216 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
Uncoded Caching and Cross-level Coded Delivery for Non-uniform File Popularity
Proactive content caching at user devices and coded delivery is studied
considering a non-uniform file popularity distribution. A novel centralized
uncoded caching and coded delivery scheme, which can be applied to large file
libraries, is proposed. The proposed cross-level coded delivery (CLCD) scheme
is shown to achieve a lower average delivery rate than the state of art. In the
proposed CLCD scheme, the same subpacketization is used for all the files in
the library in order to prevent additional zero-padding in the delivery phase,
and unlike the existing schemes in the literature, two users requesting files
from different popularity groups can be served by the same multicast message in
order to reduce the delivery rate. Simulation results indicate significant
reduction in the average delivery rate for typical Zipf distribution parameter
values.Comment: A shorter version of this paper has been presented at IEEE
International Conference on Communications (ICC) 201
- …