Optimization of hybrid cache placement for collaborative relaying

Traditional wireless multi-hop relaying systems suffer from inefficient use of bandwidth resources. This letter studies the use of content caching at distributed relays to tackle this problem and improve the performance of collaborative relaying. We propose a hybrid caching scheme that is jointly optimized with the transmission schemes, to achieve a fine balance between the signal cooperation gain and the caching diversity gain. The optimization problem of cache placement to minimize the outage probability is studied and is shown to be convex. Numerical results demonstrate significant outage performance gains over traditional relaying without caching.