438 research outputs found
On Bures fidelity of displaced squeezed thermal states
Fidelity plays a key role in quantum information and communication theory.
Fidelity can be interpreted as the probability that a decoded message possesses
the same information content as the message prior to coding and transmission.
In this paper, we give a formula of Bures fidelity for displaced squeezed
thermal states directly by the displacement and squeezing parameters and
birefly discuss how the results can apply to quantum information theory.Comment: 10 pages with RevTex require
Book of abstracts first Benelux-Japan workshop on information and communication theory, Eindhoven, The Netherlands, September 3-5, 1989
The academic and industrial embrace of space-time methods
[Guest Editors introduction to: Special issue on space-time transmission, reception, coding and signal processing]
Every episode of the classic 1966–1969 television series Star Trek begins with Captain Kirk’s (played by William Shatner) famous words : “Space: The final frontier….” While space may not be the final frontier for the information and communication theory community, it is proving to be an important and fruitful one.
In the information theory community, the notion of space can be broadly defined as the simultaneous use of multiple, possibly coupled, channels. The notions of space–time and multiple-input multiple-output (MIMO) channels are therefore often used interchangeably. The connection between space and MIMO is most transparent when we view the multiple channels as created by two or more spatially separated antennas at a wireless transmitter or receiver.
A large component of the current interest in space–time methods can be attributed to discoveries in the late 1980s and early 1990s that a rich wireless scattering environment can be beneficial when multiple antennas are used on a point-to-point link. We now know that adding antennas in a rich environment provides proportional increases in point-to-point data rates, without extra transmitted power or bandwidth
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
Information Transfer and Regulation in a Model Ecosystem with Environmental Stochasticity
The concept of regulation in ecosystems has been given considerable attention in the ecological literature, but no formal treatment has been offered. This study proposes a rigorous definition of regulation which is derived from the mathematics of information and communication theory. A theoretical, mathematical equivalent of the definition is also offered which implies serious limitations as to the value of most traditional laboratory population studies and deterministic population models in understanding regulation in ecosystems. The empirical validity of this theoretical equivalence is tested through use of a competition model of two diatoms. Other observations concerning the relationship between environmental variability and regulation are also reported
Information content versus word length in random typing
Recently, it has been claimed that a linear relationship between a measure of
information content and word length is expected from word length optimization
and it has been shown that this linearity is supported by a strong correlation
between information content and word length in many languages (Piantadosi et
al. 2011, PNAS 108, 3825-3826). Here, we study in detail some connections
between this measure and standard information theory. The relationship between
the measure and word length is studied for the popular random typing process
where a text is constructed by pressing keys at random from a keyboard
containing letters and a space behaving as a word delimiter. Although this
random process does not optimize word lengths according to information content,
it exhibits a linear relationship between information content and word length.
The exact slope and intercept are presented for three major variants of the
random typing process. A strong correlation between information content and
word length can simply arise from the units making a word (e.g., letters) and
not necessarily from the interplay between a word and its context as proposed
by Piantadosi et al. In itself, the linear relation does not entail the results
of any optimization process
Wikileaks and the limits of protocol
In this chapter, I reflect on Wikileaks and its use of technology to achieve freedom in capitalist society. Wikileaks represents an avant-garde form of media (i.e. networked, cryptographic), with traditional democratic values: opposing power and seeking the truth. At times, http://wikileaks.org appears broken and half abandoned and at other times, it is clearly operating beyond the level of government efficiency and military intelligence. It has received both high acclaim and severe criticism from human rights organisations, the mainstream media and governments. It is a really existing threat to traditional forms of power and control yet, I suggest, it is fundamentally restrained by liberal ideology of freedom and democracy and the protocological limits of cybernetic capitalism
- …