3,521 research outputs found
Information-Theoretic Bounds for Multiround Function Computation in Collocated Networks
We study the limits of communication efficiency for function computation in
collocated networks within the framework of multi-terminal block source coding
theory. With the goal of computing a desired function of sources at a sink,
nodes interact with each other through a sequence of error-free, network-wide
broadcasts of finite-rate messages. For any function of independent sources, we
derive a computable characterization of the set of all feasible message coding
rates - the rate region - in terms of single-letter information measures. We
show that when computing symmetric functions of binary sources, the sink will
inevitably learn certain additional information which is not demanded in
computing the function. This conceptual understanding leads to new improved
bounds for the minimum sum-rate. The new bounds are shown to be orderwise
better than those based on cut-sets as the network scales. The scaling law of
the minimum sum-rate is explored for different classes of symmetric functions
and source parameters.Comment: 9 pages. A 5-page version without appendices was submitted to IEEE
International Symposium on Information Theory (ISIT), 2009. This version
contains complete proofs as appendice
On Zero-Error Source Coding with Feedback
We consider the problem of zero error source coding with limited feedback
when side information is present at the receiver. First, we derive an
achievable rate region for arbitrary joint distributions on the source and the
side information. When all source pairs of source and side information symbols
are observable with non-zero probability, we show that this characterization
gives the entire rate region. Next, we demonstrate a class of sources for which
asymptotically zero feedback suffices to achieve zero-error coding at the rate
promised by the Slepian-Wolf bound for asymptotically lossless coding. Finally,
we illustrate these results with the aid of three simple examples
Network Coding for Computing: Cut-Set Bounds
The following \textit{network computing} problem is considered. Source nodes
in a directed acyclic network generate independent messages and a single
receiver node computes a target function of the messages. The objective is
to maximize the average number of times can be computed per network usage,
i.e., the ``computing capacity''. The \textit{network coding} problem for a
single-receiver network is a special case of the network computing problem in
which all of the source messages must be reproduced at the receiver. For
network coding with a single receiver, routing is known to achieve the capacity
by achieving the network \textit{min-cut} upper bound. We extend the definition
of min-cut to the network computing problem and show that the min-cut is still
an upper bound on the maximum achievable rate and is tight for computing (using
coding) any target function in multi-edge tree networks and for computing
linear target functions in any network. We also study the bound's tightness for
different classes of target functions. In particular, we give a lower bound on
the computing capacity in terms of the Steiner tree packing number and a
different bound for symmetric functions. We also show that for certain networks
and target functions, the computing capacity can be less than an arbitrarily
small fraction of the min-cut bound.Comment: Submitted to the IEEE Transactions on Information Theory (Special
Issue on Facets of Coding Theory: from Algorithms to Networks); Revised on
Aug 9, 201
Processing and Transmission of Information
Contains reports on seven research projects.Lincoln Laboratory, Purchase Order DDL B-00337U.S. ArmyU.S. NavyU.S. Air Force under Air Force Contract AF19(604)-7400National Institutes of Health (Grant MH-04737-02
Multiuser Switched Diversity Scheduling Schemes
Multiuser switched-diversity scheduling schemes were recently proposed in
order to overcome the heavy feedback requirements of conventional opportunistic
scheduling schemes by applying a threshold-based, distributed, and ordered
scheduling mechanism. The main idea behind these schemes is that slight
reduction in the prospected multiuser diversity gains is an acceptable
trade-off for great savings in terms of required channel-state-information
feedback messages. In this work, we characterize the achievable rate region of
multiuser switched diversity systems and compare it with the rate region of
full feedback multiuser diversity systems. We propose also a novel proportional
fair multiuser switched-based scheduling scheme and we demonstrate that it can
be optimized using a practical and distributed method to obtain the feedback
thresholds. We finally demonstrate by numerical examples that
switched-diversity scheduling schemes operate within 0.3 bits/sec/Hz from the
ultimate network capacity of full feedback systems in Rayleigh fading
conditions.Comment: Accepted at IEEE Transactions on Communications, to appear 2012,
funded by NPRP grant 08-577-2-241 from QNR
On Two-Pair Two-Way Relay Channel with an Intermittently Available Relay
When multiple users share the same resource for physical layer cooperation
such as relay terminals in their vicinities, this shared resource may not be
always available for every user, and it is critical for transmitting terminals
to know whether other users have access to that common resource in order to
better utilize it. Failing to learn this critical piece of information may
cause severe issues in the design of such cooperative systems. In this paper,
we address this problem by investigating a two-pair two-way relay channel with
an intermittently available relay. In the model, each pair of users need to
exchange their messages within their own pair via the shared relay. The shared
relay, however, is only intermittently available for the users to access. The
accessing activities of different pairs of users are governed by independent
Bernoulli random processes. Our main contribution is the characterization of
the capacity region to within a bounded gap in a symmetric setting, for both
delayed and instantaneous state information at transmitters. An interesting
observation is that the bottleneck for information flow is the quality of state
information (delayed or instantaneous) available at the relay, not those at the
end users. To the best of our knowledge, our work is the first result regarding
how the shared intermittent relay should cooperate with multiple pairs of users
in such a two-way cooperative network.Comment: extended version of ISIT 2015 pape
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