An efficient receiver structure for sweep-spread-carrier underwater acoustic links

In this paper, we present an improved receiver architecture for sweep-spread-carrier modulation, a spread-spectrum technique proposed to effectively contrast the effects of time dispersion over multipath propagation channels in underwater acoustic wireless links. The proposed structure is capable of taking advantage of the energy received from all propagation paths rather than only from the strongest path, as envisaged in the pioneering paper introducing this modulation technique. A hardware version of the modem was implemented in the laboratory and its behavior was assessed and compared, using standard propagation models, to that exhibited by the traditional single-path-based scheme in terms of bit error rate. Results are presented showing that gains of a few decibels can be achieved in signal-to-noise-plus-interference ratio. Issues relevant to carrier/symbol synchronization, channel estimation, and sensitivity to Doppler distortion are also addressed.