Improved Hotplug Caching Scheme Using PDAs

We consider a hotplug coded caching systems in which some users are offline at the time of delivery. A placement delivery array (PDA) is a well-known tool for constructing a coded caching scheme for dedicated caches. In this paper, we introduce the concept of PDAs for hotplug coded caching schemes and refer to it as hotplug placement delivery array (HpPDA). We give an algorithm to describe the placement and the delivery phase of a hotplug coded caching scheme using HpPDA. We show that an existing hotplug coded caching scheme given in [Y. Ma and D. Tuninetti, “On coded caching systems with offline users,” in 2022 IEEE International Symposium on Information Theory (ISIT), 2022, pp. 1133–1138] corresponds to a class of HpPDAs, and then propose a method to further improve the rate of that scheme.