746 research outputs found
Fundamental Structure of Optimal Cache Placement for Coded Caching with Heterogeneous Demands
This paper studies the caching system of multiple cache-enabled users with
heterogeneous demands. Under nonuniform file popularity, we thoroughly
characterize the structure of the optimal uncoded cache placement for the coded
caching scheme (CCS). Formulating the cache placement as an optimization
problem to minimize the average delivery rate, we identify the file grouping
structure under the optimal solution. We show that, regardless of file
popularity, there are at most three file groups under the optimal cache
placement. We further characterize the complete structure of the optimal cache
placement and obtain the closed-form solution in each possible file grouping
case. A simple algorithm is developed to obtain the final optimal cache
placement, which only computes a set of candidate closed-form solutions in
parallel. We provide insights into the file groups formed by the optimal cache
placement. The optimal placement solution also indicates that coding between
file groups may be explored during delivery, in contrast to the existing
heuristic file grouping schemes. Using the file grouping in the optimal cache
placement, we propose a new information-theoretic converse bound for coded
caching that is tighter than existing ones. Moreover, using the optimal cache
placement solution, we characterize the file subpacketization in the optimal
CCS and show that the maximum subpacketization level in the worst case scales
as for users.Comment: 19 pages, 12 figures, submitted to IEEE Trans. Information Theor
Content Caching and Delivery over Heterogeneous Wireless Networks
Emerging heterogeneous wireless architectures consist of a dense deployment
of local-coverage wireless access points (APs) with high data rates, along with
sparsely-distributed, large-coverage macro-cell base stations (BS). We design a
coded caching-and-delivery scheme for such architectures that equips APs with
storage, enabling content pre-fetching prior to knowing user demands. Users
requesting content are served by connecting to local APs with cached content,
as well as by listening to a BS broadcast transmission. For any given content
popularity profile, the goal is to design the caching-and-delivery scheme so as
to optimally trade off the transmission cost at the BS against the storage cost
at the APs and the user cost of connecting to multiple APs. We design a coded
caching scheme for non-uniform content popularity that dynamically allocates
user access to APs based on requested content. We demonstrate the approximate
optimality of our scheme with respect to information-theoretic bounds. We
numerically evaluate it on a YouTube dataset and quantify the trade-off between
transmission rate, storage, and access cost. Our numerical results also suggest
the intriguing possibility that, to gain most of the benefits of coded caching,
it suffices to divide the content into a small number of popularity classes.Comment: A shorter version is to appear in IEEE INFOCOM 201
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