542 research outputs found
On the Placement Delivery Array Design in Centralized Coded Caching Scheme
Caching is a promising solution to satisfy the ever increasing demands for
the multi-media traffics. In caching networks, coded caching is a recently
proposed technique that achieves significant performance gains over the uncoded
caching schemes. However, to implement the coded caching schemes, each file has
to be split into packets, which usually increases exponentially with the
number of users . Thus, designing caching schemes that decrease the order of
is meaningful for practical implementations. In this paper, by reviewing
the Ali-Niesen caching scheme, the placement delivery array (PDA) design
problem is firstly formulated to characterize the placement issue and the
delivery issue with a single array. Moreover, we show that, through designing
appropriate PDA, new centralized coded caching schemes can be discovered.
Secondly, it is shown that the Ali-Niesen scheme corresponds to a special class
of PDA, which realizes the best coding gain with the least . Thirdly, we
present a new construction of PDA for the centralized caching system, wherein
the cache size of each user (identical cache size is assumed at all users)
and the number of files satisfies or ( is an
integer such that ). The new construction can decrease the required
from the order of Ali-Niesen scheme to
or
respectively, while
the coding gain loss is only .Comment: 21 pages, 2 figure
From Centralized to Decentralized Coded Caching
We consider the problem of designing decentralized schemes for coded caching.
In this problem there are users each caching files out of a library of
total files. The question is to minimize , the number of broadcast
transmissions to satisfy all the user demands. Decentralized schemes allow the
creation of each cache independently, allowing users to join or leave without
dependencies. Previous work showed that to achieve a coding gain , i.e. transmissions, each file has to be divided into number of
subpackets that is exponential in .
In this work we propose a simple translation scheme that converts any
constant rate centralized scheme into a random decentralized placement scheme
that guarantees a target coding gain of . If the file size in the original
constant rate centralized scheme is subexponential in , then the file size
for the resulting scheme is subexponential in . When new users join, the
rest of the system remains the same. However, we require an additional
communication overhead of bits to determine the new user's cache
state. We also show that the worst-case rate guarantee degrades only by a
constant factor due to the dynamics of user arrival and departure
Linear Coded Caching Scheme for Centralized Networks
Coded caching systems have been widely studied to reduce the data
transmission during the peak traffic time. In practice, two important
parameters of a coded caching system should be considered, i.e., the rate which
is the maximum amount of the data transmission during the peak traffic time,
and the subpacketization level, the number of divided packets of each file when
we implement a coded caching scheme. We prefer to design a scheme with rate and
packet number as small as possible since they reflect the transmission
efficiency and complexity of the caching scheme, respectively.
In this paper, we first characterize a coded caching scheme from the
viewpoint of linear algebra and show that designing a linear coded caching
scheme is equivalent to constructing three classes of matrices satisfying some
rank conditions. Then based on the invariant linear subspaces and combinatorial
design theory, several classes of new coded caching schemes over
are obtained by constructing these three classes of matrices. It turns out that
the rate of our new rate is the same as the scheme construct by Yan et al.
(IEEE Trans. Inf. Theory 63, 5821-5833, 2017), but the packet number is
significantly reduced. A concatenating construction then is used for flexible
number of users. Finally by means of these matrices, we show that the minimum
storage regenerating codes can also be used to construct coded caching schemes.Comment: 23 page
Towards Practical File Packetizations in Wireless Device-to-Device Caching Networks
We consider wireless device-to-device (D2D) caching networks with single-hop
transmissions. Previous work has demonstrated that caching and coded
multicasting can significantly increase per user throughput. However, the
state-of-the-art coded caching schemes for D2D networks are generally
impractical because content files are partitioned into an exponential number of
packets with respect to the number of users if both library and memory sizes
are fixed. In this paper, we present two combinatorial approaches of D2D coded
caching network design with reduced packetizations and desired throughput gain
compared to the conventional uncoded unicasting. The first approach uses a
"hypercube" design, where each user caches a "hyperplane" in this hypercube and
the intersections of "hyperplanes" represent coded multicasting codewords. In
addition, we extend the hypercube approach to a decentralized design. The
second approach uses the Ruzsa-Szem\'eredi graph to define the cache placement.
Disjoint matchings on this graph represent coded multicasting codewords. Both
approaches yield an exponential reduction of packetizations while providing a
per-user throughput that is comparable to the state-of-the-art designs in the
literature. Furthermore, we apply spatial reuse to the new D2D network designs
to further reduce the required packetizations and significantly improve per
user throughput for some parameter regimes.Comment: 32 pages, 5 figure
Coded Caching Schemes with Linear Subpacketizations
In coded caching system we prefer to design a coded caching scheme with low
subpacketization and small transmission rate (i.e., the low implementation
complexity and the efficient transmission during the peak traffic times).
