Marius Oltean

ECG statistical denoising in the wavelet domain

The paper presents a denoising algorithm particularly suited to ECG signals processing. The main stage of this algorithm consists in a MAP filtering in the wavelet domain. Its effectiveness relies on the qualities of the wavelet transform and of the statistical filter used. Tests made on ECG signals, in realistic conditions, showed very promising results. The noise is almost completely removed, while the useful waveforms are preserved.

On the time-frequency localization of the wavelet signals, with application to orthogonal modulations

Orthogonal modulations are powerful techniques for digital data transmission, very well suited to radio channels. They use orthogonal basis, whose elements will be the “subcarriers” used in transmission. Some advantages of the wavelet functions compared to the windowed complex exponentials used in Orthogonal Frequency Division Multiplexing (OFDM) are highlighted. Thus, theoretical proof that Daubechies wavelets have better time-frequency localization is provided, opening new paths towards modern orthogonal modulation approaches, based on wavelets.

Wavelet OFDM performance in frequency selective fading channels

The BER performance of a wavelet-based multi-carrier modulation scheme is investigated in this paper. The channel is considered both frequency-selective and time-variant. It is shown that the time-frequency localization of the wavelet carriers has a significant influence on the BER performance, especially at certain transmission scales.

Efficient Pulse Shaping and Robust Data Transmission Using Wavelets

Recent work has shown that the use of wavelets in a data transmission chain brings several advantages. Thus, the wavelet mothers and the associated scale functions can generate orthogonal basis that obey Nyquists first criterion and these basis can be used as pulse shaping waveforms instead of raised cosine filters. Furthermore, robust multicarrier data transmission can be performed using wavelet carriers instead of the classical sine waves proposed by OFDM. By associating these benefits, the road towards new powerful transmission techniques in data transmission systems is widely opened.

Errors per scale statistics for a wavelet OFDM transmission in flat fading channels

Wavelet-based Orthogonal Frequency Division Multiplexing (WOFDM) represents a modern orthogonal modulation technique. In WOFDM, the bits to be transmitted are split into multiple streams, which are simultaneously transmitted at different rates, using wavelet carriers. Every stream is mapped to a different transmission scale and is affected differently by the time-varying radio channel. This influence is studied in the present work by computing some errors per scale measures. These statistics show what are the best transmission scales in the flat, time-variant channel and open the path towards the coded WOFDM, where the coding rate can be adapted on a per scale basis.

A physical layer simulator for WiMAX in Rayleigh fading channel

WiMAX is a wireless technology which offers high data rate transmission in broadband. In this paper, the architecture of the WiMAX physical layer simulator is presented. The main blocks are implemented with the aid of the Matlab programming language and the bit error rate (BER) curves are presented in Rayleigh fading channel.

A physical layer simulator for WiMAX

A physical layer simulator for the WiMAX technology is presented in this paper. The simulator encompasses the main blocks that build the physical layer from IEEE 802.16e. It allows to understand some of the physical layer mechanisms and techniques employed in WiMAX and to simulate various transmission scenarios. BER results are presented for some distributed permutation schemes, with different digital modulations.

Vibration signals compression with Time-Frequency Adaptive Quantization

A novel quantization method, well suited to the case of vibration signal compression is introduced in this paper. This method, applied in the domain of the Discrete Cosine Transform, is called Time-Frequency Adaptive Quantization (TFAQ) and it efficiently allocates the coding bits based on the time-frequency properties of the vibration signals. The method is compared to other transform-based compression techniques. Experiments are carried on a rich database of vibration signals, issued by the plane engines, in various stages of the flight. The results prove the superiority of TFAQ versus the other tested methods, for the experimental data set we dispose on.

Map Filtering in the Diversity-Enhanced Wavelet Domain Applied to Ecg Signals Denoising

An effective denoising method for ECG signals affected by real sources of noise is proposed in this paper. The method is based on a maximum a-posteriori (MAP) filtering in the diversity-enhanced wavelet domain, under realistic a-priori assumptions regarding the statistical properties of the wavelet coefficients of the ECG signal. In order to evaluate the performance of the method, we studied the signal-to-noise ratio (SNR) improvement factor and the degree of the denoising influence on the automatic signal segmentation procedures. The method was tested in both synthetic and real noise conditions and it showed very promising results

Time-frequency localization as mother wavelet selecting criterion for wavelet modulation

Throughout recent years, the discrete wavelet transform (DWT) was used in communications for wavelet modulation (WM). One of its features is the mother wavelets (MW) used. An important number of MW were already proposed in the literature. We investigate in this paper the selection of the MW for the WM, on the basis of its time-frequency localization. We prove, with the aid of Balian-Low theorem, that wavelets have better time-frequency localization than the elements of the bases which are used for signal decomposition in other orthogonal modulation techniques, as, for example, in orthogonal frequency division multiplexing (OFDM). A procedure for the evaluation of the time-frequency localization of MW belonging to Daubechies family is proposed. This procedure is next compared against the WM transmission on different channel types, which reveal the best MW to be used. This advantage of the WM versus OFDM is highlighted by simulation results in fading channels.