Underwater Acoustic Communication Over Doppler Spread Channels
MASSACHUSETTS INST OF TECH CAMBRIDGE
Pagination or Media Count:
This work is concerned with coherent communication by means of acoustic signals over underwater communication channels. The estimated scattering functions of real data show that underwater communication channels cannot be captured by a single, simple channel model. This thesis considers mainly a subset of underwater communication channels where the Doppler spread is more severe than the delay spread. An appropriate representation of the linear time variant channel is introduced, and the wide sense stationary uncorrelated scattering WSSUS channel assumption enables characterization in terms of scattering functions. The concept of Doppler lines is used in the derivation of a receiver for Doppler spread channels. A Decision Feedback Equalizer DFE adapted with Recursive Least Squares RLS is analyzed with respect to Doppler spread. By using the DFE with a Phase Locked Loop PLL suboptimal system behavior is found. A modified RLS called the time updated RLS TU-RLS is presented, and it is used in a new receiver. The receiver compensates both discrete and continuous Doppler spread. It is used to decode both real and simulated data, and some of these data are severely Doppler spread.
- Non-Radio Communications