Tradeoff between PHY caching and core network caching in cellular networks

Recently, physical layer (PHY) caching at the base station (BS) has been proposed to induce MIMO cooperation among peer BSs to reduce interference and improve the spectrum efficiency in the radio access network (RAN). Compared with caching at the core network (CN) gateway (CN-caching), which covers a large number of users, it may appear that PHY-caching covers less users and results in lower cache hit rate. In this paper, we analyze the tradeoff between spectrum efficiency gain induced by PHY-caching and CN-backhaul offloading gain induced by CN-caching. Specifically, we derive the Pareto optimal tradeoff between the spectrum efficiency gain and CN-backhaul offloading gain. Surprisingly, we show that even though PHY-caching covers less users than CN-caching (single cell versus multiple cells), it is still worthwhile to do PHY-caching at the BS.