155 research outputs found
On the Capacity of Free-Space Optical Intensity Channels
New upper and lower bounds are presented on the capacity of the free-space
optical intensity channel. This channel is characterized by inputs that are
nonnegative (representing the transmitted optical intensity) and by outputs
that are corrupted by additive white Gaussian noise (because in free space the
disturbances arise from many independent sources). Due to battery and safety
reasons the inputs are simultaneously constrained in both their average and
peak power. For a fixed ratio of the average power to the peak power the
difference between the upper and the lower bounds tends to zero as the average
power tends to infinity, and the ratio of the upper and lower bounds tends to
one as the average power tends to zero. The case where only an average-power
constraint is imposed on the input is treated separately. In this case, the
difference of the upper and lower bound tends to 0 as the average power tends
to infinity, and their ratio tends to a constant as the power tends to zero.Comment: To be presented at ISIT 2008 in Toront
The compound channel capacity of a class of finite-state channels
A transmitter and receiver need to be designed to guarantee reliable communication on any channel belonging to a given family of finite-state channels defined over common finite input, output, and state alphabets. Both the transmitter and receiver are assumed to be ignorant of the channel over which transmission is carried out and also ignorant of its initial state. For this scenario we derive an expression for the highest achievable rate. As a special case we derive the compound channel capacity of a class of Gilbert-Elliott channels
Bose--Einstein Condensation in the Large Deviations Regime with Applications to Information System Models
We study the large deviations behavior of systems that admit a certain form
of a product distribution, which is frequently encountered both in Physics and
in various information system models. First, to fix ideas, we demonstrate a
simple calculation of the large deviations rate function for a single
constraint (event). Under certain conditions, the behavior of this function is
shown to exhibit an analogue of Bose--Einstein condensation (BEC). More
interestingly, we also study the large deviations rate function associated with
two constraints (and the extension to any number of constraints is conceptually
straightforward). The phase diagram of this rate function is shown to exhibit
as many as seven phases, and it suggests a two--dimensional generalization of
the notion of BEC (or more generally, a multi--dimensional BEC). While the
results are illustrated for a simple model, the underlying principles are
actually rather general. We also discuss several applications and implications
pertaining to information system models
Diode laser based light sources for biomedical applications
Diode lasers are by far the most efficient lasers currently available. With the ever-continuing improvement in diode laser technology, this type of laser has become increasingly attractive for a wide range of biomedical applications. Compared to the characteristics of competing laser systems, diode lasers simultaneously offer tunability, high-power emission and compact size at fairly low cost. Therefore, diode lasers are increasingly preferred in important applications, such as photocoagulation, optical coherence tomography, diffuse optical imaging, fluorescence lifetime imaging, and terahertz imaging. This review provides an overview of the latest development of diode laser technology and systems and their use within selected biomedical applications
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