162 research outputs found
Terminated LDPC Convolutional Codes with Thresholds Close to Capacity
An ensemble of LDPC convolutional codes with parity-check matrices composed
of permutation matrices is considered. The convergence of the iterative belief
propagation based decoder for terminated convolutional codes in the ensemble is
analyzed for binary-input output-symmetric memoryless channels using density
evolution techniques. We observe that the structured irregularity in the Tanner
graph of the codes leads to significantly better thresholds when compared to
corresponding LDPC block codes.Comment: To appear in the proceedings of the 2005 IEEE International Symposium
on Information Theory, Adelaide, Australia, September 4-9, 200
Terminated and Tailbiting Spatially-Coupled Codes with Optimized Bit Mappings for Spectrally Efficient Fiber-Optical Systems
We study the design of spectrally efficient fiber-optical communication
systems based on different spatially coupled (SC) forward error correction
(FEC) schemes. In particular, we optimize the allocation of the coded bits from
the FEC encoder to the modulation bits of the signal constellation. Two SC code
classes are considered. The codes in the first class are protograph-based
low-density parity-check (LDPC) codes which are decoded using iterative
soft-decision decoding. The codes in the second class are generalized LDPC
codes which are decoded using iterative hard-decision decoding. For both code
classes, the bit allocation is optimized for the terminated and tailbiting SC
cases based on a density evolution analysis. An optimized bit allocation can
significantly improve the performance of tailbiting SC codes codes over the
baseline sequential allocation, up to the point where they have a comparable
gap to capacity as their terminated counterparts, at a lower FEC overhead. For
the considered terminated SC codes, the optimization only results in marginal
performance improvements, suggesting that in this case a sequential allocation
is close to optimal.Comment: This paper has been accepted for publication in the IEEE/OSA Journal
of Lightwave Technolog
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