Petr Sysel

Goertzel algorithm generalized to non-integer multiples of fundamental frequency

The article deals with the Goertzel algorithm, used to establish the modulus and phase of harmonic components of a signal. The advantages of the Goertzel approach over the DFT and the FFT in cases of a few harmonics of interest are highlighted, with the article providing deeper and more accurate analysis than can be found in the literature, including the memory complexity. But the main emphasis is placed on the generalization of the Goertzel algorithm, which allows us to use it also for frequencies which are not integer multiples of the fundamental frequency. Such an algorithm is derived at the cost of negligibly increasing the computational and memory complexity.

Φ-OTDR signal amplification

Phase-sensitive optical time-domain reectometry (Φ-OTDR) seems to be the most appropriate solution for acoustic vibration along standard optical fiber detection. In general the sensing system measures phase changes of the received Rayleigh back-scattered signal in the fiber. Since the back-scattered signal intensity is decreased about tens of decibels in comparison to the forward propagating pulse power level, the received signal power level is very low. That is why the main limiting parameter of the system is the power level of the back-scattered signal, which limits maximum achievable distance. For long reach sensing it is necessary to create high power optical pulses with short time-duration. Direct pulse amplification by erbium doped fiber amplifier (EDFA) is an issue because of the pulses low repetition rate. We have designed and verified a simple method using a holding beam for amplifying of pulses with low repetition rate by standard telecommunication EDFA booster instead of deployment of an expensive optical shutter. A second CW laser with a different wavelength for EDFA stabilization is used in our setup. Because a pulse losses its energy during propagation in the fiber and with longer distances by 1st order Raman amplifier (RA). In telecommunications this amplifier is used to compensate for fiber losses. The second setup uses remote amplification by remotely pumped erbium doped fiber (EDF) placed after a few tens of kilometers of sensing fiber. A pump laser is placed in the transmitter part of the system from where EDF is pumped. In this paper, we present an overview of few techniques for Φ-ODTR signals amplification and their verification by measurement.

Wiener filtering with spectrum estimation by wavelet transformation

Current methods used to improve the signal-to-noise ratio mainly employ Wiener filtering, or methods derived from it, such as spectral subtraction. All these methods assume that it is possible to determine or at least to estimate noise spectral characteristics. As can be derived, the estimation by the periodogram is not exact, but it contains a disturbance. Averaging the power spectra offers better results but the properties are simultaneously downgraded by a non-stationary disturbance. That is why the paper deals with the improvement of the power spectral density (PSD) estimation. To achieve this we use the method of thresholding wavelet-transform coefficients, which we apply to each periodogram separately. Then the resultant estimation is used for the Wiener filter. The differences between the estimations obtained by the periodogram, by averaging and by this new method are shown. When we use the wavelet transformation, a marked improvement in suppressing the disturbing signal appears. As a result, we obtain a good noise reduction while preserving a good response to changes in the nature of the disturbing signal.

Filterbank modulation techniques and its utilization in ADSL systems

The multicarrier modulations (MCM) became widely used and have been applied to wire and wireless transmission systems in recent years. This modulation techniques enable a near-perfect utilization of the provided frequency band on metallic cables and they also eliminate multipath propagation effect in terrestrial transmission. Mainly used implementations of MCM are Discrete MultiTone (DMT) and Orthogonal Frequency Division Multiplexing (OFDM). These approaches have also disadvantages, which have led to seeking new approaches to the implementation of the MCM modulation scheme. One of them is the Filtered MultiTone Modulation (FMT). In the article, the channel equalization in half-overlapped and non-overlapped FMT modulation will be compared.

Enhanced estimation of power spectral density of noise using the wavelet transform

In practice, different methods for enhancing speech hidden in noise are used but none of the available methods is universal; it is always designed for only a certain type of interference that is to be suppressed. Since enhancing speech masked in noise is of fundamental significance for further speech signal processing (subsequent recognition of speaker or type of language, compression, processing for transmission or storing, etc.), it is necessary to find a reliable method that would work even under considerable interference and will be modifiable for different types of interference and noise. The methods known to date can basically be divided into two large groups: single-channel methods and multi-channel methods. The basic problem of these methods lies in a rapid and precise method for estimating noise, on which the quality of enhancement method depends. If the noise is of stationary or quasi-stationary nature, its determination brings further difficulties. A method is proposed in the article for enhancing the estimation of power spectral density of noise using the wavelet transform.

Single-channel noise suppression by wavelets in spectral domain

The paper describes the design of a new single-channel method for speech enhancement that employs the wavelet transform. Signal decomposition is currently performed in the time domain while noise is removed on individual decomposition levels using thresholding techniques. Here the wavelet transform is applied in the spectral domain. Used as the basis is the method of spectral subtraction, which is suitable for real-time implementation because of its simplicity. The greatest problem in the spectral subtraction method is a trustworthy noise estimate, in particular when non-stationary noise is concerned. Using the wavelet transform we can achieve a more accurate power spectral density also of noise that is non-stationary. Listening tests and SNR measurements yield satisfactory results in comparison with earlier reported experience.

Comparison of interferometry based and polarization based sensing systems for use in fiber infrastructure protection

Almost all data transmissions over long distances are transmitted through optical fibers. Fiber infrastructure is therefore very important and is necessary to protect it against fiber cuts caused e.g. by digging activity. Many network operators seeking appropriate solution for self protecting infrastructure system. We performed comparative measurement of the polarization based sensing system and the interferometry based sensing system to determine the sensitivity and accuracy of both systems. The results confirmed theoretical assumptions that both systems are suitable for strain measurement and the interferometry based sensing systems are more sensitive.

Control of digital audio signal processing over communication networks

This paper deals with the design of a protocol for the control of digital audio signal processing over communication networks, primarily for TCP/IP networks, and its multi-platform parser. The application of this protocol in embedded audio processing units represents a modern approach to remote-controlled real-time processing of digital audio signals. The aim is to have the possibility to control audio signal processing in distributed processing networks over very long distances, e.g. via the Internet.