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Wyświetlanie 1-15 z 18
Tytuł:
Action-reaction based synthesis of acoustic wavefield equations
Autorzy:
Lasota, H.
Powiązania:
https://bibliotekanauki.pl/articles/331802.pdf
Data publikacji:
2011
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
The analysis of acoustic fields is usually based on the well-known mathematics of second order partial differential equations called wave equations. The author explores the duality and symmetry of linear fluid mechanics and develops two distinct equations of acoustics on the basis of a causal approach to local small-scale phenomena. Wavefields that are solutions of these equations have different composition, the spherical pressure wave being only a specific components of one of them. A new perspective on the phenomena, presented in this paper, endeavours to establish the right equilibrium between mathematical formalism and physical phenomenology in the perception of acoustic wavefields.
Źródło:
Hydroacoustics; 2011, 14; 111-118
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Source-related wavefields in fluids and dielectrics: A new way of thinking about medium dynamics
Autorzy:
Lasota, H.
Powiązania:
https://bibliotekanauki.pl/articles/331782.pdf
Data publikacji:
2013
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Acoustic and electromagnetic wave phenomena may seem to have a proper formal representation in field theory dating from the 19th century, founded on the mathematics of complex functions. This paper shows, however, that when replacing the classical spectrum-domain approach related to the assumption of harmonic timeform of signals, with a time-domain approach imposing no restriction as to the class of time evolution of source and field signals, it is possible to perform such a description of physical effects and their local, causality-driven mechanisms, that results in new revelations as to the role of both the physical medium and the wave source in initiating and conveying phenomena, otherwise perfectly familiar, that carry energy and preserve signal waveform. It appears that causality and locality are a core of dynamic linear phenomena in physical continua, leading to the creation of doubly-dynamic states that are observed, at the approach, in “frozen” conditions.
Źródło:
Hydroacoustics; 2013, 16; 145-158
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Impulse acoustic waves: dynamic conditions of unperturbed propagation
Autorzy:
Lasota, H.
Powiązania:
https://bibliotekanauki.pl/articles/332254.pdf
Data publikacji:
1999
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Secondary radiation from the wave front is calculated in the paper with the use of generalised function approach. The Dirac delta impulse ls used as a waveform for both the plane wave and the spherical pressure wave. The results have been obtained analytically thanks to particularly "friendly" features of the operation of convolution with the delta distribution. No approximations have been needed and both solutions are of awaited simple form, i.e.: the original wave displaced forwards - with the proper time delay. Dynamic equilibrium between the elastic and the kinetic aspects of mechanic energy is the only condition of undisturbed propagation of the wave. Every inhomogeneity of the medium reached by the wave breaks the equilibrium. giving birth to a new, scattered wave with features depending on boundary conditions related to the inhomogeneity. The paper gives formal mathematical proof to Fresnel intuitive explanation of the mechanism of forward-only wave propagation with no backward effect.
Źródło:
Hydroacoustics; 1999, 2; 301-306
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of ofdm technique to underwater acoustic data transmission
Autorzy:
Kochańska, I.
Lasota, H.
Powiązania:
https://bibliotekanauki.pl/articles/331798.pdf
Data publikacji:
2011
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Performances of underwater acoustic communication (UAC) digital systems are strongly related to specific transmission properties of the underwater channel. Depending on the characteristics of the channel, an architecture and modulation techniques are usually implemented that are known as reliable solutions for data transmission in difficult radio channels. The OFDM technique seems to be the most promising nowadays. The parameters of the physical layer and data link layer of ISO/OSI model are adapted to the needs of underwater communications, so as to best protect the signal from distortions and interferences typical for the underwater environment. This paper compares the performance of UAC and wireless telecommunications systems working in channels of vary different transmission parameters. Based on these parameters, some physical and link layer configurations of OFDM data transmission systems are proposed for implementation in a laboratory model and testing at a lake.
Źródło:
Hydroacoustics; 2011, 14; 91-98
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Transmission parameters of underwater communication channels
Autorzy:
Lasota, H.
Kochańska, I.
Powiązania:
https://bibliotekanauki.pl/articles/331804.pdf
Data publikacji:
2011
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
The underwater environment is tough and demanding as a communication channel for ultrasonic signals. The channel transmission characteristics in marine and inland waters depend much on local bathymetry and changing weather conditions. The architecture and performance of a reliable underwater acoustic communication (UAC) system should allow real-time adaptation of its transmission parameters to a large variety of possible channel characteristics. The paper presents an adaptation procedure based on the WSS-US statistical model developed for wireless telecommunication systems. The channel is there characterized by measurements of instantaneous channel impulse response being then a basis for estimation of the channel statistical characteristics and extraction of related parameters in the phase of communication handshake, and next used in the adaptive design of digital communication system transmission settings recorded at the physical and link layers of the communication protocol.
