Dc-free convolutional codes and dc-free turbo codes

In this paper we integrate convolutional/turbo encoding with multimode encoding to generate dc-free convolutional/turbo codes. Based on the generators of error-control codes, we employ flipping or puncturing to ensure that the coded sequences are dc-balanced. At the receiver, the channel output is first decoded by a convolutional/turbo decoder (with consideration of detection when flipping is used during encoding), and then by a dc-free decoder. We show that good spectrum performance can be obtained at the cost of an increase in complexity in the encoder and that excellent bit error rate (BER) performance can be obtained particularly when source data logic values are not equiprobable.