Design and implementation of OFDM acoustic modem for underwater communication

This paper is aimed to develop a low-complexity receiver by treating Doppler rate (phase offset) as nuisance parameter in the hybrid channel estimation. For slowly changing channels, two simple adaptive equalization schemes, based on least squares (LS) and minimum mean-squared error (MMSE) principles, are proposed. For fast-changing channels, we adopt pilot-based channel estimation for equalization. We show the bit-error-rate (BER) performance of the OFDM detectors over a set of measured channel impulse responses in the northeastern sea of Taiwan. Simulation results reveal that adaptive equalizers and pilot-based equalizer can perform quite well in calm and fast-changing channel conditions respectively.