Time-Varying Channel Estimation and Symbol Detection for Underwater Acoustic FBMC-OQAM Communications

Filter bank multicarrier (FBMC) systems with offset quadrature amplitude modulation (OQAM) need long data blocks to achieve high spectral efficiency. However, the transmission of long data blocks in underwater acoustic (UWA) communication systems often encounters the challenge of time-varying channels. This paper proposes a time-varying channel tracking method for short-range high-rate UWA FBMC-OQAM communication applications. First, a known preamble is used to initialize the channel estimation at the initial time of the signal block. Next, the estimated channel is applied to detect data symbols at several symbol periods. The detected data symbols are then reused as new pilots to estimate the next time channel. In the above steps, the unified transmission matrix model is extended to describe the time-varying channel input–output model in this paper and is used for symbol detection. Simulation results show that the channel tracking error can be reduced to less than −20 dB when the channel temporal coherence coefficient exceeds 0.75 within one block period of FBMC-OQAM signals. Compared with conventional known-pilot-based methods, the proposed method needs lower system overhead while exhibiting similar time-varying channel tracking performance. The sea trial results further proved the practicability of the proposed method.