A note on relationship between algebraic geometric codes and LDPC codes

Low-density parity-check (LDPC) codes constructed by a sparse parity-check matrix are of very fast encoding and decoding algorithms. Another kind of codes, which improved the well-known Gilbert-Varshamov bound, are algebraic geometry codes (Goppa geometry codes) from algebraic curves over finite fields. In the note, we analyze their characteristic of the two class of codes and show that the algebraic geometric codes are seldom LDPC codes.