Time-varying Channel Estimation with Inter-carrier Interference Mitigation in Underwater OFDM Systems

Channel variations caused by motility would introduce inter-carrier interference (ICI), which degrades channel estimation and data detection in underwater orthogonal frequency division multiplexing (OFDM) systems. To deal with this problem, a joint time-varying channel estimation and inter-carrier interference mitigation method is proposed in this paper, where time domain channel estimation and interference auto-cancellation are merged into an iterative scheme. Meanwhile, linear approximation is used to track the time-varying channel while interference auto-cancellation is achieved via pre-coding to reduce the sensibility of OFDM systems to frequency shifts. Unlike frequently-used opposite or conjugate mapping, which leads to an inevitable decrease in frequency utility ratio, differential coding is introduced for pre-coding without adding redundancy. Simulations show that the proposed algorithm can accurately estimate channel state information (CSI), and robustly mitigate ICI over time-varying underwater acoustic channels (UWAC).