Centralized coded caching and delivery is studied for a radio access combination network (RACN), whereby a set of H edge nodes (ENs), connected to a cloud server via orthogonal fronthaul links with limited capacity, serve a total of K user equipments (UEs) over wireless links. The cloud server is assumed to hold a library of N files, each of size F bits; and each user, equipped with a cache of size $\mu _{\text {R}} {\it\text { N F}}$ bits, is connected to a distinct set of r ENs each of which equipped with a cache of size $\mu _{\text {T}} {\it\text { N F}}$ bits, where $\mu _{\text {T}}$ , $\mu _{\text {R}} \in [{0,1}]$ are the fractional cache capacities of the UEs and the ENs, respectively. The objective is to minimize the normalized delivery time (NDT), which refers to the worst case delivery latency when each user requests a single distinct file from the library. Three coded caching and transmission schemes are considered, namely the MDS-IA, soft-transfer and zero-forcing (ZF) schemes. MDS-IA utilizes maximum distance separable (MDS) codes in the placement phase and real interference alignment (IA) in the delivery phase. The achievable NDT for this scheme is presented for $\text {r}=2$ and arbitrary fractional cache sizes $\mu _{\text {T}}$ and $\mu _{\text {R}}$ , and also for arbitrary value of r and fractional cache size $\mu _{\text {T}}$ when the cache capacity of the UE is above a certain threshold. The soft-transfer scheme utilizes soft-transfer of coded symbols to ENs that implement ZF over the edge links. The achievable NDT for this scheme is presented for arbitrary r and arbitrary fractional cache sizes $\mu _{\text {T}}$ and $\mu _{\text {R}}$ . The last scheme utilizes ZF between the ENs and the UEs without the participation of the cloud server in the delivery phase. The achievable NDT for this scheme is presented for an arbitrary value of r when the total cache size at a pair of UE and EN is sufficient to store the whole library, i.e., $\mu _{\text {T}}+\mu _{\text {R}} \geq 1$ . The results indicate that the fronthaul capacity determines which scheme achieves a better performance in terms of the NDT, and the soft-transfer scheme becomes favorable as the fronthaul capacity increases.

中文翻译：

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有干扰的缓存辅助组合网络

研究了无线电接入组合网络 (RACN) 的集中编码缓存和交付，其中一组 H 边缘节点 (EN) 通过容量有限的正交前传链路连接到云服务器，总共服务于 钾无线链路上的用户设备 (UE)。假设云服务器拥有一个库N 文件，每个大小 F位；和每个用户，配备一个大小的缓存 $\mu _{\text {R}} {\it\text { NF}}$ 位，连接到一组不同的 r 个 EN，每个 EN 都配备了一个大小的缓存 $\mu _{\text {T}} {\it\text { NF}}$ 位，其中 $\mu _{\text {T}}$ , $\mu _{\text {R}} \in [{0,1}]$ 分别是 UE 和 EN 的部分缓存容量。目标是最小化标准化交付时间 (NDT)，这是指当每个用户从库中请求单个不同文件时最坏情况下的交付延迟。考虑了三种编码缓存和传输方案，即MDS-IA, 软转移 和 迫零 (ZF)计划。MDS-IA 在放置阶段使用最大距离可分离 (MDS) 代码，在交付阶段使用实际干扰对齐 (IA)。该方案可实现的无损检测为 $\text {r}=2$ 和任意小数缓存大小 $\mu _{\text {T}}$ 和 $\mu _{\text {R}}$ ，以及任意值 r 和部分缓存大小 $\mu _{\text {T}}$ 当 UE 的缓存容量超过某个阈值时。软传输方案利用编码符号的软传输到在边缘链路上实现 ZF 的 EN。该方案可实现的无损检测是针对任意的r 和任意小数缓存大小 $\mu _{\text {T}}$ 和 $\mu _{\text {R}}$ . 最后一种方案在交付阶段使用 EN 和 UE 之间的 ZF，而无需云服务器的参与。该方案可实现的无损检测是针对任意值的r 当一对 UE 和 EN 的总缓存大小足以存储整个库时，即， $\mu _{\text {T}}+\mu _{\text {R}} \geq 1$ . 结果表明，前传容量决定了哪种方案在无损检测方面的性能更好，随着前传容量的增加，软传输方案变得有利。