Impulsive noise and carrier frequency offset cancellation for underwater acoustic OFDM communications

Underwater acoustic communication has been paid more and more attention nowadays. Orthogonal frequency division multiplexing (OFDM) technology is a promising approach to mitigate multipath, and has low computational complexity for channel equalization, thus it has been widely used for underwater acoustic communication. The Doppler which leads to carrier frequency offset (CFO) and impulsive noise in underwater acoustic channel will degrade the communication performance significantly. In this paper, we propose a novel method to estimate the impulsive noise and carrier frequency offset. We arrange the null-subcarriers at the edge of OFDM bands. Because of the CFO, there are some null-subcarrier that will be contaminated by adjacent active sub-carriers, but the number of contaminated null-subcarriers is limited, so we regard some null-subcarriers as guard null-subcarriers, which suffer from not only CFO, but also impulsive noise. The remaining null-subcarriers are treated as CFO free null-subcarriers, which only suffer from impulsive noise. We utilize such CFO free null-subcarriers to estimate impulsive noise using compressed sensing method, and then remove the impulsive noise from received signal. Consequently, the CFO is estimated via one-dimensional searching. Compared with traditional separately step-by-step method, our proposed method does not suffer from CFO when estimating the impulsive noise, thus the CFO estimation is improved. Numerical simulation demonstrates that, our proposed method improves the communication performance under the underwater acoustic channel where Doppler and impulsive noise exist.