Underwater Acoustic Spread Spectrum Communication Based on M Family N group Parallel Transmission

Due to the low data rate of direct sequence spread spectrum (DSSS) underwater acoustic communication (UAC), a higher data rate spread spectrum UAC system based on M family phase modulation signal and N groups parallel transmission (MNSS) was designed. Lake tests were conducted and the results showed that it could reach 320 bps with BER below 10-4 at within the range of 25 km. In order to further improve the data rate of spread spectrum UAC, time overlapping method are introduced in this paper. Based on the saved channel (measured in lake tests), performance of time overlapping method and MNSS are compared. Simulation results show its robustness and relative higher data rate with little performance decrease. Meanwhile, a novel method for combining multipath messages using FFT/IFFT was also addressed to improve the performance of correlators in underwater environments. Computer simulates based on saved channel show its effectiveness with at least 2 dB processing gain.