Novel Inter-file Coded Placement and D2D Delivery for a Cache-aided Fog-RAN Architecture
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This paper considers a novel cache-aided "fog" Radio Access Network (Fog-RAN) architecture including a Macro-cell Base Station (MBS) and several Small-cell Base Stations (SBSs), serving users without caches. Some users, not in the reach of SBSs, are directly served by the MBS. Other users, in the reach of SBSs, are "offloaded" and receive information only from the SBSs through high throughput links. The SBSs have their own local caches. The MBS broadcasts packets to the SBSs and the directly served users. Subsequently, the SBSs can communicate among each other such that each SBS can obtain enough information to decode demanded files by its connected users. For the proposed Fog-RAN we study the memory-loads tradeoff for the worst-case demands. The main contribution of this paper is the design of a novel inter-file coded cache placement and a novel D2D caching scheme with shared-caches to handle the inter-SBS communication phase. The proposed scheme is proved to be order optimal within a constant factor when each SBS is connected to the same number of users. As by-product, the proposed inter-file coded placement can also be used in coded caching systems with heterogeneous cache sizes, where some users have no cache. The proposed coded placement depends on the network topology only by the number of SBSs and the number of users directly served by the MBS. Then, by relaxing the requirement of topology independence, we improve the proposed scheme by designing a cache placement with a subfile division dependent on network structure, which is exactly optimal in some memory size regimes. As another by-product, we also improve the existing shared-link caching scheme with shared-caches by this novel topology-dependent subfile division and placement.
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