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1
Content available 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.
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 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.
4
Content available Underwater navigation system based on Doppler shift – measurements and error estimations
Ostrowski Zawisza, Salamon Roman, Kochańska Iwona, Marszal Jacek
Polish Maritime Research
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2020
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nr 1
180--187
EN
A new acoustic navigation system was developed to determine the position and speed of moving underwater objects such as divers and underwater vehicles. The path of an object and its speed were determined by the Doppler shifts of acoustic signals emitted by a transmitter placed on the object and received by four hydrophones installed at the periphery of the monitored body of water. The position and speed measurements were affected by errors mainly caused by acoustic reflections (returns) from the water body boundaries and surface reverberations. This paper discusses the source of the disturbances with the results of a simulation test and experimental measurements. It was demonstrated that the magnitude of the errors could be acceptable in most of the potential applications of the acoustic navigation system.
5
Content available Shallow Water Experiment of OFDM Underwater Acoustic Communications
Kochańska Iwona, Schmidt Jan H., Marszal Jacek
Archives of Acoustics
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2020
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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.
6
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.
7
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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