Bidirectional Equalization Receiver for Underwater Acoustic OFDM Systems Using Frequency-Domain Oversampling

Underwater acoustic orthogonal frequency division multiplexing (OFDM) systems suffer from frequency-selective fading and inter-carrier interference (ICI) caused by the underwater acoustic channels. As a commonly adopted solution, channel equalization is performed after two-dimensional channel estimation of the doubly selective channels. To achieve better performance, a bidirectional equalization receiver based on frequency-domain oversampling (FDO) for underwater acoustic OFDM systems is proposed. We use a pilot design that facilitates FDO based sparse channel estimation and bidirectional equalization. On one hand, FDO contributes more observations to both channel estimation and equalization. On the other hand, the bidirectional equalization structure is employed to mitigate the error propagation caused by linear minimum mean-squared error (MMSE) equalizer while maintaining low equalization complexity. Simulation and experimental results demonstrate the advantage of the proposed FDO based bidirectional equalization receiver.