The effort was made towards building a free and open piece of software that implements the Raptor codes: because the project originated from a telecommunication setting, complying to a standard looked like a good idea, thus the RFC 5053 was chosen as reference. The software is built as a library to include in your source code.
The first version of this software implements the RFC 5053 also called Raptor10, or R10, with the following features:
- binary representation is made trough packed words of 32 bits each;
- because of the previous, matrix inversion is done through GE instead of Inactivation Decoding;
- about the remaining points, an effort was made to stick to the RFC.
The standard defines the packet fields along with the ranges of the parameters to be supported. The following definitions are used throughout the code:
- K: integer number of source symbols in a single source block (8-8192)
- T: integer number of bytes that makes up a symbol (4-1024)
- N: integer number of encoding symbols coming out from the encoder; being the code systematic, we have N-K repair symbols
The basic structure of the encoder includes:
-
the calculation of L intermediate symbols from the K source symbols, where:
- L = S + H
- S is the number of LDPC constraints
- H is the number of HDPC constraints (or Half symbols constraints)
-
the calculation of the N-K repair symbols from the L intermediate symbols via the LTEnc() function. LTEnc is described in [1].
While the decoder includes:
- calculation of the L intermediate symbol from the received set of encoding symbols
- calculation of the missing source symbols by means of the intermediate symbols
This software is licensed under the GPLv3 license, making it free for everyone tu use, examine, improve and modify: see http://www.gnu.org/licenses/.
[1] RFC5053, M. Luby, A. Shokrollahi, M. Watson, T. Stockhammer, IETF Standards Track, Oct. 2007
[2] Raptor Codes, A. Shokrollahi and M. Luby, Book in Foundations and Trends in Communications and Information Theory, January 2011
