Coded Caching in Combinatorial Multi-Access Networks with Private Caches

Abstract

Content caching at the network edge plays a critical role in reducing server load and improving scalability in large-scale content delivery networks. We consider a cache-aided multi-access network in which each user is equipped with a private cache and connects to a distinct subset of access caches. A central server stores the content library and populates both private and access caches using uncoded placement. For this setting, we establish upper and lower bounds on the optimal worst-case rate under uncoded placement, leveraging the Maddah-Ali-Niesen (MAN) schemes for dedicated and combinatorial multi-access caching, and also derive a cut-set lower bound under general placement. We then propose an extension scheme that integrates the principles of the MAN schemes for dedicated and multi-access caching, generalizing them to the considered setting, at the cost of high subpacketization complexity. To address this limitation, we introduce an improved coded caching scheme for a fixed private cache size, which achieves significantly lower subpacketization while maintaining comparable rates. Under the placement strategy of the improved scheme, we further derive an index-coding-based lower bound on the rate. Numerical comparisons demonstrate that the improved scheme reduces rate and subpacketization, with performance approaching theoretical lower bounds as the multi-access connectivity increases. In addition, we present a general placement policy applicable to arbitrary private cache sizes. Finally, we show that the proposed scheme is order-optimal in certain regimes and prove its optimality when the number of access caches equals four.