Mehmet Aydinlik

Unequal Error Protecting Turbo Coded Modulation: Structure, Design, and Performance Bounds

Date: September 27, 2004

Dana Turbo codes provide excellent performance, near the theoretical Shannon limit, at the cost of bandwidth expansion. This makes them unacceptable for channels with limited power and severe bandwidth constraint. For such channels, turbo coded modulation techniques can be employed to achieve powerful codes without sacrificing bandwidth.

The Gilbert-Elliot channel model is a special case of Hidden Markov Model (HMM) channels that is commonly used to model practical channels exhibiting bursts of errors. In the first part of this thesis, turbo coded modulation schemes for the Gilbert-Elliot channel model are considered. Three design schemes are proposed and the effect of channel parameters on the performance of these schemes is studied. We also show that channel interleavers provide significant performance improvement especially for channels with long memory.

One of the major concerns in the design of communication systems is to maintain quality of service for a wide range of channel conditions. This is an important issue particularly for the applications where precise characteristics of the channel are not known. For such applications, the source data can be classified into several classes and Unequal Error Protection (UEP) can be used to effectively protect the more important classes even in poor receiving conditions. The rest of this thesis is focused on the study, design, and performance evaluation of unequal error protecting turbo codes and turbo coded modulation schemes. We propose several unequal error protecting turbo coded modulation schemes. All these schemes provide high performance gains for more important classes that can hardly be achieved using conventional coded modulation schemes.

We continue our study of the unequal error protecting turbo coded modulation scheme by deriving channel capacity and cutoff rates for different protection levels. We show that for more important classes more room is available for improvement.

Finally, we derive bounds on the performance of unequal error protecting turbo codes and turbo coded modulation schemes. These bounds serve as an important tool in predicting the performance of these codes.

Thesis Committee: Professors David Brady, John Proakis, Masoud Salehi (Advisor)