Evaluation of direct-sequence spread-spectrum modulation technique for digital data transmission with ultrasound

In most cases, radio systems are inapplicable for establishing a communication link in liquids because of the strong attenuation of radio waves at high frequencies. Acoustic or ultrasound based communication systems are often a possible alternative. However, reflections at boundaries like the water surface, the seafloor, walls of liquid-filled basins etc. cause strong multipath propagation effects, which severely disturb the communication channel. In this paper, direct-sequence spread-spectrum (DSSS) modulation, which is well-known from modern mobile communication systems, has been adapted to ultrasound based data transmission in liquids to cope with the aforementioned problem. An ultrasound system for digital data transmission has been implemented and the proposed concept has been evaluated by means of measurements.