reed solomon decoding

[srilakshmi28]

hi
i need to implement rs decoding in ccsds standards(255,223),in which the primitive element is alpha=alpha^11,i am having a code which uses alpha=2,can anyone suggest where i need to change my code,i am using c langague.its very urgent for me pls help meout

thaks

 

[bulx]

There must be a place in the code where the list of GF(256) elemens are generated and mapped to thier logarithms. This you must change to generate the GF elements using the primitve polynomial that correponds to having alpha^11 as primitve element.
-b

 

[srilakshmi28]

hi
thanks for
but when i am placing alpha^11 as my primitive element during generating the field polynomial i am
getting very large numbers and its creating errors.
pls help me out.

thanks

 

[bulx]

There is the field generator polynomial for CCSDS which is
F(x) = x8 + x7 + x2 + x + 1

and the codeword generating poly, which is
g(x) = Π(j=128 – E) to (127 + E) ( x – α^11j )

From your last reply, I guess you are talking about the second. Am I right?

I dont get how you can get any number greater that 255, because all operations are "mod 256". During which operation do you get such numbers? Encoding? Decoding?
- b

Note: α^11 is chosen to make the g(x) symmetric, α^1 will also have same ECC capacity, but circuits would be slightly bigger.

 

[gurinder]

sir
i want to know abt how to do coding in rs using awgn using qam
i will be grateful to you
thanks sir in advance