Talk:Raptor code

Rateless?

Hi,

In this edit, the edit summary says "Raptor codes are rateless". Now, I admit I've only skimmed the journal paper, but how can a code be rateless? There are a number of symbols in, and a larger number out. The processing time must be proportional (at least) to the number of input symbols; surely the standard way of stating this is "encoding takes O(k) time"! Much in the same way that we don't state that the FFT runs in O(log n) time per input sample, but that it runs in O(n log n) time... Oli Filth^{(talk|contribs)} 10:00, 13 May 2009 (UTC)[reply]

Hi, raptor codes takes an number of symbols in, let say k, and can produce a "infinite" number of encoding symbols.

"Raptor codes in this class produce a potentially inﬁnite stream of symbols" from the article ^[1]

Since each encoding symbols is the combination of the k input symbols, there is a maximum of k! different encoding symbols that can be produced. I agree that even if this is very large, it is not "infinite", but that is how the authors of the article and many people in the community are referring to this class of codes. I think we should clarify this in the article and write a sentence or two about the finite size of this "infinite" set ;). Cunchem 10:44, 13 May 2009 (UTC) —Preceding unsigned comment added by Cunchem (talk • contribs)

Understood. But in any implementation where a Raptor code is doing something useful, there will a be pre-determined number of parity (don't know if that's the correct term in this instance) bits, not a pseudo-infinite number! Oli Filth^{(talk|contribs)} 11:17, 13 May 2009 (UTC)[reply]

It exists application where you don't know in advance how many encoding symbols will be sent. For example you can transmit symbols until the message change or until the service is stopped. In this case, using a rateless code is more efficient than repeating the symbols produced by a finite block length code. But it is also true that Raptor can be used (and it is often the case) when the number of parity is pre-determined (fixed code rate). --Cunchem 12:06, 13 May 2009 (UTC) —Preceding unsigned comment added by Cunchem (talk • contribs)

Rateless codes are attractive for hybrid ARQ applications, where the receiver can request additional parity data until it is able to decode the data. Nageh (talk) 13:46, 8 January 2010 (UTC)[reply]

Or as an alternative to data carousels. Nageh (talk) 13:53, 8 January 2010 (UTC)[reply]

Raptor = Rapid Tornado?

Hej,

is there any reference for this claim. I've read through some publications of Luby and Shokrollahi and never found this explanation. Could someone please clarify this?

Best regards — Preceding unsigned comment added by 141.13.3.171 (talk) 13:33, 24 January 2012 (UTC)[reply]

I think I do recall this from some presentation slides. I will look it up. Nageh (talk) 15:40, 24 February 2012 (UTC)[reply]

^ http://ieeexplore.ieee.org/iel5/18/34354/01638543.pdf?isnumber=34354&prod=JNL&arnumber=1638543&arSt=2551&ared=2567&arAuthor=Shokrollahi%2C+A.

[1] ttp://ieeexplore.ieee.org/iel5/18/34354/01638543.pdf?isnumber=34354&prod=JNL&arnumber=1638543&arSt=2551&ared=2567&arAuthor=Shokrollahi%2C+A.

[1]