Wyniki wyszukiwania - Biblioteka Nauki

1

Shallow Water Experiment of OFDM Underwater Acoustic Communications

100%

Kochańska I. , Schmidt J. H. , Marszal J.

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2020

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tom Vol. 45, No. 1

11--18

EN

The large variability of communication properties of underwater acoustic channels, and especially the strongly varying instantaneous conditions in shallow waters, is a challenge for the designers of underwater acoustic communication (UAC) systems. The use of phase modulated signals does not allow reliable data transmission through such a tough communication channel. However, orthogonal frequency-division multiplexing (OFDM), being a multi-carrier amplitude and phase modulation technique applied successfully in the latest standards of wireless communications, gives the chance of reliable communication with an acceptable error rate. This paper describes communication tests conducted with the use of a laboratory model of an OFDM data transmission system in a shallow water environment in Wdzydze Lake.

2

Modulation-Mode Assignment in SVD-Aided Downlink Multiuser MIMO-OFDM Systems

88%

Aust S. , Ahrens A. , Benavente-Peces C. C.

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tom Vol. 57, No. 4

459-464

EN

Multicarrier transmission such as OFDM (orthogonal frequency division multiplexing) is an established technique for radio transmission systems and it can be considered as a promising approach for next generation wireless systems. However, in order to comply with the demand on increasing available data rates in particular in wireless technologies, systems with multiple transmit and receive antennas, also called MIMO (multiple-input multiple-output) systems, have become indispensable for future generations of wireless systems. Due to the strongly increasing demand in high-data rate transmission systems, frequency non-selective MIMO links have reached a state of maturity and frequency selective MIMO links are in the focus of interest. In this field, the combination of MIMO transmission and OFDM can be considered as an essential part of fulfilling the requirements of future generations of wireless systems. However, single-user scenarios have reached a state of maturity. By contrast multiple users' scenarios require substantial further research, where in comparison to ZF (zero-forcing) multiuser transmission techniques, the individual user's channel characteristics are taken into consideration in this contribution. The performed joint optimization of the number of activated MIMO layers and the number of transmitted bits per subcarrier shows that not necessarily all user-specific MIMO layers per subcarrier have to be activated in order to minimize the overall BER under the constraint of a given fixed data throughput.

3

Stealthy Information Transmission in the Terrestrial GMDSS Radiotelephone Communication

75%

Shishkin A. V. , Koshevoy V. M.

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tom Vol. 7, no. 4

541--548

EN

Audio watermarking (AW) technology is considered for stealthy information embedding directly into audio signal. Inherent in analog radiotelephone channel interferences against watermarks are analyzed. Robust encoding/decoding algorithms are presented and appropriate project of AW system named as Automatic Radio Telephone Identification System (ARTIS) is proposed. Experimental results for the practical VHF radio channel are presented. Relating on processing complexity the designed system enables imperceptibly transmit data on a rate up to 260 bit/sec in the standard VHF radio channel. ARTIS provides the full compatibility with the existing radio installation, and doesn’t require replacement of standard VHF transceivers and operational procedures. Besides, automatic identification the system may be used in the special applications, for example, under the threat of terrorist attack; generally contributes to navigation safety and information security.

4

Analiza jakości transmisji treści audio-wideo w symulowanym łączu telekomunikacyjnym z wykorzystaniem techniki OFDM

63%

Zamłyńska M. , Falkowski-Gilski P.

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tom nr 4

219--223

PL

Wdrożenie niezawodnego systemu komunikacji audio-wideo przynosi wiele korzyści. Z uwagi na fakt, że ilość dostępnego pasma stale się kurczy, badacze koncentrują się na nowatorskich metodach transmisji. Obecnie technika OFDM (Orthogonal Frequency Division Multiplexing) jest szeroko stosowana zarówno w mediach przewodowych, jak i bezprzewodowych. W pracy przedstawiono badania jakości QoS (Quality of Service) symulowanego łącza transmisji danych, przy zmiennych poziomach SNR (Signal-to-Noise Ratio) oraz BER (Bit Error Rate).

EN

Application of a reliable audio-video communication system brings many advantages. As the amount of available bandwidth continues to shrink, researchers focus on novel types of transmission. Nowadays, OFDM (Orthogonal Frequency Division Multiplexing) is widely utilized both in wired and wireless media. In this paper we investigate the QoS (Quality of Service) parameters of a simulated data transmission system, including SNR (Signal-to-Noise Ratio) and BER (Bit Error Rate).

5

Cooperative MIMO OFDM system based on Amplify and Forward Relay: Evaluation of ZF-SIC and MMSE-SIC equalization

63%

Rahman M. , Alam S. , Islam S. , Samy A. A. , Islam N. A.

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2018

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tom R. 94, nr 9

75--79

EN

In the world of wireless communication, cooperative communication is a modern and unprecedented approach which enables wireless nodes to transfer the information in a cooperative manner and finally to reach the destination without least possible deterioration. Orthogonal frequency division multiplexing (OFDM) can provide high data rate and better performance and a combination of OFDM and cooperative communication may push a wireless network forward to its next generation with enhanced reliability and efficiency. In this work, we develop a mathematical model for cooperative multiple input multiple output (MIMO) OFDM system. Results are achieved in the study to evaluate and compare bit error rate (BER) for different detection schemes. Based on the results it can be mentioned that the performance of cooperative MIMO-OFDM with space time block code (STBC) under amplify and forward (AF) relay for the MMSE-SIC detection scheme was found very satisfactory with improved signal to noise ratio (SNR).

PL

W artykule przedstawiono model matematyczny kooperacyjnej komunikacji bezprzewodowej wiele wejść, wiele wyjść (MIMO) z multipleksingiem i ortogonalnym podziałem częstotliwości (OFDM). Określono współczynnik BER (bit error rate) dla różnych metod detekcji. Najlepsze parametry otrzymano dla systemu STBC (space time block code).