43,069 research outputs found
Capacity Bounds For Multi-User Channels With Feedback, Relaying and Cooperation
Recent developments in communications are driven by the goal of
achieving high data rates for wireless communication devices. To
achieve this goal, several new phenomena need to be investigated
from an information theoretic perspective. In this dissertation,
we focus on three of these phenomena: feedback, relaying and
cooperation. We study these phenomena for various multi-user
channels from an information theoretic point of view.
One of the aims of this dissertation is to study the performance
limits of simple wireless networks, for various forms of feedback
and cooperation. Consider an uplink communication system, where
several users wish to transmit independent data to a base-station.
If the base-station can send feedback to the users, one can expect
to achieve higher data-rates since feedback can enable cooperation
among the users. Another way to improve data-rates is to make use
of the broadcast nature of the wireless medium, where the users
can overhear each other's transmitted signals. This particular
phenomenon has garnered much attention lately, where users can
help in increasing each other's data-rates by utilizing the
overheard information. This overheard information can be
interpreted as a generalized form of feedback.
To take these several models of feedback and cooperation into
account, we study the two-user multiple access channel and the
two-user interference channel with generalized feedback. For all
these models, we derive new outer bounds on their capacity
regions. We specialize these results for noiseless feedback,
additive noisy feedback and user-cooperation models and show
strict improvements over the previously known bounds.
Next, we study state-dependent channels with rate-limited state
information to the receiver or to the transmitter. This
state-dependent channel models a practical situation of fading,
where the fade information is partially available to the receiver
or to the transmitter. We derive new bounds on the capacity of
such channels and obtain capacity results for a special sub-class
of such channels.
We study the effect of relaying by considering the parallel relay
network, also known as the diamond channel. The parallel relay
network considered in this dissertation comprises of a cascade of
a general broadcast channel to the relays and an orthogonal
multiple access channel from the relays to the receiver. We
characterize the capacity of the diamond channel, when the
broadcast channel is deterministic. We also study the diamond
channel with partially separated relays, and obtain capacity
results when the broadcast channel is either semi-deterministic or
physically degraded. Our results also demonstrate that feedback to
the relays can strictly increase the capacity of the diamond
channel.
In several sensor network applications, distributed lossless
compression of sources is of considerable interest. The presence
of adversarial nodes makes it important to design compression
schemes which serve the dual purpose of reliable source
transmission to legitimate nodes while minimizing the information
leakage to the adversarial nodes. Taking this constraint into
account, we consider information theoretic secrecy, where our aim
is to limit the information leakage to the eavesdropper. For this
purpose, we study a secure source coding problem with coded side
information from a helper to the legitimate user. We derive the
rate-equivocation region for this problem. We show that the helper
node serves the dual purpose of reducing the source transmission
rate and increasing the uncertainty at the adversarial node. Next,
we considered two different secure source coding models and
provide the corresponding rate-equivocation regions
Degraded Broadcast Diamond Channels with Non-Causal State Information at the Source
A state-dependent degraded broadcast diamond channel is studied where the
source-to-relays cut is modeled with two noiseless, finite-capacity digital
links with a degraded broadcasting structure, while the relays-to-destination
cut is a general multiple access channel controlled by a random state. It is
assumed that the source has non-causal channel state information and the relays
have no state information. Under this model, first, the capacity is
characterized for the case where the destination has state information, i.e.,
has access to the state sequence. It is demonstrated that in this case, a joint
message and state transmission scheme via binning is optimal. Next, the case
where the destination does not have state information, i.e., the case with
state information at the source only, is considered. For this scenario, lower
and upper bounds on the capacity are derived for the general discrete
memoryless model. Achievable rates are then computed for the case in which the
relays-to-destination cut is affected by an additive Gaussian state. Numerical
results are provided that illuminate the performance advantages that can be
accrued by leveraging non-causal state information at the source.Comment: Submitted to IEEE Transactions on Information Theory, Feb. 201
Asymmetric Information, Financial Intermediation and the Monetary Transmission Mechanism: A Critical Review
Macroeconomic models currently used by policy makers generally assume that the workings of financial markets can be fully summarised by financial prices, because the Modigliani and Miller (1958) theorem holds. This paper argues that these models are too limited in describing how monetary policy (and other) shocks are transmitted to the economy and points to new directions. The models are too limited because they disregard an information asymmetry between borrowers and lenders and the importance of financial intermediaries not only for individual depositors but the economy as a whole. Incorporating financial market interactions into macroeconomic models will enhance the understanding of the transmission mechanisms of monetary policy and other shocks.Financial intermediaries; credit channel; monetary transmission mechanism; open economies
Nonclassical Light Generation from III-V and Group-IV Solid-State Cavity Quantum Systems
In this chapter, we present the state-of-the-art in the generation of
nonclassical states of light using semiconductor cavity quantum electrodynamics
(QED) platforms. Our focus is on the photon blockade effects that enable the
generation of indistinguishable photon streams with high purity and efficiency.
