  In this paper, we propose a novel joint caching and massive multiple-input
multiple-output (MIMO) transmission scheme, referred to as \emph{cache-aided
massive MIMO}, for multi-cell downlink transmission to multiple cache-enabled
receivers. With the proposed scheme, users who have cached (a portion of) the
files that they request are offloaded and, hence, (partially) inactive during
downlink transmission. The other users either benefit from the cache-enabled
offloading for mitigating pilot contamination or exploit the cached but
unrequested files to cancel interference during uplink channel estimation and
downlink file reception. Moreover, by redesigning the transmit precoders based
on the cache status of the users and channel state information, we gain
additional degrees of freedom for massive MIMO transmission. For a given cache
status, we analyze the equivalent content delivery rates (ECDRs), i.e., the
average rates of delivering a requested file via both caching and massive MIMO
transmission to the requesting user, for cache-aided massive MIMO employing
re-designed maximum ratio transmission (MRT), zero-forcing (ZF) precoding, and
regularized zero-forcing (RZF) precoding. Based on the derived results, the
impact of (random) uncoded caching and coded caching on the performance of the
re-designed precoding schemes is investigated. Simulation results validate our
derivations and show that caching is beneficial for precoded downlink
transmission as it enhances the transmit power allocation, mitigates intra- and
inter-cell interference, and reduces the impairment caused by pilot
contamination. Compared with conventional massive MIMO without caching and with
cache-oblivious precoding, the proposed cache-aided massive MIMO scheme
achieves a significantly higher ECDR even when the number of users approaches
the number of transmit antennas.
