83 research outputs found
Resolving Entanglements in Topological Interference Management with Alternating Connectivity
The sum-capacity of a three user interference wired network for time-varying
channels is considered. Due to the channel variations, it is assumed that the
transmitters are only able to track the connectivity between the individual
nodes, thus only the (alternating) state of the network is known. By
considering a special subset of all possible states, we show that state
splitting combined with joint encoding over the alternating states is required
to achieve the sum-capacity. Regarding upper bounds, we use a genie aided
approach to show the optimality of this scheme. This highlights that more
involved transmit strategies are required for characterizing the degrees of
freedom even if the transmitters have heavily restricted channel state
information
Advanced interference management techniques for future generation cellular networks
The demand for mobile wireless network resources is constantly on the rise, pushing
for new communication technologies that are able to support unprecedented
rates. In this thesis we address the issue by considering advanced interference
management techniques to exploit the available resources more efficiently under
relaxed channel state information (CSI) assumptions. While the initial studies
focus on current half-duplex (HD) technology, we then move on to full-duplex
(FD) communication due to its inherent potential to improve spectral efficiency.
Work in this thesis is divided into four main parts as follows.
In the first part, we focus on the two-cell two-user-per-cell interference broadcast
channel (IBC) and consider the use of topological interference management
(TIM) to manage inter-cell interference in an alternating connectivity scenario.
Within this context we derive novel outer bounds on the achievable degrees of freedom
(DoF) for different system configurations, namely, single-input single-output
(SISO), multiple-input single-output (MISO) and multiple-input multiple-output
(MIMO) systems. Additionally, we propose new transmission schemes based on
joint coding across states that exploit global topological information at the transmitter
to increase achievable DoF. Results show that when a single state has a
probability of occurrence equal to one, the derived bounds are tight with up to
a twofold increase in achievable DoF for the best case scenario. Additionally,
when all alternating connectivity states are equiprobable: the SISO system gains
11/16 DoF, achieving 96:4% of the derived outer bound; while the MISO/MIMO
scenario has a gain of 1/2 DoF, achieving the outer bound itself.
In the second part, we consider a general G-cell K-user-per-cell MIMO IBC
and analyse the performance of linear interference alignment (IA) under imperfect
CSI. Having imperfect channel knowledge impacts the effectiveness of the IA
beamformers, and leads to a significant amount of residual leakage interference.
Understanding the extent of this impact is a fundamental step towards obtaining
a performance characterisation that is more relevant to practical scenarios. The
CSI error model used is highly versatile, allowing the error to be treated either
as a function of the signal-to-noise ratio (SNR) or as independent of it. Based
on this error model, we derive a novel upper bound on the asymptotic mean
sum rate loss and quantify the DoF loss due to imperfect CSI. Furthermore,
we propose a new version of the maximum signal-to-interference plus noise ratio
(Max-SINR) algorithm which takes into account statistical knowledge of the CSI
error in order to improve performance over the naive counterpart in the presence
of CSI mismatch.
In the third part, we shift our attention to FD systems and consider weighted
sum rate (WSR) maximisation for multi-user multi-cell networks where FD base-stations
(BSs) communicate with HD downlink (DL) and uplink (UL) users. Since
WSR problems are non-convex we transform them into weighted minimum mean
squared error (WMMSE) ones that are proven to converge. Our analysis is first
carried out for perfect CSI and then expanded to cater for imperfect CSI under
two types of error models, namely, a norm-bounded error model and a stochastic
error model. Additionally, we propose an algorithm that maximises the total DL
rate subject to each UL user achieving a desired target rate. Results show that
the use of FD BSs provides significant gains in achievable rate over the use of HD
BSs, with a gain of 1:92 for the best case scenario under perfect CSI. They also
demonstrate the robust performance of the imperfect CSI designs, and confirm
that FD outperforms HD even under CSI mismatch conditions.
Finally, the fourth part considers the use of linear IA to manage interference
in a multi-user multi-cell network with FD BSs and HD users under imperfect
CSI. The number of interference links present in such a system is considerably
greater than that present in the HD network counterpart; thus, understanding
the impact of residual leakage interference on performance is even more important
for FD enabled networks. Using the same generalised CSI error model from the
second part, we study the performance of IA by characterising the sum rate and
DoF losses incurred due to imperfect CSI. Additionally, we propose two novel IA
algorithms applicable to this network; the first one is based on minimising the
mean squared error (MMSE), while the second is based on Max-SINR. The proposed
algorithms exploit statistical knowledge of the CSI error variance in order
to improve performance. Moreover, they are shown to be equivalent under certain
conditions, even though the MMSE based one has lower computational complexity.
