Improving the Degrees of Freedom in MIMO relay networks via PHY caching

In conventional relay networks, the Degrees of Freedom (DoF) is limited by the cut-set bound. In this paper, we proposed a novel physical layer (PHY) caching scheme for relay networks to achieve DoF gains over conventional relay schemes. Specifically, by properly caching a portion of the content files at the relay station (RS), the PHY topology can be opportunistically transformed from the unfavorable relay channel topology into a more favorable MIMO broadcast channel topology (cache-induced MIMO cooperation opportunity) and enjoy a large DoF gain. We first propose a novel caching scheme to significantly improve the MIMO cooperation opportunity induced by PHY caching. Then we propose both global and low complexity algorithms to maximize the DoF gain. Simulation indicates that the proposed scheme has significant gains over various baselines.