2,511 research outputs found
Hierarchical Cache-Aided Linear Function Retrieval with Security and Privacy Constraints
The hierarchical caching system where a server connects with multiple mirror
sites, each connecting with a distinct set of users, and both the mirror sites
and users are equipped with caching memories has been widely studied. However
all the existing works focus on single file retrieval, i.e., each user requests
one file, and ignore the security and privacy threats in communications. In
this paper we investigate the linear function retrieval problem for
hierarchical caching systems with content security and demand privacy, i.e.,
each user requests a linear combination of files, and meanwhile the files in
the library are protected against wiretappers and users' demands are kept
unknown to other users and unconnected mirror sites. First we propose a new
combination structure named hierarchical placement delivery array (HPDA), which
characterizes the data placement and delivery strategy of a coded caching
scheme. Then we construct two classes of HPDAs. Consequently two classes of
schemes with or without security and privacy are obtained respectively where
the first dedicates to minimizing the transmission load for the first hop and
can achieve the optimal transmission load for the first hop if ignoring the
security and privacy constraints; the second has more flexible parameters on
the memory sizes and a lower subpacketization compared with the first one, and
achieves a tradeoff between subpacketization and transmission loads.Comment: arXiv admin note: substantial text overlap with arXiv:2205.0023
Fundamental Limits of Coded Caching: Improved Delivery Rate-Cache Capacity Trade-off
A centralized coded caching system, consisting of a server delivering N
popular files, each of size F bits, to K users through an error-free shared
link, is considered. It is assumed that each user is equipped with a local
cache memory with capacity MF bits, and contents can be proactively cached into
these caches over a low traffic period; however, without the knowledge of the
user demands. During the peak traffic period each user requests a single file
from the server. The goal is to minimize the number of bits delivered by the
server over the shared link, known as the delivery rate, over all user demand
combinations. A novel coded caching scheme for the cache capacity of M= (N-1)/K
is proposed. It is shown that the proposed scheme achieves a smaller delivery
rate than the existing coded caching schemes in the literature when K > N >= 3.
Furthermore, we argue that the delivery rate of the proposed scheme is within a
constant multiplicative factor of 2 of the optimal delivery rate for cache
capacities 1/K N >= 3.Comment: To appear in IEEE Transactions on Communication
Coded Caching for a Large Number Of Users
Information theoretic analysis of a coded caching system is considered, in
which a server with a database of N equal-size files, each F bits long, serves
K users. Each user is assumed to have a local cache that can store M files,
i.e., capacity of MF bits. Proactive caching to user terminals is considered,
in which the caches are filled by the server in advance during the placement
phase, without knowing the user requests. Each user requests a single file, and
all the requests are satisfied simultaneously through a shared error-free link
during the delivery phase.
First, centralized coded caching is studied assuming both the number and the
identity of the active users in the delivery phase are known by the server
during the placement phase. A novel group-based centralized coded caching (GBC)
scheme is proposed for a cache capacity of M = N/K. It is shown that this
scheme achieves a smaller delivery rate than all the known schemes in the
literature. The improvement is then extended to a wider range of cache
capacities through memory-sharing between the proposed scheme and other known
schemes in the literature. Next, the proposed centralized coded caching idea is
exploited in the decentralized setting, in which the identities of the users
that participate in the delivery phase are assumed to be unknown during the
placement phase. It is shown that the proposed decentralized caching scheme
also achieves a delivery rate smaller than the state-of-the-art. Numerical
simulations are also presented to corroborate our theoretical results
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