Furthermore for the multi-cell case, we also derive the proper condition for
IA feasibility
Understanding Quantum Technologies 2022
Understanding Quantum Technologies 2022 is a creative-commons ebook that
provides a unique 360 degrees overview of quantum technologies from science and
technology to geopolitical and societal issues. It covers quantum physics
history, quantum physics 101, gate-based quantum computing, quantum computing
engineering (including quantum error corrections and quantum computing
energetics), quantum computing hardware (all qubit types, including quantum
annealing and quantum simulation paradigms, history, science, research,
implementation and vendors), quantum enabling technologies (cryogenics, control
electronics, photonics, components fabs, raw materials), quantum computing
algorithms, software development tools and use cases, unconventional computing
(potential alternatives to quantum and classical computing), quantum
telecommunications and cryptography, quantum sensing, quantum technologies
around the world, quantum technologies societal impact and even quantum fake
sciences. The main audience are computer science engineers, developers and IT
specialists as well as quantum scientists and students who want to acquire a
global view of how quantum technologies work, and particularly quantum
computing. This version is an extensive update to the 2021 edition published in
October 2021.Comment: 1132 pages, 920 figures, Letter forma
New Foundation in the Sciences: Physics without sweeping infinities under the rug
It is widely known among the Frontiers of physics, that âsweeping under the rugâ practice has been quite the norm rather than exception. In other words, the leading paradigms have strong tendency to be hailed as the only game in town. For example, renormalization group theory was hailed as cure in order to solve infinity problem in QED theory. For instance, a quote from Richard Feynman goes as follows: âWhat the three Nobel Prize winners did, in the words of Feynman, was to get rid of the infinities in the calculations. The infinities are still there, but now they can be skirted around . . . We have designed a method for sweeping them under the rug. [1] And Paul Dirac himself also wrote with similar tune: âHence most physicists are very satisfied with the situation. They say: Quantum electrodynamics is a good theory, and we do not have to worry about it any more. I must say that I am very dissatisfied with the situation, because this so-called good theory does involve neglecting infinities which appear in its equations, neglecting them in an arbitrary way. This is just not sensible mathematics. Sensible mathematics involves neglecting a quantity when it turns out to be smallânot neglecting it just because it is infinitely great and you do not want it!â[2] Similarly, dark matter and dark energy were elevated as plausible way to solve the
crisis in prevalent Big Bang cosmology. That is why we choose a theme here: New Foundations in the Sciences, in order to emphasize the necessity to introduce a new set of approaches in the Sciences, be it Physics, Cosmology, Consciousness etc
Rheology
This book contains a wealth of useful information on current rheology research. By covering a broad variety of rheology-related topics, this e-book is addressed to a wide spectrum of academic and applied researchers and scientists but it could also prove useful to industry specialists. The subject areas include, polymer gels, food rheology, drilling fluids and liquid crystals among others
Spatial Formats under the Global Condition
Contributions to this volume summarize and discuss the theoretical foundations of the Collaborative Research Centre at Leipzig University which address the relationship between processes of (re-)spatialization on the one hand and the establishment and characteristics of spatial formats on the other hand
Who Killed the Primary Care Strategy? A Socio-Material Analysis
This study places the intended creation and implementation of an inter-professional education strategy at the intersection of three networks. The networks in question are cultural historical activity theory (CHAT), actor network theory (ANT), and a complex healthcare organisation (NHSX). CHAT and ANT, whilst both socio-material in origin, afford quite different readings of NHSX: therefore, the former has been used to identify, distil, and decompose the organisational activity systems, and the latter has been used to problematise them. The strategy was created in 2005 and had ceased to exist by 2010. This study therefore employs CHAT and ANT accounts to trace the lifespan of the strategy through the organisation, in particular through organisational working, learning, and boundary crossing, in an attempt to explain its untimely demise. It is envisaged that this study will provide an aid to framing how socio-material approaches can be combined to support inter-professional policy construction and implementation in a way that will allow flexibility for others to adapt to their own distinctive circumstance
Spatial Formats under the Global Condition
Contributions to this volume summarize and discuss the theoretical foundations of the Collaborative Research Centre at Leipzig University which address the relationship between processes of (re-)spatialization on the one hand and the establishment and characteristics of spatial formats on the other hand
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