206,515 research outputs found
The Ergodic Capacity of Phase-Fading Interference Networks
We identify the role of equal strength interference links as bottlenecks on
the ergodic sum capacity of a user phase-fading interference network, i.e.,
an interference network where the fading process is restricted primarily to
independent and uniform phase variations while the channel magnitudes are held
fixed across time. It is shown that even though there are cross-links,
only about disjoint and equal strength interference links suffice to
determine the capacity of the network regardless of the strengths of the rest
of the cross channels. This scenario is called a \emph{minimal bottleneck
state}. It is shown that ergodic interference alignment is capacity optimal for
a network in a minimal bottleneck state. The results are applied to large
networks. It is shown that large networks are close to bottleneck states with a
high probability, so that ergodic interference alignment is close to optimal
for large networks. Limitations of the notion of bottleneck states are also
highlighted for channels where both the phase and the magnitudes vary with
time. It is shown through an example that for these channels, joint coding
across different bottleneck states makes it possible to circumvent the capacity
bottlenecks.Comment: 19 page
Interference Mitigation in Large Random Wireless Networks
A central problem in the operation of large wireless networks is how to deal
with interference -- the unwanted signals being sent by transmitters that a
receiver is not interested in. This thesis looks at ways of combating such
interference.
In Chapters 1 and 2, we outline the necessary information and communication
theory background, including the concept of capacity. We also include an
overview of a new set of schemes for dealing with interference known as
interference alignment, paying special attention to a channel-state-based
strategy called ergodic interference alignment.
In Chapter 3, we consider the operation of large regular and random networks
by treating interference as background noise. We consider the local performance
of a single node, and the global performance of a very large network.
In Chapter 4, we use ergodic interference alignment to derive the asymptotic
sum-capacity of large random dense networks. These networks are derived from a
physical model of node placement where signal strength decays over the distance
between transmitters and receivers. (See also arXiv:1002.0235 and
arXiv:0907.5165.)
In Chapter 5, we look at methods of reducing the long time delays incurred by
ergodic interference alignment. We analyse the tradeoff between reducing delay
and lowering the communication rate. (See also arXiv:1004.0208.)
In Chapter 6, we outline a problem that is equivalent to the problem of
pooled group testing for defective items. We then present some new work that
uses information theoretic techniques to attack group testing. We introduce for
the first time the concept of the group testing channel, which allows for
modelling of a wide range of statistical error models for testing. We derive
new results on the number of tests required to accurately detect defective
items, including when using sequential `adaptive' tests.Comment: PhD thesis, University of Bristol, 201
Leveraging Physical Layer Capabilites: Distributed Scheduling in Interference Networks with Local Views
In most wireless networks, nodes have only limited local information about
the state of the network, which includes connectivity and channel state
information. With limited local information about the network, each node's
knowledge is mismatched; therefore, they must make distributed decisions. In
this paper, we pose the following question - if every node has network state
information only about a small neighborhood, how and when should nodes choose
to transmit? While link scheduling answers the above question for
point-to-point physical layers which are designed for an interference-avoidance
paradigm, we look for answers in cases when interference can be embraced by
advanced PHY layer design, as suggested by results in network information
theory.
To make progress on this challenging problem, we propose a constructive
distributed algorithm that achieves rates higher than link scheduling based on
interference avoidance, especially if each node knows more than one hop of
network state information. We compare our new aggressive algorithm to a
conservative algorithm we have presented in [1]. Both algorithms schedule
sub-networks such that each sub-network can employ advanced
interference-embracing coding schemes to achieve higher rates. Our innovation
is in the identification, selection and scheduling of sub-networks, especially
when sub-networks are larger than a single link.Comment: 14 pages, Submitted to IEEE/ACM Transactions on Networking, October
201
On the Throughput Maximization in Dencentralized Wireless Networks
A distributed single-hop wireless network with links is considered, where
the links are partitioned into a fixed number () of clusters each operating
in a subchannel with bandwidth . The subchannels are assumed to be
orthogonal to each other. A general shadow-fading model, described by
parameters , is considered where denotes the
probability of shadowing and () represents the average
cross-link gains. The main goal of this paper is to find the maximum network
throughput in the asymptotic regime of , which is achieved by: i)
proposing a distributed and non-iterative power allocation strategy, where the
objective of each user is to maximize its best estimate (based on its local
information, i.e., direct channel gain) of the average network throughput, and
ii) choosing the optimum value for . In the first part of the paper, the
network hroughput is defined as the \textit{average sum-rate} of the network,
which is shown to scale as . Moreover, it is proved that in
the strong interference scenario, the optimum power allocation strategy for
each user is a threshold-based on-off scheme. In the second part, the network
throughput is defined as the \textit{guaranteed sum-rate}, when the outage
probability approaches zero. In this scenario, it is demonstrated that the
on-off power allocation scheme maximizes the throughput, which scales as
. Moreover, the optimum spectrum sharing for
maximizing the average sum-rate and the guaranteed sum-rate is achieved at M=1.Comment: Submitted to IEEE Transactions on Information Theor
Topological Interference Management with Alternating Connectivity
The topological interference management problem refers to the study of the
capacity of partially connected linear (wired and wireless) communication
networks with no channel state information at the transmitters (no CSIT) beyond
the network topology, i.e., a knowledge of which channel coefficients are zero
(weaker than the noise floor in the wireless case). While the problem is
originally studied with fixed topology, in this work we explore the
implications of varying connectivity, through a series of simple and
conceptually representative examples. Specifically, we highlight the
synergistic benefits of coding across alternating topologies
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