Asynchronous multiuser reception for underwater acoustic orthogonal frequency division multiplexing communications

Due to the large propagation delays in underwater acoustic channels, uplink synchronization is a great challenge in underwater acoustic sensor network, and thus the ability of asynchronous multiuser detection at the receiver is highly desired. A sliding iteration based asynchronous multiuser reception approach is proposed for the orthogonal frequency division multiplexing (OFDM) system, including overlapped truncation, interference cancellation, frequency- domain oversampling, multiuser channel estimation and data decoding, and interference reconstruction, which works in a sliding iteration fashion to eliminate the interference from the preceding and succeeding processing units. Simulation results show that the proposed method outperforms in terms of the bit-error-rate the block-by-block asynchronous multiuser receiver under different relative delays, and with or without channel estimation error. Pool experimental results show that the proposed approach achieves reliable two-user communications when the relative delay is no less than 1.5 times the CP duration in a multipath channel of 18 ms spreading delay.