85 research outputs found
On Coding for Cooperative Data Exchange
We consider the problem of data exchange by a group of closely-located
wireless nodes. In this problem each node holds a set of packets and needs to
obtain all the packets held by other nodes. Each of the nodes can broadcast the
packets in its possession (or a combination thereof) via a noiseless broadcast
channel of capacity one packet per channel use. The goal is to minimize the
total number of transmissions needed to satisfy the demands of all the nodes,
assuming that they can cooperate with each other and are fully aware of the
packet sets available to other nodes. This problem arises in several practical
settings, such as peer-to-peer systems and wireless data broadcast. In this
paper, we establish upper and lower bounds on the optimal number of
transmissions and present an efficient algorithm with provable performance
guarantees. The effectiveness of our algorithms is established through
numerical simulations.Comment: Appeared in the proceedings of the 2010 IEEE Information Theory
Workshop (ITW 2010, Cairo
Coded Caching for Delay-Sensitive Content
Coded caching is a recently proposed technique that achieves significant
performance gains for cache networks compared to uncoded caching schemes.
However, this substantial coding gain is attained at the cost of large delivery
delay, which is not tolerable in delay-sensitive applications such as video
streaming. In this paper, we identify and investigate the tradeoff between the
performance gain of coded caching and the delivery delay. We propose a
computationally efficient caching algorithm that provides the gains of coding
and respects delay constraints. The proposed algorithm achieves the optimum
performance for large delay, but still offers major gains for small delay.
These gains are demonstrated in a practical setting with a video-streaming
prototype.Comment: 9 page
Index Coding: Rank-Invariant Extensions
An index coding (IC) problem consisting of a server and multiple receivers
with different side-information and demand sets can be equivalently represented
using a fitting matrix. A scalar linear index code to a given IC problem is a
matrix representing the transmitted linear combinations of the message symbols.
The length of an index code is then the number of transmissions (or
equivalently, the number of rows in the index code). An IC problem is called an extension of another IC problem if the
fitting matrix of is a submatrix of the fitting matrix of . We first present a straightforward \textit{-order} extension
of an IC problem for which an index code is
obtained by concatenating copies of an index code of . The length
of the codes is the same for both and , and if the
index code for has optimal length then so does the extended code for
. More generally, an extended IC problem of having
the same optimal length as is said to be a \textit{rank-invariant}
extension of . We then focus on -order rank-invariant extensions
of , and present constructions of such extensions based on involutory
permutation matrices
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