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Global Design Methods for Raptor Codes Using Binary and Higher-Order Modulations
November 2009
Richard J. Barron, The MITRE Corporation
Caleb K. Lo, The MITRE Corporation
Jerome M. Shapiro, The MITRE Corporation
ABSTRACT
We develop accurate and robust one-dimensional EXIT chart
methods to design Raptor codes with binary and higher-order
modulations on AWGN channels. We formulate the checknode
degree distribution optimization as a linear program that
directly accounts for the pre-code error correction capability
and simultaneously optimizes over any desired range of
rate operating points. The throughput curves predicted by the
analysis are easily compared across different pre-code rates
and pre-code error-correcting capabilities. For higher-order
modulations we employ BICM on a standard Gray-mapped
16-QAM constellation. We further enhance the optimization
by applying separate check-node degree distributions to the
mapped MSBs and LSBs, which results in significant gains
compared to a single check-node degree distribution.
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