Udo Wachsmann


Coded Modulation: Theoretical Concepts and Practical Design Rules

Band 9, Kommunikations- und Informationstechnik, Herausgeber: B. Girod und J. Huber, Shaker Verlag, Aachen, ISBN 3-8265-4809-4, PDF

Abstract

In this thesis, the design and analysis of coded modulation schemes, mainly multilevel coding (MLC) schemes, are treated.  Key point is the concept of equivalent channels for the individual coding levels of an MLC scheme. Considering information theoretic parameters as well as error probabilities of these channels leads to fundamental theoretical statements on coded modulation and practical rules for design and analysis.

In particular, it is shown that coded modulation via the MLC approach is optimum in the sense of capacity.  Basic design rules how to assign rates to the individual component codes are established.  These rules are based, on the one hand, on information theoretic parameters like capacity, coding exponent and cut-off rates and on the other hand, on minimum Euclidean distance (the traditional approach) and error probability.  By means of several selected examples with powerful turbo codes as component codes, it is shown that the application of the basic design rules (except for the traditional one) to multilevel codes lead to power- and bandwidth-efficient transmission systems close to the Shannon limit.

The basic design rules are refined by treating further design aspects making the MLC principle a very attractive and flexible approach for practical applications.  The optimal dimensionality of the constituent signal set is derived leading to a gain in power and complexity efficiency. The use of hard decisions in multistage decoding is proposed as a very efficient method to substantially save complexity while the performance remains nearly unchanged.  It is shown that the proper combination of MLC and signal shaping bridges the gap between uniformly signaling and the Shannon limit.  Finally, a coding exponent analysis reveals that for finite code word length, the labeling introduced by Ungerböck and Imai leads to the most power efficient schemes.  Moreover, bit-interleaved coded modulation (BICM) using Gray labeling of signal points seems to be a relatively low complex, promising alternative approach to coded modulation.