Placement delivery arrays (PDA) can be used to design code caching schemes. In
this paper we propose a framework of constructing PDAs via Hamming distance. As
an application, two classes of coded caching schemes with linear
subpacketizations and small transmission rates are obtained.Comment: 14 page
Some new bounds of placement delivery arrays
Coded caching scheme is a technique which reduce the load during peak traffic
times in a wireless network system. Placement delivery array (PDA in short) was
first introduced by Yan et al.. It can be used to design coded caching scheme.
In this paper, we prove some lower bounds of PDA on the element and some lower
bounds of PDA on the column. We also give some constructions for optimal PDA.Comment: Coded caching scheme, placement delivery array, optima
Constructions of Coded Caching Schemes with Flexible Memory Size
Coded caching scheme recently has become quite popular in the wireless
network due to its effectively reducing the transmission amount (denote such an
amount by ) during peak traffic times. However to realize a coded caching
scheme, each file must be divided into packets which usually increases the
computation complexity of a coded caching scheme. So we prefer to construct a
caching scheme that decreases the order of for practical implementations.
In this paper, we construct four classes of new schemes where two classes can
significantly reduce the value of by increasing a little comparing with
the well known scheme proposed by Maddah-Ali and Niesen, and in the other
two classes grows sub-exponentially with by sacrificing more . It is
worth noting that a tradeoff between and , which is a hot topic in the
field of caching scheme, is proposed by our constructions. In addition, our
constructions include all the results constructed by Yan et al., (IEEE Trans.
Inf. Theory 63, 5821-5833, 2017) and some main results obtained by Shangguan et
al., (arXiv preprint arXiv:1608.03989v1) as the special cases.Comment: 18 page
A framework of constructing placement delivery arrays for centralized coded caching
In caching system, it is desirable to design a coded caching scheme with the
transmission load and subpacketization as small as possible, in order
to improve efficiency of transmission in the peak traffic times and to decrease
implementation complexity. Yan et al. reformulated the centralized coded
caching scheme as designing a corresponding array called placement
delivery array (PDA), where is the subpacketization and is the number
of users. Motivated by several constructions of PDAs, we introduce a framework
for constructing PDAs, where each row is indexed by a row vector of some matrix
called row index matrix and each column's index is labelled by an element of a
direct product set. Using this framework, a new scheme is obtained, which can
be regarded as a generalization of some previously known schemes. When is
equal to for positive integers , with and , we show that the row index matrix must be an orthogonal array if all the
users have the same memory size. Furthermore, the row index matrix must be a
covering array if the coded gain is , which is the maximal coded
gain under our framework. Consequently the lower bounds on the transmission
load and subpacketization of the schemes are derived under our framework.
Finally, using orthogonal arrays as the row index matrix, we obtain two more
explicit classes of schemes which have significantly advantages on the
subpacketization while the transmission load is equal or close to that of the
schemes constructed by Shangguan et al. (IEEE Trans. Inf. Theory, 64,
5755-5766, 2018) for the same number of users and memory size.Comment: 13 page
On Combination Networks with Cache-aided Relays and Users
Caching is an efficient way to reduce peak hour network traffic congestion by
storing some contents at the user's cache without knowledge of later demands.
Coded caching strategy was originally proposed by Maddah-Ali and Niesen to give
an additional coded caching gain compared the conventional uncoded scheme.
Under practical consideration, the caching model was recently considered in
relay network, in particular the combination network, where the central server
communicates with users (each is with a cache of files)
through immediate relays, and each user is connected to a different
subsets of relays. Several inner bounds and outer bounds were proposed for
combination networks with end-user-caches. This paper extends the recent work
by the authors on centralized combination networks with end-user caches to a
more general setting, where both relays and users have caches. In contrast to
the existing schemes in which the packets transmitted from the server are
independent of the cached contents of relays, we propose a novel caching scheme
by creating an additional coded caching gain to the transmitted load from the
server with the help of the cached contents in relays. We also show that the
proposed scheme outperforms the state-of-the-art approaches.Comment: 7 pages,2 figures, WSA 201
Multi-access Coded Caching Schemes From Cross Resolvable Designs
We present a novel caching and coded delivery scheme for a multi-access
network where multiple users can have access to the same cache (shared cache)
and any cache can assist multiple users. This scheme is obtained from
resolvable designs satisfying certain conditions which we call {\it cross
resolvable designs}. To be able to compare different multi-access coded schemes
with different number of users we normalize the rate of the schemes by the
number of users served. Based on this per-user-rate we show that our scheme
performs better than the well known Maddah-Ali - Nieson (MaN) scheme and the
recently proposed ("Multi-access coded caching : gains beyond cache-redundancy"
by Serbetci, Parrinello and Elia) SPE scheme. It is shown that the resolvable
designs from affine planes are cross resolvable designs and our scheme based on
these performs better than the MaN scheme for large memory size cases. The
exact size beyond which our performance is better is also presented. The SPE
scheme considers only the cases where the product of the number of users and
the normalized cache size is 2, whereas the proposed scheme allows different
choices depending on the choice of the cross resolvable design.Comment: 14 pages, 7 Figures and 9 tables. In this version one subsection in
Section IV and a new Section V has been adde
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