Potential of vertical line array beamforming in underwater acoustic communications

S. Ijaz ssiddiqui@ualg.pt, A.J. Silva asilva@ualg.pt and S.M. Jesus sjesus@ualg.pt
Institute for Systems and Robotics, University of Algarve
Campus de Gambelas, PT-8005-139 Faro, Portugal

Comments: download pdf file.
Ref.: X Encontro de Tecnologia em Acústica Submarina (ETAS), Rio de Janeiro, Brasil, Novembro 2011.

One of the most active research topics nowadays is to design effective signal processing techniques for underwater communications. This interest is magnified by the challenges due to uncontrollable conditions such as temperature, bathymetry and geometric changes like source and array depth variations. The attainability of even modest data rates is still a challenge due to these variations. This work addresses the use of vertical line array beamforming for the underwater communication system. The purpose of using a beamformer in this work is to seperate the different arriving paths from the transmitter to the receiver which is motivated by the fact that in real environment the arriving paths are merged into each other and it is not possible to separate them in time. In this work, the delay and sum beamformer is used, which applies different delays to each hydrophone of the vertical line array and sums the resulting output. Each of this delay is a function of angle of arrival and depth of the hydrophone. The objective of a beamformer is to apply the opposite delays to each element of the vertical line array to guarantee coherent summation of the wavefront in a particular direction. Some simulated as well as real data results are presented in this paper to show the performance of the beamformer. These beamformer results are also compared with the Doppler results to characterize different arrivals and correspond these arrivals to the Doppler variations to show that each arrival is affected by the environmental variations in a different way, resulting in different amount of Doppler.