Abstract
Finite fields have been widely used for the constructions of powerful quasi-cyclic (QC) low-density parity-check (LDPC) codes. However, due to the nature of the finite fields, the lengths of the resultant codes are quite limited. In order to achieve more flexible code lengths, two novel code construction methods are proposed in this thesis. The first is based on the affine transformation. The second is assisted by the computer search. Using these two methods, the Tanner graphs of the resultant QC-LDPC codes are cycle-4 free. Using the proposed methods, QC-LDPC codes which can achieve a competitive error–rate performance can be easily constructed with much more flexible code lengths.