Wyniki wyszukiwania - Biblioteka Nauki

1

Considerations of adaptive digital communiations in underwater acoustic channel

100%

Kochańska I.

Hydroacoustics

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2013

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tom Vol. 16

113--120

EN

Down-link communication (DLC) and air transportable communication (ATAC) buoys as well as autonomous underwater vehicles (AUV) use acoustic links for gathering oceanographic data from underwater monitoring systems. The underwater channel propagation conditions are diverse in nature and require a special adaptive approach to the communication system design. The article presents a methodology for the communication systems design, combining modern radio standards experience, and hardware equipment to design and test the adaptive underwater data transmission systems. The testbed experiments should be preceded by the test being carried out under laboratory conditions using the underwater channel impulse responses collected at numerous measurement sessions in different reservoirs.

2

Adaptive identification of time-varying impulse response of underwater acoustic communication channel

100%

Kochańska I.

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tom Vol. 18

87-94

EN

The transmission properties of underwater acoustic communication channel can change dynamically due to the movement of acoustic system transmitter and receiver or underwater objects reflecting transmitted signal. The time-varying impulse response measurement and estimation are necessary to match the physical layer of data transmission to instantaneous channel propagation conditions. Using the correlative measurement method, impulse response estimate can be obtained no more than the duration of the measurement sequence. The paper proposes a joint correlative measurement and adaptive filtration approach, applying the Kalman filter algorithm to increase the time-domain resolution of the time-varying impulse response estimation.

3

Analiza możliwości wykorzystania współczesnych metod transmisji danych w systemach łączności podwodnej

63%

Lasota H. , Kochańska I.

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tom Vol. 48, nr 9

53-56

PL

Postęp w telekomunikacji szerokopasmowej jest rezultatem rozwoju cyfrowych technik modulacji i kodowania, coraz lepiej wykorzystujących możliwości i przezwyciężających fizyczne ograniczenia przewodowych torów transmisyjnych i kanałów radiowych. Adaptacja metod transmisji danych do komunikacji podwodnej na falach akustycznych wymaga uwzględnienia specyficznych cech kanału hydroakustycznego, który łączy w sobie najtrudniejsze cechy kanałów telekomunikacyjnych. W celu pokazania możliwości wykorzystania w łączności podwodnej osiągnięć współczesnej telekomunikacji dokonano porównania istotnych własności kanałów radiowych, przewodowych i podwodnych. Wytypowano techniki modulacji stosowane w szybkich szerokopasmowych łączach telekomunikacyjnych, których aplikacja w łączności podwodnej wydaje się najbardziej uzasadniona.

EN

The progress in broadband telecommunications results from the development of digital modulation and coding techniques that are better and better matched to communication capabilities and physical limitations of cable and radio transmission channels. The adaptation of data transmission methods to underwater acoustic communications needs to consider specific features of hydroacoustic channels as they shear the most difficult features of telecommunication channels. A short comparison of radio, cable and underwater channels has been made for analysis of possibility of data transmission in underwater environment possibilities. Modulation techniques used in fast broadband telecommunication links, that seem to be suitable for underwater communications, has been indicated.

4

Stationary underwater channel experiment: Acoustic measurements and characteristics in the Bornholm area for model validations

63%

Nissen I. , Kochańska I.

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tom Vol. 19

285--296

EN

The underwater acoustical channel is time-variant, and even on small time scales there is often existing no ‘acoustical frozen ocean’. Popular is the use of WSSUS-channel transmission modeling (Wide-Sense Stationary Uncorrelated Scattering) for the stochastic description of bandpass signals in GSM mobile phones with moving participants; since this results in a halved number of model parameters. For underwater sound applications such as detection, navigation and communication this approach provides limited a-priori-knowledge for adaptive algorithms with moving cooperative participants. The FWG of the WTD71 is collecting phase-accurate channel measurements from different sea areas in different time and application scenarios, with moving and stationary communication nodes since 2001. This paper presents a SIMO experiment from 2010, with a high precision continuous observation period of eleven hours using two stationary bottom nodes, mostly uncoupled from the influence of surface waves and from the sea floor. Transmitter and receiver node with a distance of two nautical miles between them were stationary installed on the bottom in shallow watersin the Bornholm Basin of the Baltic Sea. The sound speed has been measured continuously in the water column with a moving measurement chain. The question for this experiment was: Is the WSSUS-property fulfilled in water, when participants communicate motionless with negligible current, bottom influence and movements of the surface? The answer is: No, not in this experiment.

5

Ultrawideband transmission in physical channels: a broadband interference view

51%

Lasota H. , Kochańska I. , Mazurek R.

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2014

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tom Vol. 17

129--136

EN

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.

6

Mutual Clutter Suppression Techniques for FM Sonars

45%

Marszal J. , Rudnicki M. , Jedel A. , Salamon R. , Kochańska I.

Archives of Acoustics

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2016

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tom Vol. 41, No. 4

721--729

EN

The article presents methods that help in the elimination of mutual clutter as well as the consequences of two FM sounding signal sonars operating in the same body of water and frequency band. An in-depth analysis of mutual clutter was carried out. The effects of sounding signal differentiation were determined, as was the Doppler effect on mutual clutter suppression. One of the methods analysed is of particular interest in a situation in which collaborating sonars are operating in opposite frequency modulation directions. This method is effective for both linear and hyperbolic frequency modulations. A formula was derived, identifying exactly how much quantities of clutter may be lessened. The work included comprehensive computer simulations and measurements as well as tests in real-life conditions.