中文摘要：

分析了水声通信中最佳频率的选取,提出了低载波频率条件下,通过频率映射,用一对IFFT/FFT运算直接将待发序列调制到载频上的OFDM水声通信基带传输实现方法,该方法可避免发射机的载频调制、接收机的解调及载波同步,简化了发射接收机结构。对该方法进行了理论分析、仿真试验及湖试。湖试结果为：误码率小于10^-4,5 km传输数据率9 kbps,该结果超过了国际上公认的水声通信距离×数据率=40 km·kbps的标准。试验结果表明该方法适合中近程高速水声通信。

英文摘要：

Aim. In our opinion, the simplification of base-band 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 evenly-distributed 12 000 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. 012 8 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.