OFDM system with adaptive modulation for shallow water acoustic channel environment

Adaptive modulation is a powerful technique to improve the power efficiency and to increase the data rate of communication system in the underwater acoustic channel, which has a time varying characteristics. In this paper we propose an OFDM transmission system with adaptive modulation schemes, i.e. BPSK, QPSK, and 16-QAM. The system has ability to change the modulation scheme adaptively based on the signal-to-noise ratio (SNR), while maintaining the bit error rate (BER) under 0.01. The evaluation is conducted with simulation for the flat fading channel condition, and the system showed a good performance. It show that the system has ability to change the modulation scheme adaptively, and improve the channel capacity for certain value.