Beam coding with spread spectrum orthogonal gold codes in underwater acoustic systems
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In this study, the applicability of beam coding approaches enabling coded transmission with direct sequence spread spectrum (DSSS) signals to multiple high resolution beams in underwater acoustic systems is investigated. Performance of (DSSS) signals for beam coding application is theoretically analyzed and experimentally proved. Instead of conventional (DSSS) parameters maximal length sequence and binary phase shift keying (BPSK) modulation, gold code sequences are more appropriate for multi-user applications due to their better cross-correlation function and minimum shift keying (MSK) modulation is more appropriate for constant amplitude signals due to its phase continuity. Beam coding experiments were carried out with 511 gold chips sequences with Minimum Shift Keying (MSK) modulation to spread over the frequency range of 70 - 90 kHz. The results of these experiments indicate that each coded signal can be separately detectable after signal processing in Matlab. And this shows that the beam coding approach is implementable in underwater acoustic systems.