Ldpc Encode - Decode scheme doesnt produce expected results

Hi,I'm using the communication toolbox to try and see how the ldpc encode/decode module works. I'm doing it as it should work in my opinion, but I guess I have an error somewhere and it'd be great if someone could point to that :)

I'm using the following code. the multiplication of H*codeword' does indeed equal all zeros (mod 2).

After the decoding process(as the codeword is entered flawlessly, no decoding error should happen) I would expect to see the decoded message equal to msg. However, that is not the case, and I cant even connect the decoded output and the original msg, they're completely different. Could anyone tell me where am I wrong?

Thanks a lot in advance, Alex

H = dvbs2ldpc(0.5)

l = fec.ldpcenc(H);

msg = randint(1,l.NumInfoBits,2);

codeword = encode(l,msg);

H * codeword'

c = fec.ldpcdec(H);

decoded = decode(c,codeword);

decoded - msg; % should be all zeros?

[Ed MrTz]

Hi, Alex!

I have the same doubt...cause I get the same results..... i don't recover the original msg when I decode.

Your post were from time ago.....did you find any theory?

THNX!!

Answer 1

[CT]

Decode expects LLR values as inputs. Try the code below instead.

decoded = decode(c,-sign(codeword-0.5));

sum(abs(decoded-msg))

Answer 2

[Khushboo Singh]

 please go through this. i think its working correctly.  

I = randint(1,43200);
H = dvbs2ldpc(2/3);
l = fec.ldpcenc(H);
codeword = encode(l,I);
d = fec.ldpcdec(H);
decoded = decode(d,codeword);
ans = not(xor(decoded,I)); % should be all zeros?
sparse(ans)