Suppression of effects of the synchronization error with adaptive down-conversion for underwater acoustic communication

In underwater acoustic communication, inaccurate synchronization can cause an incorrect estimation of the uniform Doppler shift and degrade the demodulation performance. In this paper, it is mathematically described how the inaccurate synchronization affects the demodulation procedure. Moreover, it is also shown theoretically that adaptive down-conversion, which has been proposed to suppress the effects of the nonuniform Doppler shift, reduces the degradation of the demodulation performance caused by the inaccurate synchronization. Furthermore, the improvement in the demodulation performance by the adaptive down-conversion is evaluated using experimental data. The demodulation results of the addition of intended synchronization errors clearly show that the adaptive down-conversion reduced the effects of the synchronization errors and improved the demodulation performance in the case of inaccurate synchronization.