Choice of Acoustics Signals Family in Multi-Users Environment
Résumé
In an underwater acoustical context, our application concerns a system immersed, with Nt transmitters and Nr slowly moving receivers. The objective is that all receivers detect the transmitted signals, to estimate the time of arrival (TOA) and then to make possible the location with several TOA (more than 3). To use the CDMA (Code Division Multiple Access) modulation, specially adapted to our problem, we have to choose a method to generate a number Ns of broad-band signals. This study is devoted to the selection of Nt signals among the Ns. The aim is to choose the most distinctly detectable ones. Firstly, in a no Doppler context, the criterion of signals selection is based on a ratio between maximum of auto-correlation and cross-correlation. Secondly, in 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. This paper will then highlight the interest of the criteria (correlation, ambiguity function) in the choice of the most appropriate signals in function of the multi-users context.