the file diversity gain and the cooperative gain, we derive the cache hit probability and the rate coverage probability. We also find the optimal caching placement balancing the tradeoff and investigate the effects of various system parameters, such as the cooperative region, the density of caching helpers, and the file popularity exponent, on the optimal caching placement.