A Differential Multiple Single Carrier Modulation Scheme for Underwater Acoustic Communications and Its Actual Evaluation Results This paper discusses actual evaluation results of a differential multiple single carrier (MSC) modulation scheme for underwater acoustic communications (UWACs). UWACs suffer from severe doublyselective channels and intercarrier interference due to nonuniform frequency offset. In addition, assuming image data communications, UWACs require improved frequency efficiency. To resolve these issues, this paper proposes a wireless transmission scheme that employs differential MSC modulation scheme. Next, this paper investigates the parameters for 8kbpsUWACs and 64kbpsUWACs aiming at wireless control of autonomous underwater vehicles and image data communications, respectively. Finally, two actual evaluation results in an acoustic experimental pool and an actual shallowsea environment confirm that the UWAC MODEMs have excellent performance on severe doublyselective channels.

Single Carrier Block Transmission Schemes for Acoustic Communications and Their Field Evaluation Results This paper proposes transmission technologies for acoustic communications in order to mitigate doublyselective environments. The single carrier block (SCB) transmission schemes using frequency domain equalization (FDE) are effective for frequency selectivity, but it suffers from performance degradation due to time selectivity. This paper proposes SCB transmission schemes for acoustic communications which introduce a frame format suitable for channel interpolation (CI), and employs cyclic delay diversity (CDD) in order to extend communication distance. In particular, the proposed schemes can mitigate tracking error caused by timevarying channels, owing to CI based on multiple estimated channel impulse responses (CIRs). Finally, it is confirmed that the proposed schemes of 8kbps have excellent performance in a delay spread of up to 10msec and a Doppler frequency of around 1Hz, on the basis of field evaluation results in terrestrial and shallow underwater environments.