Multi-frequency shift key and differential phase shift key for acoustic modem

Abstract

An underwater acoustic modem has been developed for autonomous underwater vehicles that is robust and low cost. It uses a single TI320c31 DSP chip to transmit packets of multi-frequency orthogonal chirp pulses to overcome noise and multi-path interference. It is robust and can be operated in a chirp multi-frequency shift key (CMFSK) or chirp differential phase shift key (CDPSK) mode. The MFSK mode is more robust but lower in baud rate (2000 baud) compared to the DPSK (4000 baud).