Wireless Coded Caching With Shared Caches Can Overcome the Near-Far Bottleneck

Abstract

We investigate the use of coded caching in the single-cell downlink scenario where the receiving users are randomly located inside the cell. We first show that, as a result of having users that experience very different path-loss, the real gain of the original coded caching scheme is severely reduced. We then prove that the use of shared caches - which, we stress, is a compulsory feature brought about by the subpacketization constraint in nearly every practical setting - introduces a spatial-averaging effect that allows us to recover most of the subpacketization-constrained gains that coded caching would have yielded in the error-free identical-link setting. For the ergodic-fading scenario with different pathloss, we derive tight approximations of the average (over the users) rate and of the coded caching gain by means of a basic high-SNR approximation on the point-to-point capacity. These derived expressions prove very accurate even for low SNR. We also provide a result based on the regime of large number of users which is nonetheless also valid for settings with few users. These results are extensively validated using Monte-Carlo simulations that adhere to 3GPP recommendations on system parameters for urban micro or macro cells.