A SC-DS-CDMA underwater acoustic communication system using dual spread spectrum code

Underwater acoustic channel is a time varying, strong multipath, serious Doppler frequency shift, and high noise interference channel. Aiming at the requirements of strong stability and high reliability to support reliable transmission over long distance, a direct sequence spread spectrum based on single carrier underwater acoustic communication system using dual spread spectrum code (SC-CDMA/DSSC) is proposed in this paper. And a data frame structure based on training sequence is given out according to this system. With the good correlation characteristics of the Gold sequence, it is used as spread code. The long spread code is used as the training sequence for data frame detection and synchronization, Doppler estimation and compensation, channel estimation and equalization. And the short spread code is used to spread effective data. For Doppler estimation and compensation, a delayed cross-correlation method is used to estimate the Doppler factor and then compensate the Doppler frequency shift by resampling. For channel estimation and equalization, firstly, we estimate the time-domain channel impulse response (CIR) using the training sequence, and use the single carrier frequency domain equalization (SC-FDE) algorithm for channel equalization. Simulation results show that the BER can be as low as 0 when the SNR>-9 in an environment with multipath and Doppler, the communication rate can achieve 387bps, which demonstrated that the proposed system has strong ability of anti-multipath and anti-interference.

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