Ethem Mutlu Sozer

Reliable Communications over Frequency-Selective Rapidly-Fading Channels

Date : Monday, April 21 2003

Abstract:

In this thesis, we introduced several receiver structures for channels that present extended multipath spread and fast time variations. We used underwater acoustic channel as the test channel. Before starting our discussion on the receiver structures, we presented methods to measure the channel charateristics. The first modem structure employs direct sequence spread spectrum signaling. The receiver for this modem is a RAKE filter with selective differential combining. We also introduced four iterative equalizer structures, which are based on the a posteriori probability equalizer (APP) and the decision feedback equalizer. Based on the encoding procedure, which can be a convolutional encoder or a turbo encoder, we obtain four iterative equalizer structures: APP-APP, APP-Turbo, DFE-APP, and DFE-Turbo iterative equalizers. We employed per survivor processing (PSP) and adaptive sparse channel estimators in the APP equalizer to reduce the complexity and enable operation over time varying channels. The DFE also employs an adaptive coefficient update algorithm, the recursive least squares (RLS) algorithm. We evaluated the perfromance of these modem structures using simulations, experimental studies, and a semi-analytical approach, the extrinsic information transfer (EXIT) charts. In the final section of this thesis, we introduced an underwater acoustic network and evaluated its perfromance through simulations.

Thesis Committee:
Prof. John G. Proakis (Advisor)
Prof. Masoud Salehi
Dr. Milica Stojanovic