Choice of acoustics signals family in multi-users environment

Abstract

Our application concerns a system immersed in an underwater acoustical context, with Nt transmitters and Nr slowly moving receivers. The objective is that all receivers detect the transmitted signals, in order to estimate the time of arrival (TOA) and then to facilitate the localization when several TOA (more than 3) are present. We have to choose a method to generate a number Ns of broad-band signals to use the Code Division Multiple Access (CDMA) modulation, specially adapted to our problem. This work is devoted to selecting Nt signals among the Ns available. The aim is to choose the most distinctly detectable ones. First, in a no Doppler context, the criterion of signals selection is based on a ratio between maximum of auto-correlation and cross-correlation. Second, in the presence of Doppler, we rely on Ambiguity Function which allows representing the correlation function to several frequency Doppler shifts. The choice of Nt signals is then based on ratio between maximum of auto-ambiguity and cross-ambiguity. In this paper we will highlight the relevance of the criteria (correlation, ambiguity function) in the choice of the most appropriate signals in function of the multi-users context.