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Performance of the Direct Sequence Spread Spectrum Underwater Acoustic Communication System with Differential Detection in Strong Multipath Propagation Conditions

Schmidt Jan H., Kochańska Iwona, Schmidt Aleksander M.

Archives of Acoustics

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2024

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Vol. 49, nr 1

129--140

EN

The underwater acoustic communication (UAC) operating in very shallow-water should ensure reliable transmission in conditions of strong multipath propagation, significantly disturbing the received signal. One of the techniques to achieve this goal is the direct sequence spread spectrum (DSSS) technique, which consists in binary phase shift keying (BPSK) according to a pseudo-random spreading sequence. This paper describes the DSSS data transmission tests in the simulation and experimental environment, using different types of pseudo-noise sequences: m-sequences and Kasami codes of the order 6 and 8. The transmitted signals are of different bandwidth and the detection at the receiver side was performed using two detection methods: non-differential and differential. The performed experiments allowed to draw important conclusions for the designing of a physical layer of the shallow-water UAC system. Both, m-sequences and Kasami codes allow to achieve a similar bit error rate, which at best was less than 10−3. At the same time, the 6th order sequences are not long enough to achieve an acceptable BER under strong multipath conditions. In the case of transmission of wideband signals the differential detection algorithm allows to achieve a significantly better BER (less than 10−2) than nondifferential one (BER not less than 10−1). In the case of narrowband signals the simulation tests have shown that the non-differential algorithm gives a better BER, but experimental tests under conditions of strong multipath propagation did not confirm it. The differential algorithm allowed to achieve a BER less than 10−2 in experimental tests, while the second algorithm allowed to obtain, at best, a BER less than 10−1. In addition, two indicators have been proposed for a rough assessment which of the detection algorithms under current propagation conditions in the channel will allow to obtain a better BER.

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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.

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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

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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

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.