  In this paper, we present an analytical analysis of the convergence of raptor
codes under joint decoding over the binary input additive white noise channel
(BIAWGNC), and derive an optimization method. We use Information Content
evolution under Gaussian approximation, and focus on a new decoding scheme that
proves to be more efficient: the joint decoding of the two code components of
the raptor code. In our general model, the classical tandem decoding scheme
appears to be a subcase, and thus, the design of LT codes is also possible.
