This paper considers the coded caching problem with not less files than users in relay networks, especially in combination networks. The tradeoff between the user's memory size and the worst-case download time is studied. Two novel outer bounds under the constraint of uncoded cache placement are derived. By relying on the symmetric topology of combination networks, we provide a novel caching scheme. For a single memory size, we improve the proposed scheme by using interference alignment. Our schemes are proved to be optimal under the constraint of uncoded cache placement for one specific class of combination networks and shown by numerical evaluations to outperform the state of the art.
['Kai Wan', 'Mingyue Ji', 'Pablo Piantanida', 'Daniela Tuninetti']
Combination Networks with Caches: Novel Inner and Outer Bounds with Uncoded Cache Placement