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- Experimental demonstration of a single acoustic vector sensor for JANUS performance enhancementPublication . Bozzi, Fabricio; Jesus, SergioThis study shows the underwater communication performance using an acoustic pressure-gradient vector sensor. Combining the estimated particle velocity channels with the acoustic pressure results in a cardioid-like beam steered output, which is used to improve the signal-to-noise ratio. A shallow-water field experiment was carried out using a single vector sensor as a receiver and a ship-suspended sound source, transmitting the frequency-hopped JANUS modulated signal at several ranges and directions. Bit error rate analysis demonstrates how performance can be enhanced through vector sensor channel combining. Firstly, by relating the error with beam pattern varying the azimuth steering angle. Second, by relating the error with transmitting stations, where individual channels of the vector sensor can be compared. Besides such findings, this study also presents tools for better understanding the directional characteristic, such as the design factor to combine the particle velocity to the pressure sensor and azigrams. Finally, results show that the JANUS bit error rate can be reduced up to five percent by combining the vector sensor components compared to the pressure sensor.
- Vector hydrophone passive time reversal for underwater acoustic communicationsPublication . Bozzi, Fabricio; Jesus, SergioThe use of vector hydrophones as a receiver for underwater communications has been the subject of research since such device is a compact option to pressure-only arrays. A vector hydrophone, usually called acoustic vector sensor, is a device that measures pressure and particle velocity components. This paper investigates a method to combine those channels based on passive time-reversal (PTR). Simulation and experimental data are used to quantify communication performance, comparing vector hydrophones to pressure-only arrays. The analyzed acoustic scenario consists of a shallow-water area (about 100 m), where a vector hydrophone array receives communication signals from a bottom moored source. Simulations help in the understanding of diversity by analyzing spectral characteristics of vector hydrophone channels and the PTR q-function. While in simulation, the benefits of PTR using particle velocity channels are perceptible seen by exploring diversity, communication performance with experimental data is degraded due to time-varying. Finally, the achieved performance using a single or a small array of vector hydrophones enforces its benefits for communication enhancement.
- Vector sensor steering-dependent performance in an underwater acoustic communication field experimentPublication . Bozzi, Fabricio; Jesus, SergioThis paper shows the performance resulting from combining vector sensor directional components in an underwater acoustic communication experiment. The objective is to relate performance with transmission direction and range. Receiver structures based on beamforming and passive time-reversal are tested in order to quantify and compare the steerability impact of vector sensor directional components. A shallow water experiment is carried out with a bottom fixed two-axis pressure-gradient vector sensor. A ship suspended acoustic source transmits coherent modulated communication signals at various ranges and from several directions. Results show that one vector sensor can provide an up to 10 times smaller error bit rate than a pressure sensor, favoring communication robustness without size penalty.