325 research outputs found
The Effect of Saturation on Belief Propagation Decoding of LDPC Codes
We consider the effect of LLR saturation on belief propagation decoding of
low-density parity-check codes. Saturation occurs universally in practice and
is known to have a significant effect on error floor performance. Our focus is
on threshold analysis and stability of density evolution.
We analyze the decoder for certain low-density parity-check code ensembles
and show that belief propagation decoding generally degrades gracefully with
saturation. Stability of density evolution is, on the other hand, rather
strongly affected by saturation and the asymptotic qualitative effect of
saturation is similar to reduction of variable node degree by one.Comment: Submitted to ISIT. Longer version to be submitted to IT Transactions
in preparatio
Wave-like Decoding of Tail-biting Spatially Coupled LDPC Codes Through Iterative Demapping
For finite coupling lengths, terminated spatially coupled low-density
parity-check (SC-LDPC) codes show a non-negligible rate-loss. In this paper, we
investigate if this rate loss can be mitigated by tail-biting SC-LDPC codes in
conjunction with iterative demapping of higher order modulation formats.
Therefore, we examine the BP threshold of different coupled and uncoupled
ensembles. A comparison between the decoding thresholds approximated by EXIT
charts and the density evolution results of the coupled and uncoupled ensemble
is given. We investigate the effect and potential of different labelings for
such a set-up using per-bit EXIT curves, and exemplify the method for a 16-QAM
system, e.g., using set partitioning labelings. A hybrid mapping is proposed,
where different sub-blocks use different labelings in order to further optimize
the decoding thresholds of tail-biting codes, while the computational
complexity overhead through iterative demapping remains small.Comment: presentat at the International Symposium on Turbo Codes & Iterative
Information Processing (ISTC), Brest, Sept. 201
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