Dual-Mode Modulation Based Research of Underwater Acoustic Modem

Nowadays, the construction and application of underwater acoustic (UWA) networks has received much focus in the research area of UWA communication. This paper constructed an underwater acoustic modem based on two types of spread-spectrum technique, frequency-hopping (FH) and direct sequence spread spectrum (DSSS), correspond to quaternary frequency shift keying (4FSK) and differential binary phase shift keying (DBPSK) modulation respectively. Automatic gain control algorithm, synchronous tracking, and channel coding and interleaving also were studied. A four-node multi-hop network was constructed using this underwater acoustic modem, and has been proved by several experiments in the pool and sea. The dual-mode acoustic modem may be used to build more complicated underwater acoustic communication network in the future.