Re: The GSoC project on LDPC codes

Greetings

I was very interested in this project for possible application to the
op25 project, since P25 uses several FEC codes
including RS and other block codes. I’ve brought up the gr-ldpc library
and have a few questions. Due to the hateful YAhoo mail composer, I’m
hesitant to post lengthy emails to the general list with no opportunity
for preview prior to hitting SEND, so I’ll try breaking up the list of
questions into several posts, one per question…

First question: I was getting lots of errors, seg faults, aborts, and
other misbehavior from the code, which were traced to an apparent bug in
alist.cc, all of which cleared up when I applied the following patch:

— …/…/repo/gr-ldpc/lib/alist.cc 2013-10-18 10:25:47.508781061 -0400
+++ ./alist.cc 2013-11-05 11:21:03.879972116 -0500
@@ -123,7 +123,7 @@
}

// Parse indices with non zero entries in ith row

  • for (int row = 0; row < N; row++) {
  • for (int row = 0; row < M; row++) {
    std::getline(file, line);
    ss << line;
    for (int entry = 0; entry < num_mlist[row]; entry++) {

Can you confirm, is this really a bug?

Thanks and Best

Max

Dear Max,

You are correct. It is a bug. Now I’m wondering why I didn’t get any
segmentation faults.

Probably I didn’t get any segmentation faults because, after i = M - 1,
EOF
has reached.

Thanks for the correction.

Dear Manu,

Do you have any performance numbers on your LDPC decoder? I could not
find any info, even in your presentation. Do you have also a BER
figure, or even better would be some technical report. I would love to
get some sense on the performance of your implementation.

Best,
Miklos

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