Study on M-ary Spread Spectrum Underwater Acoustic Communication

Aim at the low data rate of direct sequence spread spectrum underwater acoustic communication, a higher data rate spread spectrum system based on orthogonal sequences was designed. Lake tests were conducted and the results showed the data rate of 189 bps with BER less than 10-4 and SNR about 0 dB in the range of 25 km. In order to improve the data rate of MNSS, a time overlapping method is introduced. The simulation results, based on the real channel model, show its robustness and relative data rate improvement with slight performance decrease if the number of sequences N is small. Meanwhile, a novel method for combining multipath messages using FFT/IFFT is also proposed to improve the performance of matched filters in underwater multipath environments. Simulation results show its effectiveness.