16,415 research outputs found
On Time-Variant Distortions in Multicarrier Transmission with Application to Frequency Offsets and Phase Noise
Phase noise and frequency offsets are due to their time-variant behavior one
of the most limiting disturbances in practical OFDM designs and therefore
intensively studied by many authors. In this paper we present a generalized
framework for the prediction of uncoded system performance in the presence of
time-variant distortions including the transmitter and receiver pulse shapes as
well as the channel. Therefore, unlike existing studies, our approach can be
employed for more general multicarrier schemes. To show the usefulness of our
approach, we apply the results to OFDM in the context of frequency offset and
Wiener phase noise, yielding improved bounds on the uncoded performance. In
particular, we obtain exact formulas for the averaged performance in AWGN and
time-invariant multipath channels.Comment: 10 pages (twocolumn), 5 figure
Quantization and Compressive Sensing
Quantization is an essential step in digitizing signals, and, therefore, an
indispensable component of any modern acquisition system. This book chapter
explores the interaction of quantization and compressive sensing and examines
practical quantization strategies for compressive acquisition systems.
Specifically, we first provide a brief overview of quantization and examine
fundamental performance bounds applicable to any quantization approach. Next,
we consider several forms of scalar quantizers, namely uniform, non-uniform,
and 1-bit. We provide performance bounds and fundamental analysis, as well as
practical quantizer designs and reconstruction algorithms that account for
quantization. Furthermore, we provide an overview of Sigma-Delta
() quantization in the compressed sensing context, and also
discuss implementation issues, recovery algorithms and performance bounds. As
we demonstrate, proper accounting for quantization and careful quantizer design
has significant impact in the performance of a compressive acquisition system.Comment: 35 pages, 20 figures, to appear in Springer book "Compressed Sensing
and Its Applications", 201
Billiards with polynomial mixing rates
While many dynamical systems of mechanical origin, in particular billiards,
are strongly chaotic -- enjoy exponential mixing, the rates of mixing in many
other models are slow (algebraic, or polynomial). The dynamics in the latter
are intermittent between regular and chaotic, which makes them particularly
interesting in physical studies. However, mathematical methods for the analysis
of systems with slow mixing rates were developed just recently and are still
difficult to apply to realistic models. Here we reduce those methods to a
practical scheme that allows us to obtain a nearly optimal bound on mixing
rates. We demonstrate how the method works by applying it to several classes of
chaotic billiards with slow mixing as well as discuss a few examples where the
method, in its present form, fails.Comment: 39pages, 11 figue
On optimum parameter modulation-estimation from a large deviations perspective
We consider the problem of jointly optimum modulation and estimation of a
real-valued random parameter, conveyed over an additive white Gaussian noise
(AWGN) channel, where the performance metric is the large deviations behavior
of the estimator, namely, the exponential decay rate (as a function of the
observation time) of the probability that the estimation error would exceed a
certain threshold. Our basic result is in providing an exact characterization
of the fastest achievable exponential decay rate, among all possible
modulator-estimator (transmitter-receiver) pairs, where the modulator is
limited only in the signal power, but not in bandwidth. This exponential rate
turns out to be given by the reliability function of the AWGN channel. We also
discuss several ways to achieve this optimum performance, and one of them is
based on quantization of the parameter, followed by optimum channel coding and
modulation, which gives rise to a separation-based transmitter, if one views
this setting from the perspective of joint source-channel coding. This is in
spite of the fact that, in general, when error exponents are considered, the
source-channel separation theorem does not hold true. We also discuss several
observations, modifications and extensions of this result in several
directions, including other channels, and the case of multidimensional
parameter vectors. One of our findings concerning the latter, is that there is
an abrupt threshold effect in the dimensionality of the parameter vector: below
a certain critical dimension, the probability of excess estimation error may
still decay exponentially, but beyond this value, it must converge to unity.Comment: 26 pages; Submitted to the IEEE Transactions on Information Theor
Model for Estimation of Bounds in Digital Coding of Seabed Images
This paper proposes the novel model for estimation of bounds in digital coding of images. Entropy coding of images is exploited to measure the useful information content of the data. The bit rate achieved by reversible compression using the rate-distortion theory approach takes into account the contribution of the observation noise and the intrinsic information of hypothetical noise-free image. Assuming the Laplacian probability density function of the quantizer input signal, SQNR gains are calculated for image predictive coding system with non-adaptive quantizer for white and correlated noise, respectively. The proposed model is evaluated on seabed images. However, model presented in this paper can be applied to any signal with Laplacian distribution
Power Spectrum Constraints from Spectral Distortions in the Cosmic Microwave Background
%The content of this replacement paper is identical to the original. %We have
attempted to fix the postscript so that it will print out on %a larger number
of printers. Using recent experimental limits on distortions from COBE
FIRAS, and the large lever-arm spanning the damping of sub-Jeans scale
fluctuations to the scale of the COBE DMR fluctuations, we set a constraint on
the slope of the primordial power spectrum . It is possible to analytically
calculate the contribution over the full range of scales and redshifts,
correctly taking into account fluctuation growth and damping as well as
thermalization processes. We find that the 95\% upper limit is weakly dependent
on cosmological parameters, e.g. and for
with marginally weaker constraints for in a flat
universe.Comment: 8pg, uuencoded-tarred (& hopefully more compatible!) postscript,
CfPA-TH-94-1
Linear Redshift Distortions and Power in the PSCz Survey
We present a state-of-the-art linear redshift distortion analysis of the
recently published IRAS Point Source Catalog Redshift Survey (PSCz). The
procedure involves linear compression into 4096 Karhunen-Loeve modes culled
from a potential pool of about 3 x 10^5 modes, followed by quadratic
compression into three separate power spectra, the galaxy-galaxy,
galaxy-velocity, and velocity-velocity power spectra. Least squares fitting to
the decorrelated power spectra yields a linear redshift distortion parameter
beta = Omega_m^0.6/b = 0.41(+0.13,-0.12).Comment: Minor changes to agree with accepted version. Slight changes to power
spectrum, including one more point added at large scales, from binning points
formerly discarded as too noisy. 5 pages, including 4 embedded PostScript
figures. Accepted for publication in MNRAS Letters (pink pages). Power
spectrum data available at http://casa.colorado.edu/~ajsh/pscz
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