Optimum Watermark Detection and Embedding in Digital Images

This work concentrates on the problem of watermarking of still images using the luminance component, through the use of spread spectrum techniques, both in space (direct sequence spread spectrum or DSSS) and frequency (frequency hopping or FH), following the guidelines of Delaigle et al. (1998). The system described is able to embed watermarks and recover them with zero probability of error. The problem is faced from a statistical detection point of view through the analysis of the density function of the image to be marked. A Cauchy model is found to be very accurate and some tests are performed in order to assess improved detection quality. The resulting system turns out to be easy to encrypt and very robust to filtering and JPEG compression.Peer ReviewedPostprint (published version

New semi-blind approach to optimize turbo decoding for a cauchy α-stable impulsive noise channel

Knowledge of the noise parameters that contaminate the signal sent is  very important for many communication systems. In this work, we propose a new method to estimate the dispersion parameter of a  symmetric α-stable impulse noise (SαS) of Cauchy, from the received signal only at the iterative decoder (turbo decoder). This method is based on the FLOS (Fractional Lower Order Statistics) and the probability that binds the received signal and the signal sent in BPSK modulation (Binary Phase Shift Keying). The results obtained, in terms of RMSE (Root Mean Square Error) and BER (Bit Error Rate) show the precision and the efficiency of our approach.Keywords: Cauchy impulse noise SαS, dispersion parameter, FLOS, RMSE, BER

Estimation of stability index for symmetric {\alpha}-stable distribution using quantile conditional variance ratios

The class of $\alpha$-stable distributions is widely used in various applications, especially for modelling heavy-tailed data. Although the $\alpha$-stable distributions have been used in practice for many years, new methods for identification, testing, and estimation are still being refined and new approaches are being proposed. The constant development of new statistical methods is related to the low efficiency of existing algorithms, especially when the underlying sample is small or the underlying distribution is close to Gaussian. In this paper we propose a new estimation algorithm for stability index, for samples from the symmetric $\alpha$-stable distribution. The proposed approach is based on quantile conditional variance ratio. We study the statistical properties of the proposed estimation procedure and show empirically that our methodology often outperforms other commonly used estimation algorithms. Moreover, we show that our statistic extracts unique sample characteristics that can be combined with other methods to refine existing methodologies via ensamble methods. Although our focus is set on the symmetric $\alpha$-stable case, we demonstrate that the considered statistic is insensitive to the skewness parameter change, so that our method could be also used in a more generic framework. For completeness, we also show how to apply our method on real data linked to plasma physics

Stochastic resonance in chua's circuit driven by alpha-stable noise

Thesis (Master)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2012Includes bibliographical references (leaves: 75-80)Text in English; Abstract: Turkish and Englishx, 80 leavesThe main aim of this thesis is to investigate the stochastic resonance (SR) in Chua's circuit driven by alpha-stable noise which has better approximation to a real-world signal than Gaussian distribution. SR is a phenomenon in which the response of a nonlinear system to a sub-threshold (weak) input signal is enhanced with the addition of an optimal amount of noise. There have been an increasing amount of applications based on SR in various fields. Almost all studies related to SR in chaotic systems assume that the noise is Gaussian, which leads researchers to investigate the cases in which the noise is non-Gaussian hence has infinite variance. In this thesis, the spectral power amplification which is used to quantify the SR has been evaluated through fractional lower order Wigner Ville distribution of the response of a system and analyzed for various parameters of alpha-stable noise. The results provide a visible SR effect in Chua’s circuit driven by symmetric and skewed-symmetric alpha-stable noise distributions. Furthermore, a series of simulations reveal that the mean residence time that is the average time spent by the trajectory in an attractor can vary depending on different alpha-stable noise parameters

Stabiilsete jaotuste parameetrite hindamine : magistritöö

http://www.ester.ee/record=b3612848*es