186,199 research outputs found
Group Based Interference Alignment
In the -user single-input single-output (SISO) frequency-selective fading
interference channel, it is shown that the maximal achievable multiplexing gain
is almost surely by using interference alignment (IA). However, when the
signaling dimensions are limited, allocating all the resources to all users
simultaneously is not optimal. So, a group based interference alignment (GIA)
scheme is proposed, and it is formulated as an unbounded knapsack problem.
Optimal and greedy search algorithms are proposed to obtain group patterns.
Analysis and numerical results show that the GIA scheme can obtain a higher
multiplexing gain when the resources are limited.Comment: 3 pages, 3 figures. resubmitted to IEEE Communications Letter
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
A hybrid TIM-NOMA scheme for the SISO Broadcast Channel
Future mobile communication networks will require enhanced network efficiency
and reduced system overhead due to their user density and high data rate
demanding applications of the mobile devices. Research on Blind Interference
Alignment (BIA) and Topological Interference Management (TIM) has shown that
optimal Degrees of Freedom (DoF) can be achieved, in the absence of Channel
State Information (CSI) at the transmitters, reducing the network's overhead.
Moreover, the recently emerged Non-Orthogonal Multiple Access (NOMA) scheme
suggests a different multiple access approach, compared to the current
orthogonal methods employed in 4G networks, resulting in high capacity gains.
Our contribution is a hybrid TIM-NOMA scheme in Single-Input-Single-Output
(SISO) K-user cells, in which users are divided into T groups, and 1/T DoF is
achieved for each user. By superimposing users in the power domain, we
introduce a two-stage decoding process, managing 'inter-group' interference
based on the TIM principles, and 'intra-group' interference based on Successful
Interference Cancellation (SIC), as proposed by NOMA. We show that for high SNR
values the hybrid scheme can improve the sum rate by at least 100% when
compared to Time Division Multiple Access (TDMA).Comment: 6 pages, 6 figures, submitted to IEEE ICC'15 - IEEE SCAN Worksho
Conformation dependence of charge transfer and level alignment in nitrobenzene junctions with pyridyl anchor groups
The alignment of molecular levels with the Fermi energy in single molecule
junctions is a crucial factor in determining their conductance or the
observability of quantum interference effects. In the present study which is
based on density functional theory calculations, we explore the zero-bias
charge transfer and level alignment for nitro-bipyridyl-phenyl adsorbed between
two gold surfaces which we find to vary significantly with the molecular
conformation. The net charge transfer is the result of two opposing effects,
namely Pauli repulsion at the interface between the molecule and the leads, and
the electron accepting nature of the NO group, where only the latter which
we analyze in terms of the electronegativity of the isolated molecules depends
on the two intra-molecular torsion angles. We provide evidence that the
conformation dependence of the alignment of molecular levels and peaks in the
transmission function can indeed be understood in terms of charge transfer for
this system, and that other properties such as molecular dipoles do not play a
significant role. Our study is relevant for device design in molecular
electronics where nitrobenzene appears as a component in proposals for
rectification, quantum interference or chemical gating.Comment: 10 pages, 6 figure
A hybrid TIM-NOMA scheme for the Broadcast Channel
Future mobile communication networks will require enhanced network efficiency
and reduced system overhead. Research on Blind Interference Alignment and
Topological Interference Management (TIM) has shown that optimal Degrees of
Freedom can be achieved, in the absence of Channel State Information at the
transmitters. Moreover, the recently emerged Non-Orthogonal Multiple Access
(NOMA) scheme suggests a different multiple access approach, compared to the
orthogonal methods employed in 4G, resulting in high capacity gains. Our
contribution is a hybrid TIM-NOMA scheme in K-user cells, where users are
divided into T groups. By superimposing users in the power domain, we introduce
a two-stage decoding process, managing inter-group interference based on the
TIM principles, and intra-group interference based on Successful Interference
Cancellation, as proposed by NOMA. We show that the hybrid scheme can improve
the sum rate by at least 100% compared to Time Division Multiple Access, for
high SNR values.Comment: 11 pages, Published at "EAI Endorsed Transactions on Wireless
Spectrum
Interference Alignment for the Multi-Antenna Compound Wiretap Channel
We study a wiretap channel model where the sender has transmit antennas
and there are two groups consisting of and receivers respectively.
Each receiver has a single antenna. We consider two scenarios. First we
consider the compound wiretap model -- group 1 constitutes the set of
legitimate receivers, all interested in a common message, whereas group 2 is
the set of eavesdroppers. We establish new lower and upper bounds on the secure
degrees of freedom. Our lower bound is based on the recently proposed
\emph{real interference alignment} scheme. The upper bound provides the first
known example which illustrates that the \emph{pairwise upper bound} used in
earlier works is not tight.
The second scenario we study is the compound private broadcast channel. Each
group is interested in a message that must be protected from the other group.
Upper and lower bounds on the degrees of freedom are developed by extending the
results on the compound wiretap channel.Comment: Minor edits. Submitted to IEEE Trans. Inf. Theor
A New DoF Upper Bound and Its Achievability for -User MIMO Y Channels
This work is to study the degrees of freedom (DoF) for the -user MIMO Y
channel. Previously, two transmission frameworks have been proposed for the DoF
analysis when , where and denote the number of antennas at
each source node and the relay node respectively. The first method is named as
signal group based alignment proposed by Hua et al. in [1]. The second is named
as signal pattern approach introduced by Wang et al. in [2]. But both of them
only studied certain antenna configurations. The maximum achievable DoF in the
general case still remains unknown. In this work, we first derive a new upper
bound of the DoF using the genie-aided approach. Then, we propose a more
general transmission framework, generalized signal alignment (GSA), and show
that the previous two methods are both special cases of GSA. With GSA, we prove
that the new DoF upper bound is achievable when . The DoF
analysis in this paper provides a major step forward towards the fundamental
capacity limit of the -user MIMO Y channel. It also offers a new approach of
integrating interference alignment with physical layer network coding.Comment: 6 pages, 3 figures, submitted to IEEE ICC 2015. arXiv admin note:
text overlap with arXiv:1405.071
- …