If I have bit sequence X at Alice and correlated sequence Y at Bob. How do I use LDPC to correct errors in Y such that X = Y. All examples I've seen about classical LDPC assume X is modulated, passed through a channel, and then demodulated at Bob to calculated LLR for the LDPC decorder. In my case I don't want to send X. Sending the syndrome of X is OK, but how do I go about using that information for belief propagation at Bob and how do I get LLR?