Spatially Correlated Placement Policies for Wireless Content Caching Networks

We propose a geographic content placement policy for wireless caching networks. This policy, named Joint Caching Policy (JCP), jointly determines the caching strategy across the set of base stations (BSs) to improve the hit probability of an arbitrarily located user in the network versus caching policies where placement is independent and identically distributed across the BSs. To that end, JCP divides the BSs into groups, and executes a joint caching policy for each group, while content placement is independent across the groups. Existing joint caching policies require knowledge of user location to optimize content placement. On the other hand, JCP does not require any information on user location, and it provides a content placement policy that outperforms the one given by Independent Caching Policy (ICP), proposed by Blaszczyszyn and Giovanidis in 2015, under any user location distribution. We prove that the hit probability under JCP is lower bounded by that of ICP. We further propose an extension of JCP, named JCP-OPT, which improves the hit probability over JCP by solving a concave maximization problem, provided that there is side information about the user locations. We validate the performance of JCP and JCP-OPT via numerical evaluations and demonstrate that they can provide up to a 30% gain in hit probability over ICP.