Hypergraph-Based Analysis of Clustered Cooperative Beamforming with Application to Edge Caching

The evaluation of the performance of clustered cooperative beamforming in cellular networks generally requires the solution of complex non-convex optimization problems. In this letter, a framework based on a hypergraph formalism is proposed that enables the derivation of a performance characterization of clustered cooperative beamforming in terms of per-user degrees of freedom (DoF) via the efficient solution of a coloring problem. An emerging scenario in which clusters of cooperative base stations (BSs) arise is given by cellular networks with edge caching. In fact, clusters of BSs that share the same requested files can jointly beamform the corresponding encoded signals. Based on this observation, the proposed framework is applied to obtain quantitative insights into the optimal use of cache and backhaul resources in cellular systems with edge caching. Numerical examples are provided to illustrate the merits of the proposed framework.Comment: 10 pages, 5 figures, Submitte

Degrees of Freedom in Cached MIMO Relay Networks

It is well known that conventional cooperative relay schemes cannot provide Degrees of Freedom (DoF) gains due to the cut-set bound. In this paper, we propose a physical layer (PHY) caching scheme for relay networks to achieve DoF gains over conventional relay schemes. By properly caching some popular content at the relay station (RS), the proposed PHY caching can opportunistically transform the unfavorable relay channel topology into a more favorable MIMO broadcast channel topology (cache-induced MIMO cooperation opportunity) and enjoy a large DoF gain. Specifically, we first propose a maximum distance separable (MDS) coded PHY caching scheme to significantly improve the MIMO cooperation opportunity induced by PHY caching. Then we propose a global optimal cache content placement solution to maximize the DoF gain. We also propose a low complexity cache content placement algorithm to find a near-optimal solution without explicit knowledge of the popularity of the content files. Finally, we quantify the DoF gain w.r.t. some important system parameters. Simulations show that the proposed scheme can achieve significant throughput gains over various baselines