803 research outputs found
Interactive Joint Transfer of Energy and Information
In some communication networks, such as passive RFID systems, the energy used
to transfer information between a sender and a recipient can be reused for
successive communication tasks. In fact, from known results in physics, any
system that exchanges information via the transfer of given physical resources,
such as radio waves, particles and qubits, can conceivably reuse, at least
part, of the received resources. This paper aims at illustrating some of the
new challenges that arise in the design of communication networks in which the
signals exchanged by the nodes carry both information and energy. To this end,
a baseline two-way communication system is considered in which two nodes
communicate in an interactive fashion. In the system, a node can either send an
"on" symbol (or "1"), which costs one unit of energy, or an "off" signal (or
"0"), which does not require any energy expenditure. Upon reception of a "1"
signal, the recipient node "harvests", with some probability, the energy
contained in the signal and stores it for future communication tasks. Inner and
outer bounds on the achievable rates are derived. Numerical results demonstrate
the effectiveness of the proposed strategies and illustrate some key design
insights.Comment: 29 pages, 11 figures, Submitted in IEEE Transactions on
Communications. arXiv admin note: substantial text overlap with
arXiv:1204.192
Joint Interference Alignment and Bi-Directional Scheduling for MIMO Two-Way Multi-Link Networks
By means of the emerging technique of dynamic Time Division Duplex (TDD), the
switching point between uplink and downlink transmissions can be optimized
across a multi-cell system in order to reduce the impact of inter-cell
interference. It has been recently recognized that optimizing also the order in
which uplink and downlink transmissions, or more generally the two directions
of a two-way link, are scheduled can lead to significant benefits in terms of
interference reduction. In this work, the optimization of bi-directional
scheduling is investigated in conjunction with the design of linear precoding
and equalization for a general multi-link MIMO two-way system. A simple
algorithm is proposed that performs the joint optimization of the ordering of
the transmissions in the two directions of the two-way links and of the linear
transceivers, with the aim of minimizing the interference leakage power.
Numerical results demonstrate the effectiveness of the proposed strategy.Comment: To be presented at ICC 2015, 6 pages, 7 figure
Probing global aspects of a geometry by the self-force on a charge: Spherical thin-shell wormholes
The self-interaction for a static point charge in the space-time of a
thin-shell wormhole constructed connecting two identical Schwarzschild
geometries is calculated in a series expansion. The electrostatic self-force is
evaluated numerically. It is found to be attractive towards the throat except
for some values of the throat radius proximate to the value of the
Schwarzschild horizon for which the force is repulsive or attractive depending
on the position of the charge. The result differs from the self-force in the
space-time of the Schwarzschild black hole, where it is always repulsive from
the center. Although these wormhole and black hole geometries are locally
indistinguishable, the different topologies of both backgrounds are manifested
in the electrostatic field of a point charge.Comment: 17 pages, 4 figue
Compound Multiple Access Channels with Partial Cooperation
A two-user discrete memoryless compound multiple access channel with a common
message and conferencing decoders is considered. The capacity region is
characterized in the special cases of physically degraded channels and
unidirectional cooperation, and achievable rate regions are provided for the
general case. The results are then extended to the corresponding Gaussian
model. In the Gaussian setup, the provided achievable rates are shown to lie
within some constant number of bits from the boundary of the capacity region in
several special cases. An alternative model, in which the encoders are
connected by conferencing links rather than having a common message, is studied
as well, and the capacity region for this model is also determined for the
cases of physically degraded channels and unidirectional cooperation. Numerical
results are also provided to obtain insights about the potential gains of
conferencing at the decoders and encoders.Comment: Submitted to IEEE Transactions on Information Theor
Capacity of Wireless Ad Hoc Networks with Opportunistic Collaborative Communications
Optimal multihop routing in ad hoc networks requires the exchange of control messages at the MAC and network layer in order to set up the (centralized) optimization problem. Distributed opportunistic space-time collaboration (OST) is a valid alternative that avoids this drawback by enabling opportunistic cooperation with the source at the physical layer. In this paper, the performance of OST is investigated. It is shown analytically that opportunistic collaboration outperforms (centralized) optimal multihop in case spatial reuse (i.e., the simultaneous transmission of more than one data stream) is not allowed by the transmission protocol. Conversely, in case spatial reuse is possible, the relative performance between the two protocols has to be studied case by case in terms of the corresponding capacity regions, given the topology and the physical parameters of network at hand. Simulation results confirm that opportunistic collaborative communication is a promising paradigm for wireless ad hoc networks that deserves further investigation
Relaying Simultaneous Multicast Messages
The problem of multicasting multiple messages with the help of a relay, which
may also have an independent message of its own to multicast, is considered. As
a first step to address this general model, referred to as the compound
multiple access channel with a relay (cMACr), the capacity region of the
multiple access channel with a "cognitive" relay is characterized, including
the cases of partial and rate-limited cognition. Achievable rate regions for
the cMACr model are then presented based on decode-and-forward (DF) and
compress-and-forward (CF) relaying strategies. Moreover, an outer bound is
derived for the special case in which each transmitter has a direct link to one
of the receivers while the connection to the other receiver is enabled only
through the relay terminal. Numerical results for the Gaussian channel are also
provided.Comment: This paper was presented at the IEEE Information Theory Workshop,
Volos, Greece, June 200
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