Content deleted Content added
Line 151:
:LDPC codes and MDPC are based on the same component code: the parity checksum, and in my opinion the relationship stop there. In an LDPC codes, the number of symbols involved in a parity check is small and does not depend on the length of the code, while in MDPC the number of symbols involved in one parity check depend on the length of the code. In my opinion it is a big difference, since the encoding and the decoding algorithm will not have the same complexity. In addition, for a given length and a given dimension, an LDPC code will outperform an MDPC codes if decoded with an iterative decoding algorithm.[[User:Cunchem|Cunchem]] ([[User talk:Cunchem|talk]]) 08:40, 8 June 2009 (UTC)
:: That was my point just above; all linear codes can be defined in terms of a parity checksum. [[User:Oli Filth|Oli Filth]]<sup>([[User talk:Oli Filth|talk]]<nowiki>|</nowiki>[[Special:Contributions/Oli_Filth|contribs]])</sup> 15:31, 8 June 2009 (UTC)
=== Start again ===
Line 180 ⟶ 182:
:::: does "sqrt_d(k) ones per column" makes a matrix sparse?
:::: I think that LDPC are also characterized by there ability to be efficiently decoded by a low complexity iterative decoding algorithm. [[User:Cunchem|Cunchem]] ([[User talk:Cunchem|talk]]) 14:54, 8 June 2009 (UTC)
:::: My (rather limited) understanding of LDPC is that the bipartite graph viewpoint is identical to the parity-matrix viewpoint (it's just a mapping between codeword bits and parity constraints), therefore ''all'' linear block codes have one. In the case of LDPC, however, the sparsity of the parity matrix leads to a sparse graph, which in turn leads to an efficient decoder. So I'm still not convinced that MDPC is especially relevant. [[User:Oli Filth|Oli Filth]]<sup>([[User talk:Oli Filth|talk]]<nowiki>|</nowiki>[[Special:Contributions/Oli_Filth|contribs]])</sup> 15:31, 8 June 2009 (UTC)
:Regarding randomness, I do not recall randomness being a central criterion in the definition of LDPC codes; in fact, you could very well construct low-density parity check matrices algebraically and deterministically, it's just that randomized constructions turn out to be superior.
| |||