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.

翻译：提出了一种设备到设备（D2D）辅助的多天线编码缓存方案，旨在提升平均传输速率并降低下行链路（DL）波束赋形复杂度。本文设计了新型波束赋形与资源分配方案，利用附近用户间的本地数据交换。传输过程分为两个阶段：本地D2D内容交换与下行传输。在D2D阶段，选取部分用户子集直接与邻近用户共享内容。为此，提出了一种低复杂度的D2D模式选择算法，以找到适合D2D阶段的用户集合，其性能可与最优穷举搜索相媲美。在下行阶段，基站多播所有用户请求的剩余数据。我们识别了D2D传输能够减少传输时间的场景与条件，并进一步展示了在纯下行场景中引入D2D阶段可显著降低下行阶段的波束赋形设计复杂度。结果还表明，通过在D2D阶段部分传递请求数据，后续下行阶段可更高效地利用资源，从而提升传输速率。最终，整体内容传输性能得到大幅增强，尤其在有限信噪比（SNR）条件下。