  Caching at base stations (BSs) is a promising approach for supporting the
tremendous traffic growth of content delivery over future small-cell wireless
networks with limited backhaul. This paper considers exploiting spatial caching
diversity (i.e., caching different subsets of popular content files at
neighboring BSs) that can greatly improve the cache hit probability, thereby
leading to a better overall system performance. A key issue in exploiting
spatial caching diversity is that the cached content may not be located at the
nearest BS, which means that to access such content, a user needs to overcome
strong interference from the nearby BSs; this significantly limits the gain of
spatial caching diversity. In this paper, we consider a joint design of
frequency reuse and caching, such that the benefit of an improved cache hit
probability induced by spatial caching diversity and the benefit of
interference coordination induced by frequency reuse can be achieved
simultaneously. We obtain a closed-form characterization of the approximate
successful transmission probability for the proposed scheme and analyze the
impact of key operating parameters on the performance. We design a
low-complexity algorithm to optimize the frequency reuse factor and the cache
storage allocation. Simulations show that the proposed scheme achieves a higher
successful transmission probability than existing caching schemes.
