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pp. 141-152, vol. 18, 2015
Zawisza Jacek Ostrowski
Gdansk University of Technology, Faculty of Electronics, Telecommunications and Informatics, Department of Marine Electronic Systems, Gdańsk, Poland
Key words: positioning system; Doppler shift; homodyne detection
Abstract: The article presents a method for solving major structural problems that occur in the receiver used in the multistatic Doppler system, aimed at determination of the trajectory and velocity of a moving target. In the system two transmitters emit acoustic continuous sinusoidal waves at different frequencies. The signals, scattered from a moving target are received by four hydrophones. Beside of the echoes, much larger signals coming directly from transmitters are recorded. It has been proved that in the presence of the direct high-amplitude signal, using currently available A/D converters, there is no possibility to detect the Doppler shift of small signals. The proposed approach is based on the homodyne frequency conversion of the received signals. Subsequently, the constant component and other unwanted products of the frequency conversion are filtered. The results of computer simulation have shown the effectiveness of the adopted design solution.
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