Reed Solomon codes help required

[ahmad556]

Dear all,
I'm trying to generate 1000 bits and encode them using RS(255,239).
My question is how can I divide the 1000 bits into symboles so that I can use the gf and rsenc commands in Matlab. I wish somebody can help me soon.
thanx in advance..

 

[bulx]

in your chosen RS code, 1 symbol is 8 bits (GF(256) is the relevant field), ie just a byte. So just collect 8 bits each to form 125 bytes (symbols) from your 1000 bits. Obviously, you have to collect 239 info bytes before you can generate the 16 redundant bytes.

If 1000 bit is all you have, generate the 16 redundant bytes assuming the remaining info bytes are all zero. ie 239-125=114 zero-bytes. These need not be transmitted.
-b

 

[ahmad556]

thank you bulx for your help.. but is there anyway I can encode the whole 1000 bits if I don't want the the 114 bits to be zeros?

 

[bulx]

It is that you dont have enough bits to fill in the 239 info BYTES of the code that you want to use. So the only way is to fill those places with zeros. When you generate your redudant bytes, all your 1000 bits _are_ encoded, only that 114 zero BYTEs are _also_ encoded.

Of course you need not trasmit those zeros, which means you can send your 125 info bytes, followed by the 16 redundant bytes. At the reciever, you start decoding assuming 114 uncorrupted zero bytes were also recieved in addition. Which is to say, what goes into your decoder is 125 recieved info bytes (possibly corrupted) + 114 uncorrupted zero bytes + 16 recieved redundant bytes (possibly corrupted)
-b