This paper studies the fundamental limits of content delivery in a cache-aided broadcast network for correlated content generated by a discrete memoryless source with arbitrary joint distribution. Each receiver is equipped with a cache of equal capacity, and the requested files are delivered over a shared error-free broadcast link. A class of achievable correlation-aware schemes based on a two-step source coding approach is proposed. Library files are first compressed, and then cached and delivered using a combination of multiple-request caching schemes that are agnostic to the content correlations. The first step uses Gray-Wyner source coding to represent the library via private descriptions and descriptions that are common to more than one file. The second step then becomes a multiple-request caching problem, where the demand structure is dictated by the configuration of the compressed library, and it is interesting in its own right. The performance of the proposed two-step scheme is evaluated by comparing its achievable rate with a lower bound on the optimal peak and average rate-memory trade-offs in a two-file multiple-receiver network, and in a three-file two-receiver network. Specifically, in a network with two files and two receivers, the achievable rate matches the lower bound for a significant memory regime and it is within half of the conditional entropy of files for all other memory values. In the three-file two-receiver network, the two-step strategy achieves the lower bound for large cache capacities, and it is within half of the joint entropy of two of the sources conditioned on the third one for all other cache sizes.

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相关源缓存和交付的速率-内存权衡

本文研究了缓存辅助广播网络中内容交付的基本限制，用于由具有任意联合分布的离散无记忆源生成的相关内容。每个接收器都配备了相同容量的缓存，请求的文件通过共享的无差错广播链接传送。提出了一类基于两步源编码方法的可实现的相关感知方案。库文件首先被压缩，然后使用与内容相关性无关的多请求缓存方案的组合进行缓存和交付。第一步使用 Gray-Wyner 源代码编码通过私有描述和多个文件共有的描述来表示库。第二步然后变成多请求缓存问题，其中需求结构由压缩库的配置决定，这本身就很有趣。所提出的两步方案的性能是通过将其可实现的速率与两文件多接收器网络和三文件两接收器网络中最佳峰值和平均速率-内存权衡的下限进行比较来评估的。接收器网络。具体来说，在具有两个文件和两个接收器的网络中，可达到的速率与重要内存机制的下限相匹配，并且它在所有其他内存值的文件条件熵的一半以内。在三文件两接收器网络中，两步策略实现了大缓存容量的下限，并且对于所有其他缓存大小，它在以第三个源为条件的两个源的联合熵的一半以内。