HFM spread spectrum modulation scheme in shallow water acoustic channels

Owing to the large delay spread caused by multipath propagation and the severe Doppler Effect of the shallow water acoustic channel, a spread spectrum modulation scheme using hyperbolic frequency modulated (HFM) signal named as “HFM spread-spectrum modulation” (HFM-SS) was exploited to substantially improve the performance of communications over such channels. Apart from some advantages such as reducing influence of narrow-band noise, HFM signals provide Doppler-invariability and low power cost. The effects of multipath and Doppler shift on the proposed scheme were investigated by establishing a model of a shallow water acoustic communication system. The emulated results demonstrate that it has a good prospect for underwater acoustic communication system, especially for moving platforms. High transmission stability of this approach was validated in lake experiments carried out in the summer 2011.