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Virtual acoustic barriers for underwater protection (VAB)

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Publications

Arrival-based equalizer for underwater communication systems
Publication . Siddiqui, Salman Ijaz; Silva, António João Freitas Gomes da
One of the challenges in the present underwater acoustic communication systems is to combat the underwater channel e ects which results in time and frequency spreading of the transmitted signal. The time spreading is caused by the multipath e ect while the frequency spreading is due to the time variability of the channel. The main purpose of this work is to address these problems and propose a possible solution to minimize these e ects and to improve the performance of the underwater communication system. The passive Time Reversal (pTR) equalizer has been used in underwater communications because of its time focusing property which minimizes the time spreading e ect of the underwater channel. In order to compensate for the frequency spreading e ect, an improved version of pTR was proposed in the literature, called Frequency shift passive time reversal (FSpTR). In order to understand the e ects of geometric variations on the acoustic signals, a Doppler based analysis technique, called Time Windowed Doppler Spectrum (TWDS), is proposed in this work. The principle of TWDS is to analyze the temporal variations of the Doppler spectrum of di erent arrivals received at a hydrophone. The results show that each arrival is a ected in a di erent manner by the same environmental variation. In this dissertation, an arrival-based equalizer is proposed to compensate for the environmental variations on each arrival. Due to complex multipath structure of the underwater channel, the arrivals are merged into one another in time and it is very di cult to separate them. The beamforming technique is used, in this work, to separate di erent wavefronts on the basis of angle of arrival. The arrival-based equalizer compensates for the environmental variations on each arrival separately using the FSpTR equalizer. The proposed equalizer is tested with the real data and the results shows that the proposed approach outperforms the conventional FSpTR equalizer and provides a mean MSE gain up to 3.5 dB.
TRA - Transmit Receive Array (project plan version 2)
Publication . Zabel, F.; Martins, C.; Jesus, S. M.; Silva, A.
This report describes an update to the project plan for the development of a Transmit Receive Array (TRA). This system is under development for the Underwater Acoustic Barriers (UAB) project which aims at studying, developing and testing in the field the concept of building an underwater acoustic barrier for detecting intruders in a given area.
Underwater acoustic barrier 2007 UAB'07 Part A: the Hopavagen bay
Publication . Jesus, S. M.; Silva, A.; Zabel, F.; Martins, C.
This report describes the data acquired during the UAB’07 experiment. Part A describes the data set acquired at the Hopav°agen Bay in Norway, from 11 to 13 September 2007.
TRA - Transmit Receive Array (project plan)
Publication . Zabel, F.; Martins, C.; Jesus, S. M.; Silva, A.
This report describes a project plan for the development of a Transmit Receive Array (TRA). This system is under development for the Underwater Acoustic Barriers (UAB) project which aims at studying, developing and testing in the field the concept of building an underwater acoustic barrier for detecting intruders in a given area.
RBR thermistors array for AOB2
Publication . Zabel, F.; Martins, C.
This report describes an electronic circuit board for interfacing the RBR thermistor chain manufactured by Richard Bracker Research, Ontario (Canada), with the Acoustic Oceanographic Buoy (version 2) - AOB2. The interface consists on a set of bridge amplifiers and associated electronics for converting the NTC thermistor signals into temperature related values in the data acquisition CPU control of the AOB2. With this board the temperature measured along the RBR thermistor chain array can be monitored on real time together with the acoustic data via the wireless lan network to which the AOB2 is associated.

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Funding agency

Fundação para a Ciência e a Tecnologia

Funding programme

POCI

Funding Award Number

POCI/MAR/59008/2004

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