A novel M-ary differential underwater acoustic direct sequence spread spectrum communication system

Direct sequence spread spectrum (DSSS) provides a robust solution for shallow water acoustic communications. DSSS uses a code sequence to spread the symbols at the transmitter; the coded sequence is then modulated using phase-shift-keying (DS/PSK) or differential phase-shift-keying (DS/DPSK), [1][2] where the information data is carried by the phase of the transmitted symbols or by the relative phase of two adjacent symbols, respectively. The DS/PSK system uses coherent receivers, while the DS/DPSK system uses differential receivers. Differential receivers have lower computation complexity and are insensitive to dynamic-channel-induced phase fluctuation and thus are well suited for applications where autonomy, adaptability, and longlife battery operation are desirable.