This letter investigates the caching and delivery strategies in a multiple-input multiple-output (MIMO) fog radio access network (Fog-RAN). We focus on the small cache size scenario where the accumulated cache memories of all edge nodes (ENs) are not enough to cache the whole database. We propose a new file splitting and placement scheme tailored for the small cache size, which offers the freedom to adjust the duplication order of the cached contents to minimize the normalized delivery time (NDT). In the fronthaul delivery, we use multiple antennas to multiplex multiple messages while in the access delivery, transmitter cooperation induced by the duplicated contents among ENs is utilized to cancel interference. By jointly optimizing caching and delivery, we obtain an achievable minimum NDT. It is shown that the achievable NDT is within an additive gap of 1 to the theoretical optimum.

中文翻译：

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具有小缓存大小的无线前传的 MIMO Fog-RAN 中的内容缓存和交付

这封信调查了多输入多输出 (MIMO) 雾无线电接入网络 (Fog-RAN) 中的缓存和交付策略。我们专注于小缓存大小场景，其中所有边缘节点 (EN) 的累积缓存内存不足以缓存整个数据库。我们提出了一种为小缓存大小量身定制的新文件拆分和放置方案，它提供了调整缓存内容复制顺序的自由，以最大限度地减少标准化交付时间（NDT）。在前传交付中，我们使用多个天线来复用多个消息，而在接入交付中，通过EN之间的重复内容引起的发射机协作来消除干扰。通过联合优化缓存和交付，我们获得了可实现的最小无损检测。