The paper describes the Dual Channel Acoustic Communication Protocol (DCAP) and the results of its experimental trials. This open protocol has been developed as an extension of the SWiGacoustic standard proposed by the SWiG Working Group considering requirements and use cases. It enables networking capabilities, simultaneous low and high rate data transfer among acoustic nodes, and frequency division multiple access to the underwater channel. First, the protocol specification and the details of its implementation are described. Then, the methodology for the feasibility testing is presented, followed by the experimental trials at sea in two different environments: confined and open water. The results achieved show the feasibility of using this protocol to allow a network composed of acoustic nodes to simultaneously use low and high rate channels to exchange heterogeneous data through TDMA and FDMA.

In recent years, underwater communications have seen a growing interest pushed by marine research, oceanography, marine commercial operations, offshore oil industry and defense applications. Generally, underwater communications employ audio signals which can propagate relatively far but are also significantly affected by Doppler distortions. In fact, physical properties of the water and spatial changes due to tides, currents and waves can cause channel variations or unwanted movements of the transmitter or receiver. This study shows how to compensate for the Doppler effect in transmission employing the JANUS standard, a popular modulation scheme for underwater communication. Differently form previous work, we use the pseudo-random symbols of the JANUS preamble to measure and compensate for Doppler distortions without changing the standard. The proposed method has been tested both on the Watermark simulator and real in-field experiments. Results show that the proposed technique allows to correctly receive over 90 % of the packets even with severe Doppler, compensating relative speeds up to 5 m/s.

We present an innovative smartphone-centric tracking system for indoor and outdoor environments, based on the joint utilization of dead-reckoning and computer vision (CV) techniques. The system is explicitly designed for visually impaired people (although it could be easily generalized to other users) and it is built under the assumption that special reference signals, such as painted lines, colored tapes or tactile pavings are deployed in the environment for guiding visually impaired users along pre-defined paths. Thanks to highly optimized software, we are able to execute the CV and sensor-fusion algorithms in run-time on low power hardware such as a normal smartphone, precisely tracking the users movements.