A performance study of the high-speed, high-frequency acoustic uplink of the HERMES underwater acoustic modem

HERMES is an asymmetrical underwater acoustic modem operating in two separate frequency bands. The high data rate uplink operates between 262 kHz and 375 kHz. The downlink is designed for command-and-control and uses a lower frequency band (62-76 kHz) operated at the same source level but at a lower data rate. The acoustic uplink is capable of achieving data rates of 87768 bits-per-second (bps) in challenging environment such as ports, in the presence of heavy boat traffic. The experimental results acquired over the past year indicate that the high bit-rate uplink of HERMES can operate at this peak data rate at a range of 180 meters, a practical range for many port operations. A unique aspect of this acoustic communication system is the equalization technique, which combines multiple estimations of the underwater acoustic channels into a soft decision error correction process. This technique leads to a significant drop in the bit error rate at the sole expense of processing power.