Root Locus Plots and Iterative Decoding

A well known class of error correction codes called low-density parity-check (LDPC) codes have been the subject of a great deal of recent study in the coding community as a result of their ability to approach Shannon´s fundamental capacity limit. Crucial to the performance of these codes is the use of an iterative decoder. We describe LDPC codes and the decoding algorithm and make a connection between the fixed points of the decoding algorithm and the well-known root locus plot. Via two example LDPC codes, we describe the insights afforded by the root locus plot