12,660 research outputs found
Advanced digital modulation: Communication techniques and monolithic GaAs technology
Communications theory and practice are merged with state-of-the-art technology in IC fabrication, especially monolithic GaAs technology, to examine the general feasibility of a number of advanced technology digital transmission systems. Satellite-channel models with (1) superior throughput, perhaps 2 Gbps; (2) attractive weight and cost; and (3) high RF power and spectrum efficiency are discussed. Transmission techniques possessing reasonably simple architectures capable of monolithic fabrication at high speeds were surveyed. This included a review of amplitude/phase shift keying (APSK) techniques and the continuous-phase-modulation (CPM) methods, of which MSK represents the simplest case
Multi-mode Cavity Centric Architectures for Quantum Simulation
Near-term quantum computing technologies grapple with huge complexity
overheads, hindering their ability to induce algorithms, necessitating
engineering and scientific innovations. One class of problems of interest is
Quantum Simulation, whereby quantum systems are simulated using a quantum
computer. However, current devices are yet to surpass classical tensor network
techniques. For problems of interest, where classical simulation techniques
fail, large degrees of entanglement are required. Another challenge of
implementing quantum simulation problems is that qubits sit idle whilst
alternating simulation terms are implemented, exposing the system to
decoherence. In the near term, 2D planar superconducting lattices of
circuit-QED elements such as the transmon continue to draw substantial
attention, but they are hindered by their nearest neighbor topology and
relatively short lifespan, two problems that are problematic for quantum
simulation. One technology of particular interest is the multi-mode
superconducting resonator capable of storing multiple qubits in one device. We
observe that these cavities have a natural virtual topology that aligns
particularly well with quantum simulation problems, and exhibit much longer
lifespans in comparison to other planar superconducting hardware. In this paper
we present MUCIC, we discuss the simple integration of these devices into the
current landscape and their implications to quantum simulation, motivated by
their alignment to the quantum simulation problem, and potential as a quantum
memory candidate. We report the development of MUCICs transpiler, leading to
reductions of up to 82% in quantum simulation circuit depths. Additionally, our
investigation demonstrates improvements of up to 19.4% in converged results
from Variational Quantum Algorithms
Diversity-Multiplexing Tradeoff of Asynchronous Cooperative Diversity in Wireless Networks
Synchronization of relay nodes is an important and critical issue in
exploiting cooperative diversity in wireless networks. In this paper, two
asynchronous cooperative diversity schemes are proposed, namely, distributed
delay diversity and asynchronous space-time coded cooperative diversity
schemes. In terms of the overall diversity-multiplexing (DM) tradeoff function,
we show that the proposed independent coding based distributed delay diversity
and asynchronous space-time coded cooperative diversity schemes achieve the
same performance as the synchronous space-time coded approach which requires an
accurate symbol-level timing synchronization to ensure signals arriving at the
destination from different relay nodes are perfectly synchronized. This
demonstrates diversity order is maintained even at the presence of asynchronism
between relay node. Moreover, when all relay nodes succeed in decoding the
source information, the asynchronous space-time coded approach is capable of
achieving better DM-tradeoff than synchronous schemes and performs equivalently
to transmitting information through a parallel fading channel as far as the
DM-tradeoff is concerned. Our results suggest the benefits of fully exploiting
the space-time degrees of freedom in multiple antenna systems by employing
asynchronous space-time codes even in a frequency flat fading channel. In
addition, it is shown asynchronous space-time coded systems are able to achieve
higher mutual information than synchronous space-time coded systems for any
finite signal-to-noise-ratio (SNR) when properly selected baseband waveforms
are employed
Datacenter Traffic Control: Understanding Techniques and Trade-offs
Datacenters provide cost-effective and flexible access to scalable compute
and storage resources necessary for today's cloud computing needs. A typical
datacenter is made up of thousands of servers connected with a large network
and usually managed by one operator. To provide quality access to the variety
of applications and services hosted on datacenters and maximize performance, it
deems necessary to use datacenter networks effectively and efficiently.
Datacenter traffic is often a mix of several classes with different priorities
and requirements. This includes user-generated interactive traffic, traffic
with deadlines, and long-running traffic. To this end, custom transport
protocols and traffic management techniques have been developed to improve
datacenter network performance.
In this tutorial paper, we review the general architecture of datacenter
networks, various topologies proposed for them, their traffic properties,
general traffic control challenges in datacenters and general traffic control
objectives. The purpose of this paper is to bring out the important
characteristics of traffic control in datacenters and not to survey all
existing solutions (as it is virtually impossible due to massive body of
existing research). We hope to provide readers with a wide range of options and
factors while considering a variety of traffic control mechanisms. We discuss
various characteristics of datacenter traffic control including management
schemes, transmission control, traffic shaping, prioritization, load balancing,
multipathing, and traffic scheduling. Next, we point to several open challenges
as well as new and interesting networking paradigms. At the end of this paper,
we briefly review inter-datacenter networks that connect geographically
dispersed datacenters which have been receiving increasing attention recently
and pose interesting and novel research problems.Comment: Accepted for Publication in IEEE Communications Surveys and Tutorial
Philosophical Aspects of Quantum Information Theory
Quantum information theory represents a rich subject of discussion for those
interested in the philosphical and foundational issues surrounding quantum
mechanics for a simple reason: one can cast its central concerns in terms of a
long-familiar question: How does the quantum world differ from the classical
one? Moreover, deployment of the concepts of information and computation in
novel contexts hints at new (or better) means of understanding quantum
mechanics, and perhaps even invites re-assessment of traditional material
conceptions of the basic nature of the physical world. In this paper I review
some of these philosophical aspects of quantum information theory, begining
with an elementary survey of the theory, seeking to highlight some of the
principles and heuristics involved. We move on to a discussion of the nature
and definition of quantum information and deploy the findings in discussing the
puzzles surrounding teleportation. The final two sections discuss,
respectively, what one might learn from the development of quantum computation
(both about the nature of quantum systems and about the nature of computation)
and consider the impact of quantum information theory on the traditional
foundational questions of quantum mechanics (treating of the views of
Zeilinger, Bub and Fuchs, amongst others).Comment: LaTeX; 55pp; 3 figs. Forthcoming in Rickles (ed.) The Ashgate
Companion to the New Philosophy of Physic
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