Frequency-hopped frequency division multiplexed signaling for underwater acoustic communications between 60 and 90 kHz in ports and very shallow waters

The Hermes acoustic modem consists of a high-bit rate acoustic uplink designed to transmit high-resolution images and other information from an underwater platform located in ports and very shallow waters. This communication system is now equipped with an acoustic downlink for command-and-control purposes. This acoustic downlink uses a computationally efficient frequency-hopped, frequency division multiplexed modulation operating within the 62-89 kHz band. This paper covers the design and simulation of the acoustic downlink, with a focus on Doppler spread. The results show that, at a non-coded data rate of 5272 bits-per-second, with 9.31 ms of reverberation time and 1.5 Hz of Doppler spread, the acoustic downlink can achieve a bit-error-rate of 0.14% without any error coding at 120 m using a source level of 170 dB (re 1¿P8 at 1m).