Design and Performance Analysis of a Digital Acoustic Telemetry System

This work studies the application of current communication engineering methods to underwater acoustic telemetry. The underwater channel is modelled with data collected from channel probe experiments in Woods Hole Harbor and the Marginal Ice Zone. The experimental results indicate that the short range underwater acoustic channel may be modelled as a time dispersive fully saturated channel. In all cases the received signal phase is fully random for time intervals longer than 10 msec, and the envelope is characterized by a fully fading Nakagami PDF. It is shown that PSK modulation methods are ineffective because of the rapid phase fluctuations of received transmissions, and that the performance of the optimal partially coherent FSK receiver is almost identical to the suboptimal incoherent FSK demodulator. Adaptive equalization and impulse response measurement techniques for the underwater acoustic channel are presented. Performance of convolutional codes and sequential decoders on the Rayleigh fading channel is discussed, and complexity bounds for sequential decoding on the memoryless fading channel are discussed as a function of optimal andor available system diversity. It is shown that sequential decoding of convolutional codes is a viable technique given the contemplated data rates and currently available decoding hardware. KT