Starting with the leading platform of InGaAs quantum dots in optical
nanocavities, we review the physics of a single quantum emitter strongly
coupled to a cavity. Furthermore, we propose a complete model for photon
blockade and tunneling in III-V quantum dot cavity QED systems. Turning toward
quantum emitters with small inhomogeneous broadening, we propose a direction
for novel experiments for nonclassical light generation based on group-IV
color-center systems. We present a model of a multi-emitter cavity QED
platform, which features richer dressed-states ladder structures, and show how
it can offer opportunities for studying new regimes of high-quality photon
blockade.Comment: 64 pages, 32 figures, to appear as Chapter 3 in Advances in Atomic
Molecular and Optical Physics, Vol. 6
The Credit Channel of Monetary Policy and Housing Markets: International Empirical Evidence
This paper tests for the presence of a credit channel (particularly a bank-lending sub-channel) for monetary policy in the housing market. We argue that the importance of this channel for investment in residential housing is highly dependent on the structural features, and particularly the efficiency and institutional organization, of housing finance. We employ a VAR methodology to analyse this issue with respect to the housing markets of four European countries (Finland, Germany, Norway and the United Kingdom), which differ greatly in terms of structural features. Our results are generally consistent with the existence of a broad credit channel, whereas the bank-lending channel seems to be operational only under certain conditions. More importantly, our results are consistent with previous analyses of housing market efficiency, which strongly suggests the existence of a clear relationship between the presence of a credit (bank lending) channel, the efficiency level of housing finance, and the type of institutions that are active in mortgage provision.monetary transmission; bank lending channel; house prices; vector autoregressions
Photonic architecture for scalable quantum information processing in NV-diamond
Physics and information are intimately connected, and the ultimate
information processing devices will be those that harness the principles of
quantum mechanics. Many physical systems have been identified as candidates for
quantum information processing, but none of them are immune from errors. The
challenge remains to find a path from the experiments of today to a reliable
and scalable quantum computer. Here, we develop an architecture based on a
simple module comprising an optical cavity containing a single
negatively-charged nitrogen vacancy centre in diamond. Modules are connected by
photons propagating in a fiber-optical network and collectively used to
generate a topological cluster state, a robust substrate for quantum
information processing. In principle, all processes in the architecture can be
deterministic, but current limitations lead to processes that are probabilistic
but heralded. We find that the architecture enables large-scale quantum
information processing with existing technology.Comment: 24 pages, 14 Figures. Comment welcom
Monetary policy and risk taking : [draft january 2013]
We assess the effects of monetary policy on bank risk to verify the existence of a risk-taking channel - monetary expansions inducing banks to assume more risk. We first present VAR evidence confirming that this channel exists and tends to concentrate on the bank funding side. Then, to rationalize this evidence we build a macro model where banks subject to runs endogenously choose their funding structure (deposits vs. capital) and risk level. A monetary expansion increases bank leverage and risk. In turn, higher bank risk in steady state increases asset price volatility and reduces equilibrium output
Energy-Efficient Communication over the Unsynchronized Gaussian Diamond Network
Communication networks are often designed and analyzed assuming tight
synchronization among nodes. However, in applications that require
communication in the energy-efficient regime of low signal-to-noise ratios,
establishing tight synchronization among nodes in the network can result in a
significant energy overhead. Motivated by a recent result showing that
near-optimal energy efficiency can be achieved over the AWGN channel without
requiring tight synchronization, we consider the question of whether the
potential gains of cooperative communication can be achieved in the absence of
synchronization. We focus on the symmetric Gaussian diamond network and
establish that cooperative-communication gains are indeed feasible even with
unsynchronized nodes. More precisely, we show that the capacity per unit energy
of the unsynchronized symmetric Gaussian diamond network is within a constant
factor of the capacity per unit energy of the corresponding synchronized
network. To this end, we propose a distributed relaying scheme that does not
require tight synchronization but nevertheless achieves most of the energy
gains of coherent combining.Comment: 20 pages, 4 figures, submitted to IEEE Transactions on Information
Theory, presented at IEEE ISIT 201
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