A New DS/DPSK Underwater Acoustic Communication System

For DS/DPSK, carrier synchronization is not necessary in the receiver end, it outperforms DS/PSK systems respect to anti-frequency shift and anti-phase-jitter ability in phase changing shallow water channels, thus is considered as a robust modulation scheme in shallow water mid- and long-range acoustic communications. Traditional M-ary DSSS systems adopt difference of spread sequence, at the receiver end, differential demodulation is carried out first, and then de-spread process is performed, this method results in degradation of anti-noise performance as spreading gain was not utilized during demodulation stage. A novel differential direct sequence spread spectrum system, in which receiving bit decision was made based on sign of peak value of multiplication result of in-phase and quadrature-phase channel cross-correlation functions, is proposed in this paper. This new method is suitable for use in M-ary DSSS systems. The superior performance of this new method compared to traditional differential M-ary DSSS system in Rayleigh fading and phase fluctuating channels was valid via computer simulation.