202 research outputs found
Finite Length Analysis of Caching-Aided Coded Multicasting
In this work, we study a noiseless broadcast link serving users whose
requests arise from a library of files. Every user is equipped with a cache
of size files each. It has been shown that by splitting all the files into
packets and placing individual packets in a random independent manner across
all the caches, it requires at most file transmissions for any set of
demands from the library. The achievable delivery scheme involves linearly
combining packets of different files following a greedy clique cover solution
to the underlying index coding problem. This remarkable multiplicative gain of
random placement and coded delivery has been established in the asymptotic
regime when the number of packets per file scales to infinity.
In this work, we initiate the finite-length analysis of random caching
schemes when the number of packets is a function of the system parameters
. Specifically, we show that existing random placement and clique cover
delivery schemes that achieve optimality in the asymptotic regime can have at
most a multiplicative gain of if the number of packets is sub-exponential.
Further, for any clique cover based coded delivery and a large class of random
caching schemes, that includes the existing ones, we show that the number of
packets required to get a multiplicative gain of is at least
. We exhibit a random placement and an efficient clique cover based
coded delivery scheme that approximately achieves this lower bound. We also
provide tight concentration results that show that the average (over the random
caching involved) number of transmissions concentrates very well requiring only
polynomial number of packets in the rest of the parameters.Comment: A shorter version appeared in the 52nd Annual Allerton Conference on
Communication, Control, and Computing (Allerton), 201
Speeding up Future Video Distribution via Channel-Aware Caching-Aided Coded Multicast
Future Internet usage will be dominated by the consumption of a rich variety
of online multimedia services accessed from an exponentially growing number of
multimedia capable mobile devices. As such, future Internet designs will be
challenged to provide solutions that can deliver bandwidth-intensive,
delay-sensitive, on-demand video-based services over increasingly crowded,
bandwidth-limited wireless access networks. One of the main reasons for the
bandwidth stress facing wireless network operators is the difficulty to exploit
the multicast nature of the wireless medium when wireless users or access
points rarely experience the same channel conditions or access the same content
at the same time. In this paper, we present and analyze a novel wireless video
delivery paradigm based on the combined use of channel-aware caching and coded
multicasting that allows simultaneously serving multiple cache-enabled
receivers that may be requesting different content and experiencing different
channel conditions. To this end, we reformulate the caching-aided coded
multicast problem as a joint source-channel coding problem and design an
achievable scheme that preserves the cache-enabled multiplicative throughput
gains of the error-free scenario,by guaranteeing per-receiver rates unaffected
by the presence of receivers with worse channel conditions.Comment: 11 pages,6 figures,to appear in IEEE JSAC Special Issue on Video
Distribution over Future Interne
Multi-Antenna Coded Caching
In this paper we consider a single-cell downlink scenario where a
multiple-antenna base station delivers contents to multiple cache-enabled user
terminals. Based on the multicasting opportunities provided by the so-called
Coded Caching technique, we investigate three delivery approaches. Our baseline
scheme employs the coded caching technique on top of max-min fair multicasting.
The second one consists of a joint design of Zero-Forcing (ZF) and coded
caching, where the coded chunks are formed in the signal domain (complex
field). The third scheme is similar to the second one with the difference that
the coded chunks are formed in the data domain (finite field). We derive
closed-form rate expressions where our results suggest that the latter two
schemes surpass the first one in terms of Degrees of Freedom (DoF). However, at
the intermediate SNR regime forming coded chunks in the signal domain results
in power loss, and will deteriorate throughput of the second scheme. The main
message of our paper is that the schemes performing well in terms of DoF may
not be directly appropriate for intermediate SNR regimes, and modified schemes
should be employed.Comment: 7 pages, 2 figure
Distortion-Memory Tradeoffs in Cache-Aided Wireless Video Delivery
Mobile network operators are considering caching as one of the strategies to
keep up with the increasing demand for high-definition wireless video
streaming. By prefetching popular content into memory at wireless access points
or end user devices, requests can be served locally, relieving strain on
expensive backhaul. In addition, using network coding allows the simultaneous
serving of distinct cache misses via common coded multicast transmissions,
resulting in significantly larger load reductions compared to those achieved
with conventional delivery schemes. However, prior work does not exploit the
properties of video and simply treats content as fixed-size files that users
would like to fully download. Our work is motivated by the fact that video can
be coded in a scalable fashion and that the decoded video quality depends on
the number of layers a user is able to receive. Using a Gaussian source model,
caching and coded delivery methods are designed to minimize the squared error
distortion at end user devices. Our work is general enough to consider
heterogeneous cache sizes and video popularity distributions.Comment: To appear in Allerton 2015 Proceedings of the 53rd annual Allerton
conference on Communication, control, and computin
Broadcast Caching Networks with Two Receivers and Multiple Correlated Sources
The correlation among the content distributed across a cache-aided broadcast
network can be exploited to reduce the delivery load on the shared wireless
link. This paper considers a two-user three-file network with correlated
content, and studies its fundamental limits for the worst-case demand. A class
of achievable schemes based on a two-step source coding approach is proposed.
Library files are first compressed using Gray-Wyner source coding, and then
cached and delivered using a combination of correlation-unaware cache-aided
coded multicast schemes. The second step is interesting in its own right and
considers a multiple-request caching problem, whose solution requires coding in
the placement phase. A lower bound on the optimal peak rate-memory trade-off is
derived, which is used to evaluate the performance of the proposed scheme. It
is shown that for symmetric sources the two-step strategy achieves the lower
bound for large cache capacities, and it is within half of the joint entropy of
two of the sources conditioned on the third source for all other cache sizes.Comment: in Proceedings of Asilomar Conference on Signals, Systems and
Computers, Pacific Grove, California, November 201
An Efficient Coded Multicasting Scheme Preserving the Multiplicative Caching Gain
Coded multicasting has been shown to be a promis- ing approach to
significantly improve the caching performance of content delivery networks with
multiple caches downstream of a common multicast link. However, achievable
schemes proposed to date have been shown to achieve the proved order-optimal
performance only in the asymptotic regime in which the number of packets per
requested item goes to infinity. In this paper, we first extend the asymptotic
analysis of the achievable scheme in [1], [2] to the case of heterogeneous
cache sizes and demand distributions, providing the best known upper bound on
the fundamental limiting performance when the number of packets goes to
infinity. We then show that the scheme achieving this upper bound quickly loses
its multiplicative caching gain for finite content packetization. To overcome
this limitation, we design a novel polynomial-time algorithm based on random
greedy graph- coloring that, while keeping the same finite content
packetization, recovers a significant part of the multiplicative caching gain.
Our results show that the order-optimal coded multicasting schemes proposed to
date, while useful in quantifying the fundamental limiting performance, must be
properly designed for practical regimes of finite packetization.Comment: 6 pages, 7 figures, Published in Infocom CNTCV 201
- …