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Block transmissions are commonly used in underwater acoustic communications due to the large delay spread of the underlying channels. In this paper, we propose a novel jamming protocol based on the half-duplex nature of the underwater transceivers and the block-based transmission structure, taking advantage of the large propagation delays of underwater acoustic channels to create interference at the...
Studying on ocean ambient noise is important for understanding noise generation and propagation for designing sonar processing systems. Based on the reciprocity of the sound field, a model of distant shipping noise in range dependent environments is described in this paper. The complex pressures are calculated using a parabolic equation (PE) model. The properties of the shipping noise over a deep...
Forward scattering is a special phenomenon for bi-static sonars, and it has received much attention in recent years because it can provide a lot of useful information for estimations. In this paper, two kinds of speed estimation method are proposed for forward scattering. Very simple geometrical principles are used in the two methods, and the complex acoustic field is not needed to be calculated when...
When an object crosses the source-receiver line, a weak acoustic field aberration would be generated. However, it is often overwhelmed by strong direct blast. A lake experiment with a vertical receiver array spanning along water column was designed and conducted, with a 10 kHz pulse. The interested signal was the aberration caused by the forward scattering of a submerged object. The acoustic field...
Variable Gain Amplifier (VGA) is a crucial part of GPS receiver, because the amplitude of RF signal changes greatly in transport. So a VGA is needed to fit the signal changing. This paper presents a VGA design based on the Gilbert unit. Implemented in a 0.18um CMOS process, the circuit achieved a gain range about 20dB from 18.39dB to 38.54dB, and reached a GBW=250MHz at 38db. The total current is...
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