Cache-Aided Radio Access Networks with Partial Connectivity
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Centralized coded caching and delivery is studied for a partially-connected radio access network (RAN), whereby a set of H edge nodes (ENs) (without caches), connected to a cloud server via orthogonal fronthaul links with limited capacity, serve a total of K 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 MF bits, is connected to a distinct set of r ENs. The objective is to minimize the normalized delivery time (NDT), which refers to the worst case delivery latency when each user requests a single file from the library. Two coded caching and transmission schemes are proposed, called the MDS-IA and soft-transfer 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 r=2 and an arbitrary cache size M, and also for an arbitrary value of r when the cache capacity is above a certain threshold. The soft-transfer scheme utilizes soft-transfer of coded symbols to ENs that implement zero forcing (ZF) over the edge links. The achievable NDT for this scheme is presented for arbitrary r and cache size M. 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.
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