Achievable Degrees of Freedom of Cache-Aided Wireless Cellular Networks

Abstract

This work investigates the degrees of freedom (DoF) of a downlink cache-aided cellular network where the locations of base stations (BSs) are modeled as a regular grid topology and users within a grid cell can only communicate with four nearby BSs. We adopt a new cache placement method with uncoded prefetching tailored for network with partial connectivity. Transmission schemes with no BS cooperation, partial BS cooperation, and full BS cooperation are proposed, respectively, for different cache sizes. In particular, for no BS cooperation, interference alignment is used to coordinate signals of distinct cached contents among BSs. For partial BS cooperation, we utilize overlapping of cached contents to cancel some of the interference and align the rest by interference alignment. For full BS cooperation, zero-forcing precoding is applied to neutralize all the interference. Our results reveal that the reciprocal of per-user DoF of the cellular network decreases piecewise linearly with the cache size and the gain of BS caches is more significant for the small cache region.