Simplifying method of baseband transmission for OFDM underwater acoustic communication

Aim. In our opinion, the simplification of baseband transmission for OFDM (orthogonal frequency division multiplexing) underwater acoustic communication is both desirable and possible. In the full paper, we explain in some detail how to simplify it and also explain that simulation results and lake tests show preliminarily that the simplification is successful. In this abstract, we just add some pertinent remarks to listing the four topics of explanation. The first topic is: the selection of optimal frequency in underwater acoustic communication. The second topic is: the simplification of the traditional method of OFDM for underwater acoustic communication. In the second topic, Fig.2 shows the schematic on how to make the simplification; essentially the simplification makes unnecessary the following three things: (1) the carrier frequency modulation of transmitter, (2) demodulation of receiver, and (3) the carrier wave frequency synchronization of the receiver. The third topic is: simulation results. In this topic, we simulate the transmission of the evenlydistributed 12000 data with our method. The simulation results, shown in Fig.6 in the full paper, indicate preliminarily that, when signal to noise ratio is larger than 25 dB and when multipath spread delay is less then 0.0128 s, the bit error rate of the transmitter is less than 10^-2 without any correction. The fourth topic is: lake test results and their analysis. In this topic, we did the lake tests with the bit error rate of 10^-4. The lake test results, given in Fig.9, show that, when the transmission distance is 5 km, the data transmission ratio is 9.09 kbps. The lake test results are better than the internationally acknowledged standard of 40 km·kbps, as presented in Ref.8.