13,409 research outputs found
Fundamental Limits of Caching in Wireless D2D Networks
We consider a wireless Device-to-Device (D2D) network where communication is
restricted to be single-hop. Users make arbitrary requests from a finite
library of files and have pre-cached information on their devices, subject to a
per-node storage capacity constraint. A similar problem has already been
considered in an ``infrastructure'' setting, where all users receive a common
multicast (coded) message from a single omniscient server (e.g., a base station
having all the files in the library) through a shared bottleneck link. In this
work, we consider a D2D ``infrastructure-less'' version of the problem. We
propose a caching strategy based on deterministic assignment of subpackets of
the library files, and a coded delivery strategy where the users send linearly
coded messages to each other in order to collectively satisfy their demands. We
also consider a random caching strategy, which is more suitable to a fully
decentralized implementation. Under certain conditions, both approaches can
achieve the information theoretic outer bound within a constant multiplicative
factor. In our previous work, we showed that a caching D2D wireless network
with one-hop communication, random caching, and uncoded delivery, achieves the
same throughput scaling law of the infrastructure-based coded multicasting
scheme, in the regime of large number of users and files in the library. This
shows that the spatial reuse gain of the D2D network is order-equivalent to the
coded multicasting gain of single base station transmission. It is therefore
natural to ask whether these two gains are cumulative, i.e.,if a D2D network
with both local communication (spatial reuse) and coded multicasting can
provide an improved scaling law. Somewhat counterintuitively, we show that
these gains do not cumulate (in terms of throughput scaling law).Comment: 45 pages, 5 figures, Submitted to IEEE Transactions on Information
Theory, This is the extended version of the conference (ITW) paper
arXiv:1304.585
A New Approach to Coding in Content Based MANETs
In content-based mobile ad hoc networks (CB-MANETs), random linear network
coding (NC) can be used to reliably disseminate large files under intermittent
connectivity. Conventional NC involves random unrestricted coding at
intermediate nodes. This however is vulnerable to pollution attacks. To avoid
attacks, a brute force approach is to restrict the mixing at the source.
However, source restricted NC generally reduces the robustness of the code in
the face of errors, losses and mobility induced intermittence. CB-MANETs
introduce a new option. Caching is common in CB MANETs and a fully reassembled
cached file can be viewed as a new source. Thus, NC packets can be mixed at all
sources (including the originator and the intermediate caches) yet still
providing protection from pollution. The hypothesis we wish to test in this
paper is whether in CB-MANETs with sufficient caches of a file, the performance
(in terms of robustness) of the restricted coding equals that of unrestricted
coding.
In this paper, we examine and compare unrestricted coding to full cache
coding, source only coding, and no coding. As expected, we find that full cache
coding remains competitive with unrestricted coding while maintaining full
protection against pollution attacks
Updating Content in Cache-Aided Coded Multicast
Motivated by applications to delivery of dynamically updated, but correlated
data in settings such as content distribution networks, and distributed file
sharing systems, we study a single source multiple destination network coded
multicast problem in a cache-aided network. We focus on models where the caches
are primarily located near the destinations, and where the source has no cache.
The source observes a sequence of correlated frames, and is expected to do
frame-by-frame encoding with no access to prior frames. We present a novel
scheme that shows how the caches can be advantageously used to decrease the
overall cost of multicast, even though the source encodes without access to
past data. Our cache design and update scheme works with any choice of network
code designed for a corresponding cache-less network, is largely decentralized,
and works for an arbitrary network. We study a convex relation of the
optimization problem that results form the overall cost function. The results
of the optimization problem determines the rate allocation and caching
strategies. Numerous simulation results are presented to substantiate the
theory developed.Comment: To Appear in IEEE Journal on Selected Areas in Communications:
Special Issue on Caching for Communication Systems and Network
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