310 research outputs found
Network Coding Channel Virtualization Schemes for Satellite Multicast Communications
In this paper, we propose two novel schemes to solve the problem of finding a
quasi-optimal number of coded packets to multicast to a set of independent
wireless receivers suffering different channel conditions. In particular, we
propose two network channel virtualization schemes that allow for representing
the set of intended receivers in a multicast group to be virtualized as one
receiver. Such approach allows for a transmission scheme not only adapted to
per-receiver channel variation over time, but to the network-virtualized
channel representing all receivers in the multicast group. The first scheme
capitalizes on a maximum erasure criterion introduced via the creation of a
virtual worst per receiver per slot reference channel of the network. The
second scheme capitalizes on a maximum completion time criterion by the use of
the worst performing receiver channel as a virtual reference to the network. We
apply such schemes to a GEO satellite scenario. We demonstrate the benefits of
the proposed schemes comparing them to a per-receiver point-to-point adaptive
strategy
Optimal Energy Management for Energy Harvesting Transmitter and Receiver with Helper
We study energy harvesting (EH) transmitter and receiver, where the receiver
decodes data using the harvested energy from the nature and from an independent
EH node, named helper. Helper cooperates with the receiver by transferring its
harvested energy to the receiver over an orthogonal fading channel. We study an
offline optimal power management policy to maximize the reliable information
rate. The harvested energy in all three nodes are assumed to be known. We
consider four different scenarios; First, for the case that both transmitter
and the receiver have batteries, we show that the optimal policy is
transferring the helper harvested energy to the receiver, immediately. Next,
for the case of non-battery receiver and full power transmitter, we model a
virtual EH receiver with minimum energy constraint to achieve an optimal
policy. Then, we consider a non-battery EH receiver and EH transmitter with
battery. Finally, we derive optimal power management wherein neither the
transmitter nor the receiver have batteries. We propose three iterative
algorithms to compute optimal energy management policies. Numerical results are
presented to corroborate the advantage of employing the helper.Comment: It is a conference paper with 5 pages and one figure, submitted to
ISITA201
Monitoring induced distributed double-couple sources using Marchenko-based virtual receivers
We aim to monitor and characterize signals in the subsurface by combining
these passive signals with recorded reflection data at the surface of the
Earth. To achieve this, we propose a method to create virtual receivers from
reflection data using the Marchenko method. By applying homogeneous Green's
function retrieval, these virtual receivers are then used to monitor the
responses from subsurface sources. We consider monopole point sources with a
symmetric source signal, where the full wavefield without artefacts in the
subsurface can be obtained. Responses from more complex source mechanisms, such
as double-couple sources, can also be used and provide results with comparable
quality as the monopole responses. If the source signal is not symmetric in
time, our technique that is based on homogeneous Green's function retrieval
provides an incomplete signal, with additional artefacts. The duration of these
artefacts is limited and they are only present when the source of the signal is
located above the virtual receiver. For sources along a fault rupture, this
limitation is also present and more severe due to the source activating over a
longer period of time. Part of the correct signal is still retrieved, as well
as the source location of the signal. These artefacts do not occur in another
method which creates virtual sources as well as receivers from reflection data
at the surface. This second method can be used to forecast responses to
possible future induced seismicity sources (monopoles, double-couple sources
and fault ruptures). This method is applied to field data, where similar
results to synthetic data are achieved, which shows the potential for the
application on real data signals
Multiple-Input Multiple-Output Gaussian Broadcast Channels with Common and Confidential Messages
This paper considers the problem of the multiple-input multiple-output (MIMO)
Gaussian broadcast channel with two receivers (receivers 1 and 2) and two
messages: a common message intended for both receivers and a confidential
message intended only for receiver 1 but needing to be kept asymptotically
perfectly secure from receiver 2. A matrix characterization of the secrecy
capacity region is established via a channel enhancement argument. The enhanced
channel is constructed by first splitting receiver 1 into two virtual receivers
and then enhancing only the virtual receiver that decodes the confidential
message. The secrecy capacity region of the enhanced channel is characterized
using an extremal entropy inequality previously established for characterizing
the capacity region of a degraded compound MIMO Gaussian broadcast channel.Comment: Submitted to the IEEE Transactions on Information Theory, July 200
Distortion Minimization in Gaussian Layered Broadcast Coding with Successive Refinement
A transmitter without channel state information (CSI) wishes to send a
delay-limited Gaussian source over a slowly fading channel. The source is coded
in superimposed layers, with each layer successively refining the description
in the previous one. The receiver decodes the layers that are supported by the
channel realization and reconstructs the source up to a distortion. The
expected distortion is minimized by optimally allocating the transmit power
among the source layers. For two source layers, the allocation is optimal when
power is first assigned to the higher layer up to a power ceiling that depends
only on the channel fading distribution; all remaining power, if any, is
allocated to the lower layer. For convex distortion cost functions with convex
constraints, the minimization is formulated as a convex optimization problem.
In the limit of a continuum of infinite layers, the minimum expected distortion
is given by the solution to a set of linear differential equations in terms of
the density of the fading distribution. As the bandwidth ratio b (channel uses
per source symbol) tends to zero, the power distribution that minimizes
expected distortion converges to the one that maximizes expected capacity.
While expected distortion can be improved by acquiring CSI at the transmitter
(CSIT) or by increasing diversity from the realization of independent fading
paths, at high SNR the performance benefit from diversity exceeds that from
CSIT, especially when b is large.Comment: Accepted for publication in IEEE Transactions on Information Theor
Virtual plane-wave imaging via Marchenko redatuming
Marchenko redatuming is a novel scheme used to retrieve up- and down-going
Green's functions in an unknown medium. Marchenko equations are based on
reciprocity theorems and are derived on the assumption of the existence of so
called focusing functions, i.e. functions which exhibit time-space focusing
properties once injected in the subsurface. In contrast to interferometry but
similarly to standard migration methods, Marchenko redatuming only requires an
estimate of the direct wave from the virtual source (or to the virtual
receiver), illumination from only one side of the medium, and no physical
sources (or receivers) inside the medium. In this contribution we consider a
different time-focusing condition within the frame of Marchenko redatuming and
show how this can lead to the retrieval of virtual plane-wave responses, thus
allowing multiple-free imaging using only a 1 dimensional sampling of the
targeted model. The potential of the new method is demonstrated on a 2D
synthetic model.Comment: 12 pages, 5 figure
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