  The error floor of LDPC is revisited as an effect of dynamic message behavior
in the so-called absorption sets of the code. It is shown that if the signal
growth in the absorption sets is properly balanced by the growth of
set-external messages, the error floor can be lowered to essentially
arbitrarily low levels. Importance sampling techniques are discussed and used
to verify the analysis, as well as to discuss the impact of iterations and
message quantization on the code performance in the ultra-low BER (error floor)
regime.
