27,411 research outputs found
Source Coding When the Side Information May Be Delayed
For memoryless sources, delayed side information at the decoder does not
improve the rate-distortion function. However, this is not the case for more
general sources with memory, as demonstrated by a number of works focusing on
the special case of (delayed) feedforward. In this paper, a setting is studied
in which the encoder is potentially uncertain about the delay with which
measurements of the side information are acquired at the decoder. Assuming a
hidden Markov model for the sources, at first, a single-letter characterization
is given for the set-up where the side information delay is arbitrary and known
at the encoder, and the reconstruction at the destination is required to be
(near) lossless. Then, with delay equal to zero or one source symbol, a
single-letter characterization is given of the rate-distortion region for the
case where side information may be delayed or not, unbeknownst to the encoder.
The characterization is further extended to allow for additional information to
be sent when the side information is not delayed. Finally, examples for binary
and Gaussian sources are provided.Comment: revised July 201
Cooperative Strategies for Simultaneous and Broadcast Relay Channels
Consider the \emph{simultaneous relay channel} (SRC) which consists of a set
of relay channels where the source wishes to transmit common and private
information to each of the destinations. This problem is recognized as being
equivalent to that of sending common and private information to several
destinations in presence of helper relays where each channel outcome becomes a
branch of the \emph{broadcast relay channel} (BRC). Cooperative schemes and
capacity region for a set with two memoryless relay channels are investigated.
The proposed coding schemes, based on \emph{Decode-and-Forward} (DF) and
\emph{Compress-and-Forward} (CF) must be capable of transmitting information
simultaneously to all destinations in such set.
Depending on the quality of source-to-relay and relay-to-destination
channels, inner bounds on the capacity of the general BRC are derived. Three
cases of particular interest are considered: cooperation is based on DF
strategy for both users --referred to as DF-DF region--, cooperation is based
on CF strategy for both users --referred to as CF-CF region--, and cooperation
is based on DF strategy for one destination and CF for the other --referred to
as DF-CF region--. These results can be seen as a generalization and hence
unification of previous works. An outer-bound on the capacity of the general
BRC is also derived. Capacity results are obtained for the specific cases of
semi-degraded and degraded Gaussian simultaneous relay channels. Rates are
evaluated for Gaussian models where the source must guarantee a minimum amount
of information to both users while additional information is sent to each of
them.Comment: 32 pages, 7 figures, To appear in IEEE Trans. on Information Theor
Lecture Notes on Network Information Theory
These lecture notes have been converted to a book titled Network Information
Theory published recently by Cambridge University Press. This book provides a
significantly expanded exposition of the material in the lecture notes as well
as problems and bibliographic notes at the end of each chapter. The authors are
currently preparing a set of slides based on the book that will be posted in
the second half of 2012. More information about the book can be found at
http://www.cambridge.org/9781107008731/. The previous (and obsolete) version of
the lecture notes can be found at http://arxiv.org/abs/1001.3404v4/
A Roadmap to Reduce U.S. Food Waste by 20 Percent
The magnitude of the food waste problem is difficult to comprehend. The U.S. spends $218 billion a year -- 1.3% of GDP -- growing, processing, transporting, and disposing of food that is never eaten. The causes of food waste are diverse, ranging from crops that never get harvested, to food left on overfilled plates, to near-expired milk and stale bread. ReFED is a coalition of over 30 business, nonprofit, foundation, and government leaders committed to building a different future, where food waste prevention, recovery, and recycling are recognized as an untapped opportunity to create jobs, alleviate hunger, and protect the environment -- all while stimulating a new multi-billion dollar market opportunity. ReFED developed A Roadmap to Reduce U.S. Food Waste as a data-driven guide to collectively take action to reduce food waste at scale nationwide.This Roadmap report is a guide and a call to action for us to work together to solve this problem. Businesses can save money for themselves and their customers. Policymakers can unleash a new wave of local job creation. Foundations can take a major step in addressing environmental issues and hunger. And innovators across all sectors can launch new products, services, and business models. There will be no losers, only winners, as food finds its way to its highest and best use
Study of roles of remote manipulator systems and EVA for shuttle mission support, volume 1
Alternate extravehicular activity (EVA) and remote manipulator system (RMS) configurations were examined for their relative effectiveness in performing an array of representative shuttle and payload support tasks. Initially a comprehensive analysis was performed of payload and shuttle support missions required to be conducted exterior to a pressurized inclosure. A set of task selection criteria was established, and study tasks were identified. The EVA and RMS modes were evaluated according to their applicability for each task and task condition. The results are summarized in tabular form, showing the modes which are chosen as most effective or as feasible for each task/condition. Conclusions concerning the requirements and recommendations for each mode are presented
Rate Aware Instantly Decodable Network Codes
This paper addresses the problem of reducing the delivery time of data
messages to cellular users using instantly decodable network coding (IDNC) with
physical-layer rate awareness. While most of the existing literature on IDNC
does not consider any physical layer complications and abstract the model as
equally slotted time for all users, this paper proposes a cross-layer scheme
that incorporates the different channel rates of the various users in the
decision process of both the transmitted message combinations and the rates
with which they are transmitted. The consideration of asymmetric rates for
receivers reflects more practical application scenarios and introduces a new
trade-off between the choice of coding combinations for various receivers and
the broadcasting rate for achieving shorter completion time. The completion
time minimization problem in such scenario is first shown to be intractable.
The problem is, thus, approximated by reducing, at each transmission, the
increase of an anticipated version of the completion time. The paper solves the
problem by formulating it as a maximum weight clique problem over a newly
designed rate aware IDNC (RA-IDNC) graph. The highest weight clique in the
created graph being potentially not unique, the paper further suggests a
multi-layer version of the proposed solution to improve the obtained results
from the employed completion time approximation. Simulation results indicate
that the cross-layer design largely outperforms the uncoded transmissions
strategies and the classical IDNC scheme
Analysis of a Cooperative Strategy for a Large Decentralized Wireless Network
This paper investigates the benefits of cooperation and proposes a relay
activation strategy for a large wireless network with multiple transmitters. In
this framework, some nodes cooperate with a nearby node that acts as a relay,
using the decode-and-forward protocol, and others use direct transmission. The
network is modeled as an independently marked Poisson point process and the
source nodes may choose their relays from the set of inactive nodes. Although
cooperation can potentially lead to significant improvements in the performance
of a communication pair, relaying causes additional interference in the
network, increasing the average noise that other nodes see. We investigate how
source nodes should balance cooperation vs. interference to obtain reliable
transmissions, and for this purpose we study and optimize a relay activation
strategy with respect to the outage probability. Surprisingly, in the high
reliability regime, the optimized strategy consists on the activation of all
the relays or none at all, depending on network parameters. We provide a simple
closed-form expression that indicates when the relays should be active, and we
introduce closed form expressions that quantify the performance gains of this
scheme with respect to a network that only uses direct transmission.Comment: Updated version. To appear in IEEE Transactions on Networkin
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