Źródło:
Hydroacoustics; 2011, 14; 119-126
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Measurements of transmission properties of acoustic communication channels
Autorzy:
Kochańska, I.
Lasota, H.
Powiązania:
https://bibliotekanauki.pl/articles/331858.pdf
Data publikacji:
2012
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Tough transmission properties of shallow water acoustic channels (SWAC) highly limit the use of underwater acoustic communication (UAC) systems. An adaptive matching of modulation and signaling schemes to instantaneous channel conditions is needed for reliable data communications. This creates, however, unique challenges for designers when compared to radio transmission systems. When communication system elements are in move, the accuracy of both the measurements of channel impulse responses and estimates of transmission characteristics is strongly limited, due to rapid variations of the channel performance. This paper describes communication tests of a model of the orthogonal frequency division multiplexing (OFDM) data transmission system. developed by the authors. The measurement procedures and signal processing algorithms were, first, tested in reverberant air-acoustic channels available in the laboratory, and, next, verified in natural conditions in a lake. The air acoustics trials prove to be effective and methodically correct.
Źródło:
Hydroacoustics; 2012, 15; 91-98
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of maximum-length sequences to impulse response measurement of hydroacoustic communications systems
Autorzy:
Mazurek, R.
Lasota, H.
Powiązania:
https://bibliotekanauki.pl/articles/332528.pdf
Data publikacji:
2007
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
There is a growing interest in digital transmission of telemetry data on ultrasonic waves. The dependence of signal attenuation on squared frequency, specific to the hy-droacoustic systems, induces problems that do not exist in monochromatic, narrowband radio communications systems. For adapting the transmission parameters to current propagation conditions, a precise knowledge of instantaneous changes of channel performances is needed. Simulating and testing of broadband communications techniques require robust, reliable and efficient method of impulse response measurements in natural exploitation conditions. The paper presents the MLS (Maximum-Length Sequence) correlation method applied to impulse response measurements of electroacoustic transducers as elements of communication chain.
Źródło:
Hydroacoustics; 2007, 10; 123-130
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Modelowanie i pomiary nagłośnienia audytorium
Modelling and measurements of public address system
Autorzy:
Lasota, H.
Mazurek, R.
Powiązania:
https://bibliotekanauki.pl/articles/153774.pdf
Data publikacji:
2008
Wydawca:
Stowarzyszenie Inżynierów i Techników Mechaników Polskich
Tematy:
systemy nagłośnieniowe
kanał komunikacyjny
odpowiedź impulsowa kanału
metoda MLS
zrozumiałość mowy
public address systems
communication channel
channel impulse response
MLS technique
speech intelligibility
Opis:
Uwaga projektantów systemów nagłośnieniowych zogniskowana jest na tzw. akustyce pomieszczenia, w którym realizowany jest przekaz słowny. Zjawiska pogłosowe związane z geometrią sali audytoryjnej, wynikające z wielokrotnych odbić fali dźwiękowej uznawane są za dominujące. Artykuł podejmuje niedoceniany problem wpływu liczby i rozmieszczenia głośników w sali na jakość przekazu. Superpozycji sygnałów dochodzących do słuchacza z wielu źródeł towarzyszy zjawisko interferencji, które prowadzi do istotnej modyfikacji odbieranych sygnałów. Zniekształcenia wprowadzane przez system nagłaśniający zbadano przyjmując model systemowo-liniowy, w którym właściwości transmisyjne systemów komunikacji są określane funkcjami odpowiedzi impulsowych i funkcjami przenoszenia. Zaprezentowano wyniki symulacji i pomiarów, zwracając uwagę na wpływ, jaki zwielokrotnianie źródeł dźwięku ma na formanty - parametry fonemów istotne dla zrozumiałości mowy.
Public address systems are designed with attention focused on acoustic features of the auditory hall. Reverberation phenomena related to the hall geometry, coming from multiple reflections of the sound wave are taken for dominating ones. The paper undertakes the underestimated problem of the influence of the number and distribution of loudspeakers on the communication quality. Linear superposition of signals reaching the listener from numerous sources is accompanied by interference effects that lead to deep modification of received signals. Deformations introduced by public address system has been analyzed with the use of linear systems model in which transmission features of communication systems are characterized by impulse response functions and transfer functions. Some results of simulation and measurements has been presented, showing the influence of the use of multiple sound sources on formants - phoneme parameters important for speech intelligibility.
Źródło:
Pomiary Automatyka Kontrola; 2008, R. 54, nr 3, 3; 148-152
0032-4140
Pojawia się w:
Pomiary Automatyka Kontrola
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ultrawideband transmission in physical channels: a broadband interference view
Autorzy:
Lasota, H.
Kochańska, I.
Mazurek, R.
