AquaSeNT’s acoustic modem family employs orthogonal frequency division multiplexing (OFDM) technologies that are widely used in radio communication systems, for example, WiFi and 4G cellular networks. OFDM is a multicarrier technique: data is encoded on many sub-carrier frequencies, allowing information to be transmitted in parallel as opposed to the slower serial communication of traditional technology. The sub-carrier signals are mathematically orthogonal to each other: they are selected to minimize interference with adjacent frequencies, significantly improving the ability to cope with severe channel conditions including frequency selective fading due to multipath. Advanced error correction algorithms enhance the modem’s ability to achieve high performance communication.
The AquaSeNT OFDM acoustic modem, with its ability to send more data in reduced bandwidth, along with excellent performance in challenging acoustic environments, creates a platform for a networked communication system. The AquaSeNT networked OFDM acoustic modem adds an on-board processor with networking firmware and software. A flexible network framework enables customized protocols at many layers in the protocol stack. Users can build high performance, reliable underwater communication networks with protocols optimized specifically for their applications.
Both the OFDM acoustic modem and the OFDM networked acoustic modem operate in a 14-20 kHz bandwidth at 3.2 kbps, and have demonstrated excellent performance in challenging environments up to a range of 4km. They are designed to operate in standby mode to conserve power, and are optimized to receive and transmit signals while maximizing battery life. Users communicate with the modems during initial set up or testing via an RS232 connection using a PC-based terminal program after which the modem pair are ready for service. The AquaSeNT modem family is offered in a PVC housing rated to 200 meters, with options for deeper water housings.