A multi-beam space diversity method for long-range underwater acoustic OFDM communication in deep water

Aiming at the problems of large transmission loss,and severemultipath delay spread in long-range deep water acoustic channel,a multi-beam space diversity method for UnderWater Acoustic（UWA） Single Input Multiple Output（SIMO） Orthogonal Frequency Division Multiplexing（OFDM） communications is proposed.The model of received SIMO-OFDM signal in long-range deep water acoustic channel is established,and independent Doppler compensation and sparse channel estimation are performed for the multi-beam outputs according to different arrival angles based on wideband beamforming.Finally,multi-beam equalization is realized based on Maximum Ratio Combining（MRC）.Compared with the single-beam processing method commonly used in long-range UWA communications,the proposed method can obtain additional multipath diversity gain by combining multi-beam outputs with different arrival angles.And the used array beamforming can significantly improve the SNR of each beam output,avoiding the increased error for channel estimation caused by combining the low SNR signal received from a single element.The complexity of the proposed method is larger than that of single-beam method but lower than that of MRC with multiple elements.Simulation results based on the BELLHOP and experimental results in the South China Sea show that the BER performance of the proposed method is significantly better than that of single-beam equalization and MRC equalization.The proposed receiver has achieved error-free decoding results with the communication distance of 100 km and the data rate of 199 bps.