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1
Content available Synchronization system for underwater acoustic communications using in shallow waters
Schmidt Jan H., Schmidt Aleksander M.
Vibrations in Physical Systems
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2023
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Vol. 34, nr 1
art. no. 2023102
EN
A reliable synchronization system of the transmitted data frame has a significant impact on the efficiency of the underwater communication system. This applies in particular to communication systems dedicated to work in shallow waters, where the phenomenon of multipath permanently occurs. To overcome these difficulties, the concept of a synchronization system consisting of two broadband signals of opposite monotonicity was presented. The method of receiving these signals has been described in detail. The stochastic channel model with Rician fading and the Watermark simulator was used to test the efficiency of the synchronization system in the underwater multipath channel.
2
Content available Erratum: A new direct-sequence spread spectrum signal detection method for underwater acoustic communications in shallow-water channel (DOI: 10.21008/j.0860-6897.2021.1.06)
Kochańska Iwona
Vibrations in Physical Systems
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2022
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Vol. 33, nr 1
art. no. 2022114
3
Content available Underwater acoustic communication system using broadband signal with hyperbolically modulated frequency
Schmidt Jan H., Schmidt Aleksander M.
Vibrations in Physical Systems
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2021
|
Vol. 32, nr 1
art. no. 2021116
EN
The implementation of reliable acoustic underwater communication in shallow waters is a scientific and engineering challenge, mainly due to the permanent occurrence of the multipath phenomenon. The article presents the concept of a transmission system using a broadband signal with hyperbolically modulated frequency (HFM) to transmit data symbols and synchronize data frames. The simulation tests were carried out in channels with Rician fading, reflecting the short- and medium-range shallow water channels. The simulation also took into account the presence of additive Gaussian noise in the channel on the functioning of the receiver. The obtained results prove the high reliability of the underwater communication system based on broadband HFM signals.
4
Content available A new direct-sequence spread spectrum signal detection method for underwater acoustic communications in shallow-water channel
Kochańska Iwona
Vibrations in Physical Systems
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2021
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Vol. 32, nr 1
art. no. 2021106
EN
Direct-Sequence Spread Spectrum (DSSS) is one of the modulation and coding techniques used in Underwater Acoustic Communication (UAC) systems for reliable data transmision even at low signal levels. However, in a shallow water channel, there is a strong multipath propagation which causes a phase fluctuation of the received signal, affecting the performance of the spread-spectrum system. The article presents a differential method for DSSS signal detection. It is based on the calculation of the correlation coefficient of adjacent segments of signal at the output of filter matched to the spreading sequence used in the transmitter. A positive value of the correlation coefficient means that a given modulation symbol carries the same information bit as the previous one; a negative value means that the opposite bit has been transmitted. The reliability of the proposed method has been compared to classical method of DSSS signal detection, which consists in detecting the information directly from the signal at the output of the matched filter. Simulation and measurement tests of underwater acoustic communications in strong multipath propagation conditions have shown that the proposed method allows obtaining lower values of the DSSS transmission Bit Error Rate (BER) than the classical detection technique while maintaining the same data transmission rate.
5
Content available Simulation of direct-sequence spread spectrum data transmission system for reliable underwater acoustic communications
Kochańska Iwona, Schmidt Jan H.
Vibrations in Physical Systems
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2019
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Vol. 30, nr 1
art. no. 2019108
EN
Underwater acoustic communication (UAC) system designers tend to transmit as much information as possible, per unit of time, at as low as possible error rate. It is a particularly difficult task in a shallow underwater channel in which the signal suffers from strong time dispersion due to multipath propagation and refraction phenomena. The direct-sequence spread spectrum technique (DSSS) applied successfully in the latest standards of wireless communications, gives the chance of reliable data transmission with an acceptable error rate in a shallow underwater channel. It utilizes pseudo-random sequences to modulate data signals, and thus increases the transmitted signal resilience against the inter symbol interference (ISI) caused by multipath propagation. This paper presents the results of simulation tests of DSSS data transmission with the use of different UAC channel models using binary spreading sequences.
6
Content available Performance of coherent modulation scheme used in acoustic underwater communication system
Schmidt Jan H., Schmidt Aleksander M., Kochańska Iwona
Vibrations in Physical Systems
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2019
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Vol. 30, nr 1
art. no. 2019135
EN
The development of an acoustic underwater communication system for shallow waters is still a big scientific and construction challenge. Currently, non-coherent modulations in combination with strong channel coding are used to achieve reliable communication with low rate in such a channel. To obtain transmission with a higher transmission rate, it is required to use coherent modulation. This paper presents the assumptions of such a transmission system and the results of data transmission carried out by this system in the channel with the Rician fading, which reflects the short range shallow water channel. A digital version of the carrier phase modulation known as Phase-Shift Keying was selected for simulation.
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