On the Benefits of Asymmetric Coded Cache Placement in Combination Networks with End-User Caches

TL;DR

This paper introduces a novel asymmetric coded cache placement strategy for combination networks with end-user caches, which adapts to network topology, achieving optimality for large cache sizes and outperforming existing methods otherwise.

Contribution

The paper proposes a network topology-dependent coded cache placement scheme that is optimal for large caches and superior to existing symmetric schemes in combination networks.

Findings

Proposed scheme is information-theoretically optimal for large cache sizes.

Asymmetric placement outperforms symmetric schemes in certain scenarios.

Scheme adapts to network topology, improving efficiency.

Abstract

This paper investigates the fundamental tradeoff between cache size and download time in the (H;r;M;N) combination network, where a server with N files is connected to H relays (without caches) and each of the K:=\binom{H}{r} users (with caches of size M files) is connected to a different subset of r relays. Existing schemes fall within two categories: either use the uncoded symmetric cache placement originally proposed for the shared-link model and design delivery phase dependent on the network topology, or effectively divide the combination network into H independent shared-link networks each serving \binom{H-1}{r-1} users; in either case, the placement phase is independent of network topology. In this paper, a novel strategy is proposed where the coded cache placement is dependent on network topology. The proposed scheme is shown to be information theoretically optimal for large cache size. In addition, when not exactly optimal, the proposed scheme can also outperform existing schemes.