I am currently learning LDPC codes, I have the following general question regarding LDPC codes,
1) when encountering a term such as LDPC$(672,504)$ are we referring to the code rate or the matrix dimensions? i.e is it $(n,k)$ or $(n,n-k)$? or is it different depending on book?
2) A 3/4 LDPC matrix is used with shortening to have an effective code rate of 1/2 or less. Since the code rate is 1/4 we need to do puncturing is shortening term similar to puncturing?
3) If we have number of bits that we want to encode less than 504, say for example 64, do we need to pad first with zeros to a length of 504 in order to use the LDPC(672,504)? Assuming this notation is referring to 3/4 matrix.
Any references on LDPC would be great.