Design of SIMO <i>M</i>-QAM System for Ultrasonic Communications on Shallow Waters

In this work, we present a transmission system that uses single-carrier modulation MQAM for UAC in the ultrasonic band. It exploits the diversity that four hydrophones provide at reception in a SIMO 1×4 configuration and also includes, for each stream, a PLL for synchronization and a turbo-equalization subsystem, with FSE and DFE filters, adaptive by means of LMS algorithm, both of which are driven by an LDPC decoder decisions. The paper describes the system design and analyze its performances on trials carried out on shallow waters of the Mediterranean sea. Achievable data rates exceeding 200 kb/s between links of transmission distances longer than 200 m are obtained with a satisfactory low BER.