Underwater acoustic swept carrier communications

Underwater acoustic communication is severely affected by multipath interference. A novel idea based on the observation that the time separation between direct and multipath signals can be utilized to suppress multipath interference is developed in this thesis. -- A proposed system employs a carrier with instantaneous frequency swept periodically in time over a broad frequency range. The carrier is narrowband modulated by a message signal resulting in a time varying instantaneous spectrum of the transmitted signal. The received signal is demodulated by a bandpass tracking receiver. The low sweeping frequency determines the multipath spectrum and the degree of multipath suppression by the tracking bandpass receiver. -- Computer evaluation of the swept carrier concept together with lab and field tests conducted on a system prototype show conclusively that swept carrier communication is a feasible technique for multipath interference suppression