I’ve been looking at an erasure code by Luigi Rizzo which is based on Vandermonde matrices, since this code is used in Outernet. In fact, it is the code implemented by the zfec library. Luigi Rizzo describes his code in a paper from 1997, but the paper can be very confusing and misleading because it describes the mathematics in very little detail. I needed to go to the source code to understand how it works. Actually, the idea behind this code is very simple. Here I do a mathematical description of the code and show that it is the same as a Reed-Solomon code. This is rather weird, because Luigi Rizzo makes no mention of Reed-Solomon codes, which were first described in 1960.
In my previous post I talked about some small updates made by George Hopkins to my free-outernet project. In fact, George has been reverse engineering the
ondd binary quite in depth and he has been able to reverse engineer the LDPC code which is used for file FEC. This solves a long-standing issue of free-outernet. Formerly, LDPC decoding was not implemented, so to recover a file successfully all the file blocks had to be received correctly. Now, with LDPC decoding the file can be recovered even if some of the file blocks are lost. Thus, the performance of free-outernet in this aspect should now be the same as the performance of the closed source
ondd binary included in the official Outernet receiver. Many thanks to George, as this is a substantial improvement of free-outernet. Here I describe the latest changes made by George in free-outernet.