Frequency-domain channel estimation for nonlinear multicarrier underwater communication systems

Underwater acoustic (UWA) communications have drawn attention to many researchers in recent years. The major obstacles to reliable UWA communications include limited bandwidth, long multipath delay and large Doppler shifts of the UWA channel. Due to the hostile UWA environment, implementation of a high-speed UWA communication system often requires advanced modulation and signal processing techniques. The multicarrier modulation in the form of orthogonal frequency-division multiplexing (OFDM) has many attractive features which make it a potential candidate for UWA communications. However, the OFDM signal has a high peak-to-average-power ratio (PAPR) and hence is highly susceptible to nonlinearities in the communication link. For combating channel nonlinearities, knowledge of the nonlinear channel is essential. In this paper, we propose a novel method for the estimation of nonlinear channels in OFDM UWA communications. Compared to conventional methods, the proposed method requires a significantly smaller amount of data to achieve the channel estimation. This makes the proposed method suitable for time-varying UWA channels. The effectiveness of the proposed method is demonstrated by applying it to estimate the nonlinear channel of a simulated OFDM UWA communication system.