Abstract. We address communications between Autonomous Underwater Vehicles (AUVs), Underwater Sensors (USs) and remote operators. We assume the use of acoustic waves. Due to the Doppler effect, the communication frequency depends on the relative motion between the participants. We are interested in the Ultra Low Frequency (ULF) range, from 0.3 to 3 kHz. We relate the Doppler effect to the half-power bandwidth, versus distance. Numeric simulations are conducted. We show that the Doppler shift is significant with respect to the half-power bandwidth in the ULF band, for long distance communications.

This paper is an extension of work originally presented and published in IEEE International Multidisciplinary Conference on Engineering Technology (IMCET). This work presents a design and implementation of a moving human tracking system with obstacle avoidance. The system scans the environment by using Kinect, a 3D sensor, and tracks the center of mass of a specific user by using Processing, an open source computer programming language. An Arduino microcontroller is used to drive motors enabling it to move towards the tracked user and avoid obstacles hampering the trajectory. The implemented system is tested under different lighting conditions and the performance is analyzed using several generated depth images.

We have developed a demodulator for low data rate, asynchronous frame, and narrow bandwidth underwater acoustic communication. We aim at operation under harsh conditions, ie, low signal-to-noise ratio, and across long distances.In this paper, we pay a special attention to the efficiency of mobility support.Mobility results into the Doppler effect, which, for a demodulator, makes the carrier frequency drift arbitrarily during attempts to decode frames. The chances of success are better when the demodulator can tune into the drifted carrier frequency. This can be achieved by trying a range of possible drifted carriers. We introduce the novel idea of normalized trajectory. Each normalized trajectory produces a unique Doppler shift pattern that can be applied to tune into a drifted carrier. We demonstrate that this improvement is theoretically sound. From a practical point of view, the search space is potentially reduced. The actual gain in performance is application-specific and depends on the actual sets of trajectory parameters that are considered. We introduce the concept of normalized trajectory, discuss its integration into the demodulator, and review the performance of the new design.Trans Emerging Tel Tech. 2019;30:e3712.wileyonlinelibrary.com/journal/ett

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