BCH DVB-S2 codes for short code length LDPC

i am trying to create a BCH encoder for a DVB-S2 code based on Final draft ETSI EN 302 307 V1.2.1 (2009-04) table 5b (16200 ldpc code legnth). So i have used the following parmaters to generate the generator polynomials (g)

R = 8/9, Kbch = 14232, Nbch = 14400, t = 12, nldpc = 16200

R = 0.8889

Kbch = 14232

Nbch = 14400

t = 12

nldpc = 16200

g = x^12 + x^10 + x^9 + x^7 + x^6 + x^5 + x^3 + x^2 + x + 1

Accoridng to MATLAB, i can use this in comm.BCHEncode/comm.BCHDecode.

bchEnc = comm.BCHEncoder(Nbch,Kbch,'x^12 + x^10 + x^9 + x^7 + x^6 + x^5 + x^3 + x^2 + x + 1');
msg = randi([0 1],Kbch,1);
EncodedData = bchEnc(msg)

Error using comm.BCHEncoder/setParameters
The generator polynomial must evenly divide X^n+1, where n is the length of a full length code

However when i try this i get this error:

Error using comm.BCHEncoder/setParameters The generator polynomial must evenly divide X^n+1

So either i am using the wrong BCH encoder or ive got the polynomials wrong.

Answer 1

[Sathvik]

Hi George

By setting a generator polynomial, you are shortening the BCH code to a message length of 5 (since the default ShortMessageLength property is set to 5), which may not be ideal for your parameters. I would suggest you to set the Parameters as follows.

enc = comm.BCHEncoder(Nbch,Kbch);

This way, the generator polynomial would be created automatically

Here is an example code to verify the BCH Encoder

Kbch = 14232; 
Nbch = 14400;

% Encoding 

msg = randi([0 1], Kbch, 1); 
enc = comm.BCHEncoder(Nbch,Kbch); 
y=enc(msg); 


% Decoding 

dec = comm.BCHDecoder(Nbch,Kbch); 
z=dec(y); 
isequal(msg,z) 

ans = logical
   1

You can refer to the following documentation for more information on how you can implement your BCH code

https://www.mathworks.com/help/comm/ref/comm.bchencoder-system-object.html

Hope this helps!

[george masters]

Yes! this helps, thank you!