Sea Technology

MAY 2018

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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www.sea-technology.com May 2018 | ST 19 Full Duplex Enabled Acoustic modems generally use a single transducer for both transmitting and receiving, making full duplex impossible. It has not been reasonable or necessary to employ separate collocated transmit and receive trans- ducers because, with current technology half-duplex communications, the receiver would be saturated by the very strong transmission signal. QinetiQ North America (QNA) and its partner Optimal Systems Laboratory (OSL) have developed DOLPHIN Comms, a patented method using analog cancellation that eliminates receiver satura- tion. The result is that DOLPHIN Comms enables full-du- plex continuous underwater acoustic communications with collocated transmit and receive transducers. DOLPHIN Comms addresses the receiver saturation problem by using a secondary transmission path to ac- tively and adaptively cancel the local transmission at the receiver. For undersea communication, active cancella- tion must provide a minimum of 40 dB of analog can- cellation from the transmitter (including distortion prod- ucts) to enable full-duplex communication. In testing, DOLPHIN Comms has demonstrated more than 80 dB of analog cancellation. The DOLPHIN Comms technology has shown that it is capable of in-band, full-duplex com- munication on a wide range of frequencies. DOLPHIN Comms consists of a source with power amplifier and transmission transducer, along with a col- located receiving transducer and receiving system. The receiver is coupled to another, lower-powered transmit- ter. A feed-forward signal is applied to cancel the out- bound signal at the receiver at the input to the low-noise amplifier (LNA), preserving dynamic range at the receiv- er. This method has been implemented for both contin- uous active monostatic sonar and full-duplex acoustic communication. Full-duplex, in-band acoustic communication is pos- sible when there is sufficient dynamic range in the re- ceiving transducer and receiving electronics to permit detection and demodulation of the desired signal in the presence of the strong interference from the collocated transmission source. Digital cancellation and physical (Top) How full duplex preserves dynamic range of return- ing signals. (Bottom left) DOLPHIN receive rate versus conventional receive rates. (Bottom right) Data throughput improvements for UUV case study.

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