  A device-to-device (D2D) aided multi-antenna coded caching scheme is proposed
to improve the average delivery rate and reduce the downlink (DL) beamforming
complexity.} Novel beamforming and resource allocation schemes are proposed
where local data exchange among nearby users is exploited. The transmission is
split into two phases: local D2D content exchange and DL transmission. In the
D2D phase, subsets of users are selected to share content with the adjacent
users directly. {In this regard, a low complexity D2D mode selection algorithm
is proposed to find the appropriate set of users for the D2D phase with
comparable performance to the optimal exhaustive search. {During} the DL phase,
the base station multicasts the remaining data requested by all the users. We
identify scenarios and conditions where D2D transmission can reduce the
delivery time. Furthermore, we demonstrate how} adding the new D2D phase to the
DL-only scenario can significantly reduce the beamformer design complexity in
the DL phase. The results further highlight that by partly delivering requested
data in the D2D phase, the transmission rate can be boosted due to more
efficient use of resources during the subsequent DL phase. As a result, the
overall content delivery performance is greatly enhanced, especially in the
finite signal-to-noise (SNR) regime.
