Covert underwater communications with multiband OFDM

We consider the use of orthogonal frequency division multiplexing (OFDM) for covert acoustic telemetry. To reduce the complexity of the receiver we use a multiband approach, modulating each band by OFDM. The system has been tested at sea in a highly time-varying environment. A total bandwidth of 3.6 kHz was divided in 16 subbands. Data rates of 4.2 and 78 bit/s were adopted over ranges up to 52 km. At 78 bit/s, communication is successful at SNRs down to -8 dB, whereas the lower rate allows data transfer at SNRs down to at least -16 dB.