Vladimir Sebesta

The new PAPR reduction approach in MC-CDMA

This paper describes a new PAPR (peak to average power ratio) reduction approach in MC-CDMA (multicarrier code division multiple access) system (in so called M-modification). The spreading sequence introduces coherence among subcarriers. This is used for chip position formatting to PAPR minimization. The optimizations methods are used to get best chip interleaving sequence (namely genetic algorithm (GA) and ant colony optimization (ACO)). BER simulation in AWGN (additive white Gaussian noise) channel with clipping is presented to evaluate efficiency of this concept

Interleaving Optimization in OFDM PAPR Reduction

One of approaches in the Peak to Average Power Ratio (PAPR) reduction methods for Orthogonal Frequency Division Multiplex (OFDM) is multiple signal representation (MSR) technique. This article presents the improvement of MSR technique where multiple signal representations are produced by different interleavers. The interleavers used in this approach are optimized and integrated with phase rotation (realized as element-by-element multiplying). The simulation for two-branch classical and optimized MSR is introduced in the article. The improvement in complementary cumulative distribution function of(CCDF) PAPR is presented.

The Modified Empirical Mode Decomposition Method For Analysing The Cyclical Behavior Of Time Series.

This paper is devoted to the analysis of time series using the Empirical Mode Decomposition (EMD) method. This method decomposes the analyzed time series into a small set of narrow-band components (modes) that fully represent the original time series. The modified EMD method that eliminates excessive changes of individual mode periods is proposed and evaluated on one example application of industrial production data. In contrast to other decomposition methods, like the singular value decomposition, the empirical mode decomposition can describe the time-variation of the period of individual components.

Estimating a spectral correlation function and its errors owing to inexact frequencies

This paper is devoted to estimating a spectral correlation function using DFT. The examined signal is a simple DSB-SC signal. The aim of the paper is to analytically describe events connected with nonstandard relations between signal frequency parameters and sampling frequency. They manifest by descending the spectral correlation function modulus. Validity of the analytical description was verified using computer simulations for deviations of carrier frequency, cyclic frequency and both frequencies and variable number of the sliding DFT windows. Analysis of the errors is presented. An imperfection of the analytical relations is mostly insignificant. Founded equations are simple and allow judge consequences of the frequency faultiness without simulations.

Chaotic spreading sequences

This paper is devoted to spreading sequence generators based on a discrete-time chaos. Estimates of mean values of the spreading sequences and mean square values of the autocorrelation sequence are presented and discussed for selected cases.

Error of the signal cyclic component period estimation using the AR model

This paper deals with a method for the estimation of the signal cyclic components period using an autoregressive model. The properties of the method are explored and quantified in the case of its application to short sample size signals. A number of computer experiments has been performed using the harmonic signal corrupted by noise and the autoregressive model of the second order. The results of the experiments are represented in the graphical form. It could be noticed that the mean value of the errors could result to significant values while the variance of the error is generally almost negligible.

An one-to-one integer-number map closed to the continuous pattern

This paper is devoted to the one-to-one integer-number maps derived from the piecewise linear maps. Such digital maps usually produce several periodic sequences. The sequences can be concatenated to the long one. After that the new map can be easy assigned to the long sequence. Such map is generally characterized by local deviations from original shape of the map. In this paper, optimized concatenation with the suppressed deviations is proposed and shown. An integer-number sequence can be transformed to the binary sequence. The proposed concatenated maps were applied onto generating binary spreading sequences for the asynchronous DS/CDMA system. Good correlation properties of these sequences were verified.

Data sequences generation by integer mapping

Sequences generation in radio engineering can be realized by means of digit memory. Its advantage is obtaining a great number of different sequences. In mathematical point of view it is repeatable digit mapping application. The paper is dedicated to mappings classification, sequence properties of different classes and proposed classification application.