4,618 research outputs found
Introduction to Random Signals and Noise
Random signals and noise are present in many engineering systems and networks. Signal processing techniques allow engineers to distinguish between useful signals in audio, video or communication equipment, and interference, which disturbs the desired signal. With a strong mathematical grounding, this text provides a clear introduction to the fundamentals of stochastic processes and their practical applications to random signals and noise. With worked examples, problems, and detailed appendices, Introduction to Random Signals and Noise gives the reader the knowledge to design optimum systems for effectively coping with unwanted signals.\ud
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Key features:\ud
• Considers a wide range of signals and noise, including analogue, discrete-time and bandpass signals in both time and frequency domains.\ud
• Analyses the basics of digital signal detection using matched filtering, signal space representation and correlation receiver.\ud
• Examines optimal filtering methods and their consequences.\ud
• Presents a detailed discussion of the topic of Poisson processed and shot noise.\u
Species distribution models
Species distribution models are a group of methods often used to estimate
consequences of global change, to assess ecological status and for other ecological
applications. The main idea behind species distribution models is that the
geographical distributions of species can, to a large part, be explained by
environmental factors and that species distributions therefore can be predicted in
time or space. For robust and reliable applications, models need to be based on
sound ecological principles, predictions need to be as accurate as possible, and
model uncertainties need to be understood.
Two approaches are available for modelling entire species communities: (1) each
species can be modelled individually and independently of other species or (2)
community information can be incorporated into the models. The first study in this
thesis compares these two modelling approaches for predicting phytoplankton
assemblages in lakes. The results showed that predictive accuracy was higher when
species were modelled individually. The results also showed that phytoplankton can
be used for model-based assessment of ecological status. This finding is important
because phytoplankton is required for assessing the ecological status of European
water bodies according to the European Water Framework Directive.
Dispersal barriers in the landscape or limited dispersal ability of species might be a
reason for species being absent from suitable habitats, and these factors might
therefore affect model accuracy. The second study in this thesis examines the
influence of dispersal and the spatial configuration of ecosystems on prediction
accuracy of benthic invertebrate and phytoplankton distribution and assemblage
composition. The results showed only a minor influence of spatial configuration and
no effect of flight ability of invertebrates on model accuracy. However, the models
used may partly account for dispersal constraints, since dispersal-related factors, such
as lake surface area, are included as predictor variables. The result also showed that
composition of littoral invertebrate assemblages was easier to predict at sites located
in well-connected lake systems, possibly because the relatively unstable littoral zone
necessitates a need for species to re-colonize disturbed habitats from source
populations
Linear MMSE-Optimal Turbo Equalization Using Context Trees
Formulations of the turbo equalization approach to iterative equalization and
decoding vary greatly when channel knowledge is either partially or completely
unknown. Maximum aposteriori probability (MAP) and minimum mean square error
(MMSE) approaches leverage channel knowledge to make explicit use of soft
information (priors over the transmitted data bits) in a manner that is
distinctly nonlinear, appearing either in a trellis formulation (MAP) or inside
an inverted matrix (MMSE). To date, nearly all adaptive turbo equalization
methods either estimate the channel or use a direct adaptation equalizer in
which estimates of the transmitted data are formed from an expressly linear
function of the received data and soft information, with this latter
formulation being most common. We study a class of direct adaptation turbo
equalizers that are both adaptive and nonlinear functions of the soft
information from the decoder. We introduce piecewise linear models based on
context trees that can adaptively approximate the nonlinear dependence of the
equalizer on the soft information such that it can choose both the partition
regions as well as the locally linear equalizer coefficients in each region
independently, with computational complexity that remains of the order of a
traditional direct adaptive linear equalizer. This approach is guaranteed to
asymptotically achieve the performance of the best piecewise linear equalizer
and we quantify the MSE performance of the resulting algorithm and the
convergence of its MSE to that of the linear minimum MSE estimator as the depth
of the context tree and the data length increase.Comment: Submitted to the IEEE Transactions on Signal Processin
Adaptive Quantizers for Estimation
In this paper, adaptive estimation based on noisy quantized observations is
studied. A low complexity adaptive algorithm using a quantizer with adjustable
input gain and offset is presented. Three possible scalar models for the
parameter to be estimated are considered: constant, Wiener process and Wiener
process with deterministic drift. After showing that the algorithm is
asymptotically unbiased for estimating a constant, it is shown, in the three
cases, that the asymptotic mean squared error depends on the Fisher information
for the quantized measurements. It is also shown that the loss of performance
due to quantization depends approximately on the ratio of the Fisher
information for quantized and continuous measurements. At the end of the paper
the theoretical results are validated through simulation under two different
classes of noise, generalized Gaussian noise and Student's-t noise
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