Abstract
In this paper, we consider low density parity check (LDPC) codes as a
solution to enhance the optical transmission performance. The decoding
algorithm based on message passing algorithm uses the probability density
function of the received signal. Its efficiency thus depends on the right
evaluation of the signal distribution. We do not make here the classical
additive white Gaussian noise (AWGN) assumption, but we investigate a
chi-square based channel model which is more accurate for the description of
optical impairments. As opposed to previous chi-square based models, no
assumption on the signal power of 0 and 1 data is done. The calculation of
the logarithmic likelihood ratio (LLR) needed to implement soft LDPC decoder
is thus developed for a chi-square channel in a general manner. Computer
simulations validate the efficiency of the soft decoder for this type of
channel. The results also confirm that the adaptation of LDPC decoder to the
specific chi-square channel statistic is necessary to obtain the optimal
performance.
© 2009 IEEE
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