Selective avoidance of cycles in irregular LDPC code construction
Tao Tian
Jones, C.R.
Villasenor, J.D.
Wesel, R.D.
Electr. Eng. Dept., Univ. of California, Los Angeles, CA, USA;
This paper appears in: Communications, IEEE Transactions on
Publication Date: Aug. 2004
Volume: 52,
Issue: 8
On page(s): 1242- 1247
ISSN: 0090-6778
INSPEC Accession Number: 8091568
Digital Object Identifier: 10.1109/TCOMM.2004.833048
Current Version Published: 2004-08-30
Abstract
This letter explains the effect of graph connectivity on error-floor performance of low-density parity-check (LDPC) codes under message-passing decoding. A new metric, called extrinsic message degree (EMD), measures cycle connectivity in bipartite graphs of LDPC codes. Using an easily computed estimate of EMD, we propose a Viterbi-like algorithm that selectively avoids small cycle clusters that are isolated from the rest of the graph. This algorithm is different from conventional girth conditioning by emphasizing the connectivity as well as the length of cycles. The algorithm yields codes with error floors that are orders of magnitude below those of random codes with very small degradation in capacity-approaching capability.
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