Research on Channel Estimation in OFDM Underwater Acoustic Communications

Orthogonal frequency division multiplexing (OFDM) is a potential topic in underwater acoustic (UWA) communication to tackle the issues of the limited frequency band resources and obvious multiple interference. Nevertheless, the complex time-varying UWA environment raises the challenges from the reliable transmission in OFDM UWA communication, which is affected by the frequency offset, time delay, and noise. Therefore, signal processing method designed at the receiver is essential to accurately get messages. In this paper, we offer a novel algorithm which reconstructs the actual sparse channel number just based on received signal for underwater channel estimation with unknown sparsity. And the channel estimation algorithm based on the null subcarrier method in Doppler estimation and compensation is investigated. The simulation results denote the proposed improved orthogonal matching pursuit (OMP) algorithm can perform better than least square (LS) and OMP. We also explore the influence of the modulation modes, the number of paths and the channel estimation algorithms on estimation performance in OFDM UWA channel system.