Powiązania:
https://bibliotekanauki.pl/articles/331525.pdf
Data publikacji:
2014
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
The superposition of multipath components (MPC) of an emitted wave, formed by reflections from limiting surfaces and obstacles in the propagation area, strongly affects communication signals. In the case of modern wideband systems, the effect should be seen as a broadband counterpart of classical interference which is the cause of fading in narrowband systems. This paper shows that in wideband communications, the time- and frequency-domain approach of the linear time-invariant (LTI) systems theory does not fully reveal the significance of channelinduced distortions. A survey of MPC interference phenomena is presented, with time-evolving impulse responses and space-dependent notransfer functions. Linear prediction technique based on the autoregressive model is successfully applied as a complementary tool for speech signal distortion analysis in public address systems.
Źródło:
Hydroacoustics; 2014, 17; 129-136
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Adaptive telecommunications modems techniques for use in underwater communication systems
Autorzy:
Budzińska, I.
Lasota, H.
Mazurek, R.
Powiązania:
https://bibliotekanauki.pl/articles/331551.pdf
Data publikacji:
2003
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
hydroacoustics
underwater communication systems
data transmission
Opis:
Underwater channel data transmission is one of telecommunications most difficult problems. One way to optimise the transmission may be by adapting transmission techniques used in telecommunications modems. The articles presents two ITU-T standards: V.34 and G.992.1, known as ADSL. The possibilities and limitations of these techniques for underwater communication systems are discussed. The ADSI standard using the DMT modulation seems to be the best.
Źródło:
Hydroacoustics; 2003, 6; 285-292
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Detection on broadband signals in the field of aperture and array systems
Autorzy:
Mazurek, R.
Lasota, H.
Budzińska, I.
Powiązania:
https://bibliotekanauki.pl/articles/332465.pdf
Data publikacji:
2003
Wydawca:
Polskie Towarzystwo Akustyczne
Tematy:
acoustics
broadband signals
array systems
Opis:
Antennas and antenna arrays in low band underwater systems introduce significant linear distortions that affect the detection of broadband signals. The article gives an analysis of the distortions using the space-time impulse response method. The signal received at different directions is subjected to two types of filtration, one matched to the transmitted signal and another one matched to the distorted signal. For the purpose of the simulation the Matlab software was used. Detection performance can be greatly enhanced, if receiver design takes account of the distortions.
Źródło:
Hydroacoustics; 2003, 6; 275-284
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
OFDM modulation and adaptive equalization for underwater communications
Autorzy:
Kochańska, I.
Lasota, H.
Salamon, R.
Powiązania:
https://bibliotekanauki.pl/articles/332731.pdf
Data publikacji:
2005
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Transmission performances of a shallow underwater channel are limited due to multiple reflections of sound waves off the bottom and water surface, and to the non-stationarity caused mainly by water surface movement. In traditional narrowband telecommunication modems complex Decision Feedback Equalizers are used for minimizing the influence of intersymbol interferences caused by multipath propagation of sound waves. The article proposes adapting OFDM modulation and adaptive equalization based on Kalman filtration techniques for use in underwater communications system. The OFDM modulation is used in wideband ADSL telecommunication modems. The Kalman filtration algorithm is used for time-varying processes identification. The techniques were tested in simulation environment with promising results.
Źródło:
Hydroacoustics; 2005, 8; 77-82
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Transmission properties of a shallow hydroacoustic channel
Autorzy:
Kochańska, I.
Lasota, H.
Mazurek, R.
Adamczyk, J.
Powiązania:
https://bibliotekanauki.pl/articles/332175.pdf
Data publikacji:
2004
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
Multiple acoustic wave reflections on environment boundaries significantly reduce transmission capacity of shallow hydroacoustic channels. The use of BNM channel model being among the results of the international research project PROSIM developed within the framework of the MAST-III initiative, allowed to calculate the channel impulse response functions and perform a simulation of a digital signal transmission. This article presents the results of test transmission of binary FSK and PSK signals in a sample channel.
Źródło:
Hydroacoustics; 2004, 7; 121-128
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Transmission of digital signals in a nonstationary hydroacoustic channel
Autorzy:
Kochańska, I.
Lasota, H.
Mazurek, R.
Adamczyk, J.
Powiązania:
https://bibliotekanauki.pl/articles/332179.pdf
Data publikacji:
2004
Wydawca:
Polskie Towarzystwo Akustyczne
Opis:
From the communication point of view, transmission performances of a hydroacoustic channel are strongly limited due to multiple reflections of sound waves on the bottom and water surface, and to the nonstationarity caused mainly by water surface movement. This article presents a model of channel transmission properties which introduces nonstationarity to the channel impulse responses by assuming random variability of arrival times and amplitudes of subsequent elements of the impulse response. Transmission properties of this kind of channel have been tested in a digital simulator, using binary PSK and FSK signals. The results indicate that transmission velocity in such channels is reduced.
Źródło:
Hydroacoustics; 2004, 7; 115-120
1642-1817
Pojawia się w:
Hydroacoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 18

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