8 research outputs found
Myopic Coding in Multiple Relay Channels
In this paper, we investigate achievable rates for data transmission from
sources to sinks through multiple relay networks. We consider myopic coding, a
constrained communication strategy in which each node has only a local view of
the network, meaning that nodes can only transmit to and decode from
neighboring nodes. We compare this with omniscient coding, in which every node
has a global view of the network and all nodes can cooperate. Using Gaussian
channels as examples, we find that when the nodes transmit at low power, the
rates achievable with two-hop myopic coding are as large as that under
omniscient coding in a five-node multiple relay channel and close to that under
omniscient coding in a six-node multiple relay channel. These results suggest
that we may do local coding and cooperation without compromising much on the
transmission rate. Practically, myopic coding schemes are more robust to
topology changes because encoding and decoding at a node are not affected when
there are changes at remote nodes. Furthermore, myopic coding mitigates the
high computational complexity and large buffer/memory requirements of
omniscient coding.Comment: To appear in the proceedings of the 2005 IEEE International Symposium
on Information Theory, Adelaide, Australia, September 4-9, 200
Myopic Coding in Multiterminal Networks
This paper investigates the interplay between cooperation and achievable
rates in multi-terminal networks. Cooperation refers to the process of nodes
working together to relay data toward the destination. There is an inherent
tradeoff between achievable information transmission rates and the level of
cooperation, which is determined by how many nodes are involved and how the
nodes encode/decode the data. We illustrate this trade-off by studying
information-theoretic decode-forward based coding strategies for data
transmission in multi-terminal networks. Decode-forward strategies are usually
discussed in the context of omniscient coding, in which all nodes in the
network fully cooperate with each other, both in encoding and decoding. In this
paper, we investigate myopic coding, in which each node cooperates with only a
few neighboring nodes. We show that achievable rates of myopic decode-forward
can be as large as that of omniscient decode-forward in the low SNR regime. We
also show that when each node has only a few cooperating neighbors, adding one
node into the cooperation increases the transmission rate significantly.
Furthermore, we show that myopic decode-forward can achieve non-zero rates as
the network size grows without bound
Cooperative coding and routing in multiple-terminal wireless networks
Ph.DDOCTOR OF PHILOSOPH
On Capacity and Optimal Scheduling for the Half-Duplex Multiple-Relay Channel
We study the half-duplex multiple-relay channel (HD-MRC) where every node can
either transmit or listen but cannot do both at the same time. We obtain a
capacity upper bound based on a max-flow min-cut argument and achievable
transmission rates based on the decode-forward (DF) coding strategy, for both
the discrete memoryless HD-MRC and the phase-fading HD-MRC. We discover that
both the upper bound and the achievable rates are functions of the
transmit/listen state (a description of which nodes transmit and which
receive). More precisely, they are functions of the time fraction of the
different states, which we term a schedule. We formulate the optimal scheduling
problem to find an optimal schedule that maximizes the DF rate. The optimal
scheduling problem turns out to be a maximin optimization, for which we propose
an algorithmic solution. We demonstrate our approach on a four-node
multiple-relay channel, obtaining closed-form solutions in certain scenarios.
Furthermore, we show that for the received signal-to-noise ratio degraded
phase-fading HD-MRC, the optimal scheduling problem can be simplified to a max
optimization.Comment: Author's final version (to appear in IEEE Transactions on Information
Theory
Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics 1.0: A General Circulation Model for Simulating the Climates of Rocky Planets
Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments
with Dynamics (ROCKE-3D) is a 3-Dimensional General Circulation Model (GCM)
developed at the NASA Goddard Institute for Space Studies for the modeling of
atmospheres of Solar System and exoplanetary terrestrial planets. Its parent
model, known as ModelE2 (Schmidt et al. 2014), is used to simulate modern and
21st Century Earth and near-term paleo-Earth climates. ROCKE-3D is an ongoing
effort to expand the capabilities of ModelE2 to handle a broader range of
atmospheric conditions including higher and lower atmospheric pressures, more
diverse chemistries and compositions, larger and smaller planet radii and
gravity, different rotation rates (slowly rotating to more rapidly rotating
than modern Earth, including synchronous rotation), diverse ocean and land
distributions and topographies, and potential basic biosphere functions. The
first aim of ROCKE-3D is to model planetary atmospheres on terrestrial worlds
within the Solar System such as paleo-Earth, modern and paleo-Mars,
paleo-Venus, and Saturn's moon Titan. By validating the model for a broad range
of temperatures, pressures, and atmospheric constituents we can then expand its
capabilities further to those exoplanetary rocky worlds that have been
discovered in the past and those to be discovered in the future. We discuss the
current and near-future capabilities of ROCKE-3D as a community model for
studying planetary and exoplanetary atmospheres.Comment: Revisions since previous draft. Now submitted to Astrophysical
Journal Supplement Serie